The influence of unipolar axial magnetic field on the behaviour of vacuum arcs

The behaviour of vacuum arcs under influence of imposed unipolar axial magnetic field (AMF) is experimentally and theoretically investigated. The vacuum arc mode is studied at different arc currents based on high-speed CCD video images. In spite of applying a unipolar axial magnetic field, first signs of arc constriction appear at relatively small currents. Three different arc modes were found during the experiments. Based on generalised Ohm's law the current density distribution in the vacuum arc under influence of unipolar axial magnetic field is computed with a 3D finite-element-method (FEM) software program. The calculated current distribution confirms the vacuum arc appearance taken from CCD video film. The optimisation of distribution of AMF can generally be obtained based on such experiments and theoretical analyses.