Reduced plume oscillation amplitude in hollow cathode discharge due to enhanced electron emission from keeper electrode

Abstract

Inspired by the fact that ionization oscillations in hollow cathode plume are triggered by electron loss on keeper electrode, this paper replaced the material of keeper orifice plate with emissive ones in order to re-compensate the electron loss and checked the influence on plume oscillations. Results show that plume oscillations were indeed sensitive to exterior electron emission. When keeper orifice plate was LaB6 and short-circuited with cathode negative electrode instead of electrically floating, the oscillation amplitude and ion energy dropped by 60% and 50%, respectively, and more under lower flow rates. However, the work function being too low would contrarily increase oscillation amplitude and ion energy. The results recommended the ratio between compensation and loss current to be unity, in which case the main emission mechanism was secondary electron emission due to ion impingement. These results would help increase thruster efficiency and extend lifetime from the perspective of thruster-cathode coupling.