Relation Between Cathode Processes and Voltage Instabilities of Low Current Vacuum Arc

An image of the cathode spot of low-current (3-6 A) vacuum arc on copper was observed by streak camera with temporal resolution up to 2 ns and spatial resolution of 10 nm. Waveforms of arc current and voltage were recorded simultaneously and synchronized to the streak sweep with an accuracy of 4 ns. It was found that in general the relation between the arc voltage and cathode spot luminosity is not direct. There are luminosity fluctuations at virtually steady voltage. Meanwhile, in the case of unstable voltage, the splash of luminosity leads to the decrease of voltage and to the increase of arc current