Investigations of overvoltage breakdown
Levinson, Scott Joseph
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An experiment has been constructed to investigate the highly overvolted, electrical gas discharge for the following parameters: pressure (< 1 Torr - 1350 Torr), electrode spacing (1 and 2 cm), electric field (55-110 kV/cm) and electrode material (aluminum, brass, and graphite). In order to determine the effects of these parameters on the statistics associated with the observational time lag, an automated data acquisition system has been built to reduce large amounts of time lag data. An insulator has been placed over the anode in a number of experiments to examine the current waveforms resulting from electron space charge motion in the gap during the pre-breakdown stage. The results indicate that large^ fast rising (~ 1 ns) currents (~ 100 A) exist in the gap before a conducting plasma channel bridging the cathode and anode is formed. These initial currents appear to be the result of runaway electron space charge motion. The results of the statistical investigation indicate that: (1) the graphite electrode is a promising candidate in low jitter switching applications because of its large emissivity (~ le~/ns); (2) the statistics associated with the formative time lag are comparable to those of the statistical time lag (when graphite electrodes are used) at overvoltages as high as 400%. An apparent pressure dependency of the electron emission rate is a consequence of this result; (3) the formative time lag reaches an asymptotic value at the highest values of overvoltage investigated (- 2800%); and (4) the formative time lag is significantly larger than that predicted by the Streamer Theory (Raether's criteria), particularly at the highest values of overvoltage.