Ionization instabilities and resonant acoustic modes

A linear stability analysis of ion-acoustic and dust-acoustic waves is carried out using a multifluid model in the presence of ionization, ion drag, and collisions of ions and dust with the background neutral gas. It is found that an unstable dust-acoustic mode of nonzero real frequency can be generated via a resonance phenomenon. This resonance develops as the frequency of the dust-ion-acoustic mode is reduced sufficiently in the long-wavelength regime that it couples strongly to the dust-acoustic mode. As the charge on dust particles exceeds a threshold, multiple low-frequency modes with large growth rates are excited suddenly. Predictions of the theory are compared with experimental results [D. Samsonov and J. Goree, Phys. Rev. E 59, 1047 (1999)].