Nonlinear Theory and Simulations of Stimulated Brillouin Backscatter in Multispecies Plasmas

We present the first detailed particle-in-cell simulation studies of stimulated Brillouin scattering (SBS) in an underdense plasma composed of multi-ion species. In particular, collisionless nonlinear saturation mechanisms are well modeled, and are found to depend critically on the plasma composition. The effect of a self-consistently evolved non-Maxwellian ion distribution can be observed in detail. He, H, ${\mathrm{C}}_5$ ${\mathrm{H}}_{12}$, ${\mathrm{C}}_5$ ${\mathrm{D}}_{12}$, C${\mathrm{O}}_2$, and various mixtures of these gases are studied in these simulations. The reflectivities due to the SBS instability show many of the trends seen in experiments with these gases.