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The characteristics, breakdown probability, and statistical distribution of breakdown time delay under different du/dt in hundreds of nanoseconds pulse for millimeter gaps have been investigated by employing the statistical experimental method in this paper. The experimental results indicate that both the breakdown time delay and jitter are essentially decreased as the slope of the pulse voltage- du/dt is increased for 1-, 2-, and 4-mm gaps; in particular, increasing the value of du/dt is useful to obtain the smaller relative deviation of breakdown time delay under the same breakdown electric field. The breakdown probabilities for different gaps have been analyzed and a method of utilizing the Gaussian distribution function has been proposed which can be used for evaluating the statistical distribution of breakdown time delay. When the experimental condition is 100% breakdown probability, the breakdown time delay follows a Gaussian distribution. However, it is unsuitable for the fitting of breakdown time delay utilizing a Gaussian function for 2- and 4-mm gaps from the cumulative probability distributions of breakdown time delay because of the lower du/dt values and breakdown probabilities. [ABSTRACT FROM AUTHOR]

Megavolt-class pulsed gas switches play an important role in large pulsers as transfer switches. This article analyzes the breakdown process and characteristics of a megavolt self-triggered preionized switch under 100-ns pulses based on the optical diagnosis. It is discovered that the triggering spark illumination targeting the main cathode or anode can separately preionize the main gap. The discharge channel is likely to first form between trigger electrodes and the main anode. Based on the above deduction, the streamer velocity is calculated to be $0.54 \times 10^{6}$ – $2.34 \times 10^{6}$ m/s, proportional to the electric field. Also, parameters of the empirical formula for calculating the gas heating time are amended. Influence mechanisms of the switch jitter are also studied. Under pulsed preionization mode, the trigger gap breaks down when the main gap electric field is high enough, and the switch jitter is mainly determined by the self-triggering jitter. Nonetheless, the self-triggering jitter can be partly offset during the breakdown process if the changing rate of mean reduced electric field $d(E/p)$ / dt at the self-triggering time is higher than 1.0 $1.0\left(\mathrm{kV} \cdot \mathrm{ns}^{-1} \cdot \mathrm{cm}^{-1} \cdot \mathrm{MPa}^{-1}\right)$. Under sustaining preionization mode, the trigger gap breaks down prematurely, and the continuous arcing driven by switch leak current preionizes the main gap. Therefore, the influence of the self-triggering jitter on the switch jitter can be eliminated. [ABSTRACT FROM AUTHOR]