Closing mechanism of electrically-triggered vacuum surface flashover switch

Electrically-triggered vacuum surface flashover switches (VSFS) with fast closure, low jitter, high repetition frequency, and compact design will facilitate more efficient energy transfer in pulsed power systems. An in-depth study of the physical processes during the closing phase is the key to advancing the development of VSFS. The fast exposure images of the VSFS breakdown process are captured in this paper by the intensified charge-coupled device (ICCD). A theoretical model of the main gap closure process of VSFS is proposed according to the images. The breakdown process of the main gap is divided into three stages in the model, the escape and collision of the electron, the formation of the vacuum-stream discharge channel, and the impedance collapse of the main gap. The physical process of each stage and the critical conditions are carried out based on experimental phenomena and theoretical models. The results reveal that the increase in the collisional ionization coefficient due to the increase in gas pressure is the direct reason for the change in the main gap discharge pattern. •The electron cloud is the first phenomenon of the VSFS main-gap discharge.•The vacuum-stream discharge channel only forms in high operating voltage.•High collisional ionization coefficient leads to the vacuum-stream discharge.•The vacuum-stream discharge channel location depends on the electric field distribution.