High-current vacuum arcs. Part 1: An experimental study

The vacuum or metal-vapour arc between butt electrodes of 6¿75mm diameter, at separations up to 40mm, has been studied experimentally throughout a range of sinusoidal current loops up to 100kA peak. The appearance and properties of the copper-vapour discharge are shown to vary widely over this current range. The well known diffuse low-voltage vacuum arc which exists at a few hundred amperes develops into a constricted higher-voltage form as the current is increased, and, during 50Hz loops in excess of about 10KA peak, the arc produces grossly melted electrode spots at temperatures which are shown to be close to the boiling point of copper. High-pressure magnetically constricted arc columns develop from these large electrode spots, producing a discharge which bears many resemblances to a high-pressure high-current arc. Theoretical interpretations of these findings are presented in the companion paper.