Influence Mechanism of Cathode Materials on the Transition Process of Arc Modes in Drawn Vacuum Arcs Under External AMF

The objective of this article is to determine the influence mechanism of the cathode materials on the transition process of the arc modes in high-current drawn vacuum arcs under the external axial magnetic field (AMF). Six kinds of pure metal of Cu, W, Mo, Fe, Cr, and Al were selected as the cathode materials. A high-speed charge-coupled device (CCD) video camera was selected to record the arc appearance. The experimental results indicate that the cathode materials had a great effect on the arc modes in the high-current vacuum arcs with the application of AMF. Under the cathode of W and Mo, the arc modes turned to the constriction arc mode and the anode spot arc mode more easily than that under the cathode of Cu, Fe, Cr, and Al, with the increase of the arc current. For various cathode materials and same anode, the critical current density inputting to anode surface for the transform of vacuum arc modes was different. This should be caused by the differences in the constricted characteristics and the ion energy of the vacuum arcs, which took a significant effect on the transition process of the arc modes in the vacuum arcs under AMF. The higher ion energy would lead to a more active anode, which resulted in the positive ion and metal vapor from the anode. Moreover, the cathode materials played different roles in the various stages of the discharging process of the drawn vacuum arcs. The effect of cathode material on the transition process of the arc modes in the high-current vacuum arc mainly took in Stage II, which sustained from the end of the bridge arc column to the arc current peak and dominated the transition process of the arc modes.