Experimental study of self-breakdown voltage statistics in Cu-W electrode spark gap switches

Experiments concerning the self-breakdown voltage characteristics have been done and a simplified model has been proposed to describe the phenomena in this study. A test platform has been established to investigate the Cu-W (90 wt%) two-electrode switch working in a small airtight cavity (1.2 L). The switch was tested under the conditions of frequency of ~0.1 Hz, self-breakdown voltage of ~30 kV, and peak current of ~60 kA for more than 20000 shots. Inevitably, the process is accompanied with the insulation and electrode's aging in the switch, including the variation of gas components and electrode surface states, which eventually alters the self-breakdown voltage. The results of the experiment demonstrated that the lifetime of the switch could be divided into three stages. In the third stage, this switch showed a satisfactory reliability and stability of the self-breakdown voltage: mean of 32.4 kV and standard deviation of 2.0 %. Besides, from the view of statistics, calculation results proved that the 20000 shots' self-breakdown voltage obeyed mixed Normal distribution, whereas a continuous small sample of that simply followed Normal distribution or Weibull distribution. Moreover, it could be anticipated from the results that the Cu-W spark gap switch could have a lifetime more than 20000 shots (total charge transferred was 13259 C). However, in fact, the lifetime was terminated in advance by insulation degradation in the switch.