Charging of insulating dust grains in flowing plasmas with a directed photon flux

Abstract

The charging of the perfectly insulating dust grain in flowing plasmas and in the presence of a directed photon flux is studied using the particle-in-cell numerical simulations. In flowing plasmas a finite size dust grain acquires an electric dipole moment, and the formation of wakes in the potential and plasma density, that are more pronounced for supersonic flows, is observed. The photoelectric effect is important for the dust charging in space, planetary atmospheres and fusion reactors. Recently the possibility of the dust charge manipulation in rf discharges by the UV radiation has also been discussed. We study the total charge and charge distribution on the dust grain for different photon fluxes and different angles of the photon incidence with respect to the plasma flow. We find that the resulting positive charge on the dust surface, together with the photoelectrons, may distort spatial features in plasma in the vicinity of the dust. We compare our results with the case without the photoelectric effect. Our analysis is done in two spatial dimensions, with electrons and ions treated as individual particles.