Vacuum arc phenomena under various axial magnetic field and anode melting

Vacuum arc phenomena under various axial magnetic fields are observed using high speed VTRs. We use disk type contacts and axial magnetic fields generated by external coils. First, we confirmed the arc behavior and arc voltage under various axial magnetic fields. As already known, the behavior of vacuum arcs and arc voltage are stabilized by increasing the axial magnetic fields. Second, using small contacts (CuCr 22 mm in diameter), we observed the behavior of cathode spots and the occurrence of anode melting with various combinations of arc current and axial magnetic fields. We determined the boundary between the melting and non-melting conditions. Small contacts enable close-up snap-shots of contact surface, and we observed the detailed features of cathode spots and anode melting.