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Ignition and lifetime of low current DC vacuum arc ignited by the opening of the electrodes

The ignition and lifetime of a low current DC vacuum arc, which was ignited by the opening of the electrodes, were investigated experimentally. Copper electrodes were used and the arc current was less than 50 A. Waveforms of the voltage and current between the electrodes at the moment of the arc ignition and during the arc were measured. Lifetime of the arc was measured as a function of the arc current and output voltage of the DC current source. It appeared that, for the ignition of the arc, a voltage which was larger than a critical value should come out between the electrodes at the moment of the opening of the electrodes. After the ignition, the arc voltage consists of a certain DC level, around 20 V, and an additive high frequency component. The arc current consists of a certain DC level and a subtractive high frequency component. The lifetime of the arc is short, less than in the present condition, and increases with increasing arc current and output voltage of the current source.