NONLINEAR-INTERACTION OF WHISTLER WAVES WITH A MODULATED THIN ELECTRON-BEAM

The nonlinear theory of a thin modulated electron beam interaction wit h a monochromatic whistler wave is considered. The self-consistent set of differential equations describing the wave amplitude evolution and the beam particle motion has been solved by a computer code. Results issued from the numerical solution of the differential system are disc ussed, namely the physical features of the nonlinear beam-wave interac tion (trapping, slowing down of the beam, wave damping, multiple bunch ing, beam focusing), as well as the influence of the physical paramete rs on the wave emission: beam energy and density, initial beam velocit y distribution, and beam current modulation. It has been shown that th e trapped particles are the source of the emission; they are decelerat ed in phase with the wave and remain in Cherenkov resonance with it ow ing to a nonlinear shift of the parallel wave number. No quasiperiodic exchange of energy between the wave and the particles has been observ ed. Time evolution of the wave amplitude and the particle energy has b een explained by a simple model, as well as the multibunched structure s appearing in the particle dynamics for certain physical parameters. (C) 1998 American Institute of Physics. [S1070-664X(98)03512-5].