#### Sample records for poloidal field coils

1. Equilibrium modeling of the TFCX poloidal field coil system

SciTech Connect

Strickler, D.J.; Miller, J.B.; Rothe, K.E.; Peng, Y.K.M.

1984-04-01

The Toroidal Fusion Core Experiment (TFCX) isproposed to be an ignition device with a low safety factor (q approx. = 2.0), rf or rf-assisted startup, long inductive burn pulse (approx. 300 s), and an elongated plasma cross section (kappa = 1.6) with moderate triangularity (delta = 0.3). System trade studies have been carried out to assist in choosing an appropriate candidate for TFCX conceptual design. This report describes an important element in these system studies - the magnetohydrodynamic (MHD) equilibrium modeling of the TFCX poloidal field (PF) coil system and its impact on the choice of machine size. Reference design points for the all-super-conducting toroidal field (TF) coil (TFCX-S) and hybrid (TFCX-H) options are presented that satisfy given PF system criteria, including volt-second requirements during burn, mechanical configuration constraints, maximum field constraints at the superconducting PF coils, and plasma shape parameters. Poloidal coil current waveforms for the TFCX-S and TFCX-H reference designs consistent with the equilibrium requirements of the plasma startup, heating, and burn phases of a typical discharge scenario are calculated. Finally, a possible option for quasi-steady-state operation is discussed.

2. A method for estimating tokamak poloidal field coil currents which incorporates engineering constraints

SciTech Connect

Stewart, W.A.

1990-05-01

This thesis describes the development of a design tool for the poloidal field magnet system of a tokamak. Specifically, an existing program for determining the poloidal field coil currents has been modified to: support the general case of asymmetric equilibria and coil sets, determine the coil currents subject to constraints on the maximum values of those currents, and determine the coil currents subject to limits on the forces those coils may carry. The equations representing the current limits and coil force limits are derived and an algorithm based on Newton's method is developed to determine a set of coil currents which satisfies those limits. The resulting program allows the designer to quickly determine whether or not a given coil set is capable of supporting a given equilibrium. 25 refs.

3. Optimization of Damavand Tokamak Poloidal Field Coils Positions and Currents with PSO Algorithm

Mohammadi, M.; Dini, F.; Amrollahi, R.

2012-04-01

In order to maintain equilibrium in small or large tokamaks poloidal field coils are utilized, since the function of the poloidal magnetic field is a complex function of current density and the position of the coils, a change in any of the parameters can have a strong effect in the confinement and the magnetohydrodynamic parameters. On the other hand, considering the continuity of the current and the position of the coils, the space being searched is so big that taking all possible conditions into account becomes practically impossible. So a method should be utilized that is able to optimize the position and current of the coils without searching the whole space. This paper seeks to find a new method of deriving the plasma parameter in which a combination of the two methods of neural network and Particles Swarm Optimization is used in order to optimize the position and current of poloidal field coils in Damavand tokamak. Since in the employed methods no special topology is applied, it can be readily used to study any other tokamak.

4. A solenoid-free current start-up scenario utilizing outer poloidal field coils*

Choe, W.; Kim, J.; Ono, M.; Menard, J.; Neumeyer, C.; Wilson, J. R.

2004-11-01

Elimination of the in-board solenoid is not only required for the spherical torus reactors but would also be desirable for advanced tokamak reactors. The challenge for using only the outer PF coils for start-up is the difficulty of creating a sufficiently high quality field null region while retaining the poloidal flux needed for current ramp-up. It is shown that a few pairs of PF coils can provide a field null for a few ms with a large region of low transverse field in which an ionization avalanche can develop in the applied toroidal E-field with the aid of strong pre-ionization. Preliminary experimental and modeling work has been performed on NSTX aimed at quantifying the field null requirements in terms of the Lloyd parameter, the null size and its duration, while optimizing the loop voltage and the available flux. Different combinations of PF coils were used to investigate the relationship between the size of the region where E_TB_T/BP = 0.1 kV/m and the breakdown. Fast camera and magnetic diagnostics clearly show plasma initiation for several ms. The vacuum field patterns and flux surfaces of the generated plasma and analysis of the plasma evolution with the DINA code will be presented. *This work supported by KAIST and DoE Contract No. DE-AC02-76CH03073.

5. Optimization of Outer Poloidal Field (PF) Coil Configurations for Inductive PF Coil-only Plasma Start-up on Spherical Tori

SciTech Connect

Wonho Choe; Jayhyun Kim; Masayuki Ono

2004-04-09

The elimination of in-board ohmic heating solenoid is required for the spherical torus (ST) to function as an attractive fusion power plant. An in-board ohmic solenoid, along with the shielding needed for its insulation, increases the size and, hence, the cost of the plant. Here, we investigate using static as well as dynamic codes in ST geometries a solenoid-free start-up concept utilizing a set of out-board poloidal field coils. By using the static code, an optimization of coil positions as well as coil currents was performed to demonstrate that it is indeed possible to create a high quality multi-pole field null region while retaining significant flux (volt-seconds) needed for the subsequent current ramp-up. With the dynamic code that includes the effect of vacuum vessel eddy currents, we then showed that it is possible to maintain a large size field null region for several milliseconds in which sufficient ionization avalanche can develop in the applied toroidal electric field. Under the magnetic geometry typical of a next generation spherical torus experiment, it is shown that the well-known plasma breakdown conditions for conventional ohmic solenoid start-up of E(sub)TB(sub)T/B(sub)P {approx} (0.1-1) kV/m with V(sub)loop {approx} 6 V can be readily met while retaining significant volt-seconds {approx} 4 V-S sufficient to generate multi-MA plasma current in STs.

6. Solenoid-free toroidal plasma start-up concepts utilizing only the outer poloidal field coils and a conducting centre-post

Choe, Wonho; Kim, Jayhyun; Ono, Masayuki

2005-12-01

Eventual elimination of the in-board Ohmic heating solenoid is required for the spherical torus (ST) to function as a compact component test facility and as an attractive fusion power plant. An in-board Ohmic solenoid, along with the shielding needed for its insulation, can dramatically increase the size and, hence, the cost of the plant. Advanced tokamak reactor designs also assume no or a small in-board solenoid to reduce the size and cost of the plant. In addition, elimination of the in-board solenoid greatly reduces the coil stresses and simplifies the coil design. Here, we investigate using static as well as dynamic codes in ST geometries with two complementary solenoid-free plasma start-up approaches: one utilizes only the outer poloidal field coils to create a relatively high quality field null region while retaining significant poloidal flux, and the other takes advantage of the poloidal flux stored in the conducting centre-post to create a start-up condition similar to that of the conventional Ohmic solenoid method. We find that it is therefore possible to come up with a promising configuration, which produces a quality multi-pole field-null and sufficient loop-voltage needed for plasma initiation and significant poloidal flux for subsequent current ramp-up. The present solenoid-free start-up concept, if proved feasible, can be readily extended to higher field devices due to relatively simple physics principles and favourable scaling with the device size and toroidal field.

7. Test data from the US-Demonstration Poloidal Coil experiment

SciTech Connect

Painter, T.A.; Steeves, M.M.; Takayasu, M.; Gung, C.; Hoenig, M.O.; Tsuji, H.; Ando, T.; Hiyama, T.; Takahashi, Y.; Nishi, M.; Yoshida, K.; Okuno, K.; Nakajima, H.; Kato, T.; Sugimoto, M.; Isono, T.; Kawano, K.; Koizumi, N.; Osikiri, M.; Hanawa, H.; Ouchi, H.; Ono, M.; Ishida, H.; Hiue, H.; Yoshida, J.; Kamiyauchi, Y.; Ouchi, T.; Tajiri, F.; Kon, Y.; Shimizu, H.; Matsuzaki, Y.; Oomori, S.; Tani, T.; Oomori, K.; Terakado, T.; Yagyu, J.; Oomori, H.

1992-01-01

The US Demonstration Poloidal Field Coil (US-DPC) experiment took place successfully at the Japan Atomic Energy Research Institute (JAERI) in late 1990. The 8 MJ niobium-tin coil was leak tight; it performed very well in DC tests; it performed well in AC tests, achieving approximately 70% of its design goal. An unexpected ramp-rate barrier at high currents was identified. The barrier could not be explored in the regime of higher fields and slower ramp rates due to limitations of the background-field coils. This document presents the results of the experiment with as little editing as possible. The coil, conductor, and operating conditions are given. The intent is to present data in a form that can be used by magnet analysts and designers.

8. A method for determining poloidal coil configurations for tokamak devices

SciTech Connect

Evans, K. Jr.

1990-12-01

This paper presents a method for obtaining the locations and currents of the poloidal coil systems for a tokamak, given an desirable magnetohydrodynamic equilibrium for the device. The method involves a simultaneous minimization of the match to the desired poloidal field and the stored energy in the coils, subject to the constraints necessary to achieve decoupling of the equilibrium and inductive-current-drive (ohmic-heating) systems and to achieve a given coupling of the current-drive system with the plasma. A compendium of mutual and self-inductance formulas as they apply to tokamak systems is presented, as well as examples of how the method has been used in the design of several tokamaks. Finally, a user manual for a computer code that implements this method is provided. 14 refs., 11 figs., 1 tab.

9. NCSX Toroidal Field Coil Design

SciTech Connect

Kalish, M.; Rushinski, J.; Myatt, L.; Brooks, A.; Dahlgren, F.; Chrzanowski, J.; Reiersen, W.; Freudenberg, K.

2005-10-07

The National Compact Stellarator Experiment (NCSX) is an experimental device whose design and construction is underway at the Department of Energy's Princeton Plasma Physics Laboratory (PPPL). The primary coil systems for the NCSX device consist of the twisted plasma-shaping Modular Coils, the Poloidal Field Coils, and the Toroidal Field (TF) Coils. The TF Coils are D-shaped coils wound from hollow copper conductor, and vacuum impregnated with a glass-epoxy resin system. There are 18 identical, equally spaced TF coils providing 1/R field at the plasma. They operate within a cryostat, and are cooled by LN2, nominally, to 80K. Wedge shaped castings are assembled to the inboard face of these coils, so that inward radial loads are reacted via the nesting of each of the coils against their adjacent partners. This paper outlines the TF Coil design methodology, reviews the analysis results, and summarizes how the design and analysis support the design requirements.

10. Equilibrium field coil concepts for INTOR

SciTech Connect

Strickler, D.J.; Peng, Y.K.M.; Brown, T.G.

1981-08-01

Methods are presented for reducing ampere-turn requirements in the EF coil system. It is shown that coil currents in an EF coil system external to the toroidal field coils can be substantially reduced by relaxing the triangularity of a D-shaped plasma. Further reductions are realized through a hybrid EF coil system using both internal and external coils. Equilibrium field coils for a poloidally asymmetric, single-null INTOR configuration are presented. It is shown that the shape of field lines in the plasma scrapeoff region and divertor channel improves as triangularity is reduced, but it does so at the possible expense of achievable stable beta values.

11. Long-Term Monitoring of Hydraulic Characteristics of LHD Poloidal Coils

Takahata, Kazuya; Moriuchi, Sadatomo; Ooba, Kouki; Mito, Toshiyuki; Imagawa, Shinsaku

We present a fourteen-year data summary of the hydraulic characteristics of the large helical device (LHD) poloidal coils. The superconductors of the poloidal coils are cable-in-conduit conductors (CICC) cooled by circulated supercritical helium. The long-term operation of the LHD demonstrates that the initial hydraulic characteristics can be maintained without flow obstruction. Fine mesh filters installed at the inlet trapped impurities during cool-down of the coils, confirmed by monitoring the pressure drop of the filters. The filters have an important role in removing particles of impurities in the helium and maintaining the hydraulic characteristics of the coils.

12. Performance of current measurement system in poloidal field power supply for Experimental Advanced Superconducting Tokamak

Liu, D. M.; Li, J.; Wan, B. N.; Lu, Z.; Wang, L. S.; Jiang, L.; Lu, C. H.; Huang, J.

2016-11-01

As one of the core subsystems of the Experimental Advanced Superconducting Tokamak (EAST), the poloidal field power system supplies energy to EAST's superconducting coils. To measure the converter current in the poloidal field power system, a current measurement system has been designed. The proposed measurement system is composed of a Rogowski coil and a newly designed integrator. The results of the resistor-inductor-capacitor discharge test and the converter equal current test show that the current measurement system provides good reliability and stability, and the maximum error of the proposed system is less than 1%.

13. Performance of current measurement system in poloidal field power supply for Experimental Advanced Superconducting Tokamak.

PubMed

Liu, D M; Li, J; Wan, B N; Lu, Z; Wang, L S; Jiang, L; Lu, C H; Huang, J

2016-11-01

As one of the core subsystems of the Experimental Advanced Superconducting Tokamak (EAST), the poloidal field power system supplies energy to EAST's superconducting coils. To measure the converter current in the poloidal field power system, a current measurement system has been designed. The proposed measurement system is composed of a Rogowski coil and a newly designed integrator. The results of the resistor-inductor-capacitor discharge test and the converter equal current test show that the current measurement system provides good reliability and stability, and the maximum error of the proposed system is less than 1%.

14. Tokamak poloidal field systems. Progress report, January 1-December 31, 1979

SciTech Connect

Rogers, J.D.

1980-05-01

Work is reported on the development of superconducting tokamak poloidal field systems (TPFS). Progress is discussed on the design of a 20 MJ, 50 kA, 7.5 T superconducting pulsed energy storage coil operated in a 1 to 2 s bipolar mode from +7.5 T to -7.5 T in 1982. Conductor development for the coil is presented. A facility that uses a traction motor energy transfer system to test coils in the 20 to 100 MJ energy range is discussed. Current interrupter development and testing for protection and energy transfer circuits are also presented. The 400 kJ METS coil test preparation is under way.

15. Air core poloidal magnetic field system for a toroidal plasma producing device

DOEpatents

Marcus, Frederick B.

1978-01-01

A poloidal magnetics system for a plasma producing device of toroidal configuration is provided that reduces both the total volt-seconds requirement and the magnitude of the field change at the toroidal field coils. The system utilizes an air core transformer wound between the toroidal field (TF) coils and the major axis outside the TF coils. Electric current in the primary windings of this transformer is distributed and the magnetic flux returned by air core windings wrapped outside the toroidal field coils. A shield winding that is closely coupled to the plasma carries a current equal and opposite to the plasma current. This winding provides the shielding function and in addition serves in a fashion similar to a driven conducting shell to provide the equilibrium vertical field for the plasma. The shield winding is in series with a power supply and a decoupling coil located outside the TF coil at the primary winding locations. The present invention requires much less energy than the usual air core transformer and is capable of substantially shielding the toroidal field coils from poloidal field flux.

16. Tokamak poloidal-field systems. Progress report, January 1-December 31, 1981

SciTech Connect

Rogers, J.D.

1982-03-01

Work on the superconducting tokamak poloidal field system (TPFS) program is being redirected. The development of the 20 MJ, 50 kA, 7.5 T superconducting programmed energy storage coil is being terminated. The superconductor for the 20 MJ coil is being processed only to an intermediate state, and manufacture of the epoxy fiberglass dewar is being stopped. Further, development of the TPFS test facility is in abeyance. Change in program emphasis arises from prospective rf plasma current driven or beam heated tokamaks with programmed coil characteristics for the poloidal field being different from those to have been simulated by the 20 MJ coil and from budgetary constraints. Work is reported on the development of the coil, conductor, nonconducting dewar, and test facility to the recent time when the program change was instigated. Work in support of the Large Coil Test Facility (LCTF) and the Fusion Engineering Design (FED) Center is given. Analysis of the experiments on the 400 kJ METS coil test was completed.

17. Poloidal and toroidal fields in geomagnetic field modeling

Backus, G.

1986-02-01

The application of surface operator theory to poloidal and toroidal fields in geomagnetic field modeling is described. Surface operators are obtained for the dimensionless surface gradient; the dimensionless surface curl; the dimensionless surface Laplacian, as well as for the Funk-Hecke operators, integral operators, and axisymmetric kernels. Methods are given for interpreting satellite measurements of the geomagnetic field B, assuming B is can vary significantly and rapidly with time, and there are electric fields in the sample. Approximation schemes for ionospheric currents are also described.

18. Toroidal and poloidal magnetic fields at Venus. Venus Express observations

Dubinin, E.; Fraenz, M.; Woch, J.; Zhang, T. L.; Wei, Y.; Fedorov, A.; Barabash, S.; Lundin, R.

2013-10-01

Magnetic field and plasma measurements carried out onboard Venus Express during solar minimum conditions suggest the existence of two kinds of magnetic field configuration in the Venusian ionosphere. We interpret these as the manifestation of two different types of generation mechanisms for the induced magnetosphere. A different magnetic field topology (toroidal and poloidal) arises if the induced currents are driven either by the solar wind motional electric field or by the Faraday electric field—a conducting ionosphere sees the magnetic field carried by solar wind as a time-varying field. At the dayside, both driving agents produce a similar draping pattern of the magnetic field. However, different magnetic field signatures inherent to both induction mechanisms appear at lower altitudes in the terminator region. The conditions at low solar EUV flux when the ionosphere of Venus becomes magnetized seem to be favorable to distinguish between two different types of the induced fields. We present cases of both types of the magnetic field topology. The cases when the effects of the Faraday induction become well noticeable are especially interesting since they provide us with an example of solar wind interaction with a tiny induced dipole field immersed into the ionosphere. Another interesting case when poloidal magnetic fields are evidently displayed is observed when the IMF vector is almost aligned with the solar wind velocity. In general case, both mechanisms of induction probably complement each other.

19. Tokamak poloidal field systems. Progress report, January 1-December 31, 1980

SciTech Connect

Rogers, J.D.

1981-03-01

Work is reported on the development of superconducting tokamak poloidal field system (TPFS) program. Progress is discussed on the design of the 20 MJ, 50 kA, 7.5 T superconducting pulsed energy storage coil to be operated in a bipolar mode from +7.5 T to -7.5 T in an energy transfer period of 1.5 to 5 s in 1982 followed by extensive cyclic testing. The facility to conduct the tests uses a traction motor energy transfer system and a nonconducting dewar. Status of the hardware development for the TPFS program is presented. Current interrupter development and testing for protection and energy transfer circuits are also presented. The 400 kJ METS coil test results are given.

20. POLOIDAL MAGNETIC FIELD TOPOLOGY FOR TOKAMAKS WITH CURRENT HOLES

SciTech Connect

Puerta, Julio; Martin, Pablo; Castro, Enrique

2009-07-26

The appearance of hole currents in tokamaks seems to be very important in plasma confinement and on-set of instabilities, and this paper is devoted to study the topology changes of poloidal magnetic fields in tokamaks. In order to determine these fields different models for current profiles can be considered. It seems to us, that one of the best analytic descriptions is given by V. Yavorskij et al., which has been chosen for the calculations here performed. Suitable analytic equations for the family of magnetic field surfaces with triangularity and Shafranov shift are written down here. The topology of the magnetic field determines the amount of trapped particles in the generalized mirror type magnetic field configurations. Here it is found that the number of maximums and minimums of Bp depends mainly on triangularity, but the pattern is also depending of the existence or not of hole currents. Our calculations allow comparing the topology of configurations of similar parameters, but with and without whole currents. These differences are study for configurations with equal ellipticity but changing the triangularity parameters. Positive and negative triangularities are considered and compared between them.

1. Ring currents and poloidal magnetic fields in nuclear regions of galaxies

Lesch, H.; Crusius, A.; Schlickeiser, R.; Wielebinski, R.

1989-06-01

The origin of observed strong poloidal magnetic fields R(z) in the central regions of galaxies which have gaseous rings is discussed. In the context of galactic disk dynamo models only weak poloidal fields but strong toroidal fields result. The strength of the poloidal fields is tied to the central activity and apply known and tested ideas rigorously. A battery process on galactic scales is discussed which ensures the existence of a large-scale magnetic field in the inner galactic region. The frozen-in field may be amplified by v x B compression and turbulent stretching; the resulting field is poloidal. The central activity provides a flow field which can produce B(z) equal to or greater than B(phi).

2. Ion orbit loss and the poloidal electric field in a tokamak

SciTech Connect

Xiao, H.; Hazeltine, R.D.; Valanju, P.M.

1994-07-29

Monte Carlo simulation studies for ion orbit loss in limiter tokamaks show a poloidal asymmetry in ion loss arising from differences in ion orbit geometry. Since electron loss to the limiter is uniformly distributed because of its tiny orbit width, the nonuniform ion loss could cause a poloidal electric field that would tend to make the ion loss to the limiter more uniform. A simple analytical derivation of this poloidal electric field and a discussion of its effects ion movement and transport are also presented.

3. Spheromak reactor with poloidal flux-amplifying transformer

DOEpatents

1987-01-01

An inductive transformer in the form of a solenoidal coils aligned along the major axis of a flux core induces poloidal flux along the flux core's axis. The current in the solenoidal coil is then reversed resulting in a poloidal flux swing and the conversion of a portion of the poloidal flux to a toroidal flux in generating a spheromak plasma wherein equilibrium approaches a force-free, minimum Taylor state during plasma formation, independent of the initial conditions or details of the formation. The spheromak plasma is sustained with the Taylor state maintained by oscillating the currents in the poloidal and toroidal field coils within the plasma-forming flux core. The poloidal flux transformer may be used either as an amplifier stage in a moving plasma reactor scenario for initial production of a spheromak plasma or as a method for sustaining a stationary plasma and further heating it. The solenoidal coil embodiment of the poloidal flux transformer can alternately be used in combination with a center conductive cylinder aligned along the length and outside of the solenoidal coil. This poloidal flux-amplifying inductive transformer approach allows for a relaxation of demanding current carrying requirements on the spheromak reactor's flux core, reduces plasma contamination arising from high voltage electrode discharge, and improves the efficiency of poloidal flux injection.

4. Hall probe measurements of the poloidal magnetic field in Compact Toroidal Hybrid plasmas.

PubMed

Stevenson, B A; Knowlton, S F; Hartwell, G J; Hanson, J D; Maurer, D A

2014-09-01

A linear array of 16 Hall effect sensors has been developed to directly measure the poloidal magnetic field inside the boundary of a non-axisymmetric hybrid torsatron/tokamak plasma. The array consists of miniature gallium arsenide Hall sensor elements mounted 8 mm apart on a narrow, rotatable printed circuit board inserted into a re-entrant stainless steel tube sheathed in boron nitride. The sensors are calibrated on the bench and in situ to provide accurate local measurements of the magnetic field to aid in reconstructing the equilibrium plasma current density profiles in fully three-dimensional plasmas. Calibrations show that the sensor sensitivities agree with the nominal manufacturers specifications of 1.46 V/T. Poloidal fields measured with the Hall sensor array are found to be within 5% of poloidal fields modeled with a Biot-Savart code.

5. Hall probe measurements of the poloidal magnetic field in Compact Toroidal Hybrid plasmas

SciTech Connect

Stevenson, B. A.; Knowlton, S. F.; Hartwell, G. J. Hanson, J. D.; Maurer, D. A.

2014-09-15

A linear array of 16 Hall effect sensors has been developed to directly measure the poloidal magnetic field inside the boundary of a non-axisymmetric hybrid torsatron/tokamak plasma. The array consists of miniature gallium arsenide Hall sensor elements mounted 8 mm apart on a narrow, rotatable printed circuit board inserted into a re-entrant stainless steel tube sheathed in boron nitride. The sensors are calibrated on the bench and in situ to provide accurate local measurements of the magnetic field to aid in reconstructing the equilibrium plasma current density profiles in fully three-dimensional plasmas. Calibrations show that the sensor sensitivities agree with the nominal manufacturers specifications of 1.46 V/T. Poloidal fields measured with the Hall sensor array are found to be within 5% of poloidal fields modeled with a Biot-Savart code.

6. Current density and poloidal magnetic field for toroidal elliptic plasmas with triangularity

SciTech Connect

Martin, P.; Haines, M.G.; Castro, E.

2005-08-15

Changes in the poloidal magnetic field around a tokamak magnetic surface due to different values of triangularity and ellipticity are analyzed in this paper. The treatment here presented allows the determination of the poloidal magnetic field from knowledge of the toroidal current density. Different profiles of these currents are studied. Improvements in the analytic forms of the magnetic surfaces have also been found. The treatment has been performed using a recent published system of coordinates. Suitable analytic equations have been used for the elliptic magnetic surfaces with triangularity and Shafranov shift.

7. Method and apparatus for steady-state magnetic measurement of poloidal magnetic field near a tokamak plasma

SciTech Connect

Woolley, R.D.

1996-12-31

A method and apparatus for the steady-state measurement of poloidal magnetic field near a tokamak plasma, where the tokamak is configured with respect to a cylindrical coordinate system having z, phi (toroidal), and r axes. The method is based on combining the two magnetic field principles of induction and torque. The apparatus includes a rotor assembly having a pair of inductive magnetic field pickup coils which are concentrically mounted, orthogonally oriented in the r and z directions, and coupled to remotely located electronics which include electronic integrators for determining magnetic field changes. The rotor assembly includes an axle oriented in the toroidal direction, with the axle mounted on pivot support brackets which in turn are mounted on a baseplate. First and second springs are located between the baseplate and the rotor assembly restricting rotation of the rotor assembly about its axle, the second spring providing a constant tensile preload in the first spring. A strain gauge is mounted on the first spring, and electronic means to continually monitor strain gauge resistance variations is provided. Electronic means for providing a known current pulse waveform to be periodically injected into each coil to create a time-varying torque on the rotor assembly in the toroidal direction causes mechanical strain variations proportional to the torque in the mounting means and springs so that strain gauge measurement of the variation provides periodic magnetic field measurements independent of the magnetic field measured by the electronic integrators.

8. Method and apparatus for steady-state magnetic measurement of poloidal magnetic field near a tokamak plasma

DOEpatents

Woolley, Robert D.

1998-01-01

A method and apparatus for the steady-state measurement of poloidal magnetic field near a tokamak plasma, where the tokamak is configured with respect to a cylindrical coordinate system having z, phi (toroidal), and r axes. The method is based on combining the two magnetic field principles of induction and torque. The apparatus includes a rotor assembly having a pair of inductive magnetic field pickup coils which are concentrically mounted, orthogonally oriented in the r and z directions, and coupled to remotely located electronics which include electronic integrators for determining magnetic field changes. The rotor assembly includes an axle oriented in the toroidal direction, with the axle mounted on pivot support brackets which in turn are mounted on a baseplate. First and second springs are located between the baseplate and the rotor assembly restricting rotation of the rotor assembly about its axle, the second spring providing a constant tensile preload in the first spring. A strain gauge is mounted on the first spring, and electronic means to continually monitor strain gauge resistance variations is provided. Electronic means for providing a known current pulse waveform to be periodically injected into each coil to create a time-varying torque on the rotor assembly in the toroidal direction causes mechanical strain variations proportional to the torque in the mounting means and springs so that strain gauge measurement of the variation provides periodic magnetic field measurements independent of the magnetic field measured by the electronic integrators.

9. Method and apparatus for steady-state magnetic measurement of poloidal magnetic field near a tokamak plasma

DOEpatents

Woolley, R.D.

1998-09-08

A method and apparatus are disclosed for the steady-state measurement of poloidal magnetic field near a tokamak plasma, where the tokamak is configured with respect to a cylindrical coordinate system having z, phi (toroidal), and r axes. The method is based on combining the two magnetic field principles of induction and torque. The apparatus includes a rotor assembly having a pair of inductive magnetic field pickup coils which are concentrically mounted, orthogonally oriented in the r and z directions, and coupled to remotely located electronics which include electronic integrators for determining magnetic field changes. The rotor assembly includes an axle oriented in the toroidal direction, with the axle mounted on pivot support brackets which in turn are mounted on a baseplate. First and second springs are located between the baseplate and the rotor assembly restricting rotation of the rotor assembly about its axle, the second spring providing a constant tensile preload in the first spring. A strain gauge is mounted on the first spring, and electronic means to continually monitor strain gauge resistance variations is provided. Electronic means for providing a known current pulse waveform to be periodically injected into each coil to create a time-varying torque on the rotor assembly in the toroidal direction causes mechanical strain variations proportional to the torque in the mounting means and springs so that strain gauge measurement of the variation provides periodic magnetic field measurements independent of the magnetic field measured by the electronic integrators. 6 figs.

10. Bow-shaped toroidal field coils

SciTech Connect

Bonanos, P.

1981-05-01

Design features of Bow-Shaped Toroidal Field Coils are described and compared with circular and D shaped coils. The results indicate that bow coils can produce higher field strengths, store more energy and be made demountable. The design offers the potential for the production of ultrahigh toroidal fields. Included are representative coil shapes and their engineering properties, a suggested structural design and an analysis of a specific case.

11. On Ohmic heating in the Earth's core II: Poloidal magnetic fields obeying Taylor's constraint

Jackson, Andrew; Livermore, Philip W.; Ierley, Glenn

2011-08-01

The extremely small Ekman and magnetic Rossby numbers in the Earth's core make the magnetostrophic limit an attractive approximation to the core's dynamics. This limit leads to the need for the internal magnetic field to satisfy Taylor's constraint, associated with the vanishing of the azimuthal component of Lorentz torques averaged over every cylinder coaxial with the rotation axis. A special class of three dimensional poloidal interior magnetic fields is chosen that satisfies Taylor's constraint identically on every cylinder in a spherical shell exterior to an inner core. This class of fields, which we call small-circle conservative, demonstrates existence of interior fields satisfying Taylor's constraint, regardless of the morphology of the field on the core surface. These poloidal fields are used to examine the Ohmic dissipation present in the Earth's core. To address the question of dissipation, we demand that the 3-D core fields agree with recent observations of the core field structure on the core-mantle boundary. We use these poloidal fields to show that the true lower bound on core dissipation must necessarily lie below a value that we calculate. For 2004 we find that this lower bound must lie below 10 10 W, and when nutation constraints are also considered the bound must lie below 2 × 10 10 W. These numbers are small compared to suggested values of the order of a few TeraWatts. A more restrictive bound may be forthcoming when the time-dependency of the field is considered, using a variational data assimilation technique.

12. RESEARCH PAPERS : Secular variation of the poloidal magnetic field at the core-mantle boundary

Bhattacharyya, Archana

1998-01-01

A region of enhanced conductivity at the base of the mantle is modelled by an infinitesimally thin sheet of uniform effective conductance adjacent to the core-mantle boundary. Currents induced in this sheet by the temporally varying magnetic field produced by the geodynamo give rise to a discontinuity in the horizontal components of the poloidal magnetic field on crossing the sheet, while the radial component is continuous across the sheet. Treating the rest of the mantle as an insulator, the horizontal components of the poloidal magnetic field and their secular variation at the top of the core are determined from geomagnetic field, secular variation and secular acceleration models. It is seen that for an assumed effective conductance of the sheet of 108 S, which may be not unrealistic, the changes produced in the horizontal components of the poloidal field at the top of the core are usually <=10 per cent, but corrections to the secular variation in these components at the top of the core are typically 40 per cent, which is greater than the differences that exist between different secular variation models for the same epoch. Given the assumption that all the conductivity of the mantle is concentrated into a thin shell, the present method is not restricted to a weakly conducting mantle. Results obtained are compared with perturbation solutions.

13. Impact of toroidal and poloidal mode spectra on the control of non-axisymmetric fields in tokamaks

Lanctot, Matthew J.

2016-10-01

In several tokamaks, non-axisymmetric magnetic field studies show applied n=2 fields can lead to disruptive n=1 locked modes, suggesting nonlinear mode coupling. A multimode plasma response to n=2 fields can be observed in H-mode plasmas, in contrast to the single-mode response found in Ohmic plasmas. These effects highlight a role for n >1 error field correction in disruption avoidance, and identify additional degrees of freedom for 3D field optimization at high plasma pressure. In COMPASS, EAST, and DIII-D Ohmic plasmas, n=2 magnetic reconnection thresholds in otherwise stable discharges are readily accessed at edge safety factors q 3 and low density. Similar to previous studies, the thresholds are correlated with the overlap'' field for the dominant linear ideal MHD plasma mode calculated with the IPEC code. The overlap field measures the plasma-mediated coupling of the external field to the resonant field. Remarkably, the critical overlap fields are similar for n=1 and 2 fields with m >nq fields dominating the drive for resonant fields. Complementary experiments in RFX-Mod show fields with m fields in DIII-D elicit transport responses with differing poloidal spectrum dependences, including a reduction in toroidal angular momentum that is not fully recoverable using fields that imperfectly match the applied field. These results have motivated an international effort to document n=2 error field thresholds in order to establish control requirements for ITER. This work highlights unique requirements for n >1 control, including the need for multiple rows of coils to control selected plasma parameters for specific functions (e.g., rotation control or ELM suppression). Optimal multi-harmonic (n=1 and n=2) error field control may be achieved using control algorithms that continuously respond to time-varying 3D field sources and plasma parameters. Supported by the US DOE under DE-FC02-04ER54698.

14. Determination of plasma shape from poloidal field measurements on ISX-B

SciTech Connect

Swain, D.W.; Bates, S.; Neilson, G.H.; Peng, Y.K.M.

1980-03-01

The ISX-B tokamak has a poloidal coil system designed to produce circular, elliptical, and D-shaped plasmas. Plasma shape and low-order multipole moments of the plasma current distribution are determined from experimental measurements of B/sub Z/, B/sub R/, and/or psi around the periphery of the vacuum chamber. The experimental arrangement and method of analysis of results, using a least squares method to fit the data points to a finite current filament model, are described in this report. Plasma shape results for circular and D-shaped plasmas with b/a less than or equal to 1.5 and an analysis of the sensitivity of the technique to measurement errors are presented. The results indicate that this method gives accurate measurements of the plasma boundary and is relatively insensitivie to errors.

15. Magnetic Fields at the Center of Coils

ERIC Educational Resources Information Center

Binder, Philippe; Hui, Kaleonui; Goldman, Jesse

2014-01-01

In this note we synthesize and extend expressions for the magnetic field at the center of very short and very long current-carrying coils. Elementary physics textbooks present the following equation for the magnetic field inside a very long current-carrying coil (solenoid): B[subscript sol] = µ[subscript 0] (N/L) I, (1) where I is the current, N…

16. Gyrokinetic full f analysis of electric field dynamics and poloidal velocity in the FT2-tokamak configuration

SciTech Connect

Leerink, S.; Heikkinen, J. A.; Janhunen, S. J.; Kiviniemi, T. P.; Nora, M.; Ogando, F.

2008-09-15

The ELMFIRE gyrokinetic simulation code has been used to perform full f simulations of the FT-2 tokamak. The dynamics of the radial electric field and the creation of poloidal velocity in the presence of turbulence are presented.

17. Laminated magnet field coil sheath

DOEpatents

Skaritka, John R.

1987-12-01

a method for manufacturing a magnet cable trim coil in a sheath assembly for use in a cryogenic particle accelerator. A precisely positioned pattern of trim coil turns is bonded to a flexible substrate sheath that is capable of withstanding cryogenic operating conditions. In the method of the invention the flexible sheath, with the trim coil pattern precisely positioned thereon, is accurately positioned at a precise location relative to a bore tube assembly of an accelerator and is then bonded to the bore tube with a tape suitable for cryogenic application. The resultant assembly can be readily handled and installed within an iron magnet yoke assembly of a suitable cryogenic particle accelerator.

18. Laminated magnet field coil sheath

DOEpatents

Skaritka, J.R.

1987-05-15

A method for manufacturing a magnetic cable trim coil in a sheath assembly for use in a cryogenic particle accelerator. A precisely positioned pattern of trim coil turns is bonded to a flexible substrate sheath that is capable of withstanding cryogenic operating conditions. In the method of the invention the flexible substrate sheath, with the trim coil pattern precisely location relative to a bore tube assembly of an accelerator and is then bonded to the bore tube with a tape suitable for cryogenic application. The resultant assembly can be readily handled and installed within an iron magnet yoke assembly of a suitable cryogenic particle accelerator. 1 fig.

19. The Magnetic Field of Helmholtz Coils

ERIC Educational Resources Information Center

Berridge, H. J. J.

1975-01-01

Describes the magnetic field of Helmholtz coils qualitatively and then provides the basis for a quantitative expression. Since the mathematical calculations are very involved, a computer program for solving the mathematical expression is presented and explained. (GS)

20. Solutions for the equilibrium of static isothermal gas clouds with poloidal magnetic fields

Baureis, P.; Ebert, R.; Schmitz, F.

1989-11-01

A family of semi-analytical solutions for the equilibrium of magnetic self-gravitating gas clouds is presented. The configurations are isothermal and axially symmetric; the frozen-in magnetic field is poloidal. Formulating the equilibrium equations of such gas clouds in spherical polar coordinates, a separation of these equations provides simple representative solutions. The radial part of the density distribution is given by the characteristic inverse square of the radial coordinate. The angular parts are governed by a system of nonlinear ordinary differential equations which is solved numerically. The nonmagnetic limit is the isothermal gas sphere with infinite central density. With increasing field strength the configurations flatten. Besides the isothermal sound velocity the value of the magnetic field in the midplane is a free continuous parameter. In the limit of extremely strong fields a thin disk forms. The existence of bounded solutions is discussed, and the models are compared with configurations presented by other authors.

1. On the Sequential Control of ITER Poloidal Field Converters for Reactive Power Reduction

Yuan, Hongwen; Fu, Peng; Gao, Ge; Huang, Liansheng; Song, Zhiquan; He, Shiying; Wu, Yanan; Dong, Lin; Wang, Min; Fang, Tongzhen

2014-12-01

Sequential control applied to the International Thermonuclear Experimental Reactor (ITER) poloidal field converter system for the purpose of reactive power reduction is the subject of this investigation. Due to the inherent characteristics of thyristor-based phase-controlled converter, the poloidal field converter system consumes a huge amount of reactive power from the grid, which subsequently results in a voltage drop at the 66 kV busbar if no measure is taken. The installation of a static var compensator rated for 750 MVar at the 66 kV busbar is an essential way to compensate reactive power to the grid, which is the most effective measure to solve the problem. However, sequential control of the multi-series converters provides an additional method to improve the natural power factor and thus alleviate the pressure of reactive power demand of the converter system without any additional cost. In the present paper, by comparing with the symmetrical control technique, the advantage of sequential control in reactive power consumption is highlighted. Simulation results based on SIMULINK are found in agreement with the theoretical analysis.

2. Microturbulence studies of pulsed poloidal current drive discharges in the reversed field pinch

SciTech Connect

Carmody, D. Pueschel, M. J.; Anderson, J. K.; Terry, P. W.

2015-01-15

Experimental discharges with pulsed poloidal current drive (PPCD) in the Madison Symmetric Torus reversed field pinch are investigated using a semi-analytic equilibrium model in the gyrokinetic turbulence code GENE. PPCD cases, with plasma currents of 500 kA and 200 kA, exhibit a density-gradient-driven trapped electron mode (TEM) and an ion temperature gradient mode, respectively. Relative to expectations of tokamak core plasmas, the critical gradients for the onset of these instabilities are found to be greater by roughly a factor of the aspect ratio. A significant upshift in the nonlinear TEM transport threshold, previously found for tokamaks, is confirmed in nonlinear reversed field pinch simulations and is roughly three times the threshold for linear instability. The simulated heat fluxes can be brought in agreement with measured diffusivities by introducing a small, resonant magnetic perturbation, thus modeling the residual fluctuations from tearing modes. These fluctuations significantly enhance transport.

3. High-field superconducting nested coil magnet

NASA Technical Reports Server (NTRS)

Laverick, C.; Lobell, G. M.

1970-01-01

Superconducting magnet, employed in conjunction with five types of superconducting cables in a nested solenoid configuration, produces total, central magnetic field strengths approaching 70 kG. The multiple coils permit maximum information on cable characteristics to be gathered from one test.

4. Far-infrared polarimetry/interferometry for poloidal magnetic field measurement on ZT-40M

SciTech Connect

Erickson, R.M.

1986-06-01

The measurement of internal magnetic field profiles may be a very important step in the understanding of magnetic confinement physics issues. The measurement of plasma-induced Faraday rotation is one of the more promising internal magnetic field diagnostics. This thesis describes the development of a heterodyne polarimeter/interferometer for internal poloidal magnetic field measurement on ZT-40M. Heterodyne techniques were employed because of the insensitivity to spurious signal amplitude changes that cause errors in other methods. Initial problems in polarimetric sensitivity were observed that were ultimately found to be related to discharge-induced motions of the constrained diagnostic access on ZT-40M. Grazing incidence motions of the constrained diagnostic access on ZT-40M. Grazing incidence reflections on metallic surfaces of the diagnostic ports caused polarization changes that affected the measurement accuracy. Installation of internally threaded sleeves to baffle the reflections eliminated the sensitivity problem, and allowed useful Faraday rotation measurements to be made. Simultaneous polarimetric and interferometric measurements have also been demonstrated. The ability to assemble a working heterodyne polarimeter/interferometer is no longer in question. The extension of the present system to multichord operation requires increased laser power and efficiency.

5. POLOIDAL MAGNETIC FIELD MEASUREMENTS AND ANALYSIS WITH THE DIII-D LIBEAM SYSTEM

SciTech Connect

D.M. THOMAS

2002-08-01

For over thirty years, neutral lithium beams have been employed as a localized, noninvasive diagnostic on a variety of plasma experiments worldwide, providing a number of key physics measurements. On DIII-D the LIBEAM diagnostic has been designed to provide precise measurements of the local poloidal magnetic field in the edge region, a parameter of basic importance to understanding the stability of high performance tokamaks. We utilize the Zeeman splitting and known polarization characteristics of the collisionally excited 670.8 nm Li resonance line to interpret local magnetic field components viewed using a closely packed ({Delta}R {approx} 5 mm) array of 32 viewchords. A dual photoelastic modulator/linear polarizer combination serves to amplitude modulate the light in exact correspondence to its input polarization state. Subsequent narrowband spectral filtering using etalons and standard interference filters is used to isolate one of the three Zeeman components, and the polarization state of that component is recovered using a PC-based, multichannel digital lock-in detection system. Edge magnetic pitch angle profiles for a variety of shots have been reconstructed using a small number of chords and detailed analysis of the lockin and d.c. signal levels. Present system performance appears to be limited by etalon performance as well as various broadening mechanisms in the beam that tend to decrease the polarization fraction in the observed component. A careful analysis of this effect and some strategies for improving the measured polarization will be presented.

6. A simple model for the generation and detection of a poloidal magnetic field in laser-target interactions

Ryutov, Dmitri; Remington, Bruce

2006-10-01

When a linearly-polarized ultra-intense laser beam interacts with a target, it may generate not only toroidal but also poloidal non-oscillating magnetic field (D.D. Ryutov, B.A. Remington. AIP Conf. Proc., v. 827, p. 341, 2006; Astrophys. Space Sci., submitted, 2006). The poloidal field has a structure resembling the field of a group of four sunspots of alternating polarity. Its magnitude may reach the magnitude of an oscillating magnetic field in the incident wave. Effects of a pulse duration and ion expansion are discussed. Scaling laws determining this field are established. Detection of this field is feasible with side-on ion deflectometry. An optimum orientation of the probe beam is shown to form a 45-degree angle with the polarization plane. Examples of the distortion of an image of a rectangular grid are presented. It is concluded that the poloidal field can be identified even in the presence of the toroidal field of a comparable magnitude. Work performed for US DoE by UC LLNL under contract #W-7405-Eng-48.

7. STRUCTURAL RESPONSE OF THE DIII-D TOROIDAL FIELD COIL TO INCREASED LATERAL LOADS

SciTech Connect

REIS,E.E; CHIN,E

2003-10-01

8. Resistive demountable toroidal-field coils for tokamak reactors

SciTech Connect

Jassby, D.L.; Jacobsen, R.A.; Kalnavarns, J.; Masson, L.S.; Sekot, J.P.

1981-07-01

Readily demountable TF (toroidal-field) coils allow complete access to the internal components of a tokamak reactor for maintenance of replacement. The requirement of readily demountable joints dictates the use of water-cooled resistive coils, which have a host of decisive advantages over superconducting coils. Previous papers have shown that resistive TF coils for tokamak reactors can operate in the steady state with acceptable power dissipation (typically, 175 to 300 MW). This paper summarizes results of parametric studies of size optimization of rectangular TF coils and of a finite-element stress analysis, and examines several candidate methods of implementing demountable joints for rectangular coils constructed of plate segments.

9. Background field coils for the High Field Test Facility

SciTech Connect

Zbasnik, J.P.; Cornish, D.N.; Scanlan, R.M.; Jewell, A.M.; Leber, R.L.; Rosdahl, A.R.; Chaplin, M.R.

1980-09-22

The High Field Test Facility (HFTF), presently under construction at LLNL, is a set of superconducting coils that will be used to test 1-m-o.d. coils of prototype conductors for fusion magnets in fields up to 12 T. The facility consists of two concentric sets of coils; the outer set is a stack of Nb-Ti solenoids, and the inner set is a pair of solenoids made of cryogenically-stabilized, multifilamentary Nb/sub 3/Sn superconductor, developed for use in mirror-fusion magnets. The HFTF system is designed to be parted along the midplane to allow high-field conductors, under development for Tokamak fusion machines, to be inserted and tested. The background field coils were wound pancake-fashion, with cold-welded joints at both the inner and outer diameters. Turn-to-turn insulation was fabricated at LLNL from epoxy-fiberglass strip. The coils were assembled and tested in our 2-m-diam cryostat to verify their operation.

10. Flat RF coils in static field gradient nuclear magnetic resonance.

PubMed

Stork, H; Gädke, A; Nestle, N; Fujara, F

2009-10-01

The use of flat RF coils allows considerable gains in the sensitivity of static field gradient (SFG) nuclear magnetic resonance (NMR) experiments. In this article, this effect is studied theoretically as well as experimentally. Additionally, the flat coil geometry has been studied theoretically depending on magnetic field gradient, pulse sequence and amplifier power. Moreover, detecting the signal directly from the free induction decay (FID) turned out to be quite attractive for STRAFI-like microimaging experiments, especially when using flat coils. In addition to wound rectangular flat coils also spiral flat coils have been developed which can be manufactured by photolithography from printed circuit boards.

11. Modified van Vaals-Bergman coaxial cable coil (lambda coil) for high-field imaging.

PubMed

1996-03-01

An easily constructed, low-capacitive coupling volume coil based on the van Vaals-Bergman coaxial cable coil for high field imaging is described. The coil (designated "lambda coil") was constructed using two 5/4 length 50 omega coaxial cables matched to a 50 omega transmission line with LC bridge balun. The standing wave on the single 5/4 lambda length coaxial cable provides two points of current maxima in oppositional direction. Therefore, the four current elements necessary for effective B1 field generation can be obtained by two 5/4 lambda length coaxial cables arranged analogous to 1/2 lambda T-antenna. Capacitive coupling between the coil elements and conductive samples (i.e. animals) is minimized by simply retaining the shield of the coaxial cable for the area of voltage maxima. The lambda coil exhibited excellent performance as a volume coil with a high quality factor and highly homogeneous rf fields. Because of its dramatically simple architecture and excellent performance, the lambda coil configuration appears to be an economical alternative to the original van Vaals-Bergman design, especially for research facilities with a high field magnet and limited bore space.

12. Magnetic field pitch angle and perpendicular velocity measurements from multi-point time-delay estimation of poloidal correlation reflectometry

Prisiazhniuk, D.; Krämer-Flecken, A.; Conway, G. D.; Happel, T.; Lebschy, A.; Manz, P.; Nikolaeva, V.; Stroth, U.; the ASDEX Upgrade Team

2017-02-01

In fusion machines, turbulent eddies are expected to be aligned with the direction of the magnetic field lines and to propagate in the perpendicular direction. Time delay measurements of density fluctuations can be used to calculate the magnetic field pitch angle α and perpendicular velocity {{v}\\bot} profiles. The method is applied to poloidal correlation reflectometry installed at ASDEX Upgrade and TEXTOR, which measure density fluctuations from poloidally and toroidally separated antennas. Validation of the method is achieved by comparing the perpendicular velocity (composed of the E× B drift and the phase velocity of turbulence {{v}\\bot}={{v}E× B}+{{v}\\text{ph}} ) with Doppler reflectometry measurements and with neoclassical {{v}E× B} calculations. An important condition for the application of the method is the presence of turbulence with a sufficiently long decorrelation time. It is shown that at the shear layer the decorrelation time is reduced, limiting the application of the method. The magnetic field pitch angle measured by this method shows the expected dependence on the magnetic field, plasma current and radial position. The profile of the pitch angle reproduces the expected shape and values. However, comparison with the equilibrium reconstruction code cliste suggests an additional inclination of turbulent eddies at the pedestal position (2-3°). This additional angle decreases towards the core and at the edge.

13. High-field magnetic resonance imaging using solenoid radiofrequency coils.

PubMed

Vegh, Viktor; Gläser, Philipp; Maillet, Donald; Cowin, Gary J; Reutens, David C

2012-10-01

High-resolution magnetic resonance imaging using dedicated high-field radiofrequency micro-coils at 16.4 T (700 MHz) was investigated. Specific solenoid coils primarily using silver and copper as conductors with enamel and polyurethane coatings were built to establish which coil configuration produces the best image. Image quality was quantified using signal-to-noise ratio and signal variation over regions of interest. Benchmarking was conducted using 5-mm diameter coils, as this size is comparable to an established coil of the same size. Our 1.4-mm-diameter coils were compared directly to each other, from which we deduce performance as a function of conductor material and coating. A variety of materials and conductor coatings allowed us to choose an optimal design, which we used to image a kidney section at 10-micron resolution. We applied zero-fill extrapolation to achieve 5-micron resolution.

14. RF coil optimization: evaluation of B1 field homogeneity using field histograms and finite element calculations.

PubMed

Li, S; Yang, Q X; Smith, M B

1994-01-01

Two-dimensional (2D) finite element analysis has been used to solve the full set of Maxwell's equations for the 2D magnetic field of radiofrequency (RF) coils. The field histogram method has been applied to evaluate and optimize the magnetic field homogeneity of some commonly used RF coils: the saddle coil, the slotted tube resonator, the multiple elements coil and the birdcage resonator, as well as the radial plate coil. Each coil model represents a cross-section of an infinitely long cylinder. The optimum configuration of each of these five RF coils is suggested. It was found that field homogeneity is more strongly dependent on the coil's window angle than on any other parameter. Additionally, eddy currents in the coil's conductive elements distort the current and magnetic field distribution. The frequency dependence of this eddy current distortion is analyzed and discussed.

15. Poloidal Rotation Dynamics, Radial Electric Field, and Neoclassical Theory in the Jet Internal-Transport-Barrier Region

SciTech Connect

Crombe, K.; Oost, G. van; Andrew, Y.; Giroud, C.; Hawkes, N. C.; Parail, V.; Voitsekhovitch, I.; Zastrow, K.-D.; Hacquin, S.; Nave, M.F.F.; Ongena, J.

2005-10-07

Results from the first measurements of a core plasma poloidal rotation velocity (v{sub {theta}}) across internal transport barriers (ITB) on JET are presented. The spatial and temporal evolution of the ITB can be followed along with the v{sub {theta}} radial profiles, providing a very clear link between the location of the steepest region of the ion temperature gradient and localized spin-up of v{sub {theta}}. The v{sub {theta}} measurements are an order of magnitude higher than the neoclassical predictions for thermal particles in the ITB region, contrary to the close agreement found between the determined and predicted particle and heat transport coefficients [K.-D. Zastrow et al., Plasma Phys. Controlled Fusion 46, B255 (2004)]. These results have significant implications for the understanding of transport barrier dynamics due to their large impact on the measured radial electric field profile.

16. Transverse low-field RF coils in MRI.

PubMed

Claasen-Vujcić, T; Borsboom, H M; Gaykema, H J; Mehlkopf, T

1996-07-01

Imaging at low fields imposes a number of nonstandard requirements on the RF coil. At low fields, coil losses are dominant over patient losses. This means that even more stress is put on the quality factor Q. Furthermore, the low frequency also implies a high inductance L and/or a high capacitance C product. Just increasing the capacitance C results in a difficult optimal matching to the preamplifier as well as increased costs and higher complexity of the resonator construction. Coils with a high quality factor Q and a high inductance are thus required at low fields. Birdcage coils possess a number of advantages over saddle and solenoidal coils. However, the currently used birdcages have inherently low inductances limited by the size of the coil. The problem can be solved by a novel design in which the strip configuration for inductors is abandoned and the inductors are realized as a certain number of turns. The Q factor can be further improved by using Litz wire. Three novel transverse RF coils with high inductances are presented and compared with each other as well as to the standard coils. Both linear and quadrature modes are discussed.

17. Blob dynamics in TORPEX poloidal null configurations

Shanahan, B. W.; Dudson, B. D.

2016-12-01

3D blob dynamics are simulated in X-point magnetic configurations in the TORPEX device via a non-field-aligned coordinate system, using an isothermal model which evolves density, vorticity, parallel velocity and parallel current density. By modifying the parallel gradient operator to include perpendicular perturbations from poloidal field coils, numerical singularities associated with field aligned coordinates are avoided. A comparison with a previously developed analytical model (Avino 2016 Phys. Rev. Lett. 116 105001) is performed and an agreement is found with minimal modification. Experimental comparison determines that the null region can cause an acceleration of filaments due to increasing connection length, but this acceleration is small relative to other effects, which we quantify. Experimental measurements (Avino 2016 Phys. Rev. Lett. 116 105001) are reproduced, and the dominant acceleration mechanism is identified as that of a developing dipole in a moving background. Contributions from increasing connection length close to the null point are a small correction.

18. MAGNETIC FIELD CONFIGURATION AT THE GALACTIC CENTER INVESTIGATED BY WIDE-FIELD NEAR-INFRARED POLARIMETRY: TRANSITION FROM A TOROIDAL TO A POLOIDAL MAGNETIC FIELD

SciTech Connect

Nishiyama, Shogo; Yoshikawa, Tatsuhito; Nagata, Tetsuya; Hatano, Hirofumi; Nagayama, Takahiro; Tamura, Motohide; Matsunaga, Noriyuki; Suenaga, Takuya; Hough, James H.; Sugitani, Koji; Kato, Daisuke

2010-10-10

We present a large-scale view of the magnetic field (MF) in the central 2{sup 0} x 2{sup 0} region of our Galaxy. The polarization of point sources has been measured in the J, H, and K{sub S} bands using the near-infrared polarimetric camera SIRPOL on the 1.4 m Infrared Survey Facility telescope. Comparing the Stokes parameters between high extinction stars and relatively low extinction ones, we obtain polarization originating from magnetically aligned dust grains in the central few hundred parsecs of our Galaxy. We find that near the Galactic plane, the MF is almost parallel to the Galactic plane (i.e., toroidal configuration), but at high Galactic latitudes (|b | >0.{sup 0}4) the field is nearly perpendicular to the plane (i.e., poloidal configuration). This is the first detection of a smooth transition of the large-scale MF configuration in this region.

19. Spitzer or neoclassical resistivity: A comparison between measured and model poloidal field profiles on PBX-M

SciTech Connect

Kaye, S.M.; Hatcher, R.; Kaita, R.; Kessel, C.; LeBlanc, B.; McCune, D.C.; Paul, S.; Levinton, F.M.

1992-01-01

Direct measurements of the radial profile of the magnetic field line pitch on PBX-M coupled with model predictions of these profiles allow a critical comparison with the Spitzer and neoclassical models of plasma parallel resistivity. The measurements of the magnetic field line pitch are made by Motional Stark Effect polarimetry, while the model profiles are determined by solving the poloidal field diffusion equation in the TRANSP transport code using measured plasma profiles and assuming either Spitzer or neoclassical resistivity. The measured field pitch profiles were available for only seven cases, and the model profiles were distinguishable from each other in only three of those cases due to finite resistive diffusion times. The data in two of these three were best matched by the Spitzer model, especially in the inner half of the plasma. Portions of the measured pitch profiles for these two cases and the full profiles for other cases, however, departed significantly from both the Spitzer and neoclassical models, indicating a plasma resistivity profile different from either model.

20. Resistive toroidal-field coils for tokamak reactors

SciTech Connect

Kalnavarns, J.; Jassby, D.L.

1980-11-01

This paper analyzes the optimization of the geometry of resistive TF coils of rectangular bore for tokamak fusion test reactors and practical neutron generators. In examining the trade-offs between geometric parameters and magnetic field for reactors giving a specified neutron wall loading, either the resistive power loss or the lifetime coil cost can be minimized. Aspects of cooling, magnetic stress, and construction are addressed for several reference designs. Bending moment distributions in closed form have been derived for rectangular coils on the basis of the theory of rigid frames. Candidate methods of fabrication and of implementing demountable joints are summarized.

1. Intelligent shell feedback control in EXTRAP T2R reversed field pinch with partial coverage of the toroidal surface by a discrete active coil array

Yadikin, D.; Brunsell, P. R.; Drake, J. R.

2006-01-01

An active feedback system is required for long pulse operation of the reversed field pinch (RFP) device to suppress resistive wall modes (RWMs). A general feature of a feedback system using a discrete active coil array is a coupling effect which arises when a set of side band modes determined by the number of active coils is produced. Recent results obtained on the EXTRAP T2R RFP demonstrated the suppression of independent m = 1 RWMs using an active feedback system with a two-dimensional array of discrete active coils in the poloidal and toroidal directions. One of the feedback algorithms used is the intelligent shell feedback scheme. Active feedback systems having different number of active coils in the poloidal (Mc) and toroidal (Nc) directions (Mc × Nc = 2 × 32 and Mc × Nc = 4 × 16) are studied. Different side band effects are seen for these configurations. A significant prolongation of the plasma discharge is achieved for the intelligent shell feedback scheme using the 2 × 32 active coil configuration. This is attributed to the side band sets including only one of the dominant unstable RWMs and avoiding coupling to resonant modes. Analog proportional-integral-derivative controllers are used in the feedback system. Regimes with different values of the proportional gain are studied. The requirement of the proportional-integral control for low proportional gain and proportional-derivative control for high proportional gain is seen in the experiments.

2. The toroidal field coil design for ARIES-ST

SciTech Connect

Reiersen, W.; Dahlgren, F.; Fan, H.M.; Neumeyer, C.; Zatz, I.

2000-01-21

An evolutionary process was used to develop the toroidal field (TF) coil design for the ARIES-ST (Spherical Tokamak). Design considerations included fabricability, assembly, maintenance, energy efficiency, and structural robustness. The design addresses a number of the concerns (complexity) and criticisms (high cost, high recirculating power) of fusion. It does this by: (1) Applying advanced, but available laser forming and spray casting techniques for manufacturing the TF coil system; (2) Adopting a simple single toroidal field coil system to make assembly and maintenance much easier, the single turn design avoids the necessity of using the insulation as a structural component of the TF coils, and hence is much more robust than multi-turn designs; and (3) Using a high conductivity copper alloy and modest current densities to keep the recirculating power modest.

3. Dependence of neoclassical toroidal viscosity on the poloidal spectrum of applied nonaxisymmetric fields

SciTech Connect

Logan, Nikolas C.; Park, Jong -Kyu; Paz-Soldan, Carloa; Lanctot, Matthew J.; Smith, Sterling P.; Burrell, K. H.

2016-02-05

This paper presents a single mode model that accurately predicts the coupling of applied nonaxisymmetric fields to the plasma response that induces neoclassical toroidal viscosity (NTV) torque in DIII-D H-mode plasmas. The torque is measured and modeled to have a sinusoidal dependence on the relative phase of multiple nonaxisymmetric field sources, including a minimum in which large amounts of nonaxisymmetric drive is decoupled from the NTV torque. This corresponds to the coupling and decoupling of the applied field to a NTV-driving mode spectrum. Modeling using the perturbed equilibrium nonambipolar transport (PENT) code confirms an effective single mode coupling between the applied field and the resultant torque, despite its inherent nonlinearity. Lastly, the coupling to the NTV mode is shown to have a similar dependence on the relative phasing as that of the IPEC dominant mode, providing a physical basis for the efficacy of this linear metric in predicting error field correction optima in NTV dominated regimes.

4. Design and numerical evaluation of a volume coil array for parallel MR imaging at ultrahigh fields

PubMed Central

Pang, Yong; Wong, Ernest W.H.; Yu, Baiying

2014-01-01

In this work, we propose and investigate a volume coil array design method using different types of birdcage coils for MR imaging. Unlike the conventional radiofrequency (RF) coil arrays of which the array elements are surface coils, the proposed volume coil array consists of a set of independent volume coils including a conventional birdcage coil, a transverse birdcage coil, and a helix birdcage coil. The magnetic fluxes of these three birdcage coils are intrinsically cancelled, yielding a highly decoupled volume coil array. In contrast to conventional non-array type volume coils, the volume coil array would be beneficial in improving MR signal-to-noise ratio (SNR) and also gain the capability of implementing parallel imaging. The volume coil array is evaluated at the ultrahigh field of 7T using FDTD numerical simulations, and the g-factor map at different acceleration rates was also calculated to investigate its parallel imaging performance. PMID:24649435

5. Dependence of neoclassical toroidal viscosity on the poloidal spectrum of applied nonaxisymmetric fields

DOE PAGES

Logan, Nikolas C.; Park, Jong -Kyu; Paz-Soldan, Carloa; ...

2016-02-05

This paper presents a single mode model that accurately predicts the coupling of applied nonaxisymmetric fields to the plasma response that induces neoclassical toroidal viscosity (NTV) torque in DIII-D H-mode plasmas. The torque is measured and modeled to have a sinusoidal dependence on the relative phase of multiple nonaxisymmetric field sources, including a minimum in which large amounts of nonaxisymmetric drive is decoupled from the NTV torque. This corresponds to the coupling and decoupling of the applied field to a NTV-driving mode spectrum. Modeling using the perturbed equilibrium nonambipolar transport (PENT) code confirms an effective single mode coupling between themore » applied field and the resultant torque, despite its inherent nonlinearity. Lastly, the coupling to the NTV mode is shown to have a similar dependence on the relative phasing as that of the IPEC dominant mode, providing a physical basis for the efficacy of this linear metric in predicting error field correction optima in NTV dominated regimes.« less

6. Field Quality Optimization in a Common Coil Magnet Design

SciTech Connect

Gupta, R.; Ramberger, S.

1999-09-01

This paper presents the results of initial field quality optimization of body and end harmonics in a 'common coil magnet design'. It is shown that a good field quality, as required in accelerator magnets, can be obtained by distributing conductor blocks in such a way that they simulate an elliptical coil geometry. This strategy assures that the amount of conductor used in this block design is similar to that is used in a conventional cosine theta design. An optimized yoke that keeps all harmonics small over the entire range of operation using a single power supply is also presented. The field harmonics are primarily optimized with the computer program ROXIE.

7. Miniature coils for producing pulsed inplane magnetic fields for nanospintronics

SciTech Connect

Pawliszak, Łukasz; Zgirski, Maciej

2015-03-15

Nanospintronic and related research often requires the application of quickly rising magnetic field pulses in the plane of the studied planar structure. We have designed and fabricated sub-millimeter-sized coils capable of delivering pulses of the magnetic field up to ∼500 Oe in the plane of the sample with the rise time of the order of 10 ns. The placement of the sample above the coil allows for easy access to its surface with manipulators or light beams for, e.g., Kerr microscopy. We use the fabricated coil to drive magnetic domain walls in 1 μm wide permalloy wires and measure magnetic domain wall velocity as a function of the applied magnetic field.

8. Laboratory formation of a scaled protostellar jet by coaligned poloidal magnetic field: recent results and new exeprimental studies

Vinci, Tommaso; Revet, Guilhem; Higginson, Drew; Béard, Jérome; Burdonov, K.; Chen, Sophia; Khagani, D.; Khiar, B.; Naughton, K.; Pikuz, S.; Riconda, Caterina; Riquier, R.; Soloviev, A.; Willi, O.; Portugall, O.; Pépin, Henry; Ciardi, Andrea; Fuchs, Julien; Albertazzi, Bruno

2015-08-01

Accretion shocks in Young Stellar Objects (YSO) are a subject of great interest in astrophysics; they exhibit intense magnetic activity and are surrounded by an accretion disk from which matter falls down onto the stellar surface in the form of columns following the magnetic lines (B ~ kG) at the free-fall velocity (100-500 km/s). As a column impacts the stellar surface, a radiative shock is created which heats up the infalling flow. As a consequence, a new reverse shock forms and some oscillations are expected in the emitted radiation as a proof of this periodic dynamic, but no periodicity has yet been detected in observations.To understand the reasons for this apparent inconsistency, we have recently developped an experimental setup [B. Albertazzi et al. Science 346, 325 (2014)] in which a plasma flow (generated by a high energy laser: 1013 W/cm2 - 0.6 ns pulse) is confined inside a poloidal magnetic field (20 T). This jet has an aspect ratio >10, a temperature of tens of eV, an electron density of 1018 cm-3 and propagates at 700 km/s as show by our previous numerical work [A. Ciardi et al. Physical Review Letters, 110 (2013)]. To investigate the accretion dynamics, the jet acts as the accretion column and hits a secondary target acting as the stellar surface. We will present the recent results on generation and dynamics of the jet and the new experimental results of this configuration, namely of a supersonic reverse shock traveling within the accretion column with a speed of 100 km/s, representing a Mach number of ~ 30, and the observation of increased density structures along the edges of the interaction. This will be discussed in the light of 3D-magneto-hydrodynamic simulations which parametric variations allow to understand how the various plasma parameters affect the accretion.

