Investigation on the influence of axial magnetic field on anode melting in high-current vacuum arc

It is well known that the anode melting in high-current vacuum arc (HCVA) can lead to the increase of metal vapor density and liquid droplets around current zero and even the interruption failure. In our previous experiments of cup-shaped axial magnetic field (AMF) contacts, the obvious clockwise swirl flow of liquid copper on anode surface was detected if no external AMF was imposed. In order to clarify the influence of AMF on the anode melting mode in HCVA, a Helmholtz coil was introduced to generate different external imposed AMF which could change the AMF in arc column and a series of experiments were conducted. It was found that the anode melting was weakened and finally disappeared if an increasing homodromous AMF with respect to the AMF generated by the contacts was imposed externally. However, if a reverse AMF was imposed, an anticlockwise swirl flow of liquid copper was detected on the anode surface. The swirl flow is a main source of metal vapor and liquid droplets in HCVA, which is an inducement of arc reignition. The observed phenomenon indicates that the AMF has important influence on the performance of anode melting.