Modeling of spherical dust charging in collisionless magnetized plasmas with DiMPl

Abstract

Determining the equilibrium charge of conducting spheres in plasmas is important for interpreting Langmuir probe measurements, plasma surface interactions, and dust particle behavior. The Monte Carlo code Dust in Magnetised Plasmas (DiMPl) has been developed for the purpose of determining the forces and charging behavior of conducting spheroids under a variety of conditions and benchmarked against previous numerical results. The floating potentials of spheres in isothermal, collisionless, hydrogen plasmas as a function of magnetic field strength and size relative to the Debye length are studied using DiMPl and compared with new results from the N-body tree code (pot) and recent particle in cell measurements. The results of all three simulations are similar, identifying a small range at modest ion magnetization parameters over which the electron current is reduced relative to the ion current. The potential as a function of magnetic field strength is found to be relatively insensitive to dust size for dust smaller than the Debye length. The potential of large dust is found to depend less strongly on flow speed for modest magnetic field strengths and to decrease with increasing flow speed in the presence of strong magnetic fields for smaller dust. A semi-empirical model for the potential of small dust in a collisionless plasma as a function of magnetic field strength is developed, which reproduces the expected currents and potentials in the high and low magnetic field limit.