Ion-acoustic wave
= Ion-acoustic wave
{title2=$\omega\simeq kc_s$}
A low-<frequency> electrostatic <plasma> wave with ion inertia and a pressure restoring force, usually dominated by electron <pressure>. Weak ion <Landau damping> requires the <phase velocity> to exceed typical ion <speeds>. Electron <Landau damping> depends on the electron parallel <marginal distribution> and need not vanish even when ion damping is absent.