Generalized Bohm sheath criterion for lunar dusty plasma and its interaction with lunar surface: Dust charging, dynamics, and levitation

The emission of photoelectrons from the lunar surface due to the oblique incidence of solar ultraviolet (UV) radiation significantly affects the lunar plasma–surface interaction, which is crucial to understanding the dust charging mechanism and dust dynamics of lunar dusty plasma. In this work, a collisionless fluid model is used to study the characteristics of lunar dusty plasma-surface interaction. The general modified form of the Bohm sheath criterion that applies to dusty plasma and a dust in plasma is derived to ensure the formation of stable lunar sheath. The Bohm velocity is found to be supersonic and subsonic; however, it depends on the solar zenith angle and photocurrent density from the lunar surface as well. The discrepancy in the modified Bohm sheath criterion from the previous work due to overlooking the effect of photoelectron concentration is presented. The effects of solar zenith angle, photocurrent density, and non-Maxwellian electrons on the concentration of surface photoelectrons, local equilibrium dust charge, and charging of lunar surface are studied for lunar dusty plasma (DP) and those properties are compared with a dust in plasma (DiP) case. The temporal evolution of dust charge and trajectory of lofted dust grains along with dust levitation have been graphically illustrated.