9. Tokamak with liquid metal toroidal field coil

DOEpatents

Ohkawa, Tihiro; Schaffer, Michael J.

1981-01-01

Tokamak apparatus includes a pressure vessel for defining a reservoir and confining liquid therein. A toroidal liner disposed within the pressure vessel defines a toroidal space within the liner. Liquid metal fills the reservoir outside said liner. Electric current is passed through the liquid metal over a conductive path linking the toroidal space to produce a toroidal magnetic field within the toroidal space about the major axis thereof. Toroidal plasma is developed within the toroidal space about the major axis thereof.

10. Inboard and outboard radial electric field wells in the H- and I-mode pedestal of Alcator C-Mod and poloidal variations of impurity temperature

Theiler, C.; Churchill, R. M.; Lipschultz, B.; Landreman, M.; Ernst, D. R.; Hughes, J. W.; Catto, P. J.; Parra, F. I.; Hutchinson, I. H.; Reinke, M. L.; Hubbard, A. E.; Marmar, E. S.; Terry, J. T.; Walk, J. R.; the Alcator C-Mod Team

2014-08-01

We present inboard (HFS) and outboard (LFS) radial electric field (Er) and impurity temperature (Tz) measurements in the I-mode and H-mode pedestal of Alcator C-Mod. These measurements reveal strong Er wells at the HFS and the LFS midplane in both regimes and clear pedestals in Tz, which are of similar shape and height for the HFS and LFS. While the H-mode Er well has a radially symmetric structure, the Er well in I-mode is asymmetric, with a stronger ExB shear layer at the outer edge of the Er well, near the separatrix. Comparison of HFS and LFS profiles indicates that impurity temperature and plasma potential are not simultaneously flux functions. Uncertainties in radial alignment after mapping HFS measurements along flux surfaces to the LFS do not, however, allow direct determination as to which quantity varies poloidally and to what extent. Radially aligning HFS and LFS measurements based on the Tz profiles would result in substantial inboard-outboard variations of plasma potential and electron density. Aligning HFS and LFS Er wells instead also approximately aligns the impurity poloidal flow profiles, while resulting in a LFS impurity temperature exceeding the HFS values in the region of steepest gradients by up to 70%. Considerations based on a simplified form of total parallel momentum balance and estimates of parallel and perpendicular heat transport time scales seem to favor an approximate alignment of the Er wells and a substantial poloidal asymmetry in impurity temperature.

11. Poloidal OHMIC heating in a multipole

SciTech Connect

Holly, D.J.

1982-01-01

The feasibility of using poloidal currents to heat plasmas confined by a multipole field has been examined experimentaly in Tokapole II. The machine is operated as a toroidal octupole, with a time-varying toroidal magnetic field driving poloidal plasma currents I/sub plasma/ - 20 kA to give densities n/sub e/ - 10/sup 13/ cm/sup -3/ and temperatures T/sub e/ - 30 eV.

12. The reversed-field pinch as a poloidal-field-dominated, compact, high-power-density fusion system

SciTech Connect

Krakowski, R.A.

1988-01-01

This paper discusses the feasibility of reversed-field pinch devices as future thermonuclear reactors. Safety, cost, ion temperatures, Lawson numbers, and power densities are reviewed for these types of devices. 12 refs., 2 figs., 1 tab. (LSP)

13. Electric field depth–focality tradeoff in transcranial magnetic stimulation: simulation comparison of 50 coil designs

PubMed Central

Deng, Zhi-De; Lisanby, Sarah H.; Peterchev, Angel V.

2012-01-01

Background Various transcranial magnetic stimulation (TMS) coil designs are available or have been proposed. However, key coil characteristics such as electric field focality and attenuation in depth have not been adequately compared. Knowledge of the coil focality and depth characteristics can help TMS researchers and clinicians with coil selection and interpretation of TMS studies. Objective To quantify the electric field focality and depth of penetration of various TMS coils. Methods The electric field distributions induced by 50 TMS coils were simulated in a spherical human head model using the finite element method. For each coil design, we quantified the electric field penetration by the half-value depth, d1/2, and focality by the tangential spread, S1/2, defined as the half-value volume (V1/2) divided by the half-value depth, S1/2 = V1/2/d1/2. Results The 50 TMS coils exhibit a wide range of electric field focality and depth, but all followed a depth–focality tradeoff: coils with larger half-value depth cannot be as focal as more superficial coils. The ranges of achievable d1/2 are similar between coils producing circular and figure-8 electric field patterns, ranging 1.0–3.5 cm and 0.9–3.4 cm, respectively. However, figure-8 field coils are more focal, having S1/2 as low as 5 cm2 compared to 34 cm2 for circular field coils. Conclusions For any coil design, the ability to directly stimulate deeper brain structures is obtained at the expense of inducing wider electrical field spread. Novel coil designs should be benchmarked against comparison coils with consistent metrics such as d1/2 and S1/2. PMID:22483681

14. AC losses in a HTS coil carrying DC current in AC external magnetic field

Ogawa, J.; Zushi, Y.; Fukushima, M.; Tsukamoto, O.; Suzuki, E.; Hirakawa, M.; Kikukawa, K.

2003-10-01

We electrically measured AC losses in a Bi2223/Ag-sheathed pancake coil excited by a DC current in AC external magnetic field. Losses in the coil contain two kinds of loss components that are the magnetization losses and dynamic resistance losses. In the measurement, current leads to supply a current to the coil were specially arranged to suppress electromagnetic coupling between the coil current and the AC external magnetic field. A double pick-up coils method was used to suppress a large inductive voltage component contained in voltage signal for measuring the magnetization losses. It was observed that the magnetization losses were dependent on the coil current and that a peak of a curve of the loss factor vs. amplitude of the AC external magnetic field shifted to lower amplitude of the AC magnetic field as the coil current increased. This result suggests the full penetration magnetic field of the coil tape decreases as the coil current increases. The dynamic resistance losses were measured by measuring a DC voltage appearing between the coil terminals. It was observed that the DC voltage appearing in the coil subject to the AC external magnetic field was much larger than that in the coil subject to DC magnetic field.

15. Fuel magnetization without external field coils (AutoMag)

Slutz, Stephen; Jennings, Christopher; Awe, Thomas; Shipley, Gabe; Lamppa, Derek; McBride, Ryan

2016-10-01

Magnetized Liner Inertial Fusion (MagLIF) has produced fusion-relevant plasma conditions on the Z accelerator where the fuel was magnetized using external field coils. We present a novel concept that does not need external field coils. This concept (AutoMag) magnetizes the fuel during the early part of the drive current by using a composite liner with helical conduction paths separated by insulating material. The drive is designed so the current rises slowly enough to avoid electrical breakdown of the insulators until a sufficiently strong magnetic field is established. Then the current rises more quickly, which causes the insulators to break down allowing the drive current to follow an axial path and implode the liner. Low inductance magnetically insulated power feeds can be used with AutoMag to increase the drive current without interfering with diagnostic access. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

16. Heat flux and plasma flow in the far scrape-off layer of the inboard poloidal field null configuration in QUEST

SciTech Connect

Onchi, T.; Zushi, H.; Hanada, K.; Idei, H.; Hasegawa, M.; Nakamura, K.; Fujisawa, A.; Nagashima, Y.; Matsuoka, K.; Kuzmin, A.; Kawasaki, S.; Nakashima, H.; Higashijima, A.; Watanabe, O.; Mishra, K.; Mahira, Y.; Tashima, S.; Banerjee, S.; Nagaoka, K.

2015-08-15

Heat flux and plasma flow in the scrape-off layer (SOL) are examined for the inboard poloidal field null (IPN) configuration of the spherical tokamak QUEST. In the plasma current (I{sub p}) ramp-up phase, high heat flux (>1 MW/m{sup 2}) and supersonic flow (Mach number M > 1) are found to be present simultaneously in the far-SOL. The heat flux is generated by energetic electrons excursed from the last closed flux surface. Supersonic flows in the poloidal and toroidal directions are correlated with each other. In the quasi-steady state, sawtooth-like oscillation of I{sub p} at 20 Hz is observed. Heat flux and subsonic plasma flow in the far-SOL are modified corresponding to the I{sub p}-oscillation. The heat flow caused by motion of energetic electrons and the bulk-particle transport to the far-SOL is enhanced during the low-I{sub p} phase. Modification of plasma flow in the far SOL occurs earlier than the I{sub p} crash. The M–I{sub p} curve has a limit-cycle characteristic with sawtooth-like oscillation. Such a core–SOL relationship indicates that the far-SOL flow plays an important role in sustaining the oscillation of I{sub p} in the IPN configuration.

17. Development of a patch antenna array RF coil for ultra-high field MRI.

PubMed

Nakajima, Manabu; Nakajima, Iwao; Obayashi, Shigeru; Nagai, Yuji; Obata, Takayuki; Hirano, Yoshiyuki; Ikehira, Hiroo

2007-01-01

In radiofrequency (RF) coil design for ultra-high-field magnetic resonance (MR) imaging, short RF wavelengths present various challenges to creating a big volume coil. When imaging a human body using an ultra-high magnetic field MR imaging system (magnetic flux density of 7 Tesla or more), short wavelength may induce artifacts from dielectric effect and other factors. To overcome these problems, we developed a patch antenna array coil (PAAC), which is a coil configured as a combination of patch antennas. We prototyped this type of coil for 7T proton MR imaging, imaged a monkey brain, and confirmed the coil's utility as an RF coil for ultra-high-field MR imaging.

18. Microstrip RF surface coil design for extremely high-field MRI and spectroscopy.

PubMed

Zhang, X; Ugurbil, K; Chen, W

2001-09-01

A new type of high-frequency RF surface coil was developed for in vivo proton or other nuclei NMR applications at 7T. This is a purely distributed-element and transmission line design. The coil consists of a thin strip conductor (copper or silver) and a ground plane separated by a low-loss dielectric material with a thickness (H). Due to its specific semi-open transmission line structure, substantial electromagnetic energy is stored in the dielectric material between the thin conductor and the ground plane, which results in a reduced radiation loss and a reduced perturbation of sample loading to the RF coil compared to conventional surface coils. The coil is characterized by a high Q factor, no RF shielding, small physical coil size, lower cost, and easy fabrication. A brief theoretical description of the microstrip RF coil is given that can be used to guide the coil designs. A set of gradient-recalled echo images were acquired by using the single- and two-turn microstrip RF surface coils from both phantom and human brain at 7T, which show good penetration and sensitivity. The two-turn coil design significantly improves the B1 symmetry as predicted by the microstrip theory. The optimum H for microstrip surface coils is approximately 7 mm. This coil geometry yields a B1 penetration similar to that of conventional surface coils. SNR comparison was made between the microstrip coil and conventional surface coils with and without RF shielding. The results reveal that the novel surface coil design based on the microstrip concept makes very high-field MRI/MRS more convenient and efficient in research and future clinics.

19. Field Demonstraton of Existing Microhole Coiled Tubing Rig (MCTR) Technology

SciTech Connect

Kent Perry; Samih Batarseh; Sheriff Gowelly; Thomas Hayes

2006-05-09

20. Magnetic field uniformity of the practical tri-axial Helmholtz coils systems.

PubMed

Beiranvand, R

2014-05-01

In this paper, effects of the assembly misalignments and the manufacturing mismatches on the magnetic field uniformity of a practical tri-axial Helmholtz coils system have been modeled mathematically. These undesired effects regularly occur in any practical tri-axial Helmholtz coils system. To confirm the mathematical calculations, a tri-axial Helmholtz coils system has been constructed and the uniformity of its magnetic field has been measured under different conditions. The experimental results are in good agreement with the mathematical analyses.

1. Cavity resonator coil for high field magnetic resonance imaging.

PubMed

Solis, S E; Tomasi, D; Rodriguez, A O

2007-01-01

A variant coil of the high frequency cavity resonator coil was experimentally developed according to the theoretical frame proposed by Mansfield in 1990. This coil design is similar to the popular birdcage coil but it has the advantage that it can be easily built following the physical principles of the cavity resonators [1]. The equivalent circuit approach was used to compute the resonant frequency of this coil design, and compared the results with those frequency values obtained with theory. A transceiver coil composed of 4 cavities with a rod length of 4.5 cm, and a resonant frequency of 170.29 MHz was built. Phantom images were then acquired to test its viability using standard imaging sequences. The theory facilitates its development for high frequency MRI applications of animal models.

2. Numerical study of the magnetic field diffusion in the toroidal field coils of the TFTR

SciTech Connect

Preis, H.

1983-01-01

The diffusion of the vertical magnetic field through the toroidal field coils is numerically analyzed in TFTR. Two different excitations of the vertical field are assumed whose behavior can be described by either a step function or a ramp function. Using the computer code FEDIFF, the distribution of the eddy currents in the windings and casing of the toroidal field coils, as well as their time behavior, is calculated for these functions. From integration of the eddy current functions over their pulse length, the energy dissipated by them is obtained. Finally, the magnetic field of the eddy currents within the torous is calculated. Based upon this field, which is represented as a function of time and space coordinates, the influence of this diffusion upon the field curvature index is described.

3. Fabrication of superconducting tunnel junctions with embedded coil for applying magnetic field

Yamaguchi, Kenji; Nakagawa, Hiroshi; Aoyagi, Masahiro; Naruse, Masato; Myoren, Hiroaki; Taino, Tohru

2016-11-01

We have proposed and demonstrated a superconducting tunnel junction (STJ) with an embedded coil for applying a magnetic field. The STJ was fabricated on the coil, which was embedded in a Si substrate. The coil in the Si substrate consists of superconducting microstrip lines and applies a magnetic field to the STJ to suppress the dc Josephson current. The embedded coil was designed with a line and space of 3 μm and a thickness of 120 nm. To planarize the coil, we employed chemical mechanical polishing (CMP) in our fabrication process. In this STJ, the maximum current of the embedded coil was 28 mA, which corresponded to the maximum magnetic field of 11.76 mT.

4. From poloidal to toroidal: Detection of a well-ordered magnetic field in the high-mass protocluster G35.2–0.74 N

SciTech Connect

Qiu, Keping; Zhang, Qizhou; Menten, Karl M.; Liu, Hauyu B.; Tang, Ya-Wen

2013-12-20

We report the detection of an ordered magnetic field threading a cluster-forming clump in the molecular cloud G35.2–0.74 using Submillimeter Array observations of polarized dust emission. We resolve the morphology of the magnetic field in the plane of sky and detect a great turn of 90° in the field direction: over the northern part of the clump, where a velocity gradient is evident, the magnetic field is aligned along the long axis of the clump, whereas in the southern part, where the velocity structure appears relatively uniform, the field is aligned perpendicular to the clump. Taking into account early single-disk data, we suggest that the clump forms as its parent cloud collapses more along the magnetic field. The northern part of the clump carries over angular momentum from the cloud, forming a fast rotating system, and the magnetic field is pulled into a toroidal configuration. In contrast, the southern part is not significantly rotating and retains a poloidal field. A statistical analysis of the observed polarization dispersion yields a field strength of ∼1 mG. Detailed calculations support our hypothesis of a rotationally twisted magnetic field in the northern part. The observations suggest that the magnetic field may play a critical role in the formation of the dense clump, while in its further dynamical evolution, rotation and turbulence can also be important. In addition, our observations provide evidence for a wide-angle outflow driven from a strongly rotating region whose magnetic field is largely toroidal.

5. Measurement of Poloidal Velocity on the National Spherical Torus Experiment

SciTech Connect

Ronald E. Bell and Russell Feder

2010-06-04

A diagnostic suite has been developed to measure impurity poloidal flow using charge exchange recombination spectroscopy on the National Spherical Torus Experiment. Toroidal and poloidal viewing systems measure all quantities required to determine the radial electric field. Two sets of up/down symmetric poloidal views are used to measure both active emission in the plane of the neutral heating beams and background emission in a radial plane away from the neutral beams. Differential velocity measurements isolate the line-integrated poloidal velocity from apparent flows due to the energy-dependent chargeexchange cross section. Six f/1.8 spectrometers measure 276 spectra to obtain 75 active and 63 background channels every 10 ms. Local measurements from a similar midplane toroidal viewing system are mapped into two dimensions to allow the inversion of poloidal line-integrated measurements to obtain local poloidal velocity profiles. Radial resolution after inversion is 0.6-1.8 cm from the plasma edge to the center.

6. Magnetic field sensitivity at 7-T using dual-helmholtz transmit-only coil and 12-channel receive-only bended coil.

PubMed

Kim, Kyoung-Nam; Ryu, Yeunchul; Seo, Jeung-Hoon; Kim, Young-Bo

2016-11-01

The purpose of this study was to combine a dual-Helmholtz (DH) transmit (Tx)-only coil and 12-channel receive (Rx)-only bended phased array (PA) coil to improve the magnetic flux (|B1 |) sensitivity in the superior-to-inferior (S-I) direction during human brain magnetic resonance imaging (MRI) at 7-T. The proposed coil combination was primarily implemented by electromagnetic (EM) simulation and compared with the 16-leg birdcage coil and 8-channel PA coil, which are generally used for the Tx- and Rx-only modes, respectively. The optimal coil combinations for the proposed structure were determined by |B1 | field calculations using the |BT(+) | and |BR(-) | fields, which are respectively the transmit and receive components of the |B1 | field. The coil performance was then evaluated by a bench test and 7-T MRI experiment. The results of the computational calculations indicated that the |BT(+) | field of the DH coil was distributed similarly to that of the 16-leg birdcage coil despite the fewer conducting legs of the former. However, the 12-channel Rx-only bended PA coil had clearly higher |BR(-) | profiles compared to the 8-channel PA coil. The results of the 7-T in vivo experiment showed that the proposed combination of the DH Tx-only coil and 12-channel Rx-only bended PA coil had better |B1 | field homogeneity in the sagittal slice as well as higher |B1 | field sensitivity during human brain MRI compared to an 8-channel Rx-only PA coil. SCANNING 38:515-524, © 2015 Wiley Periodicals, Inc.

7. Design of a High Field Nb3Al Common Coil Magnet

SciTech Connect

Xu, Qingjin; Sasaki, Kenichi; Nakamoto, Tatsushi; Terashima, Akio; Tsuchiya, Kiyosumi; Yamamoto, Akira; Kikuchi, Akihiro; Takeuchi, Takao; Sabbi, GianLuca; Caspi, Shlomo; Ferracin, Paolo; Felice, Helene; Hafalia, Ray; Zlobin, Alexander; Barzi, Emauela; Yamada, Ryuji

2009-10-19

A high field Nb{sub 3}Al common coil magnet is under development as an R&D of 'Advanced Superconducting Magnets for the LHC Luminosity Upgrade', in the framework of the CERN-KEK cooperation program. The goal of this research is to demonstrate the feasibility of high field magnet wound with Nb{sub 3}Al cable. The common coil approach and the shell-based structure were adopted in the design of this magnet. Besides three Nb{sub 3}Al coils, two Nb{sub 3}Sn coils were included to increase the peak field of the whole magnet. The two types of coils were designed with different straight lengths to reduce the peak field of the Nb{sub 3}Sn coils. The peak fields of the Nb{sub 3}Al and Nb{sub 3}Sn coils are 13.1 T and 11.8 T respectively. An aluminum shell together with four aluminum rods applies stress to the coils to overcome the Lorenz force during excitation. Two different support structures for the superconducting coils were introduced in this paper. The development status is also presented.

8. Resonant Mode Reduction in Radiofrequency Volume Coils for Ultrahigh Field Magnetic Resonance Imaging.

PubMed

Pang, Yong; Xie, Zhentian; Li, Ye; Xu, Duan; Vigneron, Daniel; Zhang, Xiaoliang

2011-07-28

In a multimodal volume coil, only one mode can generate homogeneous Radiofrequency (RF) field for Magnetic Resonance Imaging. The existence of other modes may increase the volume coil design difficulties and potentially decreases coil performance. In this study, we introduce common-mode resonator technique to high and ultrahigh field volume coil designs to reduce the resonant mode while maintain the homogeneity of the RF field. To investigate the design method, the common-mode resonator was realized by using a microstrip line which was split along the central to become a pair of parallel transmission lines within which common-mode currents exist. Eight common-mode resonators were placed equidistantly along the circumference of a low loss dielectric cylinder to form a volume coil. Theoretical analysis and comparison between the 16-strut common-mode volume coil and a conventional 16-strut volume coil in terms of RF field homogeneity and efficiency was performed using Finite-Difference Time-Domain (FDTD) method at 298.2 MHz. MR imaging experiments were performed by using a prototype of the common-mode volume coil on a whole body 7 Tesla scanner. FDTD simulation results showed the reduced number of resonant modes of the common-mode volume coil over the conventional volume coil, while the RF field homogeneity of the two type volume coils was kept at the same level. MR imaging of a water phantom and a kiwi fruit showing the feasibility of the proposed method for simplifying the volume coil design is also presented.

9. Magnetic-field sensing coil embedded in ceramic for measuring ambient magnetic field

DOEpatents

Takahashi, Hironori

2004-02-10

A magnetic pick-up coil for measuring magnetic field with high specific sensitivity, optionally with an electrostatic shield (24), having coupling elements (22) with high winding packing ratio, oriented in multiple directions, and embedded in ceramic material for structural support and electrical insulation. Elements of the coil are constructed from green ceramic sheets (200) and metallic ink deposited on surfaces and in via holes of the ceramic sheets. The ceramic sheets and the metallic ink are co-fired to create a monolithic hard ceramic body (20) with metallized traces embedded in, and placed on exterior surfaces of, the hard ceramic body. The compact and rugged coil can be used in a variety of environments, including hostile conditions involving ultra-high vacuum, high temperatures, nuclear and optical radiation, chemical reactions, and physically demanding surroundings, occurring either individually or in combinations.

10. Superconducting FCL using a combined inducted magnetic field trigger and shunt coil

DOEpatents

2007-10-16

A single trigger/shunt coil is utilized for combined induced magnetic field triggering and shunt impedance. The single coil connected in parallel with the high temperature superconducting element, is designed to generate a circulating current in the parallel circuit during normal operation to aid triggering the high temperature superconducting element to quench in the event of a fault. The circulating current is generated by an induced voltage in the coil, when the system current flows through the high temperature superconducting element.

11. Innovations in Quasi-Poloidal Stellarator Design

Nelson, B. E.; Lyon, J. F.; Freudenberg, K. D.; Fogarty, P. J.; Benson, R. D.; Madhukar, M.

2006-10-01

The Quasi-Poloidal Stellarator (QPS) is being developed with very low plasma aspect ratio, 1/2-1/4 that of existing stellarators. Design innovation is driven by both the complex 3-D geometry and the need for reduced cost and risk in fabrication, so QPS differs significantly in design and construction from other toroidal devices. An internally cooled, compacted cable conductor consisting of stranded copper filaments wound around an internal copper cooling tube was developed that can be wound into complex 3-D shapes. This conductor is wound directly onto the complex, highly accurate, stainless steel coil winding forms. Simplified coil winding procedures lead to faster fabrication and reduced technical risk. A full-size prototype of the largest and most complex of the winding forms has been cast using a patternless process (machined sand molds) and a high-temperature pour, which resulted in <1/10 the major weld repairs of similar sand castings using conventional patterns, and machined to high precision. A vacuum-tight cover is welded over each coil pack and a high-temperature cyanate ester resin is used for vacuum pressure impregnation of the coils because it has several important advantages over the usual epoxy. The completed coils are then installed in an external vacuum vessel.

12. INTERCOMPARISON OF PERFORMANCE OF RF COIL GEOMETRIES FOR HIGH FIELD MOUSE CARDIAC MRI

PubMed Central

Constantinides, Christakis; Angeli, S.; Gkagkarellis, S.; Cofer, G.

2012-01-01

Multi-turn spiral surface coils are constructed in flat and cylindrical arrangements and used for high field (7.1 T) mouse cardiac MRI. Their electrical and imaging performances, based on experimental measurements, simulations, and MRI experiments in free space, and under phantom, and animal loading conditions, are compared with a commercially available birdcage coil. Results show that the four-turn cylindrical spiral coil exhibits improved relative SNR (rSNR) performance to the flat coil counterpart, and compares fairly well with a commercially available birdcage coil. Phantom experiments indicate a 50% improvement in the SNR for penetration depths ≤ 6.1 mm from the coil surface compared to the birdcage coil, and an increased penetration depth at the half-maximum field response of 8 mm in the 4-spiral cylindrical coil case, in contrast to 2.9 mm in the flat 4-turn spiral case. Quantitative comparison of the performance of the two spiral coil geometries in anterior, lateral, inferior, and septal regions of the murine heart yield maximum mean percentage rSNR increases of the order of 27–167% in vivo post-mortem (cylindrical compared to flat coil). The commercially available birdcage outperforms the cylindrical spiral coil in rSNR by a factor of 3–5 times. The comprehensive approach and methodology adopted to accurately design, simulate, implement, and test radiofrequency coils of any geometry and type, under any loading conditions, can be generalized for any application of high field mouse cardiac MRI. PMID:23204945

13. Understanding distortions in the DIII-D tokamak magnetic field trim coils

Paulsen, R. T.; Paz-Soldan, C.; Strait, E. J.

2016-10-01

Trim coils were originally incorporated onto the DIII-D tokamak to reduce the error fields that arise from distortions in the preexisting coils that confine the plasma. However, as a result of numerous obstacles crowding DIII-D prior to their installation, the effective geometries of the trim coils were forced to stray from a nominal rectangular shape, causing the trim coils to induce error fields of their own apart from the ones they serve to combat. Since these secondary error fields have the potential to hamper plasma operation, it is imperative to discover to what extent the trim coil geometry is understood. This work seeks to investigate the observed magnetic field measurements for the energized trim coils in the absence of plasma, assess the distortions, and compare these calculations to the same quantities estimated for schematics of the as-built trim coil configurations. Furthermore, measurements taken with plasma with and without trim coils are analyzed by tools for extracting the optimal current for error field correction and compared to the predictions for the as-built system. Supported by US DOE DE-FC02-04ER54698 and SULI program.

14. Application of NASTRAN to TFTR toroidal field coil structures

NASA Technical Reports Server (NTRS)

Chen, S. J.; Lee, E.

1978-01-01

The primary applied loads on the TF coils were electromagnetic and thermal. The complex structure and the tremendous applied loads necessitated computer type of solutions for the design problems. In the early stage of the TF coil design, many simplified finite element models were developed for the purpose of investigating the effects of material properties, supporting schemes, and coil case material on the stress levels in the case and in the copper coil. In the more sophisticated models that followed the parametric and scoping studies, the isoparametric elements, such as QUAD4, HEX8, and HEXA, were used. The analysis results from using these finite element models and the NASTRAN system were considered accurate enough to provide timely design information.

15. A Modified Alderman-Grant Coil Makes Possible an Efficient Cross-Coil Probe for High Field Solid-state NMR of Lossy Biological Samples

PubMed Central

Grant, Christopher V.; Yang, Yuan; Glibowicka, Mira; Wu, Chin H.; Park, Sang Ho; Deber, Charles M.; Opella, Stanley J.

2009-01-01

The design, construction, and performance of a cross-coil double-resonance probe for solid-state NMR experiments on lossy biological samples at high magnetic fields are described. The outer coil is a Modified Alderman-Grant Coil (MAGC) tuned to the 1H frequency. The inner coil consists of a multi-turn solenoid coil that produces a B1 field orthogonal to that of the outer coil. This results in a compact nested cross-coil pair with the inner solenoid coil tuned to the low frequency detection channel. This design has several advantages over multiple-tuned solenoid coil probes, since RF heating from the 1H channel is substantially reduced, it can be tuned for samples with a wide range of dielectric constants, and the simplified circuit design and high inductance inner coil provides excellent sensitivity. The utility of this probe is demonstrated on two electrically lossy samples of membrane proteins in phospholipid bilayers (bicelles) that are particularly difficult for conventional NMR probes. The 72-residue polypeptide embedding the transmembrane helices 3 and 4 of the Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) (residues 194 – 241) requires a high salt concentration in order to be successfully reconstituted in phospholipid bicelles. A second application is to paramagnetic relaxation enhancement applied to the membrane-bound form of Pf1 coat protein in phospholipid bicelles where the resistance to sample heating enables high duty cycle solid-state NMR experiments to be performed. PMID:19733108

16. A Modified Alderman-Grant Coil makes possible an efficient cross-coil probe for high field solid-state NMR of lossy biological samples

Grant, Christopher V.; Yang, Yuan; Glibowicka, Mira; Wu, Chin H.; Park, Sang Ho; Deber, Charles M.; Opella, Stanley J.

2009-11-01

The design, construction, and performance of a cross-coil double-resonance probe for solid-state NMR experiments on lossy biological samples at high magnetic fields are described. The outer coil is a Modified Alderman-Grant Coil (MAGC) tuned to the 1H frequency. The inner coil consists of a multi-turn solenoid coil that produces a B 1 field orthogonal to that of the outer coil. This results in a compact nested cross-coil pair with the inner solenoid coil tuned to the low frequency detection channel. This design has several advantages over multiple-tuned solenoid coil probes, since RF heating from the 1H channel is substantially reduced, it can be tuned for samples with a wide range of dielectric constants, and the simplified circuit design and high inductance inner coil provides excellent sensitivity. The utility of this probe is demonstrated on two electrically lossy samples of membrane proteins in phospholipid bilayers (bicelles) that are particularly difficult for conventional NMR probes. The 72-residue polypeptide embedding the transmembrane helices 3 and 4 of the Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) (residues 194-241) requires a high salt concentration in order to be successfully reconstituted in phospholipid bicelles. A second application is to paramagnetic relaxation enhancement applied to the membrane-bound form of Pf1 coat protein in phospholipid bicelles where the resistance to sample heating enables high duty cycle solid-state NMR experiments to be performed.

17. A Modified Alderman-Grant Coil makes possible an efficient cross-coil probe for high field solid-state NMR of lossy biological samples.

PubMed

Grant, Christopher V; Yang, Yuan; Glibowicka, Mira; Wu, Chin H; Park, Sang Ho; Deber, Charles M; Opella, Stanley J

2009-11-01

The design, construction, and performance of a cross-coil double-resonance probe for solid-state NMR experiments on lossy biological samples at high magnetic fields are described. The outer coil is a Modified Alderman-Grant Coil (MAGC) tuned to the (1)H frequency. The inner coil consists of a multi-turn solenoid coil that produces a B(1) field orthogonal to that of the outer coil. This results in a compact nested cross-coil pair with the inner solenoid coil tuned to the low frequency detection channel. This design has several advantages over multiple-tuned solenoid coil probes, since RF heating from the (1)H channel is substantially reduced, it can be tuned for samples with a wide range of dielectric constants, and the simplified circuit design and high inductance inner coil provides excellent sensitivity. The utility of this probe is demonstrated on two electrically lossy samples of membrane proteins in phospholipid bilayers (bicelles) that are particularly difficult for conventional NMR probes. The 72-residue polypeptide embedding the transmembrane helices 3 and 4 of the Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) (residues 194-241) requires a high salt concentration in order to be successfully reconstituted in phospholipid bicelles. A second application is to paramagnetic relaxation enhancement applied to the membrane-bound form of Pf1 coat protein in phospholipid bicelles where the resistance to sample heating enables high duty cycle solid-state NMR experiments to be performed.

18. Uniform magnetic fields generated by circular current-carrying coils. [for spacecraft

NASA Technical Reports Server (NTRS)

Williams, V. L.; Cain, J. C.

1975-01-01

The study described was carried out to evaluate known systems of circular coils with a view toward their application on board the space probes Ranger 1, Ranger 2, and Explorer 10. Particular attention is given to a new method, developed during the investigation, for determining the constants of systems composed of 6 to 8 coils. Such systems were found to generate magnetic fields of very high uniformity. By using advanced computational techniques, it proved possible to evaluate the field uniformity of various systems without recourse to complex analytical methods. Means of evaluating the influence of coil dimensions on the uniformity of the field of any system are described.

19. On the SAR and field inhomogeneity of birdcage coils loaded with the human head.

PubMed

Jin, J; Chen, J

1997-12-01

Birdcage coils are widely used as a radiofrequency (RF) resonator in magnetic resonance imaging (MRI) because of their capability to produce a highly homogeneous B1 field over a large volume within the coil. When they are employed for high-frequency MRI, the interaction between the electromagnetic field and the object to be imaged deteriorates the B1-field homogeneity and increases the specific absorption rate (SAR) in the object. To investigate this problem, a finite-element method (FEM) is developed to analyze the SAR and the B1 field in a two-dimensional (2D) model of a birdcage coil loaded with a 2D model of a human head. The electric field, magnetic field, and SAR distributions are shown, and a comprehensive study is carried out for both linear and quadrature birdcage coils at 64, 128, 171, and 256 MHz. It is shown that to generate the same value of the B1 field, the SAR is increased significantly with the frequency, and for the same imaging method the SAR produced by a quadrature coil is significantly lower than that of a linear coil. It is also shown that the B1-field inhomogeneity is increased significantly with the frequency.

20. Optimized parallel transmit and receive radiofrequency coil for ultrahigh-field MRI of monkeys.

PubMed

Gilbert, Kyle M; Gati, Joseph S; Barker, Kevin; Everling, Stefan; Menon, Ravi S

2016-01-15

Monkeys are a valuable model for investigating the structure and function of the brain. To attain the requisite resolution to resolve fine anatomical detail and map localized brain activation requires radiofrequency (RF) coils that produce high signal-to-noise ratios (SNRs) both spatially (image SNR) and temporally. Increasing the strength of the static magnetic field is an effective method to improve SNR, yet this comes with commensurate challenges in RF coil design. First, at ultrahigh field strengths, the magnetic field produced by a surface coil in a dielectric medium is asymmetric. In neuroimaging of rhesus macaques, this complex field pattern is compounded by the heterogeneous structure of the head. The confluence of these effects results in a non-uniform flip angle, but more markedly, a suboptimal circularly polarized mode with reduced transmit efficiency. Secondly, susceptibility-induced geometric distortions are exacerbated when performing echo-planar imaging (EPI), which is a standard technique in functional studies. This requires receive coils capable of parallel imaging with low noise amplification during image reconstruction. To address these challenges at 7T, this study presents a parallel (8-channel) transmit coil developed for monkey imaging, along with a highly parallel (24-channel) receive coil. RF shimming with the parallel-transmit coil produced significant advantages-the transmit field was 38% more uniform than a traditional circularly polarized mode and 54% more power-efficient, demonstrating that parallel-transmit coils should be used for monkey imaging at ultrahigh field strengths. The receive coil had the ability to accelerate along an arbitrary axis with at least a three-fold reduction factor, thereby reducing geometric distortions in whole-brain EPI.

1. Bucking Coil Efficiency Correction for 5'' PMT Exposed to an External Magnetic Field

Llodra, Anthony; Reinhold, Joerg

2014-03-01

This research was conducted in support of the Hall C upgrade activities at Thomas Jefferson National Accelerator Facility (JLab). We propose to employ bucking coils in order to maximize the collection efficiency of the 5'' PMTs installed on the Cherenkov detector, which could potentially be exposed to external magnetic field produced by the Super Conducting Super High Momentum Spectrometer (SHMS) magnet. In this research project a 5'' PMT was placed in a light tight cylinder with a fiber optic cable. The cylinder was centered within a set of Helmholtz coils to produce a constant external magnetic field. Furthermore, the cylinder was wrapped with 20 coils of standard 12 gauge cable to act as the bucking coil. With the intensity of the LED source, and the magnitude of the external magnetic field fixed at a carefully determined value, data was taken to determine if the collection efficiency of the PMT was indeed affected. With a decrease in collection efficiency confirmed, further data were taken. A range of current (0-6 A) was applied to the bucking coils, while ADC spectra were analyzed in intervals of 0.25 A. The data indicated that in an external magnetic field of approximately 3 Gauss, the 5'' PMT collection efficiency is maximized with the bucking coil current set to approximately 3.5 A. Thus, the data conclusively indicates that the bucking coil system will indeed maximize the collection efficiency of the 5'' PMT. Florida International University.

2. Nested Helmholtz coil design for producing homogeneous transient rotating magnetic fields.

PubMed

Podaru, George; Moore, John; Dani, Raj Kumar; Prakash, Punit; Chikan, Viktor

2015-03-01

Electromagnets that can produce strong rotating magnetic fields at kHz frequencies are potentially very useful to exert rotating force on magnetic nanoparticles as small as few nanometers in size. In this article, the construction of a pulsed high-voltage rotating electromagnet is demonstrated based on a nested Helmholtz coil design. The energy for the coils is provided by two high-voltage discharge capacitors. The triggered spark gaps used in the experiments show sufficient accuracy to achieve the high frequency rotating magnetic field. The measured strength of the rotating magnetic field is 200 mT. This magnetic field is scalable by increasing the number of turns on the coils, by reducing the dimensions of the coils and by increasing the discharge current/voltage of the capacitors.

3. A new technique to optimize coil winding path for the arbitrarily distributed magnetic field and application to CHS-qa modular coils

Abe, M.; Nakayama, T.; Okamura, S.; Matsuoka, K.

2004-11-01

A new technique to calculate an arbitrarily shaped coil winding path for a target magnetic field distribution has been developed. The technique is called DUCAS (Design tool Using Current potentials And SVD, SVD= Singular Value Decomposition). The coil winding surface (CWS) is modeled by triangular finite elements (FEs). The SVD is applied on the response matrix from the current potentials (CPs) of the FE nodes to the magnetic field, to get eigen distribution functions of CPs and singular values (SVs). Using the eigen functions with large SVs, the CP distribution is determined on the CWS so as to reproduce a given magnetic field distribution. Discrete coil shapes are determined along the contour (flow) lines of CPs. The arbitrarily formed CWS is acceptable in DUCAS. We applied the DUCAS on CHS-qa (quasi-axisymmetric Compact Helical System) modular coils and confirmed that the technique is applicable on designs of helical system modular coils.

4. A simple model for estimating a magnetic field in laser-driven coils

Fiksel, Gennady; Fox, William; Gao, Lan; Ji, Hantao

2016-09-01

Magnetic field generation by laser-driven coils is a promising way of magnetizing plasma in laboratory high-energy-density plasma experiments. A typical configuration consists of two electrodes—one electrode is irradiated with a high-intensity laser beam and another electrode collects charged particles from the expanding plasma. The two electrodes are separated by a narrow gap forming a capacitor-like configuration and are connected with a conducting wire-coil. The charge-separation in the expanding plasma builds up a potential difference between the electrodes that drives the electrical current in the coil. A magnetic field of tens to hundreds of Teslas generated inside the coil has been reported. This paper presents a simple model that estimates the magnetic field using simple assumptions. The results are compared with the published experimental data.

5. A simple model for estimating a magnetic field in laser-driven coils

DOE PAGES

Fiksel, Gennady; Fox, William; Gao, Lan; ...

2016-09-26

Magnetic field generation by laser-driven coils is a promising way of magnetizing plasma in laboratory high-energy-density plasma experiments. A typical configuration consists of two electrodes—one electrode is irradiated with a high-intensity laser beam and another electrode collects charged particles from the expanding plasma. The two electrodes are separated by a narrow gap forming a capacitor-like configuration and are connected with a conducting wire-coil. The charge-separation in the expanding plasma builds up a potential difference between the electrodes that drives the electrical current in the coil. A magnetic field of tens to hundreds of Teslas generated inside the coil has beenmore » reported. This paper presents a simple model that estimates the magnetic field using simple assumptions. Lastly, the results are compared with the published experimental data.« less

6. A simple model for estimating a magnetic field in laser-driven coils

SciTech Connect

Fiksel, Gennady; Fox, William; Gao, Lan; Ji, Hantao

2016-09-26

Magnetic field generation by laser-driven coils is a promising way of magnetizing plasma in laboratory high-energy-density plasma experiments. A typical configuration consists of two electrodes—one electrode is irradiated with a high-intensity laser beam and another electrode collects charged particles from the expanding plasma. The two electrodes are separated by a narrow gap forming a capacitor-like configuration and are connected with a conducting wire-coil. The charge-separation in the expanding plasma builds up a potential difference between the electrodes that drives the electrical current in the coil. A magnetic field of tens to hundreds of Teslas generated inside the coil has been reported. This paper presents a simple model that estimates the magnetic field using simple assumptions. Lastly, the results are compared with the published experimental data.

7. Effects of coil orientation on the electric field induced by TMS over the hand motor area

Laakso, Ilkka; Hirata, Akimasa; Ugawa, Yoshikazu

2014-01-01

Responses elicited by transcranial magnetic stimulation (TMS) over the hand motor area depend on the position and orientation of the stimulating coil. In this work, we computationally investigate the induced electric field for multiple coil orientations and locations in order to determine which parts of the brain are affected and how the sensitivity of motor cortical activation depends on the direction of the electric field. The finite element method is used for calculating the electric field induced by TMS in two individual anatomical models of the head and brain. The orientation of the coil affects both the strength and depth of penetration of the electric field, and the field strongly depends on the direction of the sulcus, where the target neurons are located. The coil position that gives the strongest electric field in the target cortical region may deviate from the closest scalp location by a distance on the order of 1 cm. Together with previous experimental data, the results support the hypothesis that the cortex is most sensitive to fields oriented perpendicular to the cortical layers, while it is relatively insensitive to fields parallel to them. This has important implications for targeting of TMS. To determine the most effective coil position and orientation, it is essential to consider both biological (the direction of the targeted axons) and physical factors (the strength and direction of the electric field).

8. A method for determining poloidal rotation from poloidal asymmetry in toroidal rotation (invited).

PubMed

Chrystal, C; Burrell, K H; Grierson, B A; Lao, L L; Pace, D C

2014-11-01

A new diagnostic has been developed on DIII-D that determines the impurity poloidal rotation from the poloidal asymmetry in the toroidal angular rotation velocity. This asymmetry is measured with recently added tangential charge exchange viewchords on the high-field side of the tokamak midplane. Measurements are made on co- and counter-current neutral beams, allowing the charge exchange cross section effect to be measured and eliminating the need for atomic physics calculations. The diagnostic implementation on DIII-D restricts the measurement range to the core (r/a < 0.6) where, relative to measurements made with the vertical charge exchange system, the spatial resolution is improved. Significant physics results have been obtained with this new diagnostic; for example, poloidal rotation measurements that significantly exceed neoclassical predictions.

9. Insert Coil Test for HEP High Field Magnets Using YBCO Coated Conductor Tapes

SciTech Connect

Lombardo, V.; Barzi, E.; Turrioni, D.; Zlobin, A.V.; /Fermilab

2011-06-15

The final beam cooling stages of a Muon Collider may require DC solenoid magnets with magnetic fields of 30-50 T. In this paper we present progress in insert coil development using commercially available YBa{sub 2}Cu{sub 3}O{sub 7-{delta}} Coated Conductor. Technological aspects covered in the development, including coil geometry, insulation, manufacturing process and testing are summarized and discussed. Test results of double pancake coils operated in liquid nitrogen and liquid helium are presented and compared with the performance of YBa{sub 2}Cu{sub 3}O{sub 7-{delta}} tape short samples.

10. [Design and field calculation of coil array for transcranial magnetic stimulation (TMS) based on genetic algorithm].

PubMed

Liu, Jicheng; Huang, Kama; Guo, Lanting; Zhang, Hong; Hu, Yayi

2005-04-01

It is the intent of this paper to locate the activation point in Transcranial Magnetic Stimulation (TMS) efficiently. The schemes of coil array in torus shape is presented to get the electromagnetic field distribution with ideal focusing capability. Then an improved adaptive genetic algorithm (AGA) is applied to the optimization of both value and phase of the current infused in each coil. Based on the calculated results of the optimized current configurations, ideal focusing capability is drawn as contour lines and 3-D mesh charts of magnitude of both magnetic and electric field within the calculation area. It is shown that the coil array has good capability to establish focused shape of electromagnetic distribution. In addition, it is also demonstrated that the coil array has the capability to focus on two or more targets simultaneously.

11. Decoupling of excitation and receive coils in pulsed magnetic resonance using sinusoidal magnetic field modulation

Tseytlin, Mark; Epel, Boris; Sundramoorthy, Subramanian; Tipikin, Dmitriy; Halpern, Howard J.

2016-11-01

In pulsed magnetic resonance, the excitation power is many orders of magnitude larger than that induced by the spin system in the receiving coil or resonator. The receiver must be protected during and immediately after the excitation pulse to allow for the energy stored in the resonator to dissipate to a safe level. The time during which the signal is not detected, the instrumental dead-time, can be shortened by using magnetically decoupled excitation and receive coils. Such coils are oriented, with respect to each other, in a way that minimizes the total magnetic flux produced by one coil in the other. We suggest that magnetically decoupled coils can be isolated to a larger degree by tuning them to separate frequencies. Spins are excited at one frequency, and the echo signal is detected at another. Sinusoidal magnetic field modulation that rapidly changes the Larmor frequency of the spins between the excitation and detection events is used to ensure the resonance conditions for both coils. In this study, the relaxation times of trityl-CD3 were measured in a field-modulated pulsed EPR experiment and compared to results obtained using a standard spin echo method. The excitation and receive coils were tuned to 245 and 256.7 MHz, respectively. Using an available rapid-scan, cross-loop EPR resonator, we demonstrated an isolation improvement of approximately 20-30 dB due to frequency decoupling. Theoretical analysis, numerical simulations, and proof-of-concept experiments demonstrated that substantial excitation-detection decoupling can be achieved. A pulsed L-band system, including a small volume bi-modal resonator equipped with modulation coils, was constructed to demonstrate fivefold dead-time reduction in comparison with the standard EPR experiment. This was achieved by detuning of the excitation and receive coils by 26 MHz and using sinusoidal modulation at 480 kHz.

12. Simulation of concomitant magnetic fields on fast switched gradient coils used in advanced application of MRI

Salinas-Muciño, G.; Torres-García, E.; Hidalgo-Tobon, S.

2012-10-01

The process to produce an MR image includes nuclear alignment, RF excitation, spatial encoding, and image formation. To form an image, it is necessary to perform spatial localization of the MR signals, which is achieved using gradient coils. MRI requires the use of gradient coils that generate magnetic fields, which vary linearly with position over the imaging volume. Safety issues have been a motivation to study deeply the relation between the interaction of gradient magnetic field and the peripheral nerve stimulation. In this work is presented a numerical modeling between the concomitant magnetic fields produced by the gradient coils and the electric field induced in a cube with σ conductivity by the gradient field switching in pulse sequences as Eco planar Imaging (EPI), due to this kind of sequence is the most used in advance applications of magnetic resonance imaging as functional MRI, cardiac imaging or diffusion.

13. Field Error Analysis and a Correction Scheme for the KSTAR device

You, K.-I.; Lee, D. K.; Jhang, Hogun; Lee, G.-S.; Kwon, K. H.

2000-10-01

Non-axisymmetric error fields can lead to tokamak plasma performance degradation and ultimately premature plasma disruption, if some error field components are larger than threshold values. The major sources of the field error include the unavoidable winding irregularities of the poloidal field coils during manufacturing, poloidal field and toroidal field coils misalignments during installation, stray fields from bus and lead wires between coils and power supplies, and welded joints of the vacuum vessel. Numerical simulation results are presented for Fourier harmonics of the error field obtained on the (m,n) = (2,1) resonant flux surface with a coil current set for the reference equilibrium configuration. Field error contributions are considered separately for all major error sources. An error correction scheme designed to reduce key components of the total net error field is also discussed in relation to the field error correction coils inside the vacuum vessel.

14. Cooldown performance of an inner vertical field coil for the Large Helical Device

SciTech Connect

Takahata, K.; Mito, T.; Satow, T.

1996-07-01

A single cooldown test of an Inner Vertical (IV) field coil for the Large Helical Device (LHD) was started on February 1 of 1995, and the superconducting transition of the coil was confirmed on February 23. The coil is a forced-flow type using a cable-in-conduit (CIC) conductor and weighing about 16 tons. The total cooldown time was about 250 hours, not including suspended time. Pressure drop characteristics were measured during the cooldown, and the same results were obtained as the R and D coil previously tested. The cooldown time could be reduced by indirect cooling using stainless steel sleeves with cooling pipes. The indirect cooling is effective for the CIC conductor which has no subchannel because otherwise an adequate mass flow cannot be obtained due to a high pressure drop in the high temperature region. The temperature distribution in the vertical direction was also examined during the indirect cooling.

15. Kilotesla Magnetic Field due to a Capacitor-Coil Target Driven by High Power Laser

PubMed Central

Fujioka, Shinsuke; Zhang, Zhe; Ishihara, Kazuhiro; Shigemori, Keisuke; Hironaka, Youichiro; Johzaki, Tomoyuki; Sunahara, Atsushi; Yamamoto, Naoji; Nakashima, Hideki; Watanabe, Tsuguhiro; Shiraga, Hiroyuki; Nishimura, Hiroaki; Azechi, Hiroshi

2013-01-01

Laboratory generation of strong magnetic fields opens new frontiers in plasma and beam physics, astro- and solar-physics, materials science, and atomic and molecular physics. Although kilotesla magnetic fields have already been produced by magnetic flux compression using an imploding metal tube or plasma shell, accessibility at multiple points and better controlled shapes of the field are desirable. Here we have generated kilotesla magnetic fields using a capacitor-coil target, in which two nickel disks are connected by a U-turn coil. A magnetic flux density of 1.5 kT was measured using the Faraday effect 650 μm away from the coil, when the capacitor was driven by two beams from the GEKKO-XII laser (at 1 kJ (total), 1.3 ns, 0.53 or 1 μm, and 5 × 1016 W/cm2). PMID:23378905

16. Dipole antennas for ultrahigh-field body imaging: a comparison with loop coils.

PubMed

Raaijmakers, A J E; Luijten, P R; van den Berg, C A T

2016-09-01

Although the potential of dipole antennas for ultrahigh-field (UHF) MRI is largely recognized, they are still relatively unknown to the larger part of the MRI community. This article intends to provide electromagnetic insight into the general operating principles of dipole antennas by numerical simulations. The major part focuses on a comparison study of dipole antennas and loop coils at frequencies of 128, 298 and 400 MHz. This study shows that dipole antennas are only efficient radiofrequency (RF) coils in the presence of a dielectric and/or conducting load. In addition, the conservative electric fields (E-fields) at the ends of a dipole are negligible in comparison with the induced E-fields in the center. Like loop coils, long dipole antennas perform better than short dipoles for deeply located imaging targets and vice versa. When the optimal element is chosen for each depth, loop coils have higher B1 (+) efficiency for shallow depths, whereas dipole antennas have higher B1 (+) efficiency for large depths. The cross-over point depth decreases with increasing frequency: 11.6, 6.2 and 5.0 cm for 128, 298 and 400 MHz, respectively. For single elements, loop coils demonstrate a better B1 (+) /√SARmax ratio for any target depth and any frequency. However, one example study shows that, in an array setup with loop coil overlap for decoupling, this relationship is not straightforward. The overlapping loop coils may generate increased specific absorption rate (SAR) levels under the overlapping parts of the loops, depending on the drive phase settings. Copyright © 2015 John Wiley & Sons, Ltd.

17. Integrated Design System of Toroidal Field Coil for CFETR

Luo, Zhiren; Liu, Xufeng; Du, Shuangsong; Wang, Zhongwei; Song, Yuntao

2016-09-01

Integrating engineering software is meaningful but challenging for a system code of a fusion device. This issue is seldom considered by system codes currently. Therefore, to discuss the issue, the Integrated Design System of TF Coil (IDS-TFC) has been worked out, which consists of physical calculation, CAD, and Finite Element Analysis (FEA). Furthermore, an Integrated and Automatically Optimized Method (IAOM) has been created to address the integration and interfaces. The method utilizes a geometry parameter to connect each design submodule and achieve automatic optimization. Double-objectives optimization has been realized, confirming it is feasible to integrate and optimize engineering design and physical calculation. Moreover, IDS-TFC can also serve as a useful reference of integrated design processing for subsequent fusion design. supported by the National Magnetic Confinement Fusion Science Program of China (Nos. 2014GB110000, 2014GB110002)

18. Design and Performance of the First Dual-Coil Magnet at the Wuhan National High Magnetic Field Center

Peng, T.; Sun, Q. Q.; Zhang, X.; Xu, Q.; Xiao, H. X.; Herlach, F.; Pan, Y.; Li, L.

2013-03-01

The first 80 T dual-coil magnet was manufactured and tested at the Wuhan National High Magnetic Field Center (WHMFC). The inner coil consists of 8 layers of 2.8 mm × 4.3 mm CuNb microcomposite wire developed in China; the bore diameter is 14 mm and the outer diameter 135 mm. The outer coil was wound directly on the inner coil with 12 layers of 3 mm × 6 mm soft copper. Each conductor layer of both coils was reinforced by Zylon/epoxy composite. The inner and outer coil were driven by a 1.6 MJ/5.12 mF capacitor bank and by eight 1 MJ/3.2 mF modules, respectively. At the voltage of 14.3 kV for the inner coil and 22 kV for the outer coil, the inner and outer coils produced peak fields of 48.5 T and 34.5 T respectively, which gave a total field of 83 T. This was the first combined operation of the new capacitor banks installed at the WHMFC. We present details of the design, manufacture and test of the dual-coil magnet and discuss crucial material properties. Based on this experience, a second dual-coil magnet will be designed; the enhanced design will be discussed. With the total energy of 12.6 MJ, peak field up to 90 T is expected.

19. Magnetic Field Generation by a Laser-Driven Capacitor-Coil Target

Cheng, Jessica; Gao, Lan

2016-10-01

Magnetic fields generated by currents flowing through a capacitor-coil target were characterized using ultrafast proton radiography at the OMEGA EP Laser System. Two 1.25 kJ, 1-ns laser pulses propagated through the laser entrance holes in one foil of the capacitor, and were focused to the other with an intensity of 3 ×1016 W/cm2. The intense laser-solid interaction induced a high voltage between the foils and generated a large current in the connecting coil. The proton data show tens of kA current producing tens of Tesla magnetic fields at the center of the coil. Theoretical lumped circuit models based on the experimental parameters were developed to simulate the target behavior and calculate the time evolution of the current in the coil. The models take into account important elements such as plasmas conditions for building up the voltage, the capacitance between the gap, the resistive heating and skin effect to gain insights on the field generation mechanism. Applications to other coil geometries and magnetic field configurations will also be described.

20. Electromagnetic fields in the human body due to switched transverse gradient coils in MRI.

PubMed

While, Peter T; Forbes, Larry K

2004-07-07

Magnetic resonance imaging scans impose large gradient magnetic fields on the patient. Modern imaging techniques require this magnetic field to be switched rapidly for good resolution. However, it is believed that this can also lead to the unwanted side effect of peripheral nerve stimulation, which proves to be a limiting factor to the advancement of MRI technology. This paper establishes an analytical model for the fields produced within an MRI scanner by transverse gradient coils of known current density. Expressions are obtained for the magnetic induction vector and the electric field vector, as well as for the surface charge and current densities that are induced on the patient's body. The expressions obtained are general enough to allow the study of any combination of gradient coils whose behaviour can be approximated by Fourier series. For a realistic example coil current density and switching function, it is found that spikes of surface charge density are induced on the patient's body as the gradient field is switched, as well as loops of surface current density that mimic the coil current density. For a 10 mT m(-1) gradient field with a rise time of 100 micros, the magnitude of the radial electric field at the body is found to be 10.3 V m(-1). It is also found that there is a finite limit to radial electric field strength as rise time approaches zero.

1. Ultrafast proton radiography of the magnetic fields generated by a laser-driven coil current

DOE PAGES

Gao, Lan; Ji, Hantao; Fiksel, Gennady; ...

2016-04-15

Magnetic fields generated by a current flowing through a U-shaped coil connecting two copper foils were measured using ultrafast proton radiography. Two ~ 1.25 kJ, 1-ns laser pulses propagated through laser entrance holes in the front foil and were focused to the back foil with an intensity of ~ 3 x 1016 W/cm2. The intense laser-solid interaction induced a high voltage between the copper foils and generated a large current in the connecting coil. The proton data show ~ 40-50 T magnetic fields at the center of the coil ~ 3-4 ns after laser irradiation. In conclusion, the experiments providemore » significant insight for future target designs that aim to develop a powerful source of external magnetic fields for various applications in high-energy-density science.« less

2. Ultrafast proton radiography of the magnetic fields generated by a laser-driven coil current

SciTech Connect

Gao, Lan; Ji, Hantao; Fiksel, Gennady; Fox, William; Evans, Michelle; Alfonso, Noel

2016-04-15

Magnetic fields generated by a current flowing through a U-shaped coil connecting two copper foils were measured using ultrafast proton radiography. Two ~ 1.25 kJ, 1-ns laser pulses propagated through laser entrance holes in the front foil and were focused to the back foil with an intensity of ~ 3 x 1016 W/cm2. The intense laser-solid interaction induced a high voltage between the copper foils and generated a large current in the connecting coil. The proton data show ~ 40-50 T magnetic fields at the center of the coil ~ 3-4 ns after laser irradiation. In conclusion, the experiments provide significant insight for future target designs that aim to develop a powerful source of external magnetic fields for various applications in high-energy-density science.

3. Three-dimensional magnetic nanoparticle imaging using small field gradient and multiple pickup coils

Sasayama, Teruyoshi; Tsujita, Yuya; Morishita, Manabu; Muta, Masahiro; Yoshida, Takashi; Enpuku, Keiji

2017-04-01

We propose a magnetic particle imaging (MPI) method based on third harmonic signal detection using a small field gradient and multiple pickup coils. First, we developed a system using two pickup coils and performed three-dimensional detection of two magnetic nanoparticle (MNP) samples, which were spaced 15 mm apart. In the experiments, an excitation field strength of 1.6 mT was used at an operating frequency of 3 kHz. A DC gradient field with a typical value of 0.2 T/m was also used to produce the so-called field-free line. A third harmonic signal generated by the MNP samples was detected using the two pickup coils, and the samples were then mechanically scanned to obtain field maps. The field maps were subsequently analyzed using the nonnegative least squares method to obtain three-dimensional position information for the MNP samples. The results show that the positions of the two MNP samples were estimated with good accuracy, despite the small field gradient used. Further improvement in MPI performance will be achieved by increasing the number of pickup coils used.

4. Density Threshold for Edge Poloidal Flow Generation

Daniels, N.; Ware, A. S.; Newman, D. E.; Hidalgo, C.

2004-11-01

A numerical transport model is used to examine a density threshold for the onset of an edge poloidal velocity shear layer in toroidal devices. This work is motivated by recent experimental results from the TJ-II stellarator which indicate a critical density threshold for the development of an edge poloidal velocity shear layer [1]. Edge shear-flow layers are commonly observed in toroidal confinement devices, even in L-mode discharges. The numerical transport model has been used to examine internal transport barriers and front propagation of internal transport barriers [2]. The transport model couples together density, ion temperature, electron temperature, poloidal flow, toroidal flow, radial electric field, and a fluctuation envelope equation which includes a shear-suppression factor. In this work, we present results from a series of cases using parameters that are typical of TJ-II discharges. The dependence of the critical density threshold on flow damping and Reynolds stress drive is investigated. [1] C. Hidalgo, M. A. Pedrosa, L. Garcia, and A. Ware, "Direct experimental evidence of coupling between sheared flows development and increasing in level of turbulence in the TJ-II stellarator", submitted to Phys. Rev. E. [2] D. E. Newman, B. A. Carreras, D. Lopez-Bruna, P. H. Diamond, and V. B. Lebedev, Phys. Plasmas 5, 938 (1998).

5. Plasma response based RMP coil geometry optimization for an ITER plasma

Zhou, Lina; Liu, Yueqiang; Liu, Yue; Yang, Xu

2016-11-01

Based on an ITER 15MA Q  =  10 inductive scenario, a systematic numerical investigation is carried out in order to understand the effect of varying the geometry of the magnetic coils, used for controlling the edge localized modes in tokamaks, on the plasma response to the resonant magnetic perturbation (RMP) fields produced by these coils. Toroidal computations show that both of the plasma response based figures of merit—one is the pitch resonant radial field component near the plasma edge and the other is the plasma displacement near the X-point of the separatrix—consistently yield the same prediction for the optimal coil geometry. With a couple of exceptions, the presently designed poloidal location of the ITER upper and lower rows of RMP coils is close to the optimum, according to the plasma response based criteria. This holds for different coil current configurations with n  =  2, 3, 4, as well as different coil phasing between the upper and lower rows. The coils poloidal width from the present design, on the other hand, is sub-optimal for the upper and lower rows. Modelling also finds that the plasma response amplitude sharply decreases by moving the middle row RMP coils of ITER from the designed radial location (just inside the inner vacuum vessel) outwards (outside the outer vacuum vessel). The decay rate is sensitively affected by the middle row coils’ poloidal coverage for low-n (n  =  1, 2) RMP fields, but not for high-n (n  =  4) fields.

6. Electromagnetic modeling of REBCO high field coils by the H-formulation

Xia, Jing; Bai, Hongyu; Lu, Jun; Gavrilin, Andrew V.; Zhou, Youhe; Weijers, Hubertus W.

2015-12-01

In this paper, we employ the anisotropic bulk approximation to successfully implement the electromagnetic modeling of superconducting coils wound with rare-earth-barium-copper-oxide (REBCO) tapes based on the H-formulation, in which the field-dependent critical current density and highly nonlinear E-J characteristic are considered. The total number of turns in the stacks of REBCO pancake coils is up to several thousand. We validate the anisotropic bulk model by comparing the ac loss of a small four-pancake coil between the bulk model and the original model which takes the actual thickness of the superconducting layer into account. Then, the anisotropic bulk model is used to investigate the self-field problem of the REBCO prototype coils of the National High Magnetic Field Laboratory 32 {{T}} all-superconducting magnet. The field and current density distributions are obtained, and an obvious shielding effect is observed at the top and bottom of the coils. The ac losses in the first and second cycles are calculated. The former is crucial to the design of the cooling system and the latter relates to the routine consumption of the liquid helium. It is found that the ac loss in the first cycle is 2.6 times as large as that in the second cycle. We also study the ac loss dependences on some key parameters (the critical current, n-value and ramp rate of the applied current). It is found that both in the first and second cycles, the ac loss increases with decreasing critical current. Moreover, the influence of the n-value on the ac loss is negligible. In addition, the ac loss decreases logarithmically with increasing ramp rate. However, the average power loss increases linearly with increasing ramp rate. We also compare some analytical estimates with the simulation result for the ac loss of the dual prototype coils. It is found that the results of Bean’s slab model are closer to the simulation result. The presented model is a useful tool to help us understand

7. Enhanced trapped field performance of bulk high-temperature superconductors using split coil, pulsed field magnetization with an iron yoke

Ainslie, M. D.; Fujishiro, H.; Mochizuki, H.; Takahashi, K.; Shi, Y.-H.; Namburi, D. K.; Zou, J.; Zhou, D.; Dennis, A. R.; Cardwell, D. A.

