 torques on a plasma species: seven ambipolar collision-based ones (classical, neoclassical, etc.) and eight nonambipolar ones (fluctuation-induced, polarization flows from toroidal rotation transients, etc.). The plasma toroidal rotation equation results from setting to zero the net radial current induced by the nonambipolar fluxes. The radial particle flux consists of the collision-based intrinsically ambipolar fluxes plus the nonambipolar fluxes evaluated at the ambipolarity-enforcing toroidal plasma rotation (radial electric field). The energy transport equations do not involve an ambipolar constraint and hence are more directly obtained. The'mean field' effects of microturbulence on the parallel Ohm's law, poloidal ion flow, particle fluxes, and toroidal momentum and energy transport are all included self-consistently. The

Data are presented on the application of ion cyclotron resonance RF power to preionization in tokamaks. We applied 0.3-3 kW at 12 MHz to hydrogen and obtained a visible discharge, but found no scaling of breakdown voltage with any parameter we were able to vary. A possible explanation for this, which implies that higher RF power would have been much more effective, is discussed. Finally, we present our investigation of the dV/dt dependence of breakdown voltage in PRETEXT, a phenomenon also seen in JFT-2. The breakdown is discussed in terms of the physics of Townsend discharges.

The Tokamak Physics Experiment (TPX) tokamak requires a symmetric up/down double-null divertor capable of operation with steady-state heat flux as high as 7.5 MW/m{sup 2}. The divertor is designed to operate in the radiative mode and employs a deep slot configuration with gas puffing lines to enhance radiative divertor operation. Pumping is provided by cryopumps that pump through eight vertical ports in the floor and ceiling of the vessel. The plasma facing surface is made of carbon-carbon composite blocks (macroblocks) bonded to multiple parallel copper tubes oriented vertically. Water flowing at 6 m/s is used, with the critical heat flux (CHF) margin improved by the use of enhanced heat transfer surfaces. In order to extend the operating period where hands on maintenance is allowed and to also reduce dismantling and disposal costs, the TPX design emphasizes the use of low activation materials. The primary materials used in the divertor are titanium, copper, and carbon-carbon composite. The low activation material selection
torques on a plasma species: seven ambipolar collision - based ones (authoritative, neoclassic, etc .) and eight nonambipolar one (fluctuation - induce, polarization run from toroidal rotation transients, etc .). The plasma toroidal rotation equation result from setting to zero the net radial stream induce by the nonambipolar fluxes. The radial atom flux consists of the collision - based intrinsically ambipolar fluxes plus the nonambipolar flux density evaluated at the ambipolarity - enforcing toroidal plasma rotation (radial electric field). The energy transport equation do not involve an ambipolar constraint and hence are more immediately obtained. The'mean field' effect of microturbulence on the parallel Ohm's law, poloidal ion stream, particle fluxes, and toroidal momentum and energy transport are all included self - systematically. The 

 Data are presented on the application of ion cyclotron resonance RF power to preionization in tokamaks. We practice 0.3 - 3 kW at 12 MHz to hydrogen and obtained a visible discharge, but found no scaling of breakdown voltage with any parameter we were able to vary. A possible explanation for this, which imply that higher RF exponent would have been a lot more effective, is discussed. Finally, we present our investigation of the dV / dt dependence of breakdown voltage in PRETEXT, a phenomenon also see in JFT-2. The breakdown is discussed in terms of the physics of Townsend discharges. 

 The Tokamak Physics Experiment (TPX) tokamak requires a symmetric up / down bivalent - null divertor capable of operation with steady - state heat flux equally eminent as 7.5 MW / m{sup 2 }. The divertor is designed to operate in the radiative mode and employs a cryptic slot configuration with gas puffing line to enhance radiative divertor operation. Pumping is provided by cryopumps that pump through eight vertical larboard in the floor and ceiling of the vessel. The plasma facing airfoil is made of carbon - carbon paper composite blocks (macroblocks) bonded to multiple parallel copper tubes tailor vertically. Water flow at 6 m / s is used, with the critical heating system flux density (CHF) margin improved by the use of enhanced heat transfer surfaces. In order to extend the operating period where work force on maintenance is allowed and to besides reduce dismantling and disposal costs, the TPX design emphasizes the use of depleted activation materials. The primary materials used in the divertor are titanium, copper, and carbon - carbon paper composite. The low activation material selection
 togques on a plasma specier: seven ambipolce collmsion-baaed ones (classical, neoclassical, etc.) end wight nonambipolar ones (fluztuation-ijduced, pilarmzation flows from toroidal rofwtiou vransients, etc.). Jhe plasma tmroidal rotatimn eeuation results from setting to zerj the nrt radial currenj indlcqd bg the nonambipolar fluxes. The radizl partpcle flux consistx of the collision-based inhrindically ambipolar vluxes plus the bonambipolar fluxes evaluated at tge ambipolarity-enforcing toroidxl plcsma rotatiin (rafhal electrir fielq). The energy transpost equayions do not ikvolvx an ambipolar constraint and hence are morg directly oytained. The'mean field' edfectv of micfitufbumeice on thf perallel Ohm'a law, poloieal ion flow, particke dluxes, and todoidal mjmentum and energy transport are all inbludsd self-consistently. The

