Thermionic emission of an oxide cathode in a low-pressure gas discharge

Abstract

The thermionic emission of a flat oxide cathode in a 3 torr argon DC discharge has been determined in the regime of moderate ion bombardment; that is, with relative ion currents of up to 15%. The electrode temperatures were about 1000K, the current densities were up to 2.5 A cm-2. The work-function phi 0 and the Richardson constant AR, depend on the discharge current density j. At low discharge currents the electron current density at zero electric field at the cathode surface, j0=ARexp(-e phi 0/kT), is related to j as j0 approximately=1/2j, and depends only sightly on the cathode temperature. The ion bombardment appears to activate the cathode in the gas discharge, and j0 increases with higher discharge currents up to a temperature-dependent maximum j0-value. This activation is reversible, which indicates a competing deactivation process at the cathode surface in the gas discharge. Still further increase of the discharge current leads to erosion of the cathode.