Optical measurement of breakdown processes inpolymethylmethacrylate under nanosecond pulse voltage application

摘要

High-speed framing photography has revealed the propagationnvelocity of breakdown channel in polymethylate (PMMA) to be between 30nand 120 kmf/s for positive 50-kV point voltage. The waveforms of thenprebreakdown current in PMMA are essentially the same as those in liquidndielectrics. The breakdown time lag was precisely measured from thencurrent. A linear relation between formative time lag and gap spacing isnobserved for gap length greater than a critical value, indicatingnanother constant propagation velocity in this region. The velocity isndeduced from the relation to be 2.2 km/s. This value is fairly close tonthat of longitudinal waves in the solid