SRS-SBS competition and nonlinear laser energy absorption in a high temperature plasma

Abstract

Stimulated Raman and Brillouin scattering of laser radiation in a plasma corona are outstanding issues for the inertial confinement fusion. Stimulated Raman scattering may produce absorption of a significant fraction of laser energy near the plasma quarter critical density associated with plasma cavitation and generation of hot electrons. By contrast, stimulated Brillouin scattering operates in a lower density plasma and prevents the laser light access to the absorption region. In the present paper, we report the results of analysis of competition of these two parametric instabilities with a series of one-dimensional kinetic simulations of laser-plasma interactions. We revised several flexible methods for controlling the SRS-SBS competition in inertial fusion plasmas. Suppression of SBS favors SRS excitation, electron acceleration and cavitation. The latter process makes an important contribution to the laser absorption by trapping the backscattered light. Consequently, by controlling the Brillouin backscattering through variation such plasma parameters as ion acoustic wave damping, divergence of the plasma expansion velocity or the laser bandwidth, we demonstrate the possibility of controlling the level of nonlinear laser absorption and scattering in a hot, weakly collisional plasma.