Investigation of the mechanisms leading to the electrical breakdown of a triggered water gaps

The breakdown of a triggered, plane-parallel electrode system with water dielectric has been investigated. The gap was triggered by a discharge initiated at an electrically isolated trigger pin, positioned in the center of one of the electrodes, using a 500 ns voltage pulse. A 5000 fps CCD-camera monitored events occurring in the gap during such a discharge and the intensity variations of a laser beam transmitted through the electrode gap was also monitored. The results indicate the initiation, expansion and collapse of a gas bubble generated at the trigger electrode. The subsequent application of a voltage between the plane electrodes results in the complete breakdown of the gap due to the trigger discharge. The effect of a delay time between the trigger pulse and the application of the main gap voltage was consistent with the growth and collapse of the trigger-initiated bubble.