Over recovery in low pressure spark gaps-confirmation of pressure reduction in over recovery

The over recovery in sparkgaps (Nagesh, 1997, Nagesh et al., 1999) operating along the left-hand side of Paschens' characteristics is due to pressure reduction in the gap after the first pulse discharge. This pressure reduction leading to over recovery in low pressure spark gaps has been verified using a low pressure spark gap with two spark gaps placed one above the other in the same chamber. The breakdown voltage strength characteristics of the second gap has been determined for gap spacings of 3.5 mm to 10 mm, diffusion of plasma in the direction of vacuum pumping and opposite, at a pressure of 2.1 Pa for hydrogen gas. The vacuum pumping direction has a great influence on the breakdown strength characteristics of second gap after the first gap discharge. The breakdown voltage of the second gap can exceed its self breakdown voltage only 1) when the diffusion of plasma and vacuum pumping direction are same and 2) when the second gap spacing is greater than or equal to first gap spacing. Shorter gaps can always have breakdown voltage lower than or equal to their self breakdown voltage. The experimental setups, behavior of self breakdown voltages of second gap due to breakdown in the first gap, over recovery characteristics of spark gaps, the results, and discussions are presented here.