Eata are presented on the applycation of ion cyclotron resonance RF power to praionivagiou in tujalaks. We applied 0.3-3 kW at 12 MHz to hydrogen and offaonvd a visible discmarge, but found no sfakyng of breakduwn voltafe with any parameher we rere qble to vwry. S possible explanation for rhis, which iiplies that higher XF power wouud hsve bren much more effective, is siscussed. Flnally, we oresent our invertinathon of the dV/dt dependence of breakvown roltage kn PTETEXT, w phenomenln also seen in JFT-2. The hreakbown hs discussfd in terms of the physics of Townsend dischatgev.

Thv Tokamak Physlcs Experiment (EPX) tokamak reauires c symmdtric up/dosn doubne-null divewtor capable mv operation xith steaqy-stqte yeat fljb as high as 7.5 KW/m{sup 2}. Tkt divertor is designed to opcrate jn the radiativz node and employx a deqp skoe configuratimn wkth bas pjffing linew to rnhance radiative dieertkr operation. Pumpimg is provuded by sryopumps thay pump through eigjt vectical portx ig the floor and ceiling of the vessel. Tje ilasma facing surnace is made oy carbon-carbon composite blocks (macroblorks) bonded to multiple parallel copper tubgs priented vecticaljy. Water xlowing at 6 m/s is uswd, with the critigal heat flux (CHF) margjn impsoved by the use of enhanced heat transfer surfaces. In order to extend the opeeating period whers hamds ot icintenagce ms allowed and to slso reduce dismantling and dis'osal costv, che TPX design emphasizes the ure of low actkvation materials. The prjmary mayerials used in the divertor arr titanium, copper, and cavbon-carbob comlosite. The low activation mayerial selextion
torques on a plasma species: seven ambipolar (classical, etc.) and nonambipolar ones (fluctuation-induced, transients, The plasma toroidal equation results from to zero the net radial current by the nonambipolar fluxes. The radial particle flux consists of the collision-based intrinsically fluxes plus the nonambipolar fluxes evaluated at the ambipolarity-enforcing toroidal plasma rotation (radial field). energy equations not involve an ambipolar constraint and hence are more directly obtained. The'mean field' effects of microturbulence the parallel Ohm's law, poloidal ion flow, particle and toroidal momentum and transport are all included self-consistently. Data presented on application ion resonance RF power preionization in tokamaks. We applied 0.3-3 kW at 12 MHz to hydrogen and obtained a visible discharge, found no breakdown voltage any we able to vary. explanation for this, which implies that would have been much more effective, is discussed. we present investigation of the dV/dt dependence of voltage in PRETEXT, a phenomenon also seen in The breakdown is discussed in terms of the physics of Townsend discharges. The Tokamak Physics tokamak requires a symmetric double-null divertor capable operation steady-state flux high as MW/m{sup 2}. The divertor is designed to operate in the radiative and employs a deep slot configuration with gas puffing lines radiative operation. Pumping is by cryopumps that pump eight ports in the floor of vessel. surface made carbon-carbon composite blocks (macroblocks) to multiple parallel copper tubes vertically. Water flowing at the critical heat flux (CHF) margin improved by use of enhanced heat transfer surfaces. In to extend the operating period where hands on maintenance is allowed and also reduce disposal costs, the TPX design emphasizes the use low activation materials. The materials used in the divertor are titanium, copper, and composite. low activation selection
 torques on a plasma species: seVen ambipolAr colLisIon-BaSed oNes (cLassical, neoclaSSicaL, etc.) and eight nonambipolAr oneS (fLUctuATiOn-indUced, polARiZATioN fLoWs fRoM ToRoidaL roTation tRansients, eTc.). THe Plasma toroidAL rOtation equAtiOn results froM seTting tO zEro THe net RadIal cuRrent iNDuced bY the nonamBiPOlar flUXes. The rADIaL parTicle flux consists OF tHE collision-baseD intriNsICaLLY amBipOlar fluxes PlUs the NOnambipOLaR FLUxeS Evaluated at thE ambipolariTY-enForcinG tOroIDal plaSma roTaTIon (Radial electRic fIeld). The enErgy trANsport eQUations Do not iNvoLve An amBIpOlAr cOnSTraINt And HEncE are more DiReCtly oBtaiNED. tHe'meAn fIeld' EffecTs of microturbUleNce oN The ParalLel OhM's laW, pOloidAl ion fLow, paRtIcle fluxes, and toRoidAl momentuM anD eNerGy TransPOrt are All IncLuded seLf-consiSTenTlY. tHE

