Effects of Adding Ferromagnetic Material on Vacuum Arc Motion

A cup-shaped axial magnetic field (AMF) contact incorporating a ferromagnetic ring was compared with flat and conventional cup-shaped contacts using fixed-gap triggered vacuum arcs. The experiments used a 12 mm contact gap, and the illustrated initial-expansion sequences were obtained at a peak current of 4 kA. High-speed images were acquired at 10,000 frames per second with a spatial resolution of 1280 by 800 pixels and an exposure of 1 microsecond. Finite element field maps show a central high-field region for the conventional contact and an off-center high-field band for the ferromagnetic contact. The maps correspond to a separate 5 mm gap and therefore support a qualitative comparison rather than a matched-gap field-to-motion correlation. In the arc-column images, apparent lateral development to the contact extent occurs at approximately 1.80 ms for the ferromagnetic contact and 2.40 ms for the conventional contact. The cathode spot measurements are defined as a projected horizontal span, which describes lateral extent without assuming rotational symmetry. Three traces per contact type indicate comparatively steadier intervals for the AMF contacts than for the flat contact. These observations support further investigation of field shaping; they do not establish three-dimensional uniformity or improved interruption capability.