Relativistic Vlasov-Maxwell Simulations of the Seed Pulse Amplification in Plasmas by Stimulated Raman and Brillouin Backscattering

Abstract

We apply a Eulerian Vlasov code for the numerical solution of the relativistic Vlasov-Maxwell equations to study the problem of the amplification of an ultra-short seed pulse via stimulated Raman or Brillouin backscattering from a long pump pulse, assumed to have an envelope with a constant amplitude, in plasmas. An analysis of the spectra of waves which participate in the amplification processes is presented, calculated by the numerical code, showing good agreement with the available predicted theoretical values. The evolution showing the pump depletion, accompanied by the counter-propagating seed-pulse amplification, compression and increased steepness of the waveform is also presented, and accurate contour plots of the distribution functions. In recent numerical simulations, it has also been shown that besides the stimulated Raman backscattering SRBS and the stimulated Brillouin backscattering SBBS, other high and low frequency kinetic instabilities can occur when evolving modes develop in the modified distribution functions during the evolution of the system. We study the wave effects of these kinetic instabilities on the stimulated Raman scattering and stimulated Brillouin scattering short pulses amplification processes. The absence of spurious noise in grid based Eulerian Vlasov codes allows to follow the evolution of the system with a fully kinetic description and accurate representation of the phase-space structures coexisting and interacting in the electron distribution function. We present results which compare favourably with what can be obtained from particle-in-cell (PIC) codes.