Cathode spot movements and chopping current of pure graphite and copper-graphite in vacuum

In the paper, the cathode spot movements and chopping current of pure graphite and copper-impregnated metallized graphite (Cu-C) in vacuum were investigated. It can be found that cathode spot movements produce an arc erosion pattern composed of a large number of craters with varying distances between them. The size of the craters is less than 3 μm in diameter. This pattern indicates that the cathode spot walk randomly on the surface. Whereas, cathode spots initiated selectively on the Cu phases in Cu-C materials. The diameter of the cathode spots depends on the dimension of the Cu phases and the displacement of a cathode spot moving is equal to the distance between the Cu phases. Meanwhile, the chopping current of Cu-C is 1.18 A, far larger than that of pure graphite. The phenomenon can be explained by the different characteristics of the cathode spot movement.