High coulomb triggered vacuum flashover switch

As high energy pulsed power sources become more compact, switching components are needed which complement the reduced size energy store while maintaining high discharge capability previously performed by several individual switches. This paper discusses an operational triggered vacuum switch which holds off voltages to 20 kV for several minutes duration. It can be triggered reliably over a range from 2 kV to 20 kV, discharges at peak current as high as 1 MA, and operates with a charge transfer of up to 50 coulombs for hundreds of discharges without requiring maintenance. Triggering is accomplished by irradiating a dielectric flashover surface from a low voltage (2-5 kV) spark source. Triggering delay is less than 600 ns at 10 kV or higher. The switch design is derived from an earlier high power vacuum flashover switch prototype originally developed as a 40 kV isolation switch within a closed vacuum inductive energy store. Modifications include re-design of the flashover dielectric to serve both as a vacuum enclosure and discharge cable support, reduction of the number of vacuum to atmospheric interface surfaces to improve sealing, use of aluminum electrodes with ceramic lining to reduce size and weight while minimizing conductor erosion during discharge and designing small expendable electrode inserts for simple, low cost replacement. The switch is used routinely in applications including operation of a 56 kJ, 700 kA magnetic swager for forming high current cable terminations, where discharge occurs at approximately 5 minute intervals.