Multiscale Modeling of Dust Charging in Simulated Lunar Environment Conditions

A key aspect of dust adhesion to space equipment is the accumulation of charge under the space plasma environment. Recent models and experiments show possible negative charging of dust grains under vacuum ultra-violet (VUV) illumination. Macroscopic potential measurements conducted during a test campaign show that both positive and negative average charging can be reached under VUV irradiation pending on vacuum chamber configuration, suggesting that both situations can exist at lunar surface. Simulations of dust charging at microscopic scale are conducted with the SPIS software to evaluate electrical charge and electric field amplifications induced by the granular structure of the lunar regolith. A multilayer pile of dust is modeled under lunar conditions. Grains from the first two layers tend to microscopically acquire both negative and positive charge patches when illuminated with a 45 degrees VUV incidence angle, this differential charging being less pronounced under normal incidence angle. It is also found that dust deeply buried in the lunar soil may charge more negative due to the collection of environmental electron only. This effect is thought to reinforce the grain supercharging model presented by other authors. We show, however, that such charge development may be limited by electrical conduction pending on dust electrical properties.