The initial expansion process in triggered vacuum arc under different axial magnetic field distributions

The motion of cathode spots in the initial expansion process of triggered vacuum arc under bell-shaped and saddle-shaped AMF was investigated with the aid of high-speed digital camera with exposure time of 2 microseconds. Experimental results indicated that cathode spots expanded faster under saddle-shaped AMF than under bell-shaped AMF. Furthermore, the motion of cathode spots slowed down between 15 kA and 20 kA in the case of bell-shaped AMF, whereas, cathode spots tended to quicken up with the increase of arc current under saddle-shaped AMF. Based on the images of cathode spots, it was proposed that the concentration of cathode spots at relatively high current and strong central AMF could also inhibit the outward motion in the initial expansion process.