2016-07-01

Investigating and predicting the magnetization of bulk superconducting materials and developing practical magnetizing techniques is crucial to using them as trapped field magnets in engineering applications. The pulsed field magnetization (PFM) technique is considered to be a compact, mobile and relative inexpensive way to magnetize bulk samples, requiring shorter magnetization times (on the order of milliseconds) and a smaller and less complicated magnetization fixture; however, the trapped field produced by PFM is generally much smaller than that of slower zero field cooling or field cooling techniques, particularly at lower operating temperatures. In this paper, the PFM of two, standard Ag-containing Gd-Ba-Cu-O samples is carried out using two types of magnetizing coils: (1) a solenoid coil, and (2) a split coil, both of which make use of an iron yoke to enhance the trapped magnetic field. It is shown that a significantly higher trapped field can be achieved using a split coil with an iron yoke, and in order to explain these how this arrangement works in detail, numerical simulations using a 2D axisymmetric finite element method based on the H -formulation are carried to qualitatively reproduce and analyze the magnetization process from both electromagnetic and thermal points of view. It is observed that after the pulse peak significantly less flux exits the bulk when the iron core is present, resulting in a higher peak trapped field, as well as more overall trapped flux, after the magnetization process is complete. The results have important implications for practical applications of bulk superconductors as such a split coil arrangement with an iron yoke could be incorporated into the design of a portable, high magnetic field source/magnet to enhance the available magnetic field or in an axial gap-type bulk superconducting electric machine, where iron can be incorporated into the stator windings to (1) improve the trapped field from the magnetization process

8. Poloidal Asymmetries in Edge Transport Barriers

Churchill, R. M.

2014-10-01

Investigations of the poloidal structure within edge transport barriers on Alcator C-Mod using novel impurity measurements are presented, revealing large poloidal variations of parameters within a flux surface in the H-mode pedestal region, and significantly reduced poloidal variation in L-mode or I-mode pedestals. These measurements provide complete sets of impurity density, temperature, flow velocity, and electrostatic potential at both the low- and high-field side midplane, utilizing the Gas Puff-CXRS technique. Uncertainties in magnetic equilibrium reconstructions require assumptions to be made in order to properly align the LFS/HFS profiles. In H-mode plasmas, if profiles are aligned assuming impurity temperature is constant on a flux surface, large potential asymmetries would result (eΔΦ /Te ~ 0 . 6). If instead total pressure is assumed constant on a flux-surface, then the measured potential asymmetry is significantly reduced, but large in-out asymmetries result in the impurity temperature (>1.7x). This shows that impurity temperature and potential can not both be flux functions in the pedestal region. In both alignment cases, large asymmetries in impurity density (>6x) are present in H-mode plasmas. In I-mode plasmas, which lack an electron density pedestal but do have a temperature pedestal, the poloidal variation of impurity temperature is weaker (~1.3x) and the impurity density nearly symmetric between the LFS and HFS. These measurements indicate that the sharp gradients in the pedestal region, particularly of main ion density, have a significant effect on the poloidal and radial distribution of impurities, which could have important implications for the prediction of impurity contamination in future fusion reactors such as ITER. Estimates of particle and heat transport timescales suggest that the radial and parallel transport timescales are of the same order in the pedestal region of C-Mod, supporting the idea that two-dimensional transport effects

9. Toroid field coil shear key installation study, DOE task No. 22

SciTech Connect

Jones, C.E.; Meier, R.W.; Yuen, J.L.

1995-01-09

Concepts for fitting and installation of the scissor keys, triangular keys, and truss keys in the ITER Toroidal Field (TF) Coil Assembly were developed and evaluated. In addition, the process of remote removal and replacement of a failed TF coil was considered. Two concepts were addressed: central solenoid installed last (Naka Option 1) and central solenoid installed first (Naka Option 2). In addition, a third concept was developed which utilized the favorable features of both concepts. A time line for installation was estimated for the Naka Option 1 concept.

10. Analytical results for the pulsed operation of high field constant stress coils

Vanbockstal, Luc; Askenazy, Salomon; Herlach, Fritz; Schneider-Muntau, Hans-Jorg

1994-07-01

Based on the analytical expressions for the radial current density in coils optimized for constant stress, the implications for pulsed operation are discussed; the pulse duration, peak power and energy are determined. A cut-off on the current density, which peaks at the inside of the coil, limits the localized heating and increases the pulse duration at the expense of center field or materials requirements. From the relation between strength, conductivity and cut-off level, optimal properties of construction materials are determined.

11. Effects of Receive-Only Inserts on SAR, B1+ Field and Tx Coil Performance

PubMed Central

Krishnamurthy, Narayanan; Zhao, Tiejun; Ibrahim, Tamer S

2013-01-01

Purpose To evaluate the effect of different cylindrical and close conforming receive only array designs on spin excitation and specific absorption rate (SAR) of a 7 Tesla transmit only head coil. Materials and Methods We developed FDTD models of different receive only array geometries. Cylindrical and close fitting helmet arrays with varying copper trace widths; a TEM Tx coil model and two head models were used in numerical simulations. Tx coil coupling was experimentally measured and validated with FDTD modeling. Results Changing copper trace width of loops in array models caused subtle changes in RF absorption (<5%). Changes in SAR distribution were observed in the head models with Rx-only inserts. Peak SAR increased (−1 to +15%) in different tissues for a mean B1+ in the brain of 2 μT. Total absorption in the head models for 1 Watt forward power increased (5 to 21%) in the heads with Rx-only inserts. Changes in RF absorption with different Rx-inserts indicate a change in RF radiation of the Tx coil even when changes in B1+ and coupling between ports of Tx coil were minimal. Conclusion Changes in local/global SAR and subtle changes in B1+ field distributions were observed with the presence of Rx-only inserts. Thus, incorporation of the receive-only array effects are needed when evaluating SAR and designing RF transmit pulse waveform parameters for shimming and/or Tx-SENSE for 7 T MRI. PMID:23913474

12. Zylon-reinforced high magnetic field coils for the K.U. Leuven pulsed field laboratory

Rosseel, K.; Herlach, F.; Boon, W.; Bruynseraede, Y.

2001-01-01

PBO Zylon ® fibers have been used for the internal reinforcement of pulsed magnets. Due to the very high packing density (80%) of these fibers, vacuum impregnation of Zylon reinforced coils is difficult. Impregnation test were performed using pressure-vacuum impregnation and wet winding. A prototype series of coils for 60-70 T with 1-2 ms pulse duration was designed and wound, using wet winding for both the internal Zylon and external carbon fiber reinforcement. Special precautions were taken to avoid insulation breakdown at the transitions between conductor layers. Furthermore, axial movement of the conductor wires was restrained by strong axial compression of the coil with a steel shell casing. These modifications were incorporated into an 80 T coil made of Zylon and soft Cu. The design, construction and performance of this coil are discussed.

13. Comparison of birdcage and phase array coil using FDTD for the B(1) homogeneity in high field MRI.

PubMed

Seo, J H; Heo, H Y; Han, B H; Lee, S Y

2007-01-01

RF coils play an important role to acquire MR images with the maintenance of high homogeneity in high field MR system more than 3.0 T. Many kinds of RF coils such as birdcage coil, STR, surface coil, and phase array coil have been used, however, the good uniformity of a coil has always been an issue. In this paper, comparison of B(1) homogeneity between birdcage and phase array coil was investigated using FDTD method at 3.0 T MRI in order to develop RF coils with the high uniformity. Three different configurations of the FDTD simulation were performed like as using a free space configuration, water phantom configuration, and head mesh model. B1 homogeneity was calculated to the case of birdcage coil and 8-channel phase array coil in each configuration of simulation. Improvement on the homogeneity of the images and reduction of standing wave effect was achieved with comparing the real MR images with the result from simulation.

14. Evaluation method for in situ electric field in standardized human brain for different transcranial magnetic stimulation coils.

PubMed

Iwahashi, Masahiro; Gomez-Tames, Jose; Laakso, Ilkka; Hirata, Akimasa

2017-03-21

This study proposes a method to evaluate the electric field induced in the brain by transcranial magnetic stimulation (TMS) to realize focal stimulation in the target area considering the inter-subject difference of the brain anatomy. The TMS is a non-invasive technique used for treatment/diagnosis, and it works by inducing an electric field in a specific area of the brain via a coil-induced magnetic field. Recent studies that report on the electric field distribution in the brain induced by TMS coils have been limited to simplified human brain models or a small number of detailed human brain models. Until now, no method has been developed that appropriately evaluates the coil performance for a group of subjects. In this study, we first compare the magnetic field and the magnetic vector potential distributions to determine if they can be used as predictors of the TMS focality derived from the electric field distribution. Next, the hotspots of the electric field on the brain surface of ten subjects using six coils are compared. Further, decisive physical factors affecting the focality of the induced electric field by different coils are discussed by registering the computed electric field in a standard brain space for the first time, so as to evaluate coil characteristics for a large population of subjects. The computational results suggest that the induced electric field in the target area cannot be generalized without considering the morphological variability of the human brain. Moreover, there was no remarkable difference between the various coils, although focality could be improved to a certain extent by modifying the coil design (e.g., coil radius). Finally, the focality estimated by the electric field was more correlated with the magnetic vector potential than the magnetic field in a homogeneous sphere.

15. Evaluation method for in situ electric field in standardized human brain for different transcranial magnetic stimulation coils

Iwahashi, Masahiro; Gomez-Tames, Jose; Laakso, Ilkka; Hirata, Akimasa

2017-03-01

This study proposes a method to evaluate the electric field induced in the brain by transcranial magnetic stimulation (TMS) to realize focal stimulation in the target area considering the inter-subject difference of the brain anatomy. The TMS is a non-invasive technique used for treatment/diagnosis, and it works by inducing an electric field in a specific area of the brain via a coil-induced magnetic field. Recent studies that report on the electric field distribution in the brain induced by TMS coils have been limited to simplified human brain models or a small number of detailed human brain models. Until now, no method has been developed that appropriately evaluates the coil performance for a group of subjects. In this study, we first compare the magnetic field and the magnetic vector potential distributions to determine if they can be used as predictors of the TMS focality derived from the electric field distribution. Next, the hotspots of the electric field on the brain surface of ten subjects using six coils are compared. Further, decisive physical factors affecting the focality of the induced electric field by different coils are discussed by registering the computed electric field in a standard brain space for the first time, so as to evaluate coil characteristics for a large population of subjects. The computational results suggest that the induced electric field in the target area cannot be generalized without considering the morphological variability of the human brain. Moreover, there was no remarkable difference between the various coils, although focality could be improved to a certain extent by modifying the coil design (e.g., coil radius). Finally, the focality estimated by the electric field was more correlated with the magnetic vector potential than the magnetic field in a homogeneous sphere.

16. Passive magnetic field cancellation device by multiple high-Tc superconducting coils

Gu, C.; Zou, S.; Han, Z.; Qu, T.-M.

2010-04-01

A passive magnetic field cancellation device (PMFCD) is designed. The PMFCD could automatically cancel the field as an active cancellation system did; however it requires no power sources and feedback systems. The capability of the PMFCD is based on the principle that a closed loop can resist flux variation and keep the flux constant inside. The closed loop in the PMFCD is formed by connecting two pairs of high temperature superconductor Helmholtz coils with different radii in series. More important thing is that the ratio of the radius and the turn number between the coils has to satisfy a number of conditions, with which 100% cancellation can be reached. Theoretical methods to obtain the turn number ratio and radius ratio are the major part of the paper. Numerical simulation was followed, aiming to evaluate field distribution under a cancellation state and correct the theoretical values.

17. DESIGN, FABRICATION, INSTALLATION AND TESTING OF IN-VESSEL CONTROL COILS FOR DIII-D

SciTech Connect

ANDERSON, PM; BAXI, CB; KELLMAN, AG; REIS, EE; ROBINSON, JI

2002-10-01

OAK A271 DESIGN, FABRICATION, INSTALLATION AND TESTING OF IN-VESSEL CONTROL COILS FOR DIII-D. Since 1995, DIII-D has performed correction of magnetic field imperfections using a set of six external picture frame coils located on the vessel mid-plane. Recently, these coils have also demonstrated significant benefits when used for feedback of the resistive wall mode, an instability that limits the plasma performance at high beta. Modeling has shown that substantial performance improvements can be achieved by installing new coils inside the vessel and expanding the poloidal coverage above and below the mid-plane. Two prototype internal coils were installed in 2001 and have been tested successfully. installation of a set of twelve internal coils and magnetic sensors in the DIII-D tokamak is to be completed in December 2002. The design requirement for the new coil system was to maximize the magnetic field at the plasma edge, operate with a frequency range of dc to 1000 Hz, and fit behind the existing graphite wall tiles. The coil design adopted and installed is a water-cooled hollow copper conductor insulated with polyamide and housed inside a stainless steel tube that forms a vacuum boundary. The coil is rigidly mounted to the inside of the vacuum vessel. The primary challenge in the design of these coils was in joining of both the copper conductor and the stainless tube without overheating the polyamide insulator.

SciTech Connect

Qu, Hao; Zhang, Tao; Han, Xiang; Wen, Fei; Zhang, Shoubiao; Kong, Defeng; Wang, Yumin; Gao, Yu; Huang, Canbin; Cai, Jianqing; Gao, Xiang

2015-08-15

An X-mode polarized V band (50 GHz–75 GHz) radial and poloidal correlation reflectometry is designed and installed on Experimental Advanced Superconducting Tokamak (EAST). Two frequency synthesizers (12 GHz–19 GHz) are used as sources. Signals from the sources are up-converted to V band using active quadruplers and then coupled together for launching through one single pyramidal antenna. Two poloidally separated antennae are installed to receive the reflected waves from plasma. This reflectometry system can be used for radial and poloidal correlation measurement of the electron density fluctuation. In ohmically heated plasma, the radial correlation length is about 1.5 cm measured by the system. The poloidal correlation analysis provides a means to estimate the fluctuation velocity perpendicular to the main magnetic field. In the present paper, the distance between two poloidal probing points is calculated with ray-tracing code and the propagation time is deduced from cross-phase spectrum. Fluctuation velocity perpendicular to the main magnetic field in the core of ohmically heated plasma is about from −1 km/s to −3 km/s.

PubMed

Qu, Hao; Zhang, Tao; Han, Xiang; Wen, Fei; Zhang, Shoubiao; Kong, Defeng; Wang, Yumin; Gao, Yu; Huang, Canbin; Cai, Jianqing; Gao, Xiang

2015-08-01

An X-mode polarized V band (50 GHz-75 GHz) radial and poloidal correlation reflectometry is designed and installed on Experimental Advanced Superconducting Tokamak (EAST). Two frequency synthesizers (12 GHz-19 GHz) are used as sources. Signals from the sources are up-converted to V band using active quadruplers and then coupled together for launching through one single pyramidal antenna. Two poloidally separated antennae are installed to receive the reflected waves from plasma. This reflectometry system can be used for radial and poloidal correlation measurement of the electron density fluctuation. In ohmically heated plasma, the radial correlation length is about 1.5 cm measured by the system. The poloidal correlation analysis provides a means to estimate the fluctuation velocity perpendicular to the main magnetic field. In the present paper, the distance between two poloidal probing points is calculated with ray-tracing code and the propagation time is deduced from cross-phase spectrum. Fluctuation velocity perpendicular to the main magnetic field in the core of ohmically heated plasma is about from -1 km/s to -3 km/s.

20. Inductive plasma current start-up by the outer vertical field coil in a spherical tokamak

Mitarai, Osamu

1999-12-01

Plasma current-start up induced by an outer vertical field coil is studied during the ignition access phase in a spherical tokamak reactor. We have illustrated the concept that the plasma current of ~50 MA could be induced by the outer vertical field coil in the proposed spherical tokamak with the help of the small central solenoid flux of +/-5 V s and the strong heating power less than 100 MW for the internal inductance of icons/Journals/Common/ell" ALT="ell" ALIGN="TOP"/>i~0.4-0.8 without the help of bootstrap current and non-inductive current drive power. The required condition to achieve this operation scenario is that the flux produced by the equilibrium vertical field is larger than the inductive flux. Current start-up operation is achieved by adding the small ohmic heating solenoid flux for the flux waveform adjustment because the flux from the outer vertical field coil cannot solely induce the desired plasma current waveform in the case of the preprogramming of the heating power.

1. B1 field homogeneity and SAR calculations for the birdcage coil.

PubMed

Ibrahim, T S; Lee, R; Baertlein, B A; Robitaille, P M

2001-02-01

The finite-difference time-domain (FDTD) method is used to model a birdcage resonator. All the coil components, including the wires, lumped capacitors and the source, are geometrically modelled together. As such, the coupling effects within the birdcage, including the interactions of coil, source and human head, are accurately computed. A study of the transverse magnetic (B1) field homogeneity and the specific absorption rate (SAR) is presented on an anatomically detailed human head model at 64 and 200 MHz representing 1.5 and 4.7 T MRI systems respectively. Unlike that at 64 MHz, the B1 field distribution is found to be inhomogeneous at 200 MHz. Also, high local SAR values are observed in the tissue near the source due to the coupling between the source and the head at 200 MHz.

2. B1 field homogeneity and SAR calculations for the birdcage coil

Ibrahim, T. S.; Lee, R.; Baertlein, B. A.; Robitaille, P.-M. L.

2001-02-01

The finite-difference time-domain (FDTD) method is used to model a birdcage resonator. All the coil components, including the wires, lumped capacitors and the source, are geometrically modelled together. As such, the coupling effects within the birdcage, including the interactions of coil, source and human head, are accurately computed. A study of the transverse magnetic (B1) field homogeneity and the specific absorption rate (SAR) is presented on an anatomically detailed human head model at 64 and 200 MHz representing 1.5 and 4.7 T MRI systems respectively. Unlike that at 64 MHz, the B1 field distribution is found to be inhomogeneous at 200 MHz. Also, high local SAR values are observed in the tissue near the source due to the coupling between the source and the head at 200 MHz.

3. Synchronous Generator with HTS-2G field coils for Windmills with output power 1 MW

Kovalev, K.; Kovalev, L.; Poltavets, V.; Samsonovich, S.; Ilyasov, R.; Levin, A.; Surin, M.

2014-05-01

Nowadays synchronous generators for wind-mills are developed worldwide. The cost of the generator is determined by its size and weight. In this deal the implementation of HTS-2G generators is very perspective. The application of HTS 2G field coils in the rotor allows to reduce the size of the generator is 1.75 times. In this work the design 1 MW HTS-2G generator is considered. The designed 1 MW HTS-2G generator has the following parameters: rotor diameter 800 mm, active length 400 mm, phase voltage 690V, rotor speed 600 min-1 rotor field coils with HTS-2G tapes. HTS-2G field coils located in the rotating cryostat and cooled by liquid nitrogen. The simulation and optimization of HTS-2G field coils geometry allowed to increase feed DC current up to 50A. Copper stator windings are water cooled. Magnetic and electrical losses in 1 MW HTS-2G generator do not exceed 1.6% of the nominal output power. In the construction of HTS-2G generator the wave multiplier with ratio 1:40 is used. The latter allows to reduce the total mass of HTS-2G generator down to 1.5 tons. The small-scale model of HTS-2G generator with output power 50 kW was designed, manufactured and tested. The test results showed good agreement with calculation results. The manufacturing of 1 MW HTS-2G generator is planned in 2014. This work is done under support of Rosatom within the frames of Russian Project "Superconducting Industry".

4. Repair of a water-cooled field coil for a hydroelectric motor/generator

SciTech Connect

Miller, L.J. III

1983-01-01

Four reversible pump/turbine units at TVA's Raccoon Mountain Pumped-Storage Plant were placed in service in 1978 to 1979. The stator and rotor windings for the motor/generators are direct water cooled. This paper describes repairs to a water-cooled coil of one of the 24 field poles of Unit No. 3 motor/generator placed in service in February 1979.

5. Magnetic wall decoupling method for monopole coil array in ultrahigh field MRI: a feasibility test.

PubMed

Yan, Xinqiang; Zhang, Xiaoliang; Wei, Long; Xue, Rong

2014-04-01

Ultrahigh field (UHF) MR imaging of deeply located target in high dielectric biological samples faces challenges due to the reduced penetration depth at the corresponding high frequencies. Radiative coils, e.g., dipole and monopole coils, have recently been applied for UHF MRI applications to obtain better signal-noise-ratio (SNR) in the area deep inside the human head and body. However, due to the unique structure of radiative coil elements, electromagnetic (EM) coupling between elements in radiative coil arrays cannot be readily addressed by using traditional decoupling methods such as element overlapping and L/C decoupling network. A new decoupling method based on induced current elimination (ICE) or magnetic wall technique has recently been proposed and has demonstrated feasibility in designing microstrip transmission line (MTL) arrays and L/C loop arrays. In this study, an array of two monopole elements decoupled using magnetic wall decoupling technique was designed, constructed and analyzed numerically and experimentally to investigate the feasibility of the decoupling technique in radiative coil array designs for MR imaging at 7 T. An L-shaped capacitive network was employed as the matching circuit and the reflection coefficients (S11) of the monopole element achieved -30 dB or better. Isolation between the two monopole elements was improved from about -10 dB (without decoupling treatment) to better than -30 dB with the ICE/magnetic wall decoupling method. B1 maps and MR images of the phantom were acquired and SNR maps were measured and calculated to evaluate the performance of the ICE/magnetic wall decoupling method. Compared with the monopole elements without decoupling methods, the ICE-decoupled array demonstrated more independent image profiles from each element and had a higher SNR in the peripheral area of the imaging subject. The experimental and simulation results indicate that the ICE/magnetic wall decoupling technique might be a promising solution

6. Bucking Coil Implementation on PMT for Active Cancelling of Magnetic Field

SciTech Connect

Gogami, T; Asaturyan, A; Bono, J; Baturin, P; Chen, C; Chiba, A; Chiga, N; Fujii, Y; Hashimoto, O; Kawama, D; Maruta, T; Maxwell, V; Mkrtchyan, A; Nagao, S; Nakamura, S N; Reinhold, J; Shichijo, A; Tang, L; Taniya, N; Wood, S A; Ye, Z

2013-11-01

Aerogel and water Cerenkov detectors were employed to tag kaons for a lambda hypernuclear spectroscopic experiment which used the (e,e'K{sup +}) reaction in experimental Hall C at Jefferson Lab (JLab E05-115). Fringe fields from the kaon spectrometer magnet yielded ~5 Gauss at the photomultiplier tubes (PMT) for these detectors which could not be easily shielded. As this field results in a lowered kaon detection efficiency, we implemented a bucking coil on each photomultiplier tubes to actively cancel this magnetic field, thus maximizing kaon detection efficiency.

7. RF Magnetic Field Uniformity of Rectangular Planar Coils for Resonance Imaging

DTIC Science & Technology

2016-02-04

determines the detected NQR signal strength from the material. In this paper , two rectangular planar coils are tuned to 28.1MHz resonant frequency of...coil with square-shaped overlapping turns along the 135mm length of the coil. This paper compares these two coils to determine which has a more...induced. The results of this paper determine the type of rectangular coil to be used in a “grid array” of coils for quadrupole resonance imaging

8. 3D position estimation using a single coil and two magnetic field sensors.

PubMed

Tadayon, P; Staude, G; Felderhoff, T

2015-01-01

This paper presents an algorithm which enables the estimation of relative 3D position of a sensor module with two magnetic sensors with respect to a magnetic field source using a single transmitting coil. Starting with the description of the ambiguity problem caused by using a single coil, a system concept comprising two sensors having a fixed spatial relation to each other is introduced which enables the unique determination of the sensors' position in 3D space. For this purpose, an iterative two-step algorithm is presented: In a first step, the data of one sensor is used to limit the number of possible position solutions. In a second step, the spatial relation between the sensors is used to determine the correct sensor position.

9. Phase diagram of rod-coil diblock copolymer melts by self-consistent field theory

Yan, Dadong; Tang, Jiuzhou; Jiang, Ying; Zhang, Xinghua; Chen, Jeff

A unified phase diagram is presented for rod-coil diblock copolymer melts in the isotropic phase regime as a function of the asymmetric parameter. The study is based on free-energy calculation, which incorporates three-dimensional spatial variations of the volume fraction with angular dependence. The wormlike-chain model is used in a self-consistent field treatment. Body-centered cubic, A15, hexagonal, gyroid, and lamellar structures where the rod segments are packed inside the convex rod-coil interface are found stable. As the conformational asymmetric parameter increases, the A15 phase region expands and the gyroid phase region reduces. The stability of the structures is analyzed by concepts such as packing frustration, spinodal limit, and interfacial curvature.

10. Strongly magnetized accretion discs require poloidal flux

Salvesen, Greg; Armitage, Philip J.; Simon, Jacob B.; Begelman, Mitchell C.

2016-08-01

Motivated by indirect observational evidence for strongly magnetized accretion discs around black holes, and the novel theoretical properties of such solutions, we investigate how a strong magnetization state can develop and persist. To this end, we perform local simulations of accretion discs with an initially purely toroidal magnetic field of equipartition strength. We demonstrate that discs with zero net vertical magnetic flux and realistic boundary conditions cannot sustain a strong toroidal field. However, a magnetic pressure-dominated disc can form from an initial configuration with a sufficient amount of net vertical flux and realistic boundary conditions. Our results suggest that poloidal flux is a necessary prerequisite for the sustainability of strongly magnetized accretion discs.

11. Development of effective power supply using electric double layer capacitor for static magnetic field coils in fusion plasma experiments.

PubMed

Inomoto, M; Abe, K; Yamada, T; Kuwahata, A; Kamio, S; Cao, Q H; Sakumura, M; Suzuki, N; Watanabe, T; Ono, Y

2011-02-01

A cost-effective power supply for static magnetic field coils used in fusion plasma experiments has been developed by application of an electric double layer capacitor (EDLC). A prototype EDLC power supply system was constructed in the form of a series LCR circuit. Coil current of 100 A with flat-top longer than 1 s was successfully supplied to an equilibrium field coil of a fusion plasma experimental apparatus by a single EDLC module with capacitance of 30 F. The present EDLC power supply has revealed sufficient performance for plasma confinement experiments whose discharge duration times are an order of several seconds.

12. Feasibility study for reduction of the screening current induced field in a 2G high temperature superconducting coil

Hwang, Y. J.; Jang, J. Y.; Ahn, M. C.; Park, Y. G.; Lee, S. G.

2016-10-01

This paper reports the effects of thermal energy on reducing the overshoot of the current sweep cycle method to reduce the screening current-induced field (SCF) in a 2G high temperature superconducting (HTS) coil. A disadvantage of the current sweep cycle method is the necessity for large overshoot in the coil current. For a 2G HTS coil, excessive overshooting of the coil current is undesirable (Yanagisawa et al 2012 AIP Conf. Proc. 1434 1373-8). In an effort to circumvent this overshooting problem, the thermal energy effect was investigated in combination with the current sweep cycle method based on experiments in this study. The experimental results show that greater SCF reduction in the HTS coil was obtained upon increasing thermal energy by heater current.

13. Theoretical explanation for strong poloidal impurity asymmetry in tokamak pedestals

Espinosa, Silvia

2016-10-01

Stronger impurity density in-out poloidal asymmetries than predicted by the most comprehensive neoclassical models have been measured in H-mode tokamak pedestals during the last decade. However, these pioneering theories neglect the impurity diamagnetic drift, while recent measurements indicate that it can be of the same order as the ExB drift that is retained. In order to keep both drifts self-consistently, stronger radial gradients of the impurity density must be allowed. As a result, radial impurity flow effects need to be included for the first time. These effects substantially alter the parallel impurity flow. The resulting modification in the impurity friction with the banana regime background ions then allows stronger poloidal variation of the impurity density, temperature and potential. Even the six-fold high field side accumulation of boron density measured on Alcator C-Mod can be explained without invoking anomalous transport. Moreover, the potential can no longer be assumed to be a flux function since the impurity density variation gives a poloidally varying potential that results in strong poloidal variation of the radial electric field. The fact that the magnitude of the negative radial electric field and the impurity temperature are both larger on the low field side is also correctly predicted. Finally, this pedestal neoclassical model with radial flows may provide insight on how to control impurity accumulation in JET. Supported by DOE Grant DE-FG0291ER54109 and La Caixa Fellowship.

14. Coil system for plasmoid thruster

NASA Technical Reports Server (NTRS)

Eskridge, Richard H. (Inventor); Lee, Michael H. (Inventor); Martin, Adam K. (Inventor); Fimognari, Peter J. (Inventor)

2010-01-01

A coil system for a plasmoid thruster includes a bias coil, a drive coil and field coils. The bias and drive coils are interleaved with one another as they are helically wound about a conical region. A first field coil defines a first passage at one end of the conical region, and is connected in series with the bias coil. A second field coil defines a second passage at an opposing end of the conical region, and is connected in series with the bias coil.

15. Geometrical Design of a Scalable Overlapping Planar Spiral Coil Array to Generate a Homogeneous Magnetic Field

PubMed Central

Jow, Uei-Ming; Ghovanloo, Maysam

2014-01-01

We present a design methodology for an overlapping hexagonal planar spiral coil (hex-PSC) array, optimized for creation of a homogenous magnetic field for wireless power transmission to randomly moving objects. The modular hex-PSC array has been implemented in the form of three parallel conductive layers, for which an iterative optimization procedure defines the PSC geometries. Since the overlapping hex-PSCs in different layers have different characteristics, the worst case coil-coupling condition should be designed to provide the maximum power transfer efficiency (PTE) in order to minimize the spatial received power fluctuations. In the worst case, the transmitter (Tx) hex-PSC is overlapped by six PSCs and surrounded by six other adjacent PSCs. Using a receiver (Rx) coil, 20 mm in radius, at the coupling distance of 78 mm and maximum lateral misalignment of 49.1 mm (1/√3 of the PSC radius) we can receive power at a PTE of 19.6% from the worst case PSC. Furthermore, we have studied the effects of Rx coil tilting and concluded that the PTE degrades significantly when θ > 60°. Solutions are: 1) activating two adjacent overlapping hex-PSCs simultaneously with out-of-phase excitations to create horizontal magnetic flux and 2) inclusion of a small energy storage element in the Rx module to maintain power in the worst case scenarios. In order to verify the proposed design methodology, we have developed the EnerCage system, which aims to power up biological instruments attached to or implanted in freely behaving small animal subjects’ bodies in long-term electrophysiology experiments within large experimental arenas. PMID:24782576

16. Development of rotating magnetic field coil system in the HIST spherical torus device

Yoshikawa, T.; Kikuchi, Y.; Yamada, S.; Hashimoto, S.; Nishioka, T.; Fukumoto, N.; Nagata, M.

2007-11-01

Coaxial Helicity Injection (CHI) is one of most attractive methods to achieve non-inductive current drive in spherical torus devices. The current drive mechanism of CHI relies on MHD relaxation process of rotating kink behavior [1], so that there is a possibility to control the CHI by using an externally applied rotating magnetic field (RMF). We have recently started to develop a RMF coil system in the HIST spherical torus device. Eight coils are located above and below the midplane at four toroidal locations so that the RMF is resonant with n = 1 rotating kink mode driven by the CHI. In addition, the RMF coil set is installed inside a flux conserver of 5 mm thickness (cut-off frequency ˜ 170 Hz) so that the RMF penetrates into the plasma. The coil winding is made of 20 turns of enameled copper circular wires (1.5 mm^2 conductor cross section), covered with a thin stainless steal case of 0.5 mm thickness (cut-off frequency ˜ 710 kHz). The RMF system is driven by an IGBT inverter power supply (nominal current: 1 kA, nominal voltage: 1 kV) with an operating frequency band from 10 kHz to 30 kHz. The estimated amplitude of RMF neglecting effects of image current at the flux conserver is a few tens Gauss at around the magnetic axis. A preliminary experimental result will be shown in the conference. [1] M. Nagata, et al., Physics of Plasmas 10, 2932 (2003).

17. Geometrical Design of a Scalable Overlapping Planar Spiral Coil Array to Generate a Homogeneous Magnetic Field.

PubMed

Jow, Uei-Ming; Ghovanloo, Maysam

2012-12-21

We present a design methodology for an overlapping hexagonal planar spiral coil (hex-PSC) array, optimized for creation of a homogenous magnetic field for wireless power transmission to randomly moving objects. The modular hex-PSC array has been implemented in the form of three parallel conductive layers, for which an iterative optimization procedure defines the PSC geometries. Since the overlapping hex-PSCs in different layers have different characteristics, the worst case coil-coupling condition should be designed to provide the maximum power transfer efficiency (PTE) in order to minimize the spatial received power fluctuations. In the worst case, the transmitter (Tx) hex-PSC is overlapped by six PSCs and surrounded by six other adjacent PSCs. Using a receiver (Rx) coil, 20 mm in radius, at the coupling distance of 78 mm and maximum lateral misalignment of 49.1 mm (1/√3 of the PSC radius) we can receive power at a PTE of 19.6% from the worst case PSC. Furthermore, we have studied the effects of Rx coil tilting and concluded that the PTE degrades significantly when θ > 60°. Solutions are: 1) activating two adjacent overlapping hex-PSCs simultaneously with out-of-phase excitations to create horizontal magnetic flux and 2) inclusion of a small energy storage element in the Rx module to maintain power in the worst case scenarios. In order to verify the proposed design methodology, we have developed the EnerCage system, which aims to power up biological instruments attached to or implanted in freely behaving small animal subjects' bodies in long-term electrophysiology experiments within large experimental arenas.

18. TPX correction coil studies

SciTech Connect

Hanson, J.D.

1994-11-03

Error correction coils are planned for the TPX (Tokamak Plasma Experiment) in order to avoid error field induced locked modes and disruption. The FT (Fix Tokamak) code is used to evaluate the ability of these correction coils to remove islands caused by symmetry breaking magnetic field errors. The proposed correction coils are capable of correcting a variety of error fields.

19. Method of sustaining a radial electric field and poloidal plasma rotation over most of the cross-section of a tokamak

DOEpatents

Darrow, Douglass S.; Ono, Masayuki

1990-03-06

A radial electric field of a desired magnitude and configuration is created throughout a substantial portion of the cross-section of the plasma of a tokamak. The radial electric field is created by injection of a unidirectional electron beam. The magnitude and configuration of the radial electric field may be controlled by the strength of the toroidal magnetic field of the tokamak.

20. Method of sustaining a radial electric field and poloidal plasma rotation over most of the cross-section of a tokamak

DOEpatents

Darrow, Douglass S.; Ono, Masayuki

1990-01-01

A radial electric field of a desired magnitude and configuration is created hroughout a substantial portion of the cross-section of the plasma of a tokamak. The radial electric field is created by injection of a unidirectional electron beam. The magnitude and configuration of the radial electric field may be controlled by the strength of the toroidal magnetic field of the tokamak.

1. Series-field-coil ion beam diode experiment and numerical simulation

SciTech Connect

Mendel, C.W. Jr.; Quintenz, J.P.; Zagar, D.M.; Johnson, P.R.; Anderson, R.J.; Widner, M.M.

1984-08-01

An experiment with a series-field-coil intense ion beam diode operating at the 1.6-MV, 0.8-TW level is described. The diode operates in the extraction mode with a 20-cm focal length. The diode design procedure is described together with some of the essential ion diode theory used in this design process. The experiment produced a well-focused ion beam while verifying some of the theoretical assumptions about ion diodes of this type. The experimental results are compared with numerical computer simulations and excellent agreement is obtained.

2. Using a modified 3D-printer for mapping the magnetic field of RF coils designed for fetal and neonatal imaging.

PubMed

Vavoulas, Alexander; Vaiopoulos, Nicholas; Hedström, Erik; Xanthis, Christos G; Sandalidis, Harilaos G; Aletras, Anthony H

2016-08-01

An experimental setup for characterizing the magnetic field of MRI RF coils was proposed and tested. The setup consisted of a specially configured 3D-printer, a network analyzer and a mid-performance desktop PC. The setup was tested on a single loop RF coil, part of a phased array for fetal imaging. Then, the setup was used for determining the magnetic field characteristics of a high-pass birdcage coil used for neonatal MR imaging with a vertical static field. The scattering parameter S21, converted into power ratio, was used for mapping the B1 magnetic field. The experimental measurements from the loop coil were close to the theoretical results (R=0.924). A high degree of homogeneity was measured for the neonatal birdcage RF coil. The development of MR RF coils is time consuming and resource intensive. The proposed experimental setup provides an alternative method for magnetic field characterization of RF coils used in MRI.

3. Using a modified 3D-printer for mapping the magnetic field of RF coils designed for fetal and neonatal imaging

Vavoulas, Alexander; Vaiopoulos, Nicholas; Hedström, Erik; Xanthis, Christos G.; Sandalidis, Harilaos G.; Aletras, Anthony H.

2016-08-01

An experimental setup for characterizing the magnetic field of MRI RF coils was proposed and tested. The setup consisted of a specially configured 3D-printer, a network analyzer and a mid-performance desktop PC. The setup was tested on a single loop RF coil, part of a phased array for fetal imaging. Then, the setup was used for determining the magnetic field characteristics of a high-pass birdcage coil used for neonatal MR imaging with a vertical static field. The scattering parameter S21, converted into power ratio, was used for mapping the B1 magnetic field. The experimental measurements from the loop coil were close to the theoretical results (R = 0.924). A high degree of homogeneity was measured for the neonatal birdcage RF coil. The development of MR RF coils is time consuming and resource intensive. The proposed experimental setup provides an alternative method for magnetic field characterization of RF coils used in MRI.

4. Magnetic wall decoupling method for monopole coil array in ultrahigh field MRI: a feasibility test

PubMed Central

Yan, Xinqiang; Zhang, Xiaoliang; Wei, Long

2014-01-01

Ultrahigh field (UHF) MR imaging of deeply located target in high dielectric biological samples faces challenges due to the reduced penetration depth at the corresponding high frequencies. Radiative coils, e.g., dipole and monopole coils, have recently been applied for UHF MRI applications to obtain better signal-noise-ratio (SNR) in the area deep inside the human head and body. However, due to the unique structure of radiative coil elements, electromagnetic (EM) coupling between elements in radiative coil arrays cannot be readily addressed by using traditional decoupling methods such as element overlapping and L/C decoupling network. A new decoupling method based on induced current elimination (ICE) or magnetic wall technique has recently been proposed and has demonstrated feasibility in designing microstrip transmission line (MTL) arrays and L/C loop arrays. In this study, an array of two monopole elements decoupled using magnetic wall decoupling technique was designed, constructed and analyzed numerically and experimentally to investigate the feasibility of the decoupling technique in radiative coil array designs for MR imaging at 7 T. An L-shaped capacitive network was employed as the matching circuit and the reflection coefficients (S11) of the monopole element achieved –30 dB or better. Isolation between the two monopole elements was improved from about –10 dB (without decoupling treatment) to better than –30 dB with the ICE/magnetic wall decoupling method. B1 maps and MR images of the phantom were acquired and SNR maps were measured and calculated to evaluate the performance of the ICE/magnetic wall decoupling method. Compared with the monopole elements without decoupling methods, the ICE-decoupled array demonstrated more independent image profiles from each element and had a higher SNR in the peripheral area of the imaging subject. The experimental and simulation results indicate that the ICE/magnetic wall decoupling technique might be a promising

5. Unscented transform-based uncertainty analysis of rotating coil transducers for field mapping

Arpaia, P.; De Matteis, E.; Schiano Lo Moriello, R.

2016-03-01

The uncertainty of a rotating coil transducer for magnetic field mapping is analyzed. Unscented transform and statistical design of experiments are combined to determine magnetic field expectation, standard uncertainty, and separate contributions of the uncertainty sources. For nonlinear measurement models, the unscented transform-based approach is more error-proof than the linearization underlying the "Guide to the expression of Uncertainty in Measurements" (GUMs), owing to the absence of model approximations and derivatives computation. When GUM assumptions are not met, the deterministic sampling strategy strongly reduces computational burden with respect to Monte Carlo-based methods proposed by the Supplement 1 of the GUM. Furthermore, the design of experiments and the associated statistical analysis allow the uncertainty sources domain to be explored efficiently, as well as their significance and single contributions to be assessed for an effective setup configuration. A straightforward experimental case study highlights that a one-order-of-magnitude reduction in the relative uncertainty of the coil area produces a decrease in uncertainty of the field mapping transducer by a factor of 25 with respect to the worst condition. Moreover, about 700 trials and the related processing achieve results corresponding to 5 × 106 brute-force Monte Carlo simulations.

6. Uniform magnetic fields and double-wrapped coil systems: improved techniques for the design of bioelectromagnetic experiments.

PubMed

Kirschvink, J L

1992-01-01

A common mistake in biomagnetic experimentation is the assumption that Helmholtz coils provide uniform magnetic fields; this is true only for a limited volume at their center. Substantial improvements on this design have been made during the past 140 years with systems of three, four, and five coils. Numerical comparisons of the field uniformity generated by these designs are made here, along with a table of construction details and recommendations for their use in experiments in which large volumes of uniform intensity magnetic exposures are needed. Double-wrapping, or systems of bifilar windings, can also help control for the non-magnetic effects of the electric coils used in many experiments. In this design, each coil is wrapped in parallel with two separate, adjacent strands of copper wire, rather than the single strand used normally. If currents are flowing in antiparallel directions, the magnetic fields generated by each strand will cancel and yield virtually no external magnetic field, whereas parallel currents will yield an external field. Both cases will produce similar non-magnetic effects of ohmic heating, and simple measures can reduce the small vibration and electric field differences. Control experiments can then be designed such that the only major difference between treated and untreated groups is the presence or absence of the magnetic field. Double-wrapped coils also facilitate the use of truly double-blind protocol, as the same apparatus can be used either for experimental or control groups.

7. Nonlinear Dynamics of a Magnetically Driven Duffing-Type Spring-Magnet Oscillator in the Static Magnetic Field of a Coil

ERIC Educational Resources Information Center

2012-01-01

We study the nonlinear oscillations of a forced and weakly dissipative spring-magnet system moving in the magnetic fields of two fixed coaxial, hollow induction coils. As the first coil is excited with a dc current, both a linear and a cubic magnet-position dependent force appear on the magnet-spring system. The second coil, located below the…

8. Characterizing and calibrating a large Helmholtz coil at low ac magnetic field levels with peak magnitudes below the earth's magnetic field

Schill, Robert A.; Hoff, Karin

2001-06-01

Characterizing and calibrating a low impedance large Helmholtz coil generating 60 Hz magnetic fields with amplitudes well below the earth's magnetic field is difficult and imprecise when coil shielding is not available and noise is an issue. Parameters influencing the calibration process such as temperature and coil impedance need to be figured in the calibration process. A simple and reliable calibration technique is developed and used to measure low amplitude fields over a spatial grid using a standard Hall effect probe gaussmeter. These low amplitude fields are typically hard or impossible to detect in the presence of background fields when using the gaussmeter in the conventional manner. Standard deviations of two milligauss and less have been achieved over a spatial grid in a uniform field region. Theoretical and measured fields are compared yielding reasonable agreement for a large coil system designed and built for bioelectromagnetic experiments at the University of Nevada at Las Vegas using simple tools. Theoretical results need to be compared with and adjusted in accord with measurements taken over a large parameter space within the design constraints of the coil. Magnetic field measurements made over a four year period are shown to be consistent. Characterizing and calibrating large Helmholtz coils can be performed with rulers, levels, plumb lines, and inexpensive gaussmeters.

9. Measurements on Subscale Y-Ba-Cu-O Racetrack Coils at 77 K and Self-Field

SciTech Connect

Wang, X.; Caspi, S.; Cheng, D. W.; Dietderich, D. R.; Felice, H.; Ferracin, P.; Godeke, A.; Joseph, J. M.; Lizarazo, J.; Prestemon, S. O.; Sabbi, G.

2009-10-19

YBa{sub 2}Cu{sub 3}O{sub 7-{delta}} (YBCO) tapes carry significant amount of current at fields beyond the limit of Nb-based conductors. This makes the YBCO tapes a possible conductor candidate for insert magnets to increase the bore field of Nb{sub 3}Sn high-field dipoles. As an initial step of the YBCO insert technology development, two subscale racetrack coils were wound using Kapton-insulated commercial YBCO tapes. Both coils had two layers; one had 3 turns in each layer and the other 10 turns. The coils were supported by G10 side rails and waxed strips and not impregnated. The critical current of the coils was measured at 77 K and self-field. A 2D model considering the magnetic-field dependence of the critical current was used to estimate the expected critical current. The measured results show that both coils reached 80%-95% of the expected values, indicating the feasibility of the design concept and fabrication process.

10. Influence of demagnetization coil configuration on residual field in an extremely magnetically shielded room: Model and measurements

Knappe-Grueneberg, Silvia; Schnabel, Allard; Wuebbeler, Gerd; Burghoff, Martin

2008-04-01

The Berlin magnetically shielded room 2 (BMSR-2) features a magnetic residual field below 500pT and a field gradient level less than 0.5pT/mm, which are needed for very sensitive human biomagnetic recordings or low field NMR. Nevertheless, below 15Hz, signals are compromised by an additional noise contribution due to vibration forced sensor movements in the field gradient. Due to extreme shielding, the residual field and its homogeneity are determined mainly by the demagnetization results of the mumetal shells. Eight different demagnetization coil configurations can be realized, each results in a characteristic field pattern. The spatial dc flux density inside BMSR-2 is measured with a movable superconducting quantum interference device system with an accuracy better than 50pT. Residual field and field distribution of the current-driven coils fit well to an air-core coil model, if the high permeable core and the return lines outside of the shells are neglected. Finally, we homogenize the residual field by selecting a proper coil configuration.

11. Design and Fabrication of Helmholtz Coils to Study the Effects of Pulsed Electromagnetic Fields on the Healing Process in Periodontitis: Preliminary Animal Results

PubMed Central

Haghnegahdar, A; Khosrovpanah, H; Andisheh-Tadbir, A; Mortazavi, Gh; Saeedi Moghadam, M; Mortazavi, SMJ; Zamani, A; Haghani, M; Shojaei Fard, M; Parsaei, H; Koohi, O

2014-01-01

Background: Effects of electromagnetic fields on healing have been investigated for centuries. Substantial data indicate that exposure to electromagnetic field can lead to enhanced healing in both soft and hard tissues. Helmholtz coils are devices that generate pulsed electromagnetic fields (PEMF). Objective: In this work, a pair of Helmholtz coils for enhancing the healing process in periodontitis was designed and fabricated. Method: An identical pair of square Helmholtz coils generated the 50 Hz magnetic field.  This device was made up of two parallel coaxial circular coils (100 turns in each loop, wound in series) which were separated from each other by a distance equal to the radius of one coil (12.5 cm). The windings of our Helmholtz coil was made of standard 0.95mm wire to provide the maximum possible current. The coil was powered by a function generator.  Results: The Helmholtz Coils generated a uniform magnetic field between its coils. The magnetic field strength at the center of the space between two coils was 97.6 μT. Preliminary biological studies performed on rats show that exposure of laboratory animals to pulsed electromagnetic fields enhanced the healing of periodontitis. Conclusion: Exposure to PEMFs can lead to stimulatory physiological effects on cells and tissues such as enhanced healing of periodontitis. PMID:25505775

12. Plasma Current Start-up by ECW and Vertical Field in the TST-2 Spherical Tokamak

Mitarai, Osamu; Takase, Yuichi; Ejiri, Akira; Shiraiwa, Syunichi; Kasahara, Hiroshi; Yamada, Takuma; Ohara, Shinya; TST-2 Team; Nakamura, Kazuo; Iyomasa, Atsuhiro; Hasegawa, Makoto; Idei, Hiroshi; Sakamoto, Mizuki; Hanada, Kazuaki; Satoh, Kohnosuke; Zushi, Hideki; TRIAM Group; Nishino, Nobuhiro

Plasma current start-up and ramp-up to 10 kA have been demonstrated in the TST-2 spherical tokamak without the use of the central solenoid. Only the electron cyclotron wave (ECW) and the outer equilibrium field coils are used. The plasma current evolution depends on the poloidal coil arrangement. It is also demonstrated that the plasma current start-up can take place without the field null.

13. High-field 13C NMR spectroscopy of tissue in Vivo. A double-resonance surface-coil probe

Reo, Nicholas V.; Ewy, Coleen S.; Siegfried, Barry A.; Ackerman, Joseph J. H.

A double-resonance surface-coil NMR probe is described for performance of high-field (8.5 T) proton decoupled carbon-13 experiments with tissue in vivo. The probe may be accommodated in standard, 89 mm i.d. clear bore, commercial spectrometers and is suitable for studies utilizing small laboratory animals such as mice, hamsters, and rats. A coaxial coil design is employed (10 mm diameter 13C coil, 20 mm diameter 1H coil) which provides ca. 40 dB attenuation between the 13C observe and 1H decouple channels. The inherent efficiency of the surface-coil configuration provides a sensitivity comparable to a commercial probe of the same nominal dimension (10 mm Helmholtz coil) and assures adequate decoupling in conductive samples with ca. 3-5 W power. In the absence of 13C isotopic enrichment, NMR spectra of rat leg, liver, and brain in vivo provide signalto-noise sufficient for 10 min time resolution. Administration of 100 mg of 90% 13C-labeled glucose into a peripheral vein of a ca. 300 g rat resulted in a liver glucose resonance which could be monitored with good signal-to-noise and 3 min time resolution.

14. Performance of pancake coils of parallel co-wound Ag/BSCCO tape conductors in static and ramped magnetic fields

SciTech Connect

Schwenterly, S.W.; Lue, J.W.; Lubell, M.S.; Walker, M.S.; Hazelton, D.W.; Haldar, P.; Rice, J.A.; Hoehn, J.G. Jr.; Motowidlo, L.R.

1994-12-31

Critical Currents are reported for several Ag/BSCCO single-pancake coils in static magnetic fields ranging from 0 to 5 T and temperatures from 4.2 K to 105 K. The sample coils were co-wound of one to six tape conductors in parallel. Since the closed loops formed in such an arrangement could lead to eddy current heating or instability in changing fields, one of the coils was also tested in helium gas, in fields ramped at rates of up to 1.5 T/s. For these quasi-adiabatic tests, at each temperature the transport current was set just below the critical value for a preset static field of 3.3 or 4.9 T. The field was then rapidly ramped down to zero, held for 20 sec, and then ramped back up to the original value. The maximum observed temperature transient of about 1.7 K occurred at 9 K, for a field change of 4.75 T. The temperature transients became negligible when the sample was immersed in liquid helium. Above 30 K, the transients were below 1 K. These results give confidence that parallel co-wound HTSC coils are stable in a rapidly-ramped magnetic field, without undue eddy current heating.

15. Demonstration Model Development of the Force-Balanced Coil for SMES

Nomura, Shinichi; Kasuya, Koji; Tanaka, Norihiro; Tsuboi, Kenji; Tsutsui, Hiroaki; Shimada, Ryuichi; Ninomiya, Akira; Ishigohka, Takashi

In large-scale SMES, the superconducting coils require special considerations for induced electromagnetic forces to limit allowable tensile stress. Force-balanced coil (FBC) is a helically wound hybrid coil of toroidal field coils and a solenoid. The FBC can significantly reduce the required mass of the structure for induced electromagnetic forces. In order to demonstrate the feasibility of the FBC concept for SMES, the authors have developed a superconducting model coil. The outer diameter of the model FBC is 0.53m. The hand-made winding, using NbTi/Cu composite strands with a diameter of 1.17mm, was finished with 10584 poloidal turns after four months. The helical windings of the model FBC were neither impregnated with epoxy resin nor reinforced with stainless steel wires. Three test runs were conducted with liquid helium cooling at intervals of several months. The number of quench tests was 81 in total. The first quench current was 293A, which was 53% of the critical coil current. The training phenomena could be observed even after the coil was warmed up to room temperature. After successive quenches the quench current was improved to 476A, corresponding to 86% of the critical coil current, and it was successfully excited up to 6.1T.

16. Comparison study of toroidal-field divertors for a compact reversed-field pinch reactor

SciTech Connect

Bathke, C.G.; Krakowski, R.A.; Miller, R.L.

1985-01-01

Two divertor configurations for the Compact Reversed-Field Pinch Reactor (CRFPR) based on diverting the minority (toroidal) field have been reported. A critical factor in evaluating the performance of both poloidally symmetric and bundle divertor configurations is the accurate determination of the divertor connection length and the monitoring of magnetic islands introduced by the divertors, the latter being a three-dimensional effect. To this end the poloidal-field, toroidal-field, and divertor coils and the plasma currents are simulated in three dimensions for field-line tracings in both the divertor channel and the plasma-edge regions. The results of this analysis indicate a clear preference for the poloidally symmetric toroidal-field divertor. Design modifications to the limiter-based CRFPR design that accommodate this divertor are presented.

17. Analyzing the uniformity of the generated magnetic field by a practical one-dimensional Helmholtz coils system.

PubMed

Beiranvand, R

2013-07-01

Using the Helmholtz coils system is one of the most suitable approaches which have been introduced for generating uniform magnetic fields. In this paper, uniformity of the generated magnetic field by a practical one-dimensional (1D) Helmholtz coils system has been analyzed, mathematically. For this purpose, relationships between the magnetic field uniformity and different practical unavoidable mismatches have been extracted. The theoretical analysis clearly demonstrates the effect of assembly misalignments and manufacturing mismatches on the magnetic field achieved by a practical 1D Helmholtz coils system. The given analyses have been confirmed by the experimental results which are in good agreement with the calculated values. This analysis and the experimental results illustrate that to achieve a very high uniform magnetic field, practical assembly misalignments, and manufacturing mismatches must be as small as possible, and the background magnetic field distortion must be avoided, too. The results of this work are important in the design of instruments and systems where Helmholtz coils are used.

18. A study of the electromagnetic characteristics of no-insulation GdBCO racetrack coils under an external magnetic ripple field

Choi, Y. H.; Yang, D. G.; Kim, Y. G.; Kim, S. G.; Song, J. B.; Lee, H. G.

2016-04-01

Here we report the effect of an external magnetic ripple field on the electromagnetic characteristics of GdBCO racetrack coils being operated with a constant DC current. Two types of GdBCO racetrack coils, one wound without turn-to-turn insulation (NI) and the other wound with Kapton tape (INS), were examined under external ripple fields generated by a permanent magnet mounted on a rotor, which was driven by a separate AC motor. The voltage fluctuations and magnetic field variations were measured with respect to the external ripple field intensity (B ERF), rotating speed, and the operating condition. When the INS and NI coils were exposed to an external ripple field (herein, I op = 80 A, B ERF = 2 mT, and 5 rpm), a voltage fluctuation occurred because a time-varying magnetic field interacted with an electric circuit creating an electromotive force. The peak-to-peak voltage (V pp = 0.29 mV) of the NI coil was ∼1.86 times lower than that (0.54 mV) of the INS coil, because the voltage response of the NI coil lagged behind dB/dt due to the existence of turn-to-turn contact. Furthermore, the V pp of the INS coil increased with increasing B ERF and rotating speed, while those of the NI coil were barely affected due to the delay of electromagnetic induction. In excessive current and ripple field conditions (I op = 1.125 I c, B ERF = 8 mT, and 50 rpm) the INS coil eventually quenched while the NI coil did not, implying that the electromagnetic stability of the NI coil in excessive time-varying field conditions was superior to that of the INS coil.

19. Air core notch-coil magnet with variable geometry for fast-field-cycling NMR

Kruber, S.; Farrher, G. D.; Anoardo, E.

2015-10-01

In this manuscript we present details on the optimization, construction and performance of a wide-bore (71 mm) α -helical-cut notch-coil magnet with variable geometry for fast-field-cycling NMR. In addition to the usual requirements for this kind of magnets (high field-to-power ratio, good magnetic field homogeneity, low inductance and resistance values) a tunable homogeneity and a more uniform heat dissipation along the magnet body are considered. The presented magnet consists of only one machined metallic cylinder combined with two external movable pieces. The optimal configuration is calculated through an evaluation of the magnetic flux density within the entire volume of interest. The magnet has a field-to-current constant of 0.728 mT/A, allowing to switch from zero to 0.125 T in less than 3 ms without energy storage assistance. For a cylindrical sample volume of 35 cm3 the effective magnet homogeneity is lower than 130 ppm.

20. Air core notch-coil magnet with variable geometry for fast-field-cycling NMR.

PubMed

Kruber, S; Farrher, G D; Anoardo, E

2015-10-01

In this manuscript we present details on the optimization, construction and performance of a wide-bore (71 mm) α-helical-cut notch-coil magnet with variable geometry for fast-field-cycling NMR. In addition to the usual requirements for this kind of magnets (high field-to-power ratio, good magnetic field homogeneity, low inductance and resistance values) a tunable homogeneity and a more uniform heat dissipation along the magnet body are considered. The presented magnet consists of only one machined metallic cylinder combined with two external movable pieces. The optimal configuration is calculated through an evaluation of the magnetic flux density within the entire volume of interest. The magnet has a field-to-current constant of 0.728 mT/A, allowing to switch from zero to 0.125 T in less than 3 ms without energy storage assistance. For a cylindrical sample volume of 35 cm(3) the effective magnet homogeneity is lower than 130 ppm.

1. Impact of plasma poloidal rotation on resistive wall mode instability in toroidally rotating plasmas

SciTech Connect

Aiba, N.; Shiraishi, J.; Tokuda, S.

2011-02-15

Stability of resistive wall mode (RWM) is investigated in a cylindrical plasma and an axisymmetric toroidal plasma by taking into account not only toroidal rotation but also poloidal rotation. Since the Doppler shifted frequency is responsible for the RWM stability, the modification of this Doppler shifted frequency by poloidal rotation affects the rotation effect on RWM. When a poloidal rotation frequency is not so large, the effect of poloidal rotation on the RWM stability can be approximately treated with the modified toroidal rotation frequency. In a toroidal plasma, this modified frequency is determined by subtracting a toroidal component of the rotation parallel to the magnetic field from the toroidal rotation frequency. The poloidal rotation that counteracts the effect of the Doppler shift strongly reduces the stabilizing effect of toroidal rotation, but by changing the rotational direction, the poloidal rotation enhances this stabilizing effect. This trend is confirmed in not only a cylindrical plasma but also a toroidal plasma. This result indicates that poloidal rotation produces the dependence of the critical toroidal rotation frequency for stabilizing RWM on the rotational direction of toroidal rotation in the same magnetic configuration.

2. Concentric Loop Surface Coil

Hernández-Flores, R.; Rodríguez-González, A. O.; Salgado-Lujambio, P.; Barrios-Alvarez, F. A.

2002-08-01

A surface coil for MRI consisted of two concentric loops was developed for brain imaging. Prior to build the coil prototype, the magnetic field (B1) generated by the coil was numerically simulated. This field simulation is based on the Biot-Savart law for the circular- and square-shaped loops. From these theoretical results, we can appreciate an improvement on the B1 homogeneity. Brain images obtained at 1.5 Tesla show a good sensitivity in a particular region of interest. Also, these images compared well against images obtained with a circular-shaped coil. This receiver coil can generate high quality brain images.

3. Nonambipolarity, orthogonal conductivity, poloidal flow, and torque

SciTech Connect

Hulbert, G.W.; Perkins, F.W.

1989-02-01

Nonambipolar processes, such as neutral injection onto trapped orbits or ripple-diffusion loss of ..cap alpha..-particles, act to charge a plasma. A current j/sub r/ across magnetic surfaces must arise in the bulk plasma to maintain charge neutrality. An axisymmetric, neoclassical model of the bulk plasma shows that these currents are carried by the ions and exert a j/sub r/B/sub theta/R/c torque in the toroidal direction. A driven poloidal flow V/sub theta/ = E/sub r/'c/B must also develop. The average current density is related to the radial electric field E/sub r/' = E/sub r/ + v/sub /phi//B/sub theta//c in a frame moving with the plasma via the orthogonal conductivity = sigma/sub /perpendicular//E/sub r/', which has the value sigma/sub /perpendicular// = (1.65epsilon/sup 1/2/)(ne/sup 2/..nu../sub ii//M..cap omega../sub theta//sup 2/) in the banana regime. If an ignited plasma loses an appreciable fraction ..delta.. of its thermonuclear ..cap alpha..-particles by banana ripple diffusion, then the torque will spin the plasma to sonic rotation in a time /tau//sub s/ approx. 2/tau//sub E//..delta.., /tau//sub E/ being the energy confinement time. 10 refs., 1 fig.

4. Investigation of the B1 field distribution and RF power deposition in a birdcage coil as functions of the number of coil legs at 4.7 T, 7.0 T, and 11.7 T

Seo, Jeung-Hoon; Han, Sang-Doc; Kim, Kyoung-Nam

2015-06-01

The proper design of birdcage (BC) coils plays a very important role in the acquisition of highresolution magnetic resonance imaging (MRI) of small animals such as rodents. In this context, we investigate multiple-leg (8-, 16-, 32-, 64-, and 128-leg) BC coils operating at ultra-high fields (UHF) of 7.0 T and 11.7 T and a high-field (HF) of 4.7 T for rodent magnetic resonance imaging (MRI). Primarily, Our study comparatively examines the parameters of the radiofrequency (RF) transmission (|B1 +|)-field, the magnetic flux (|B1|)-field, and RF power deposition (RF-PD) as functions of the number of BC-coil legs via finite-difference time-domain (FDTD) calculations under realistic loading conditions with a biological phantom. In particular, the specific ratio |E/B1 +| is defined for predicting RF-PD values in different coil structures. Our results indicate that the optimal number of legs of the BC coil can be chosen for different resonance frequencies of 200 MHz, 300 MHz, and 500 MHz and that this choice can be lead to superior |B1 +|-field intensity and |B1|-field homogeneity and decreased RF-PD. We believe that our approach to determining the optimal number of legs for a BC coil can contribute to rodent MR imaging.

5. Neoclassical Poloidal and Toroidal Velocities of Impurity Ions

Wong, S. K.; Chan, V. S.; Solomon, W. M.

2008-11-01

The poloidal and toroidal velocities of impurity ions in a two-ion species plasma for large aspect ratio circular flux surfaces are calculated in the banana and Pfirsch-Schulter regimes of neoclassical theory. The toroidal velocity is allowed to be comparable to the thermal speed of the impurity ions. Closed form expressions are obtained for these velocities in terms of the radial electric field as well as density and temperature gradients. The standard kinetic derivation adopted is compared with the moment approach to the same problems in the case of small toroidal velocities. Comparisons of the calculated poloidal velocity with experimental observations in DIII-D [1] show improved agreement due to the allowance of larger toroidal flows. 6pt [1] W.M. Solomon, Phys. Plasmas 13, 056116 (2006).

6. Demountable, High field High-Temperature Superconductor TF coils for flexible steady-state fusion experiments

Michael, Phillip; Bromberg, Leslie; Vieira, Rui; Minervini, Joseph; Galea, Christopher; Hensley, Sarah; Whyte, Dennis

2014-10-01

The excellent properties of HTS materials (e.g., YBCO) at high fields and elevated temperatures (>20 K), offer operational advantages for fusion machines, but results in challenges. For fusion devices, the ability to disassemble the TF coil is very attractive as it provides direct access to maintain the vacuum vessel, first wall and other components in a timely manner. High current conductors, made from multiple thin tapes, are not available but are being developed. Quench protection is a serious issue with HTS magnets, and novel means are needed to detect normal zones and to quickly discharge the magnet. Potential cables designs, demountable magnets and solutions to quench and protection issues for an HTS TF magnet for the Vulcan device (long term PMI studies) will be described. We also describe means for making continuous, persistent loops with HTS tapes. These loops offer an alternative to expensive monoliths for field control for complex geometries, such as stellarator-like fields. Partially supported by US DOE DE-FC02-93ER54186.

7. Increasing Magnetic-Field Capability of MIFEDS Using an Inductively Coupled Coil

Barnak, D. H.; Chang, P.-Y.; Fiksel, G.; Betti, R.; Taylor, C.

2013-10-01

Magnetized high-energy-density plasma (HEDP) science is a very active and relatively unexplored field that has applications in inertial confinement fusion (ICF), astrophysical plasma science, and basic plasma physics. A self-contained device, the magneto-inertial fusion electrical discharge system (MIFEDS) was developed at the Laboratory for Laser Energetics to conduct magnetized HEDP experiments on both the OMEGA and OMEGA EP Laser Systems. Extremely high magnetic fields are a necessity for magnetized HEDP and continue to drive the redevelopment of the MIFEDS device. The MIFEDS device has recently been upgraded to quadruple the stored energy, reduce the internal impedance of the device, and double the magnetic field. A redesign of the MIFEDS targets allows for robust and repeatable operation and for accommodation of various experimental arrangements. A new design for an inductively coupled coil for MIFEDS is presented. Details of this new design and its performance are provided, as well as a brief overview of the critical design features and limitations. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944 and DE-FC02-04ER54789 (Fusion Science Center).

