Electrode erosion of repetitive long-life gas spark switch with large current load in airtight chamber

To improve the two-electrode gas spark switch with electrodes made of Cu-W alloy (of composition 30 wt% Cu and 70 wt% W), we experimentally investigated the electrodes' erosion mass and surface condition varying with the number of shots. The experiments were conducted in an airtight chamber (1.2 L) which was filled with dry air and without gas blowing system, and under some extremely strict conditions including repetitive frequency of 0.1 Hz, self-breakdown voltage of 30 kV, and peak current of 75 kA for over 5 000 shots. The results showed the cathode electrode erosion rate was 6.3×10^-6 cm³/C, more than that of the anode electrode, 5.5×10^-6 cm³/C, indicating more erosion on the cathode. There were many craters, saliences, and cracks on the surfaces of both operated electrodes. The self-breakdown voltage of the tested switch increased in the test process; at the 5 800th shot, the switch did not breakdown under voltage of 45 kV, and hence was determined as being failed. Besides, the surfaces of PTFE insulators in the switch got new elements, like Cu and W, but lost some F component. Therefore, under the conditions of sealed chamber and being driven by large current, the reaction between melted and ejected electrode materials and insulator which produced electro-negative gas was speculated as the main reason for the switch failure.