Charging time scales and magnitudes of dust and spacecraft potentials in space plasma scenarios

Abstract

We investigate the interaction of dust with space plasmas and spacecraft with a special focus on the typical values of equilibrium charge and the typical time scales required to reach them. It is well known that objects in space become charged through the combination of a number of different processes: the photoelectric effect, the collection of free electrons and ions from the plasma, and by secondary electron emission due to the impact of highly energetic particles. In the equilibrium state, currents between the plasma and the charged object are balanced. However, perturbations on the orbit of the charged body and perturbations of the distribution of plasma particles may lead to time dependent deviations in charge. In this study, we are interested in order of magnitude estimates of these deviations as well as the time scales on which a charged body in space recovers to the equilibrium charge. Our study includes Maxwellian and Kappa plasma particle distribution functions and the role of motion on charged dust, as well as the effect of dust impacts on time dependent spacecraft potentials. We derive simple relationships on order of magnitude estimates and on time scales of different charging processes and apply our results to charged dust in the heliosphere and spacecraft potential analysis of the Magnetospheric MultiScale Mission around the Earth.