Effects of collision-enhanced charging on dust crystal

Abstract

Numerical simulations of monolayer dust crystals in a radio frequency (RF) complex plasma were performed to examine the crystal structure and quantify the effects of including the collision-enhanced ion current in the charging model. A gaseous electronics conference (GEC) cell similar to a previous experimental work was modeled for a range of RF voltages, using a continuum description for the plasma and a particle description for dust grains. The time history of each dust grain was monitored. The dust charge was computed using both the orbital motion limited and the collision-enhanced charging (CEC) model applicable to the sheath region. The dust model accounted for the electric force, ion drag force, neutral drag force, gravity, and the ion wake. The CEC model produced a lower charge and lower electric force which agreed better with the experimental data. Then dust crystals composed of 40–100 grains were modeled and the levitation height and inter-particle spacing of the resulting crystals was examined. Including the collision-enhanced current reduced the inter-particle spacing but only had a minor effect on the levitation height.