Numerical method for dynamic dust charge in molecular dynamics simulations of laboratory and lunar dusty plasma environments

A novel per-time step, per-particle efficient and accurate numerical method for modeling dynamic dust charge in dusty plasma simulations is presented. A variety of charging currents are implemented, and any charging current with an analytical expression or empirical value can be included. While work on charge-varying dust has long existed in the literature, our numerical model provides significant improvements to the spatial and temporal evolution of dust charge for molecular dynamics simulations of dusty plasma. When charge time exceeds simulation time, we allow for non-equilibrium dust charge by coupling the charge convergence to the simulation time step. The model is verified with the well-known Spitzer potential and tested with a simple laboratory RF-plasma discharge background plasma and Particle-In-Cell lunar surface output background plasma. When both gradients in the plasma profiles and gravity are included, the steady state is a dynamic equilibrium, where particles oscillate when using the dynamic dust charge model as opposed to stationary equilibrium for static dust charge. Modeling varying or dynamic dust charge allows exploring new complex dynamics with simulations, such as ion-acoustic waves, dust heating, lunar cavity dust transport, and in general, dynamic equilibrium conditions, which can arise from dynamic dust charge.