Anode current density distribution in diffuse vacuum arcs and axial magnetic field

The objective of this paper is to experimentally determine the influence of axial magnetic field (AMF) B_AMF on the anode current density distribution in diffuse vacuum arcs. In the experiment, a split-anode and a butt type cathode were selected. Both electrodes have a contact diameter of 60 mm. The anode surface was divided into four regions: one central region (Area I) and three symmetrical-disposed peripheral annular-arc regions (Area II, III and IV). The central region of split-anode was selected with diameter of 20 mm. The contact material was CuCr25 (25% Cr). The arc current I_arc in the tests ranged from 4 to 14 kA (rms) at 50 Hz. The opening velocity was 2.4 m/s. The currents of the four areas on the anode contact were measured by four Rogowski coils situated outside the vacuum chamber. An external uniform AMF BAMF ranged from 0 to 110 mT was applied in the experiment. The arc modes observation was recorded by a high-speed CCD video camera. The experimental results reveal that the current density distribution on the anode surface is non-uniform in the diffuse arc mode, which is concentrated in the central region. Moreover, the results indicate that the current density of the anode central region at current peak J_AREAI^PEAK exponentially decreases with the increasing of the AMF B_AMF at a given arc current. The dependence of J_AREAI^PEAK on B_AMF with a variation of the arc current IARC was determined as J_AREAI^PEAK = (2.20 I_ARC + 0.069 I_ARC²)B_AMF^-0.22, where the corresponding B_AMF ranged from 20 to 110 mT and the corresponding I_ARC ranged from 4 to 14 kA.