A charging model for a dust cloud with a size distribution and a nonuniform potential Original Research Article

When considering the problem of calculating the charge on an individual grain as part of a dust cloud immersed in a moderate-temperature ambient plasma, the potential at equilibrium cannot in general be taken to be the same on the surfaces of the constituent grains. When charging currents (such as the secondary-electron current) which have a dependence on grain size apart from the cross-sectional area (∼ r2) are present, the grain surface potential will vary from grain to grain. The secondary-electron current is considered in this paper along with the primary ion and electron currents to be the mechanisms involved in grain charging. We present a new charging model which includes a redefinition of the notion of equilibrium in a dust cloud with streaming currents. It is shown that, under specific conditions for the dust and plasma, oppositely charged grains may exist without the necessity of a temperature fluctuation. This is a new result and has promising implications for current areas of research such as coagulation in protoplanetary disks and gravitoelectrodynamics in planetary rings.