Model of a diffuse column vacuum arc with cathode jets burning in parallel with a high-current plasma column

The behavior of the high-current diffuse columnar arc in vacuum is considered. A single cathode spot jet appearing to the side of a high-current plasma column is studied using a two-dimensional magnetohydrodynamic model. The plasma expansion and current flow in the jet are affected by the presence of the main column and the applied axial magnetic field (AMF). Increasing the current in the plasma column causes the arc voltage to increase, in turn affecting the displaced parallel jet. For instance, the current density near the anode for the parallel jet increases by factor of 1.8 in the case of a 15 kA plasma column. In this case, its anode sheath potential drop increases from a negative voltage drop of about 1 V toward zero. When the arc voltage exceeds a critical value, the anode sheath potential of the jet changes from negative to positive. The displaced jet can continue burning only if the anode supplies a significant fraction of its near-anode plasma. We apply this model to study experimentally observed changes in the high-current arc behavior in an AMF. The observed mode transitions of the arc column appear to be related to a critical arc voltage condition.