Relativistic electron beam acceleration by nonlinear scattering of electromagnetic waves in a magnetized plasma

Abstract

Acceleration and heating of a relativistic electron beam due to nonlinear electron Landau and cyclotron damping of electromagnetic waves in a magnetized plasma are investigated theoretically and numerically on the basis of the relativistic kinetic wave and transport equations derived from the relativistic Vlasov–Maxwell equations. Two electromagnetic waves interact nonlinearly with the relativistic electron beam, satisfying the resonance condition of ωk−ωk′−(k⊥−k⊥′)vd−(k∥−k∥′)vb≃mωce, where vb and vd are the parallel and perpendicular velocities of the relativistic electron beam, respectively, and ωce is the relativistic electron cyclotron frequency for the electron beam. The beat waves whose frequency is near the frequency of the extraordinary wave are excited by two electromagnetic waves. The beat waves resonate with the relativistic electron beam and accelerate efficiently. Nonlinear electron Landau and cyclotron damping of the electromagnetic waves has been studied by the numerical analysis of the relativistic nonlinear wave-particle coupling coefficients, assuming the relativistic electron beam with the relativistic drifted Maxwellian momentum distribution without the cross-field drift (vd=0), and it was verified that the highly relativistic electron beam with the energy of βmec2≲5TeV can be accelerated efficiently by the Compton scattering and the beat-wave excited extraordinary waves, where β=(1−vb2∕c2)−1∕2. For comparison, the equations of motion for the beam electrons trapped in the beat wave in the frame of reference moving with vb are analyzed. The detailed acceleration mechanism was clarified and the qualitative agreement with the numerical results was obtained.