Voltage recovery studies for a high energy spark gap

An investigation of the voltage recovery vs time for a high energy spark gap has been performed with N2, air , SF5 , and mixtures of these as filler gases and with copper-tungsten, stainless steel, and graphite electrodes. The goal of the work was to determine the main parameters affecting the free recovery (no gas flow) of the spark gap. The percentage voltage recovery of a spark gap was measured by applying two (1 - coswt) or two ( 1 -exp(-t/RC)) successive pulses with varying parameters. The important factors that determine the percentage voltage recovery include the charging rate, the gas pressure, the energy deposited in the spark gap, the statistical delay time, and the attachment coefficient of the gas. The time to 90% voltage recovery, at a gap pressure of 1 atm, is about 1.5 ms in SF5 and SFs-No gas mixtures, 2 ms in a i r , and 3 ms in N2. The i n i t i al temperature after spark gap breakdown was measured spectroscopically by a two-line intensity ratio method. The gas density variation (or the temperature variation) was examined by Mach-Zehnder interferometry. The thermal expansion velocity evaluated from the interferograms is about 10^ to 10^ cm/s. The spatial position of the pulse pair with different delay times has been observed for plane electrodes. The results show that the breakdown position is determined by the density variations between electrodes and Paschen's Law, as expected. The Edels voltage recovery model was used to predict the theoretical voltage recovery. It is in quantitative agreement with the experimental data.