Over recovery in low pressure sparkgaps

The recovery characteristics of the low pressure sparkgaps in the time interval of 300 /spl mu/s to 50 ms by the influence of 1) gap spacings of 2.5 and 10 mm, 2) pulse voltages of 45 kV rising in 2.5 /spl mu/s for positive and negative polarities, and 3) the pressure range of 1.3-34.7 Pa, have been determined for hydrogen, argon, and deuterium gases. A two-pulse system, capable of generating two pulses rising to 45 kV each in 2.5 /spl mu/s and separated by a variable delay of 100 /spl mu/s to 50 ms, has been used to study the recovery characteristics. It has been observed that the breakdown voltage under the second pulse is higher than the breakdown voltage under the first pulse along the left-hand side of Paschen's characteristics [1] and this has been defined as over recovery (>100% recovery) in these studies. The over recovery was found to be up to 120% and is dependent on the gas pressure {<23 Pa for argon, <12.1 Pa for H/sub 2/, <4.5 Pa, -ve polarity, and <14.3 Pa, +ve polarity for D/sub 2/ gases}, discharge current magnitude (>1 kA), and its reversal. This over recovery in low pressure sparkgaps is due to pressure reduction in the gap after the first pulse discharge. This finding seems to have been reported for the first time. The recovery times are independent of gas pressure for negative polarity. It increases with pressure for positive polarity. It increases with increase in molecular weight of the gas in the gap. Shorter gaps recover faster than longer gaps. The experimental setups, principal of over recovery, measurement of breakdown voltages, and currents, results and discussions are presented here.