A particle beam is a stream of charged or neutral particles. In particle accelerators, these particles can move with a velocity close to the speed of light. There is a difference between the creation and control of charged particle beams and neutral particle beams, as only the first type can be manipulated to a sufficient extent by devices based on electromagnetism. The manipulation and diagnostics of charged particle beams at high kinetic energies using particle accelerators are main topics of accelerator physics. Sources Charged particles such as electrons, positrons, and protons may be separated from their common surrounding. This can be accomplished by e.g. thermionic emission or arc discharge. The following devices are commonly used as sources for particle beams: Ion source Cathode ray tube, or more specifically in one of its parts called electron gun. This is also part of traditional television and computer screens. Photocathodes may also be built in as a part of an electron gun, using the photoelectric effect to separate particles from their substrate. Neutron beams may be created by energetic proton beams which impact on a target, e.g. of beryllium material. (see article Particle therapy) Bursting a Petawatt Laser onto a titanium foil to produce a proton beam. Manipulation Acceleration Charged beams may be further accelerated by use of high resonant, sometimes also superconducting, microwave cavities. These devices accelerate particles by interaction with an electromagnetic field. Since the wavelength of hollow macroscopic, conducting devices is in the radio frequency (RF) band, the design of such cavities and other RF devices is also a part of accelerator physics. More recently, plasma acceleration has emerged as a possibility to accelerate particles in a plasma medium, using the electromagnetic energy of pulsed high-power laser systems or the kinetic energy of other charged particles. This technique is under active development, but cannot provide reliable beams of sufficient quality at present. Guidance In all cases, the beam is steered with dipole magnets and focused with quadrupole magnets. With the end goal of reaching the desired position and beam spot size in the experiment. Applications High-energy physics High-energy particle beams are used for particle physics experiments in large facilities; the most common examples being the Large Hadron Collider and the Tevatron. Synchrotron radiation Electron beams are employed in synchrotron light sources to produce X-ray radiation with a continuous spectrum over a wide frequency band which is called synchrotron radiation. This