Controlling dust charge in complex plasmas

Abstract

A dusty plasma is a four-component plasma consisting of electrons, ions, neutral gas, and microparticles (dust) which collect charge from the surrounding plasma environment. They can be found in every regime of plasma physics - from ice in planetary rings to eroded materials in fusion devices. Academics view dust as a potential tool; the coupling between the equilibrium properties of the dust and the properties of the background plasma gives isolated particles potential as a minimally-perturbative plasma diagnostic, while the ability to measure individual and collective particle behavior through direct observation instead of instrumental inference makes them extremely appealing as an analog for studying the behavior of soft-body systems or as a tool for investigating statistical mechanics. Conversely, most practical plasma applications view dust as a nuisance that needs to be avoided or removed. Both sets of interest are ultimately hindered by our lack of direct and independent control over the most fundamental property of the dust - the charge.

The research presented in this dissertation focuses on investigating and developing techniques to exert control over the equilibrium charge of dust suspended in a plasma, specifically whether it can be accomplished with minimal perturbation of the background plasma. The details and results of two experiments are presented: In the first, an electric field oscillating at a frequency greater than the dust response, but less than the ion-neutral collision rate is applied in an attempt to generate a net increase in ion collection. In the second, an ultraviolet (UV) source is used to generate photoelectric currents from the particles to shed excess negative charge. A computational project examining the role of particle geometry in photoelectric charging is also presented.