SOURCE OF HIGH-BETA ELECTRON-EMISSION SITES ON BROAD-AREA HIGH-VOLTAGE ALLOY ELECTRODES

Two recently developed techniques have been used sequentially in an attempt to define the nature of high- beta field emission sites on a commercial-alloy, broad-area, electrode surface. The techniques involved were: (i) an in-situ electron optical method for locating and examining the emission site; and (ii) a high-resolution spectrometer for determining the energy spectra of the electrons field emitted from this site. Furthermore, following these measurements, the elemental composition of the emission area was determined by electron microprobe X-ray analysis. Observations, which cast further doubt upon the traditional concept of field-enhancing microprojections, indicate that the sites are non-metallic and probably consist of impurities located at cracks or grain boundaries in the surface. Tentative hypotheses are proposed for the emission mechanism and include provision for an unstable situation caused by the effects of adsorbed gas atoms.