Investigations of arc instabilities in DC vacuum arcs

Investigations of low currents vacuum arcs (< 30 A) have been performed on CuCr, Cu and W contact materials in order to evaluate their chopping current behavior. Results show that the arc burning between CuCr contacts is relatively stable with an average lifetime of 16 ms at 7A, in the presented test set-up. On the other hand, Cu and W contacts are less stable and more predisposed to current chop. They need a larger current to sustain an arc of a similar average lifetime, with 25 A for copper and about 27 A for tungsten. For approximatively the same average arc lifetime, it was observed that the magnitude of the arc noise, i.e. the voltage fluctuations, between both Cu and W contact pairs could reach values higher than 1500 V, whereas the ones of CuCr stayed limited below 300 V. This result denotes differences that could be exploited in further studies to assess the fundamental under-lying physical process of the life and death cycle of the cathode spots.