8. Reliability data to improve high magnetic field coil design for high velocity coilguns.

SciTech Connect

Kaye, Ronald John; Mann, Gregory Allen

2003-09-01

Coilguns have demonstrated their capability to launch projectiles to 1 km/s, and there is interest in their application for long-range precision strike weapons. However, the incorporation of cooling systems for repetitive operation will impact the mechanical design and response of the future coils. To assess the impact of such changes, an evaluation of the ruggedness and reliability of the existing 50 mm bore coil designed in 1993 was made by repeatedly testing at stress levels associated with operation in a coilgun. A two-coil testbed has been built with a static projectile where each coil is energized by its own capacitor bank. Simulation models of the applied forces generated in this testbed have been created with the SLINGSHOT circuit code to obtain loads equivalent to the worst-case anticipated in a 50 mm coilgun that could launch a 236 g projectile to 2 km/s. Bench measurements of the seven remaining coils built in 1993 have been used to evaluate which coils were viable for testing, and only one was found defective. Measurements of the gradient of the effective coil inductance in the presence of the projectile were compared to values from SLINGSHOT, and the agreement is excellent. Repeated testing of the HFC5 coil built in 1993 has demonstrated no failures after 205 shots, which is an order of magnitude greater than any number achieved in previous testing. Although this testing has only been done on two coils, the results are encouraging as it demonstrates there are no fundamental weak links in the design that will cause a very early failure. Several recommendations for future coil designs are suggested based on observations of this study.

9. SQUIDs vs. Faraday coils for ultlra-low field nuclear magnetic resonance: experimental and simulation comparison

SciTech Connect

Matlashov, Andrei N; Espy, Michelle A; Kraus, Robert H; Sayukov, Igor M; Schultz, Larry J; Urbaitis, Algis V; Volegov, Petr L; Wurden, Caroline J

2010-01-01

Nuclear magnetic resonance (NMR) methods are widely used in medicine, chemistry and industry. One application area is magnetic resonance imaging or MRI. Recently it has become possible to perform NMR and MRI in ultra-low field (ULF) regime that requires measurement field strengths only of the order of 1 Gauss. These techniques exploit the advantages offered by superconducting quantum interference devices or SQUIDs. Our group at LANL has built SQUID based MRI systems for brain imaging and for liquid explosives detection at airports security checkpoints. The requirement for liquid helium cooling limits potential applications of ULF MRI for liquid identification and security purposes. Our experimental comparative investigation shows that room temperature inductive magnetometers provide enough sensitivity in the 3-10 kHz range and can be used for fast liquid explosives detection based on ULF NMR/MRI technique. We describe an experimental and computer simulation comparison of the world's first multichannel SQUID based and Faraday coils based instruments that are capable of performing ULF MRI for liquids identification.

10. Optimum coil shape for a given volume of conductor to obtain maximum central field in an air core solenoid

SciTech Connect

Hernandez, P.

1995-02-01

This paper is an expansion of engineering notes prepared in 1961 to address the question of how to wind circular coils so as to obtain the maximum axial field with the minimum volume of conductor. At the time this was a germain question because of the advent of superconducting wires which were in very limited supply, and the rapid push for generation of very high fields, with little concern for uniformity.

11. Influence of piston and magnetic coils on the field-dependent damping performance of a mixed-mode magnetorheological damper

2016-05-01

This work presents a 2D simulation study of a mixed-mode magnetorheological (MR) damper in which the influence of the geometric elements of the piston and magnetic coil on the MR damper’s performance is investigated by using the Ansoft Maxwell software tool. Four results of the simulation, which are magnetic flux density (B), MR fluid yield stress (τ 0), {τ }0{L}a and W{τ }0{L}a, are used to compare the performance of the MR damper. Multiplication of the yield stress by the active operating mode length ({τ }0{L}a) represents the variable portion of the active (on-state) damping force of the flow mode motion, while the value of W{τ }0{L}a represents the active damping force of the shear mode motion. The contribution of each operating mode (shear and flow) is related to the mixed-mode geometry and piston velocity. Therefore, each operating mode is evaluated separately. In this work, a total of 154 simulations are done in which 74, 20 and 60 simulations are conducted to analyse the effect of the piston radius, coil dimensions (width and length) and coil boundary lengths, respectively, on the performance of the MR damper. The simulation results show that increasing the piston radius can increase the W{τ }0{L}a value and reduce the value. For a given area of magnetic coil housing, a greater housing length in the axial direction of the piston can increase the achieved yield stress of the MR fluid and hence consequently the performance of the MR damper. A minimum boundary length is needed around the magnetic coil in order to attain a supreme magnetic field distribution. However, there is an optimised value for axial coil boundary lengths, which are the lengths of the upper and lower mixed-mode areas.

12. Angular dependence of direct current decay in a closed YBCO double-pancake coil under external AC magnetic field and reduction by magnetic shielding

Geng, J.; Zhang, H.; Li, C.; Zhang, X.; Shen, B.; Coombs, T. A.

2017-03-01

High T c superconducting (HTS) coils are ideal candidates in the use of high field magnets. HTS coils carrying a direct current, however, suffer a non-negligible loss when they are exposed to an external AC magnetic field. Although this phenomenon is well known, no study concerning AC magnetic field angular dependence of direct current decay has ever been shown. In this work, we experimentally investigate the direct current decay characteristics in a closed double pancake coil made of a YBCO coated conductor under external AC field. AC field of different angles with respect to the coil plane is applied. Results show that the current decay rate presents a strong angular dependence. The fastest decay occurs when the field is parallel to the coil plane, in which case the surface of the tape in the outermost layer experiences most flux variation. To reduce the decay rate, we propose wrapping superconducting tapes around the outermost layer of the coil to shield external AC field. This method significantly reduces direct current decay rate under parallel field, without affecting the perpendicular self-field of the coil.

13. The intrinsic conformational features of amino acids from a protein coil library and their applications in force field development.

PubMed

Jiang, Fan; Han, Wei; Wu, Yun-Dong

2013-03-14

The local conformational (φ, ψ, χ) preferences of amino acid residues remain an active research area, which are important for the development of protein force fields. In this perspective article, we first summarize spectroscopic studies of alanine-based short peptides in aqueous solution. While most studies indicate a preference for the P(II) conformation in the unfolded state over α and β conformations, significant variations are also observed. A statistical analysis from various coil libraries of high-resolution protein structures is then summarized, which gives a more coherent view of the local conformational features. The φ, ψ, χ distributions of the 20 amino acids have been obtained from a protein coil library, considering both backbone and side-chain conformational preferences. The intrinsic side-chain χ(1) rotamer preference and χ(1)-dependent Ramachandran plot can be generally understood by combining the interaction of the side-chain Cγ/Oγ atom with two neighboring backbone peptide groups. Current all-atom force fields such as AMBER ff99sb-ILDN, ff03 and OPLS-AA/L do not reproduce these distributions well. A method has been developed by combining the φ, ψ plot of alanine with the influence of side-chain χ(1) rotamers to derive the local conformational features of various amino acids. It has been further applied to improve the OPLS-AA force field. The modified force field (OPLS-AA/C) reproduces experimental (3)J coupling constants for various short peptides quite well. It also better reproduces the temperature-dependence of the helix-coil transition for alanine-based peptides. The new force field can fold a series of peptides and proteins with various secondary structures to their experimental structures. MD simulations of several globular proteins using the improved force field give significantly less deviation (RMSD) to experimental structures. The results indicate that the local conformational features from coil libraries are valuable for

14. A target field design of open multi-purpose RF coil for musculoskeletal MR imaging at 3T.

PubMed

Gao, Fei; Zhang, Rui; Zhou, Diange; Wang, Xiaoying; Huang, Kefu; Zhang, Jue

2016-10-01

Musculoskeletal MR imaging under multi-angle situations plays an increasingly important role in assessing joint and muscle tissues system. However, there are still limitations due to the closed structures of most conventional RF coils. In this study, a time-harmonic target-field method was employed to design open multi-purpose coil (OMC) for multi-angle musculoskeletal MR imaging. The phantom imaging results suggested that the proposed OMC could achieve homogeneously distributed magnetic field and high signal-to-noise ratio (SNR) of 239.04±0.83 in the region of interest (ROI). The maximum temperature in the heating hazard test was 16°C lower than the standard regulation, which indicated the security of the designed OMC. Furthermore, to demonstrate the effectiveness of the proposed OMC for musculoskeletal MR imaging, especially for multi-angle imaging, a healthy volunteer was examined for MR imaging of elbow, ankle and knee using OMC. The in vivo imaging results showed that the proposed OMC is effective for MR imaging of musculoskeletal tissues at different body parts, with satisfied B1 field homogeneity and SNR. Moreover, the open structure of the OMC could provide a large joint movement region. The proposed open multi-purpose coil is feasible for musculoskeletal MR imaging, and potentially, it is more suitable for the evaluation of musculoskeletal tissues under multi-angle conditions.

15. Type-I superconductor pick-up coil in superconducting quantum interference device-based ultra-low field nuclear magnetic resonance

SciTech Connect

Hwang, Seong-min Kim, Kiwoong; Kyu Yu, Kwon; Lee, Seong-Joo; Hyun Shim, Jeong; Körber, Rainer; Burghoff, Martin

2014-02-10

In ultra-low field nuclear magnetic resonance (ULF-NMR) with strong prepolarization field (B{sub p}), type-II superconducting pick-up coils may be vulnerable to flux pinning from the strong B{sub p}. Pick-up coils made of NbTi, Nb, and Pb were evaluated in terms of acquired NMR signal quality. The type-II pick-up coils showed degraded signals above 61 mT maximum exposure, while the Pb pick-up coil exhibited no such degradation. Furthermore, a negative counter pulse following a strong B{sub p} was shown to follow magnetic hysteresis loop to unpin the trapped flux in the type-II pick-up coil and restore the NMR signal.

16. Superconducting magnetic coil

DOEpatents

Aized, Dawood; Schwall, Robert E.

1996-06-11

A superconducting magnetic coil includes a plurality of sections positioned axially along the longitudinal axis of the coil, each section being formed of an anisotropic high temperature superconductor material wound about a longitudinal axis of the coil and having an associated critical current value that is dependent on the orientation of the magnetic field of the coil. The cross section of the superconductor, or the type of superconductor material, at sections along the axial and radial axes of the coil are changed to provide an increased critical current at those regions where the magnetic field is oriented more perpendicularly to the conductor plane, to thereby increase the critical current at these regions and to maintain an overall higher critical current of the coil.

17. Superconducting magnetic coil

DOEpatents

Aized, D.; Schwall, R.E.

1999-06-22

A superconducting magnetic coil includes a plurality of sections positioned axially along the longitudinal axis of the coil, each section being formed of an anisotropic high temperature superconductor material wound about a longitudinal axis of the coil and having an associated critical current value that is dependent on the orientation of the magnetic field of the coil. The cross section of the superconductor, or the type of superconductor material, at sections along the axial and radial axes of the coil are changed to provide an increased critical current at those regions where the magnetic field is oriented more perpendicularly to the conductor plane, to thereby increase the critical current at these regions and to maintain an overall higher critical current of the coil. 15 figs.

18. Superconducting magnetic coil

DOEpatents

Aized, Dawood; Schwall, Robert E.

1999-06-22

A superconducting magnetic coil includes a plurality of sections positioned axially along the longitudinal axis of the coil, each section being formed of an anisotropic high temperature superconductor material wound about a longitudinal axis of the coil and having an associated critical current value that is dependent on the orientation of the magnetic field of the coil. The cross section of the superconductor, or the type of superconductor material, at sections along the axial and radial axes of the coil are changed to provide an increased critical current at those regions where the magnetic field is oriented more perpendicularly to the conductor plane, to thereby increase the critical current at these regions and to maintain an overall higher critical current of the coil.

19. Mechanism of notable difference in the field delay times of no-insulation layer-wound and pancake-wound REBCO coils

Suetomi, Y.; Yanagisawa, K.; Nakagome, H.; Hamada, M.; Maeda, H.; Yanagisawa, Y.

2016-10-01

The characteristic magnetic field delay time for a no-insulation (NI) REBCO layer-wound coil is three orders of magnitude longer than that for a NI REBCO double-pancake coil. In a NI layer-wound coil, the circumferential current firstly flows along the periphery of the coil winding, and then it diffuses from the top and bottom turns into the middle turns of the winding, resulting in a long characteristic magnetic field delay time due to the current diffusion process. In contrast, the characteristic magnetic field delay time for a NI double-pancake coil is dominated by the circumferential current decay in individual turns. On the basis of a derived scaling law, the characteristic magnetic field delay time for a NI REBCO layer-wound coil for a 400 MHz LTS/REBCO nuclear magnetic resonance (NMR) magnet is 37 h, while that for a NI REBCO double-pancake coil is only <1 min. Thus, it is demonstrated that a double-pancake-winding is greatly preferred to a layer-winding for NMR applications from the view point of the characteristic magnetic field delay time.

20. Uncertainty analysis of the magnetic field measurement by the translating coil method in axisymmetric magnets

Arpaia, Pasquale; De Vito, Luca; Kazazi, Mario

2016-12-01

In the uncertainty assessment of magnetic flux measurements in axially symmetric magnets by the translating coil method, the Guide to the Uncertainty in Measurement and its supplement cannot be applied: the voltage variation at the coil terminals, which is the actual measured quantity, affects the flux estimate and its uncertainty. In this paper, a particle filter, implementing a sequential Monte-Carlo method based on Bayesian inference, is applied. At this aim, the main uncertainty sources are analyzed and a model of the measurement process is defined. The results of the experimental validation point out the transport system and the acquisition system as the main contributions to the uncertainty budget.

1. RF Head Coil Design with Improved RF Magnetic Near-Fields Uniformity for Magnetic Resonance Imaging (MRI) Systems.

PubMed

Sohn, Sung-Min; DelaBarre, Lance; Gopinath, Anand; Vaughan, John Thomas

2014-08-01

Higher magnetic field strength in magnetic resonance imaging (MRI) systems offers higher signal-to-noise ratio (SNR), contrast, and spatial resolution in MR images. However, the wavelength in ultra-high fields (7 tesla and beyond) becomes shorter than the human body at the Larmor frequency with increasing static magnetic field (B0) of MRI system. At short wavelengths, interference effect appears resulting in non- uniformity of the RF magnetic near-field (B1) over the subject and MR images may have spatially anomalous contrast. The B1 near-field generated by the transverse electromagnetic (TEM) RF coil's microstrip line element has a maximum near the center of its length and falls off towards both ends. In this study, a double trapezoidal shaped microstrip transmission line element is proposed to obtain uniform B1 field distribution by gradual impedance variation. Two multi-channel RF head coils with uniform and trapezoidal shape elements were built and tested with a phantom at 7T MRI scanner for comparison. The simulation and experimental results show stronger and more uniform B1(+) near-field with the trapezoidal shape.

2. DESIGN, FABRICATION, INSTALLATION, TESTING AND INITIAL RESULTS OF IN-VESSEL CONTROL COILS FOR DIII-D

SciTech Connect

ANDERSON,P.M; BAXI,C.B; KELLMAN,A.G; REIS,E.E

2003-10-01

OAK-B135 Since 1995, DIII-D has performed correction of magnetic field imperfections using a set of six external picture frame coils located on the vessel mid-plane. In 2000, these coils also demonstrated benefits when used for feedback of the resistive wall mode, an instability that limits the plasma performance at high beta. Modeling has shown that substantial performance improvements could be achieved by installing new coils inside the vessel and expanding the poloidal coverage above and below the mid-plane. Two prototype internal coils were installed in 2001 and were power tested successfully after several bakes to 350 C. A full set of twelve internal coils and related magnetic sensors are now operational in the DIII-D tokamak. The design requirements for the new coil system was to maximize the magnetic field at the plasma edge, operate with a frequency range of dc to 1000 Hz, and fit behind the existing graphite wall tiles. The coil design adopted and installed is a water-cooled hollow copper conductor insulated with polyamide and housed inside a stainless steel tube that forms a vacuum boundary. The coil is rigidly mounted to the inside of the vacuum vessel. The primary challenge in the design of these coils wa sin joining of both the copper conductor and the stainless tube without overheating the polyamide insulator. Elastic-plastic analysis was used to demonstrate acceptable thermal stresses during baking conditions. Analysis determined the optimum water cooling channel diameter. The coils were tested in high toroidal field to the limit of the power supply of 4.5 kA DC with inductance-limited current for frequencies between 300 Hz and 1000 Hz. Recent results are presented.

3. Coiled tubing operations and services

SciTech Connect

Jaworsky, A.S. II )

1991-11-01

Coiled tubing offers many advantages over conventional jointed tubing used for drilling in oil fields, including time savings, pumping flexibility, fluid placement, reduced formation damage and safety. The article gives an overview of coiled tubing history and development. Operating concepts are explained, along with descriptions of the major equipment and components associated with coiled tubing use in the oil field today.

4. Improved Coil for Hydrogen Dissociators

NASA Technical Reports Server (NTRS)

Vessot, R.

1984-01-01

Flat coil has rigid printed circuit substrate. New coil structure minimizes RF electric field near glass walls of plasma vessel; therefore reduces direct electron bombardment of glass. Design lends itself well to high production and standardized dimensions.

5. Poloidal asymmetries in edge transport barriersa)

Churchill, R. M.; Theiler, C.; Lipschultz, B.; Hutchinson, I. H.; Reinke, M. L.; Whyte, D.; Hughes, J. W.; Catto, P.; Landreman, M.; Ernst, D.; Chang, C. S.; Hager, R.; Hubbard, A.; Ennever, P.; Walk, J. R.

2015-05-01

Measurements of impurities in Alcator C-Mod indicate that in the pedestal region, significant poloidal asymmetries can exist in the impurity density, ion temperature, and main ion density. In light of the observation that ion temperature and electrostatic potential are not constant on a flux surface [Theiler et al., Nucl. Fusion 54, 083017 (2014)], a technique based on total pressure conservation to align profiles measured at separate poloidal locations is presented and applied. Gyrokinetic neoclassical simulations with XGCa support the observed large poloidal variations in ion temperature and density, and that the total pressure is approximately constant on a flux surface. With the updated alignment technique, the observed in-out asymmetry in impurity density is reduced from previous publishing [Churchill et al., Nucl. Fusion 53, 122002 (2013)], but remains substantial ( n z , H / n z , L ˜ 6 ). Candidate asymmetry drivers are explored, showing that neither non-uniform impurity sources nor localized fluctuation-driven transport are able to explain satisfactorily the impurity density asymmetry. Since impurity density asymmetries are only present in plasmas with strong electron density gradients, and radial transport timescales become comparable to parallel transport timescales in the pedestal region, it is suggested that global transport effects relating to the strong electron density gradients in the pedestal are the main driver for the pedestal in-out impurity density asymmetry.

6. Residue-specific force field based on protein coil library. RSFF2: modification of AMBER ff99SB.

PubMed

Zhou, Chen-Yang; Jiang, Fan; Wu, Yun-Dong

2015-01-22

Recently, we developed a residue-specific force field (RSFF1) based on conformational free-energy distributions of the 20 amino acid residues from a protein coil library. Most parameters in RSFF1 were adopted from the OPLS-AA/L force field, but some van der Waals and torsional parameters that effectively affect local conformational preferences were introduced specifically for individual residues to fit the coil library distributions. Here a similar strategy has been applied to modify the Amber ff99SB force field, and a new force field named RSFF2 is developed. It can successfully fold α-helical structures such as polyalanine peptides, Trp-cage miniprotein, and villin headpiece subdomain and β-sheet structures such as Trpzip-2, GB1 β-hairpins, and the WW domain, simultaneously. The properties of various popular force fields in balancing between α-helix and β-sheet are analyzed based on their descriptions of local conformational features of various residues, and the analysis reveals the importance of accurate local free-energy distributions. Unlike the RSFF1, which overestimates the stability of both α-helix and β-sheet, RSFF2 gives melting curves of α-helical peptides and Trp-cage in good agreement with experimental data. Fitting to the two-state model, RSFF2 gives folding enthalpies and entropies in reasonably good agreement with available experimental results.

7. Radio frequency magnetic field mapping of a 3 Tesla birdcage coil: experimental and theoretical dependence on sample properties.

PubMed

Alecci, M; Collins, C M; Smith, M B; Jezzard, P

2001-08-01

The RF B(1) distribution was studied, theoretically and experimentally, in phantoms and in the head of volunteers using a 3 T MRI system equipped with a birdcage coil. Agreement between numerical simulation and experiment demonstrates that B(1) distortion at high field can be explained with 3D full-Maxwell calculations. It was found that the B(1) distribution in the transverse plane is strongly dependent on the dielectric properties of the sample. We show that this is a consequence of RF penetration effects combined with RF standing wave effects. In contrast, along the birdcage coil z-axis the B(1) distribution is determined mainly by the coil geometry. In the transverse plane, the region of B(1) uniformity (within 10% of the maximum) was 15 cm with oil, 6 cm with distilled water, 11 cm with saline, and 10 cm in the head. Along z the B(1) uniformity was 9 cm with phantoms and 7 cm in the head.

8. Effects of rippled fields due to ferritic inserts and ELM mitigation coils on energetic ion losses in a 15 MA inductive scenario in ITER

Shinohara, K.; Tani, K.; Oikawa, T.; Putvinski, S.; Schaffer, M.; Loarte, A.

2012-09-01

The energetic ion loss has been assessed using the F3D-OFMC code for a 15 MA inductive scenario with Q = 10 and the latest information on the first wall geometry, the implementation of ferritic inserts (FI) and the ELM mitigation/control coils. Alpha particles and NB ions generated by the neutral beam injectors with the injection energy of 1 MeV are well confined and the heat load on the first wall is negligibly small and allowable for the magnetic background by the toroidal field coils and FI. However, an increase in the loss of these energetic ions is observed when the magnetic field by the ELM coils is applied. The increase in the loss fraction is larger for NB ions than for alpha particles under the ELM coil field. The origin of the expelled NB ions is dominantly trapped ions generated in the peripheral region due to a high-density plasma of the 15 MA scenario.

9. Proposal of High-Frequency Magnetic Field Immunity Test for Medical Devices, and Design and Development of Coil for the Test

Yamamoto, Takahiko; Koshiji, Kohji

Medical devices have been obliged to satisfy electromagnetic compatibility by revision of the pharmaceutical affairs law. However, even if the medical devices satisfy the electromagnetic compatibility based on the law, it is not necessarily safe. Sometimes, malfunctions of cardiac pacemaker are caused by the magnetic field leaked from an induction heating cooker. In this paper, a new method of electromagnetic susceptability (EMS) evaluation is proposed, and a loop coil for the magnetic field immunity test in the frequency range from 10kHz to 3MHz is designed and developed. As a result, the loop coil made on an experimental basis generated uniform magnetic field with a fluctuation within 3.3dB in the loop coil pane and 5.6dB along the coil axis.

10. Modelization of the thermal coupling between the ITER TF coil conductor and the structure cooling circuit

Gauthier, F.; Bessette, D.; Hoa, C.; Rousset, B.; Lacroix, B.

2016-12-01

The ITER Toroidal Field (TF) coils are required not to quench during the most demanding event: a plasma disruption followed by a fast discharge of the Central Solenoid (CS), the Poloidal Field (PF) coils and the Correction Coils (CC). This event creates large heat deposition in the ITER magnet stainless steel structures in addition to the conductor AC losses. In order to prevent quench occurring in the TF conductor, cooling channels, implemented in the TF coil structure (TFCS), have to remove a large fraction of the heat deposited. The first integrated TF and structure mock-up has been manufactured and then tested in the HELIOS cryogenic test facility (CEA Grenoble) to determine the thermal coupling between the TFCS and the TF conductor, both actively cooled by supercritical helium at 4.4 K and 5 bar. It consists in a stainless steel casing, a cooling pipe glued with resin in the casing groove, winding pack (WP) ground insulation, a radial plate and a copper dummy cable-in-conduit-conductor (CICC). Steady state as well as transient thermal characterizations have been completed in May 2015. Simulation results by thermal hydraulic codes (VENECIA/SuperMagnet) and some of the experimental data are presented and discussed. The thermal coupling between the helium in the cooling tube and the TF coil structure is then modelled as an equivalent heat transfer coefficient in order to simplify the thermal hydraulic (TH) models. Comparison between simplified coupling and detailed coupling is presented.

11. High-field double-pancake superconducting coils and a method of winding

DOEpatents

Materna, Peter A.

1985-01-01

A double-pancake coil having first and second pancakes may comprise a plurality of conductor means, each conductor means having a different grade and having one or more conductors, wherein each pancake of said double-pancake coil is comprised of inner and outer turns; wherein said inner turns are comprised of at least one of said conductor means wound about an axis and nested within one another; wherein said outer turns are comprised of said inner conductor means and at least one other conductor means co-wound about said inner turns and nested within one another; wherein each of said conductor means is wound along said axis from said first pancake to said second pancake at a different turn.

12. High-field double-pancake superconducting coils and a method of winding

DOEpatents

Materna, P.A.

1984-01-31

A double-pancake coil having first and second pancakes may comprise a plurality of conductor means, each conductor means having a different grade and having one or more conductors, wherein each pancake of said double-pancake coil is comprised of inner and outer turns; wherein said inner turns are comprised of at least one of said conductor means wound about an axis and nested within one another; wherein said outer turns are comprised of said inner conductor means and at least one other conductor means co-wound about said inner turns and nested within one another; wherein each of said conductor means is wound along said axis from said first pancake to said second pancake at a different turn.

13. Gradiometer pick-up coil design for a low field SQUID-MRI system.

PubMed

Seton, H C; Hutchison, J M; Bussell, D M

1999-05-01

We describe the use of liquid helium-cooled (4.2 K) gradiometer coils and a DC superconducting quantum interference device (SQUID) preamplifier to improve the SNR of magnetic resonance imaging (MRI) at 0.01 T. Gradiometer windings are used both to reduce lossy interactions with the MRI system's room temperature magnet and gradient coils and also to reject interference from more distant sources, which reduces the need for RF shielding. We have tested both axial and planar (figure-of-eight) gradiometer configurations. The figure-of-eight gradiometer has a more rapid fall-off in sensitivity with increasing distance from its windings than the axial gradiometer, but this is compensated for by reduced lossy interactions and improved interference rejection. We have used the system to image the human arm.

14. Increasing the signal-to-noise ratio by using vertically stacked phased array coils for low-field magnetic resonance imaging.

PubMed

Liang, Dandan; Hui, Hon Tat; Yeo, Tat Soon

2012-11-01

A new method is introduced to increase the signal-to-noise ratio (SNR) in low-field magnetic resonance imaging (MRI) systems by using a vertically stacked phased coil array. It is shown theoretically that the SNR is increased with the square root of the number of coils in the array if the array signals are properly combined to remove the mutual coupling effect. Based on this, a number of vertically stacked phased coil arrays have been designed and characterized by a numerical simulation method. The performance of these arrays confirms the significant increase of SNR by increasing the number of coils in the arrays. This provides a simple and efficient method to improve the SNR for low-field MRI systems.

15. Vortex dynamics in a thin superconducting film with a non-uniform magnetic field applied at its center with a small coil

DOE PAGES

Lemberger, Thomas R.; Loh, Yen Lee

2016-10-27

This article models the dynamics of vortices that are generated in the middle of a thin, large-area, superconducting film by a low-frequency magnetic field from a small coil, motivated by a desire to better understand measurements of the superconducting coherence length made with a two-coil apparatus. When the applied field exceeds a critical value, vortices and antivortices originate near the middle of the film at the radius where the Lorentz force of the screening supercurrent is largest. The Lorentz force from the screening supercurrent pushes vortices toward the center of the film and antivortices outward. In an experiment, vortices aremore » detected as an increase in mutual inductance between drive coil and a coaxial “pickup” coil on the opposite side of the film. Lastly, the model shows that the essential features of measurements are well described when vortex pinning and the attendant hysteresis are included.« less

16. Vortex dynamics in a thin superconducting film with a non-uniform magnetic field applied at its center with a small coil

SciTech Connect

Lemberger, Thomas R.; Loh, Yen Lee

2016-10-27

This article models the dynamics of vortices that are generated in the middle of a thin, large-area, superconducting film by a low-frequency magnetic field from a small coil, motivated by a desire to better understand measurements of the superconducting coherence length made with a two-coil apparatus. When the applied field exceeds a critical value, vortices and antivortices originate near the middle of the film at the radius where the Lorentz force of the screening supercurrent is largest. The Lorentz force from the screening supercurrent pushes vortices toward the center of the film and antivortices outward. In an experiment, vortices are detected as an increase in mutual inductance between drive coil and a coaxial “pickup” coil on the opposite side of the film. Lastly, the model shows that the essential features of measurements are well described when vortex pinning and the attendant hysteresis are included.

17. Vortex dynamics in a thin superconducting film with a non-uniform magnetic field applied at its center with a small coil

Lemberger, Thomas R.; Loh, Yen Lee

2016-10-01

This paper models the dynamics of vortices that are generated in the middle of a thin, large-area, superconducting film by a low-frequency magnetic field from a small coil, motivated by a desire to better understand measurements of the superconducting coherence length made with a two-coil apparatus. When the applied field exceeds a critical value, vortices and antivortices originate near the middle of the film at the radius where the Lorentz force of the screening supercurrent is largest. The Lorentz force from the screening supercurrent pushes vortices toward the center of the film and antivortices outward. In an experiment, vortices are detected as an increase in mutual inductance between the drive coil and a coaxial "pickup" coil on the opposite side of the film. The model shows that the essential features of measurements are well described when vortex pinning and the attendant hysteresis are included.

18. Comparison of Poloidal Velocity Meassurements to Neoclassical Theory on the National Spherical Torus Experiment

SciTech Connect

Bell, R E; Kaye, S M; Kolesnikov, R A; LeBlance, B P; Rewolldt, G; Wang, W X

2010-04-07

Knowledge of poloidal velocity is necessary for the determination of the radial electric field, Er, which along with its gradient is linked to turbulence suppression and transport barrier formation. Recent measurements of poloidal flow on conventional tokamaks have been reported to be an order of magnitude larger than expected from neoclassical theory. In contrast, recent poloidal velocity measurements on the NSTX spherical torus [S. M. Kaye et al., Phys. Plasmas 8, 1977 (2001)] are near or below neoclassical estimates. A novel charge exchange recombination spectroscopy diagnostic is used, which features active and passive sets of up/down symmetric views to produce line-integrated poloidal velocity measurements that do not need atomic physics corrections. Local profiles are obtained with an inversion. Poloidal velocity measurements are compared with neoclassical values computed with the codes NCLASS [W. A. Houlberg et al., Phys. Plasmas 4, 3230 (1997)] and GTC-Neo [W. X. Wang, et al., Phys. Plasmas 13, 082501 (2006)], which has been updated to handle impurities. __________________________________________________

19. Geodesic acoustic modes with poloidal mode couplings ad infinitum

Singh, Rameswar; Gürcan, Ö. D.

2017-02-01

Geodesic acoustic modes (GAMs) are studied including all poloidal mode (m) couplings within a drift reduced Braginskii framework. An exact analytical formula for GAM frequency is given within the toroidal Hasegawa Mima model with the full finite larmor radius effect and poloidal mode couplings ad infinitum using a scalar continued fraction formulation, which results from reduction of the semi-infinite chain of interactions that is obtained from the nearest neighbor coupling pattern due to geodesic curvature. This pattern can be described by a semi-infinite chain model of the GAM with the mode-mode coupling matrix elements proportional to the radial wave number kr. In the more general case of multi-field description of the GAM, the infinite chain can be reduced to a renormalized bi-nodal chain with a matrix continued fraction formulation. The convergence study of the linear GAM dispersion with respect to kr and the m-spectra confirms that the coupling beyond m = 1 is sustained only when kr ≠ 0 and the higher m couplings become important with increasing kr and increasing ion to electron temperature ratio τi.

20. MULTI-MODE ERROR FIELD CORRECTION ON THE DIII-D TOKAMAK

SciTech Connect

SCOVILLE, JT; LAHAYE, RJ

2002-10-01

OAK A271 MULTI-MODE ERROR FIELD CORRECTION ON THE DIII-D TOKAMAK. Error field optimization on DIII-D tokamak plasma discharges has routinely been done for the last ten years with the use of the external ''n = 1 coil'' or the ''C-coil''. The optimum level of correction coil current is determined by the ability to avoid the locked mode instability and access previously unstable parameter space at low densities. The locked mode typically has toroidal and poloidal mode numbers n = 1 and m = 2, respectively, and it is this component that initially determined the correction coil current and phase. Realization of the importance of nearby n = 1 mode components m = 1 and m = 3 has led to a revision of the error field correction algorithm. Viscous and toroidal mode coupling effects suggested the need for additional terms in the expression for the radial ''penetration'' field B{sub pen} that can induce a locked mode. To incorporate these effects, the low density locked mode threshold database was expanded. A database of discharges at various toroidal fields, plasma currents, and safety factors was supplement4ed with data from an experiment in which the fields of the n = 1 coil and C-coil were combined, allowing the poloidal mode spectrum of the error field to be varied. A multivariate regression analysis of this new low density locked mode database was done to determine the low density locked mode threshold scaling relationship n{sub e} {proportional_to} B{sub T}{sup -0.01} q{sub 95}{sup -0.79} B{sub pen} and the coefficients of the poloidal mode components in the expression for B{sub pen}. Improved plasma performance is achieved by optimizing B{sub pen} by varying the applied correction coil currents.

1. Proton spectral editing in the inhomogeneous radiofrequency field of a surface coil using modified stimulated echoes.

PubMed

Lahrech, H; Briguet, A

1990-11-01

It is shown that the modified stimulated echo sequence, [theta](+/- x +/- y)-t1-[theta](+ x)-t2/2-[2 theta](+ x)-t2/2- [theta](+ x)-t1-Acq(+/- x +/- y), denoted as MSTE[2 theta]x according to the exciter phase of the 2 theta pulse, is able to perform proton spectral editing without difference spectra. On the other hand, this sequence appears to be suitable for spatial localization. Sensitivity and spatial selectivity of MSTE and conventional stimulated echo sequence (STE) are briefly compared. MSTE is applied to editing lactate in the rat brain using the locally restricted excitation of a surface coil.

2. A poloidal section neutron camera for MAST upgrade

SciTech Connect

Sangaroon, S.; Weiszflog, M.; Cecconello, M.; Conroy, S.; Ericsson, G.; Wodniak, I.; Keeling, D.; Turnyanskiy, M. [EURATOM Collaboration: MAST Team

2014-08-21

The Mega Ampere Spherical Tokamak Upgrade (MAST Upgrade) is intended as a demonstration of the physics viability of the Spherical Tokamak (ST) concept and as a platform for contributing to ITER/DEMO physics. Concerning physics exploitation, MAST Upgrade plasma scenarios can contribute to the ITER Tokamak physics particularly in the field of fast particle behavior and current drive studies. At present, MAST is equipped with a prototype neutron camera (NC). On the basis of the experience and results from previous experimental campaigns using the NC, the conceptual design of a neutron camera upgrade (NC Upgrade) is being developed. As part of the MAST Upgrade, the NC Upgrade is considered a high priority diagnostic since it would allow studies in the field of fast ions and current drive with good temporal and spatial resolution. In this paper, we explore an optional design with the camera array viewing the poloidal section of the plasma from different directions.

3. ITER Side Correction Coil Quench model and analysis

Nicollet, S.; Bessette, D.; Ciazynski, D.; Duchateau, J. L.; Gauthier, F.; Lacroix, B.

2016-12-01

Previous thermohydraulic studies performed for the ITER TF, CS and PF magnet systems have brought some important information on the detection and consequences of a quench as a function of the initial conditions (deposited energy, heated length). Even if the temperature margin of the Correction Coils is high, their behavior during a quench should also be studied since a quench is likely to be triggered by potential anomalies in joints, ground fault on the instrumentation wires, etc. A model has been developed with the SuperMagnet Code (Bagnasco et al., 2010) for a Side Correction Coil (SCC2) with four pancakes cooled in parallel, each of them represented by a Thea module (with the proper Cable In Conduit Conductor characteristics). All the other coils of the PF cooling loop are hydraulically connected in parallel (top/bottom correction coils and six Poloidal Field Coils) are modeled by Flower modules with equivalent hydraulics properties. The model and the analysis results are presented for five quench initiation cases with/without fast discharge: two quenches initiated by a heat input to the innermost turn of one pancake (case 1 and case 2) and two other quenches initiated at the innermost turns of four pancakes (case 3 and case 4). In the 5th case, the quench is initiated at the middle turn of one pancake. The impact on the cooling circuit, e.g. the exceedance of the opening pressure of the quench relief valves, is detailed in case of an undetected quench (i.e. no discharge of the magnet). Particular attention is also paid to a possible secondary quench detection system based on measured thermohydraulic signals (pressure, temperature and/or helium mass flow rate). The maximum cable temperature achieved in case of a fast current discharge (primary detection by voltage) is compared to the design hot spot criterion of 150 K, which includes the contribution of helium and jacket.

4. Accurate Shim-Coil Design and Magnet-Field Profiling by a Power-Minimization-Matrix Method

Hoult, D. I.; Deslauriers, R.

The design of a single correction coil that annuls, with minimal power consumption, the field inhomogeneity associated with a specific magnet is described. The design strategy used is also shown to be advantageous for the production of high-accuracy, power-efficient shim coils, "drift-free" shims (i.e., no slow mainfield drift following a change of shim current), and high-homogeneity "shielded" magnets. Starting with a description of field inhomogeneity in a spherical-harmonic basis set, the cylindrical-surface current-density function needed to annul inhomogeneity is calculated, with minimization of electrical power dissipation, by a simple matrix formulation. The inclusion of design constraints, such as the annulment of mutual inductance between zonal shims and the magnet, is highlighted and production of the current-density function with both wire and cut sheet is briefly discussed. Insights are presented as to why the method, unlike some, gives a smooth current-density function lacking spurious high-frequency ripples, and experimental and numerical tests are reported that reveal the efficacy of the computational procedures.

5. Global electromagnetic induction in the moon and planets. [poloidal eddy current transient response

NASA Technical Reports Server (NTRS)

Dyal, P.; Parkin, C. W.

1973-01-01

Experiments and analyses concerning electromagnetic induction in the moon and other extraterrestrial bodies are summarized. The theory of classical electromagnetic induction in a sphere is first considered, and this treatment is extended to the case of the moon, where poloidal eddy-current response has been found experimentally to dominate other induction modes. Analysis of lunar poloidal induction yields lunar internal electrical conductivity and temperature profiles. Two poloidal-induction analytical techniques are discussed: a transient-response method applied to time-series magnetometer data, and a harmonic-analysis method applied to data numerically Fourier-transformed to the frequency domain, with emphasis on the former technique. Attention is given to complicating effects of the solar wind interaction with both induced poloidal fields and remanent steady fields. The static magnetization field induction mode is described, from which are calculated bulk magnetic permeability profiles. Magnetic field measurements obtained from the moon and from fly-bys of Venus and Mars are studied to determine the feasibility of extending theoretical and experimental induction techniques to other bodies in the solar system.

6. Mathematical model to determine the dimensions of superconducting cylindrical coils with a given central field - the case study for MgB2 conductors with isotropic Ic(B) characteristic

Pitel, Jozef; Melišek, Tibor; Tropeano, Matteo; Nardelli, Davide; Tumino, Andrea

2016-08-01

In this work, we present a mathematical model which enables to design cylindrical coils with a given central field, made of the superconducting conductor with isotropic Ic(B) characteristic. The model results in a computer code that enables to find out the coil dimensions, and to calculate the coil parameters such as critical current, maximum field in the winding and field non-uniformity on the coil axis. The Ic(B) characteristic of the conductor is represented by the set of data measured in discrete points. This approach allows us to express the Ic(B) as a function linearized in parts. Then, it is possible to involve the central field of the coil, coil dimensions, and parameters of the conductor, including its Ic(B) characteristic, in one equation which can be solved using ordinary numerical non-linear methods. Since the coil dimensions and conductor parameters are mutually linked in one equation with respect to a given coil central field, it is possible to analyze an influence of one parameter on the other one. The model was applied to three commercially available MgB2/Ni/Cu conductors produced by Columbus Superconductors. The results of simulations with the Ic(B) data at 20 K illustrate that there exists a set of winding geometries that generate a required central field, changing from a disc shape to long thin solenoid. Further, we analyze how the thickness of stabilizing copper influences the coil dimensions, overall conductor length, coil critical current, maximum field in the winding. An influence of the safety coefficient in operating current on coil dimensions and other above mentioned parameters is studied as well. Finally, we compare the coil dimensions, overall conductor length as well as coil critical current and maximum field in the winding if the value of required central field changes between 1 and 3 T.

7. RF Head Coil Design with Improved RF Magnetic Near-Fields Uniformity for Magnetic Resonance Imaging (MRI) Systems

PubMed Central

Sohn, Sung-Min; DelaBarre, Lance; Gopinath, Anand; Vaughan, John Thomas

2015-01-01

Higher magnetic field strength in magnetic resonance imaging (MRI) systems offers higher signal-to-noise ratio (SNR), contrast, and spatial resolution in MR images. However, the wavelength in ultra-high fields (7 tesla and beyond) becomes shorter than the human body at the Larmor frequency with increasing static magnetic field (B0) of MRI system. At short wavelengths, interference effect appears resulting in non- uniformity of the RF magnetic near-field (B1) over the subject and MR images may have spatially anomalous contrast. The B1 near-field generated by the transverse electromagnetic (TEM) RF coil’s microstrip line element has a maximum near the center of its length and falls off towards both ends. In this study, a double trapezoidal shaped microstrip transmission line element is proposed to obtain uniform B1 field distribution by gradual impedance variation. Two multi-channel RF head coils with uniform and trapezoidal shape elements were built and tested with a phantom at 7T MRI scanner for comparison. The simulation and experimental results show stronger and more uniform B1+ near-field with the trapezoidal shape. PMID:25892746

8. Tokamak Physics EXperiment (TPX): Toroidal field magnet design, development and manufacture. SDRL 32, Coil assembly documentation. Volume 5

SciTech Connect

Weber, C.M.

1995-08-18

This document is intended to address the contract requirement for providing coil assembly documentation, as required in the applicable Statement of Work: Provide preliminary procedures and preliminary design and supporting analysis of the equipment, fixtures, and hardware required to integrate and align the impregnated coil assemblies with the coil cases and intercoil structure. Each of the three major processes associated with the coil case and intercoil structure (ICS), TF Case Fabrication, Coil Preparation for Case Assembly are examined in detail. The specific requirements, processes, equipment, and technical concerns for each of these assembly processes is presented.

9. Modular coils: a promising toroidal-reactor-coil system

SciTech Connect

Chu, T.K.; Furth, H.P.; Johnson, J.L.; Ludescher, C.; Weimer, K.E.

1981-04-01

The concept of modular coils originated from a need to find reactor-relevant stellarator windings, but its usefulness can be extended to provide an externally applied, additional rotational transform in tokamaks. Considerations of (1) basic principles of modular coils, (2) types of coils, (3) types of configurations (general, helically symmetric, helically asymmetric, with magnetic well, with magnetic hill), (4) types of rotational transform profile, and (5) structure and origin of ripples are given. These results show that modular coils can offer a wide range of vacuum magnetic field configurations, some of which cannot be obtained with the classical stellarator or torsatron coil configuration.

10. Main Characteristics of the VLF Magnetic Field Waves Recorded by the Search Coil Magnetometer Experiment Onboard the CUSP Sounding Rocket

Pinçon, J.; Krasnoselskikh, V.; de Feraudy, H.; Rezeau, L.; Robert, P.; Pfaff, R. F.

2003-12-01

The CUSP rocket is a NASA Black Brant X sounding rocket dedicated to the exploration of the electrodynamic coupling, pulsations, and acceleration processes in the dayside cusp and the boundary layer interface. The launch occured on December 14, 2002, from Ny Åleysund, Spitzbergen (79° N) during Bz negative conditions. We present the magnetic field waves measurement collected in the frequency range [10 Hz - 10 kHz] by the three axis Search Coil Magnetometer (SCM) experiment onboard CUSP. The observations reveal the presence of intense field fluctuations corresponding to ELF hiss which is only seen on closed field lines and hence can be used to define the magnetic boundary of the cusp. Several data analysis techniques were applied to the 3 components of the magnetic field fluctuations associated with the ELF hiss to obtain information regarding the wave polarization and the wave vector directions. The magnetic field wave data are compared with simultaneous observations of electric field wave data to further enhance our understanding of these wave phenomena. The main results coming from this detailed study are presented and discussed.

11. The poloidal distribution of turbulent fluctuations in the Mega-Ampere Spherical Tokamak

SciTech Connect

Antar, G.Y.; Counsell, G.; Ahn, J.-W.; Yang, Y.; Price, M.; Tabasso, A.; Kirk, A.

2005-03-01

Recently, it was shown that intermittency observed in magnetic fusion devices is caused by large-scales events with high radial velocity reaching about 1/10th of the sound speed (called avaloids or blobs) [G. Antar et al., Phys. Rev. Lett. 87 065001 (2001)]. In the present paper, the poloidal distribution of turbulence is investigated on the Mega-Ampere Spherical Tokamak [A. Sykes et al., Phys. Plasmas 8 2101 (2001)]. To achieve our goal, target probes that span the divertor strike points are used and one reciprocating probe at the midplane. Moreover, a fast imaging camera that can reach 10 {mu}s exposure time looks tangentially at the plasma allowing us to view a poloidal cut of the plasma. The two diagnostics allow us to have a rather accurate description of the particle transport in the poloidal plane for L-mode discharges. Turbulence properties at the low-field midplane scrape-off layer are discussed and compared to other poloidal positions. On the low-field target divertor plates, avaloids bursty signature is not detected but still intermittency is observed far from the strike point. This is a consequence of the field line expansion which transforms a structure localized in the poloidal plane into a structure which expands over several tens of centimeters at the divertor target plates. Around the X point and in the high-field side, however, different phenomena enter into play suppressing the onset of convective transport generation. No signs of intermittency are observed in these regions. Accordingly, like 'normal' turbulence, the onset of convective transport is affected by the local magnetic curvature and shear.

12. The poloidal distribution of turbulent fluctuations in the Mega-Ampère Spherical Tokamak

Antar, G. Y.; Counsell, G.; Ahn, J.-W.; Yang, Y.; Price, M.; Tabasso, A.; Kirk, A.

2005-03-01

Recently, it was shown that intermittency observed in magnetic fusion devices is caused by large-scales events with high radial velocity reaching about 1/10th of the sound speed (called avaloids or blobs) [G. Antar et al., Phys. Rev. Lett. 87 065001 (2001)]. In the present paper, the poloidal distribution of turbulence is investigated on the Mega-Ampère Spherical Tokamak [A. Sykes et al., Phys. Plasmas 8 2101 (2001)]. To achieve our goal, target probes that span the divertor strike points are used and one reciprocating probe at the midplane. Moreover, a fast imaging camera that can reach 10μs exposure time looks tangentially at the plasma allowing us to view a poloidal cut of the plasma. The two diagnostics allow us to have a rather accurate description of the particle transport in the poloidal plane for L-mode discharges. Turbulence properties at the low-field midplane scrape-off layer are discussed and compared to other poloidal positions. On the low-field target divertor plates, avaloids bursty signature is not detected but still intermittency is observed far from the strike point. This is a consequence of the field line expansion which transforms a structure localized in the poloidal plane into a structure which expands over several tens of centimeters at the divertor target plates. Around the X point and in the high-field side, however, different phenomena enter into play suppressing the onset of convective transport generation. No signs of intermittency are observed in these regions. Accordingly, like "normal" turbulence, the onset of convective transport is affected by the local magnetic curvature and shear.

13. Borehole induction coil transmitter

DOEpatents

2002-01-01

A borehole induction coil transmitter which is a part of a cross-borehole electromagnetic field system that is used for underground imaging applications. The transmitter consists of four major parts: 1) a wound ferrite or mu-metal core, 2) an array of tuning capacitors, 3) a current driver circuit board, and 4) a flux monitor. The core is wound with several hundred turns of wire and connected in series with the capacitor array, to produce a tuned coil. This tuned coil uses internal circuitry to generate sinusoidal signals that are transmitted through the earth to a receiver coil in another borehole. The transmitter can operate at frequencies from 1-200 kHz and supplies sufficient power to permit the field system to operate in boreholes separated by up to 400 meters.

14. Impurity poloidal asymmetries and plasma rotation in the PDX Tokamak

Brau, K.

Vertical poloidal asymmetries of carbon and oxygen in the PDX Tokamak were monitored under a variety of discharge conditions in circular plasmas. Near the edge of the plasma and in the region beyond the limiter, the asymmetries appear to be caused by local impurity recycling, variations in the length of the emitting region, and effects due to vertical ion drifts. In the case of C V impurities, the sign and magnitude of the asymmetry is in qualitative agreement with the predictions of a quasi-neoclassical fluid model of impurity transport. A two dimensional computer code is used to simulate different models of poloidal asymmetries, including: (1) poloidally asymmetric source function, (2) charge exchange recombination with neutral hydrogen, (3) poloidally asymmetric electron ensity and temperature profiles, (4) poloidally varying anomalous radial diffusion coefficient, and (5) the quasi-neoclassical fluid model.

15. Dielectric strength, swelling and weight loss of the ITER Toroidal Field Model Coil insulation after low temperature reactor irradiation

Humer, K.; Weber, H. W.; Hastik, R.; Hauser, H.; Gerstenberg, H.

2000-04-01

The insulation system for the Toroidal Field Model Coil of ITER is a fiber reinforced plastic (FRP) laminate, which consists of a combined Kapton/R-glass-fiber reinforcement tape, vacuum-impregnated with an epoxy DGEBA system. Pure disk shaped laminates, FRP/stainless-steel sandwiches, and conductor insulation prototypes were irradiated at 5 K in a fission reactor up to a fast neutron fluence of 10 22 m -2 ( E>0.1 MeV) to investigate the radiation induced degradation of the dielectric strength of the insulation system. After warm-up to room temperature, swelling, weight loss, and the breakdown strength were measured at 77 K. The sandwich swells by 4% at a fluence of 5×10 21 m-2 and by 9% at 1×10 22 m-2. The weight loss of the FRP is 2% at 1×10 22 m-2. The dielectric strength remained unchanged over the whole dose range.

16. Dual Optimization Method of RF and Quasi-Static Field Simulations for Reduction of Eddy Currents Generated on 7T RF Coil Shielding

PubMed Central

Zhao, Yujuan; Zhao, Tiejun; Raval, Shailesh B.; Krishnamurthy, Narayanan; Zheng, Hai; Harris, Chad T.; Handler, William B.; Chronik, Blaine A.; Ibrahim, Tamer S.

2015-01-01

Purpose To optimize the design of radiofrequency (RF) shielding of transmit coils at 7T and reduce eddy currents generated on the RF shielding when imaging with rapid gradient waveforms. Methods One set of a four-element, 2×2 Tic-Tac-Toe (TTT) head coil structure is selected and constructed to study eddy currents on the RF coil shielding. The generated eddy currents are quantitatively studied in the time and frequency domains. The RF characteristics are studied using the finite-difference time-domain (FDTD) method. Five different kinds of RF shielding were tested on a 7T MRI scanner with phantoms and in-vivo human subjects. Results The eddy current simulation method is verified by the measurement results. Eddy currents induced by solid/intact and simple-structured slotted RF shielding can significantly distort the gradient fields. EPI images, B1+ maps and S matrix measurements verified that the proposed slot pattern can suppress the eddy currents while maintaining the RF characteristics of the transmit coil. Conclusion The presented dual-optimization method could be used to design the RF shielding and reduce the gradient field-induced eddy currents while maintaining the RF characteristics of the transmit coil. PMID:25367703

17. Residue-specific force field based on the protein coil library. RSFF1: modification of OPLS-AA/L.

PubMed

Jiang, Fan; Zhou, Chen-Yang; Wu, Yun-Dong

2014-06-26

Traditional protein force fields use one set of parameters for most of the 20 amino acids (AAs), allowing transferability of the parameters. However, a significant shortcoming is the difficulty to fit the Ramachandran plots of all AA residues simultaneously, affecting the accuracy of the force field. In this Feature Article, we report a new strategy for protein force field parametrization. Backbone and side-chain conformational distributions of all 20 AA residues obtained from protein coil library were used as the target data. The dihedral angle (torsion) potentials and some local nonbonded (1-4/1-5/1-6) interactions in OPLS-AA/L force field were modified such that the target data can be excellently reproduced by molecular dynamics simulations of dipeptides (blocked AAs) in explicit water, resulting in a new force field with AA-specific parameters, RSFF1. An efficient free energy decomposition approach was developed to separate the corrections on ϕ and ψ from the two-dimensional Ramachandran plots. RSFF1 is shown to reproduce the experimental NMR (3)J-coupling constants of AA dipeptides better than other force fields. It has a good balance between α-helical and β-sheet secondary structures. It can successfully fold a set of α-helix proteins (Trp-cage and Homeodomain) and β-hairpins (Trpzip-2, GB1 hairpin), which cannot be consistently stabilized by other state-of-the-art force fields. Interestingly, the RSFF1 force field systematically overestimates the melting temperature (and the stability of native state) of these peptides/proteins. It has a potential application in the simulation of protein folding and protein structure refinement.

18. Analysis of Uniformity of Magnetic Field Generated by the Two-Pair Coil System.

PubMed

Kędzia, P; Czechowski, T; Baranowski, M; Jurga, J; Szcześniak, E

2013-05-01

In this paper we use a simple analysis based on properties of the axial field generated by symmetrical multipoles to reveal all possible distributions of two coaxial pairs of circular windings, which result in systems featuring zero octupole and 32 pole magnetic moments (six-order systems). Homogeneity of magnetic field of selected systems is analyzed. It has been found that one of the derived systems generates homogenous magnetic field whose volume is comparable to that yielded by the eight-order system. The influence of the current distribution and the windings placement on the field homogeneity is considered. The table, graphs and equations given in the paper facilitate the choice of the most appropriate design for a given problem. The systems presented may find applications in low field electron paramagnetic resonance imaging, some functional f-MRI (nuclear magnetic resonance imaging) and bioelectromagnetic experiments requiring the access to the working space from all directions.

19. Local measure of the electromagnetic field in magnetic resonance coils: How do simulations help to disentangle the contributions of the electric and magnetic fields?

PubMed

Dillmann, Baudouin; Dubois, Luc; Paleczny, Erick; Trébosc, Julien; Amoureux, Jean-Paul; Pourpoint, Frédérique; Lafon, Olivier

The development of probes for Nuclear Magnetic Resonance (NMR) spectroscopy of metabolites, biomolecules or materials requires the accurate determination of the radio-frequency (RF) magnetic field strength, B1, at the position of the sample since this RF-field strength is related to the signal sensitivity and the excitation bandwidth. The Ball Shift (BS) technique is a commonly employed test bench method to measure the B1 value. Nevertheless, the influence of the RF electric field, E1, on BS is often overlooked. Herein, we derive, from Maxwell equations, an analytical expression of the BS, which shows the contribution of both the electric and magnetic energies to the BS value. This equation shows that the BS allows quantifying the B1 field strength only in regions where the electric energy is small with respect to the magnetic one. The numerical simulations of electromagnetic (EM) field and energy prove that this condition is fulfilled at 100.5MHz inside the electrically balanced coil of a double-resonance (1)H/X 4mm Magic Angle Spinning (MAS) probe since for that circuit, the center of the coil is an antinode for the B1 standing wave and a node for the E1 one. We also show that the simulated BS values agree well with the experimental ones. Conversely, NMR experiments show that the contribution of the electric energy to BS becomes significant when the X channel of this probe is connected to a frequency splitter. In that case, the use of BS method to estimate the B1 value is compromised.

20. Neoclassical ion heat flux and poloidal flow in a tokamak pedestal

Kagan, Grigory; Catto, Peter J.

2010-05-01

In the core of a tokamak, turbulent transport normally dominates over neoclassical. The situation could be different in a high confinement (or H) mode pedestal, where the former may be suppressed by a strongly sheared equilibrium electric field. On the other hand, this very field makes conventional neoclassical results inapplicable in the pedestal by significantly modifying ion drift orbits. We present the first calculation of the banana regime neoclassical ion heat flux and poloidal flow in the pedestal accounting for the strong E × B drift inherent to this tokamak region. Interestingly, we find that due to the electric field the pedestal poloidal ion flow can change its direction as compared with its core counterpart. This result elucidates the discrepancy between the conventional banana regime predictions and recent experimental measurements of the impurity flow performed at Alcator C-Mod.

1. High poloidal beta equilibria in TFTR limited by a natural inboard poloidal field null

SciTech Connect

Sabbagh, S.A.; Gross, R.A.; Mauel, M.E.; Navratil, G.A. . Dept. of Applied Physics); Bell, M.G.; Bell, R.; Bitter, M.; Bretz, N.L.; Budny, R.V.; Bush, C.E.; Chance, M.S.; Efthimion, P.C.; Fredrickson, E.D.; Hatcher, R.; Hawryluk, R.J.; Hirshman, S.P.; Janos, A.C.; Jardin, S.C.; Jassby, D.L.; Manickam, J.; McCune, D.C.; McGuire, K.M.; Medley, S.S.; Mueller, D.; Nagayama, Y.; Ow

1991-07-01

Recent operation of the Tokamak Fusion Test Reactor TFTR, has produced plasma equilibria with values of {Lambda} {triple bond} {beta}{sub p eq} + l{sub i}/2 as large as 7, {epsilon}{beta}{sub p dia} {triple bond} 2{mu}{sub 0}{epsilon}/{much lt}B{sub p}{much gt}{sup 2} as large as 1.6, and Troyon normalized diamagnetic beta, {beta}{sub N dia} {triple bond} 10{sup 8}<{beta}{sub t}{perpendicular}>aB{sub 0}/I{sub p} as large as 4.7. When {epsilon}{beta}{sub p dia} {approx gt} 1.25, a separatrix entered the vacuum chamber, producing a naturally diverted discharge which was sustained for many energy confinement times, {tau}{sub E}. The largest values of {epsilon}{beta}{sub p} and plasma stored energy were obtained when the plasma current was ramped down prior to neutral beam injection. The measured peak ion and electron temperatures were as large as 24 keV and 8.5 keV, respectively. Plasma stored energy in excess of 2.5 MJ and {tau}{sub E} greater than 130 msec were obtained. Confinement times of greater than 3 times that expected from L-mode predictions have been achieved. The fusion power gain. Q{sub DD}, reached a values of 1.3 {times} 10{sup {minus}3} in a discharge with I{sub p} = 1 MA and {epsilon}{beta}{sub p dia} = 0.85. A large, sustained negative loop voltage during the steady state portion of the discharge indicates that a substantial non-inductive component of I{sub p} exists in these plasmas. Transport code analysis indicates that the bootstrap current constitutes up to 65% of I{sup p}. Magnetohydrodynamic (MHD) ballooning stability analysis shows that while these plasmas are near, or at the {beta}{sub p} limit, the pressure gradient in the plasma core is in the first region of stability to high-n modes. 24 refs., 10 figs.

2. Easy characterization of the radio-frequency field of 13C NMR coils with aluminium-27 NMR

Jehenson, P.

1998-02-01

Determining the Radio-Frequency field distribution of Nuclear Magnetic Resonance (NMR) coils is difficult and time-consuming for the low sensitivity carbon 13. We show that this can conveniently be done using Aluminium-27 NMR (much larger signal/noise ratio and shorter acquisition time for both spectra and images, same measured field distribution, much cheaper samples/phantoms). La détermination de la distribution du champ radio-fréquence de sondes de Résonance Magnétique Nucléaire (RMN) est difficile et prend du temps dans le cas du carbone 13 qui a une faible sensibilité et est utilisé, par exemple, dans les études in vivo. Nous montrons ici que cela peut être fait plus simplement et rapidement en utilisant la RMN de l'Aluminium 27 (bien meilleur rapport signal/bruit et temps d'acquisition plus court pour les spectres et les images, même distribution de champ mesurée, échantillons/fantômes beaucoup moins chers.

3. Toroidal modelling of RMP response in ASDEX Upgrade: coil phase scan, q 95 dependence, and toroidal torques

Liu, Yueqiang; Ryan, D.; Kirk, A.; Li, Li; Suttrop, W.; Dunne, M.; Fischer, R.; Fuchs, J. C.; Kurzan, B.; Piovesan, P.; Willensdorfer, M.; the ASDEX Upgrade Team; the EUROfusion MST1 Team

2016-05-01

The plasma response to the vacuum resonant magnetic perturbation (RMP) fields, produced by the ELM control coils in ASDEX Upgrade experiments, is computationally modelled using the MARS-F/K codes (Liu et al 2000 Phys. Plasmas 7 3681, Liu et al 2008 Phys. Plasmas 15 112503). A systematic investigation is carried out, considering various plasma and coil configurations as in the ELM control experiments. The low q plasmas, with {{q}95}˜ 3.8 (q 95 is the safety factor q value at 95% of the equilibrium poloidal flux), responding to low n (n is the toroidal mode number) field perturbations from each single row of the ELM coils, generates a core kink amplification effect. Combining two rows, with different toroidal phasing, thus leads to either cancellation or reinforcement of the core kink response, which in turn determines the poloidal location of the peak plasma surface displacement. The core kink response is typically weak for the n  =  4 coil configuration at low q, and for the n  =  2 configuration but only at high q ({{q}95}˜ 5.5 ). A phase shift of around 60 degrees for low q plasmas, and around 90 degrees for high q plasmas, is found in the coil phasing, between the plasma response field and the vacuum RMP field, that maximizes the edge resonant field component. This leads to an optimal coil phasing of about 100 (-100) degrees for low (high) q plasmas, that maximizes both the edge resonant field component and the plasma surface displacement near the X-point of the separatrix. This optimal phasing closely corresponds to the best ELM mitigation observed in experiments. A strong parallel sound wave damping moderately reduces the core kink response but has minor effect on the edge peeling response. For low q plasmas, modelling shows that both the resonant electromagnetic torque and the neoclassical toroidal viscous (NTV) torque (due to the presence of 3D magnetic field perturbations) contribute to the toroidal flow damping, in particular near the

4. Measuring Earth's Local Magnetic Field Using a Helmholtz Coil

ERIC Educational Resources Information Center

Williams, Jonathan E.

2014-01-01

In this paper, I present a low-cost interactive experiment for measuring the strength of Earth's local magnetic field. This activity can be done in most high schools or two-year physics laboratories with limited resources, yet will have a tremendous learning impact. This experiment solidifies the three-dimensional nature of Earth's…

5. The Magnetic Field Structure of a Snowflake Divertor

SciTech Connect

Ryutov, D D; Cohen, R H; Rognlien, T D; Umansky, M V

2008-05-30

The snowflake divertor exploits a tokamak geometry in which the poloidal magnetic field null approaches second order; the name stems from the characteristic hexagonal, snowflake-like, shape of the separatrix for an exact second-order null. The proximity of the poloidal field structure to that of a second-order null substantially modifies edge magnetic properties compared to the standard X-point geometry; this, in turn, affects the edge plasma behavior. Modifications include: (1) The flux expansion near the null-point becomes 2-3 times larger; (2) The connection length between the equatorial plane and divertor plate significantly increases; (3) Magnetic shear just inside the separatrix becomes much larger; and (4) In the open-field-line region, the squeezing of the flux-tubes near the null-point increases, thereby causing stronger decoupling of the plasma turbulence in the divertor legs and in the main SOL. These effects can be used to reduce the power load on the divertor plates and/or to suppress the 'bursty' component of the heat flux. It is emphasized that the snowflake divertor can be created by a relatively simple set of poloidal field coils situated beyond the toroidal field coils. Analysis of the robustness of the proposed divertor configuration with respect to changes of the plasma current distribution is presented and it is concluded that, even if the null is close to the second order, the configuration is quite robust.

6. Alternating current losses in superconducting coils

NASA Technical Reports Server (NTRS)

Wipf, S. L.; Guderjahn, C. A.

1972-01-01

Report examines relationship between coil loss and frequency and heat loss in coil as a function of the magnetic field H. Information is of value to manufacturers of superconducting magnets, motors and generators.

