Electro-optical measurement of transient insulator surface charging in vacuum



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Texas Tech University


Electro-optical measurements of the electric field along insulator surfaces in vacuum during the few nanoseconds prior to insulator flashover have been performed. The Pockels effect in KDP and the Kerr effect in nitrobenzene are used in conjunction with a polarization interferometer to measure the interfacial fields for KDP/vacuum and nylon/vacuum interfaces. The insulators are subjected to pulsed fields of approximately 1 X 10 V/m with a risetime of a few nanoseconds. Result indicate that insulator surface charging and cathode field enhancement occur, followed by plasma formation near the cathode which propagates toward the anode at approximately one tenth the speed of light. Voltage collapse across the insulator occurs approximately one nanosecond after the plasma formation has reached the anode.