`Local¿ conditioning of broad-area vacuum-insulated high-voltage electrodes

A new in situ `local¿ conditioning technique is described for improving the hold-off capability of a high-voltage vacuum gap. This involves spatially locating individual prebreakdown electron emission sites and then selectively eliminating them by some form of `zapping¿ probe. Three types of probe have been evaluated, namely focused ion and electron beams, and needle spark knocking. For OFHC copper electrodes, the ion-beam probe was consistently the most effective, routinely giving an improvement of 200% in the insulating capability of the gap. As a control, the performance of this `local¿ conditioning technique is compared with the conventional glow-discharge and gas-sputtering `total-electrode¿ conditioning techniques.