The frequency and damping of ion acoustic waves in collisional and collisionless two-species plasma

The dispersion properties of ion acoustic waves (IAW) are sensitive to the strength of ion-ion collisions in multi-species plasma in which the different species usually have differing charge-to-mass ratios. The modification of the frequency and damping of the fast and slow acoustic modes in a plasma composed of light (low Z) and heavy (high Z) ions is considered. In the fluid limit where the light ion scattering mean free path, λth is smaller than the acoustic wavelength, λ = 2π/k, the interspecies friction and heat flow carried by the light ions scattering from the heavy ions causes the damping. In the collisionless limit, kλlh >> 1, Landau damping by the light ions provides the dissipation. In the intermediate regime when kλlh ∼ 1, the damping is at least as large as the sum of the collisional and Landau damping