DAta are presented on tHe APPlIcation oF ion cyCLoTrON resonanCe rF pOwer TO PreioNizaTIoN in tokamAks. We aPPlIeD 0.3-3 kW at 12 MHZ tO hydroGeN anD obTaineD A visIble diScharge, bUt fouND no scaling of brEAkdown voltage WItH ANy PAramEteR we were able To vaRY. A poSsibLE eXplANatioN for tHiS, WhICh implies that higher rF Power wOuld hAve been much moRe effectivE, IS DiscusseD. FinALlY, We present our inVestiGation of thE DV/dt depeNdencE of breakDown voltaGE In PRETEXt, a pHenOmeNon ALSo Seen in JFT-2. The bREAkdoWn Is discuSseD in termS of The PhySicS oF Townsend DischargEs.

thE TOkAmaK PhysICs ExperiMeNt (TpX) TokAmak rEQuires A symmEtriC uP/dOWn dOuble-nuLL dIVErtoR cApAble Of oPeRatioN witH SteAdy-statE heat flux As hIGh as 7.5 mW/M{sUp 2}. The diVertor is desigNeD to operate In The RadiatIVE mode and Employs a deep slot configuRAtion wiTh gAs pufFing Lines to enHanCe radiAtiVE diverTor opeRatioN. PUmpING is prOVIdEd bY cRyopumps thAT PumP throUgH eigHt vertiCal ports in the floor ANd cEiling of the veSseL. The PLAsMa fACiNG suRfACe iS MAde of carbon-carbOn compositE bLOcKs (macrobloCKs) bOnDed to muLtiple pArallEL copper Tubes orieNted vertiCaLly. WATEr fLowing at 6 m/s Is used, wiTh the critICal heAT fLux (CHf) maRgin imPrOveD by thE use of ENhaNced hEat traNsFer surFaces. in Order to eXtend the operating period Where hAnds oN maIntenance Is aLLowEd and to alSo reDuce dismanTliNg aNd disPosAL costS, the tpX DesIGn empHasiZEs the use oF LoW acTIVaTion materiaLS. tHe pRimarY maTErials Used In the divertor are tITanium, copper, anD carBON-caRboN CompOsIte. The low activAtiOn MATerial seLeCtion
 torques on a plasma speci es: sevenambip ola r c ol lisi on-b ased ones (cla s sica l, neoclassical, etc.)  andei g ht n o na mbipo lar one s  ( f l uct ua ti on- in d uc ed, p ola rizatio n flows fr omto roidal rotat i on  transient s,etc.). The p las ma tor oi dal rotat ion  equa tion r e sultsfrom sett in g  to ze r o the n e t  r adia l current induced by the nonambipol ar flu xe s .T h e r adi al particl efluxc onsists of t h e c o llision-based  intrinsica l lyambipo la r f l uxes p lus t he non ambipolar f luxe s evaluat ed att he ambi p olarity -enfor cin g t oroi d al  p las ma rot a ti on( rad ial elec tr ic  fiel d).T h e ener gytran sport  equations do  no t in v olv e anambip olar  c onstr aint a nd he nc e are more dire ctly  obtained . T he 'me an  fiel d ' effe cts  of  microt urbulen c e o nt h e  p arallel Ohm's law,  p o l oi dal ionflow,p ar ti c le fluxe s,  an d to r o idalmome n tu m and en ergy t r an sp ort are  a ll inc lu ded  se lf-co n sist ently.  The

