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The acceleration of a charged particle is achievable only by means of an electric field. An electric field can arise from a number of processes that include the motion of plasma across magnetic fields lines, charge separation, and time varying magnetic fields.
Acceleration of charged particles in laboratory plasmas is achieved by applying a potential gradient between metallic conductors (cathodes and anodes); by producing time varying magnetic fields such as in betatrons; by radio frequency (RF) fields applied to accelerating cavities as in linear accelerators (LINACS); and by beat frequency oscillators or wake-field accelerators that use either the electric field of lasers or charged particle beams to accelerate particles.
The magnetospheric plasma is essentially collisionless. In such a plasma, electric fields aligned along the magnetic field direction freely accelerate particles. Electrons and ions are accelerated in opposite directions, giving rise to a current along the magnetic field lines.
The possibility of producing electric fields by the space-charge effect to accelerate positive ions to high energies was first discussed by Alfv\'{e}n and Wernholm in 1952. They were unsuccessful in their attempt to experimentally accelerate ions in the collective field of clouds of electrons, probably because of the low intensity of electron beam devices available then. However, proof of principle came in 1961 when Plyutto reported the first successful experiment in which ions were collectively accelerated. By 1975, the collective acceleration of ions had become a wide-spread area of research. Luce reported collectively accelerating both light and heavy ions to multi-MeV energies, producing an intense burst of D-D neutrons and nuclear reactions leading to the identification of several radioisotopes. Luce used a plasma-focus device and attributed the collective beam to intense current vortex filaments in the pinched plasma. Subsequently in 1979, Destler, Hoeberling, Kim, and Bostick collectively accelerated carbon ions to energies in excess of 170 MeV using a 6 MeV electron beam. Individual ion energies up to several GeV using pulsed-power generators have been suggested in particle-in-cell simulations of collective ion acceleration processes.
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The Los Alamos neutron Science Center (LANSCE) is a two-mile long, 800 mega-electron-volt proton linear accelerator for experiments supporting defense and civilian research. |
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