Experimental investigation on the dynamic of cathode spot of vacuum arc in external transverse magnetic field

In this paper, the dynamic of single cathode spot (CS) in external transverse magnetic field (TMF) up to 200mT is investigated experimentally. The constant arc current of 40A is used in this work, with which there is only one CS. Experiments are conducted with Cu and CuCr25 butt contacts in a demountable vacuum chamber. The gap distance is fixed at 4mm. The uniform constant TMF (Bt) within the inter-contacts region is supplied by Nd-Fe-B permanent magnets. Images of CS are photographed through the observation window by a digital high-speed camera with an exposure time of 2μs. Experimental results show that the velocity Vr of retrograde motion of CS on both Cu and CuCr25 cathode increases linearly with external TMF with a proportional coefficient Kr in a certain range of Bt, and then increases nonlinearly and slowly with further increased of Bt. The proportional coefficients Kr are about 109 m/(s T) and 190 m/(s T) respectively for Cu and CuCr25 cathode.