Hall Thruster Cathode Flow Impact on Coupling Voltage and Cathode Life

Abstract

The cathode coupling voltage in Hall thrusters, which is the voltage difference between the cathode and the thruster beam plasma potential, is considered an indicator of the ease with which electrons flow from cathode to anode.Historically, the coupling voltage has beenminimizedby increasing the amount of propellant injected through the hollow cathode due to early observations that thismaximizes the discharge (or anode) efficiency.However, recent experiments described here show that the total thruster efficiency is independent of the cathode flow over the range from 5 to 10%of the propellant injected into the thruster body through the anode. For this reason, cathode flow rates can be reduced closer to the classic plume mode limit characteristic of the hollow cathode design without impacting the total thruster efficiency. Such reductions in cathode flow rate can significantly extend the cathode life, especially for higher-power Hall thrusters with larger discharge currents, where the normal Hall thruster cathode flow split will significantly exceed the optimum level for cathode operation and life.