VOLTAGE-CURRENT CHARACTERISTICS OF A DIFFUSION VACUUM ARC.

The arc voltage for a low-current vacuum arc between copper electrodes was measured in dependence on current (in the 50-340 A range), electrode separation (4. 5-36 mm) and two anode diameters (11 and 20 mm). The results show that the anode-cathode voltage contains a dc component U//o on which the oscillation component DELTA U//a is superimposed. It is found that a critical solid angle omega //c//r subtended by the anode at the cathode center exists which divided the voltage characteristics into two regions. At large solid angle, if omega greater than omega //c//r, the magnitude of the U//o component is approximately constant and the voltage fluctuation component has a low amplitude. For omega less than omega //c//r variations of U//o with solid angle have been found and DELTA U//a exhibits large amplitude fluctuations. The results can be explained on the basis of two criteria representing the mechanism of phenomena in the anode regions, i. e. , the critical solid angle and the critical power density on the anode.