Self-excited oscillations of charged dust grains in the plasma sheath

Dust particulates trapped in the sheath region around the rf or above the negative dc electrode in plasma discharges frequently form regular lattice structures. Stable structures have been formed in the laboratory and their phase transitions have been studied under neutral gas pressures varying over three orders of magnitude. In all circumstances, except at the lowest pressures, the phase transitions from a solid state structure to a fluid or gas like state can be induced by reducing the gas pressure, and conversely, a gas or liquid phase can be made to condense by increasing the pressure. The transition is attributed to an increasing (decreasing) effective particulate temperature. A mechanism that enables an understanding of the particulate heating under the variable pressure is presented. The essential feature of this mechanism is the time variation of the external potential well in which the particulates find themselves as the plasma conditions are varied. (orig.)