Optical investigation of arc spot formation on cold cathodes in air

The column of a high current arc was magnetically blown against a cathode positioned perpendicularly to the arc axis. A linearly increasing voltage was applied to this electrode. It was shown by high-speed photography that the arc spot ignition is initiated by an intensified light emission on the cathode within an area of approximately 40- mu m diam. SEM micrographs from the traces produced during the ignition phase revealed that craters with diameters of some micrometers are formed within a burning spot, which corresponds in size to the optical spot. They are similar in size and shape to the craters formed by vacuum arcs on cathodes of the same material.<
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