Implementation of an Entropy Closure Model for 2-D Hybrid Hall Thruster Simulations

An entropy closure formulation for Hall thrusters was implemented in a radial-axial hybrid simulation. We modeled the entropy production and its scaling with effective collision frequency and magnetic field. This entropy source was used in an entropy transport equation resulting in a differential equation for the effective electron mobility. With this formulation, the effective electron mobility is a computed variable. This paper presents the results of 2-D hybrid simulations of a laboratory Hall thruster that incorporate this model and compares these results to simulations using both Bohm and experimental measurements for the mobility. Simulations were also performed using this model for varying discharge voltage and background gas density. The background gas density is found to have a significant effect on the computed discharge current. The entropy closure model is found to better capture the current-voltage characteristics that are measured experimentally than other models used for electron transport.