Shear-Based Model for Electron Transport in Hybrid Hall Thruster Simulations

An electron cross-field transport model based on instantaneous simulated plasma properties is incorporated into a radial-axial hybrid simulation of a Hall plasma thruster. The model is used to capture the reduction of fluctuation-based anomalous transport that is seen experimentally in the region of high axial shear in the electron fluid. Similar transport barriers are observed by the magnetic confinement fusion community due to shear suppression of plasma turbulence through an increase in the decorrelation rate of plasma eddies. The model assumes that the effective Hall parameter can be computed as the sum of the classical term, a near-wall conductivity term, and a fluctuation-based term that includes the effect of shear. A comparison is made between shear-based, experimental, and Bohm-type models for cross-field transport. Although the shear-based model predicts a wider transport barrier than experimentally observed, overall, it better predicts measured plasma properties than the Bohm model, particularly in the case of electron temperature and electric potential. The shear-based transport model also better predicts the breathing-mode oscillations and time-averaged discharge current than both the Bohm and experimental mobility models. The plasma property that is most sensitive to adjustment of the fitting parameters used in the shear-based model is the plasma density. Applications of these fitting parameters in other operating conditions and thruster geometries are examined in order to determine the robustness and portability of the model. Without changing the fitting parameters, the simulation was able to reproduce macroscopic properties, such as thrust and efficiency, of an SPT-100-type thruster within 30% and match qualitative expectations for a bismuth-fueled Hall thruster.