ENERGY EXTRACTION FROM INTENSE ELECTRON-BEAMS IN HOT PLASMAS BY ELECTRON-CYCLOTRON WAVES

A hot weakly relativistic plasma in a magnetic field is considered in the slab description with an electron distribution which is the sum of an isotropic Maxwellian function plus a second shifted Maxwellian function describing an electron population drifting along the external magnetic field. The interaction of such a beam-plasma system with ordinary and extraordinary electron cyclotron waves propagating in a direction perpendicular to the external magnetic field and to the beam is studied. The physical system is analyzed in the geometrical optics limit and also by means of a wave-dynamical treatment. A resonance layer due to the beam appears where the condition omega(ce)=gamma-omega is verified, where gamma = (1 - v0(2)/c2)-1/2 and v0 is the beam drift velocity. If the electron beam has a sufficiently high density, an ordinary wave coming from the high-field side can be converted into an extraordinary mode precisely at omega(ce)=gamma-omega, propagating then up to the upper-hybrid layer where electron Bernstein waves are generated. When the beam density exceeds a definite threshold value, a multiple conversion process also directly involving the Bernstein waves takes place at omega(ce)=gamma-omega. The excitation of the Bernstein modes enhances the amplification of the injected waves. For definite values of the relevant parameters of the problem, the injected electromagnetic waves are Strongly amplified, the electrostatic field associated to the Bernstein mode bunching the electrons of the beam in a direction perpendicular to that along which the beam is flowing.