Relativistic electron beam acceleration by cascading nonlinear Landau damping of electromagnetic waves in a plasma

Abstract

Acceleration and heating of a relativistic electron beam by cascading nonlinear Landau damping involving three or four intense electromagnetic waves in a plasma are studied theoretically based on kinetic wave equations and transport equations derived from relativistic Vlasov–Maxwell equations. Three or four electromagnetic waves excite successively two or three nonresonant beat-wave-driven relativistic electron plasma waves with a phase velocity near the speed of light [vp=c(1−γ−2p)1/2, γp=ω/ωpe]. Three beat waves interact nonlinearly with the electron beam and accelerate it to a highly relativistic energy γpmec2 more effectively than by the usual nonlinear Landau damping of two electromagnetic waves. It is proved that the electron beam can be accelerated to more highly relativistic energy in the plasma whose electron density decreases temporally with an appropriate rate because of the temporal increase of γp.