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

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, N 2 , H 2 , O 2 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.