Electron beam interaction with lower hybrid waves at Cherenkov and cyclotron resonances

Cyclotron and Cherenkov resonant interactions between a radially confined e lectron beam spiraling in a magnetoplasma and a quasi-monochromatic lower h ybrid wave are considered. The main physical process consists of the nonlin ear self-organization of part of the beam electrons, forming dynamically st able bunches that are continuously decelerated or accelerated while keeping resonance with the emitted wave. For the Cherenkov and anomalous Doppler r esonances, such bunches exist during an infinitely long time; the main diff erence between both cases is that, for the cyclotron resonance, the gain of energy supplied by the longitudinal motion of the beam electrons is mainly spent to increase their perpendicular energy, and only a small part of it, proportional to the ratio of the wave frequency to the electron gyrofreque ncy, is given for wave radiation. For the normal Doppler resonance case, el ectron bunches also appear during the nonlinear wave-particle evolution. Ho wever, electrons lose perpendicular energy and are accelerated along the lo ngitudinal direction. As formed bunches do not have a high stability, the i nteraction of the beam electrons with the wave weakens rather quickly, wher eas the wave radiation decreases as a function of the distance from the inj ector. (C) 2001 American Institute of Physics.