The Use of an Anode Probe Hole Technique to Study Conditioning Processes between Arced Copper Electrodes in Vacuum

The high voltage breakdown strength of pre-arced copper electrodes in vacuum is studied using a novel technique. The conditioning effect of arcing on the arc anode and arc cathode is correlated with the subsequent behavior of the gap under high dc voltages. It is found that the arc cathode is the least conditioned electrode and that under the conditions of the present investigation, field emission (FE) seems to be the breakdown initiating mechanism. Some FE sites appear to be formed by the breaking of cold welds upon contact opening. The relevance of the present results to the design of vacuum circuit breakers is briefly discussed.