A non-neutral multi-fluid moment model for Hall effect thrusters

The state-of-the-art Hall effect thruster simulations use the drift-diffusion approximation for electrons and the quasineutral assumption. These simplifications reduce the computational cost of the model but prevent the self-consistent resolution of non-neutral regions (i.e., sheaths) and inertial effects, which may contribute to cross-field electron transport by augmenting the effective electron collision frequency. In this work, a two-dimensional, multi-fluid, five-moment model for electrons and ions in a Hall effect thruster is developed. The model retains inertial terms for electrons and does not assume quasineutrality. A simplified one-dimensional model is used for the neutral gas. An energy-limited boundary condition is presented to account for the virtual cathode and truncation of the electron velocity distribution function in sheaths in the presence of secondary electron emission. We compare the model results to particle-in-cell Monte Carlo collision simulations and discuss the advantages and limitations of the presented multi-fluid moment approach.