Lifetime and Stability of Carbon Cold Cathodes

Abstract

We present the results of tests measuring the life of carbon cold cathodes and determining what conditions limit the life of the cathode. Cathode life and stability are important for a broad range of applications, including displays, electron sources for satellite thrusters, x-ray tubes and microwave devices. Cathodes were tested in vacuum chambers using different gas environments as well as in sealed and gettered glass envelopes. We measured emission current half-lives of 10,000 - 20,000 hours or more in sealed display devices, depending on operating conditions. The presence of a significant oxygen or water partial pressure degrades the life of the cathode. After removing the gases the decay rate was restored to near the original value. A similar partial pressure of hydrogen gas has little or no effect on the life of the cathode. Initial results of operation in a xenon environment indicate carbon cold cathodes are much more robust compared to microtip cathodes. These results will be discussed with respect to the various applications considered for carbon cold cathodes.

(AASERT-97) Development of a Field Emitter Cathode for Low-Power Hall Thrusters

“…These cathodes can operate at 400 V at pressures greater than 750 mTorr of nitrogen without being damaged. While performance degradation has been observed for the diamond and carbon film cathodes while operating in oxygen-rich environments 38 ,it is anticipated that the cathode performance will be much more stable in the inert gas environment of a xenon plasma thruster. In a plasma environment with virtual anodes, space-charge effects will limit the electron current that escapes through the sheath to the plasma.…”