Charging of dust grain clusters in flowing plasmas

Abstract

Summary form only given. Dusty plasmas are ionized gases containing charged dust grains and exhibiting completely new physical features such as charge variability on grain particles, collective grain-grain interactions, self-organization, and formation of various stable structures. One of the most important parameters is the charge on dust grains. The charge on dust particles can fluctuate randomly in response to fluctuations in plasma parameters. Dusty plasma can be strongly coupled, i.e., the interaction potential energy between dust grains can exceed their kinetic energy. The formation of dusty plasma crystals, fullerene-like and nano-tube dust structures, and large dust agglomerates was observed. The information about charging of an isolated grain can not be used for interpretation of the dust charging in the presence of many grains. The main issue is to understand grain-induced collective processes in the charging of dust grains when their collective interactions become important. A new 2D Particle-In-Cell (PIC) computer code is developed to study the process of grain charging in dusty plasma clusters and structures. The code allows for studies of metallic and dielectric dust particles of different materials, sizes and shapes in anisotropic plasmas. The 2D simulation domain is a part of an infinite plasma with the plasma potential at boundaries set to zero. The dust grains are placed near the center of the 2D box. The potential at dust edges can be fixed or built by collecting plasma particles (floating potential). Since dusty plasmas represent a thermodynamically open system with the high rate of plasma absorption on grains, the flowing plasma is modeled by injecting the plasma macro-particles at one of boundaries thus supplying new drifting electrons and ions. The charging process is assumed to be only due to the mechanism of the collected plasma particles on dust grains. The PIC code was used to investigate the dynamics of the charging of dust grain clusters in contact with low temperature plasmas. Plasma macro-particles which cross the dust grain boundaries are assumed to be absorbed. The time dependent charging of dust grains and discrete fluctuations of the charge on dust particles around the steady-state value are studied. The potential variation in grain's sheath regions, plasma charge density distribution close to the grains, and non-screened tail of the grain's potential due to the effects of other grains are investigated. The non-uniformity of the potential around the dust particles and the dependence of the charge value on the ion drift velocity are explained. The results provide important physical insights into the collective charging process of dust grain clusters.