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UBC Theses and Dissertations

Recovery processes in spark channel. Gautam, Mangal Sen


The increase in breakdown potential of a spark channel, formed by discharging a high current pulse between tungsten electrodes, has been studied at times after the current pulse ceases. The dependence of the breakdown potential on time is called the recovery characteristic of the spark channel. The characteristics have been measured for spark channels in air, hydrogen, nitrogen, argon and sulfur hexafluoride. Two new methods of measuring the spark channel temperature and diameter are described. In the first, the temperature is determined from the breakdown potential of an auxiliary spark gap in the second, the temperature is deduced by measuring the velocity of sound in the channel with piezo-electric pressure probes. The results indicate that the maximum diameter of the channel is determined by the interaction between the channel and gas in the surrounding vessel. Temperature measurements agree with the results of earlier workers. By using layered electrodes with tungsten surfaces, it is shown that the recovery characteristic of air sparks is controlled by the cooling effects of the electrodes. Measurements on hydrogen sparks, demonstrate that the breakdown potential increases significantly 10 ¯¹ sees after the spark channel is formed. Changes produced by doping the hydrogen with water vapour and oxygen indicate that this delayed increase in breakdown potential is produced by the adsorption of hydrogen onto the tungsten electrode surfaces.

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