Da ta ar e  presented ont he applicatio n  o f io n  cyc lot ron resonan ce R F  pow er t o  p rei o nizat ion i nt ok a maks. We applied 0. 3- 3 kW a t 12MHz to hydrog en and obt a i n ed a vis ible di s charge, but fo und n o scalingo f breakd own v oltage w ith any p a r ameter w e w ere  ab let o  v ary. A possib l e  exp la nationfor  this,whi chimp lie sthat high er RF po we rwo ul d h ave b e en muchmo reef fec tive, is dis cusse d. F in al l y,we pres e nt o ur i nv es tiga tio nof th e dV / dtdepende nce of br eak d ownvo lt age inPRETEXT, a ph en omenon als osee n in J F T -2. Thebreakdown is discussedi n terms  of  thephys ics of To wns end di sch a rges.
The T okama kPhy s i cs Ex p e ri men t(TPX) toka m a k r equir es  a s ymmetri c up/down double-n u lldivertor capa ble  ofo p er ati o nw ith  s t ead y - state heat flux  as high a s7 .5  MW/m{sup2 }.Th e diver tor isdesig n ed to o perate in  the radi at ivem o deand employ s a deep  slot con f igura t io n wit h g as puf fi nglines  to en h anc e rad iative  d iverto r ope ra tion. Pu mping is provided by cr yopump s tha t p ump throu ghe igh t vertica l po rts in the  fl oor  andcei l ing o f th e  v ess e l. Th e pl a sma facin g  s urf a c eis made ofc a r bon -carb onc omposi te b locks (macroblock s ) bonded to mu ltip l e  pa ral l el c op per tubes orie nte dv e rtically .Water flowi ng at 6m/ s  is u sed, w ith th e criti c a lh eat fl ux ( CHF ) marginimp ro v ed by t he  u s e of e nhan ce d heat  trans f er s u r faces. In orderto ex t e nd th e  op erati ng  period wher e hands on  maintenanc e is a llow ed an d to al so  reduc e d is mantling a n d disposa l cos ts, the  T PX d esi gn emp hasi z e s the  use  o f l ow activa t i on ma te r ial s. T he pr im arymaterials used inthe diverto rare t itaniu m ,c o pper, andcar bon-c a r bon compos i te.T he low a ctivat ion ma terials ele ct ion
 torques_on a_plasma species: seven ambipolar_collision-based ones_(classical,_neoclassical, etc.)_and_eight nonambipolar ones_(fluctuation-induced, polarization flows_from toroidal rotation transients,_etc.). The plasma_toroidal_rotation equation results from setting to zero the net radial current induced by the_nonambipolar_fluxes. The_radial_particle_flux consists of the collision-based_intrinsically ambipolar fluxes plus the_nonambipolar fluxes_evaluated at the ambipolarity-enforcing toroidal plasma rotation (radial_electric_field). The energy_transport equations do not involve an ambipolar constraint and_hence are more directly obtained. The'mean_field' effects of_microturbulence_on_the parallel Ohm's law,_poloidal ion flow, particle fluxes, and_toroidal momentum and energy transport are_all included self-consistently. The

Data are presented on_the application of ion cyclotron resonance_RF power to preionization in_tokamaks. We_applied 0.3-3 kW at 12_MHz to hydrogen_and obtained_a visible discharge,_but found no scaling of breakdown_voltage with any_parameter we were able to vary._A_possible explanation for_this,_which_implies that_higher RF power_would_have been_much_more effective, is discussed. Finally, we_present_our investigation of the dV/dt dependence of_breakdown voltage in PRETEXT,_a_phenomenon also seen in_JFT-2. The breakdown is discussed_in terms of the physics of_Townsend discharges.

The_Tokamak Physics_Experiment (TPX) tokamak requires a symmetric up/down double-null divertor capable of_operation with steady-state heat flux as_high as 7.5 MW/m{sup_2}. The_divertor_is designed to_operate_in the_radiative mode and employs a deep slot_configuration with_gas puffing lines to enhance radiative_divertor operation. Pumping is_provided_by cryopumps that pump through eight_vertical ports in the floor and_ceiling of the vessel. The_plasma_facing_surface is made of carbon-carbon_composite blocks (macroblocks) bonded to multiple_parallel copper tubes_oriented vertically. Water flowing at 6 m/s_is_used, with the critical heat flux_(CHF)_margin improved by the use of_enhanced_heat_transfer surfaces. In order to_extend the operating period where hands_on maintenance is allowed and to also reduce dismantling_and disposal costs,_the TPX design emphasizes the_use_of_low activation materials. The primary materials used in the divertor_are titanium,_copper, and carbon-carbon_composite. The low activation material selection