A new perspective on the gas conditioning of high-voltage vacuum-insulated electrodes

Abstract

An optical imaging techniques have been used to study the influence of various residual gas environments (P approximately=10-5 mbar) on both the I-V characteristics of a vacuum gap and the spatial and temporal behaviour of the associated population of electron emission sites on OFHC planar Cu electrodes. Whilst Ne, N2, H2, O2 and CO can influence the mean fluctuations of the gap current, only He and Ar result in a significant and predictable decrease in the total gap current with time, i.e. give rise to a 'conditioning' effect. However, the effectiveness of the conditioning process by these gas species is found to be dependent on the gap voltage, with He being active in the voltage in the voltage range 5-11 kV, and Ar in the range 8-15 kV. Also, the long-term permanence of gas conditioning can be influenced by a subsequent temperature cycling of the cathode within the range 30-250 degrees C. These new experimental findings are shown to give further support to a recently proposed 'electronic' model of gas conditioning, whereby the effect is achieved as a result of gas/ion implantation, and subsequent electron trap formation within a metal-insulator emitting microstructure.