Ammonia hollow cathodes were tested at interelectrode pressures near atmospheric to determine if they may be suitable for arcjet thruster applications. At high interelectrode pressures, standrd tantalum hollow cathodes were found to emit the electrons from a small spot on the cathode body or orifice plate. This concentrated spot emission may cause melting, and shorten the cathode lifetime. In an attempt to prevent exterior spot emission, hollow cathode bodies and orifice plates were constructed from boron nitride which is an electrical insulator, but the orifice plates melted and/or eroded at high interelectrode pressures. The most suitable hollow cathodes tested included a refractory metal orifice plate in a boron nitride body, with the insert insulated electrically from the orifice plate. In addition, the hollow cathode interior was evacuated to assure a low pressure at the insert surface, thus promoting diffuse electron emission. At high interelectrode pressures, the electrons tended to flow through the orifice plate rather than through the orifice, which could result in overheating of the orifice plate. Using a carefully aligned centerline anode, electron flow through the orifice could be sustained at interelectrode pressures up to 500 Torr - but the current flow path still occassionally jumped from the orifice to the orifce plate. Based on these tests, it appears that a hollow cathode would operate most effectively at pressures in the arcjet regime with a refractory, chemically stable, and electrically insulating cathode body and orifice plate.
Hollow cathodes for arcjet thrusters
Hohlkathoden fuer elektrothermische Antriebe
AIAA-Papers ; May ; 1-7
1987
7 Seiten, 14 Bilder, 6 Quellen
Aufsatz (Konferenz)
Englisch
Hollow cathodes for arcjet thrusters
AIAA | 1987
|Online Contents | 1993
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