Investigation of the Redistribution of Kinetic Energy in a Microgravity Complex (Dusty) Plasma

Abstract

In the presence of gravity, the micron-sized charged dust particles in a complex plasma are compressed to thin layers, but under the microgravity conditions of the Plasma Kristall-4 (PK-4) experiment on the International Space Station (ISS), the particles fill the plasma, and we can investigate properties of a three-dimensional multi-particle system. This dissertation examines the change in the spatial ordering and thermal state of the particle system created when dust particles are stopped by periodic oscillations of the electric field, known as polarity switching, in a dc glow discharge plasma. Data from the ISS is compared against experiments performed using a ground reference version of PK-4 and numerical MD code simulations. Initial results show substantive differences in the velocity distribution functions between experiments on the ground and in microgravity. The dust cloud in microgravity gains thermal energy at the application of polarity switching, a periodic oscillation of the electric field. This change in energy is seen in multiple plasma conditions (power, pressure) and whenever there is a change in the electric field direction, not just when polarity switching is applied. Simulation results suggest that this may be due to a modification in the dust screening length at the onset of polarity switching. Experimental measurements and simulations show that an extended time (much greater than the Epstein drag decay) is required to dissipate this energy back into the plasma. This larger timescale for dissipation than compared to Epstein drag is likely due to the ability of the interparticle structural energy to serve as an energy sink for the dust cloud.