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

In the presence of gravity, the micron-sized charged dust particles in a complex plasma are compressed to thin layers, but under microgravity conditions, such as the Plasma Kristall-4 (PK-4) experiment on the International Space Station (ISS), the particles fill the plasma volume which allows the study of a 3D multi-particle system. When dust particles are injected into a dc glow discharge plasma they flow along an axial electric field until stopped by periodic oscillations of the electric field (polarity switching). This oscillation creates a change in the spatial ordering and thermal state of the particle system.



Data from the ISS is compared against experiments performed using a ground reference version of PK-4 and numerical simulations. 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. Simulation results suggest that this may be due to a modification in the plasma Debye 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.