Cathode spot velocity of vacuum arcs

The retrograde velocity of vacuum arcs in a transverse magnetic field was investigated theoretically and experimentally. Using two opto-transistors the retrograde velocities of vacuum arcs were measured. The influence of cathode surface contamination on the spot velocity was eliminated. The retrograde velocities were measured as functions of the magnetic induction, the arc current, the electrode spacing and the cathode material (copper, titanium and 316 stainless steel). With copper as the cathode material, the arc voltage as functions of magnetic induction, arc current and electrode spacing were also measured. A model for the retrograde motion mechanism of vacuum arcs is developed. The arc velocity calculated according to this model agrees quantitatively with the reported measurements as well as qualitatively with the previously available experimental data.