Measurement of the thermal properties of a weakly-coupled complex (dusty) plasma

Abstract

Knowledge of the velocity space distribution function facilitates the characterization of the thermal and dynamical properties of a system. In this work, a comprehensive series of experiments and numerical simulations are used to measure the velocity space distribution function of the microparticle component of a dusty plasma. In particular, this work introduces the use of stereoscopic particle image velocimetry techniques in the area of dusty plasma. This dissertation presents the results of extensive simulations of the PIV measurement technique, as applied to dusty plasmas, and thediscusses the first measurements of the three-dimensional velocity space distribution function of a weakly-coupled dusty plasma.

This work demonstrates that it is possible to simultaneously measure all three velocity components over an illuminated slice of a dust cloud, allowing for a more accurate measure of the transport and energy properties of the dust cloud. From these measurements, the velocity space distribution function of a stable weakly-coupled complex dusty plasmas has been constructed for a wide range of experimental conditions.

From the simulations, it is found that there is a unique mapping function that relates measured PIV distribution to the underlying particle velocity space distribution function provided that the PIV analysis is applied to dust particles that have a size distribution that is nearly monodisperse. This mapping function is strongly dependent on the number density of the microparticle component that is being measured.

Experiments are performed using dust clouds composed of either 1.2 ± 0.5 µm alumina particles, 6.22 µm diameter melamine microspheres or 3.02 µm diameter silica microspheres. From the measured distribution functions, the bulk kinetic temperature of the microparticle component was extracted as a function of the neutral gas pressure. It was found that the bulk kinetic temperature of the microparticle component was anisotropic and significantly larger than the other plasma species. The heating mechanism responsible for these large temperatures is a function of the neutral pressure and appears to be more efficient with higher dust number densities.