On non-linear excitation of voids in dusty plasmas
  The void, which is a dust-free region inside the dust cloud in the plasma, results from a balance of the electrostatic force and the ion drag force on a dust particulate. The ion drag force having numerous forms, some of which are based on models whereas others are driven from first principles. To explain the generation of voids, Avinash et al.[K. Avinash, A. Bhattacharjee, and S. Hu, AIP.CP649, III ICPDP, (2002)p121]proposed a time-dependent nonlinear model that describes the void as a result of an instability. We augment this model by incorporating the grain drift and by replacing the ion-drag force by that derived by Khrapak et al., in a spherical configuration. It has been revealed that the void formation is a threshold phenomenon, i.e., it depends on the grain size. Furthermore, the void possesses a sharp boundary beyond which the dust density goes down and may present a corrugated aspect. For higher values of the grain size, the use of both ion drag forces leads to voids of a same dimension, though for grains of small sizes the Avinash force drives voids of a higher dimension. 
E. Nebbat, R. Annou and R. Bharuthram