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Description:
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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 . |