The effect of penetrating radiation on the initiation of unipolar arcs

Abstract

The rate of unipolar arcing to a Ti sample which had been activated by 7 MeV protons impinging on part of it after passing through an NZ atmosphere has been observed t o be considerably reduced compared t o the rate of arcing on the unirradiated part of the sample. This observation, first made in the DITE Tokamak, was confirmed by laboratory arcing studies on Ti and stainless steel specimens. It has been shown to be the consequence of irradiation through a gaseous atmosphere and to be avoidable by irradiation in uacuo.The mechansim for this effect has been explored and appears to arise from secondary electrons produced in the gaseous atmosphere by the incident protons which then cause radiation damage in arc-initiating insulating inclusions in the metal samples.The sensitivity of these inclusions to radiation damage and the consequent suppression of their role in arc initiation has obvious implications for arcing in Tokamaks.Other technological areas which involve electrical breakdown phenomena may also be amenable to beneficial treatment by irradiation with penetrating ions.