Investigations of the plasma conditions in the sheath using dust grain as probes.

Abstract

Dust particles can be levitated against gravity in the sheath of the plasma, and different types of ordered structures can be formed by adjusting the pressure and power of the system. To explain the formation and stability of the ordered structures, it is important to know the plasma parameters such as temperature and number densities of the plasma species, the charges on dust particles, electric fields that accelerate the particles, the ion wake field formed downstream of the dust grains, as well as the ion flow velocities. The main focus of this dissertation is to determine these quantities that are difficult to measure experimentally. In a dusty plasma experiment, the dust grains themselves can be used as probes to measure plasma parameters as the perturbations produce by the grains are minimal. In this study, a molecular dynamics simulation of ion and dust dynamics is used to probe the plasma characteristics. The simulation allows calculation of the charges collected by the dust particles, including the effects of ion-neutral collisions. The model is used to investigate the variations in the electron and ion density within the sheath region. The results obtained from this study agree with the previous numerical and experimental studies, and also allow the ion flow velocities to be determined. The potential structure around the dust grains that is responsible for the attraction between the same polarity charged dust grains is also resolved using this model.