The Influence of Axial Magnetic Field Distribution on High-Current Vacuum Arc

The influence of the distribution of axial magnetic fields (AMFs) was investigated experimentally with three pairs of specially designed testing electrodes generating a conventional bell-shaped AMF profile and different saddle-shaped AMF distributions. The characteristics of high-current vacuum arcs (HCVAs) up to 20 kA (rms), e.g., the shape of the arc column and the distribution of cathode spots, were investigated with the aid of a high-speed digital camera with an exposure time of 2 mus. Experimental results further manifested the distinct influence of AMF distribution on the characteristics of HCVAs. Saddle-shaped AMFs could resist the constriction of HCVAs more efficiently than traditional bell-shaped AMFs. Furthermore, cathode spots in saddle-shaped AMFs distributed more uniformly than that in bell-shaped AMFs. It was found that AMFs in the central region of saddle-shaped AMFs should not be too weak. Otherwise, cathode spots would be out of control in the central region as observed in experiments. The ldquooptimalrdquo minimal AMF in the central region was estimated to be about 3-4 mT/kA.