Development of a five-moment electron fluid model for cross-field plasma discharges

Modeling of cross-field plasma discharge is challenging due to the multi-scale nature of the problem. A fully kinetic model for ions, electrons, and neutrals is a high-fidelity approach but can be computationally expensive for practical applications. An alternative is to use full-fluid or hybrid models, commonly applying the drift-diffusion approximation for electrons and assuming quasineutrality. However, these simplifications prevent the self-consistent resolution of non-neutral regions (i.e., sheaths) and electron inertial effects, e.g., gradient of the azimuthal velocity due to the ExB drift, which may contribute to cross-field electron transport. In this work, a two-dimensional, multi-fluid, five-moment model for a Hall effect thruster discharge plasma is developed which retains non-neutral and inertial effects. A simplified quasi-steady 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 proposed multi-fluid five-moment approach.