Experimental Investigation of a Large Diameter Cathode


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Experimental Investigation of a Large Diameter Cathode


Abstract

A large-diameter lanthanum hexaboride hollow cathode has been experimentally investigated at discharge currents of 20 to 225 A as part of the development of the RF-Controlled Hollow Cathode. Hollow cathodes used in the next generation of Hall thrusters will have to produce 300 to 700 A of discharge current while operating for tens of thousands of hours. This large-diameter cathode is a proof-of-concept experiment intended to address both long-life and high-current operation. Cathode current-voltage characteristics and temperature profiles were measured with varied discharge currents, mass flow rates, and gas species. Using krypton allowed for plasma ignition at lower voltages than argon for comparable flow rates, and current-voltage characteristics measured with krypton qualitatively match cathode behavior in the literature. While operating at 20 A, cathode temperatures decreased for both argon and krypton with increasing mass flow, contrasting with prior large-cathode behavior. Finally, heater-insulating boron nitride was found to chemically interact with tungsten wire heaters at high temperatures causing frequent heater failures; graphite standoffs are a proposed solution.