Simulation of nonlinear, kinetic stimulated Brillouin scattering

A parameter study of stimulated Brillouin scattering is presented, that covers a large parameter space of laser intensity and plasma density (I = 1 − 10 1014W/cm2, n/nc = 0.03 − 0.69). The relative importance of kinetic effects in SBS driven ion-acoustic waves is examined in a hybrid PIC model in which electrons are approximated by an isothermal Boltzmann distribution and which allows the detailed study of ion kinetic effects. A regime of weak kinetic effects, where phenomenological terms within a fluid model are likely to work is identified. The hydrodynamic model HarmoNHY [1], using a reduced decompo-sition model complements the investigation and allows to define the phenomenological parameters of the nonlinear frequency shift within the regime of weak kinetic effects. A recent analysis [2] of the parametric instability of ion acoustic waves has emphasised the importance of the parametric decay of the driven ion acoustic wave into subharmonics. Indeed the inclusion of subharmonics into HarmoNHY is found to be one of the necessary ingredients to reproduce the kinetic results