7. Fano coil-type resonances: a plasmonic tool for magnetic field enhancement (Conference Presentation)

Panaro, Simone; Proietti Zaccaria, Remo; Toma, Andrea

2016-09-01

Spintronics and spin-based technology rely on the ultra-fast unbalance of the electronic spin population in quite localized spatial regions. However, as a matter of fact, the low susceptibility of conventional materials at high frequencies strongly limits these phenomena, rendering the efficiency of magnetically active devices insufficient for application purposes. Among the possible strategies which can be envisaged, plasmonics offers a direct approach to increase the effect of local electronic unbalancing processes. By confining and enhancing free radiation in nm-size spatial regions, plasmonic nano-assemblies have demonstrated to support very intense electric and magnetic hot-spots. In particular, very recent studies have proven the fine control of magnetic fields in Fano resonance condition. The near-field-induced out-of-phase oscillation of localized surface plasmons has manifested itself with the arising of magnetic sub-diffractive hot-spots. Here, we show how this effect can be further boosted in the mid-infrared regime via the introduction of higher order plasmonic modes. The investigated system, namely Moon Trimer Resonator, combines the high efficiency of a strongly coupled nano-assembly in Fano interferential condition with the elevated tunability of the quadrupolar resonance supported by a moon-like geometry. The fine control of the apical gap in this unique nanostructure, characterizes a plasmonic device able to tune its resonance without any consequence on the magnetic hot-spot size, thus enabling an efficient squeezing in the infrared.

8. Coiled tubing solves multiple downhole problems

SciTech Connect

Bedford, S. ); Smith, I. )

1994-11-01

Declining reservoir pressure and water breakthrough in the UK North Sea Magnus field has coincided with general advances in application of coiled tubing and a continuous drive to reduce operating costs, particularly in a climate of weak oil prices. These factors have led to a dramatic increase in diversity and volume of coiled tubing interventions. In the following article, coiled tubing interventions, and results of those interventions, are discussed. An assessment of future coiled tubing activity on Magnus field is provided.

9. The structure and poloidal dynamics of blob filaments in TJ-K

Garland, S.; Fuchert, G.; Ramisch, M.; Hirth, T.

2016-04-01

Relatively dense, field-aligned, filament-like structures (blobs) have been observed to propagate radially and poloidally through the scrape-off layer (SOL) in magnetically confined fusion plasmas, and contribute significantly to SOL transport. A detailed understanding of blob structure and dynamics, and their dependence on magnetic field geometry, is important in magnetic confinement physics for the prediction of heat loads on reactor wall facing components, as well as for understanding plasma confinement and neutral particle recycling. Experimentally deduced centre of mass poloidal blob velocity components, obtained using the conditional averaging technique, have been compared to an analytical blob model which has been simplified to express blob velocity in terms of the magnetic field curvature vector. Background flows are not incorporated into the analytical model, and must be added in to obtain good agreement with the experimental data. In addition, the 3D structure of blobs in TJ-K has been investigated using the conditional average of density fluctuations in two toroidally separated poloidal planes. Blobs are observed to be aligned to a flux tube near to the last closed flux surface, in the blob birth region. However at positions further along the blob trajectory, the structures do not deform according to the magnetic shear, rather they remain rigid, and retain their original form.

10. Coil Creep and Skew-Quadrupole Field Components in the Tevatron

SciTech Connect

Annala, G.; Harding, D.J.; Syphers, M.J.; /Fermilab

2011-07-11

During the start-up of Run II of the Tevatron Collider program, several issues surfaced which were not present, or not seen as detrimental, during Run I. These included the repeated deterioration of the closed orbit requiring orbit smoothing every two weeks or so, the inability to correct the closed orbit to desired positions due to various correctors running at maximum limits, regions of systematically strong vertical dipole corrections, and the identification of very strong coupling between the two transverse degrees-of-freedom. It became apparent that many of the problems being experienced operationally were connected to a deterioration of the main dipole magnet alignment, and remedial actions were undertaken. However, the alignment alone was not enough to explain the corrector strengths required to handle transverse coupling. With one exception, strong coupling had generally not been an issue in the Tevatron during Run I. Based on experience with the Main Ring, the Tevatron was designed with a very strong skew quadrupole circuit to compensate any quadrupole alignment and skew quadrupole field errors that might present themselves. The circuit was composed of 48 correctors placed evenly throughout the arcs, 8 per sector, evenly placed in every other cell. Other smaller circuits were installed but not initially needed or commissioned. These smaller circuits were composed of individual skew quadrupole correctors on either side of the long straight sections. These circuits were tuned by first bringing the horizontal and vertical tunes near each other. The skew quadrupoles were then adjusted to minimize tune split, usually to less than 0.003. Initially, the main skew quad circuit (designated T:SQ) could accomplish this global decoupling with only 4% of its possible current, and the smaller circuits were not required at all. The start-up of Run Ib was complicated by what was later discovered to be a rolled triplet quadrupole magnet in one of the Interaction Regions

11. Statistical analysis of the Nb3Sn strand production for the ITER toroidal field coils

Vostner, A.; Jewell, M.; Pong, I.; Sullivan, N.; Devred, A.; Bessette, D.; Bevillard, G.; Mitchell, N.; Romano, G.; Zhou, C.

2017-04-01

The ITER toroidal field (TF) strand procurement initiated the largest Nb3Sn superconducting strand production hitherto. The industrial-scale production started in Japan in 2008 and finished in summer 2015. Six ITER partners (so-called Domestic Agencies, or DAs) are in charge of the procurement and involved eight different strand suppliers all over the world, of which four are using the bronze route (BR) process and four the internal-tin (IT) process. In total more than 500 tons have been produced including excess material covering losses during the conductor manufacturing process, in particular the cabling. The procurement is based on a functional specification where the main strand requirements like critical current, hysteresis losses, Cu ratio and residual resistance ratio are specified but not the strand production process or layout. This paper presents the analysis on the data acquired during the quality control (QC) process that was carried out to ensure the same conductor performance requirements are met by the different strand suppliers regardless of strand design. The strand QC is based on 100% billet testing and on applying statistical process control (SPC) limits. Throughout the production, samples adjacent to the strand pieces tested by the suppliers are cross-checked (‘verified’) by their respective DAs reference labs. The level of verification was lowered from 100% at the beginning of the procurement progressively to approximately 25% during the final phase of production. Based on the complete dataset of the TF strand production, an analysis of the SPC limits of the critical strand parameters is made and the related process capability indices are calculated. In view of the large-scale production and costs, key manufacturing parameters such as billet yield, number of breakages and piece-length distribution are also discussed. The results are compared among all the strand suppliers, focusing on the difference between BR and IT processes. Following

12. Dependence of B1+ and B1− Field Patterns of Surface Coils on the Electrical Properties of the Sample and the MR Operating Frequency

PubMed Central

Vaidya, Manushka V.; Collins, Christopher M.; Sodickson, Daniel K.; Brown, Ryan; Wiggins, Graham C.; Lattanzi, Riccardo

2016-01-01

In high field MRI, the spatial distribution of the radiofrequency magnetic (B1) field is usually affected by the presence of the sample. For hardware design and to aid interpretation of experimental results, it is important both to anticipate and to accurately simulate the behavior of these fields. Fields generated by a radiofrequency surface coil were simulated using dyadic Green’s functions, or experimentally measured over a range of frequencies inside an object whose electrical properties were varied to illustrate a variety of transmit (B1+) and receive (B1−) field patterns. In this work, we examine how changes in polarization of the field and interference of propagating waves in an object can affect the B1 spatial distribution. Results are explained conceptually using Maxwell’s equations and intuitive illustrations. We demonstrate that the electrical conductivity alters the spatial distribution of distinct polarized components of the field, causing “twisted” transmit and receive field patterns, and asymmetries between |B1+| and |B1−|. Additionally, interference patterns due to wavelength effects are observed at high field in samples with high relative permittivity and near-zero conductivity, but are not present in lossy samples due to the attenuation of propagating EM fields. This work provides a conceptual framework for understanding B1 spatial distributions for surface coils and can provide guidance for RF engineers. PMID:27795697

13. Magnetic field shimming of a permanent magnet using a combination of pieces of permanent magnets and a single-channel shim coil for skeletal age assessment of children

Terada, Y.; Kono, S.; Ishizawa, K.; Inamura, S.; Uchiumi, T.; Tamada, D.; Kose, K.

2013-05-01

We adopted a combination of pieces of permanent magnets and a single-channel (SC) shim coil to shim the magnetic field in a magnetic resonance imaging system dedicated for skeletal age assessment of children. The target magnet was a 0.3-T open and compact permanent magnet tailored to the hand imaging of young children. The homogeneity of the magnetic field was first improved by shimming using pieces of permanent magnets. The residual local inhomogeneity was then compensated for by shimming using the SC shim coil. The effectiveness of the shimming was measured by imaging the left hands of human subjects and evaluating the image quality. The magnetic resonance images for the child subject clearly visualized anatomical structures of all bones necessary for skeletal age assessment, demonstrating the usefulness of combined shimming.

14. Magnetic field shimming of a permanent magnet using a combination of pieces of permanent magnets and a single-channel shim coil for skeletal age assessment of children.

PubMed

Terada, Y; Kono, S; Ishizawa, K; Inamura, S; Uchiumi, T; Tamada, D; Kose, K

2013-05-01

We adopted a combination of pieces of permanent magnets and a single-channel (SC) shim coil to shim the magnetic field in a magnetic resonance imaging system dedicated for skeletal age assessment of children. The target magnet was a 0.3-T open and compact permanent magnet tailored to the hand imaging of young children. The homogeneity of the magnetic field was first improved by shimming using pieces of permanent magnets. The residual local inhomogeneity was then compensated for by shimming using the SC shim coil. The effectiveness of the shimming was measured by imaging the left hands of human subjects and evaluating the image quality. The magnetic resonance images for the child subject clearly visualized anatomical structures of all bones necessary for skeletal age assessment, demonstrating the usefulness of combined shimming.

15. Experimental identification of the kink instability as a poloidal flux amplification mechanism for coaxial gun spheromak formation.

PubMed

Hsu, S C; Bellan, P M

2003-05-30

The magnetohydrodynamic kink instability is observed and identified experimentally as a poloidal flux amplification mechanism for coaxial gun spheromak formation. Plasmas in this experiment fall into three distinct regimes which depend on the peak gun current to magnetic flux ratio, with (I) low values resulting in a straight plasma column with helical magnetic field, (II) intermediate values leading to kinking of the column axis, and (III) high values leading immediately to a detached plasma. Onset of column kinking agrees quantitatively with the Kruskal-Shafranov limit, and the kink acts as a dynamo which converts toroidal to poloidal flux. Regime II clearly leads to both poloidal flux amplification and the development of a spheromak configuration.

16. The impact of poloidal asymmetries on tungsten transport in the core of JET H-mode plasmas

SciTech Connect

Angioni, C.; Pütterich, T.; Bilato, R.; Casson, F. J.; Giroud, C.; Mantica, P.; Helander, P.

2015-05-15

Recent progress in the understanding and prediction of the tungsten behaviour in the core of JET H-mode plasmas with ITER-like wall is presented. Particular emphasis is given to the impact of poloidal asymmetries of the impurity density. In particular, it is shown that the predicted reduction of temperature screening induced by the presence of low field side localization of the tungsten density produced by the centrifugal force is consistent with the observed tungsten behaviour in a JET discharge in H-mode baseline scenario. This provides first evidence of the role of poloidal asymmetries in reducing the strength of temperature screening. The main differences between plasma parameters in JET baseline and hybrid scenario discharges which affect the impact of poloidally asymmetric density on the tungsten radial transport are identified. This allows the conditions by which tungsten accumulation can be avoided to be more precisely defined.

17. Pulse Coil Tester

NASA Technical Reports Server (NTRS)

Simon, Richard A.

1988-01-01

Set of relays tested easily and repeatedly. Pulse coil tester causes coil under test to generate transient voltage; waveform indicates condition of coil. Tester accommodates assembly of up to four coils at a time.

18. Triple Halo Coil: Development and Comparison with Other TMS Coils

Rastogi, Priyam; Hadimani, Ravi; Jiles, David

Transcranial Magnetic Stimulation (TMS) is a non-invasive stimulation technique that can be used for the treatment of various neurological disorders such as Parkinson's Disease, PTSD, TBI and anxiety by regulating synaptic activity. TMS is FDA approved for the treatment of major depressive disorder. There is a critical need to develop deep TMS coils that can stimulate deeper regions of the brain without excessively stimulating the cortex in order to provide an alternative to surgical methods. We have developed a novel multi-coil configuration called Triple Halo Coil'' (THC) that can stimulate deep brain regions. Investigation of induced electric and magnetic field in these regions have been achieved by computer modelling. Comparison of the results due to THC configuration have been conducted with other TMS coils such as Halo Coil'', circular coil and Figure of Eight'' coil. There was an improvement of more than 15 times in the strength of magnetic field, induced by THC configuration at 10 cm below the vertex of the head when compared with the Figure of Eight'' coil alone. Carver Charitable Trust.

19. High-Field Quench Behavior and Protection of $Bi_2 Sr_2 Ca Cu_2 O_x$ Coils: Minimum and Maximum Quench Detection Voltages

SciTech Connect

Shen, Tengming; Ye, Liyang; Turrioni, Daniele; Li, Pei

2015-01-01

Small insert coils have been built using a multifilamentary Bi2Sr2CaCu2Ox round wire, and characterized in background fields to explore the quench behaviors and limits of Bi2Sr2CaCu2Ox superconducting magnets, with an emphasis on assessing the impact of slow normal zone propagation on quench detection. Using heaters of various lengths to initiate a small normal zone, a coil was quenched safely more than 70 times without degradation, with the maximum coil temperature reaching 280 K. Coils withstood a resistive voltage of tens of mV for seconds without quenching, showing the high stability of these coils and suggesting that the quench detection voltage shall be greater than 50 mV to not to falsely trigger protection. The hot spot temperature for the resistive voltage of the normal zone to reach 100 mV increases from ~40 K to ~80 K with increasing the operating wire current density Jo from 89 A/mm2 to 354 A/mm2 whereas for the voltage to reach 1 V, it increases from ~60 K to ~140 K, showing the increasing negative impact of slow normal zone propagation on quench detection with increasing Jo and the need to limit the quench detection voltage to < 1 V. These measurements, coupled with an analytical quench model, were used to access the impact of the maximum allowable voltage and temperature upon quench detection on the quench protection, assuming to limit the hot spot temperature to <300 K.

20. Magnetic field dependent stability and quench behavior and degradation limits in conduction-cooled MgB2 wires and coils

PubMed Central

Ye, Liyang; Cruciani, Davide; Xu, Minfeng; Mine, Susumu; Amm, Kathleen; Schwartz, Justin

2015-01-01

Long lengths of metal/MgB2 composite conductors with high critical current density (Jc), fabricated by the power-in-tube (PIT) process, have recently become commercially available. Owing to its electromagnetic performance in the 20 K – 30 K range and relatively low cost, MgB2 may be attractive for a variety of applications. One of the key issues for magnet design is stability and quench protection, so the behavior of MgB2 wires and magnets must be understood before large systems can emerge. In this work, the stability and quench behavior of several conduction-cooled MgB2 wires are studied. Measurements of the minimum quench energy and normal zone propagation velocity are performed on short samples in a background magnetic field up to 3 T and on coils in self-field and the results are explained in terms of variations in the conductor architecture, electrical transport behavior, operating conditions (transport current and background magnetic field) and experimental setup (short sample vs small coil). Furthermore, one coil is quenched repeatedly with increasing hot-spot temperature until Jc is decreased. It is found that degradation during quenching correlates directly with temperature and not with peak voltage; a safe operating temperature limit of 260 K at the surface is identified. PMID:25883414

1. Magnetic field dependent stability and quench behavior and degradation limits in conduction-cooled MgB2 wires and coils

Ye, Liyang; Cruciani, Davide; Xu, Minfeng; Mine, Susumu; Amm, Kathleen; Schwartz, Justin

2015-03-01

Long lengths of metal/MgB2 composite conductors with high critical current density (Jc), fabricated by the powder-in-tube process, have recently become commercially available. Owing to its electromagnetic performance in the 20-30 K range and relatively low cost, MgB2 may be attractive for a variety of applications. One of the key issues for magnet design is stability and quench protection, so the behavior of MgB2 wires and magnets must be understood before large systems can emerge. In this work, the stability and quench behavior of several conduction-cooled MgB2 wires are studied. Measurements of the minimum quench energy and normal zone propagation velocity are performed on short samples in a background magnetic field up to 3 T and on coils in self-field and the results are explained in terms of variations in the conductor architecture, electrical transport behavior, operating conditions (transport current and background magnetic field) and experimental setup (short sample versus small coil). Furthermore, one coil is quenched repeatedly with increasing hotspot temperature until Jc is decreased. It is found that degradation during quenching correlates directly with temperature and not with peak voltage; a safe operating temperature limit of 260 K at the surface is identified.

2. Magnetic field dependent stability and quench behavior and degradation limits in conduction-cooled MgB2 wires and coils.

PubMed

Ye, Liyang; Cruciani, Davide; Xu, Minfeng; Mine, Susumu; Amm, Kathleen; Schwartz, Justin

2015-03-01

Long lengths of metal/MgB2 composite conductors with high critical current density (Jc), fabricated by the power-in-tube (PIT) process, have recently become commercially available. Owing to its electromagnetic performance in the 20 K - 30 K range and relatively low cost, MgB2 may be attractive for a variety of applications. One of the key issues for magnet design is stability and quench protection, so the behavior of MgB2 wires and magnets must be understood before large systems can emerge. In this work, the stability and quench behavior of several conduction-cooled MgB2 wires are studied. Measurements of the minimum quench energy and normal zone propagation velocity are performed on short samples in a background magnetic field up to 3 T and on coils in self-field and the results are explained in terms of variations in the conductor architecture, electrical transport behavior, operating conditions (transport current and background magnetic field) and experimental setup (short sample vs small coil). Furthermore, one coil is quenched repeatedly with increasing hot-spot temperature until Jc is decreased. It is found that degradation during quenching correlates directly with temperature and not with peak voltage; a safe operating temperature limit of 260 K at the surface is identified.

3. Effect of neutral gas heating on the wave magnetic fields of a low pressure 13.56 MHz planar coil inductively coupled argon discharge

SciTech Connect

Jayapalan, Kanesh K. Chin, Oi-Hoong

2014-04-15

The axial and radial magnetic field profiles in a 13.56 MHz (radio frequency) laboratory 6 turn planar coil inductively coupled plasma reactor are simulated with the consideration of the effect of neutral gas heating. Spatially resolved electron densities, electron temperatures, and neutral gas temperatures were obtained for simulation using empirically fitted electron density and electron temperature and heuristically determined neutral gas temperature. Comparison between simulated results and measured fields indicates that neutral gas heating plays an important role in determining the skin depth of the magnetic fields.

4. Effect of neutral gas heating on the wave magnetic fields of a low pressure 13.56 MHz planar coil inductively coupled argon discharge

Jayapalan, Kanesh K.; Chin, Oi-Hoong

2014-04-01

The axial and radial magnetic field profiles in a 13.56 MHz (radio frequency) laboratory 6 turn planar coil inductively coupled plasma reactor are simulated with the consideration of the effect of neutral gas heating. Spatially resolved electron densities, electron temperatures, and neutral gas temperatures were obtained for simulation using empirically fitted electron density and electron temperature and heuristically determined neutral gas temperature. Comparison between simulated results and measured fields indicates that neutral gas heating plays an important role in determining the skin depth of the magnetic fields.

5. Poloidal rotation and its relation to the potential vorticity flux

SciTech Connect

McDevitt, C. J.; Diamond, P. H.; Guercan, Oe. D.; Hahm, T. S.

2010-11-15

A kinetic generalization of a Taylor identity appropriate to a strongly magnetized plasma is derived. This relation provides an explicit link between the radial mixing of a four-dimensional (4D) gyrocenter fluid and the poloidal Reynolds stress. This kinetic analog of a Taylor identity is subsequently utilized to link the turbulent transport of poloidal momentum to the mixing of potential vorticity. A quasilinear calculation of the flux of potential vorticity is carried out, yielding diffusive, turbulent equipartition, and thermoelectric convective components. Self-consistency is enforced via the quasineutrality relation, revealing that for the case of a stationary small amplitude wave population, deviations from neoclassical predictions of poloidal rotation can be closely linked to the growth/damping profiles of the underlying drift wave microturbulence.

6. Design, fabrication, and testing of the pulse coils for the Large Coil Test Facility

SciTech Connect

Chipley, K.K.; Parrelli, A.P.

1983-01-01

The Large Coil Test Facility (LCTF) will be able to test up to six large superconducting coils similar to those required for a tokamak reactor. In order to simulate the transient vertical field that will be part of the magnetic environment of an operating tokamak reactor, a set of pulse coils will be used in the facility. This set of two coils can be positioned in the bore of any of the test coils to provide a transient magnetic field to that particular coil. This paper describes the final design of the pulse coils and discusses the fabrication techniques used to build these coils. An extensive testing program has been carried out during fabrication to ensure that the coils will function satisfactorily.

7. High field Nb/sub 3/Sn Axicell insert coils for the Mirror Fusion Test Facility-B (MFTF-B) axicell configuration. Final report

SciTech Connect

Baldi, R.W.; Tatro, R.E.; Scanlan, R.M.; Agarwal, K.L.; Bailey, R.E.; Burgeson, J.E.; Kim, I.K.; Magnuson, G.D.; Mallett, B.D.; Pickering, J.L.

1984-03-01

Two 12-tesla superconducting insert coils are being designed by General Dynamics Convair Division for the axicell regions of MFTF-B for Lawrence Livermore National Laboratory. A major challenge of this project is to ensure that combined fabrication and operational strains induced in the conductor are within stringent limitations of the relatively brittle Nb/sub 3/Sn superconductor filaments. These coils are located in the axicell region of MFTF-B. They have a clear-bore diameter of 36.195cm (14.25 inches) and consist of 27 double pancakes (i.e., 54 pancakes per coil) would on an electrically insulated 304LN stainless steel/bobbin helium vessel. Each pancake has 57 turns separated by G-10CR insulation. The complete winding bundle has 4.6 million ampere-turns and uniform current density of 2007 A/cm/sup 2/. In conjunction with the other magnets in the system, they produce a 12-tesla central field and a 12.52-tesla peak field. A multifilamentary Nb/sub 3/Sn conductor was selected to meet these requirements. The conductor consists of a monolithic insert soldered into a copper stabilizer. Sufficient cross-sectional area and work-hardening of the copper stabilizer has been provided for the conductor to self-react the electromagnetic Lorentz force induced hoop stresses with normal operational tensile strains less than 0.07 percent.

8. Impact of poloidal convective cells on momentum flux in tokamaks

Garbet, X.; Asahi, Y.; Donnel, P.; Ehrlacher, C.; Dif-Pradalier, G.; Ghendrih, P.; Grandgirard, V.; Sarazin, Y.

2017-01-01

Radial fluxes of parallel momentum due to E× B and magnetic drifts are shown to be correlated in tokamak plasmas. This correlation comes from the onset of poloidal convective cells generated by turbulence. The entire process requires a symmetry breaking mechanism, e.g. a mean shear flow. An analytical calculation shows that anti-correlation between the poloidal and parallel components of the turbulent Reynolds stress results in anti-correlation of the fluxes of parallel momentum generated by E× B and curvature drifts.

9. Dynamics of poloidal flows in enhanced reverse shear bifurcation

SciTech Connect

Srinivasan, R.; Avinash, K.

2005-07-15

A simple reduced enhanced reverse shear (RERS) model is constructed to study the dynamics of poloidal flows during the ERS transition. This model predicts that a reversal of poloidal flow shear occurs just prior to the transition, as seen in experiment [R. E. Bell et al., Phys. Rev. Lett. 81, 1429 (1998)]. This transition front propagates until the radial location where the safety factor (q) is minimum and becomes locked there due to insufficient input power to overcome the threshold requirement for the bifurcation. This study also reveals that there can be many routes to ERS transition depending upon various tunable parameters.

10. Reduction of poloidal magnetic flux consumption during plasma current ramp-up in DEMO relevant plasma regimes

Wakatsuki, T.; Suzuki, T.; Hayashi, N.; Shiraishi, J.; Sakamoto, Y.; Ide, S.; Kubo, H.; Kamada, Y.

2017-01-01

The method for reducing a poloidal magnetic flux consumption of external coils is investigated to reduce the size of the central solenoid (CS) in the DEMO reactor. The reduction of the poloidal magnetic flux consumption during a plasma current ramp-up phase by electron cyclotron (EC) heating is investigated using an integrated modeling code suite, TOPICS. A strongly reversed shear q profile tends to be produced if intense off-axis EC heating is applied to obtain a large reduction of the flux consumption. In order to overcome this tendency, we find a method to obtain the optimum temperature profile which minimizes the poloidal flux consumption for a wide range of the q profile. We try to reproduce the optimum temperature profile for a weakly reversed shear q profile using six EC rays of 20 MW. As a result, the resistive flux consumption during the current ramp-up can be reduced by 63% from the estimation using the Ejima constant of 0.45 and the total flux consumption can be reduced by 20% from the conventional estimation. In addition, we find that the resistive flux consumption is closely related to the volume averaged electron temperature and not to the profile shape. Using this relation, the required heating power is estimated to be 31 MW based on a well established global confinement scaling, ITER L-89P. As a result, it is clarified that the poloidal magnetic flux consumption can be reduced by 20% using 20-31 MW of EC heating for a weakly reversed shear q profile. This reduction of the flux consumption accounts for 10% reduction of the CS radius.

11. Normal conducting transfer coil for SQUID NDE

2004-03-01

We have investigated the performance of a normal conducting transfer coil (n-coil) for nondestructive evaluation with a SQUID. The transfer efficiency, which depends on frequency and wire impedance, has been calculated for several coil designs to determine the performance of the n-coil. We have fabricated a 30 mm diameter n-coil and examined its performance with a high-TC SQUID. If both the pick-up coil and the input coil have 50 turns, then at high frequencies the magnetic field produced by the input coil becomes 50% of the magnetic field at the pick-up coil, with a low cut-off frequency of 2 kHz. The experimental result agrees well with a numerical calculation, which suggests a magnitude of magnetic field detected by our SQUID equal to the magnitude of the quasi-uniform magnetic field produced by the input coil. We also confirmed that the thermal noise of the n-coil, produced by its normal resistance, does not become higher than the intrinsic magnetic field noise of the SQUID.

12. Excitation of Poloidal standing Alfven waves through drift resonance wave-particle interaction (Invited)

Dai, L.; Takahashi, K.; Wygant, J. R.; Chen, L.; Bonnell, J. W.; Cattell, C. A.; Thaller, S. A.; Kletzing, C.; Smith, C. W.; MacDowall, R. J.; Baker, D. N.; Blake, J. B.; Fennell, J. F.; Claudepierre, S. G.; Funsten, H. O.; Reeves, G. D.; Spence, H.

2013-12-01

Charged particles trapped in the magnetosphere undergo a longitudinal drift motion around the Earth induced by the magnetic field curvature and gradient. The resonant wave-particle interaction associated with the drift motion is important for understanding the dynamics of the ring current and radiation belt particles. Using cross-spectral analysis of electric field, magnetic field, and ion flux data from the Van Allen Probe (RBSP) spacecraft, we present direct evidence identifying the generation of a fundamental mode standing poloidal wave through drift-resonance interactions in the inner magnetosphere. Intense azimuthal electric field (E φ ) oscillations as large as 10mV/m are observed associated with radial magnetic field (Br) oscillations in the dawn-noon sector near but south of the magnetic equator at L~5. The observed wave period, Eφ/Br, and the 90 degrees phase lag between Br and Eφ are all consistent with fundamental mode standing poloidal waves. Phase shifts between particle fluxes and wave electric fields clearly demonstrate a drift resonance with ~90 keV ring current ions. The estimated earthward gradient of ion phase space density provides free energy source for wave generation through the drift-resonance instability. To our knowledge, this is the first unambiguous observation of drift-resonance wave-particle interaction driving poloidal wave oscillations in the magnetosphere. Similar drift-resonance process should occur ubiquitously in collisionless plasma systems. One example is the ';fishbone' instability in fusion plasma devices. In addition, our observations have important implications for the long-standing mysterious origin of Giant Pulsations detected on the ground.

13. Magnet Coil Shorted Turn Detector

SciTech Connect

Dinkel, J.A.; Biggs, J.E.

1994-03-01

The Magnet Coil Shorted Turn Detector has been developed to facilitate the location of shorted turns in magnet coils. Finding these shorted turns is necessary to determine failure modes that are a necessary step in developing future production techniques. Up to this point, coils with shorted turns had the insulation burned off without the fault having been located. This disassembly process destroyed any chance of being able to find the fault. In order to maintain a flux balance in a coupled system such as a magnet coil, the current in a shorted turn must be opposed to the incident current. If the direction of the current in each conductor can be measured relative to the incident current, then the exact location of the short can be determined. In this device, an AC voltage is applied to the magnet under test. A small hand held B-dot pickup coil monitors the magnetic field produced by current in the individual magnet conductors. The relative phase of this pickup coil voltage is compared to a reference signal derived from the input current to detect a current reversal as the B-dot pickup coil is swept over the conductors of the coil under test. This technique however, is limited to only those conductors that are accessible to the hand held probe.

14. Shock and soliton structures induced by poloidal flow in tokamaks

Taniuti, T.; Watanabe, K.; Ishii, Y.; Wakatani, M.

1991-04-01

When poloidal flow velocity, Up, becomes close to epsilon C sub s in tokamaks, fluid motion inside the flux surface is governed by a forced KdV equation in the small dissipation limit, where epsilon is an inverse aspect ratio and C sub s is a sound velocity. This implies that a stationary soliton structure appears at the inside region of toroidal plasma or theta is approx. pi, where theta is a poloidal angle. In the limit of large dissipation a forced Burgers equation is more appropriate. This case corresponds to an appearance of shock structure. When an averaged poloidal flow velocity is very close to epsilon C sub s, a shock may be seen in the outer region of toroidal plasma or theta is approx. 0. With the increase of the absolute vakue of (Up-epsilon C sub s) the shock position moves from theta is approx. 0 to theta is approx. pi. Recent tokamak experiments show the existence of poloidal flow with Up is approx. epsilon C sub s in the transition phase from L mode to H mode. Implications of the results in the experiment are discussed.

15. Analysis of specific absorption rate and internal electric field in human biological tissues surrounding an air-core coil-type transcutaneous energy transmission transformer.

PubMed

Shiba, Kenji; Zulkifli, Nur Elina Binti; Ishioka, Yuji

2016-11-21

In this study, we analyzed the internal electric field E and specific absorption rate (SAR) of human biological tissues surrounding an air-core coil transcutaneous energy transmission transformer. Using an electromagnetic simulator, we created a model of human biological tissues consisting of a dry skin, wet skin, fat, muscle, and cortical bone. A primary coil was placed on the surface of the skin, and a secondary coil was located subcutaneously inside the body. The E and SAR values for the model representing a 34-year-old male subject were analyzed using electrical frequencies of 0.3-1.5 MHz. The transmitting power was 15 W, and the load resistance was 38.4 Ω. The results showed that the E values were below the International Commission on Non-ionizing Radiation Protection (ICNIRP) limit for the general public exposure between the frequencies of 0.9 and 1.5 MHz, and SAR values were well below the limit prescribed by the ICNIRP for the general public exposure between the frequencies of 0.3 and 1.2 MHz.

16. MODELING OF COUPLED EDGE STOCHASTIC AND CORE RESONANT MAGNETIC FIELD EFFECTS IN DIVERTED TOKAMAKS

SciTech Connect

EVANS, T.E.; MOYER, R.A.

2002-06-01

Attaining the highest performance in poloidally diverted tokamaks requires resonant magnetic perturbation coils to avoid core instabilities (locked, resistive wall and neoclassical tearing modes). These coils also perturb the pedestal and edge region, causing varying degrees of stochasticity with remnant islands. The effects of the DIII-D locked mode control coil on the edge and core of Ohmic plasmas are modeled with the field line integration code TRIP3D and compared with experimental measurements. Without detailed profile analysis and field line integration, it is difficult to establish whether a given response is due to a ''core mode'' or an ''edge stochastic boundary.'' In diverted Ohmic plasmas, the boundary stochastic layer displays many characteristics associated with such layers in non-diverted tokamaks. Comparison with stochastic boundary results from non-diverted tokamaks indicates that a significant difference in diverted tokamaks is a ''focusing'' of the magnetic field line loss into the vicinity of the divertor.

17. Magnetic propulsion of a magnetic device using three square-Helmholtz coils and a square-Maxwell coil.

PubMed

Ha, Yong H; Han, Byung H; Lee, Soo Y

2010-02-01

We introduce a square coil system for remote magnetic navigation of a magnetic device without any physical movements of the coils. We used three square-Helmholtz coils and a square-Maxwell coil for magnetic propulsion of a small magnet along the desired path. All the square coils are mountable on a cubic frame that has an opening to accommodate a living subject. The square-Helmholtz coils control the magnetic propulsion direction by generating uniform magnetic field along the desired direction while the square-Maxwell coil controls the propulsion force by generating magnetic gradient field. We performed magnetic propulsion experiments with a down-scaled coil set and a three-channel coil driver. Experimental results demonstrate that we can use the square coil set for magnetic navigation of a magnetic device without any physical movements of the coils.

18. Helical axis stellarator with noninterlocking planar coils

DOEpatents

Reiman, Allan; Boozer, Allen H.

1987-01-01

A helical axis stellarator using only noninterlocking planar, non-circular coils, generates magnetic fields having a magnetic well and large rotational transform with resultant large equilibrium beta.

19. Coiled-Coil Design: Updated and Upgraded.

PubMed

Woolfson, Derek N

2017-01-01

α-Helical coiled coils are ubiquitous protein-folding and protein-interaction domains in which two or more α-helical chains come together to form bundles. Through a combination of bioinformatics analysis of many thousands of natural coiled-coil sequences and structures, plus empirical protein engineering and design studies, there is now a deep understanding of the sequence-to-structure relationships for this class of protein architecture. This has led to considerable success in rational design and what might be termed in biro de novo design of simple coiled coils, which include homo- and hetero-meric parallel dimers, trimers and tetramers. In turn, these provide a toolkit for directing the assembly of both natural proteins and more complex designs in protein engineering, materials science and synthetic biology. Moving on, the increased and improved use of computational design is allowing access to coiled-coil structures that are rare or even not observed in nature, for example α-helical barrels, which comprise five or more α-helices and have central channels into which different functions may be ported. This chapter reviews all of these advances, outlining improvements in our knowledge of the fundamentals of coiled-coil folding and assembly, and highlighting new coiled coil-based materials and applications that this new understanding is opening up. Despite considerable progress, however, challenges remain in coiled-coil design, and the next decade promises to be as productive and exciting as the last.

20. Auxiliary coil controls temperature of RF induction heater

NASA Technical Reports Server (NTRS)

1966-01-01

Auxiliary coil controls the temperature of an RF induction furnace that is powered by a relatively unstable RF generator. Manual or servoed adjustments of the relative position of the auxiliary coil, which is placed in close proximity to the RF coil, changes the looseness of the RF coil and hence the corresponding heating effect of its RF field.

1. A Mechanical Coil Insertion System for Endovascular Coil Embolization of Intracranial Aneurysms

PubMed Central

Haraguchi, K.; Miyachi, S.; Matsubara, N.; Nagano, Y.; Yamada, H.; Marui, N.; Sano, A.; Fujimoto, H.; Izumi, T.; Yamanouchi, T.; Asai, T.; Wakabayashi, T.

2013-01-01

Summary Like other fields of medicine, robotics and mechanization might be introduced into endovascular coil embolization of intracranial aneurysms for effective treatment. We have already reported that coil insertion force could be smaller and more stable when the coil delivery wire is driven mechanically at a constant speed. Another background is the difficulty in synchronizing operators' minds and hands when two operators control the microcatheter and the coil respectively. We have therefore developed a mechanical coil insertion system enabling a single operator to insert coils at a fixed speed while controlling the microcatheter. Using our new system, the operator manipulated the microcatheter with both hands and drove the coil using foot switches simultaneously. A delivery wire force sensor previously reported was used concurrently, allowing the operator to detect excessive stress on the wire. In vitro coil embolization was performed using three methods: simple mechanical advance of the coil; simple mechanical advance of the coil with microcatheter control; and driving (forward and backward) of the coil using foot switches in addition to microcatheter control. The system worked without any problems, and did not interfere with any procedures. In experimental coil embolization, delivery wire control using the foot switches as well as microcatheter manipulation helped to achieve successful insertion of coils. This system could offer the possibility of developing safer and more efficient coil embolization. Although we aim at total mechanization and automation of procedures in the future, microcatheter manipulation and synchronized delivery wire control are still indispensable using this system. PMID:23693038

2. Neoclassical ion heat flux and poloidal flow in a tokamak pedestal

Kagan, Grigory; Catto, Peter J.

2009-11-01

In the core of a tokamak, neoclassical transport normally dominates over classical while itself being dominated by turbulent transport. The situation may be different in a high confinement (or H) mode pedestal, where the latter is effectively suppressed by a strongly sheared equilibrium electric field. On the other hand, this very field makes conventional neoclassical results inapplicable in the pedestal by significantly modifying ion drift orbits. We present the first calculation of the banana regime neoclassical ion heat flux and poloidal flow in the pedestal accounting for the strong ExB drift inherent to this tokamak region. Interestingly, the fact that ion heat conductivity depends on the local values of the electric field and its shear allows us to hypothesize about possible shapes of the global electric field and density profiles in the pedestal. We also find that due to the electric field the pedestal poloidal ion flow is likely to change its direction as compared to its core counterpart. This result elucidates the discrepancy between the conventional banana regime predictions and recent experimental measurements of the impurity flow performed at Alcator C-Mod.

3. Excitation of poloidal standing Alfvén waves through drift resonance wave-particle interaction

Dai, Lei; Takahashi, Kazue; Wygant, John R.; Chen, Liu; Bonnell, John; Cattell, Cynthia A.; Thaller, Scott; Kletzing, Craig; Smith, Charles W.; MacDowall, Robert J.; Baker, Daniel N.; Blake, J. Bernard; Fennell, Joseph; Claudepierre, Seth; Funsten, Herbert O.; Reeves, Geoffrey D.; Spence, Harlan E.

2013-08-01

Drift-resonance wave-particle interaction is a fundamental collisionless plasma process studied extensively in theory. Using cross-spectral analysis of electric field, magnetic field, and ion flux data from the Van Allen Probe (Radiation Belt Storm Probes) spacecraft, we present direct evidence identifying the generation of a fundamental mode standing poloidal wave through drift-resonance interactions in the inner magnetosphere. Intense azimuthal electric field (Eφ) oscillations as large as 10mV/m are observed, associated with radial magnetic field (Br) oscillations in the dawn-noon sector near but south of the magnetic equator at L˜5. The observed wave period, Eφ/Br ratio and the 90° phase lag between Br and Eφ are all consistent with fundamental mode standing Poloidal waves. Phase shifts between particle fluxes and wave electric fields clearly demonstrate a drift resonance with ˜90 keV ring current ions. The estimated earthward gradient of ion phase space density provides a free energy source for wave generation through the drift-resonance instability. A similar drift-resonance process should occur ubiquitously in collisionless plasma systems. One specific example is the "fishbone" instability in fusion plasma devices. In addition, our observations have important implications for the long-standing mysterious origin of Giant Pulsations.

4. The interaction of high-m guided poloidal alfven waves with magnetospheric electrons and the ionosphere

Rankin, R.; Sydorenko, D.

2014-12-01

Poloidal mode Alfven waves are often generated in Earth's magnetosphere following interplanetary shocks and/or pressure pulses acting on the magnetopause. These disturbances can excite resonant field line oscillations with frequencies in the mHz range by launching fast mode waves that couple energy to field line resonances. This direct action of the solar wind on the magnetosphere can perhaps explain waves with relatively small azimuthal wavenumbers (m), but not the observed range of waves with m~40-50 on L-shells around 5 or 6. These waves are strongly guided along geomagnetic field lines to the ionosphere, and are generally thought to particle driven, e.g., as a result of bounce-resonance wave-particle interactions following activation of the ring current. This is not the only possible source mechanism as there is evidence of wave generation before the ring current has reacted significantly to shock passage. Putting aside the source mechanism, high-m poloidal modes with strong east west directed electric fields are important primarily because they can elevate differential energy flux for electron energies in the range of 100's of keV to several MeV. In this paper we use observations of guided poloidal mode Alfven waves to constrain a ULF wave model that describes not only how waves evolve on geomagnetic field lines, but also their interaction with a dynamic height-resolved ionosphere. The ionosphere and neutral atmosphere are specified in the model using the IRI and MSIS models. These regions react to waves and precipitation through heating and cooling, ionization, recombination, and chemical reactions. We present detailed results of the interaction of a poloidal wave observed by the Eiscat radar, and demonstrate that the model used can reproduce all aspects of the radar observations. We consider mechanisms for pulsed precipitation accompanying this wave, which causes a phase difference of ~90 degrees between observed temperature and density spikes. We also

5. Numerical optimization of a three-channel radiofrequency coil for open, vertical-field, MR-guided, focused ultrasound surgery using the hybrid method of moment/finite difference time domain method.

PubMed

Xin, Xuegang; Wang, Di; Han, Jijun; Feng, Yanqiu; Feng, Qianjin; Chen, Wufan

2012-07-01

The numerical optimization of a three-channel radiofrequency (RF) coil with a physical aperture for the open, vertical-field, MR-guided, focused ultrasound surgery (MRgFUS) system using the hybrid method of moment (MoM)/finite difference time domain (FDTD) method is reported. The numerical simulation of the current density distribution on an RF coil with a complicated irregular structure was performed using MoM. The electromagnetic field simulation containing the full coil-tissue interactions within the region of interest was accomplished using the FDTD method. Huygens' equivalent box with six surfaces smoothly connected the MoM and FDTD method. An electromagnetic model of the human pelvic region was reconstructed and loaded in the FDTD zone to optimize the three-channel RF coil and compensate for the lower sensitivity at the vertical field. In addition, the numerical MoM was used to model the resonance, decoupling and impedance matching of the RF coil in compliance with engineering practices. A prototype RF coil was constructed to verify the simulation results. The results demonstrate that the signal-to-noise ratio and the homogeneity of the B(1) field were both greatly improved compared with previously published results.

6. Further progresses in the development of large MgB2 Superconducting Coils for the Ignitor Experiment

Tumino, A.; Grasso, G.; Coppi, B.

2013-10-01

Intermediate temperature superconducting cables have been adopted for the fabrication of the largest poloidal field coils of the Ignitor experiment. This is an important step toward achieving better duty cycles in Ignitor-like machines with innovative magnet technologies compared to traditional superconductors. The commercially available MgB2 strands manufactured by Columbus Superconductors can achieve the target specifications for the considered coils, about 5 meters of outer diameter and maximum field on the conductor below 5 T. These cables are also compatible with the Ignitor cryogenic system, which is designed to cool the machine at about 30 K, although MgB2 may use colder gas at 10 K. The preliminary cable design includes about 300 MgB2 multifilamentary strands of 1 mm in diameter and a copper tube for the He-gas flow in the center. Recently we have succeeded in the development of MgB2 strands with a further improvement in design and electrical properties for cable application. Reaching of a higher critical current density and better current sharing properties between the different strands is allowed by the newest design. The implementation of this progress in wire performance and its impact on the coil design will be discussed. US DOE partly sponsored.

7. Plasma boundary and SOL studies of ECH-plasmas in TJ-II stellarator with diagnosed mobile poloidal limiters

de la Cal, E.; Brañas, B.; Tabarés, F. L.; Tafalla, D.; Fraguas, A. L.; Pedrosa, M. A.; Tribaldos, V.; Ascasibar, E.; Herranz, J.; Pastor, I.; TJ-II Team

2001-03-01

TJ-II is a medium size (major radius R=1.5 m, average minor plasma radius a<0.2 m, on axis magnetic field B=1 T) helical axis stellarator operating in its first phase with up to 600 kW of ECH power. Two mobile poloidal limiters can control the last closed magnetic surface (LCMS) and diagnose the plasma boundary with a set of Langmuir probes and with CCD-cameras equipped with interference filters. In the described experiments, plasmas with different minor radii interact either with the toroidal limiter or with the mobile poloidal limiters. The electron density and temperature profiles are characterised in the plasma centre, boundary and scape-off layer (SOL) for the different configurations. The global energy for the different configurations is compared and the ratio of the energy confinement time to that obtained by the LHD-scaling-law, seem to be improved when inserting the poloidal limiters. Finally, it is discussed whether the large connection lengths obtained in certain poloidal limiter SOL regions effectively reduce the plasma size, making the definition of the plasma minor radius ambiguous.

8. Poloidal divertor experiment with applied E vector x B vector/B/sup 2/ drift

SciTech Connect

Strait, E J

1980-05-01

It has been proposed that the E vector x B vector/B/sup 2/ drift arising from an externally applied electric field could be used in a tokamak or other toroidal device to remove plasma and impurities from the region near the wall and to reduce the amount of plasma striking the wall, either assisting or replacing a conventional magnetic field divertor. A poloidal magnetic divertor (without pumping chamber) was added to the Wisconsin Levitated Toroidal Octupole, and the octupole was operated with a tokamak-like magnetic field configuration (q = 0.7). A radial electric field was applied in the scrape-off zone, causing an E vector x B vector/B/sup 2/ drift with a large poloidal component. This reduced plasma flux reaching the wall of the toroid by up to a factor of 5 beyond the effect of the magnetic divertor, for divertor configurations with both high and low magnetic mirror ratios, in good agreement with a simple theoretical model. Plasma density and density scale length were also reduced in the scrape-off zone, in qualitative agreement with the model. This was not accompanied by any new instabilities in the scrape-off zone, nor by any appreciable degradation of confinement of the central plasma.

9. Design of the coolant system for the Large Coil Test Facility pulse coils

SciTech Connect

Bridgman, C.; Ryan, T.L.

1983-01-01

The pulse coils will be a part of the Large Coil Test Facility in Oak Ridge, Tennessee, which is designed to test six large tokamak-type superconducting coils. The pulse coil set consists of two resistive coaxial solenoid coils, mounted so that their magnetic axis is perpendicular to the toroidal field lines of the test coil. The pulse coils provide transient vertical fields at test coil locations to simulate the pulsed vertical fields present in tokamak devices. The pulse coils are designed to be pulsed for 30 s every 150 s, which results in a Joule heating of 116 kW per coil. In order to provide this capability, the pulse coil coolant system is required to deliver 6.3 L/s (100 gpm) of subcooled liquid nitrogen at 10-atm absolute pressure. The coolant system can also cool down each pulse coil from room temperature to liquid nitrogen temperature. This paper provides details of the pumping and heat exchange equipment designed for the coolant system and of the associated instrumentation and controls.

10. Predictions of the poloidal asymmetries and transport frequencies in KSTAR

SciTech Connect

Bae, C. Lee, S. G.; Terzolo, L.; Stacey, W. M.

2014-01-15

The extended neoclassical rotation theory formulated in Miller flux surface geometry enables unprecedented neoclassical calculations of the poloidal asymmetries in density, rotation velocities, electrostatic potential along the flux surfaces, and of the inertial (Reynolds stress) and gyroviscous transport frequencies, which are strong functions of these asymmetries. This paper presents such calculations of the poloidal asymmetries and non-negligible inertial and gyroviscous transport frequencies in two KSTAR (Korea Superconducting Tokamak Advanced Research) [Kwon et al., Nucl. Fusion 51, 094006 (2011)] Neutral Beam Injection H-mode discharges. The in-out asymmetries in the velocities are an order of magnitude larger than their up-down asymmetries. The magnitudes of the predicted inertial and gyroviscous transport frequencies depend on the magnitudes of the density and velocity asymmetries. The neoclassically predicted density asymmetries are shown to correspond with the reported measurements in tokamaks and the predicted carbon toroidal velocities agree very well with the measurements in KSTAR.

11. Poloidal velocity of impurity ions in neoclassical theory

Wong, S. K.; Chan, V. S.; Solomon, W. M.

2008-08-01

A formula for the poloidal velocity of impurity ions in a two-species plasma is derived from neoclassical theory in the banana regime, with corrections from the boundary layer separating the trapped and transiting ions. The formula is applicable to plasmas with toroidal rotations that can approach the thermal speeds of the ions. Using the formula to determine the poloidal velocity of C+6 ions in a recently reported experiment [W. M. Solomon et al., Phys. Plasmas 13, 056116 (2006)] leads to agreement in the direction of the central region when it is otherwise from theories without strong toroidal rotations. Comparisons among these theories are made, demonstrating the degree of uncertainty of theoretical predictions.

12. Determining Electrical Properties Based on B1 Fields Measured in an MR Scanner Using a Multi-channel Transmit/Receive Coil: a General Approach

PubMed Central

Liu, Jiaen; Zhang, Xiaotong; Van de Moortele, Pierre-Francois; Schmitter, Sebastian

2013-01-01

Electrical Property Tomography (EPT) is a recently developed noninvasive technology to image the electrical conductivity and permittivity of biological tissues at Larmor frequency in Magnetic Resonance (MR) scanners. The absolute phase of the complex radio-frequency (RF) magnetic field (B1) is necessary for electrical property calculation. However, due to the lack of practical methods to directly measure the absolute B1 phases, current EPT techniques have been achieved with B1 phase estimation based on certain assumptions on object anatomy, coil structure and/or electromagnetic wave behavior associated with the main magnetic field, limiting EPT from a larger variety of applications. In this study, using a multi-channel transmit/receive coil, the framework of a new general approach for EPT has been introduced, which is independent on the assumptions utilized in previous studies. Using a human head model with realistic geometry, a series of computer simulations at 7T were conducted to evaluate the proposed method under different noise levels. Results showed that the proposed method can be used to reconstruct the conductivity and permittivity images with noticeable accuracy and stability. The feasibility of this approach was further evaluated in a phantom experiment at 7T. PMID:23743673

13. Terrace retro-reflector array for poloidal polarimeter on ITER.

PubMed

Imazawa, R; Kawano, Y; Ono, T; Kusama, Y

2011-02-01

A new concept of a terrace retro-reflector array (TERRA) as part of the poloidal polarimeter for ITER is proposed in this paper. TERRA reflects a laser light even from a high incident angle in the direction of the incident-light path, while a conventional retro-reflector array cannot. Besides, TERRA can be installed in a smaller space than a corner-cube retro-reflector. In an optical sense, TERRA is equivalent to a Littrow grating, the blaze angle of which varies, depending on the incident angle. The reflected light generates a bright and dark fringe, and the bright fringe is required to travel along the incident-light path to achieve the objects of laser-aided diagnostics. In order to investigate the propagation properties of laser light reflected by TERRA, we have developed a new diffraction formula. Conditions for the propagation of the bright fringe in the direction of the incident light have been obtained using the Littrow grating model and have been confirmed in a simulation applying the new diffraction formula. Finally, we have designed laser transmission optics using TERRA for the ITER poloidal polarimeter and have calculated the light propagation of the system. The optical design obtains a high transmission efficiency, with 88.6% of the incident power returned. These results demonstrate the feasibility of applying TERRA to the ITER poloidal polarimeter.

14. Error Field Correction in ITER

SciTech Connect

Park, Jong-kyu; Boozer, Allen H.; Menard, Jonathan E.; Schaffer, Michael J.

2008-05-22

A new method for correcting magnetic field errors in the ITER tokamak is developed using the Ideal Perturbed Equilibrium Code (IPEC). The dominant external magnetic field for driving islands is shown to be localized to the outboard midplane for three ITER equilibria that represent the projected range of operational scenarios. The coupling matrices between the poloidal harmonics of the external magnetic perturbations and the resonant fields on the rational surfaces that drive islands are combined for different equilibria and used to determine an ordered list of the dominant errors in the external magnetic field. It is found that efficient and robust error field correction is possible with a fixed setting of the correction currents relative to the currents in the main coils across the range of ITER operating scenarios that was considered.

15. A signal input coil made of superconducting thin film for improved signal-to-noise ratio in a high-Tc SQUID-based ultra-low field nuclear magnetic resonance system

Chen, Kuen-Lin; Hsu, Chin-Wei; Ku, Yue-Bai; Chen, Hsin-Hsien; Liao, Shu-Hsien; Wang, Li-Min; Horng, Herng-Er; Yang, Hong-Chang

2013-11-01

Resonant coupling schemes are commonly used in SQUID-based ultra-low field (ULF) nuclear magnetic resonance (NMR) systems to couple the spin relaxation signals from samples to the SQUID. Generally, in NMR systems, a resonant coupling scheme is composed of two solenoid coils which are made of enamel insulated wires and a capacitor connected in series. In this work, we tried to replace the metal solenoid input coil with a planar high-Tc superconducting spiral coil to improve the signal-to-noise ratio (SNR) of the ULF NMR signal. A measurement of the free induction decay signal of water protons was performed to demonstrate the improved performance of the system. This improvement is due to the fact that the planar superconducting spiral coil possesses a higher mutual inductance with the SQUID. Therefore, it is a promising way to enhance the SNR of high-Tc SQUID-based ULF NMR/MRI systems.

16. Electromagnetic Gun With Commutated Coils

NASA Technical Reports Server (NTRS)

Elliott, David G.

1991-01-01

Proposed electromagnetic gun includes electromagnet coil, turns of which commutated in sequence along barrel. Electrical current fed to two armatures by brushes sliding on bus bars in barrel. Interaction between armature currents and magnetic field from coil produces force accelerating armature, which in turn, pushes on projectile. Commutation scheme chosen so magnetic field approximately coincides and moves with cylindrical region defined by armatures. Scheme has disadvantage of complexity, but in return, enables designer to increase driving magnetic field without increasing armature current. Attainable muzzle velocity increased substantially.

17. Internal split field generator

DOEpatents

Thundat,; George, Thomas [Knoxville, TN; Van Neste, Charles W [Kingston, TN; Vass, Arpad Alexander [Oak Ridge, TN

2012-01-03

A generator includes a coil of conductive material. A stationary magnetic field source applies a stationary magnetic field to the coil. An internal magnetic field source is disposed within a cavity of the coil to apply a moving magnetic field to the coil. The stationary magnetic field interacts with the moving magnetic field to generate an electrical energy in the coil.

18. Coil system for a mirror-based hybrid reactor

SciTech Connect

Hagnestal, A.; Agren, O.; Moiseenko, V. E.

2012-06-19

Two different superconducting coil systems for the SFLM Hybrid study - a quadrupolar mirror based fusion-fission reactor study - are presented. One coil system is for a magnetic field with 2 T at the midplane and a mirror ratio of four. This coil set consists of semiplanar coils in two layers. The alternative coil system is for a downscaled magnetic field of 1.25 T at the midplane and a mirror ratio of four, where a higher {beta} is required to achieve sufficient the neutron production. This coil set has one layer of twisted 3D coils. The 3D coils are expected to be considerably cheaper than the semiplanar, since NbTi superconductors can be used for most coils instead of Nb3Sn due to the lower magnetic field.

19. Coil Welding Aid

NASA Technical Reports Server (NTRS)

Wiesenbach, W. T.; Clark, M. C.

1983-01-01

Positioner holds coil inside cylinder during tack welding. Welding aid spaces turns of coil inside cylinder and applies contact pressure while coil is tack-welded to cylinder. Device facilitates fabrication of heat exchangers and other structures by eliminating hand-positioning and clamping of individual coil turns.

20. Simultaneous poloidal measurements using new magnetically driven reciprocating probes in COMPASS

Dejarnac, R.; Gunn, J. P.; Dimitrova, M.; Hron, M.; Panek, R.; Pascal, J.-Y.; Saragosti-Chausy, C.; Tamain, P.; the COMPASS Team

2016-03-01

Particles and heat transport in the scrape-off layer (SOL) of tokamaks is not yet fully understood. COMPASS is a small-size tokamakp where the edge plasma is well diagnosed in view of studying the competition between the parallel and the cross-field transport in the SOL. In order to better characterize SOL dynamics, in particular the poloidal asymmetry of the main parameters' radial profiles, two new in-situ magnetically driven reciprocating manipulators have been recently installed in COMPASS. These manipulators, the so-called pecker probes, are two additional poloidal measurement points to the existing two (vertical and horizontal) reciprocating manipulators. The pecker probes are located at the low field side of COMPASS at ±47.5o with respect to the outer mid-plane and are equipped with identical tunnel probe heads, providing simultaneous measurements of the ion saturation current density Jsat, the electron temperature Te and the parallel Mach number M// with high temporal resolution. In this paper, a detailed description of the pecker probe system in COMPASS is described and first measurements are presented.

1. A Compact Non-Planar Coil Design for the SFLM Hybrid

Hagnestål, A.; Ågren, O.; Moiseenko, V. E.

2012-08-01

A non-planar single layer semiconductor coil set for a version of the Straight Field Line Mirror Hybrid concept with reduced magnetic field has been computed. The coil set consists of 30 coils that are somewhat similar to baseball coils with skewed sides. The coil set has been modeled with filamentary current distributions and basic scaling assumptions have been made regarding the coil widths. This coil set is expected to be considerably cheaper than a previous computed coil set. The coils can probably be produced with technologies known today.

2. Intra-coil interactions in split gradient coils in a hybrid MRI-LINAC system

Tang, Fangfang; Freschi, Fabio; Sanchez Lopez, Hector; Repetto, Maurizio; Liu, Feng; Crozier, Stuart

2016-04-01

An MRI-LINAC system combines a magnetic resonance imaging (MRI) system with a medical linear accelerator (LINAC) to provide image-guided radiotherapy for targeting tumors in real-time. In an MRI-LINAC system, a set of split gradient coils is employed to produce orthogonal gradient fields for spatial signal encoding. Owing to this unconventional gradient configuration, eddy currents induced by switching gradient coils on and off may be of particular concern. It is expected that strong intra-coil interactions in the set will be present due to the constrained return paths, leading to potential degradation of the gradient field linearity and image distortion. In this study, a series of gradient coils with different track widths have been designed and analyzed to investigate the electromagnetic interactions between coils in a split gradient set. A driving current, with frequencies from 100 Hz to 10 kHz, was applied to study the inductive coupling effects with respect to conductor geometry and operating frequency. It was found that the eddy currents induced in the un-energized coils (hereby-referred to as passive coils) positively correlated with track width and frequency. The magnetic field induced by the eddy currents in the passive coils with wide tracks was several times larger than that induced by eddy currents in the cold shield of cryostat. The power loss in the passive coils increased with the track width. Therefore, intra-coil interactions should be included in the coil design and analysis process.

3. Optimized Geometry for Superconducting Sensing Coils

NASA Technical Reports Server (NTRS)

Eom, Byeong Ho; Pananen, Konstantin; Hahn, Inseob

2008-01-01

An optimized geometry has been proposed for superconducting sensing coils that are used in conjunction with superconducting quantum interference devices (SQUIDs) in magnetic resonance imaging (MRI), magnetoencephalography (MEG), and related applications in which magnetic fields of small dipoles are detected. In designing a coil of this type, as in designing other sensing coils, one seeks to maximize the sensitivity of the detector of which the coil is a part, subject to geometric constraints arising from the proximity of other required equipment. In MRI or MEG, the main benefit of maximizing the sensitivity would be to enable minimization of measurement time. In general, to maximize the sensitivity of a detector based on a sensing coil coupled with a SQUID sensor, it is necessary to maximize the magnetic flux enclosed by the sensing coil while minimizing the self-inductance of this coil. Simply making the coil larger may increase its self-inductance and does not necessarily increase sensitivity because it also effectively increases the distance from the sample that contains the source of the signal that one seeks to detect. Additional constraints on the size and shape of the coil and on the distance from the sample arise from the fact that the sample is at room temperature but the coil and the SQUID sensor must be enclosed within a cryogenic shield to maintain superconductivity.

4. Prototype detectors for measuring poloidal magnetic flux with an ion beam probe

Crowley, T. P.; Demers, D. R.; Fimognari, P. J.; Kile, T. D.

2016-10-01

Development of a detector and associated techniques to determine the localized magnetic flux, and therefore poloidal magnetic field and current density profile, in an axisymmetric plasma device is underway. This will provide invaluable information on equilibrium, transport and stability studies of fusion plasmas. A singly charged ion beam is injected into the plasma and the detector located outside the plasma measures doubly charged ions created within a cm-scale sample volume of the plasma. The ions are split into beamlets at the detector. The toroidal angle of the beam's velocity is determined by measuring the fraction of the beamlets that strike detection plates and wires. The corresponding angle is used to determine the beam's toroidal velocity component. Due to canonical momentum conservation, that toroidal velocity is proportional to the poloidal flux function in the sample volume. We have built several prototype detectors and measured the angle of a 45 keV potassium ion beam. The cross-section of the plasma that can be studied will be maximized and system costs will be minimized if the detector has a direct view of the plasma and is operated close to it. However, this subjects the detector to noise due to UV-induced photoelectrons and plasma particles. We have conducted experiments that demonstrate reductions of this noise to facilitate measurement of ion beam signals. Experimental and design results will be presented. This work is supported by US DoE Award No. DE-SC0006077.

5. Poloidal flow damping with potato orbits in tokamaks

SciTech Connect

Shaing, K.C.

2005-10-01

The poloidal flow damping rate in the vicinity of the magnetic axis in tokamaks is calculated using the time-dependent plasma viscosity. It is found that the damping rate is of the order of {nu}{sub ii}/f{sub t}{sup 2}, where {nu}{sub ii} is the ion-ion collision frequency, and f{sub t} is the fraction of the trapped potatoes. The corresponding neoclassical polarization or inertia enhancement factor is [1+({sigma}{sub p}q{sup 2}/f{sub t})], where {sigma}{sub p} is a numerical number of the order of unity, and q is the safety factor.

6. Remote detected Low-Field MRI using an optically pumped atomic magnetometer combined with a liquid cooled pre-polarization coil

Hilschenz, Ingo; Ito, Yosuke; Natsukawa, Hiroaki; Oida, Takenori; Yamamoto, Tetsuya; Kobayashi, Tetsuo

2017-01-01

Superconducting quantum interference devices are widely used in basic and clinical biomagnetic measurements such as low-field magnetic resonance imaging and magnetoencephalography primarily because they exhibit high sensitivity at low frequencies and have a wide bandwidth. The main disadvantage of these devices is that they require cryogenic coolants, which are rather expensive and not easily available. Meanwhile, with the advances in laser technology in the past few years, optically pumped atomic magnetometers (OPAMs) have been shown to be a good alternative as they can have adequate noise levels and are several millimeters in size, which makes them significantly easier to use. In this study, we used an OPAM module operating at a Larmor frequency of 5 kHz to acquire NMR and MRI signals. This study presents these initial results as well as our initial attempts at imaging using this OPAM module. In addition, we have designed a liquid-cooled pre-polarizing coil that reduces the measurement time significantly.

7. Remote detected Low-Field MRI using an optically pumped atomic magnetometer combined with a liquid cooled pre-polarization coil.

PubMed

Hilschenz, Ingo; Ito, Yosuke; Natsukawa, Hiroaki; Oida, Takenori; Yamamoto, Tetsuya; Kobayashi, Tetsuo

2017-01-01

Superconducting quantum interference devices are widely used in basic and clinical biomagnetic measurements such as low-field magnetic resonance imaging and magnetoencephalography primarily because they exhibit high sensitivity at low frequencies and have a wide bandwidth. The main disadvantage of these devices is that they require cryogenic coolants, which are rather expensive and not easily available. Meanwhile, with the advances in laser technology in the past few years, optically pumped atomic magnetometers (OPAMs) have been shown to be a good alternative as they can have adequate noise levels and are several millimeters in size, which makes them significantly easier to use. In this study, we used an OPAM module operating at a Larmor frequency of 5kHz to acquire NMR and MRI signals. This study presents these initial results as well as our initial attempts at imaging using this OPAM module. In addition, we have designed a liquid-cooled pre-polarizing coil that reduces the measurement time significantly.

8. Protective link for superconducting coil

DOEpatents

Umans, Stephen D.

2009-12-08

A superconducting coil system includes a superconducting coil and a protective link of superconducting material coupled to the superconducting coil. A rotating machine includes first and second coils and a protective link of superconducting material. The second coil is operable to rotate with respect to the first coil. One of the first and second coils is a superconducting coil. The protective link is coupled to the superconducting coil.

9. Coiling of viscous jets

Ribe, Neil M.

