Modeling the energetic tail of a dusty plasma's electron energy distribution and its effect on dust grain charge and behavior

Abstract

A model for a weakly ionized dusty plasma is proposed in which UV or x-ray radiation continuously creates free electrons at high energy, which then cool through collisions with a cold neutral gas before recombining. The transition of a free electron from high energy at birth to low energy at demise implies that the electron energy distribution is not the simple Maxwellian of an isolated system in thermal equilibrium, but instead has a high-energy tail that depends on the recombination time. This tail can have a major effect on dust grain charging because the flux of tail electrons can be substantial even if the density of tail electrons is small. Detailed analytic and numerical calculations of dust grain charging show that situations exist in which a small high-energy tail dominates charge behavior. This implies that dust grain charge in terrestrial and space dusty plasmas may be significantly underestimated if a Maxwellian distribution is assumed and the non-thermal dynamics are neglected.

Phase and Morphology of Water-ice Grains Formed in a Cryogenic Laboratory Plasma

“…Although the coalescence of water molecules into ice grains is slower due to the lower collision frequencies and larger intermolecular spacing, ice can still nucleate and grow, since sublimation is also comparatively weaker at these pressures and temperatures. Both the nucleation mechanism (Bellan 2022) and the growth process (Bellan 2020) rely on ice gaining a sufficient amount of charge through electron collection, a condition satisfied in both protoplanetary and interstellar environments (Nicolov & Bellan 2023). While the rates of observed processes will differ from those in the laboratory, and further theoretical work must be done to establish the form of this scaling, the fundamental mechanisms should remain valid.…”