FACTORS INFLUENCING THE STABILITY OF COLD-CATHODES FORMED BY COATING A PLANAR ELECTRODE WITH A METAL-INSULATOR COMPOSITE

Abstract

An investigation has been undertaken into the stability of populations of electron emission sites on extended-area, composite-coated cathodes for applied fields of ≤ 20 MV/m. These cathodes have been shown to give rise to total current instabilities (S) typically in the range 10 to 40 % for total emission currents of ≤ 100 µA. An optical imaging technique has revealed that the current instability is associated with temporal changes in the emission site distributions which appear to be influenced by the coating composition. Operation under increased pressure H2, N2, O2 and CO environments (P ≤ 10-4 mbar) has been shown to only slightly degrade the current stability. Furthermore, extended tests have revealed that emission sites on the composite cathodes are resistant to He-conditioning.