Hybrid Particle-in-Cell Erosion Modeling of Two Hall Thrusters

An axisymmetric hybrid particle-in-cell model of the Hall thruster plasma discharge has been upgraded to simulate the erosion of the thruster acceleration channel, the degradation of which is the main life-limiting factor of the propulsion system. Evolution of the thruster geometry as a result of material removal due to sputtering is modeled by calculating wall erosion rates, stepping the grid boundary by a chosen time step and altering the computational mesh between simulation runs. The code is first tuned to predict the nose cone erosion of a 200-W Busek Hall thruster, the BHT-200. Simulated erosion profiles from the first 500 h of operation compare favorably with experimental data. The thruster is then subjected to a virtual life test that predicts a lifetime of 1330 h, well within the empirically determined range of 1287-1519 h. The model is then applied to the BHT-600, a higher-power thruster, to reproduce wear of its exit ring configuration over 932 h of firing. Though some optimized code features remain the same, others need adjustment to achieve comparable erosion results. Better understanding of the physics of anomalous plasma transport and low-energy sputtering are identified as the most pressing needs for improved lifetime models.