A Two-Dimensional (z-θ) Fluid/PIC Simulation of Coaxial Hall Thrusters

This paper describes a 2-dimensional simulation of a coaxial Hall thruster that was developed in the axial-azimuthal (z θ) computational space. Most computational studies of closed-drift Hall accelerators have been in one dimension (1D) along the axial direction or in two dimensions (2D) in the axial and radial dimensions. These 1D and 2D models have had reasonable success in describing the overall behavior of the plasma discharge. However, in these descriptions, the axial transport of electrons is modeled in an ad hoc fashion, usually with a prescribed cross-field mobility. The cross-field electron mobility is likely to be influenced/established by the azimuthal dynamics. Azimuthal perturbations arise from the established equilibrium and, if properly correlated, result in a net axial transport of electrons. The numerical model developed in this study self-consistently evolves the azimuthal electron drifts, and makes no use of ad hoc transport models. Preliminary analysis of the results indicates that azimuthal plasma instabilities do contribute to the axial electron transport process. However, both numerical and theoretical challenges still need to be addressed as there were notable discrepancies in terms of the time averaged ion velocity and electron density characteristics as compared with experimental findings. These differences are partly attributed to spurious “spikes” in the plasma potential, the origins of which are yet to be identified.