Visualization and characterization of high-current diffuse vacuum arcs on axial magnetic field contacts

We have investigated the behavior of drawn vacuum arcs for several designs of axial magnetic field (AMF) contacts using high-speed digital photography and arc voltage measurements, As the peak current was increased, a gradual transition occurred in the arc appearance from a multiple cathode-spot arc to the high-current diffuse mode, and then to a high-current diffuse columnar mode. Two relatively simple models based on the literature are used to explain the results. The first is an empirical criterion for using the arc voltage behavior to determine the maximum arc current for which an AMF geometry can produce a high-current diffuse mode from the initial bridge column arc. The second model predicts the highest arc current that can be forced into a fully diffuse mode for given values of the AMF and the contact arcing radius. The predictions of these models are compared to our experimental and analytical results.