Ion acoustic waves in plasmas with light and heavy ions

Abstract

The damping and dispersion of ion acoustic waves in a plasma with two ion species has been studied. We have investigated the transition from collisional to collisionless regimes using the Grad 13-moment approximation. Two branches of the ion dispersion relation have been found. The fast mode has a similar velocity as in plasmas with one ion species, but a much stronger damping rate due to the friction force between light and heavy ions. The effect of friction disappears when both ion species have the same charge-to-mass ratio. The heavy ions with a low degree of ionization strongly increase the magnitude of the fast ion acoustic wave damping. The slow ion acoustic wave is also found in the collisionless region, but this mode vanishes when its frequency approaches the ion-ion collision frequency. The stimulated Brillouin scattering from two ion species plasmas has been discussed in the context of recent experimental data. It is shown that stimulated Brillouin scattering reflectivity from the laser-produced plasma is dramatically increased when both ion species have the same charge-to-mass ratio.