Ionization instability of acoustic modes in dusty plasma with ion drag and charging dynamics

The excitation of the zero frequency mode (which may be the precursor to the void phenomenon in a dusty plasma) at high dust densities is examined taking into account the effects due to grain charging dynamics. The two acoustic modes considered are the dust acoustic mode and the dust electroacoustic mode. These effects are shown to reduce the threshold of the instability. The reduction is mainly due to the increase in the ion attachment frequency with the dust space charge. At high dust density, the destabilization caused by the reduction in the phase-velocity due to small qd and adiabatic dust charge fluctuations also become important. The relevance of these results to recently observed “voids” in dusty plasmas is briefly discussed.