2004-11-01

A stream of viscous fluid falling from a sufficient height onto a surface forms a series of regular coils. I use a numerical model for a deformable fluid thread to predict the coiling frequency as a function of the thread's radius, the flow rate, the fall height, and the fluid viscosity. Three distinct modes of coiling can occur: viscous (e.g. toothpaste), gravitational (honey falling from a moderate height) and inertial (honey falling from a great height). When inertia is significant, three states of steady coiling with different frequencies can exist over a range of fall heights. The numerically predicted coiling frequencies agree well with experimental measurements in the inertial coiling regime.

10. Characteristics of bowl-shaped coils for transcranial magnetic stimulation

Yamamoto, Keita; Suyama, Momoko; Takiyama, Yoshihiro; Kim, Dongmin; Saitoh, Youichi; Sekino, Masaki

2015-05-01

Transcranial magnetic stimulation (TMS) has recently been used as a method for the treatment of neurological and psychiatric diseases. Daily TMS sessions can provide continuous therapeutic effectiveness, and the installation of TMS systems at patients' homes has been proposed. A figure-eight coil, which is normally used for TMS therapy, induces a highly localized electric field; however, it is challenging to achieve accurate coil positioning above the targeted brain area using this coil. In this paper, a bowl-shaped coil for stimulating a localized but wider area of the brain is proposed. The coil's electromagnetic characteristics were analyzed using finite element methods, and the analysis showed that the bowl-shaped coil induced electric fields in a wider area of the brain model than a figure-eight coil. The expanded distribution of the electric field led to greater robustness of the coil to the coil-positioning error. To improve the efficiency of the coil, the relationship between individual coil design parameters and the resulting coil characteristics was numerically analyzed. It was concluded that lengthening the outer spherical radius and narrowing the width of the coil were effective methods for obtaining a more effective and more uniform distribution of the electric field.

11. The poloidal distribution of type-III edge localized modes in the Mega-Ampere spherical tokamak (MAST)

SciTech Connect

Antar, G.Y.

2006-05-15

This article describes the poloidal plasma particle distribution of type-III edge localized modes (ELMs) in the Mega-Ampere spherical tokamak [R.-J. Akers et al., Phys. Plasmas 9, 3919 (2002)]. A fast imaging camera with 10 {mu}s exposure time is used to record the D{sub {alpha}} light coming from the entire poloidal cross section. Furthermore, three sets of probes, triggered at the same time, acquired at 1 MHz, and located at different poloidal, radial, and toroidal locations in the tokamak are used. ELMs are observed to affect the D{sub {alpha}} emission throughout the low-field scrape-off layer; on the high-field side, however, this effect is found to be small. The results obtained by imaging agree with the pointwise measurements using Langmuir probes. The radial propagation is shown to occur at a speed of 250 m/s, whereas the toroidal convection from the top to the bottom of the plasma is shown to be consistent with a transport at the local sound speed. Strong correlation amplitudes are reported among the probes that are poloidally and toroidally separated by several meters. The study of the cross-correlation coefficients as a function of the frequency indicates that this correlation is caused by the low-frequency component of the signal and that the high-frequency part is not correlated. Consequently, the filamentary structures are interpreted as caused by the onset of turbulence during an ELM and do not constitute the ELM itself.

12. Innovative applications stimulate coiled tubing development

SciTech Connect

Sas-Jaworsky, A. II; Bell, S.

1996-06-01

Coiled tubing (CT) is increasingly becoming a viable option to many conventional well operations worldwide. Advanced technology, new equipment and recent field applications have shown CT to be a lower-cost, reliable and effective tool for drilling and recompleting certain wells. Seven example applications from two recent coiled tubing technical conferences are described.

13. Helical axis stellarator with noninterlocking planar coils

DOEpatents

Reiman, A.; Boozer, A.H.

1984-03-06

The present invention generates stellarator fields having favorable properties (magnetic well and large rotational transform) by a simple coil system consisting only of unlinked planar non-circular coils. At large rotational transform toroidal effects on magnetic well and rotational transform are small and can be ignored. We do so herein, specializing in straight helical systems.

14. Immune responses to coiled coil supramolecular biomaterials.

PubMed

Rudra, Jai S; Tripathi, Pulak K; Hildeman, David A; Jung, Jangwook P; Collier, Joel H

2010-11-01

Self-assembly has been increasingly utilized in recent years to create peptide-based biomaterials for 3D cell culture, tissue engineering, and regenerative medicine, but the molecular determinants of these materials' immunogenicity have remained largely unexplored. In this study, a set of molecules that self-assembled through coiled coil oligomerization was designed and synthesized, and immune responses against them were investigated in mice. Experimental groups spanned a range of oligomerization behaviors and included a peptide from the coiled coil region of mouse fibrin that did not form supramolecular structures, an engineered version of this peptide that formed coiled coil bundles, and a peptide-PEG-peptide triblock bioconjugate that formed coiled coil multimers and supramolecular aggregates. In mice, the native peptide and engineered peptide did not produce any detectable antibody response, and none of the materials elicited detectable peptide-specific T cell responses, as evidenced by the absence of IL-2 and interferon-gamma in cultures of peptide-challenged splenocytes or draining lymph node cells. However, specific antibody responses were elevated in mice injected with the multimerizing peptide-PEG-peptide. Minimal changes in secondary structure were observed between the engineered peptide and the triblock peptide-PEG-peptide, making it possible that the triblock's multimerization was responsible for this antibody response.

15. An interim report on the materials and selection criteria analysis for the Compact Ignition Tokamak Toroidal Field Coil Turn-to-Turn Insulation System

SciTech Connect

Campbell, V.W.; Dooley, J.B.; Hubrig, J.G.; Janke, C.J.; McManamy, T.J.; Welch, D.E.

1990-01-01

Design criteria for the Compact Ignition Tokamak, Toroidal-Field (TF) Coil, Turn-to-Turn Insulation System require an insulation sheet and bonding system that will survive cryogenic cycling in a radiation environment and maintain structural integrity during exposure to the significant compressive and shear loads associated with each operating cycle. For thermosetting resin systems, a complex interactive dependency exists between optimum peak value, in-service property performance capabilities of candidate generic materials; key handling and processing parameters required to achieve their optimum in-service property performance as an insulation system; and suitability of their handling and processing parameters as a function of design configuration and assembly methodology. This dependency is assessed in a weighted study matrix in which two principal programmatic approaches for the development of the TF Coil Subassembly Insulation System have been identified. From this matrix study, two viable approaches to the fabrication of the insulation sheet were identified: use of a press-formed sheet bonded in place with epoxy for mechanical bonding and tolerance take-up and formation of the insulation sheet by placement of dry cloth and subsequent vacuum pressure impregnation. Laboratory testing was conducted to screen a number of combinations of resins and hardeners on a generic basis. These combinations were chosen for their performance in similar applications. Specimens were tested to screen viscosity, thermal-shock tolerance, and cryogenic tolerance. Cryogenic shock and cryogenic temperature proved to be extremely lethal to many combinations of resin, hardener, and cure. Two combinations survived: a heavily flexibilized bisphenol A resin with a flexibilized amine hardener and a bisphenol A resin with cycloaliphatic amine hardener. 7 refs., 12 figs., 6 tabs.

16. Pulsed-coil magnet systems for applying uniform 10-30 T fields to centimeter-scale targets on Sandia's Z facility.

PubMed

Rovang, D C; Lamppa, D C; Cuneo, M E; Owen, A C; McKenney, J; Johnson, D W; Radovich, S; Kaye, R J; McBride, R D; Alexander, C S; Awe, T J; Slutz, S A; Sefkow, A B; Haill, T A; Jones, P A; Argo, J W; Dalton, D G; Robertson, G K; Waisman, E M; Sinars, D B; Meissner, J; Milhous, M; Nguyen, D N; Mielke, C H

2014-12-01

Sandia has successfully integrated the capability to apply uniform, high magnetic fields (10-30 T) to high energy density experiments on the Z facility. This system uses an 8-mF, 15-kV capacitor bank to drive large-bore (5 cm diameter), high-inductance (1-3 mH) multi-turn, multi-layer electromagnets that slowly magnetize the conductive targets used on Z over several milliseconds (time to peak field of 2-7 ms). This system was commissioned in February 2013 and has been used successfully to magnetize more than 30 experiments up to 10 T that have produced exciting and surprising physics results. These experiments used split-magnet topologies to maintain diagnostic lines of sight to the target. We describe the design, integration, and operation of the pulsed coil system into the challenging and harsh environment of the Z Machine. We also describe our plans and designs for achieving fields up to 20 T with a reduced-gap split-magnet configuration, and up to 30 T with a solid magnet configuration in pursuit of the Magnetized Liner Inertial Fusion concept.

17. Pulsed-coil magnet systems for applying uniform 10-30 T fields to centimeter-scale targets on Sandia's Z facility

Rovang, D. C.; Lamppa, D. C.; Cuneo, M. E.; Owen, A. C.; McKenney, J.; Johnson, D. W.; Radovich, S.; Kaye, R. J.; McBride, R. D.; Alexander, C. S.; Awe, T. J.; Slutz, S. A.; Sefkow, A. B.; Haill, T. A.; Jones, P. A.; Argo, J. W.; Dalton, D. G.; Robertson, G. K.; Waisman, E. M.; Sinars, D. B.; Meissner, J.; Milhous, M.; Nguyen, D. N.; Mielke, C. H.

2014-12-01

Sandia has successfully integrated the capability to apply uniform, high magnetic fields (10-30 T) to high energy density experiments on the Z facility. This system uses an 8-mF, 15-kV capacitor bank to drive large-bore (5 cm diameter), high-inductance (1-3 mH) multi-turn, multi-layer electromagnets that slowly magnetize the conductive targets used on Z over several milliseconds (time to peak field of 2-7 ms). This system was commissioned in February 2013 and has been used successfully to magnetize more than 30 experiments up to 10 T that have produced exciting and surprising physics results. These experiments used split-magnet topologies to maintain diagnostic lines of sight to the target. We describe the design, integration, and operation of the pulsed coil system into the challenging and harsh environment of the Z Machine. We also describe our plans and designs for achieving fields up to 20 T with a reduced-gap split-magnet configuration, and up to 30 T with a solid magnet configuration in pursuit of the Magnetized Liner Inertial Fusion concept.

18. Pulsed-coil magnet systems for applying 10-30 Tesla Fields to cm-scale targets on Sandia's Z facility

DOE PAGES

Rovang, Dean C.; Lamppa, Derek C.; Cuneo, Michael Edward; ...

2014-12-04

We have successfully integrated the capability to apply uniform, high magnetic fields (10–30 T) to high energy density experiments on the Z facility. This system uses an 8-mF, 15-kV capacitor bank to drive large-bore (5 cm diameter), high-inductance (1–3 mH) multi-turn, multi-layer electromagnets that slowly magnetize the conductive targets used on Z over several milliseconds (time to peak field of 2–7 ms). This system was commissioned in February 2013 and has been used successfully to magnetize more than 30 experiments up to 10 T that have produced exciting and surprising physics results. These experiments used split-magnet topologies to maintain diagnosticmore » lines of sight to the target. We then describe the design, integration, and operation of the pulsed coil system into the challenging and harsh environment of the Z Machine. We also describe our plans and designs for achieving fields up to 20 T with a reduced-gap split-magnet configuration, and up to 30 T with a solid magnet configuration in pursuit of the Magnetized Liner Inertial Fusion concept.« less

19. Pulsed-coil magnet systems for applying uniform 10–30 T fields to centimeter-scale targets on Sandia's Z facility

SciTech Connect

Rovang, D. C. Lamppa, D. C.; Cuneo, M. E.; Owen, A. C.; McKenney, J.; Johnson, D. W.; Radovich, S.; Kaye, R. J.; McBride, R. D.; Alexander, C. S.; Awe, T. J.; Slutz, S. A.; Sefkow, A. B.; Haill, T. A.; Jones, P. A.; Argo, J. W.; Dalton, D. G.; Robertson, G. K.; Waisman, E. M.; Sinars, D. B.; and others

2014-12-15

Sandia has successfully integrated the capability to apply uniform, high magnetic fields (10–30 T) to high energy density experiments on the Z facility. This system uses an 8-mF, 15-kV capacitor bank to drive large-bore (5 cm diameter), high-inductance (1–3 mH) multi-turn, multi-layer electromagnets that slowly magnetize the conductive targets used on Z over several milliseconds (time to peak field of 2–7 ms). This system was commissioned in February 2013 and has been used successfully to magnetize more than 30 experiments up to 10 T that have produced exciting and surprising physics results. These experiments used split-magnet topologies to maintain diagnostic lines of sight to the target. We describe the design, integration, and operation of the pulsed coil system into the challenging and harsh environment of the Z Machine. We also describe our plans and designs for achieving fields up to 20 T with a reduced-gap split-magnet configuration, and up to 30 T with a solid magnet configuration in pursuit of the Magnetized Liner Inertial Fusion concept.

20. Pulsed-coil magnet systems for applying 10-30 Tesla Fields to cm-scale targets on Sandia's Z facility

SciTech Connect

Rovang, Dean C.; Lamppa, Derek C.; Cuneo, Michael Edward; Owen, Albert; Mckenney, John; Johnson, Drew; Radovich, Shawn; Kaye, Ronald J.; McBride, Ryan D; Alexander, C. Scott; Awe, Thomas James; Slutz, Stephen A.; Sefkow, Adam B; Haill, Thomas A.; Jones, Peter Andrew; Argo, Jeffrey W; Dalton, Devon; Robertson, Grafton Kincannon; Waisman, Eduardo Mario; Sinars, Daniel Brian; Meissner, Joel; Milhous, Mark; Nguyen, Doan; Mielke, Chuck

2014-12-04

We have successfully integrated the capability to apply uniform, high magnetic fields (10–30 T) to high energy density experiments on the Z facility. This system uses an 8-mF, 15-kV capacitor bank to drive large-bore (5 cm diameter), high-inductance (1–3 mH) multi-turn, multi-layer electromagnets that slowly magnetize the conductive targets used on Z over several milliseconds (time to peak field of 2–7 ms). This system was commissioned in February 2013 and has been used successfully to magnetize more than 30 experiments up to 10 T that have produced exciting and surprising physics results. These experiments used split-magnet topologies to maintain diagnostic lines of sight to the target. We then describe the design, integration, and operation of the pulsed coil system into the challenging and harsh environment of the Z Machine. We also describe our plans and designs for achieving fields up to 20 T with a reduced-gap split-magnet configuration, and up to 30 T with a solid magnet configuration in pursuit of the Magnetized Liner Inertial Fusion concept.

1. Startup of Large Coil Test Facility

SciTech Connect

Haubenreich, P.N.; Bohanan, R.E.; Fietz, W.A.; Luton, J.N.; May, J.R.

1984-01-01

The Large Coil Test Facility (LCTF) is being used to test superconducting toroidal field coils about one-third the size of those for INTOR. Eventually, six different coils from four countries will be tested. Operations began in 1983 with acceptance testing of the helium refrigerator/liquefier system. Comprehensive shakedown of the facility and tests with the first three coils (from Japan, the United States, and Switzerland) were successfully accomplished in the summer of 1984. Currents up to 10,200 A and fields up to 6.4 T were reached. Data were obtained on performance of refrigerator, helium distribution, power supplies, controls, and data acquisition systems and on the acoustic emission, voltages, currents, and mechanical strains during charging and discharging the coils.

2. NCSX Trim Coil Design

SciTech Connect

M. Kalish, A. Brooks, J. Rushinski, R. Upcavage

2009-05-29

The National Compact Stellarator Experiment (NCSX) was being constructed at the Princeton Plasma Physics Laboratory in partnership with Oak Ridge National Laboratory before work was stopped in 2008. The objective of this experiment was to develop the stellarator concept and evaluate it's potential as a model for future fusion power plants. Stellarator design requires very precisely positioned Modular Coils of complex shape to form 3D plasmas. In the design of NCSX, Trim Coils were required to compensate for both the positioning of the coils during assembly and the fabrication tolerances of the Modular Coils. Use of the Trim Coils allowed for larger tolerances increasing ease of assembly and decreasing overall cost. A set of Trim coils was developed to suppress the toroidal flux in island regions due to misalignment, magnetic materials, and eddy currents. The requirement imposed upon the design forced the toroidal flux in island regions below 10% of the total toroidal flux in the plasma. An analysis was first performed to evaluate candidate Trim Coil configurations iterating both the size, number, and position of the coils. The design was optimized considering both performance and cost while staying within the tight restraints presented by the space limited geometry. The final design of the Trim Coils incorporated a 48 Coil top bottom symmetric set. Fabrication costs were minimized by having only two coil types and using a planar conventional design with off the shelf commercial conductor. The Trim Coil design incorporated supports made from simple structural shapes assembled together in a way which allowed for adjustment as well as accommodation for the tolerance build up on the mating surfaces. This paper will summarize the analysis that led to the optimization of the Trim Coils set, the trim coil mechanical design, thermal and stress analysis, and the design of the supporting Trim Coil structure.

3. Open coil structure for bubble-memory-device packaging

NASA Technical Reports Server (NTRS)

Chen, T. T.; Ypma, J. E.

1975-01-01

Concept has several important advantages over close-wound system: memory and coil chips are separate and interchangeable; interconnections in coil level are eliminated by packing memory chip and electronics in single structure; and coil size can be adjusted to optimum value in terms of power dissipation and field uniformity.

4. Electromagnetic pump stator coil

DOEpatents

Fanning, Alan W.; Dahl, Leslie R.

1996-01-01

An electrical stator coil for an electromagnetic pump includes a continuous conductor strip having first and second terminals at opposite ends thereof and an intermediate section disposed therebetween. The strip is configured in first and second coil halves, with the first coil half including a plurality of windings extending from the first terminal to the intermediate section, and the second coil half including a plurality of windings extending from the second terminal to the intermediate section. The first and second coil halves are disposed coaxially, and the first and second terminals are disposed radially inwardly therefrom with the intermediate section being disposed radially outwardly therefrom.

5. Electromagnetic pump stator coil

DOEpatents

Fanning, A.W.; Dahl, L.R.

1996-06-25

An electrical stator coil for an electromagnetic pump includes a continuous conductor strip having first and second terminals at opposite ends thereof and an intermediate section disposed therebetween. The strip is configured in first and second coil halves, with the first coil half including a plurality of windings extending from the first terminal to the intermediate section, and the second coil half including a plurality of windings extending from the second terminal to the intermediate section. The first and second coil halves are disposed coaxially, and the first and second terminals are disposed radially inwardly therefrom with the intermediate section being disposed radially outwardly therefrom. 9 figs.

6. Observation of dust torus with poloidal rotation in direct current glow discharge plasma

SciTech Connect

Kaur, Manjit Bose, Sayak; Chattopadhyay, P. K. Sharma, Devendra; Ghosh, J.; Saxena, Y. C.

2015-03-15

Observation of dust cloud rotation in parallel-plate DC glow discharge plasma is reported here. The experiments are carried out at high pressures (∼130 Pa) with a metallic ring placed on the lower electrode (cathode). The dust cloud rotates poloidally in the vertical plane near the cathode surface. This structure is continuous toroidally. Absence of magnetic field rules out the possibility of E × B induced ion flow as the cause of dust rotation. The dust rotational structures exist even with water cooled cathode. Therefore, temperature gradient driven mechanisms, such as thermophoretic force, thermal creep flow, and free convection cannot be causing the observed dust rotation. Langmuir probe measurement reveals the existence of a sharp density gradient near the location of the rotating dust cloud. The gradient in the density, giving rise to a gradient in the ion drag force, has been identified as the principal cause behind the rotation of dust particles.

7. Preliminary skyshine calculations for the Poloidal Diverter Tokamak Experiment

Nigg, D. W.; Wheeler, F. J.

1981-01-01

A calculational model is presented to estimate the radiation dose, due to the skyshine effect, in the control room and at the site boundary of the Poloidal Diverter Experiment (PDX) facility at Princeton University which requires substantial radiation shielding. The required composition and thickness of a water-filled roof shield that would reduce this effect to an acceptable level is computed, using an efficient one-dimensional model with an Sn calculation in slab geometry. The actual neutron skyshine dose is computed using a Monte Carlo model with the neutron source at the roof surface obtained from the slab Sn calculation, and the capture gamma dose is computed using a simple point-kernel single-scatter method. It is maintained that the slab model provides the exact probability of leakage out the top surface of the roof and that it is nearly as accurate as and much less costly than multi-dimensional techniques.

8. FIRST 100 T NON-DESTRUCTIVE MAGNET OUTER COIL SET

SciTech Connect

J. BACON; A. BACA; ET AL

1999-09-01

The controlled power outer coil set of the first 100 T non-destructive (100 T ND) magnet is described. This magnet will be installed as part of the user facility research equipment at the National High Magnetic Field laboratory (NHMFL) Pulsed Field Facility at Los Alamos National Laboratory. The 100 T ND controlled power outer coil set consists of seven nested, mechanically independent externally reinforced coils. These coils, in combination, will produce a 47 T platform field in a 225-mm diameter bore. Using inertial energy storage a synchronous motor/generator provides ac power to a set of seven ac-dc converters rated at 64 MW/80 MVA each. These converters energize three independent coil circuits to create 170 MJ of field energy in the outer coil set at the platform field of 47 T. Each coil consists of a multi-layer winding of high strength conductor supported by an external high strength stainless steel shell. Coils with the highest magnetic loads will utilize a reinforcing shell fabricated from highly cold worked 301 stainless steel strip. The autofrettage conditioning method will be used to pre-stress the coils and thereby limit conductor and reinforcement strains to the elastic range. The purpose of pre-stressing the coils is to attain a design life of 10,000 full field pulses. The operation and conditioning of the coil set will be described along with special features of its design, magnetic and structural analyses and construction.

9. Spaced-based search coil magnetometers

Hospodarsky, George B.

2016-12-01

Search coil magnetometers are one of the primary tools used to study the magnetic component of low-frequency electromagnetic waves in space. Their relatively small size, mass, and power consumption, coupled with a good frequency range and sensitivity, make them ideal for spaceflight applications. The basic design of a search coil magnetometer consists of many thousands of turns of wire wound on a high permeability core. When a time-varying magnetic field passes through the coil, a time-varying voltage is induced due to Faraday's law of magnetic induction. The output of the coil is usually attached to a preamplifier, which amplifies the induced voltage and conditions the signal for transmission to the main electronics (usually a low-frequency radio receiver). Search coil magnetometers are usually used in conjunction with electric field antenna to measure electromagnetic plasma waves in the frequency range of a few hertz to a few tens of kilohertzs. Search coil magnetometers are used to determine the properties of waves, such as comparing the relative electric and magnetic field amplitudes of the waves, or to investigate wave propagation parameters, such as Poynting flux and wave normal vectors. On a spinning spacecraft, they are also sometimes used to determine the background magnetic field. This paper presents some of the basic design criteria of search coil magnetometers and discusses design characteristics of sensors flown on a number of spacecraft.

10. Tx/Rx Head Coil Induces Less RF Transmit-Related Heating than Body Coil in Conductive Metallic Objects Outside the Active Area of the Head Coil

PubMed Central

Nagy, Zoltan; Oliver-Taylor, Aaron; Kuehne, Andre; Goluch, Sigrun; Weiskopf, Nikolaus

2017-01-01

11. Tx/Rx Head Coil Induces Less RF Transmit-Related Heating than Body Coil in Conductive Metallic Objects Outside the Active Area of the Head Coil.

PubMed

Nagy, Zoltan; Oliver-Taylor, Aaron; Kuehne, Andre; Goluch, Sigrun; Weiskopf, Nikolaus

2017-01-01

12. Coil bobbin for stable superconducting coils

SciTech Connect

Kashima, T.; Yamanaka, A.; Nishijima, S.; Okada, T.

1996-12-31

The coil bobbin for a.c. coils have been prepared with the high strength polyethylene fiber (DF) reinforced plastics (DFRP) or with hybrid composites reinforced by DF and glass fiber (GF). The coils with the bobbin were found to be markedly stable. The DF has a large negative thermal expansion coefficient and hence the circumferential thermal strain of bobbin can be designed by changing the ratio of DF to GF layer thickness (DF/GF). It was found that the thermal expansion coefficient in the circumferential direction of the outer surface changed from negative to positive with increasing DF/GF and became nearly zero at a DF/GF of approximately 5.1 kA rms class a.c. coils having a bobbin with a negative thermal expansion coefficient or small thermal contraction in the circumferential direction were fabricated and were confirmed to show higher quench current than that with a GFRP bobbin.

13. Engineered coiled-coil protein microfibers.

PubMed

Hume, Jasmin; Sun, Jennifer; Jacquet, Rudy; Renfrew, P Douglas; Martin, Jesse A; Bonneau, Richard; Gilchrist, M Lane; Montclare, Jin Kim

2014-10-13

The fabrication of de novo proteins able to self-assemble on the nano- to meso-length scales is critical in the development of protein-based biomaterials in nanotechnology and medicine. Here we report the design and characterization of a protein engineered coiled-coil that not only assembles into microfibers, but also can bind hydrophobic small molecules. Under ambient conditions, the protein forms fibers with nanoscale structure possessing large aspect ratios formed by bundles of α-helical homopentameric assemblies, which further assemble into mesoscale fibers in the presence of curcumin through aggregation. Surprisingly, these biosynthesized fibers are able to form in conditions of remarkably low concentrations. Unlike previously designed coiled-coil fibers, these engineered protein microfibers can bind the small molecule curcumin throughout the assembly, serving as a depot for encapsulation and delivery of other chemical agents within protein-based 3D microenvironments.

14. Poloidal rotation driven by nonlinear momentum transport in strong electrostatic turbulence

Wang, Lu; Wen, Tiliang; Diamond, P. H.

2016-10-01

Virtually, all existing theoretical works on turbulent poloidal momentum transport are based on quasilinear theory. Nonlinear poloidal momentum flux—< {{\\tilde{v}}r}\\tilde{n}{{\\tilde{v}}θ}> is universally neglected. However, in the strong turbulence regime where relative fluctuation amplitude is no longer small, quasilinear theory is invalid. This is true at the all-important plasma edge. In this work, nonlinear poloidal momentum flux < {{\\tilde{v}}r}\\tilde{n}{{\\tilde{v}}θ}> in strong electrostatic turbulence is calculated using the Hasegawa-Mima equation, and is compared with quasilinear poloidal Reynolds stress. A novel property is that symmetry breaking in fluctuation spectrum is not necessary for a nonlinear poloidal momentum flux. This is fundamentally different from the quasilinear Reynold stress. Furthermore, the comparison implies that the poloidal rotation drive from the radial gradient of nonlinear momentum flux is comparable to that from the quasilinear Reynolds force. Nonlinear poloidal momentum transport in strong electrostatic turbulence is thus not negligible for poloidal rotation drive, and so may be significant to transport barrier formation.

15. Two-Dimensional MHD Simulations of Tokamak Plasmas with Poloidal Flow

Guazzotto, L.; Betti, R.

2002-11-01

A two- dimensional MHD code has been developed to simulate the temporal evolution of Tokamak plasmas with an imposed poloidal flow. The code is fully compressible and can resolve the shock structures arising when the poloidal velocity is of the order of the poloidal sound speed (V_θ ˜ Cs B_θ/B) near the plasma edge, where the plasma is cold and the sound speed is low. The poloidal flow is assigned as an initial condition with a velocity profile ranging from subsonic to supersonic near the edge. It is found that a continuous band of shocks is formed near the edge. Such shocks travel poloidally, leaving behind a pedestal structure similar to the one predicted in Ref. 1 [R. Betti and J. P. Freidberg, Phys. Plasmas 7, 2439 (2000)]. Here, the pedestal is defined as a sharp discontinuity in the pressure, temperature, and density profiles. The pedestal height is modulated in the poloidal angle; it is maximum on the outboard side (θ = 0) and minimum on the inboard (θ = π). Furthermore, both poloidal and toroidal flows develop a shear layer at the location of the pedestal. The large velocity shear (both poloidal and toroidal) occurring in the pedestal region is likely to suppress turbulent eddies and reduce anomalous transport. This work was supported by the U.S. Department of Energy Office of Inertial Confinement Fusion under Cooperative Agreement No. DE-FC03-92SF19460.

16. Two-dimensional magnetohydrodynamic simulations of poloidal flows in tokamaks and MHD pedestal

Guazzotto, L.; Betti, R.

2011-09-01

Poloidal rotation is routinely observed in present-day tokamak experiments, in particular near the plasma edge and in the high-confinement mode of operation. According to the magnetohydrodynamic (MHD) equilibrium theory [R. Betti and J. P. Freidberg, Phys. Plasmas 7, 2439 (2000)], radial discontinuities form when the poloidal velocity exceeds the poloidal sound speed (or rather, more correctly, the poloidal magneto-slow speed). Two-dimensional compressible magnetohydrodynamic simulations show that the transonic discontinuities develop on a time scale of a plasma poloidal revolution to form an edge density pedestal and a localized velocity shear layer at the pedestal location. While such an MHD pedestal surrounds the entire core, the outboard side of the pedestal is driven by the transonic discontinuity while the inboard side is caused by a poloidal redistribution of the mass. The MHD simulations use a smooth momentum source to drive the poloidal flow. Soon after the flow exceeds the poloidal sound speed, the density pedestal and the velocity shear layer form and persist into a quasi steady state. These results may be relevant to the L-H transition, the early stages of the pedestal and edge transport barrier formation.

17. Two-dimensional magnetohydrodynamic simulations of poloidal flows in tokamaks and MHD pedestal

SciTech Connect

Guazzotto, L.; Betti, R.

2011-09-15

Poloidal rotation is routinely observed in present-day tokamak experiments, in particular near the plasma edge and in the high-confinement mode of operation. According to the magnetohydrodynamic (MHD) equilibrium theory [R. Betti and J. P. Freidberg, Phys. Plasmas 7, 2439 (2000)], radial discontinuities form when the poloidal velocity exceeds the poloidal sound speed (or rather, more correctly, the poloidal magneto-slow speed). Two-dimensional compressible magnetohydrodynamic simulations show that the transonic discontinuities develop on a time scale of a plasma poloidal revolution to form an edge density pedestal and a localized velocity shear layer at the pedestal location. While such an MHD pedestal surrounds the entire core, the outboard side of the pedestal is driven by the transonic discontinuity while the inboard side is caused by a poloidal redistribution of the mass. The MHD simulations use a smooth momentum source to drive the poloidal flow. Soon after the flow exceeds the poloidal sound speed, the density pedestal and the velocity shear layer form and persist into a quasi steady state. These results may be relevant to the L-H transition, the early stages of the pedestal and edge transport barrier formation.

18. Correcting coils in end magnets of accelerators

Kassab, L. R.; Gouffon, P.

1998-05-01

We present an empirical investigation of the correcting coils behavior used to homogenize the field distribution of the race-track microtron accelerator end magnets. These end magnets belong to the second stage of the 30.0 MeV cw electron accelerator under construction at IFUSP, the race-track microtron booster, in which the beam energy is raised from 1.97 to 5.1 MeV. The correcting coils are attached to the pole faces and are based on the inhomogeneities of the magnetic field measured. The performance of these coils, when operating the end magnets with currents that differ by +/-10% from the one used in the mappings that originated the coils copper leads, is presented. For one of the magnets, adjusting conveniently the current of the correcting coils makes it possible to homogenize field distributions of different intensities, once their shapes are practically identical to those that originated the coils. For the other one, the shapes are changed and the coils are less efficient. This is related to intrinsic factors that determine the inhomogeneities. However, we obtained uniformity of 0.001% in both cases.

19. Optimal Coil Orientation for Transcranial Magnetic Stimulation

PubMed Central

Richter, Lars; Neumann, Gunnar; Oung, Stephen; Schweikard, Achim; Trillenberg, Peter

2013-01-01

We study the impact of coil orientation on the motor threshold (MT) and present an optimal coil orientation for stimulation of the foot. The result can be compared to results of models that predict this orientation from electrodynamic properties of the media in the skull and from orientations of cells, respectively. We used a robotized TMS system for precise coil placement and recorded motor-evoked potentials with surface electrodes on the abductor hallucis muscle of the right foot in 8 healthy control subjects. First, we performed a hot-spot search in standard (lateral) orientation and then rotated the coil in steps of 10° or 20°. At each step we estimated the MT. For navigated stimulation and for correlation with the underlying anatomy a structural MRI scan was obtained. Optimal coil orientation was 33.1±18.3° anteriorly in relation to the standard lateral orientation. In this orientation the threshold was 54±18% in units of maximum stimulator output. There was a significant difference of 8.0±5.9% between the MTs at optimal and at standard orientation. The optimal coil orientations were significantly correlated with the direction perpendicular to the postcentral gyrus (). Robotized TMS facilitates sufficiently precise coil positioning and orientation to study even small variations of the MT with coil orientation. The deviations from standard orientation are more closely matched by models based on field propagation in media than by models based on orientations of pyramidal cells. PMID:23593200

20. Study on cross section of high temperature superconducting coil

Ishiguri, Shinichi; Yamaguchi, Mitsugi; Fukui, Satoshi; Ogawa, Jun; Sato, Takao

2007-01-01

It is in particular of importance for HTS coils to secure a larger central magnetic field and/or a large stored energy with shorter length of HTS tapes. The critical current of an HTS tape depends on both the flux density and the flux angle against tapes. From this point, the performance improvement of HTS coils is taken into account with an analytical model. The minimum volume coil derived from the Fabry Factor constant curve is taken concerning the original coil shape, which is often employed in low temperature superconducting coils. The coil critical current was analyzed in consideration of the anisotropic properties of the tape. The electric field of HTS tapes in the coil was calculated at the coil critical current and the high electric field portion were cut out. The optimal coil cross section is obtained by iterating this calculation process. As a result, the critical current and the stored energy density of the coil were improved. The stored energy density increased about 17% and the central magnetic field was almost kept constant regardless of 19% reduction of HTS tapes, as compared with the original coil with the rectangular cross section.

1. MEMS switch integrated radio frequency coils and arrays for magnetic resonance imaging

Bulumulla, S. B.; Park, K. J.; Fiveland, E.; Iannotti, J.; Robb, F.

2017-02-01

Surface coils are widely used in magnetic resonance imaging and spectroscopy. While smaller diameter coils produce higher signal to noise ratio (SNR) closer to the coil, imaging larger fields of view or greater distance into the sample requires a larger overall size array or, in the case of a channel count limited system, larger diameter coils. In this work, we consider reconfiguring the geometry of coils and coil arrays such that the same coil or coil array may be used in multiple field of view imaging. A custom designed microelectromechanical systems switch, compatible with magnetic resonance imaging, is used to switch in/out conductive sections and components to reconfigure coils. The switch does not degrade the SNR and can be opened/closed in 10 μ s, leading to rapid reconfiguration. Results from a single coil, configurable between small/large configurations, and a two-coil phased array, configurable between spine/torso modes, are presented.

2. Method and apparatus for balancing the magnetic field detecting loops of a cryogenic gradiometer using trimming coils and superconducting disks

SciTech Connect

Lutes, C.L.

1982-03-16

An apparatus for and a method of measuring the difference in intensity between two coplanar magnetic field vector components at two different points in space. The device is comprised of two interconnected, relatively large, loop patterns of opposite, flux cancelling, winding sense. One or both loops include a trimming element that is itself formed of two interconnected, relatively small, loop patterns of opposite, flux cancelling, winding sense. The device is analyzed for imbalance between the two large loops and is then balanced by placing a balancing superconducting disk of the proper characteristic in or near one of the two small loops of the trimming element. The so-trimmed apparatus forms a gradiometer of substantially improved mensuration.

3. Coiling Viscous Jets

1996-11-01

A thin stream of glycerine or other viscous fluid poured onto a horizontal plane from a sufficient height piles up in a regular coil. In its steady state, this motion is analogous to the coiling of a flexible rope (L. Mahadevan and J.B. Keller, Proc. Roy. Soc.(A) to appear.). This analogy is used to solve the nonlinear free-boundary problem for the frequency of coiling and the coil radius. The results are compared with experimental results that go back to the the work of G.I. Taylor (1969).

4. Artificial Neural Networks: a viable tool to design heat load smoothing strategies for the ITER Toroidal Field coils

Froio, A.; Bonifetto, R.; Carli, S.; Quartararo, A.; Savoldi, L.; Zanino, R.

2015-12-01

In superconducting tokamaks, cryoplants provide the helium needed to cool the superconducting magnet systems. The evaluation of the heat load from the magnets to the cryoplant is fundamental for the design of the latter and the assessment of suitable strategies to smooth the heat load pulses induced by the pulsed plasma scenarios is crucial for the operation. Here, a simplified thermal-hydraulic model of an ITER Toroidal Field (TF) magnet, based on Artificial Neural Networks (ANNs), is developed and inserted into a detailed model of the ITER TF winding and casing cooling circuits based on the state-of-the-art 4C code, which also includes active controls. The low computational effort requested by such a model allows performing a fast parametric study, to identify the best smoothing strategy during standard plasma operation. The ANNs are trained using 4C simulations, and the predictive capabilities of the simplified model are assessed against 4C simulations, both with and without active smoothing, in terms of accuracy and computational time.

5. Null field formation and ohmic start-up in the CDX-U

Rosenberg, Adam; Menard, Jon; Majeski, Richard; Kaita, Robert; Munsat, Tobin; Hoffman, Daniel

1999-11-01

The Current Drive eXperiment - Upgrade (CDX-U) is a small spherical torus with a limited solenoid flux (< 150mWb), a toroidally continuous and conducting stainless-steel vacuum vessel, and a pulse length on the order of the vessel L/R time. Because of these factors, to accurately predict the fields in the device one must do dynamic modelling of the vacuum vessel response to the ohmic and poloidal field coils. This facilitates the determination of the necessary current waveforms to generate a poloidal field null, which is critical to plasma current formation. A code has been written which takes as its input any cylindrically symmetric conducting structure and any coil currents. It then breaks up the structure into many smaller rings, then uses the basic circuit equations along with matrix diagonalization to efficiently determine the vessel current and thus the total magnetic field as a function of space and time. The code has been tested against experimental data and the results will be presented.

6. Minimax current density gradient coils: analysis of coil performance and heating.

PubMed

Poole, Michael S; While, Peter T; Lopez, Hector Sanchez; Crozier, Stuart

2012-08-01

Standard gradient coils are designed by minimizing the inductance or resistance for an acceptable level of gradient field nonlinearity. Recently, a new method was proposed to minimize the maximum value of the current density in a coil additionally. The stated aim of that method was to increase the minimum wire spacing and to reduce the peak temperature in a coil for fixed efficiency. These claims are tested in this study with experimental measurements of magnetic field and temperature as well as simulations of the performance of many coils. Experimental results show a 90% increase in minimum wire spacing and 40% reduction in peak temperature for equal coil efficiency and field linearity. Simulations of many more coils indicate increase in minimum wire spacing of between 50 and 340% for the coils studied here. This method is shown to be able to increase coil efficiency when constrained by minimum wire spacing rather than switching times or total power dissipation. This increase in efficiency could be used to increase gradient strength, duty cycle, or buildability.

7. Effects of beam-driven poloidal rotation on the neoclassical bootstrap current

SciTech Connect

Lin-Liu, Y.R.; Hinton, F.L.

1996-12-31

Unbalanced neutral beam injection drives toroidal and poloidal rotations in a tokamak plasma. The beam toroidal momentum input drives the toroidal rotation, and the parallel friction between the thermal ions and fast ions induces the poloidal rotation. A theory of the beam-driven poloidal rotation and its effects on energy transport was given recently by Hinton and Kim. In this work, we extend their considerations to the effects on the neoclassical bootstrap current. For parameters of interest in present neutral beam heated tokamaks, the magnitude of the beam-driven poloidal rotation can be significantly larger than that of the standard neoclassical value due to the ion temperature gradient. The presence of this driven poloidal rotation will manifest itself in modification of the neoclassical bootstrap current. In the case of coinjection, the driven poloidal rotation is in the opposite direction to the rotation driven by the temperature gradient, therefore it enhances the bootstrap current. In comparison with the standard theoretical predictions of the neutral beam-driven current, that enhancement in the bootstrap current varies with the beam and plasma parameters. A calculation of the parallel transport coefficients associated with the driven poloidal flow in finite-aspect ratio tokamaks will be presented. Experimental conditions for observing the enhancement in bootstrap current will be discussed.

8. Practical Aspects of Birdcage Coils

Doty, F. David; Entzminger, George; Hauck, Cory D.; Staab, John P.

1999-05-01

Numerical modeling and experimental results are presented for a variety of birdcages for high-field MRI microscopy. The data include the first published numerical calculations and experimental measurements of magnetic filling factors of birdcages or other MRI coils. Fast, 3D calculations for shielded coils are demonstrated using the Biot-Savart law along with energy minimization. It is shown that the near-field, higher-order inhomogeneity effects remaining after a first-order, asymmetry correction may easily exceed 20% in situations where it is desirable to maximize filling factor. It is also found that an order-of-magnitude improvement in the accuracy of predicted capacitor values may be achieved by using a more detailed circuit model of the birdcage resonator.

9. Practical aspects of birdcage coils.

PubMed

Doty, F D; Entzminger, G; Hauck, C D; Staab, J P

1999-05-01

Numerical modeling and experimental results are presented for a variety of birdcages for high-field MRI microscopy. The data include the first published numerical calculations and experimental measurements of magnetic filling factors of birdcages or other MRI coils. Fast, 3D calculations for shielded coils are demonstrated using the Biot-Savart law along with energy minimization. It is shown that the near-field, higher-order inhomogeneity effects remaining after a first-order, asymmetry correction may easily exceed 20% in situations where it is desirable to maximize filling factor. It is also found that an order-of-magnitude improvement in the accuracy of predicted capacitor values may be achieved by using a more detailed circuit model of the birdcage resonator.

10. AC loss measurements in HTS coil assemblies with hybrid coil structures

Jiang, Zhenan; Long, Nicholas J.; Staines, Mike; Badcock, Rodney A.; Bumby, Chris W.; Buckley, Robert G.; Amemiya, Naoyuki

2016-09-01

Both AC loss and wire cost in coil windings are critical factors for high temperature superconductor (HTS) AC machinery applications. We present AC loss measurement results in three HTS coil assemblies at 77 K and 65 K which have a hybrid coil structure comprising one central winding (CW) and two end windings (EWs) wound with ReBCO and BSCCO wires with different self-field I c values at 77 K. All AC loss results in the coil assemblies are hysteretic and the normalized AC losses in the coil assemblies at different temperatures can be scaled with the I c value of the coil assemblies. The normalised results show that AC loss in a coil assembly with BSCCO CW can be reduced by using EWs wound with high I c ReBCO wires, whilst further AC loss reduction can be achieved by replacing the BSCCO CW with ReBCO CW. The results imply that a flexible hybrid coil structure is possible which considers both AC loss and wire cost in coil assemblies.

11. Poloidal flux linkage requirements for the International Thermonuclear Experimental Reactor

SciTech Connect

Jardin, S.C.; Kessel, C.; Pomphrey, N.

1994-01-01

We have applied two computational models to calculate the poloidal flux linkage requirements for the current ramp-up and for the flattop phase of the proposed International Thermonuclear Experimental Reactor (ITER). For the current ramp-up phase, we have used the TSC code to simulate the entire current ramp-up period as described in the TAC-3 Physics Report. We have extended the time of the simulation to cover the full current penetration time, that is, until the loop voltage is a constant throughout the plasma. Sensitivity studies have been performed with respect to current ramp-up time, impurity concentration, and to the time of onset of auxiliary heating. We have also used a steady state plasma equilibrium code that has the constant loop voltage constraint built in to survey the dependence of the steady state loop-voltage on the density and temperature profiles. This calculation takes into account the plasma bootstrap current contribution, including non-circular and collisional corrections. The results can be displayed as contours of the loop-voltage on a POPCON like diagram.

12. Collapse tests expand coiled tubing uses

SciTech Connect

Walker, E.J.; Mason, C.M. )

1990-03-05

Tests on coiled tubing have allowed the authors' company to decrease well work costs for some operations, especially squeeze cementing. They conducted collapse tests of 1.5 in. (0.095 in. and 0.109-in. wall thickness) and 1.75-in. (0.109-in. wall thickness) OD coiled tubing while under imposed axial load and differential pressure. These tests were performed to define accurate field operating limits for this size of coiled tubing. Findings from these tests are reported and discussed.

13. Poloidal variation of high-Z impurity density in Alcator C-Mod ICRF-heated plasmas

Reinke, Matthew

2012-10-01

The poloidal variation of molybdenum density is measured in the core of ICRF-heated Alcator C-Mod plasmas and found to exhibit strong in/out asymmetries. Existing neoclassical parallel impurity transport theory is extended to include the effects of fast-ions and is shown to agree quantitatively with C-Mod measurements. The flux-surface variation of molybdenum is well described by nz(θ)/=1+nz,c cos(θ)+nz,ssin(θ), where -0.2 < nz,c/ < 0.3 and -0.1 < nz,s/ < 0.1 are observed over a wide range of Ohmic, L/I-mode and EDA H-mode plasmas for r/a < 0.9. The in/out asymmetry, nz,c/, is determined by a combination of centrifugal force due to toroidal rotation, leading to low-field side (LFS) accumulation, and poloidal electric fields sustained by magnetic trapping of cyclotron heated minority ions, leading to high field side (HFS) accumulation. While LFS accumulation due to centrifugal effects has been seen on other tokamaks, this represents the first observation of the effect driven entirely by intrinsic rotation. Scans of the D(H) resonance layer are shown to modify the in/out asymmetry by altering the fast-ion temperature anisotropy, T-/T||, and changing the ICRF power density, PRF/ne, either by ramping down the input power or increasing the density is found to reduce HFS accumulation. Observations of up/down asymmetries nz,s/, of molybdenum density are found to disagree with existing theories in the trace limit, nzZ^2/ni 1, in the collisionless main-ion regime. The link between nz(θ) and poloidal rotation, vθ, is emphasized, as both are assumed to be determined by neoclassical parallel impurity transport, and a more rigorous test of theory which includes matching asymmetries and vθ is discussed. The use of the poloidal variation in nz as a diagnostic for Eθ and T-/T|| as well as the impact of nz,c/ on radial transport are also discussed.

14. Modeling Endovascular MRI Coil Coupling with Transmit RF Excitation

PubMed Central

Venkateswaran, Madhav; Unal, Orhan; Hurley, Samuel; Samsonov, Alexey; Wang, Peng; Fain, Sean; Kurpad, Krishna

2016-01-01

Objective To model inductive coupling of endovascular coils with transmit RF excitation for selecting coils for MRI-guided interventions. Methods Independent and computationally efficient FEM models are developed for the endovascular coil, cable, transmit excitation and imaging domain. Electromagnetic and circuit solvers are coupled to simulate net B1+ fields and induced currents and voltages. Our models are validated using the Bloch Siegert B1+ mapping sequence for a series-tuned multimode coil, capable of tracking, wireless visualization and high resolution endovascular imaging. Results Validation shows good agreement at 24, 28 and 34 μT background RF excitation within experimental limitations. Quantitative coil performance metrics agree with simulation. A parametric study demonstrates trade off in coil performance metrics when varying number of coil turns. Tracking, imaging and wireless marker multimode coil features and their integration is demonstrated in a pig study. Conclusion Developed models for the multimode coil were successfully validated. Modeling for geometric optimization and coil selection serves as a precursor to time-consuming and expensive experiments. Specific applications demonstrated include parametric optimization, coil selection for a cardiac intervention and an animal imaging experiment. Significance Our modular, adaptable and computationally efficient modeling approach enables rapid comparison, selection and optimization of inductively-coupled coils for MRI-guided interventions. PMID:26960218

15. Coiled bodies without coilin.

PubMed Central

Bauer, D W; Gall, J G

1997-01-01

Nuclei assembled in vitro in Xenopus egg extract contain coiled bodies that have components from three different RNA processing pathways: pre-mRNA splicing, pre-rRNA processing, and histone pre-mRNA 3'-end formation. In addition, they contain SPH-1, the Xenopus homologue of p80-coilin, a protein characteristic of coiled bodies. To determine whether coilin is an essential structural component of the coiled body, we removed it from the egg extract by immunoprecipitation. We showed that nuclei with bodies morphologically identical to coiled bodies (at the light microscope level) formed in such coilin-depleted extract. As expected, these bodies did not stain with antibodies against coilin. Moreover, they failed to stain with an antibody against the Sm proteins, although Sm proteins associated with snRNAs were still present in the extract. Staining of the coilin- and Sm-depleted coiled bodies was normal with antibodies against two nucleolar proteins, fibrillarin and nucleolin. Similar results were observed when Sm proteins were depleted from egg extract: staining of the coiled bodies with antibodies against the Sm proteins and coilin was markedly reduced but bright nucleolin and fibrillarin staining remained. These immunodepletion experiments demonstrate an interdependence between coilin and Sm snRNPs and suggest that neither is essential for assembly of nucleolar components in coiled bodies. We propose that coiled bodies are structurally heterogeneous organelles in which the components of the three RNA processing pathways may occur in separate compartments. Images PMID:9017596

16. Anomalies in the applied magnetic fields in DIII-D and their implications for the understanding of stability experiments

SciTech Connect

Luxon, J. L.; Schaffer, M. J.; Jackson, G. L.; Leuer, J. A.; Nagy, A.; Scoville, J. T.; Strait, E. J.

2003-12-01

Small non-axisymmetric magnetic fields are known to cause serious loss of stability in tokamaks leading to loss of confinement and abrupt termination of plasma current (disruptions). The best known examples are the locked mode and the resistive wall mode. Understanding of the underlying field anomalies (departures in the hardware-related fields from ideal toroidal and poloidal fields on a single axis) and the interaction of the plasma with them is crucial to tokamak development. Results of both locked mode experiments and resistive wall mode experiments done in DIII-D tokamak plasmas have been interpreted to indicate the presence of a significant anomalous field. New measurements of the magnetic field anomalies of the hardware systems have been made on DIII-D. The measured field anomalies due to the plasma shaping coils in DIII-D are smaller than previously reported. Additional evaluations of systematic errors have been made. New measurements of the anomalous fields of the ohmic heating and toroidal coils have been added. Such detailed in situ measurements of the fields of a tokamak are unique. The anomalous fields from all of the coils are one third of the values indicated from the stability experiments. These results indicate limitations in the understanding of the interaction of the plasma with the external field. They indicate that it may not be possible to deduce the anomalous fields in a tokamak from plasma experiments and that we may not have the basis needed to project the error field requirements of future tokamaks.

17. The role of parallel and poloidal heat flux in setting the detachment threshold in DIII-D

Hill, D. N.; Allen, S. L.; Lasnier, C. J.; McLean, A. G.; Petrie, T. W.; Leonard, A. W.; Groth, M.

2014-10-01

Experimental results show that the threshold density for divertor detachment is reduced even as the parallel scrape-off-layer (SOL) heat flux (q| |) is more than doubled, contrary to expectation. The work is part of a systematic study to identify the physics basis for obtaining detached divertors in future high power burning plasma experiments, consistent with requirements for high confinement steady-state operation. Parallel heat flux [PSOL * (Btor /Bpol) / 2 πRλq ; λq is the SOL width] is independent of poloidal flux expansion and is commonly used to quantify the divertor heat flux challenge. In these experiments, the parallel heat flux was varied either by changing the heating power (thereby PSOL), plasma current (the SOL width), or toroidal field (the projection of PSOL onto Btor). The data point to poloidal-field physics effects (e.g., neutral penetration field, line length, and impurity radiation volume) playing a dominant role in setting the detachment threshold. Comparison with 2D simulation will be shown. Work supported by the US DOE under DE-AC52-07NA27344 and DE-FC02-04ER54698.

18. A volume birdcage coil with an adjustable sliding tuner ring for neuroimaging in high field vertical magnets: ex and in vivo applications at 21.1 T

PubMed Central

Qian, Chunqi; Masad, Ihssan S.; Rosenberg, Jens T.; Elumalai, Malathy; Brey, William W.; Grant, Samuel C.; Gor’kov, Peter L.

2012-01-01

A tunable 900 MHz transmit/receive volume coil was constructed for 1H MR imaging of biological samples in a 21.1 T vertical bore magnet. To accommodate a diverse range of specimen and RF loads at such a high frequency, a sliding-ring adaptation of a low-pass birdcage was implemented through simultaneous alteration of distributed capacitance. To make efficient use of the constrained space inside the vertical bore, a modular probe design was implemented with a bottom-adjustable tuning and matching apparatus. The sliding ring coil displays good homogeneity and sufficient tuning range for different samples of various dimensions representing large span of RF loads. High resolution in vivo and ex vivo images of large rats (up to 350 g), mice and human postmortem tissues were obtained to demonstrate coil functionality and to provide examples of potential applications at 21.1 T. PMID:22750638

19. Eight channel transmit array volume coil using on-coil radiofrequency current sources

PubMed Central

Kurpad, Krishna N.; Boskamp, Eddy B.

2014-01-01

Background At imaging frequencies associated with high-field MRI, the combined effects of increased load-coil interaction and shortened wavelength results in degradation of circular polarization and B1 field homogeneity in the imaging volume. Radio frequency (RF) shimming is known to mitigate the problem of B1 field inhomogeneity. Transmit arrays with well decoupled transmitting elements enable accurate B1 field pattern control using simple, non-iterative algorithms. Methods An eight channel transmit array was constructed. Each channel consisted of a transmitting element driven by a dedicated on-coil RF current source. The coil current distributions of characteristic transverse electromagnetic (TEM) coil resonant modes were non-iteratively set up on each transmitting element and 3T MRI images of a mineral oil phantom were obtained. Results B1 field patterns of several linear and quadrature TEM coil resonant modes that typically occur at different resonant frequencies were replicated at 128 MHz without having to retune the transmit array. The generated B1 field patterns agreed well with simulation in most cases. Conclusions Independent control of current amplitude and phase on each transmitting element was demonstrated. The transmit array with on-coil RF current sources enables B1 field shimming in a simple and predictable manner. PMID:24834418

20. Arrays of mutually coupled receiver coils: theory and application.

PubMed

Wright, S M; Magin, R L; Kelton, J R

1991-01-01

Specialized receiver coils having a small sensitive region can provide an improvement in SNR for MR imaging and spectroscopy, at the expense of limiting the usable field of view. This work presents a technique for designing coil arrays that allows the size and location of the sensitive region to be selected remotely. Only one element of the coil array is directly connected to the receiver, allowing flexibility in system design and implementation. A method is presented for the analysis and design of mutually coupled coil arrays of any number of elements of arbitrary shape. The analysis includes mutual coupling effects between primary coils, to allow multiple primary coils to be used simultaneously. A controller system allows remote selection of the sensitive region and automatically matches the impedance of the array to the preamplifier. Results obtained using a mutually coupled coil array designed for spine imaging are shown.

1. Commercial applications for COIL

Solomon, Wayne C.; Carroll, David L.; King, D. M.; Fockler, L. A.; Stromberg, D. S.; Sexauer, M.; Milmoe, A.; Sentman, Lee H.

2000-01-01

The chemical oxygen-iodine laser (COIL) is a high power, fiber deliverable tool, which can be used for a number of different industrial applications. COIL is of particular interest because of its short fiber deliverable wavelength, high scaleable continuous wave power, and excellent material interaction properties. In past research the University of Illinois at Urbana-Champaign identified and decommissioning and decontamination (DD) of nuclear facilities as a primary focus for COIL technology. DD will be a major challenge in the coming decades. The use of a robotically driven fiber delivered cutting/ablation tool in contaminated areas promises to lower risks to workers for the DD mission. Further, the high cutting speed of COIL will significantly reduce the time required to cut contaminated equipment, reducing costs. The high power of COIL will permit the dismantling of thick stacks of piping and equipment as well as reactor vessels. COIL is very promising for the removal of material from contaminated surfaces, perhaps to depths thicker than an inch. Laser cutting and ablation minimizes dust and fumes, which reduces the required number of high efficiency particulate accumulator filters, thus reducing costly waste disposal. Other potential industrial applications for COIL are shipbuilding, automotive manufacturing, heavy machinery manufacturing, tasks requiring underwater cutting or welding, and there appear to be very promising applications for high powers lasers in the oil industry.

2. Coil in coil - components for the high voltage superconducting resistive current limiter CULT 110

Elschner, S.; Stemmle, M.; Breuer, F.; Walter, H.; Frohne, C.; Noe, M.; Bock, J.

2008-02-01

The German government (BMBF/VDI) funded project CULT 110 is presently the largest European current limiter project and aims at the development of a one-phase resistive limiter for the voltage level of 110 kV. The contribution presents the actual state of development of the superconducting components. As in the successful predecessor project CURL 10 these are made of melt cast processed BSCCO 2212 bulk material, however monofilar instead of bifilar coils are used. The electrical protection concept is based on a normal conducting coil arranged around a superconducting coil and connected in parallel. Simultaneously this coil serves as an electrical bypass and, under fault conditions, generates a magnetic field for quench homogenisation. Since no continuously connected shunt is needed, a much higher voltage during faults can be applied. The rules for an optimum superconductor and coil design are given and the viability of the whole concept is demonstrated by both, experiment and numerical simulation.

3. [Development of RF coil of permanent magnet mini-magnetic resonance imager and mouse imaging experiments].

PubMed

Hou, Shulian; Xie, Huantong; Chen, Wei; Wang, Guangxin; Zhao, Qiang; Li, Shiyu

2014-10-01

In the development of radio frequency (RF) coils for better quality of the mini-type permanent magnetic resonance imager for using in the small animal imaging, the solenoid RF coil has a special advantage for permanent magnetic system based on analyses of various types.of RF coils. However, it is not satisfied for imaging if the RF coils are directly used. By theoretical analyses of the magnetic field properties produced from the solenoid coil, the research direction was determined by careful studies to raise further the uniformity of the magnetic field coil, receiving coil sensitivity for signals and signal-to-noise ratio (SNR). The method had certain advantages and avoided some shortcomings of the other different coil types, such as, birdcage coil, saddle shaped coil and phased array coil by using the alloy materials (from our own patent). The RF coils were designed, developed and made for keeled applicable to permanent magnet-type magnetic resonance imager, multi-coil combination-type, single-channel overall RF receiving coil, and applied for a patent. Mounted on three instruments (25 mm aperture, with main magnetic field strength of 0.5 T or 1.5 T, and 50 mm aperture, with main magnetic field strength of 0.48 T), we performed experiments with mice, rats, and nude mice bearing tumors. The experimental results indicated that the RF receiving coil was fully applicable to the permanent magnet-type imaging system.

4. Nonaxisymmetric field effects on Alcator C-Moda)

Wolfe, S. M.; Hutchinson, I. H.; Granetz, R. S.; Rice, J.; Hubbard, A.; Lynn, A.; Phillips, P.; Hender, T. C.; Howell, D. F.; La Haye, R. J.; Scoville, J. T.

2005-05-01

A set of external coils (A-coils) capable of producing nonaxisymmetric, predominantly n =1, fields with different toroidal phase and a range of poloidal mode m spectra has been used to determine the threshold amplitude for mode locking over a range of plasma parameters in Alcator C-Mod [I. H. Hutchinson, R. Boivin, F. Bombarda, P. Bonoli, S. Fairfax, C. Fiore, J. Goetz, S. Golovato, R. Granetz, M. Greenwald et al., Phys. Plasmas 1, 1511 (1994)]. The threshold perturbations and parametric scalings, expressed in terms of (B21/BT), are similar to those observed on larger, lower field devices. The threshold is roughly linear in density, with typical magnitudes of order 10-4. This result implies that locked modes should not be significantly more problematic for the International Thermonuclear Experimental Reactor [I. P. B. Editors, Nucl. Fusion 39, 2286 (1999)] than for existing devices. Coordinated nondimensional identity experiments on the Joint European Torus [Fusion Technol. 11, 13 (1987)], DIII-D [Fusion Technol. 8, 441 (1985)], and C-Mod, with matching applied mode spectra, have been carried out to determine more definitively the field and size scalings. Locked modes on C-Mod are observed to result in braking of core toroidal rotation, modification of sawtooth activity, and significant reduction in energy and particle confinement, frequently leading to disruptions. Intrinsic error fields inferred from the threshold studies are found to be consistent in amplitude and phase with a comprehensive model of the sources of field errors based on "as-built" coil and bus-work details and coil imperfections inferred from measurements using in situ magnetic diagnostics on dedicated test pulses. Use of the A-coils to largely cancel the 2/1 component of the intrinsic nonaxisymmetric field has led to expansion of the accessible operating space in C-Mod, including operation up to 2 MA plasma current at 8 T.

5. Two-dimensional MHD simulations of tokamak plasmas with poloidal flow

Hu, Bo; Betti, R.

2006-10-01

It has been shown [1] that, according to the ideal MHD equilibrium theory, poloidal flow in a tokamak can give rise to a pedestal structure with the pressure, density and velocity developing sharp discontinuities in their radial profiles. Such a pedestal arises when the poloidal velocity exceeds the poloidal sound speed. Since the poloidal sound speed vanishes at the separatrix, it is conceivable that evena rather slow poloidal flow can become transonic near the plasma edge, thus inducing a pedestal in the hydrodynamic profiles. While equilibrium calculations [1-4] of such a pedestal are well established, only a few two-dimensional time-dependent simulations have been carried out [5]. Here, we show the preliminary results from a two dimensional MHD code that simulates the formation of the pedestal starting from a poloidal velocity profile that becomes supersonic at the plasma edge. This work was supported by US-DOE under Contract DE-FG02-93ER54215. [1] Betti and Freidberg, Phys. Plasmas 7, 2439 (2000). [2] Guazzotto, Betti, Manickam and Kaye, Phys. Plasmas 11, 604 (2004). [3] Guazzotto and Betti, Phys. Plasmas 12, 056107 (2005). [4] Thyagaraja and McClements, Phys. Plasmas 13, 062502 (2006). [5] Gardiner, Betti and Guazzotto, Bull. Am. Phys. Soc. 46, No. 8, 166 (2001).

6. Coil spring venting arrangement

DOEpatents

McCugh, R.M.

1975-10-21

A simple venting device for trapped gas pockets in hydraulic systems is inserted through a small access passages, operated remotely, and removed completely. The device comprises a small diameter, closely wound coil spring which is pushed through a guide temporarily inserted in the access passage. The guide has a central passageway which directs the coil spring radially upward into the pocket, so that, with the guide properly positioned for depth and properly oriented, the coil spring can be pushed up into the top of the pocket to vent it. By positioning a seal around the free end of the guide, the spring and guide are removed and the passage is sealed.

7. ELECTRICAL COIL STRUCTURE

DOEpatents

Baker, W.R.; Hartwig, A.

1962-09-25

A compactly wound electrical coil is designed for carrying intense pulsed currents such as are characteristic of controlled thermonuclear reaction devices. A flat strip of conductor is tightly wound in a spiral with a matching flat strip of insulator. To provide for a high fluid coolant flow through the coil with minimum pumping pressure, a surface of the conductor is scored with parallel transverse grooves which form short longitudinal coolant pasaages when the conductor is wound in the spiral configuration. Owing to this construction, the coil is extremely resistant to thermal and magnetic shock from sudden high currents. (AEC)

8. Correction coil cable

DOEpatents

Wang, S.T.

1994-11-01

A wire cable assembly adapted for the winding of electrical coils is taught. A primary intended use is for use in particle tube assemblies for the Superconducting Super Collider. The correction coil cables have wires collected in wire array with a center rib sandwiched therebetween to form a core assembly. The core assembly is surrounded by an assembly housing having an inner spiral wrap and a counter wound outer spiral wrap. An alternate embodiment of the invention is rolled into a keystoned shape to improve radial alignment of the correction coil cable on a particle tube in a particle tube assembly. 7 figs.

9. Fast damping of poloidal Alfven waves by bounce-resonant ions: observations and modeling

Wang, C.; Rankin, R.; Sydorenko, D.; Zong, Q.

2015-12-01

Interplanetary shocks and solar wind dynamic pressure variations can excite intense ultra-low-frequency (ULF) waves in the inner magnetosphere. An analysis of two interplanetary shocks observed by Cluster on 7 November 2004 and 30 August 2001 shows that the poloidal waves excited in these events are damped away rapidly in tens of minutes. This damping is the result of wave-particle interactions involving H+ and O+ ions with energies in the range of several to a few tens of keV [Wang et al., J. Geophys. Res., 2015]. Damping is found to be more effective in the plasmasphere boundary layer due to the relatively higher proportion of Landau resonant ions that exists in that region. In the November 2004 shock event it has been suggested that energy-dispersed ions observed travelling parallel and anti-parallel direction to the geomagnetic field immediately after the shockare locally accelerated rather than originating from Earth's ionosphere. We use test-particle simulations to show that adiabatic advection of the particle differential flux caused bydrift-bounce-resonance with ULF waves is responsible for the energy-dispersed ions observed in these events. In the simulations,Liouville's theorem is used to reconstruct the iondistribution function and differential flux in a model dipole magnetosphere.It is shown that flux modulations of H and O ions can be reproduced when test-particle ions are advanced in the electric fields of the 3D ULF wave model we have developed.

