Effect of six pure metals cathode on constricted characteristics of high-current vacuum arcs subject to axial magnetic field

Abstract

The objective of this paper is to quantitatively determine the effect of the six pure metals cathode on the constricted characteristics of high-current vacuum arcs subject to axial magnetic field (AMF). To measure the current density in anode surface, a butt-type split-contact with four axisymmetrical areas was selected as the anode, with the material of CuCr25. A plate contact was selected as cathode, under six pure metals material, including Cu, W, Mo, Fe, Cr, Al, respectively. The experimental arc current was 10 kA (rms) at 50 Hz. The opening velocity was 2.0 m s−1. The currents of the four areas in the anode surface were measured using four Rogowski coils situated outside the vacuum chamber. An external uniform AMF of 74 mT was applied during the experiment. The observed arc modes were recorded by a high-speed CCD video camera. The experimental results indicate that, in the diffuse arc mode, the cathode materials effect the constricted characteristics of the vacuum arcs. The vacuum arc column with the cathode of W and Mo constricted more severe than that in Cu, Fe, Cr and Al. For the cathode of Cu, Fe, Cr and Al, the uneven distribution of anode current density was mainly at the previous stage before the current peak. After the current peak, the difference of the average current density between the central area to other three periphery areas reduced continually. However, for the cathode of W and Mo, the uneven distribution of anode current density maintained during the whole arcing time. Moreover, the influence of the six pure cathode contacts on the constricted characteristics mainly focused on the spreading angle of the plasma jet and the numbers of the jet sources in the cathode surface. With a greater number of cathode spots, the distribution of the arc current density should be more uniform.