Collisional effects on ion-acoustic waves in a nonequilibrium plasma

For a nonisothermal plasma (Te ≫ Ti), there is a range of wavenumbers, λe−1 < k < λe−1εT−3/2, such that electrons and ions are weakly and strongly collisional, respectively. Here, λe is the electron-ion mean free path and εT = Ti/Te. Using a hybrid description, the ion-acoustic dispersion relation corresponding to this wavenumber regime is derived and analyzed. It is found that the dominant collisional effects are due to electron-ion collisions and ion viscosity. The electron-ion collision smears out the wave-particle resonance of slow electrons. Consequently, it reduces the electron Landau damping rate by an order εe1/2 (εe = 1/kλe) and increases the phase velocity by an order εe3/4. The ion viscosity increases the damping rate by an order εT5/2/εe.