10. Coil Knotting during Endovascular Coil Embolization for Ruptured MCA Aneurysm

PubMed Central

Kwon, S.C.; Lyo, I.U.; Shin, S.H.; Park, J.B.; Kim, Y.

2008-01-01

Summary Complications during coil embolization of cerebral aneurysms include thromboembolic events, hemorrhagic complications related to procedural aneurysmal rupture and parent vessel perforation, and coil-related complications. The present report describes a rare coil-related complication involving spontaneous coil knotting. PMID:20557732

11. A periodic table of coiled-coil protein structures.

PubMed

Moutevelis, Efrosini; Woolfson, Derek N

2009-01-23

Coiled coils are protein structure domains with two or more alpha-helices packed together via interlacing of side chains known as knob-into-hole packing. We analysed and classified a large set of coiled-coil structures using a combination of automated and manual methods. This led to a systematic classification that we termed a "periodic table of coiled coils," which we have made available at http://coiledcoils.chm.bris.ac.uk/ccplus/search/periodic_table. In this table, coiled-coil assemblies are arranged in columns with increasing numbers of alpha-helices and in rows of increased complexity. The table provides a framework for understanding possibilities in and limits on coiled-coil structures and a basis for future prediction, engineering and design studies.

12. Mitochondrial Proteins Containing Coiled-Coil-Helix-Coiled-Coil-Helix (CHCH) Domains in Health and Disease.

PubMed

Modjtahedi, Nazanine; Tokatlidis, Kostas; Dessen, Philippe; Kroemer, Guido

2016-03-01

Members of the coiled-coil-helix-coiled-coil-helix (CHCH) domain-containing protein family that carry (CX9C) type motifs are imported into the mitochondrion with the help of the disulfide relay-dependent MIA import pathway. These evolutionarily conserved proteins are emerging as new cellular factors that control mitochondrial respiration, redox regulation, lipid homeostasis, and membrane ultrastructure and dynamics. We discuss recent insights on the activity of known (CX9C) motif-carrying proteins in mammals and review current data implicating the Mia40/CHCHD4 import machinery in the regulation of their mitochondrial import. Recent findings and the identification of disease-associated mutations in specific (CX9C) motif-carrying proteins have highlighted members of this family of proteins as potential therapeutic targets in a variety of human disorders.

13. Enhancing Induction Coil Reliability

Kreter, K.; Goldstein, R.; Yakey, C.; Nemkov, V.

2014-12-01

In induction hardening, thermal fatigue is one of the main copper failure modes of induction heat treating coils. There have been papers published that describe this failure mode and others that describe some good design practices. The variables previously identified as the sources of thermal fatigue include radiation from the part surface, frequency, current, concentrator losses, water pressure and coil wall thickness. However, there is very little quantitative data on the factors that influence thermal fatigue in induction coils is available in the public domain. By using finite element analysis software this study analyzes the effect of common design variables of inductor cooling, and quantifies the relative importance of these variables. A comprehensive case study for a single shot induction coil with Fluxtrol A concentrator applied is used for the analysis.

14. Sextupole correction coils for SSC model dipoles

SciTech Connect

Rechen, J.B.; Gilbert, W.S.; Hassenzahl, W.V.

1985-05-01

Local correction of the sextupole error field is proposed for the dipoles of the SSC. This requirement is imposed on the design by the high field quality required both during injection at low fields and during colliding beam operation at high fields. Error fields in the main dipole windings due to superconductor magnetization and conductor misplacements and unwanted sextupole and decapole magnetic field terms. To correct the sextupole error field we have constructed sextupole coils made of a single layer of superconducting wire and have mounted them with high precision on the stainless steel bore tube. These correction coils have been operated with 1 meter long SSC model dipoles in both the self-powered and externally-powered modes. The sextupole field in the bore has been reduced by as much as a factor of 50. The level of correction depends strongly on the angular alignment of the correction coil with respect to the sextupole error field it is to correct. Results of tests, performance of the correction coils and alignment requirements for the system are presented.

15. Linear Rogowski coil

Nassisi, V.; Delle Side, D.

2017-02-01

Nowadays, the employment and development of fast current pulses require sophisticated systems to perform measurements. Rogowski coils are used to diagnose cylindrical shaped beams; therefore, they are designed and built with a toroidal structure. Recently, to perform experiments of radiofrequency biophysical stresses, flat transmission lines have been developed. Therefore, in this work we developed a linear Rogowski coil to detect current pulses inside flat conductors. The system is first approached by means of transmission line theory. We found that, if the pulse width to be diagnosed is comparable with the propagation time of the signal in the detector, it is necessary to impose a uniform current as input pulse, or to use short coils. We further analysed the effect of the resistance of the coil and the influence of its magnetic properties. As a result, the device we developed is able to record pulses lasting for some hundreds of nanoseconds, depending on the inductance, load impedance, and resistance of the coil. Furthermore, its response is characterized by a sub-nanosecond rise time (˜100 ps). The attenuation coefficient depends mainly on the turn number of the coil, while the fidelity of the response depends both on the magnetic core characteristics and on the current distribution along the plane conductors.

16. Linear Rogowski coil.

PubMed

Nassisi, V; Delle Side, D

2017-02-01

Nowadays, the employment and development of fast current pulses require sophisticated systems to perform measurements. Rogowski coils are used to diagnose cylindrical shaped beams; therefore, they are designed and built with a toroidal structure. Recently, to perform experiments of radiofrequency biophysical stresses, flat transmission lines have been developed. Therefore, in this work we developed a linear Rogowski coil to detect current pulses inside flat conductors. The system is first approached by means of transmission line theory. We found that, if the pulse width to be diagnosed is comparable with the propagation time of the signal in the detector, it is necessary to impose a uniform current as input pulse, or to use short coils. We further analysed the effect of the resistance of the coil and the influence of its magnetic properties. As a result, the device we developed is able to record pulses lasting for some hundreds of nanoseconds, depending on the inductance, load impedance, and resistance of the coil. Furthermore, its response is characterized by a sub-nanosecond rise time (∼100 ps). The attenuation coefficient depends mainly on the turn number of the coil, while the fidelity of the response depends both on the magnetic core characteristics and on the current distribution along the plane conductors.

17. Coiled transmission line pulse generators

DOEpatents

McDonald, Kenneth Fox

2010-11-09

Methods and apparatus are provided for fabricating and constructing solid dielectric "Coiled Transmission Line" pulse generators in radial or axial coiled geometries. The pour and cure fabrication process enables a wide variety of geometries and form factors. The volume between the conductors is filled with liquid blends of monomers, polymers, oligomers, and/or cross-linkers and dielectric powders; and then cured to form high field strength and high dielectric constant solid dielectric transmission lines that intrinsically produce ideal rectangular high voltage pulses when charged and switched into matched impedance loads. Voltage levels may be increased by Marx and/or Blumlein principles incorporating spark gap or, preferentially, solid state switches (such as optically triggered thyristors) which produce reliable, high repetition rate operation. Moreover, these Marxed pulse generators can be DC charged and do not require additional pulse forming circuitry, pulse forming lines, transformers, or an a high voltage spark gap output switch. The apparatus accommodates a wide range of voltages, impedances, pulse durations, pulse repetition rates, and duty cycles. The resulting mobile or flight platform friendly cylindrical geometric configuration is much more compact, light-weight, and robust than conventional linear geometries, or pulse generators constructed from conventional components. Installing additional circuitry may accommodate optional pulse shape improvements. The Coiled Transmission Lines can also be connected in parallel to decrease the impedance, or in series to increase the pulse length.

18. Underbalanced coiled tubing sidetrack successful

SciTech Connect

1995-12-18

The technique of drilling through a completion string, underbalanced, with coiled tubing eliminated some of the problems encountered with overbalanced drilling in a group of offset wells. This project confirmed that performing drilling operations in live wells can be carried out safely and effectively. Dalen is a sour gas field in the eastern part of The Netherlands and produces from vertical fractures in the Zechstein carbonate reservoir. The proposal for Dalen 2 was to abandon the lower section of the original hole and subsequently sidetrack conventionally to the top of the reservoir, run and cement a 5-in. liner, complete the well with a 5-in. monobore completion, and install the christmas tree. This part of the operation would be performed with a workover hoist. Thereafter, a 3 3/4-in. hole would be drilled through the completion and into the reservoir, underbalanced with coiled tubing. The drilling proposal had to address a number of key issues: creating underbalanced conditions; handling sour gas production at surface; handling and treating drilling fluids at surface; removing drilled solids from the returned fluid system; and deploying a long coiled tubing drilling bottom hole assembly (BHA) into a live well. The paper discusses planning, legislative issues, well preparation, the drilling program, and lessons learned.

19. Zero-plasma-current equilibria generated by tilted planar coils

Li, J.; Israeli, B.; Hammond, K. C.; Volpe, F. A.

2016-10-01

It is known that a periodic toroidal arrangement of tilted planar coils, combined with vertical field coils, can generate a helical magnetic field. One question, though, is: is this coil-set a generator or an amplifier of rotational transform? In other words, is a finite plasma-current needed? A numerical scan of coil-currents shows that configurations exist, for which no plasma-current is needed, and yet torsatron plasmas of finite volume can be obtained. The case of six tilted circular coils has been examined in great detail because of its relevance to the CIRCUS device operated by Columbia, a generalization of the two-tilted-coil CNT stellarator, also at Columbia. More axisymmetric configurations featuring a higher number of tilted circular coils are also being investigated. The calculations are performed with the aid of a numerical field-line tracer and the VMEC equilibrium solver, slightly modified to reflect the simplicity of the coil geometry: the coils are not discretized; instead, their field is evaluated by means of analytical expressions. This allows for faster calculations and rapid, fine scans of large parameter spaces.

20. Shaped magnetic field pulses by multi-coil repetitive transcranial magnetic stimulation (rTMS) differentially modulate anterior cingulate cortex responses and pain in volunteers and fibromyalgia patients

PubMed Central

2013-01-01

Background Repetitive transcranial magnetic stimulation (rTMS) has shown promise in the alleviation of acute and chronic pain by altering the activity of cortical areas involved in pain sensation. However, current single-coil rTMS technology only allows for effects in surface cortical structures. The ability to affect activity in certain deep brain structures may however, allow for a better efficacy, safety, and tolerability. This study used PET imaging to determine whether a novel multi-coil rTMS would allow for preferential targeting of the dorsal anterior cingulate cortex (dACC), an area always activated with pain, and to provide preliminary evidence as to whether this targeted approach would allow for efficacious, safe, and tolerable analgesia both in a volunteer/acute pain model as well as in fibromyalgia chronic pain patients. Methods Part 1: Different coil configurations were tested in a placebo-controlled crossover design in volunteers (N = 16). Tonic pain was induced using a capsaicin/thermal pain model and functional brain imaging was performed by means of H215O positron emission tomography – computed tomography (PET/CT) scans. Differences in NRS pain ratings between TMS and sham treatment (NRSTMS-NRSplacebo) which were recorded each minute during the 10 minute PET scans. Part 2: 16 fibromyalgia patients were subjected to 20 multi-coil rTMS treatments over 4 weeks and effects on standard pain scales (Brief Pain Inventory, item 5, i.e. average pain NRS over the last 24 hours) were recorded. Results A single 30 minute session using one of 3 tested rTMS coil configurations operated at 1 Hz consistently produced robust reduction (mean 70% on NRS scale) in evoked pain in volunteers. In fibromyalgia patients, the 20 rTMS sessions also produced a significant pain inhibition (43% reduction in NRS pain over last 24 hours), but only when operated at 10 Hz. This degree of pain control was maintained for at least 4 weeks after the final session

1. Analytic approach to the design of transverse gradient coils with co-axial return paths.

PubMed

Bowtell, R; Peters, A

1999-03-01

Transverse gradient coils with co-axial return paths offer reduced acoustic noise compared with standard cylindrical gradient coils, due to local force balancing, and can also easily be made to have a length to diameter ratio that is less than one. Analytic expressions for the magnetic field and vector potential generated by this type of coil are described here, along with a formula for calculating the coil inductance. It is shown that these expressions allow the implementation of powerful analytic methods of coil design, as well as the incorporation of active magnetic screening. It is also demonstrated how the mathematics specifies the best parameters to use when designing coils with small numbers of elements. A head gradient coil for use at 3.0 T has been designed using the analytic approach described here. The process of coil design and construction is outlined and the performance of the coil in comparison with a similar standard cylindrical coil is described.

2. Development of real-time rotating waveplate Stokes polarimeter using multi-order retardation for ITER poloidal polarimeter

SciTech Connect

Imazawa, R. Kawano, Y.; Ono, T.; Itami, K.

2016-01-15

The rotating waveplate Stokes polarimeter was developed for ITER (International Thermonuclear Experimental Reactor) poloidal polarimeter. The generalized model of the rotating waveplate Stokes polarimeter and the algorithm suitable for real-time field-programmable gate array (FPGA) processing were proposed. Since the generalized model takes into account each component associated with the rotation of the waveplate, the Stokes parameters can be accurately measured even in unideal condition such as non-uniformity of the waveplate retardation. Experiments using a He-Ne laser showed that the maximum error and the precision of the Stokes parameter were 3.5% and 1.2%, respectively. The rotation speed of waveplate was 20 000 rpm and time resolution of measuring the Stokes parameter was 3.3 ms. Software emulation showed that the real-time measurement of the Stokes parameter with time resolution of less than 10 ms is possible by using several FPGA boards. Evaluation of measurement capability using a far-infrared laser which ITER poloidal polarimeter will use concluded that measurement error will be reduced by a factor of nine.

3. Development of real-time rotating waveplate Stokes polarimeter using multi-order retardation for ITER poloidal polarimeter

Imazawa, R.; Kawano, Y.; Ono, T.; Itami, K.

2016-01-01

The rotating waveplate Stokes polarimeter was developed for ITER (International Thermonuclear Experimental Reactor) poloidal polarimeter. The generalized model of the rotating waveplate Stokes polarimeter and the algorithm suitable for real-time field-programmable gate array (FPGA) processing were proposed. Since the generalized model takes into account each component associated with the rotation of the waveplate, the Stokes parameters can be accurately measured even in unideal condition such as non-uniformity of the waveplate retardation. Experiments using a He-Ne laser showed that the maximum error and the precision of the Stokes parameter were 3.5% and 1.2%, respectively. The rotation speed of waveplate was 20 000 rpm and time resolution of measuring the Stokes parameter was 3.3 ms. Software emulation showed that the real-time measurement of the Stokes parameter with time resolution of less than 10 ms is possible by using several FPGA boards. Evaluation of measurement capability using a far-infrared laser which ITER poloidal polarimeter will use concluded that measurement error will be reduced by a factor of nine.

4. Phase and sensitivity of receiver coils in magnetic resonance imaging

PubMed Central

McVeigh, E. R.; Bronskill, M. J.; Henkelman, R. M.

2007-01-01

Receiver coil response is a major cause of nonuniformities in magnetic resonance images. The spatial dependence of the sensitivity and phase of single-saddle receiver coils has been investigated quantitatively by calculating the H1 field and comparing the results with measurements of a uniform phantom. Agreement between the measurements and calculations is excellent. A method is developed which corrects for both the nonuniform sensitivity and the phase shifts introduced by receiver coils. PMID:3796476

5. Coiled tubing technology advances to a bright future

SciTech Connect

Ghiselin, R.

1998-07-01

This supplement contains six short articles on coiled tubing, its advantages, performance, and materials. The articles are: Coiled Tubing--On the Brink of a New Millennium; CT Advances Promise a Broad, Dynamic Future; Performance, Safety and Cost Make the Case for HPCT; Fast and Accurate, CTD Helps Drillers Hit Their Targets; Composite Tubing Rapidly Proves Advantages in the Field; and People and Performance are Key to Coiled Tubing Growth.

6. Laminar flow effects in the coil planet centrifuge

NASA Technical Reports Server (NTRS)

Herrmann, F. T.

1984-01-01

The coil planet centrifuge designed by Ito employs flow of a single liquid phase, through a rotating coiled tube in a centrifugal force field, to provide a separation of particles based on sedimentation rates. Mathematical solutions are derived for the linear differential equations governing particle behavior in the coil planet centrifuge device. These solutions are then applied as the basis of a model for optimizing particle separations.

7. Linear and non-linear numerical simulations of poloidal Alfven waves

Ribeiro, A.

2013-05-01

Among the many of numerical simulations of MHD turbulence, few studies had been made of Alfven waves interacting with realistic boundaries. Thus, we have developed a novel hybrid spectral/finite element code, which is capable of simulate properly realistic boundaries properties. Our model is based on a Fourier decompositions of all variables in the azimuthal direction and on a finite element projection in the meridian plan. In order to simulate realistic boundary conditions for the magnetic field we solve the induction equation enforcing continuity of the magnetic field H at the interface with the external insulating medium through a Interior Penalty Galerkin method (IPG) [1]. I will present the results of our investigation of Alfven waves propagating in a cylinder filled of liquid metal submitted to an axial magnetic field. Poloidal Alfven waves are excited magnetically by imposing an azimuthal current pulse at the bottom of the cylinder. In the linear axisymmetric model we find a good agreement with previous experiments in liquid metals by Lundquist and by Lenhert and more recently by Alboussiere et al [2]. This axisymmetric study is extended to the non linear regime, where the amplitudes of the perturbations are comparable to the external applied magnetic field,in this conditions a complex response is found due to waves waves interactions. [1] J. L. Guermond, J.L Leorat, F. Luddens, C. Nore, A. Ribeiro. Effects of discontinuous magnetic permeability on magnetodynamic problems, Journal of Computational Physics Volume 230, Issue 16, 10 July 2011, Pages 6299 -- 6319. [2] T. Alboussiere, P. Cardin, F. Debray, H. C. Nataf, F. Plunian, A. Ribeiro, D. Schmitt, Experimental evidence of Alfven wave propagation in a Gallium alloy, Physics of fluids, 2011, vol. 23, nb 9.

8. Heterogeneous Superconducting Low-Noise Sensing Coils

NASA Technical Reports Server (NTRS)

Hahn, Inseob; Penanen, Konstantin I.; Ho Eom, Byeong

2008-01-01

A heterogeneous material construction has been devised for sensing coils of superconducting quantum interference device (SQUID) magnetometers that are subject to a combination of requirements peculiar to some advanced applications, notably including low-field magnetic resonance imaging for medical diagnosis. The requirements in question are the following: The sensing coils must be large enough (in some cases having dimensions of as much as tens of centimeters) to afford adequate sensitivity; The sensing coils must be made electrically superconductive to eliminate Johnson noise (thermally induced noise proportional to electrical resistance); and Although the sensing coils must be cooled to below their superconducting- transition temperatures with sufficient cooling power to overcome moderate ambient radiative heat leakage, they must not be immersed in cryogenic liquid baths. For a given superconducting sensing coil, this combination of requirements can be satisfied by providing a sufficiently thermally conductive link between the coil and a cold source. However, the superconducting coil material is not suitable as such a link because electrically superconductive materials are typically poor thermal conductors. The heterogeneous material construction makes it possible to solve both the electrical- and thermal-conductivity problems. The basic idea is to construct the coil as a skeleton made of a highly thermally conductive material (typically, annealed copper), then coat the skeleton with an electrically superconductive alloy (typically, a lead-tin solder) [see figure]. In operation, the copper skeleton provides the required thermally conductive connection to the cold source, while the electrically superconductive coating material shields against Johnson noise that originates in the copper skeleton.

SciTech Connect

Vazquez, F.; Solis, S. E.; Rodriguez, A. O.

2008-08-11

The RF coil arrays are an important part in Magnetic Resonance Imaging, since they are the main device for transmission and reception of the magnetic resonance signal. An RF coil array with a new configuration based on the Kepler's Lenten pretzel for the geocentric path of Mars is proposed in this work. The evenly distributed trajectories may serve as the basic configuration to form a coil array to adequately cover a region of interest for magnetic resonance experiments. The main goal is to investigate the electromagnetic properties of this coil array geometry to obtain an optimal design for its further construction. Hence, the electromagnetic properties of the coil array were numerical simulated using the finite element method and the quasi-static approach. Resulting simulations showed that there is an important concentration of magnetic field lines at the centre of the coil array. This is an advantage over other coil arrays where the magnetic field usually decreased at their geometrical centre. Both the electric and magnetic fields had also a very good uniformity. These characteristics made this coil design a good candidate for applications where the use of multi-coil technology is mandatory.

10. Superconductor coil geometry and ac losses

NASA Technical Reports Server (NTRS)

Pierce, T. V., Jr.; Zapata, R. N.

1976-01-01

An empirical relation is presented which allows simple computation of volume-averaged winding fields from central fields for coils of small rectangular cross sections. This relation suggests that, in certain applications, ac-loss minimization can be accomplished by use of low winding densities, provided that hysteresis losses are independent of winding density. The ac-loss measurements on coils wound of twisted multifilamentary composite superconductors show no significant dependence on ac losses on winding density, thus permitting the use of winding density as an independent design parameter in loss minimization.

11. Influence of the poloidal equilibrium flow and flow shear on the tearing mode instabilities in tokamak plasmas

Ming, Yue; Zhou, Deng

2017-01-01

The effect of the poloidal equilibrium flow and flow shear on the tearing mode instabilities for tokamak plasmas is investigated. The vorticity equation is derived and approximately solved for large poloidal mode numbers (m). Asymptotic matching of the inner solution to the outer solution can approximately give the classical tearing mode stability index Δ' . For typical plasma parameters with positive flow shear, we notice that the poloidal mean flows have a beneficial effect on the classical tearing mode and vice versa. To study the modes with arbitrary poloidal mode numbers, we numerically solve the vorticity equation for delta prime ( Δ' ) for typical plasma parameters with positive flow shear at the rational surface and the resulting Δ' with large m also decreases with increasing poloidal flow velocity, consistent with the approximate analytical large m results. Our numerical calculations indicate that the poloidal mean flow with positive flow shear has beneficial influence on the stabilization of classical tearing modes in tokamak plasmas.

12. Coiled coils and SAH domains in cytoskeletal molecular motors.

PubMed

Peckham, Michelle

2011-10-01

Cytoskeletal motors include myosins, kinesins and dyneins. Myosins move along tracks of actin filaments, whereas kinesins and dyneins move along microtubules. Many of these motors are involved in trafficking cargo in cells. However, myosins are mostly monomeric, whereas kinesins are mostly dimeric, owing to the presence of a coiled coil. Some myosins (myosins 6, 7 and 10) contain an SAH (single α-helical) domain, which was originally thought to be a coiled coil. These myosins are now known to be monomers, not dimers. The differences between SAH domains and coiled coils are described and the potential roles of SAH domains in molecular motors are discussed.

13. MRI surface-coil pair with strong inductive coupling.

PubMed

Mett, Richard R; Sidabras, Jason W; Hyde, James S

2016-12-01

A novel inductively coupled coil pair was used to obtain magnetic resonance phantom images. Rationale for using such a structure is described in R. R. Mett et al. [Rev. Sci. Instrum. 87, 084703 (2016)]. The original rationale was to increase the Q-value of a small diameter surface coil in order to achieve dominant loading by the sample. A significant improvement in the vector reception field (VRF) is also seen. The coil assembly consists of a 3-turn 10 mm tall meta-metallic self-resonant spiral (SRS) of inner diameter 10.4 mm and outer diameter 15.1 mm and a single-loop equalization coil of 25 mm diameter and 2 mm tall. The low-frequency parallel mode was used in which the rf currents on each coil produce magnetic fields that add constructively. The SRS coil assembly was fabricated and data were collected using a tissue-equivalent 30% polyacrylamide phantom. The large inductive coupling of the coils produces phase-coherency of the rf currents and magnetic fields. Finite-element simulations indicate that the VRF of the coil pair is about 4.4 times larger than for a single-loop coil of 15 mm diameter. The mutual coupling between coils influences the current ratio between the coils, which in turn influences the VRF and the signal-to-noise ratio (SNR). Data on a tissue-equivalent phantom at 9.4 T show a total SNR increase of 8.8 over the 15 mm loop averaged over a 25 mm depth and diameter. The experimental results are shown to be consistent with the magnetic resonance theory of the emf induced by spins in a coil, the theory of inductively coupled resonant circuits, and the superposition principle. The methods are general for magnetic resonance and other types of signal detection and can be used over a wide range of operating frequencies.

14. TEM transmission line coil with double nuclear capability.

PubMed

Erickson, Matthew G; Kurpad, Krishna N; Holmes, James H; Fain, Sean B

2007-10-01

MR imaging and spectroscopy requires RF fields of high homogeneity. Quadrature volume coils meeting this requirement include the birdcage coil and the TEM resonator. We describe here a quadrature volume coil designed around a modified coaxial transmission line in which multiple inner conductors are arrayed on a circular perimeter and surrounded by a common shield. Current antinodes are established at appropriate points on the inner conductors by series transmission line stubs, either open circuit or short circuit, which terminate the line. Quadrature phasing is generated by a novel circuit constructed from a pair of high-performance current baluns and a commercial quadrature hybrid. The coil is a "pure" TEM coil as it is simply a resonant transmission line. There is no mode structure to consider. The construction of a prototype quadrature four-element coil is described and preliminary test results from this coil in a 4.7T horizontal bore magnet are reported. A related double nuclear coil design for (3)He and (1)H in which two linear transmission line coils are arrayed on a circular perimeter and simultaneously tuned and matched to their respective frequencies is also described. Preliminary tests from this coil in a 1.5T clinical scanner are reported.

15. Modelling plasma response to RMP fields in ASDEX Upgrade with varying edge safety factor and triangularity

Li, L.; Liu, Y. Q.; Kirk, A.; Wang, N.; Liang, Y.; Ryan, D.; Suttrop, W.; Dunne, M.; Fischer, R.; Fuchs, J. C.; Kurzan, B.; Piovesan, P.; Willensdorfer, M.; Zhong, F. C.; the ASDEX Upgrade Team; the EUROfusion MST1 Team

2016-12-01

Toroidal computations are performed using the MARS-F code (Liu et al 2000 Phys. Plasmas 7 3681), in order to understand correlations between the plasma response and the observed mitigation of the edge localized modes (ELM) using resonant magnetic perturbation fields in ASDEX Upgrade. In particular, systematic numerical scans of the edge safety factor reveal that the amplitude of the resonant poloidal harmonic of the response radial magnetic field near the plasma edge, as well as the plasma radial displacement near the X-point, can serve as good indicators for predicting the optimal toroidal phasing between the upper and lower rows of coils in ASDEX Upgrade. The optimal coil phasing scales roughly linearly with the edge safety factor {{q}95} , for various choices of the toroidal mode number n  =  1-4 of the coil configuration. The optimal coil phasing is also predicted to vary with the upper triangularity of the plasma shape in ASDEX Upgrade. Furthermore, multiple resonance effects of the plasma response, with continuously varying {{q}95} , are computationally observed and investigated.

16. Compact stellarators with modular coils.

PubMed

Garabedian, P R

2000-07-18

Compact stellarator designs with modular coils and only two or three field periods are now available; these designs have both good stability and quasiaxial symmetry providing adequate transport for a magnetic fusion reactor. If the bootstrap current assumes theoretically predicted values a three field period configuration is optimal, but if that net current turns out to be lower, a device with two periods and just 12 modular coils might be better. There are also attractive designs with quasihelical symmetry and four or five periods whose properties depend less on the bootstrap current. Good performance requires that there be a satisfactory magnetic well in the vacuum field, which is a property lacking in a stellarator-tokamak hybrid that has been proposed for a proof of principle experiment. In this paper, we present an analysis of stability for these configurations that is based on a mountain pass theorem asserting that, if two solutions of the problem of magnetohydrodynamic equilibrium can be found, then there has to be an unstable solution. We compare results of our theory of equilibrium, stability, and transport with recently announced measurements from the large LHD experiment in Japan.

17. Compact stellarators with modular coils

PubMed Central

Garabedian, P. R.

2000-01-01

Compact stellarator designs with modular coils and only two or three field periods are now available; these designs have both good stability and quasiaxial symmetry providing adequate transport for a magnetic fusion reactor. If the bootstrap current assumes theoretically predicted values a three field period configuration is optimal, but if that net current turns out to be lower, a device with two periods and just 12 modular coils might be better. There are also attractive designs with quasihelical symmetry and four or five periods whose properties depend less on the bootstrap current. Good performance requires that there be a satisfactory magnetic well in the vacuum field, which is a property lacking in a stellarator-tokamak hybrid that has been proposed for a proof of principle experiment. In this paper, we present an analysis of stability for these configurations that is based on a mountain pass theorem asserting that, if two solutions of the problem of magnetohydrodynamic equilibrium can be found, then there has to be an unstable solution. We compare results of our theory of equilibrium, stability, and transport with recently announced measurements from the large LHD experiment in Japan. PMID:10899993

18. Measuring the orthogonality error of coil systems

USGS Publications Warehouse

Heilig, B.; Csontos, A.; Pajunpää, K.; White, Tim; St. Louis, B.; Calp, D.

2012-01-01

Recently, a simple method was proposed for the determination of pitch angle between two coil axes by means of a total field magnetometer. The method is applicable when the homogeneous volume in the centre of the coil system is large enough to accommodate the total field sensor. Orthogonality of calibration coil systems used for calibrating vector magnetometers can be attained by this procedure. In addition, the method can be easily automated and applied to the calibration of delta inclination–delta declination (dIdD) magnetometers. The method was tested by several independent research groups, having a variety of test equipment, and located at differing geomagnetic observatories, including: Nurmijärvi, Finland; Hermanus, South Africa; Ottawa, Canada; Tihany, Hungary. This paper summarizes the test results, and discusses the advantages and limitations of the method.

19. Aneurysm permeability following coil embolization: packing density and coil distribution

PubMed Central

Chueh, Ju-Yu; Vedantham, Srinivasan; Wakhloo, Ajay K; Carniato, Sarena L; Puri, Ajit S; Bzura, Conrad; Coffin, Spencer; Bogdanov, Alexei A; Gounis, Matthew J

2015-01-01

Background Rates of durable aneurysm occlusion following coil embolization vary widely, and a better understanding of coil mass mechanics is desired. The goal of this study is to evaluate the impact of packing density and coil uniformity on aneurysm permeability. Methods Aneurysm models were coiled using either Guglielmi detachable coils or Target coils. The permeability was assessed by taking the ratio of microspheres passing through the coil mass to those in the working fluid. Aneurysms containing coil masses were sectioned for image analysis to determine surface area fraction and coil uniformity. Results All aneurysms were coiled to a packing density of at least 27%. Packing density, surface area fraction of the dome and neck, and uniformity of the dome were significantly correlated (p<0.05). Hence, multivariate principal components-based partial least squares regression models were used to predict permeability. Similar loading vectors were obtained for packing and uniformity measures. Coil mass permeability was modeled better with the inclusion of packing and uniformity measures of the dome (r2=0.73) than with packing density alone (r2=0.45). The analysis indicates the importance of including a uniformity measure for coil distribution in the dome along with packing measures. Conclusions A densely packed aneurysm with a high degree of coil mass uniformity will reduce permeability. PMID:25031179

20. Design and optimization of efficient magnetic coils for biomedical applications

Ram Rakhyani, Anil Kumar

Magnetic fields are permeable to the biological tissues and can induce electric field in the conductive structures. Some medical devices take advantage of this ability to transfer energy from the source to the receiving site without direct contact. Prosthetic devices such as retinal implants use time-varying magnetic field to achieve wireless power transfer to the implanted magnetic coil. However, devices such as magnetic stimulators use the induction principle to create an electric field at the stimulation site. Efficiency of these devices is primarily dependent on the design of the magnetic coils. Therefore, in this work, we designed and validated efficient magnetic coils for wireless power transfer to implanted devices and magnetic stimulation of the peripheral nerves. Typical wireless power transfer (WPT) systems uses two-coil based design to achieve contactless power transfer to the implanted electronics. These systems achieve low power transfer efficiency (< 30%) and frequency bandwidth. Moreover, efficient wireless system requires high coupling and load variation tolerance during device operation. To design an electromagnetic safe WPT system, the power absorbed by the tissue and radiated field due to the proximal magnetic coils needs to be minimized. In this work, we proposed a multi-coil power transfer system which solves some of the current challenges. The proposed multi-coil WPT system achieves more than twice the power transfer efficiency, controllable voltage gain, wider frequency bandwidth, higher tolerance to coupling and load variations, lower absorbed power in the tissue and lower radiated field from the magnetic coil than a comparable two-coil system. In this work, we have developed analytic models of the multi-coil WPT system and validated the accuracy of the solutions using experiments. Magnetic coils play an important role in controlling the distribution of induced electric field inside the nerve during magnetic stimulation. In the past

1. Correction coil cable

DOEpatents

Wang, Sou-Tien

1994-11-01

A wire cable assembly (10, 310) adapted for the winding of electrical coils is taught. A primary intended use is for use in particle tube assemblies (532) for the superconducting super collider. The correction coil cables (10, 310) have wires (14, 314) collected in wire arrays (12, 312) with a center rib (16, 316) sandwiched therebetween to form a core assembly (18, 318 ). The core assembly (18, 318) is surrounded by an assembly housing (20, 320) having an inner spiral wrap (22, 322) and a counter wound outer spiral wrap (24, 324). An alternate embodiment (410) of the invention is rolled into a keystoned shape to improve radial alignment of the correction coil cable (410) on a particle tube (733) in a particle tube assembly (732).

2. Coiled tubing drilling requires economic and technical analyses

SciTech Connect

Gary, S.C. )

1995-02-20

Field experience has proven that coiled tubing drilling is a technical and economic option on some wells; however, coiled tubing drilling is not the solution to every drilling prospect or production-enhancement job. To determine if coiled tubing drilling is viable, the geographic, technical, and economic aspects of each project must be considered in detail. Generally, with some limitations, coiled tubing drilling is feasible primarily when jointed pipe cannot be used effectively. Also, coiled tubing drilling may be more appropriate because of some special well site requirements, such as environmental regulations requiring less surface disturbance. The paper discusses technical considerations which need to be considered, economic feasibility, limitations of well types (new shallow wells, conventional reentry, through-tubing reentry, and underbalanced drilling), and outlook for further growth in the coiled tubing drilling industry.

3. Performance verification tests of JT-60SA CS model coil

Obana, Tetsuhiro; Murakami, Haruyuki; Takahata, Kazuya; Hamaguchi, Shinji; Chikaraishi, Hirotaka; Mito, Toshiyuki; Imagawa, Shinsaku; Kizu, Kaname; Natsume, Kyohei; Yoshida, Kiyoshi

2015-11-01

As a final check of the coil manufacturing method of the JT-60 Super Advanced (JT-60SA) central solenoid (CS), we verified the performance of a CS model coil. The model coil comprised a quad-pancake wound with a Nb3Sn cable-in-conduit conductor. Measurements of the critical current, joint resistance, pressure drop, and magnetic field were conducted in the verification tests. In the critical-current measurement, the critical current of the model coil coincided with the estimation derived from a strain of -0.62% for the Nb3Sn strands. As a result, critical-current degradation caused by the coil manufacturing process was not observed. The results of the performance verification tests indicate that the model coil met the design requirements. Consequently, the manufacturing process of the JT-60SA CS was established.

4. Parametric Study of HTS Coil Quench Protection Strategies

Seibert, Joseph; Zarnstorff, Michael; Zhai, Yuhu

2016-10-01

Next generation fusion devices require high magnetic fields to adequately contain burning plasmas. Use of high temperature superconducting (HTS) coils to generate these magnetic fields would lower energy cost of operation as well as increase stability of the superconducting state compared to low temperature superconducting coils. However, use of HTS coils requires developing quench protection strategies to prevent damage to the coils. One technique involves the utilization of copper discs and other conductors mutually coupled to the HTS coil to quickly extract the current from the coil. Another technique allows conduction between HTS turns to reduce the current in the coil during quench. This project describes a parametric study of the HTS coil and resistive-conductor setup in order to determine limiting cases of the geometry in an attempt to optimize current extraction and coil protection during quench scenarios. This work was supported in part by the U.S. Department of Energy, Office of Science, Office of Workforce Development for Teachers and Scientists (WDTS) under the Science Undergraduate Laboratory Internship (SULI) program.

5. TESLA Coil Research

DTIC Science & Technology

1992-05-01

Sloan’s work was actually predated by the earlier work of Nikola Tesla . Sloan mistakenly identified " Tesla Coils" as lumped tuned resonators. The...Lefvw WsnJ L REPORT o]i 3. REPRT TYPE AND OATES COVEIRD May 1992 Special/Aug 1992 - May 1992 Z TITLE AND 5U§nUT S. FUNDING NUMIHRS Tesla Coil Research...STATEMENT 1211. ’ISTRIUUTION COOD Approved for public release; dis~ribution is unlimited 13. ABSTRACT (Masrmum 200 worw) High repetition rate Tesla

6. Meiosis specific coiled-coil proteins in Shizosaccharomyces pombe.

PubMed

Ohtaka, Ayami; Saito, Takamune T; Okuzaki, Daisuke; Nojima, Hiroshi

2007-05-18

Many meiosis-specific proteins in Schizosaccharomyces pombe contain coiled-coil motifs which play essential roles for meiotic progression. For example, the coiled-coil motifs present in Meu13 and Mcp7 are required for their function as a putative recombinase cofactor complex during meiotic recombination. Mcp6/Hrs1 and Mcp5/Num1 control horsetail chromosome movement by astral microtubule organization and anchoring dynein respectively. Dhc1 and Ssm4 are also required for horsetail chromosome movement. It is clear from these examples that the coiled-coil motif in these proteins plays an important role during the progression of cells through meiosis. However, there are still many unanswered questions on how these proteins operate. In this paper, we briefly review recent studies on the meiotic coiled-coil proteins in Sz. pombe.

7. Meiosis specific coiled-coil proteins in Shizosaccharomyces pombe

PubMed Central

Ohtaka, Ayami; Saito, Takamune T; Okuzaki, Daisuke; Nojima, Hiroshi

2007-01-01

Many meiosis-specific proteins in Schizosaccharomyces pombe contain coiled-coil motifs which play essential roles for meiotic progression. For example, the coiled-coil motifs present in Meu13 and Mcp7 are required for their function as a putative recombinase cofactor complex during meiotic recombination. Mcp6/Hrs1 and Mcp5/Num1 control horsetail chromosome movement by astral microtubule organization and anchoring dynein respectively. Dhc1 and Ssm4 are also required for horsetail chromosome movement. It is clear from these examples that the coiled-coil motif in these proteins plays an important role during the progression of cells through meiosis. However, there are still many unanswered questions on how these proteins operate. In this paper, we briefly review recent studies on the meiotic coiled-coil proteins in Sz. pombe. PMID:17509158

8. New directions in the design of MRI gradient coils

Baig, Tanvir Noor

9. Method and apparatus for magnetic resonance imaging and spectroscopy using microstrip transmission line coils

DOEpatents

Zhang, Xiaoliang; Ugurbil, Kamil; Chen, Wei

2006-04-04

Apparatus and method for MRI imaging using a coil constructed of microstrip transmission line (MTL coil) are disclosed. In one method, a target is positioned to be imaged within the field of a main magnetic field of a magnet resonance imaging (MRI) system, a MTL coil is positioned proximate the target, and a MRI image is obtained using the main magnet and the MTL coil. In another embodiment, the MRI coil is used for spectroscopy. MRI imaging and spectroscopy coils are formed using microstrip transmission line. These MTL coils have the advantageous property of good performance while occupying a relatively small space, thus allowing MTL coils to be used inside restricted areas more easily than some other prior art coils. In addition, the MTL coils are relatively simple to construct of inexpensive components and thus relatively inexpensive compared to other designs. Further, the MTL coils of the present invention can be readily formed in a wide variety of coil configurations, and used in a wide variety of ways. Further, while the MTL coils of the present invention work well at high field strengths and frequencies, they also work at low frequencies and in low field strengths as well.

10. E × B flow velocity deduced from the poloidal motion of fluctuation patterns in neutral beam injected L-mode plasmas on KSTAR

Lee, W.; Leem, J.; Yun, G. S.; Park, H. K.; Ko, S. H.; Choi, M. J.; Wang, W. X.; Budny, R. V.; Ethier, S.; Park, Y. S.; Luhmann, N. C.; Domier, C. W.; Lee, K. D.; Ko, W. H.; Kim, K. W.

2016-05-01

A method for direct assessment of the equilibrium E × B flow velocity ( E ×B flow shear is responsible for the turbulence suppression and transport reduction in tokamak plasmas) is investigated based on two facts. The first one is that the apparent poloidal rotation speed of density fluctuation patterns is close to the turbulence rotation speed in the direction perpendicular to the local magnetic field line within the flux surface. And the second "well-known" fact is that the turbulence rotation velocity consists of the equilibrium E × B flow velocity and intrinsic phase velocity of turbulence in the E × B flow frame. In the core region of the low confinement (L-mode) discharges where a strong toroidal rotation is induced by neutral beam injection, the apparent poloidal velocities (and turbulence rotation velocities) are good approximations of the E ×B flow velocities since linear gyrokinetic simulations suggest that the intrinsic phase velocity of the dominant turbulence is significantly lower than the apparent poloidal velocity. In the neutral beam injected L-mode plasmas, temporal and spatial scales of the measured turbulence are studied by comparing with the local equilibrium parameters relevant to the ion-scale turbulence.

11. Coil planet centrifugation as a means for small particle separation

NASA Technical Reports Server (NTRS)

Herrmann, F. T.

1983-01-01

The coil planet centrifuge uses a centrifugal force field to provide separation of particles based on differences in sedimentation rates by flow through a rotating coiled tube. Three main separations are considered: (1) single phase fresh sheep and human erythrocytes, (2) single phase fixed heep and human erythrocytes, and (3) electrophoretically enhanced single phase fresh sheep and human erythrocytes.

12. Poloidal flow and toroidal particle ring formation in a sessile drop driven by megahertz order vibration.

PubMed

Rezk, Amgad R; Yeo, Leslie Y; Friend, James R

2014-09-23

Poloidal flow is curiously formed in a microliter sessile water drop over 157-225 MHz because of acoustic streaming from three-dimensional standing Lamb waves in a lithium niobate substrate. The flow possesses radial symmetry with downwelling at the center and upwelling around the periphery of the drop. Outside this frequency range, the attenuation occurs over a length scale incompatible with the drop size and the poloidal flow vanishes. Remarkably, shear-induced migration was found to drive toroidal particle ring formation with diameters inversely proportional to the frequency of the acoustic irradiation.

13. Performance correlation between YBa2Cu3O7-δ coils and short samples for coil technology development

Wang, X.; Dietderich, D. R.; Godeke, A.; Gourlay, S. A.; Marchevsky, M.; Prestemon, S. O.; Sabbi, G. L.

2016-06-01

A robust fabrication technology is critical to achieve the high performance in YBa2Cu3O{}7-δ (YBCO) coils as the critical current of the brittle YBCO layer is subject to the strain-induced degradation during coil fabrication. The expected current-carrying capability of the magnet and its temperature dependence are two key inputs to the coil technology development. However, the expected magnet performance is not straightforward to determine because the short-sample critical current depends on both the amplitude and orientation of the applied magnetic field with respect to the broad surface of the tape-form conductor. In this paper, we present an approach to calculate the self-field performance limit for YBCO racetrack coils at 77 and 4.2 K. Critical current of short YBCO samples was measured as a function of the applied field perpendicular to the conductor surface from 0 to 15 T. This field direction limited the conductor critical current. Two double-layer racetrack coils, one with three turns and the other with 10 turns, were wound and tested at 77 and 4.2 K. The test coils reached at least 80% of the expected critical current. The ratio between the coil critical currents at 77 and 4.2 K agreed well with the calculation. We conclude that the presented approach can determine the performance limit in YBCO racetrack coils based on the short-sample critical current and provide a useful guideline for assessing the coil performance and fabrication technology. The correlation of the coil critical current between 77 K and 4.2 K was also observed, allowing the 77 K test to be a cost-effective tool for the development of coil technology.

14. Coiled coil interactions for the targeting of liposomes for nucleic acid delivery

Oude Blenke, Erik E.; van den Dikkenberg, Joep; van Kolck, Bartjan; Kros, Alexander; Mastrobattista, Enrico

2016-04-01

encapsulating a splice correcting oligonucleotide or siRNA. These peptide-functionalized vesicles are highly stable in solution but start to cluster when vesicles modified with complementary peptides are mixed together, demonstrating that the peptides quickly coil and crosslink the vesicles. When one of the peptides was anchored to the cell membrane using a hydrophobic cholesterol anchor, vesicles functionalized with the complementary peptide could be docked to these cells, whereas non-functionalized cells did not show any vesicle tethering. Although the anchored peptides do not have a downstream signaling pathway, microscopy pictures revealed that after four hours, the majority of the docked vesicles were internalized by endocytosis. Finally, for the first time, it was shown that the coiled coil assembly at the interface between the vesicles and the cell membrane induces active uptake and leads to cytosolic delivery of the nucleic acid cargo. Both the siRNA and the splice correcting oligonucleotide were functionally delivered, resulting respectively in the silencing or recovery of luciferase expression in the appropriate cell lines. These results demonstrate that the docking to the cell by coiled coil interaction can induce active uptake and achieve the successful intracellular delivery of otherwise membrane impermeable nucleic acids in a highly specific manner. Electronic supplementary information (ESI) available: Two videos of the experiment are shown in Fig. 5, demonstrating the distinctive characteristics of the peptide pair in a mixed population of cells are available in online. Video S1 shows the experiment in the bright field channel including the green channel (calcein-AM stained unfunctionalized cells) and orange channel (rhodamine labeled liposomes). Video S2 shows the exact same frames but combining the fluorescent channels only, including the blue channel for Hoechst nuclear staining. Both videos consist of 31 frames at a frame rate of 5 fps. The labeled liposomes

15. An orientable search coil

Holt, P. J.; Poblocki, M.

2017-01-01

We provide a design for a low cost orientable search coil that can be used to investigate the variation of magnetic flux with angle. This experiment is one of the required practical activities in the current A level physics specification for the AQA examination board in the UK. We demonstrate its performance and suggest other suitable investigations that can be undertaken.

16. Imprinted Clay Coil Vessels

ERIC Educational Resources Information Center

Lohr, Tresa Rae

2006-01-01

The author teaches clay vessel construction in the fifth grade, and it is amazing what can be accomplished in one forty-five minute period when the expectations are clarified in the initial lesson. The author introduces clay coil vessels with a discussion of the sources of clay and how clay relates to fifth-grade science curriculum concepts such…

17. Pulse Test of Coil Insulation

NASA Technical Reports Server (NTRS)

Kroy, Ralph E.

1987-01-01

Waveform of back-electromotive force reveals defects. Simple pulse test reveals defects in inductor coils. Devised for use on servovalve solenoid coils on Space Shuttle, test also applicable to transformer windings, chokes, relays, and the like.

18. Optimization of the detection coil of high-Tc superconducting quantum interference device-based nuclear magnetic resonance for discriminating a minimum amount of liver tumor of rats in microtesla fields

Chen, Hsin-Hsien; Huang, Kai-Wen; Yang, Hong-Chang; Horng, Herng-Er; Liao, Shu-Hsien

2013-08-01

This study presents an optimization of the detection coil of high-Tc superconducting quantum interference device (SQUID)-based nuclear magnetic resonance (NMR) in microtesla fields for discriminating a minimum amount of liver tumor in rats by characterizing the longitudinal relaxation rate, T1-1, of tested samples. The detection coil, which was coupled to the SQUID through a flux transformer, was optimized by varying the copper wires' winding turns and diameters. When comparing the measured NMR signals, we found that the simulated NMR signal agrees with simulated signals. When discriminating liver tumors in rats, the averaged longitudinal relaxation rate was observed to be T1-1 = 3.3 s-1 for cancerous liver tissue and T1-1 = 6.6 s-1 for normal liver tissue. The results suggest that it can be used to successfully discriminate cancerous liver tissue from normal liver tissues in rats. The minimum amount of samples that can be detected is 0.2 g for liver tumor and 0.4 g for normal liver tissue in 100 μT fields. The specimen was not damaged; it can be used for other pathological analyses. The proposed method provides more possibilities for examining undersized specimens.

19. Anomalous toroidal field penetration in Tormac V

SciTech Connect

Feinberg, B.; Vaucher, B. G.; Shaw, R. S.; Vella, M. C.

1981-07-01

We investigate magnetic field penetration into a cool, collisional, magnetized plasma in Tormac V. Magnetic probe and laser interferometer studies reveal anomalous penetration of the applied toroidal field into a plasma with an initial parallel bias toroidal field. The applied poloidal field, however, formed a well-defined magnetic front which was effective at sweeping up particles. Lastly, strong shear in the vacuum magnetic field does not inhibit the apparent decoupling of the applied toroidal field from the applied poloidal field.

20. Coiled-tubing applications for blowout-control operations

SciTech Connect

Adams, N.J.; Mack, S.K.; Fannin, V.R.; Rocchi, T.

1996-05-01

Coiled-tubing drilling is now being used in various operations. Its complete field of applications is not currently established. Coiled tubing used for well control while drilling is a new field where its limits are being explored. This paper provides guidelines on topics to be considered in determining the applicability of coiled tubing for well-control problems. The information provided is based on recent field experiences with several well-control problems when drilling vent and relief wells. In some cases, coiled-tubing drilling capabilities, by necessity, were significantly extended beyond levels the industry considered to be upper limits. Well control cannot always be handled by coiled tubing. It is a special-application tool that can handle many situations and is, in some cases, clearly the optimum choice for the application. This paper presents guidelines for selecting coiled tubing for each application and discusses economics. It also describes coiled-tubing operations for regaining control of blowout wells in certain situations and gives technical requirements for planning and executing these types of jobs. Case histories where coiled-tubing units (CTUs) have been used to regain control of drilling and producing wells are provided for illustration.

1. Parametric design of tri-axial nested Helmholtz coils

SciTech Connect

Abbott, Jake J.

2015-05-15

This paper provides an optimal parametric design for tri-axial nested Helmholtz coils, which are used to generate a uniform magnetic field with controllable magnitude and direction. Circular and square coils, both with square cross section, are considered. Practical considerations such as wire selection, wire-wrapping efficiency, wire bending radius, choice of power supply, and inductance and time response are included. Using the equations provided, a designer can quickly create an optimal set of custom coils to generate a specified field magnitude in the uniform-field region while maintaining specified accessibility to the central workspace. An example case study is included.

2. Parametric design of tri-axial nested Helmholtz coils.

PubMed

Abbott, Jake J

2015-05-01

This paper provides an optimal parametric design for tri-axial nested Helmholtz coils, which are used to generate a uniform magnetic field with controllable magnitude and direction. Circular and square coils, both with square cross section, are considered. Practical considerations such as wire selection, wire-wrapping efficiency, wire bending radius, choice of power supply, and inductance and time response are included. Using the equations provided, a designer can quickly create an optimal set of custom coils to generate a specified field magnitude in the uniform-field region while maintaining specified accessibility to the central workspace. An example case study is included.

3. Wet Winding Improves Coil Encapsulation

NASA Technical Reports Server (NTRS)

Hill, A. J.

1987-01-01

Wet-winding process encapsulates electrical coils more uniformily than conventional processes. Process requires no vacuum pump and adapts easily to existing winding machines. Encapsulant applied to each layer of wire as soon as added to coil. Wet-winding process eliminates voids, giving more uniformly encapsulated coil.

4. ECH Plasma Experiments on an Internal Coil Device with a High Temperature Superconductor Coil

SciTech Connect

Ogawa, Yuichi; Morikawa, Junji; Ohkuni, Kotaro; Yamakoshi, Shigeo; Goto, Takuya; Mito, Toshiyuki; Yanagi, Nagato; Iwakuma, Masataka

2005-01-15

Self-organization related with relaxation phenomenon is playing an important role in various aspects of magnetic confined plasmas. Recently a relaxation theory including the plasma flow has been developed by Mahajan-Yoshida, and a new relaxation state has been identified. The two-fluid relaxation condition is given by {beta} + (V/V{sub A}){sup 2} = const. To study a self-organized structure with strong plasma flow, we have introduced an internal coil device. By inducing a radial electric field with appropriate methods, we could drive a toroidal plasma flow, and confine a high beta plasma in a core region. The internal coil device Mini-RT with a high temperature superconductor(HTS) coil(Rc=0.15m, Ic=50kA) has been constructed. The vacuum chamber is 1 m in diameter and {approx}0.7 m in height. The magnetic field strength near the internal coil is around 0.1 T, and a radio-frequency wave of 2.45 GHz is applied for the plasma production. We have started ECH plasma experiments with the coil supported mechanically. The electron density, which has a peak near the internal coil, is of order 10{sup 16} m{sup -3}, reaching the cut-off density of the microwave. While, the electron temperature is of order 10 eV with a broad profile. Estimated energy confinement time is of order 10{sup -(5-6)} sec. The levitation experiment of the HTS coil has been carried out. The position of the HTS coil is measured with laser sensors, and is feedback-controlled with the levitation coil current. We have succeeded to levitating the HTS coil during one hour with an accuracy of less than 20 {omega}m. A preliminary experiment for the plasma production at the floating condition of the HTS coil has been initiated. It is affirmed that the levitation system works well and plasma with separatrix configuration is produced.

5. Coupled wave model for large magnet coils

NASA Technical Reports Server (NTRS)

Gabriel, G. J.

1980-01-01

A wave coupled model based on field theory is evolved for analysis of fast electromagnetic transients on superconducting coils. It is expected to play a useful role in the design of protection methods against damage due to high voltages or any adverse effects that might arise from unintentional transients. The significant parameters of the coil are identified to be the turn to turn wave coupling coefficients and the travel time of an electromagnetic disturbance around a single turn. Unlike circuit theoretic inductor, the coil response evolves in discrete steps having durations equal to this travel time. It is during such intervals that high voltages are likely to occur. The model also bridges the gap between the low and high ends of the frequency spectrum.

6. Gas Filled Coaxial Accelerator with Compression Coil

NASA Technical Reports Server (NTRS)

Espy, Patrick N. (Inventor)

1976-01-01

A self-energized plasma compressor which compresses plasma discharged from a coaxial plasma generator. The device includes a helical shaped coil which is coaxially aligned with the center axis of the coaxial plasma generator. The plasma generator creates a current through the helical coil which, in turn, generates a time varying magnetic field that generates a force which acts radially upon the plasma. A seal is carried on the end of the coaxial plasma generator for containing gas therein. As the plasma is accelerated out the outer end of the generator, it forces the gas outwardly also compressing such. Beads are carried adjacent the small end of the helical shaped coil for being accelerated to hypervelocities by the plasma and gas. As a result of utilizing gas in the coaxial plasma generator, such minimizes ablation of the beads as well as accelerates such to higher velocities.

7. Apparatus and method for reducing inductive coupling between levitation and drive coils within a magnetic propulsion system

DOEpatents

Post, Richard F.

2001-01-01

An apparatus and method is disclosed for reducing inductive coupling between levitation and drive coils within a magnetic levitation system. A pole array has a magnetic field. A levitation coil is positioned so that in response to motion of the magnetic field of the pole array a current is induced in the levitation coil. A first drive coil having a magnetic field coupled to drive the pole array also has a magnetic flux which induces a parasitic current in the levitation coil. A second drive coil having a magnetic field is positioned to attenuate the parasitic current in the levitation coil by canceling the magnetic flux of the first drive coil which induces the parasitic current. Steps in the method include generating a magnetic field with a pole array for levitating an object; inducing current in a levitation coil in response to motion of the magnetic field of the pole array; generating a magnetic field with a first drive coil for propelling the object; and generating a magnetic field with a second drive coil for attenuating effects of the magnetic field of the first drive coil on the current in the levitation coil.

8. Testing neoclassical and turbulent effects on poloidal rotation in the core of DIII-D

SciTech Connect

Chrystal, C.; Burrell, K. H.; Staebler, G. M.; Kinsey, J. E.; Lao, L. L.; Grassie, J. S. de; Grierson, B. A.; Solomon, W. M.; Wang, W. X.; Rhodes, T. L.; Schmitz, L.; Mordijck, S.; Meneghini, O.

2014-07-15

Experimental tests of ion poloidal rotation theories have been performed on DIII-D using a novel impurity poloidal rotation diagnostic. These tests show significant disagreements with theoretical predictions in various conditions, including L-mode plasmas with internal transport barriers (ITB), H-mode plasmas, and QH-mode plasmas. The theories tested include standard neoclassical theory, turbulence driven Reynolds stress, and fast-ion friction on the thermal ions. Poloidal rotation is observed to spin up at the formation of an ITB and makes a significant contribution to the measurement of the E{sup →}×B{sup →} shear that forms the ITB. In ITB cases, neoclassical theory agrees quantitatively with the experimental measurements only in the steep gradient region. Significant quantitative disagreement with neoclassical predictions is seen in the cores of ITB, QH-, and H-mode plasmas, demonstrating that neoclassical theory is an incomplete description of poloidal rotation. The addition of turbulence driven Reynolds stress does not remedy this disagreement; linear stability calculations and Doppler backscattering measurements show that disagreement increases as turbulence levels decline. Furthermore, the effect of fast-ion friction, by itself, does not lead to improved agreement; in QH-mode plasmas, neoclassical predictions are closest to experimental results in plasmas with the largest fast ion friction. Predictions from a new model that combines all three effects show somewhat better agreement in the H-mode case, but discrepancies well outside the experimental error bars remain.

9. Poloidal flow driven by ion-temperature-gradient turbulence in tokamaks

SciTech Connect

Rosenbluth, M.N.; Hinton, F.L.

1998-01-01

We show that linear collisionless processes do not damp poloidal flows driven by ion-temperature-gradient (ITG) turbulence. Since these flows play an important role in saturating the level of the turbulence, this level, as well as the transport caused by ITG modes, may be overestimated by gyrofluid simulations, which employ linear collisionless rotation damping. {copyright} {ital 1998} {ital The American Physical Society}

10. Poloidal tilting symmetry of high order tokamak flux surface shaping in gyrokinetics

Ball, Justin; Parra, Felix I.; Barnes, Michael

2016-04-01

A poloidal tilting symmetry of the local nonlinear δ f gyrokinetic model is demonstrated analytically and verified numerically. This symmetry shows that poloidally rotating all the flux surface shaping effects with large poloidal mode number by a single tilt angle has an exponentially small effect on the transport properties of a tokamak. This is shown using a generalization of the Miller local equilibrium model to specify an arbitrary flux surface geometry. With this geometry specification we find that, when performing an expansion in large flux surface shaping mode number, the governing equations of gyrokinetics are symmetric in the poloidal tilt of the high order shaping effects. This allows us to take the fluxes from a single configuration and calculate the fluxes in any configuration that can be produced by tilting the large mode number shaping effects. This creates a distinction between tokamaks with mirror symmetric flux surfaces and tokamaks without mirror symmetry, which is expected to have important consequences for generating toroidal rotation using up-down asymmetry.

11. Coil Tolerance Impact on Plasma Surface Quality for NCSX

SciTech Connect

Art Brooks; Wayne Reiersen

2003-10-20

The successful operation of the National Compact Stellarator Experiment (NCSX) machine will require producing plasma configurations with good flux surfaces, with a minimum volume of the plasma lost to magnetic islands or stochastic regions. The project goal is to achieve good flux surfaces over 90% of the plasma volume. NCSX is a three period device designed to be operated with iota ranging from {approx}0.4 on axis to {approx}0.7 at the edge. The field errors of most concern are those that are resonant with 3/5 and 3/6 modes (for symmetry preserving field errors) and the 1/2 and 2/3 modes (for symmetry breaking field errors). In addition to losses inherent in the physics configuration itself, there will be losses from field errors arising from coil construction and assembly errors. Some of these losses can be recovered through the use of trim coils or correction coils. The impact of coil tolerances on plasma surface quality is evaluated herein for the NCSX design. The methods used in this evaluation are discussed. The ability of the NCSX trim coils to correct for field errors is also examined. The results are used to set coils tolerances for the various coil systems.

12. Preliminary design of a superconducting coil array for NASA prototype magnetic balance. M.S. Thesis

NASA Technical Reports Server (NTRS)

Alishahi, M. M.

1980-01-01

Using a computer program a partly optimized configuration for a supeconducting version of side and lift coil system of NASA-MIT prototype is presented. Cable size for the mentioned coils and also for superconducting drag and magnetizing coils regarding the overall computed field was determined.

13. Modular tokamak magnetic system

DOEpatents

Yang, Tien-Fang

1988-01-01

A modular tokamak system comprised of a plurality of interlocking moldules. Each module is comprised of a vacuum vessel section, a toroidal field coil, moldular saddle coils which generate a poloidal magnetic field and ohmic heating coils.

14. A multi-slot surface coil for MRI of dual-rat imaging at 4 T

Solis, S. E.; Wang, R.; Tomasi, D.; Rodriguez, A. O.

2011-06-01

A slotted surface coil inspired by the hole-and-slot cavity magnetron was developed for magnetic resonance imaging of obese rats at 4 T. Full-wave analysis of the magnetic field was carried out at 170 MHz for both the slotted and circular-shaped coils. The noise figure values of two coils were investigated via the numerical calculation of the quality factors. Fat simulated phantoms to mimic overweight rats were included in the analysis with weights ranging from 300 to 900 g. The noise figures were 1.2 dB for the slotted coil and 2.4 dB for the circular coil when loaded with 600 g of simulated phantom. A slotted surface coil with eight circular slots and a circular coil with similar dimensions were built and operated in the transceiver mode, and their performances were experimentally compared. The imaging tests in phantoms demonstrated that the slotted surface coil has a deeper RF-sensitivity and better field uniformity than the single-loop RF-coil. High quality images of two overweight Zucker rats were acquired simultaneously with the slotted surface coil using standard spin-echo pulse sequences. Experimental results showed that the slotted surface coil outperformed the circular coil for imaging considerably overweight rats. Thus, the slotted surface coil can be a good tool for MRI experiments in rats on a human whole-body 4 T scanner.

15. A microstrip transmission line volume coil for human head MR imaging at 4T.

PubMed

Zhang, Xiaoliang; Ugurbil, Kamil; Chen, Wei

2003-04-01

A high-frequency RF volume coil based on the use of microstrip transmission line (MTL) has been developed for in vivo 1H MR applications on the human head at 4T. This coil is characterized by major advantages: (i) completely distributed coil circuit, (ii) high-quality factor (Q), (iii) simple coil structure, and (iv) better sensitivity and less signal-intensity variation in the MR image of the human head compared with an RF shielded birdcage coil of similar coil size. The proposed MTL volume coil does not require additional RF shielding for preventing Q degradation from radiation losses due to the unique MTL structure; thus, it provides a maximal useable space inside the volume coil when compared with most volume coils available at high fields with the same overall coil size. The intrinsic B(1) distribution of the MTL volume coil effectively compensates for the dielectric resonance effect at 4T and improves the signal homogeneity in human head MR images in the transaxial planes. The results of this study demonstrate that the MTL volume coil design provides an efficient and simple solution to RF volume coil design for human MR studies at high fields.

16. Mid-Range Coil Array for Magnetic Resonance Imaging of Small Animals

SciTech Connect

Solis, S. E.; Tomasi, D.; Rodriguez, A. O.

2008-08-11

The vast majority of articles on MRI RF coils over the past two decades have focused on large coils, where sample losses dominate, or on micro-coils, where sample and capacitor losses are negligible. Few have addressed the mid-range coils, seen in the majority of small-animal applications, where all the sources of loss are important, for example, mouse brain and body coils from 125 to 750 MHz. We developed a four-saddle coil array for magnetic resonance imaging of small animals. The saddle coil elements in the array were evenly distributed to cover the rat's head. The coil array was tuned to the resonant frequency of 170 MHz. Due to the close proximity of the coil elements, it was necessary to decouple the coil array using nonmagnetic trimmers and, it was operated in the transceiver mode and quadrature-driven. To test the coil array performance at high field, phantom images were acquired with our saddle coil array and standard pulse sequences on a research-dedicated 4 Tesla scanner. Ex vivo brain images of a rat were also acquired, and proved the feasibility of the scaled version of a saddle coil array and, its compatibility with standard pulse sequences when used in a high field magnetic resonance imager.

