Effect of External Cathode Azimuthal Position on Hall-Effect Thruster Plume and Diagnostics

Abstract

The T-220HT Hall-effect thruster was tested with the external cathode at different azimuthal locations to determine the effect of an external cathode on the far-field plume. The cathode is mounted in two configurations: 1) on top of the thruster, perpendicular to the plane of plume measurements, and 2) in the plane of plume measurements. The thruster was tested at discharge voltages of 150–300 V at a constant discharge current of 9 A on krypton propellant. The vacuum facility operating pressure was below for all operating conditions. Noticeable changes in the plume ion current density were measured that indicate plume asymmetry. With the cathode in the plane of the probes, the ion current density peak increases by up to 43% and the divergence angle decreases by up to 2.6 deg. However, there is less than a 5 V shift in the ion energy distribution, and the distribution shape remains constant. The results indicate that an external cathode alters the plume symmetry and creates a region of increased ion flux. An analysis of the cathode generated species densities indicates that the increase in ion current density is caused by nonuniform ingestion of cathode neutrals and nonuniform electron density near the cathode. This phenomenon can affect thruster plume measurements as well as the orientation of thrusters for satellite integration.