Effect of mass fluctuation on collective models in dusty plasma

The grains immersed in plasma get eroded by the ions falling on to them. As a consequence, they exhibit self-consistent mass fluctuations due to perturbations in the plasma charging currents. The grain mass is then a dynamical variable. The modifications in the plasma dielectric properties are investigated and new ultra-low frequency modes are shown to exist in the plasma. Due to the dynamic character of the dust grain electric charge, dusty plasma that contain dust grains of high charge and mass, exhibit new and interesting aspects with respect to already known negative-ion plasmas. Indeed, dust grains when immersed in a plasma acquire their charge via numerous and competing processes, such as photoelectric effect, thermo-ionic effect, secondary emission and plasma particles capture by the grains. As a matter of fact, the electrons are captured by the grains, whereas the ions exchange charge with it, and hence the mass of the grain does not increase appreciably. Any wave motion in the plasma induces particle density perturbations, which in turn affect self-consistently the particle currents falling on to the grains. Consequently, as a response, the grain charge would fluctuate, giving rise to many collective effects [1, 2]. So far, the grain mass has been considered constant. Although, in realistic environments, e.g., astrophysical situations, the grain mass is variable. Indeed, the grain may be eroded also, under the effect of numerous processes such as sputtering, that is ejection of surface atoms of the grains due to striking ions, chemical sputtering, grain-grain collisions and grain disruption [3]. The grain mass is then a dynamical variable coupled to other variables such as particle density. The effect of grain sputtering on self-qravltatlnq dusty plasma dielectric properties has been investigated, and it has been shown that grain mass fluctuation is at the root of a new instability [4]. In this note we propose to investigate the effect of self-consistent grain mass fluctuations that are a response to perturbations in the plasma charging currents on wave propagation along with instability processes. New modes in the ultra-low frequency range are found.