Plasma–particulate interactions in nonuniform plasmas with finite flows

The polarization force on a charged particulate or ‘‘dust’’ grain in a nonuniform plasma with finite ion flows and an external electric field is derived, based on a fluid approximation for the background plasma. This polarization force is proportional to the magnitude of the spatial gradient of the Debye length, and acts in the direction of decreasing Debye length. When the ion flow velocity is sufficiently large compared to ion thermal velocities, ions do not participate in the formation of sheaths around negatively charged particulates and the electron Debye length must be employed, since sheaths comprise only a deficiency of electrons. If the ion flow velocity is small, the contribution of the ion flow to the polarization force is proportional to the spatial gradient of the flow kinetic energy and is thus usually negligible. The expressions describing the plasma–particulate interaction may be applied to the modeling of contaminant behavior in materials-processing plasmas.