17. A multi-slot surface coil for MRI of dual-rat imaging at 4T

SciTech Connect

Solis, S.E.; Tomasi, D.; Solis, S.E.; Wang, R.; Tomasi, D.; Rodriguez, A.O.

2011-07-01

A slotted surface coil inspired by the hole-and-slot cavity magnetron was developed for magnetic resonance imaging of obese rats at 4 T. Full-wave analysis of the magnetic field was carried out at 170 MHz for both the slotted and circular-shaped coils. The noise figure values of two coils were investigated via the numerical calculation of the quality factors. Fat simulated phantoms to mimic overweight rats were included in the analysis with weights ranging from 300 to 900 g. The noise figures were 1.2 dB for the slotted coil and 2.4 dB for the circular coil when loaded with 600 g of simulated phantom. A slotted surface coil with eight circular slots and a circular coil with similar dimensions were built and operated in the transceiver mode, and their performances were experimentally compared. The imaging tests in phantoms demonstrated that the slotted surface coil has a deeper RF-sensitivity and better field uniformity than the single-loop RF-coil. High quality images of two overweight Zucker rats were acquired simultaneously with the slotted surface coil using standard spin-echo pulse sequences. Experimental results showed that the slotted surface coil outperformed the circular coil for imaging considerably overweight rats. Thus, the slotted surface coil can be a good tool for MRI experiments in rats on a human whole-body 4 T scanner.

18. Test results from the Wendelstein 7-X stellarator demonstration coil

Heller, R.; Maurer, W.; Sapper, J.; Schauer, F.; Schönewolf, I.; Ulbricht, A.; Wüchner, F.; Zahn, G.

2000-08-01

Wendelstein 7-X (W 7-X) is a stellarator plasma experiment currently under construction in Greifswald, Germany. It is an advanced stellarator with a magnet system consisting of 50 non-planar superconducting main field coils and 20 superconducting planar auxiliary coils in modular toroidal arrangement. The auxiliary system is foreseen for the variation of plasma parameters which allows extensive plasma studies in wide parameter ranges. The characteristic dimensions of a coil are: 3.5 m in height, 2.5 m in width and 1.0 m in thickness. In order to prove the fabricability and the electromagnetic, thermohydraulic and mechanical performance of the coils, a full-size demonstration coil was built by industry and delivered to the Forschungszentrum Karlsruhe for testing. Here, the coil was prepared for installation at the test facility TOSKA beside the EURATOM LCT coil. This coil delivers a background field which allows the simulation of different load cases occurring later in the experimental device. The aim of the test was the investigation of the mechanical properties and behaviour of the bedding between winding block and casing. In this paper, the electromagnetic results obtained during the test will be presented.

19. Bipolar electrical coil based on YBCO bulks: initial tests

Alvarez, A.; Suárez, P.; Ceballos, J. M.; Pérez, B.; Werfel, F.; Floegel-Delor, U.

2008-02-01

In the field of the application of HTS in electrical motors, most prototypes are made using superconducting coils based on tape and located in the position where copper coils work in a similar conventional motor. Other prototypes use superconducting bulks (usually disk-shaped) in those positions where normal magnets should work in similar conventional motors. But it is very unusual to find designs using electrical coils based on bulks. This is a challenge whose main problem is the difficulty in machining the superconductor bulks to get the proper shape because of the impossibility of bending the material to wind coils. The design of a bipolar single-turn coil made from a superconducting YBCO disk was proposed by the group of Electrical Application of Superconductors, at the University of Extremadura, several years ago to be an element for the design of a modular two-phase inductor for an air core axial-flux motor. The shape of each coil looks like an 'S'. When a current flows through the circuit, two opposite magnetic fields appear in the upper and lower halves of the piece. Until now, attempts to get a good superconducting circuit by cutting a YBCO disk into the required shape have failed because of cracks appearing in the crystal during the process. Last year, our group at the University of Extremadura began to work with ATZ GmbH who have improved the machining process and made the coils. In this paper we present the coil and the first tests carried out.

20. Nuclear magnetic resonance apparatus having semitoroidal rf coil for use in topical NMR and NMR imaging

DOEpatents

Fukushima, Eiichi; Roeder, Stephen B. W.; Assink, Roger A.; Gibson, Atholl A. V.

1986-01-01

An improved nuclear magnetic resonance (NMR) apparatus for use in topical magnetic resonance (TMR) spectroscopy and other remote sensing NMR applications includes a semitoroidal radio-frequency (rf) coil. The semitoroidal rf coil produces an effective alternating magnetic field at a distance from the poles of the coil, so as to enable NMR measurements to be taken from selected regions inside an object, particularly including human and other living subjects. The semitoroidal rf coil is relatively insensitive to magnetic interference from metallic objects located behind the coil, thereby rendering the coil particularly suited for use in both conventional and superconducting NMR magnets. The semitoroidal NMR coil can be constructed so that it emits little or no excess rf electric field associated with the rf magnetic field, thus avoiding adverse effects due to dielectric heating of the sample or to any other interaction of the electric field with the sample.

1. Electrospun Buckling Coils

Xin, Yu; Reneker, Darrell

2009-03-01

Electrospinning offers a useful way to produce fibers with micron and nanometer scale diameter. The present work deals with the buckling phenomenon characteristic of a jet impinging upon the surface of collector. A viscous jet may have either tensile or compressive forces along its axis. The periodic buckling that is often observed is attributed to the occurrence of compressive forces as the jet decelerates at the collector. With the increase of axial compressive stresses along the jet, a jet with circular cross sections first buckles by formation of sharp folds, and then by formation of coils. The resulting buckling patterns include zigzag patterns and coils that which can be controlled by changing parameters, such as density, viscosity, conductivity, voltage, polymer concentration, distance and volumetric flow rate. Uniformly buckled polymer fibers can be made at a rate of one turn per microsecond. An experimental apparatus was built to continuously collect buckling coils of nylon 6, from a water surface, into a multilayer sheet. These small springs'' and sheets will be tested for mechanical properties needed in biomedical applications.

2. Focused Magnetic Resonance Coupling Coils for Electromagnetic Therapy Applications.

PubMed

Yeung, Sai Ho; Pradhan, Raunaq; Feng, Xiaohua; Zheng, Yuanjin

2015-11-01

This paper presents the design and construction of a pair of figure-of-eight coils, coupled by magnetic resonance coupling (MRC), which could generate (150 V/m per Ampere) electric field at the focal points for electromagnetic therapy related applications. The E field generated at the targeted site would be significantly enhanced under the same amount of current flowing through the MRC figure-of-eight coils compared to normal coils, due to the superposition of E field contributed by the coils. Furthermore, the MRC figure-of-eight coil is designed and the results are verified in theory, simulation, and experiments. In the ex vivo tissue measurement, 35% current and 82% ohmic power improvements were observed. Since it can enhance the current and ohmic power, the MRC figure-of-eight coils are promising solutions for electromagnetic therapy applications. The potential applications of the coils include noninvasive radio frequency (RF) stimulation, thermoacoustic imaging, electromagnetic field therapies, and RF ablation, etc.

3. Choice of coils for a fusion reactor

PubMed Central

Alexander, Romeo; Garabedian, Paul R.

2007-01-01

In a fusion reactor a hot plasma of deuterium and tritium is confined by a strong magnetic field to produce helium ions and release energetic neutrons. The 3D geometry of a stellarator provides configurations for such a device that reduce net toroidal current that might lead to disruptions. We construct smooth coils generating an external magnetic field designed to prevent the plasma from deteriorating. PMID:17640879

4. Critical Current Measurements in Commercial Tapes, Coils, and Magnets.

Gubser, D. U.; Soulen, R. J., Jr.; Fuller-Mora, W. W.; Francavilla, T. L.

1996-03-01

We have measured a number of tapes, coils, and magnets produced by commercial vendors and determined their properties as functions of magnetic field and temperature. The tapes were measured at the National High Magnetic Field Laboratory in magnetic fields to 20 tesla and at temperatures of 4.2 K, 27 K, 65 K, and 77 K. For the tapes we report critical currents and current-voltage characteristics. Six inch diameter coils were measured at NRL in zero magnetic field. Critical currents, current-voltage characteristics, and reliability studies are reported for the coils. Larger 10 inch diameter coils, which are to be used in a 200 hp superconducting motor, were also measured and results will be presented. The talk will also review the status of the most recent tests of the superconducting motor.

5. Numerical dosimetry of transcranial magnetic stimulation coils

Crowther, Lawrence; Hadimani, Ravi; Jiles, David

2014-03-01

Transcranial magnetic stimulation (TMS) is a non-invasive neuromodulation technique capable of stimulating neurons by means of electromagnetic induction. TMS can be used to map brain function and shows promise for the diagnosis and treatment of neurological and psychiatric disorders. Calculation of fields induced in the brain are necessary to accurately identify stimulated neural tissue during TMS. This allows the development of novel TMS coil designs capable of stimulating deeper brain regions and increasing the localization of stimulation that can be achieved. We have performed numerical calculations of magnetic and electric field with high-resolution anatomically realistic human head models to find these stimulated brain regions for a variety of proposed TMS coil designs. The realistic head models contain heterogeneous tissue structures and electrical conductivities, yielding superior results to those obtained from the simplified homogeneous head models that are commonly employed. The attenuation of electric field as a function of depth in the brain and the localization of stimulating field have been methodically investigated. In addition to providing a quantitative comparison of different TMS coil designs the variation of induced field between subjects has been investigated. We also show the differences in induced fields between adult, adolescent and child head models to preemptively identify potential safety issues in the application of pediatric TMS.

6. Stellarator Coil Design and Plasma Sensitivity

SciTech Connect

Long-Poe Ku and Allen H. Boozer

2010-11-03

The rich information contained in the plasma response to external magnetic perturbations can be used to help design stellarator coils more effectively. We demonstrate the feasibility by first devel- oping a simple, direct method to study perturbations in stellarators that do not break stellarator symmetry and periodicity. The method applies a small perturbation to the plasma boundary and evaluates the resulting perturbed free-boundary equilibrium to build up a sensitivity matrix for the important physics attributes of the underlying configuration. Using this sensitivity information, design methods for better stellarator coils are then developed. The procedure and a proof-of-principle application are given that (1) determine the spatial distributions of external normal magnetic field at the location of the unperturbed plasma boundary to which the plasma properties are most sen- sitive, (2) determine the distributions of external normal magnetic field that can be produced most efficiently by distant coils, (3) choose the ratios of the magnitudes of the the efficiently produced magnetic distributions so the sensitive plasma properties can be controlled. Using these methods, sets of modular coils are found for the National Compact Stellarator Experiment (NCSX) that are either smoother or can be located much farther from the plasma boundary than those of the present design.

7. TEST PLAN FOR MONITORING COOLING COILS IN A LABORATORY SETTING

SciTech Connect

Don B. Shirey, III

2002-04-01

The objective of this research project is to understand and quantify the moisture removal performance of cooling coils at part-load conditions. The project will include a comprehensive literature review, detailed measurement of cooling coil performance in a laboratory facility, monitoring cooling systems at several field test sites, and development/validation of engineering models that can be used in energy calculations and building simulations. This document contains the detailed test plan for monitoring cooling coil performance in a laboratory setting. Detailed measurements will be taken on up to 10 direct expansion (DX) and chilled water cooling coils in various configurations to understand the impact of coil geometry and operating conditions on transient moisture condensation and evaporation.

8. Electromagnetic design of superconducting dipoles based on sector coils

Rossi, L.; Todesco, Ezio

2007-11-01

We study the coil layouts of superconducting dipoles for particle accelerators based on the sector geometry. We show that a simple model based on a sector coil with a wedge allows us to derive an equation giving the short sample field as a function of the aperture, coil width, cable properties, and superconducting material. The equation agrees well with the actual results of several dipole coils that have been built in the past 30 years. The improvements due to the grading technique and the iron yoke are also studied. The proposed equation can be used as a benchmark to judge the efficiency of the coil design, and to carry out a global optimization of an accelerator layout.

9. Magnetically Damped Furnace Bitter Magnet Coil 1

NASA Technical Reports Server (NTRS)

Bird, M. D.

1997-01-01

A magnet has been built by the National High Magnetic Field Laboratory for NASA on a cost reimbursement contract. The magnet is intended to demonstrate the technology and feasibility of building a magnet for space based crystal growth. A Bitter magnet (named after Francis Bitter, its inventor) was built consisting of four split coils electrically in series and hydraulically in parallel. The coils are housed in a steel vessel to reduce the fringe field and provide some on-axis field enhancement. The steel was nickel plated and Teflon coated to minimize interaction with the water cooling system. The magnet provides 0.14 T in a 184 mm bore with 3 kW of power.

10. Common Coil Magnet System for VLHC

SciTech Connect

Gupta, R.

1999-02-12

This paper introduces the common coil magnet system for the proposed very large hadron collider (VLHC). In this system, the high energy booster (HEB), the injector to VLHC, is integrated as the iron dominated low field aperture within the coldmass of the common coil magnet design introduced earlier. This 4-in-1 magnet concept for a 2-in-1 machine should provide a major cost reduction in building and operating VLHC. Moreover, the proposed design reduces the field quality problems associated with the large persistent currents in Nb{sub 3}Sn magnets. The paper also shows that the geometric field harmonics can be made small. In this preliminary magnetic design. the current dependence in harmonics is significant but not umnanageable.

11. An improved asymmetric gradient coil design for high-resolution MRI head imaging.

PubMed

Tang, Fangfang; Liu, Feng; Freschi, Fabio; Li, Yu; Repetto, Maurizio; Giaccone, Luca; Wang, Yaohui; Crozier, Stuart

2016-12-21

12. Collisionality Scaling of Main-ion Toroidal and Poloidal Rotation in Low Torque DIII-D Plasmas

SciTech Connect

B A Grierson, et al

2013-05-10

In tokamak plasmas with low levels of toroidal rotation, the radial electric fi eld Er is a combination of pressure gradient and toroidal and poloidal rotation components, all having similar magnitudes. In order to assess the validity of neoclassical poloidal rotation theory for determining the poloidal rotation contribution to Er , Dα emission from neutral beam heated tokamak discharges in DIII-D [J.L. Luxon, Nucl. Fusion 42 , 614 (2002)] has been evaluated in a sequence of low torque (electron cyclotron resonance heating and balanced diagnostic neutral beam pulse) discharges to determine the local deuterium toroidal rotation velocity. By invoking the radial force balance relation the deuterium poloidal rotation can be inferred. It is found that the deuterium poloidal low exceeds the neoclassical value in plasmas with collisionality νi < 0: 1, being more ion diamagnetic, and with a stronger dependence on collisionality than neoclassical theory predicts. At low toroidal rotation, the poloidal rotation contribution to the radial electric fi eld and its shear is signi cant. The eff ect of anomalous levels of poloidal rotation on the radial electric fi eld and cross fi eld heat transport is investigated for ITER parameters.

13. Stacked phased array coils for increasing the signal-to-noise ratio in magnetic resonance imaging.

PubMed

Dandan Liang; Hon Tat Hui; Tat Soon Yeo; Bing Keong Li

2013-02-01

A new concept of using a stacked phased coil array to increase the signal-to-circuit noise ratio (SCNR) in magnetic resonance imaging (MRI) is introduced. Unlike conventional phased coil arrays, the proposed stacked phased coil array is constructed by stacking the coil elements closely together in the vertical direction. Through a proper combination of the coil terminal voltages, the SCNR is shown to increase with the square root of the number of coil elements. A prototype two-element array is constructed and an experimental method is designed to determine the combiner coefficients in a simulated MRI electromagnetic field environment. The experimental results show that the mutual coupling effect among the array coils can be totally removed and the combiner output voltage increases with the number of coil elements. This demonstrates the feasibility of the proposed method.

14. Feasibility study of a new RF coil design for prostate MRI

Ha, Seunghoon; Roeck, Werner W.; Cho, Jaedu; Nalcioglu, Orhan

2014-09-01

The combined use of a torso-pelvic RF array coil and endorectal RF coil is the current state-of-the-art in prostate MRI. The endorectal coil provides high detection sensitivity to acquire high-spatial resolution images and spectroscopic data, while the torso-pelvic coil provides large coverage to assess pelvic lymph nodes and pelvic bones for metastatic disease. However, the use of an endorectal coil is an invasive procedure that presents difficulties for both patients and technicians. In this study, we propose a novel non-invasive RF coil design that can provide both image signal to noise ratio and field of view coverage comparable to the combined torso-pelvic and endorectal coil configuration. A prototype coil was constructed and tested using a pelvic phantom. The results demonstrate that this new design is a viable alternative for prostate MRI

15. Magnetic field transfer device and method

DOEpatents

Wipf, S.L.

1990-02-13

A magnetic field transfer device includes a pair of oppositely wound inner coils which each include at least one winding around an inner coil axis, and an outer coil which includes at least one winding around an outer coil axis. The windings may be formed of superconductors. The axes of the two inner coils are parallel and laterally spaced from each other so that the inner coils are positioned in side-by-side relation. The outer coil is outwardly positioned from the inner coils and rotatable relative to the inner coils about a rotational axis substantially perpendicular to the inner coil axes to generate a hypothetical surface which substantially encloses the inner coils. The outer coil rotates relative to the inner coils between a first position in which the outer coil axis is substantially parallel to the inner coil axes and the outer coil augments the magnetic field formed in one of the inner coils, and a second position 180[degree] from the first position, in which the augmented magnetic field is transferred into the other inner coil and reoriented 180[degree] from the original magnetic field. The magnetic field transfer device allows a magnetic field to be transferred between volumes with negligible work being required to rotate the outer coil with respect to the inner coils. 16 figs.

16. Magnetic field transfer device and method

DOEpatents

Wipf, Stefan L.

1990-01-01

A magnetic field transfer device includes a pair of oppositely wound inner coils which each include at least one winding around an inner coil axis, and an outer coil which includes at least one winding around an outer coil axis. The windings may be formed of superconductors. The axes of the two inner coils are parallel and laterally spaced from each other so that the inner coils are positioned in side-by-side relation. The outer coil is outwardly positioned from the inner coils and rotatable relative to the inner coils about a rotational axis substantially perpendicular to the inner coil axes to generate a hypothetical surface which substantially encloses the inner coils. The outer coil rotates relative to the inner coils between a first position in which the outer coil axis is substantially parallel to the inner coil axes and the outer coil augments the magnetic field formed in one of the inner coils, and a second position 180.degree. from the first position, in which the augmented magnetic field is transferred into the other inner coil and reoriented 180.degree. from the original magnetic field. The magnetic field transfer device allows a magnetic field to be transferred between volumes with negligible work being required to rotate the outer coil with respect to the inner coils.

17. A study of poloidal asymmetries in the pedestal region

Churchill, R. M.; Lipschultz, B.; Lisgo, S.; Reimold, F.; Goldstein, J.; Alcator C-Mod Team Team

2011-10-01

Simultaneous CXRS measurements of boron density, velocity, and temperature in the pedestal region (0 . 8 < r / a < 1 . 05) at the low- and high-field sides (LFS and HFS) of Alcator C-Mod allow studies of variations in boron density and total velocity on a flux surface. While previous studies used different neutral sources (a 50keV hydrogen neutral beam at the LFS and a thermal D2 gas puff at the HFS) to localize CXRS measurements we have recently expanded our diagnostic set to allow thermal gas CXRS at both locations, thus removing uncertainties due to different measurement techniques and cross-section. We have also upgraded our modelling capability to utilize the DIVIMP code, which uses the plasma-neutral code combination of OSM-EIRENE to determine the local neutral density. Comparisons between CXRS methods using different neutral sources will be shown as well as an exploration of whether the constants K(ψ) and ω(ψ) in the description of V =K/(ψ) n B + ω (ψ)R2 ∇ ϕ are constant on a flux surface as typically assumed. The above comparisons will be shown for a variety of H-mode and I-mode plasmas. Supported by USDoE award DE-FC02-99ER54512.

18. Spheromak aspect-ratio effects on poloidal flux amplification

Hooper, E. B.; McLean, H. S.; Romero-Talamas, C. A.; Wood, R. D.

2008-11-01

A short experimental run at the end of SSPX operation examined the effect of increasing the flux conserver length-to-aspect ration, L/R, from 1 to 1.2, thereby reducing the formation threshold for λgun=μ0Igun/ψgun from 10 m-1 to 7.5 m-1 with a corresponding increase in power efficiency [1]. Resistive MHD (NIMROD) simulations of flux amplification which agreed well with experiment at L/R=1 [2] agree fairly well with L/R=1.2 and have been extended to L/R=1.6, just under the tilt-mode stability limit (1.67) for an isolated spheromak. At the longest length, helicity injection changes from a chaotic relaxation process to a steady, high amplitude n=1 mode which opens the field lines throughout most of the flux conserver. Calculations are presented to elucidate the characteristics of the chaos for the standard flux-conserver dimensions. Comparisons are made among the simulations to determine the optimum'' L/R based on a trade-off between spheromak buildup efficiency and low mode activity. [1] R. D. Wood, et al., submitted to Phys. Rev. Letters. [2] E. B. Hooper, et al., Nucl. Fusion 47, 1064 (2007).

19. Evaluating passively shielded gradient coil configurations for optimal eddy current compensation

Sanchez Lopez, Hector; Poole, Michael; Crozier, Stuart

2010-05-01

In magnetic resonance imaging, rapidly switching magnetic fields are used to spatially encode the signal. The temporal change of these fields induces eddy currents in nearby conducting structures of the scanner. These eddy currents, in turn, generate a secondary magnetic field that opposes and distorts the desired gradient field. Eddy current compensation methods are generally applied assuming that the primary and secondary magnetic field gradients possess similar spatial characteristics in the imaging volume (field matching). In this work an optimization method is used to deform the shape of the coil support and/or a highly conductive passive shield in order to improve the field matching and reduce the inductive coupling between the gradient coil and the passive shield. Using the residual field after eddy current compensation as the objective function, the coil support and/or conducting surfaces were deformed to obtain passively shielded x- and z-gradient coils with improved field matching and eddy current compensation. Assuming a single frequency, quasi-static simulation, it was demonstrated that the residual field was reduced up to 24 times by reshaping the coil and passive shield surfaces due to the improved field matching. However, using transient analyses we showed that in the case of the passively shielded x-gradient coil the residual field may only be reduced by five times from a cylindrical coil configuration. A bulge shape is created in the conducting surface as a mechanism of matching the field and at the same time reducing the mutual inductive coupling between the coil and the passive shield. An actively shielded coil with control over the magnetic field produced by the induced current was used as a reference coil that produces the minimal residual field. The actively shielded gradient coil produces minimal residual field for short and long pulses in the transient analyses.

20. Operation of a 400MHz NMR magnet using a (RE:Rare Earth)Ba2Cu3O7-x high-temperature superconducting coil: Towards an ultra-compact super-high field NMR spectrometer operated beyond 1GHz.

PubMed

Yanagisawa, Y; Piao, R; Iguchi, S; Nakagome, H; Takao, T; Kominato, K; Hamada, M; Matsumoto, S; Suematsu, H; Jin, X; Takahashi, M; Yamazaki, T; Maeda, H

2014-10-18

High-temperature superconductors (HTS) are the key technology to achieve super-high magnetic field nuclear magnetic resonance (NMR) spectrometers with an operating frequency far beyond 1GHz (23.5T). (RE)Ba2Cu3O7-x (REBCO, RE: rare earth) conductors have an advantage over Bi2Sr2Ca2Cu3O10-x (Bi-2223) and Bi2Sr2CaCu2O8-x (Bi-2212) conductors in that they have very high tensile strengths and tolerate strong electromagnetic hoop stress, thereby having the potential to act as an ultra-compact super-high field NMR magnet. As a first step, we developed the world's first NMR magnet comprising an inner REBCO coil and outer low-temperature superconducting (LTS) coils. The magnet was successfully charged without degradation and mainly operated at 400MHz (9.39T). Technical problems for the NMR magnet due to screening current in the REBCO coil were clarified and solved as follows: (i) A remarkable temporal drift of the central magnetic field was suppressed by a current sweep reversal method utilizing ∼10% of the peak current. (ii) A Z2 field error harmonic of the main coil cannot be compensated by an outer correction coil and therefore an additional ferromagnetic shim was used. (iii) Large tesseral harmonics emerged that could not be corrected by cryoshim coils. Due to those harmonics, the resolution and sensitivity of NMR spectra are ten-fold lower than those for a conventional LTS NMR magnet. As a result, a HSQC spectrum could be achieved for a protein sample, while a NOESY spectrum could not be obtained. An ultra-compact 1.2GHz NMR magnet could be realized if we effectively take advantage of REBCO conductors, although this will require further research to suppress the effect of the screening current.

1. External split field generator

DOEpatents

Thundat, Thomas George [Knoxville, TN; Van Neste, Charles W [Kingston, TN; Vass, Arpad Alexander [Oak Ridge, TN

2012-02-21

A generator includes a coil disposed about a core. A first stationary magnetic field source may be disposed on a first end portion of the core and a second stationary magnetic field source may be disposed on a second end portion of core. The first and second stationary magnetic field sources apply a stationary magnetic field to the coil. An external magnetic field source may be disposed outside the coil to apply a moving magnetic field to the coil. Electrical energy is generated in response to an interaction between the coil, the moving magnetic field, and the stationary magnetic field.

2. Dynamics of axisymmetric E x B and poloidal flows in tokamaks

SciTech Connect

Hinton, F.L.; Rosenbluth, M.N.

1998-07-01

As a result of turbulence and finite Larmor radius effects, random radial currents are present in a tokamak plasma, and these drive sheared axisymmetric poloidal flows. The authors model these currents with a noise source with given statistical properties and calculate the linear kinetic response to this source. Without collisions, there is no long term damping of these flows; when collisions are included, poloidal flows are damped. The mean square potential associated with these flows is given in terms of the linear response function they calculate and a model correlation function for the current source. Without collisions, the mean square E {times} B flow increases linearly with time, but with collisions, it reaches a steady state. In the long correlation time limit, the collisionless residual flows are important in determining the mean square E {times} B flow.

3. Coiled tubing; Operations and services

SciTech Connect

Welch, J.L.; Stephens, R.K. )

1992-09-01

This paper reports on coiled tubing units which are used for many types of remedial well operations, including sand plugbacks, cement squeezes, fill cleanouts, underreaming, acid stimulations, and fishing. Fishing operations include removal of inflatable bridge plugs, lock mandrels stuck in profile nipples, coiled tubing, coiled tubing bottomhole assemblies (BHAs) and wireline. Recommended guidelines for selecting candidates, proper tool string configuration and operational techniques are presented here to assist coiled tubing supervisors and company representatives in the planning and implementation of efficient and effective fishing operations. Treatment of these areas are not intended to be exhaustive, but rather generally representative of common applications. Each fishing operation requires individualized analysis and planning.

4. Poloidal radiation asymmetries during disruption mitigation by massive gas injection on the DIII-D tokamak

Eidietis, N. W.

2016-10-01

Measurements of poloidal asymmetry in the radiated power during thermal quench (TQ) mitigation by massive gas injection (MGI) on DIII-D show poloidal peaking in the radiated heat flux at the wall generally consistent with 3D resistive MHD modeling, that indicates a large n=1 tearing mode causes these asymmetries. Radiation asymmetries are a concern to ITER because they can cause localized melting of the first wall even if globally the mitigation successfully radiates 100% of the plasma thermal energy. Toroidal radiation asymmetries have been well-studied, but until now the equally important poloidal asymmetries were not well constrained. Radiation emissivity profiles are reconstructed by tomographic inversion of AXUV photodiode arrays, from which the peaking measurements are derived. The poloidal peaking measurements are compared to NIMROD 3D resistive MHD simulations. Qualitatively, the measured and modeled peaking evolve similarly. In both cases, peaking during the TQ changes little with toroidal phase, consistent with predictions of n=1 MHD during the TQ producing the asymmetry. Quantitatively, the measured TQ peaking amplitudes are comparable to but consistently higher than the modeled values. This is a result of the measured radiation exhibiting high emissivity lobes at larger minor radius (and outside the separatrix) than the modeled cases, which may indicate incomplete treatment of the plasma-neutral interaction at the plasma edge in the model. This work, combined with previous measurement and modeling and toroidal radiation asymmetries, provides a basis for constraining localized mitigation radiation heat flux in ITER. Work supported by US DOE under DE-FC02-04ER54698.

5. Discrete-coil investigations of modular stellarator configurations

SciTech Connect

Lilliequist, C.G.

1985-10-01

The existence of a vacuum magnetic well is generally accepted as a prerequisite to start-up. The special set of modular-stellarator configurations selected for the present computational investigation was derived from coefficients and equations that produced finite-beta wells in a continuous-current-sheet representation. The corresponding coils did not produce magnetic wells in a vacuum when their field configuration was investigated with a discrete-coil code. Vacuum magnetic wells have been identified through the use of this discrete-coil code in previous Heliac and stellarator studies. Therefore, these finite-beta magnetic wells could be the consequence of the continuous-current-sheet model: a conjecture that is supported by the linear scaling of the magnetic hills found in the present work as a function of the separation between the coils used. In addition to magnetic field profiles, comparisons are shown here of ripple, rotational transform, and flux-surface shapes for the discrete-coil, modular stellarators under study. Initially, each of the significant parameters affecting the shape of the control surface upon which the coils lie and the deformation of the individual coils was varied separately in search of a vacuum magnetic well in the parameter neighborhood of the successful finite-beta configuration.

6. Multi-channel poloidal correlation reflectometry on experimental advanced superconducting tokamak

Qu, H.; Zhang, T.; Han, X.; Xiang, H. M.; Wen, F.; Geng, K. N.; Wang, Y. M.; Kong, D. F.; Cai, J. Q.; Huang, C. B.; Gao, Y.; Gao, X.; Zhang, S.

2016-11-01

A new multi-channel poloidal correlation reflectometry is developed at Experimental Advanced Superconducting Tokamak. Eight dielectric resonator oscillators with frequencies of 12.5 GHz, 13.5 GHz, 14.5 GHz, 15 GHz, 15.5 GHz, 16 GHz, 17 GHz, and 18 GHz are used as sources. Signals from the sources are up-converted to V band using active quadruplers and then coupled together. The output waves are launched by one single antenna after passing through a 20 dB directional coupler which can provide the reference signal. Two poloidally separated antennae are installed to receive the reflected waves from plasma. The reference and reflected signals are down-converted by mixing with a quadrupled signal from a phase-locked source with a frequency of 14.2 GHz and the IF signals pass through the filter bank. The resulting signals from the mixers are detected by I/Q demodulators. The setup enables the measurement of density fluctuation at 8 (radial) × 2 (poloidal) spatial points. A coherent mode with an increasing velocity from 50 kHz to 100 kHz is observed by using the system. The mode is located in the steep gradient region of the pedestal.

7. Multi-channel poloidal correlation reflectometry on experimental advanced superconducting tokamak.

PubMed

Qu, H; Zhang, T; Han, X; Xiang, H M; Wen, F; Geng, K N; Wang, Y M; Kong, D F; Cai, J Q; Huang, C B; Gao, Y; Gao, X; Zhang, S

2016-11-01

A new multi-channel poloidal correlation reflectometry is developed at Experimental Advanced Superconducting Tokamak. Eight dielectric resonator oscillators with frequencies of 12.5 GHz, 13.5 GHz, 14.5 GHz, 15 GHz, 15.5 GHz, 16 GHz, 17 GHz, and 18 GHz are used as sources. Signals from the sources are up-converted to V band using active quadruplers and then coupled together. The output waves are launched by one single antenna after passing through a 20 dB directional coupler which can provide the reference signal. Two poloidally separated antennae are installed to receive the reflected waves from plasma. The reference and reflected signals are down-converted by mixing with a quadrupled signal from a phase-locked source with a frequency of 14.2 GHz and the IF signals pass through the filter bank. The resulting signals from the mixers are detected by I/Q demodulators. The setup enables the measurement of density fluctuation at 8 (radial) × 2 (poloidal) spatial points. A coherent mode with an increasing velocity from 50 kHz to 100 kHz is observed by using the system. The mode is located in the steep gradient region of the pedestal.

8. Elliptical Muon Helical Cooling Channel Coils

SciTech Connect

Kahn, S. A.; Flanagan, G.; Lopes, M. L.; Yonehara, K.

2013-09-01

A helical cooling channel (HCC) consisting of a pressurized gas absorber imbedded in a magnetic channel that provides solenoid, helical dipole and helical quadrupole fields has shown considerable promise in providing six-dimensional phase space reduction for muon beams. The most effective approach to implementing the desired magnetic field is a helical solenoid (HS) channel composed of short solenoid coils arranged in a helical pattern. The HS channel along with an external solenoid allows the B$_z$ and B$_{\\phi}$ components along the reference orbit to be set to any desired values. To set dB$_{\\phi}$/dr to the desired value for optimum focusing requires an additional variable to tune. We shall show that using elliptical shaped coils in the HS channel allows the flexibility to achieve the desired dB$_{\\phi}$/dr on the reference orbit without significant change to B$_z$ and B$_{\\phi}$.

9. Theory of the quadrature elliptic birdcage coil.

PubMed

Leifer, M C

1997-11-01

This paper presents the theory of the quadrature birdcage coil wound on an elliptic cylindrical former. A conformal transformation of the ellipse to a circular geometry is used to derive the optimal sampling of the continuous surface current distribution to produce uniform magnetic fields within an elliptic cylinder. The analysis is rigorous for ellipses of any aspect ratio and shows how to produce quadrature operation of the elliptic birdcage with a conventional hybrid combiner. Insight gained from the transformation is also used to analyze field homogeneity, find the optimal RF shield shape, and specify component values to produce the correct current distribution in practice. Measurements and images from a 16-leg elliptic birdcage coil at both low and high frequencies show good quadrature performance, homogeneity, and sensitivity.

10. Two-Slotted Surface Coil Array for Magnetic Resonance Imaging at 4 Tesla

SciTech Connect

Solis, S. E.; Hernandez, J. A.; Rodriguez, A. O.; Tomasi, D.

2008-08-11

Arrays of antennas have been widely accepted for magnetic resonance imaging applications due to their high signal-to-noise ratio (SNR) over large volumes of interest. A new surface coil based on the magnetron tube and called slotted surface coil, has been recently introduced by our group. This coil design experimentally demonstrated a significant improvement over the circular-shaped coil when used in the receive-only mode. The slotted coils formed a two-sheet structure with a 90 deg. separation and each coil had 6 circular slots. Numerical simulations were performed using the finite element method for this coil design to study the behaviour of the array magnetic field. Then, we developed a two-coil array for brain magnetic resonance imaging to be operated at the resonant frequency of 170 MHz in the transceiver mode. Phantom images were acquired with our coil array and standard pulse sequences on a research-dedicated 4 Tesla scanner. Numerical simulations demonstrated that electromagnetic interaction between the coil elements is negligible, and that the magnetic field showed a good uniformity. In vitro images showed the feasibility of this coil array for standard pulses for high field magnetic resonance imaging.

11. NSTX Protection And Interlock Systems For Coil And Powers Supply Systems

SciTech Connect

X. Zhao, S. Ramakrishnan, J. Lawson, C.Neumeyer, R. Marsala, H. Schneider, Engineering Operations

2009-09-24

NSTX at Princeton Plasma Physics Laboratory (PPPL) requires sophisticated plasma positioning control system for stable plasma operation. TF magnetic coils and PF magnetic coils provide electromagnetic fields to position and shape the plasma vertically and horizontally respectively. NSTX utilizes twenty six coil power supplies to establish and initiate electromagnetic fields through the coil system for plasma control. A power protection and interlock system is utilized to detect power system faults and protect the TF coils and PF coils against excessive electromechanical forces, overheating, and over current. Upon detecting any fault condition the power system is restricted, and it is either prevented from initializing or suppressed to de-energize coil power during pulsing. Power fault status is immediately reported to the computer system. This paper describes the design and operation of NSTX's protection and interlocking system and possible future expansion.

12. A Parallel Coiled-Coil Tetramer with Offset Helices

SciTech Connect

Liu,J.; Deng, Y.; Zheng, Q.; Cheng, C.; Kallenbach, N.; Lu, M.

2006-01-01

Specific helix-helix interactions are fundamental in assembling the native state of proteins and in protein-protein interfaces. Coiled coils afford a unique model system for elucidating principles of molecular recognition between {alpha} helices. The coiled-coil fold is specified by a characteristic seven amino acid repeat containing hydrophobic residues at the first (a) and fourth (d) positions. Nonpolar side chains spaced three and four residues apart are referred to as the 3-4 hydrophobic repeat. The presence of apolar amino acids at the e or g positions (corresponding to a 3-3-1 hydrophobic repeat) can provide new possibilities for close-packing of {alpha}-helices that includes examples such as the lac repressor tetramerization domain. Here we demonstrate that an unprecedented coiled-coil interface results from replacement of three charged residues at the e positions in the dimeric GCN4 leucine zipper by nonpolar valine side chains. Equilibrium circular dichroism and analytical ultracentrifugation studies indicate that the valine-containing mutant forms a discrete {alpha}-helical tetramer with a significantly higher stability than the parent leucine-zipper molecule. The 1.35 {angstrom} resolution crystal structure of the tetramer reveals a parallel four-stranded coiled coil with a three-residue interhelical offset. The local packing geometry of the three hydrophobic positions in the tetramer conformation is completely different from that seen in classical tetrameric structures yet bears resemblance to that in three-stranded coiled coils. These studies demonstrate that distinct van der Waals interactions beyond the a and d side chains can generate a diverse set of helix-helix interfaces and three-dimensional supercoil structures.

13. A novel radio frequency coil for veterinary magnetic resonance imaging system

Meng, Bin; Huang, Kai-Wen; Wang, Wei-Min

2010-07-01

In this article, a novel designed radio frequency (RF) coil is designed and built for the imaging of puppies in a V-shape permanent magnetic resonance imaging (MRI) system. Two sets of Helmholtz coil pairs with a V-shape structure are used to improve the holding of an animal in the coil. The homogeneity and the sensitivity of the RF field in the coil are analysed by theoretical calculation. The size and the shape of the new coil are optimized and validated by simulation through using the finite element method (FEM). Good magnetic resonance (MR) images are achieved on a shepherd dog.

14. Method of preloading superconducting coils by using materials with different thermal expansion coefficients

DOEpatents

Heim, J.R.

1993-02-23

The invention provides a high magnetic field coil. The invention provides a preloaded compressive force to the coil maintain the integrity of the coil. The compressive force is obtained by reinforcing the coil with two materials of different thermal expansion rates and then heating the coil to 700 C to obtain the desired compression. The embodiment of the invention uses Nb[sub 3]Sn as the conducting wire, since Nb[sub 3]Sn must be heated to 700 C to cause a reaction which makes Nb[sub 3]Sn superconducting.

15. Method of preloading superconducting coils by using materials with different thermal expansion coefficients

DOEpatents

Heim, Joseph R.

1993-01-01

The invention provides a high magnetic field coil. The invention provides a preloaded compressive force to the coil maintain the integrity of the coil. The compressive force is obtained by reinforcing the coil with two materials of different thermal expansion rates and then heating the coil to 700.degree. C. to obtain the desired compression. The embodiment of the invention uses Nb.sub.3 Sn as the conducting wire, since Nb.sub.3 Sn must be heated to 700.degree. C. to cause a reaction which makes Nb.sub.3 Sn superconducting.

16. Measured strain in Nb3Sn coils during excitation and quence

SciTech Connect

Caspi, S.; Barlett, S.E.; Dietderich, D. R.; Ferracin, P.; Gourlay, S. A.; Hannaford, C. R.; Hafalia, A.R.; Lietzke, A.F.; Mattafirri, S.; Nyman, M.; Sabbi, G.

2005-06-01

The strain in a high field Nb{sub 3}Sn coil was measured during magnet assembly, cool-down, excitation and spot heater quenches. Strain was measured with a full bridge strain gauge mounted directly over the turns and impregnated with the coil. Two such coils were placed in a 'common coil' fashion capable of reaching 11 T at 4.2 K. The measured steady state strain in the coil is compared with results obtained using the FEM code ANSYS. During quenches, the transient strain (due to temperature rise) was also measured and compared with the calculated mechanical time response to a quench.

17. Measured Strain of Nb3Sn Coils During Excitation and Quench

SciTech Connect

Caspi, S.; Bartlett, S.E.; Dietderich, D.R.; Ferracin, P.; Gourlay, S.A.; Hannaford, C.R.; Hafalia, A.R.; Lietzke, S.; Mattafirri,M.; Nyman, M.; Sabbi, G.

2005-04-16

The strain in a high field Nb{sub 3}Sn coil was measured during magnet assembly, cool-down, excitation and spot heater quenches. Strain was measured with a full bridge strain gauge mounted directly over the turns and impregnated with the coil. Two such coils were placed in a ''common coil'' fashion capable of reaching 11T at 4.2K. The measured steady state strain in the coil is compared with results obtained using the FEM code ANSYS. During quenches, the transient strain (due to temperature rise) was also measured and compared with the calculated mechanical time response to a quench.

18. Development of the SSC (Superconducting Super Collider) trim coil beam tube assembly

SciTech Connect

Skaritka, J.; Kelly, E.; Schneider, W.; Shutt, R.; Thompson, P.; Wanderer, P.; Willen, E.; Bintinger, D.; Coluccio, R.; Schieber, L.

1987-01-01

The Superconducting Super Collider uses approx. =9600 dipole magnets. The magnets have been carefully designed to exhibit minimal magnetic field harmonics. However, because of superconductor magnetization effects, iron saturation and conductor/coil positioning errors, certain harmonic errors are possible and must be corrected by use of multipole correctors called trim coils. For the most efficient use of axial space in the magnet, and lowest possible current, a distributed internal correction coil design is planned. The trim coil assembly is secured to the beam tube, a uhv tube with special strength, size, conductivity and vacuum. The report details the SSC trim coil/beam tube assembly specifications, history, and ongoing development.

19. Effect of Metal Proximity on a Pulsed Copper Coil

Johnson, H. K.; Schaffner, D. A.; Brown, M. R.; Kaur, M.; Fiedler-Kawaguchi, C.

2016-10-01

Generating and accelerating plasma in a stainless steel chamber affects the magnetic fields inside. These effects will decrease the field due to a pulsed coil (which will later be used to accelerate plasma) inside the chamber. This work is being done in conjunction with the Swarthmore Spheromak Experiment. Both facilities are collaborating in an attempt to accelerate and compress plasma as part of ARPA-E's Accelerating Low-Cost Plasma Heating and Assembly (ALPHA) program. Measurements of the impact of the chamber on the coil's magnetic fields were made using a B-dot probe inside the coil, which was placed at incremental distances from a metal plate. As the coil is moved from the plate, the plate's interference with the field was seen to exponentially decay. This process was repeated for stainless steel, aluminum, and copper, and a range of voltages (500-800V). At least seventy percent of the original signal was recovered within two inches. Pulsing the coil inside the stainless steel chamber resulted in signals about one third the strength of those measured outside of the chamber. The results of this experiment will be used to guide development of the stainless steel pulse-coil system for the Swarthmore ALPHA project. Work supported by ARPA-E ALPHA program.

20. Measured and simulated poloidal asymmetries of the FTU S.O.L. in the toroidal limiter configuration

Leigheb, M.; Ridolfini, V. Pericoli; Zagorski, R.

The scrape-off layer (SOL) of FTU in the magnetic configuration generated by a TZM (Molybdenum) toroidal limiter has been studied by an array of reciprocating Langmuir probes extended over a large part of the poloidal angle, and the results have been compared with the 2-dimensional multifluid SOL code EPIT. A comparison with the previous poloidal limiter configuration with the same main plasma conditions, showed at the last closed magnetic surface (LCMS) longer and more poloidally uniform connection lengths, and a corresponding better uniformity of SOL plasma parameters. Asymmetry of electron density is observed, which can be associated with the recycling of plasma near the toroidal limiter plates in a configuration with long connection lengths. Electron temperature appears to be less dependent of power entering the SOL than in the old poloidal limiter configuration. Experimentally observed dependence of the edge plasma condition on Lcon has been confirmed by the results of the 2D code EPIT.

1. Indirect measurement of poloidal rotation using inboard-outboard asymmetry of toroidal rotation and comparison with neoclassical predictions

Bortolon, A.; Camenen, Y.; Karpushov, A. N.; Duval, B. P.; Andrebe, Y.; Federspiel, L.; Sauter, O.; the TCV Team

2013-02-01

An alternative experimental spectroscopic measurement of poloidal plasma rotation in toroidally confined plasmas is proven effective in the TCV tokamak. Charge exchange recombination measurements of the toroidal rotation profile over the full mid-plane plasma diameter are used to infer the complete bi-dimensional flow structure of the intrinsic C6+ impurity, which includes its poloidal component. For divergence free flows, the difference between the toroidal rotation frequency ft = ut/R at the inboard and outboard locations on the same flux surface is proportional to the poloidal rotation. This indirect measurement provides increased accuracy as the measured quantity ft,in - ft,out≈4qup/Raxis(q is the local safety factor) is larger than the intrinsic uncertainties of a direct spectroscopic measurement of poloidal velocity. The method is applied in a variety of TCV ohmic and electron cyclotron heated L-mode plasmas in the banana-plateau collisionality regime (0.2<\

2. An improved asymmetric gradient coil design for high-resolution MRI head imaging

Tang, Fangfang; Liu, Feng; Freschi, Fabio; Li, Yu; Repetto, Maurizio; Giaccone, Luca; Wang, Yaohui; Crozier, Stuart

2016-12-01

3. Collapse pressure of coiled tubing

SciTech Connect

Yang, Y.S.

1996-09-01

The collapse pressure is a measure of an external force required to collapse a tube in the absence of internal pressure. It is defined as the minimum pressure required to yield the tube in the absence of internal pressure. Coiled tubing is sometimes used in high-pressure wells. If the external pressure becomes too high, the coiled tubing will collapse. This could not only lead to serious well-control problems, but may result in extensive fishing operations. A reliable safety criterion of collapse pressure for the coiled tubing is needed by the coiled tubing operators. Theoretical models of collapse pressure are well developed for perfectly round coiled tubing but not for oval coiled tubing. Coiled tubing is initially manufactured with nearly perfect roundness, sometimes having a small ovality (typically {le} 0.5%). Perfectly round CT becomes oval owing to the plastic mechanical deformation of the coiled tubing as it spooled on and off the reel and over the gooseneck. As the cycling continues, the ovality usually increases. This ovality significantly decreases the collapse failure pressure as compared to perfectly round tubing. In this paper, an analytical model of collapse pressure for oval tubing under axial tension or compression is developed based on elastic instability theory and the von Mises criterion. The theoretical model shows satisfactory agreement with experimental data.

4. COIL technology development at Boeing

Hurlock, Steve C.

2002-05-01

The historical COIL contributions at the McDonnell Douglas Research Laboratory, the Rocketdyne Division of Rockwell International and Boeing's Laser and Electro-Optic Systems organization are briefly described. The latter organization now contains the capabilities of the two heritage organizations. Boeing's new high pressure sealed COIL is also described.

5. Replaceable Sleeve Protects Welder Coil

NASA Technical Reports Server (NTRS)

Baker, W. L.; Simpson, C., E.

1983-01-01

New replaceable carbon insert for deflection coil in electron-beam welder promises to decrease maintenance costs. Inserts made from materials other than carbon (not yet tried) are less expensive, thus reducing costs even further. With carbon insert, deflection coils last longer and are easier to maintain.

6. An Asymmetric Birdcage Coil for Small-animal MR Imaging at 7T.

PubMed

Kim, Kyoung-Nam; Han, Sang-Doc; Seo, Jeung-Hoon; Heo, Phil; Yoo, Dongkyeom; Im, Geun Ho; Lee, Jung Hee

2016-09-30

The birdcage (BC) coil is currently being utilized for uniform radiofrequency (RF) transmit/receive (Tx/Rx) or Tx-only configuration in many magnetic resonance (MR) imaging applications, but insufficient magnetic flux (|B1|) density and their non-uniform distribution still exists in high-field (HF) environments. We demonstrate that the asymmetric birdcage (ABC) transmit/receive (Tx/Rx) volume coil, which is a modified standard birdcage (SBC) coil with the end ring split into two halves, is suitable for improving the |B1| sensitivity in 7T small-animal MR imaging. Cylindrical SBC and ABC coils with 35 mm diameter were constructed and bench tested for mouse body MR imaging at 300 MHz using a 7T scanner. To assess the ABC coil performance, computational electromagnetic (EM) simulation and 7T MR experiment were performed by using a cylindrical phantom and in vivo mouse body and quantitatively compared with the SBC coil in terms of |B1| distribution, RF transmit (|B1(+)|) field, and signal-to-noise ratio (SNR). The bench measurements of the two BC coils are similar, yielding a quality value (Q-value) of 74.42 for the SBC coil and 77.06 for the ABC coil. The computational calculation results clearly show that the proposed ABC coil offers superior |B1| field and |B1(+)| field sensitivity in the central axial slice compared with the SBC coil. There was also high SNR and uniformly distributed flip angle (FA) under the loaded condition of mouse body in the 7T experiment. Although ABC geometry allows a further increase in the |B1| field and |B1(+)| field sensitivity in only the central axial slice, the geometrical modification of the SBC coil can make a high performance RF coil feasible in the central axial slice and also make target imaging possible in the diagonal direction.

7. Magnetic Field Line Topology of the Scrape-Off Layer in the Compact Stellarator NCSX

Grossman, Arthur; Mioduszewski, Peter; Fenstermacher, Max; Koniges, Alice; Rognlien, Tom

2001-10-01

The magnetic topology of the plasma boundary of the proposed compact stellarator NCSX is investigated using the MFBE[1] and VMEC2000[2] codes. The VMEC code provides a free boundary equilibrium and the magnetics from external coils and bootstrap plasma currents inside the last closed magnetic surface (LCMS). The MFBE code uses these results to calculate the magnetic fields of these finite beta equilibria outside the LCMS in a form suitable for line tracing. The Poincaré plots of field lines started outside the LCMS indicate preservation of initial radial ordering of field lines up to intersections with vacuum vessel and plasma facing components. A large flux expansion of field lines is observed between the midplane and tips of the banana shaped cross-section, due to the presence of a nearby poloidal field null used to create the banana shape. TRIM coils used to heal islands just within the LCMS appear to reduce stochasticity just outside the LCMS as well as enhance an island structure outside the LCMS. Field lines are observed to move in and out radially as they are followed toroidally. Power and particle control design based on these observations include the limiting structure geometry and baffles designed to intersect islands outside the LCMS. [1] E.Strumberger, Nuclear Fusion 37 1997 19. [2] S.Hirshman, Comp. Phys. Commun. 43 1986 143.

8. The Coil Method in Contemporary Ceramics

ERIC Educational Resources Information Center

Nigrosh, Leon I.

1976-01-01

For centuries coil building has been the primary method of making pottery the world over. Many classrooms still reflect this preference for symmetrical coil building. Describes coil building and what forms can be made from it. (Author/RK)

9. Helically Coiled Graphene Nanoribbons.

PubMed

Daigle, Maxime; Miao, Dandan; Lucotti, Andrea; Tommasini, Matteo; Morin, Jean-François

2017-03-07

Graphene is a zero-gap, semiconducting 2D material that exhibits outstanding charge-transport properties. One way to open a band gap and make graphene useful as a semiconducting material is to confine the electron delocalization in one dimension through the preparation of graphene nanoribbons (GNR). Although several methods have been reported so far, solution-phase, bottom-up synthesis is the most promising in terms of structural precision and large-scale production. Herein, we report the synthesis of a well-defined, helically coiled GNR from a polychlorinated poly(m-phenylene) through a regioselective photochemical cyclodehydrochlorination (CDHC) reaction. The structure of the helical GNR was confirmed by (1) H NMR, FT-IR, XPS, TEM, and Raman spectroscopy. This Riemann surface-like GNR has a band gap of 2.15 eV and is highly emissive in the visible region, both in solution and the solid state.

10. Overview of torus magnet coil production at Fermilab for the Jefferson Lab 12-GeV Hall B upgrade

DOE PAGES

Krave, S.; Velev, G.; Makarov, A.; ...

2016-02-29

Fermi National Accelerator Laboratory (Fermilab) fabricated the torus magnet coils for the 12 GeV Hall B upgrade at Jefferson Laboratory (JLab). The production consisted of 6 large superconducting coils for the magnet and 2 spare coils. The toroidal field coils are approximately 2 m x 4 m x 5 cm thick. Each of these coils consists of two layers, each of which has 117 turns of copper-stabilized superconducting cable which will be conduction cooled by helium gas. Due to the size of the coils and their unique geometry, Fermilab designed and fabricated specialized tooling and, together with JLab, developed uniquemore » manufacturing techniques for each stage of the coil construction. In conclusion, this paper describes the tooling and manufacturing techniques required to produce the six production coils and two spare coils needed by the project.« less

11. Overview of torus magnet coil production at Fermilab for the Jefferson Lab 12-GeV Hall B upgrade

SciTech Connect

Krave, S.; Velev, G.; Makarov, A.; Nobrega, F.; Kiemschies, O.; Robotham, B.; Elementi, L.; Elouadrhiri, Latifa; Luongo, Cesar; Kashy, David H.; Wiseman, Mark A.

2016-02-29

Fermi National Accelerator Laboratory (Fermilab) fabricated the torus magnet coils for the 12 GeV Hall B upgrade at Jefferson Laboratory (JLab). The production consisted of 6 large superconducting coils for the magnet and 2 spare coils. The toroidal field coils are approximately 2 m x 4 m x 5 cm thick. Each of these coils consists of two layers, each of which has 117 turns of copper-stabilized superconducting cable which will be conduction cooled by helium gas. Due to the size of the coils and their unique geometry, Fermilab designed and fabricated specialized tooling and, together with JLab, developed unique manufacturing techniques for each stage of the coil construction. In conclusion, this paper describes the tooling and manufacturing techniques required to produce the six production coils and two spare coils needed by the project.

12. Numerical Study of a Crossed Loop Coil Array for Parallel Magnetic Resonance Imaging

SciTech Connect

Hernandez, J.; Solis, S. E.; Rodriguez, A. O.

2008-08-11

A coil design has been recently proposed by Temnikov (Instrum Exp Tech. 2005;48;636-637), with higher experimental signal-to-noise ratio than that of the birdcage coil. It is also claimed that it is possible to individually tune it with a single chip capacitor. This coil design shows a great resemble to the gradiometer coil. These results motivated us to numerically simulate a three-coil array for parallel magnetic resonance imaging and in vivo magnetic resonance spectroscopy with multi nuclear capability. The magnetic field was numerical simulated by solving Maxwell's equations with the finite element method. Uniformity profiles were calculated at the midsection for one single coil and showed a good agreement with the experimental data. Then, two more coils were added to form two different coil arrays: coil elements were equally distributed by an angle of a 30 deg. angle. Then, uniformity profiles were calculated again for all cases at the midsection. Despite the strong interaction among all coil elements, very good field uniformity can be achieved. These numerical results indicate that this coil array may be a good choice for magnetic resonance imaging parallel imaging.

13. Induction magnetometer using a high-Tc superconductor coil

2010-05-01

An induction magnetometer consisting of a search coil and an inverting operational amplifier is simple in structure and in signal transferring mechanism from the magnetic field input to the voltage output. Because this magnetometer is based on Faraday's law of induction, it has a lower cutoff frequency r/(2πL), where r is the resistance of the coil and L is its inductance. An attempt has been made to lower the cutoff frequency of the induction magnetometer by using a high-Tc superconductor coil. With a pancake coil (inner diameter ≈18 cm and outer diameter ≈23 cm, 92 turns, 3.23 mH) made of a Bismuth strontium calcium copper oxide (BSCCO) superconductor tape of 5 mm in width and 0.23 mm in thickness, the cutoff frequency achieved was 1.7 Hz which is much lower than that obtained with a bulky copper search coil which is typically in the range of 10-20 Hz. In the experiment, an inverting amplifier was made with a complementary metal-oxide semiconductor operational amplifier and was immersed in liquid nitrogen together with a BSCCO high-Tc superconducting coil. Discussion is made on the resolution of the induction magnetometer using a high-Tc superconductor search coil.

14. Progress on the Focus Coil for the MICE Channel

SciTech Connect

Yang, S.Q.; Lau, W.; Senanayake, R.S.; Witte, H.; Green, M.A.; Drumm, P.; Ivanyushenkov, Y.

2005-05-13

This report describes the progress on the magnet part of the absorber focus coil module for the international Muon Ionization Cooling Experiment (MICE). MICE consists of two cells of a SFOFO cooling channel that is similar to that studied in Feasibility 2 study of a neutrino factory [1]. The MICE absorber focus coil module consists of a pair of superconducting solenoids, mounted on an aluminum mandrel. The coil package is in its own vacuum vessel located around an absorber. The absorber is within a separate vacuum vessel that is within the warm bore of the focusing magnet. The superconducting focus coils may either be run in the solenoid mode (with the two coils at the same polarity) or in the gradient mode (with the coils at opposite polarity, causing the field direction to flip within the magnet bore). The coils will be cooled using a pair of small 4 K coolers. This report discusses the progress on the MICE focusing magnets, the magnet current supply system, and the quench protection system.

15. Structural and biochemical characterizations of an intramolecular tandem coiled coil protein.

PubMed

Shin, Donghyuk; Kim, Gwanho; Kim, Gyuhee; Zheng, Xu; Kim, Yang-Gyun; Lee, Sangho

2014-12-12

Coiled coil has served as an excellent model system for studying protein folding and developing protein-based biomaterials. Most designed coiled coils function as oligomers, namely intermolecular coiled coils. However, less is known about structural and biochemical behavior of intramolecular coiled coils where coiled coil domains are covalently linked in one polypeptide. Here we prepare a protein which harbors three coiled coil domains with two short linkers, termed intramolecular tandem coiled coil (ITCC) and characterize its structural and biochemical behavior in solution. ITCC consists of three coiled coil domains whose sequences are derived from Coil-Ser and its domain swapped dimer. Modifications include positioning E (Glu) residue at "e" and K (Lys) at "g" positions throughout heptad repeats to enhance ionic interaction among its constituent coiled coil domains. Molecular modeling of ITCC suggests a compact triple helical bundle structure with the second and the third coiled coil domains forming a canonical coiled coil. ITCC exists as a mixture of monomeric and dimeric species in solution. Small-angle X-ray scattering reveals ellipsoidal molecular envelopes for both dimeric and monomeric ITCC in solution. The theoretically modeled structures of ITCC dock well into the envelopes of both species. Higher ionic strength shifts the equilibrium into monomer with apparently more compact structure while secondary structure remains unchanged. Taken together, our results suggest that our designed ITCC is predominantly monomeric structure through the enhanced ionic interactions, and its conformation is affected by the concentration of ionic species in the buffer.

16. The Use of Correcting Coils in End Magnets Accelerators

Kassab, L. R. P.; Gouffon, P.

1997-05-01

The end magnets of the race-track microtron booster (L.R.P. Kassab, PhD Thesis, IFUSP, 1996) , which is the second stage of the 30.0 MeV cw electron accelerator under construction at IFUSP, play a fundamental role in terms of the beam quality. Their efficiency depends on the behavior of the magnetic fields that deflect, focus and return the beam to the accelerating section. The use of correcting coils, based on the inhomogeneities of the magnetic field and attached to the pole faces, assured uniformity of 10-5. We present the performance of these coils when operating the end magnets with currents that differ from the one used in the mappings that originated the coils copper leads. For one of the magnets, adjusting conveniently the current of the correcting coils, made it possible to homogenize field distributions of different intensities, once their shapes are identical to those that originated the coils. For the other one, the shapes are smoothly changed and the coils are less efficient. This is related to intrinsic factors that determine the inhomogeneities. However, in both cases we obtained uniformity of 10-5.

17. Performance of a 12-coil superconducting bumpy torus magnet facility

NASA Technical Reports Server (NTRS)

Roth, J. R.; Holmes, A. D.; Keller, T. A.; Krawczonek, W. M.

1972-01-01

The bumpy torus facility consists of 12 superconducting coils, each 19 cm i.d. and capable of 3.0 teslas on their axes. The coils are equally spaced around a toroidal array with a major diameter of 1.52 m, and are mounted with the major axis of the torus vertical in a single vacuum tank 2.6 m in diameter. Final shakedown tests of the facility mapped out its magnetic, cryogenic, vacuum, mechanical, and electrical performance. The facility is now ready for use as a plasma physics research facility. A maximum magnetic field on the magnetic axis of 3.23 teslas was held for a period of more than sixty minutes without a coil normalcy. The design field was 3.00 teslas. The steady-state liquid helium boil-off rate was 87 liters per hour of liquid helium without the coils charged. The coil array was stable when subjected to an impulsive loading, even with the magnets fully charged. When the coils were charged to a maximum magnetic field of 3.35 teslas, the system was driven normal without damage.

18. Study on performance improvements of a high-temperature superconducting coil with a lattice-shape cross section

Ishiguri, S.; Oka, T.; Fukui, S.; Ogawa, J.; Sato, T.

2008-07-01

For designing inexpensive high-temperature superconducting (HTS) coils, it is essential to obtain large magnetic fields and stored energy with shorter lengths of HTS tape. To improve the performance of a coil, it is necessary to improve its transport-current performance. The critical current and n-value of an HTS tape were measured at various magnetic field magnitudes and angles at 77 K. The HTS tape employed in the coil was Bi-2223/Ag tape. From this measured data, fitting equations of the critical current and n-values were obtained. With these fitting equations, coil critical currents were analyzed according to our analytical model. The analysis showed that relatively large electric fields are generated at coil edges, inhibiting improvement of the transport-current performance of the coil. To solve this problem, we propose an HTS coil, which is produced by cutting and displacing the central portion of the rectangular cross section. By this rearrangement, the magnetic field distribution changes, resulting in an improvement in the coil critical current. We calculated performances of the proposed coil by varying the magnitude of displaced coils while maintaining a constant total HTS tape length. We found that there is an optimum cross section shape of the proposed coil, which provides improvements in the stored energy and the central magnetic field. In particular, the stored energy improves by approximately 43% compared with a rectangular cross section coil employing the same HTS tape length.

19. Higher-order harmonic transmission-line RF coil design for MR applications.

PubMed

Zhang, Xiaoliang; Zhu, Xiao-Hong; Chen, Wei

2005-05-01

A novel concept based on the use of higher-order harmonic resonances in a transmission-line resonator is introduced for the design of high-frequency RF coils at high and ultrahigh fields, where conventional RF coil designs present difficulties and limitations. To demonstrate this concept, we successfully designed and fabricated a 400-MHz RF coil for rat imaging using a second-harmonic resonant microstrip transmission line. This coil has a high Q-factor, reduces coil-cable interactions without the use of a matching balun, and has a broad range for tuning the coil's resonant frequency at the loaded condition. This work demonstrates that the use of higher-order harmonics in a transmission-line resonator provides an alternative, efficient approach to the design of large and high-frequency RF coils.

20. Coiled tubing - Operations and services

SciTech Connect

Gronseth, J.M. )

1993-04-01

Drilling with a continuous (rather than jointed) drill string is an old concept that is gaining new attention as a result of recent advances made in coiled tubing and drilling technology. The development of larger diameter, reliable, high-strength coiled tubing and smaller diameter, positive displacement motors, orienting tools, surveying systems and fixed cutting drill bits have given drilling with a continuous drill string a capability that was previously unattainable. Like its many other uses, (e.g., squeeze cementing, wellbore cleanouts, flow initiation, logging) the continuity of coiled tubing gives it several advantages over conventional drill strings. These include: drilling underbalanced safely, significantly reduced trip time, continuous circulation, smaller surface requirements. Coiled tubing drilling operations have smaller surface lease requirements than most conventional rigs due to the smaller footprint of the coiled tubing unit and associated equipment. Current coiled tubing drilling operations have the following limitations: conventional rig assistance is required for well preparation; conventional rigs must assist in running long protective and production casing strings or liners; hole sizes are smaller; working depth capabilities are shallower, coiled tubing life is less. This paper goes on to discuss the history of continuous drill strings and includes information on tubing units, circulating systems, drilling fluids, well control systems, downhole tools, orientation tools, and bottomhole assemblies. It then gives a cost comparison and an application of this type of drilling.
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