The design of a cathode to operate in an oxygen-rich environment

Abstract

The primary problem with Hall plasma accelerator operation on oxygen is poor cathode performance and short lifetime. The primary problem with micro Hall thrusters is the absence of a stable low power cathode. Cathodes traditionally used for both applications employ thermionic emitters which are not efficient and which are easily oxidized in an oxygen-rich environment. The field emitter cathode presented in this report has the potential of filling both vacancies since it does not require a high-power heater and can be scaled down with the size of the thruster. The advantages to using Hf and HfC as emitting materials are low work functions and high resistance to oxygen poisoning. Preliminary investigations proved that HfC emitters can operate in 7.6 mTorr oxygen pressure environments. The initial cathode design employs an electrostatic lens that also acts as an ion filter to prevent thruster ions from bombarding the field emitters while decelerating the electron beam and keeping it focused to ensure efficient performance. Electron trajectories through the cathode and ion filtering capabilities are presented in this report as predicted by the charged particle code, MAGIC. © 1997 American Institute of Physics.