Ion-acoustic instability of the positive column

The excitation characteristics of the current-driven ion acoustic instability are studied, using a linearized kinetic model for a weakly ionized, unmagnetized plasma. Convective instability is predicted for typical low-pressure positive column conditions. The calculated spatial growth rates show a variation with frequency, which is similar to that of the amplitude variation with frequency of the self-excited instability measured in our positive column experiments in helium and argon. The comparison between theory and experiment indicates that ion Landau damping is significant for typical experimental conditions.