Experimental investigation on the influence of axial magnetic field on the lifetime of cathode spot of vacuum arc

In this paper, the characteristic of the lifetime of CS of vacuum arc with single CS in external axial magnetic field (AMF) up to 220mT is investigated experimentally at a constant arc current of 20A. Experiments are conducted with Cu and CuCr25 butt contacts in a demountable vacuum chamber. The uniform constant AMF (Bn) within the inter-contacts region is supplied by Nd-Fe-B permanent magnets. The arc voltage are measured by a high-voltage probe respectively, and recorded by an oscilloscope with a sample rate of 1.25GS/s, i.e., a time resolution of 0.8ns. The influence of AMF on the lifetime of CS is mainly investigated through a statistical analysis on the oscillation of arc voltage caused by the extinguishment of an old CS and the formation of a new CS. Experimental results show that the lifetime of CS exhibited a distribution similar to a Gaussian distribution, where its average value is approximately ranging from 80ns to 110ns under applied AMFs. Result also indicated that, the average lifetimes of CS of both Cu and CuCr25 electrodes increase significantly with Bn in a certain range of external AMF, e.g., 0≤Bn≤60mT, after which it decrease slowly with further increase of external AMF (60mT ≤Bn≤220mT). In addition, the average lifetime of CS of CuCr25 electrode is longer that of Cu electrode.