Optical observation on a low current instability in vacuum discharge

In order to clarify the instability phenomena of a low current in the vacuum, the optical characteristics of a low current vacuum arc was investigated by using Cu, CuCr, CuW CuBi, and AgWC electrodes. We measured the spectrum-line intensity distribution during arc discharging for each electrode. It was found that for Cu, CuCc CuBi, and AgWC electrodes, the total of the spectrum intensity from 300nm to 900 (i.e. evaporation quantity) increase in the order of Cu, CuCc CuBi, and AgWC, and the chopping current decrease in the same order. The spectrum intensity of pure Cu and Cu alloy was investigated. It was found that the intensity peak (Um) decrease in the order of Cu, CuCr and CuBi, but the chopping current did not increased in the same order. It decreased in the same order with the decline speed of the intensity (dU/dt). The chopping current is mainly determined by the evaporation quantity and the thermal properties of the additives in Cu alloy. We also observed the intensities during arc voltage oscillating for each electrode. It was found for every electrode that the oscillation voltage rises to the same direction with the arc voltage, and the spectrum intensity sharply decreases at the arc voltage oscillation. It supports the view that spotless discharge (a kind of glow discharge) occurred during this period.