Investigations on trigger process of triple-gap laser triggered multi-stage vacuum switch

To develop high voltage pulsed power closing switch utilizing the advantages of vacuum gap, a laser triggered multi-stage vacuum switch (LTMVS) is proposed in this paper. Trigger process of triple-gap LTMVS is analyzed based on a detachable vacuum chamber. Closing processes and time-delay characteristics of different gaps in LTMVS are studied later. The results convey that, trigger process of LTMVS can be separated to two periods, the trigger of laser triggered gap, and the cascade breakdown of series connected short gaps under impulse voltage with DC superimposition. Breakdown sequences of cascade gaps are not in stable order, and its delay time mainly depends on the initially breakdown gap. The increase of laser energy and operating voltage benefit to both reducing the delay time of triggered gap and cascade gaps. Under 30 mJ laser energy, delay time of 4 mm laser triggered gap can be controlled within 25.8 ± 1.3ns, and breakdown delay time of 0.8 mm vacuum gap reaches 79 ± 2.5ns. Suggestions for the developments of LTMVS are given based on above researches. •Performance of LTMVS depends on the interactions of series gaps' switching.•Cascade breakdown of series vacuum gaps present unstable sequences.•Delay time of vacuum breakdown under impulse voltage with DC superimposition.•Higher laser energy and voltage ratio can reduce vacuum breakdown delay time.