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 nun. The anode surface was divided into four regions: one central region (Area I) and three symmetrical-disposed peripheral annular-arc regions (Area 11, 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 B-AMF 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 J(ARC) was determined as J(AreaI)(Peak) = (2.20 I-ARC + 0.069 I-ARC(2))B-AMF(-0.22), where the corresponding BAMF ranged from 20 to 110 mT and the corresponding I-ARC., ranged from 4 to 14 kA.