The paper reports on numerical study of the energy loss in spark gap switches. The operation of the switches is analyzed using the Braginsky model which allows calculation of the time dependence of the spark channel resistance. The Braginsky equation is solved simultaneously with generator circuit equations for different load types. Based on the numerical solutions, expressions which determine both the energy released in a spark gap switch and the switching time are derived.
This article presents the electrical and mechanical design of a compact 13-stage 0.5-MV Marx generator operating at a pulse repetition frequency (PRF) of 100 Hz. The fast-switching process of the generator is based on spark gaps, operated under pressurized air and leading to the generation of an output pulsed voltage with a peak of 0.5 MV and a rise time of 15 ns when operated on a 300-load. Corona-stabilized electrodes are installed near the main gap of the switches to improve their operational stability and increase the PRF. To ensure compactness, the Marx generator is housed in a cylindrical metal vessel with a height of 92 cm and an outer diameter of 34 cm, having a total volume of 74 L. A highly accurate simulation using both PSpice and CST software packages was used to predict the impulse waveform at the output of the generator and to help in optimizing the generator design. The tests show a good agreement between the experimental data and the theoretical predictions.
Power thyristors triggered in impact-ionization wave mode are capable to replace spark gap switches, bringing major advantages into repetitive pulsed power industrial applications. Low power thyristors remained for the moment out of the research focus, most likely because of the challenging driver, which must provide a sufficiently fast and powerful triggering pulse. This paper describes subnanosecond switching of standard off-the-shelf low-power thyristors in impact-ionization wave mode, running by the PCSS trigger generator based on the laser diode and GaAs switches. Several types of thyristors with a rated voltage from 0.6 kV to 2.2 kV have been tested running by both a commercial FID and by the tailored PCSS generators. The triggering and current flow stages were examined. For the 1.6 kV thyristor (TO-247 package), the following parameters have been obtained: switching time 250 ps, dI/dt up to 12 kA/μs, amplitude 85 A and FWHM about 60 ns. In this mode, the first 103 pulses have not revealed any thyristor degradation.
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