Collisional charging of dust particles by suprathermal plasmas. II -- Regularized Kappa distributions

Abstract: We study the effects of the velocity distribution functions of the plasma particles on the equilibrium charge of dust grains, acquired through inelastic collisions of the particles with the grains. This paper is the second in a series of two papers on the subject. Here, we consider the charging process when the plasma particles are statistically described by the recently proposed regularized Kappa distribution functions, which allow for extreme suprathermal states, characterized by extremely low values of the kappa index, previously forbidden to the standard Kappa distributions, whose effects on dust charging were studied in Paper I of this series. We analyse the effects that extreme suprathermal states of the plasma particles have on dust charging and verify conditions for the uncommon result of positive equilibrium charge, employing two different models for the regularized Kappa distributions, one with kinetic temperature dependent on the kappa index, and another where the temperature is kappa-independent.