Electrical Facility Effects on Hall-Effect-Thruster Cathode Coupling: Discharge Oscillations and Facility Coupling

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The physical mechanisms that govern the electrical interaction between the Hall-effect-thruster electrical circuit and the conductive vacuum-facility walls are not fully understood. As a representative test bed, an Aerojet Rocketdyne T-140 Hall-effect thruster is operated at 3.05 kW and a xenon mass flow rate of with a vacuum facility operating neutral pressure of , corrected for xenon. Two electrical witness plates, representative of the facility chamber walls, are placed 2.3 m radially outward from thruster centerline and 4.3 m axially downstream from the thruster exit plane. The cathode is radially translated from 18.1 to 77.8 cm away from the thruster centerline. At each cathode position, the discharge current and the electrical waveform of the radial and axial plates are simultaneously measured. As the cathode radial position changes from 18.1 to 77.8 cm from the thruster centerline, the discharge-current oscillation frequency decreases between 17 and 35% for the electrically grounded thruster-body case, and between 15 and 23% for the electrically floating thruster-body case. The analysis of the electron current collected by the radial plate suggests that electrons directly sourced from the cathode impinge on the radial plate at large cathode positions. Overall, the results of this work show that the chamber walls act as an artificial electrical boundary condition that keeps the Hall-effect-thruster plume plasma potential to within certain bounds.