Three-dimensional neutralizer effects on a Hall-effect thruster near plume

The near plume of an SPT100-like Hall thruster is simulated with a hybrid particle-in-cell/fluid code to assess the three-dimensional effects of the neutralizer for two different asymmetric positions. The electron fluid model accounts for the effects of both magnetization and collisions, and closes the momentum equation with a simple polytropic closure for the electron temperature. The observed asymmetries are small in the majority of the plasma plume properties and in the achieved magnetic thrust and torque, which also show consistent trends with the available experimental characterizations. The only exception is represented by the 3D electric and electron current densities, which show persistent asymmetries that tend to diminish as the neutralizer is placed both farther downstream and radially outward, outside of the magnetic separatrix. These findings permit to justify the use of axisymmetric codes for Hall-effect thruster performance estimation. The results on the neutralizer asymmetry effects are found robust to different polytropic coefficients (i.e. electron temperature gradients). Finally, the comparison of the adopted polytropic closure model against an advanced one including the energy balance equation shows relevant differences in the electron temperature but still a good agreement in the electron current density map.

Automated summary

The simulation of a near plume of an SPT100-like Hall thruster reveals small asymmetries in most plasma plume properties and achieved magnetic thrust and torque. However, the 3D electric and electron current densities show persistent asymmetries that decrease with changes in the neutralizer position. The comparison of different polytropic coefficients and closure models for the electron temperature highlights differences in temperature but good agreement in current density.