Characteristics of the Output Voltage Generated by Switch Prefire in Multistage Linear Transformer Drivers

Linear transformer drivers (LTDs) are considered the most promising technology for future large-scale pulsed-power accelerators. The large number of gas switches in LTD modules might result in frequent prefire failures. This article simulated and analyzed the characteristics of the output voltages of an LTD during gas switch prefire. It was found that this output voltage was affected mainly by the brick parameters, number of series stages, and magnetic saturation. In a multistage LTD, the output voltage waveform of a switch prefire fault is usually overdamped. Based on a 28-stage LTD in the conceptual design of a CZ-15 Z-pinch driver, the output voltages and effects of prefire failures in different modes were also examined. The results revealed that the maximum operating coefficient of the gas switches that ensured no chain failure after a single switch prefiring was 0.72 when the charging voltage was $\pm$ 80 kV. For a stage prefiring, the maximum operating coefficient should be lower than 0.43. The prefiring of a group of four stages in a series was highly likely to result in switch chain discharge in the LTD. The voltage generated by cascading failures may adversely affect the insulation of the secondary water transmission line at the upstream stages.