Thermal Effect on AMF Electrodes at Different Opening Speeds

The erosion and thermal states at current zero for the axial magnetic field (AMF) electrodes after high-current vacuum arcs (HCVAs) were studied at an average opening speed of 2 m/s. The results obtained are compared with similar results received earlier at an average opening speed of 1 m/s. The discharge was ignited in a demountable vacuum chamber by opening the contacts and was fed with the half-sine current pulse of 10 ms in duration. To determine the thermal state of the surface of the electrodes at zero current, a Phantom MIRO M310 high-speed video camera with a Carl Zeiss 100 mm F2 lens was used. In addition, the surface of the electrodes after the arc exposure was photographed by a Canon camera. The study showed that at the same current an increase of the opening speed leads to an increase in the thermal effect on the electrodes. Besides, the work revealed that at high opening speed (HOS) the process of appearances of erosion traces on the cathodes and, especially, on the anodes, is significantly different. The estimations made in the work showed that the difference in erosion traces on the anode is associated not only with an increase in the thermal effect but also with a change in the momentum transferred to the anode by cathode jets due to jets relaxation in the interaction with the secondary anode plasma in a long arc.