Vacuum flashover characteristics of laminated polystyrene insulators

Laminated insulators consist of multiple layers of thin dielectric material stacked with metal films or thin metal layers. The formed stack withstands higher voltage than an equivalent, thick single-layer insulator. In the past materials like polyester, polycarbonate and polyamides have been used with values as high as 350 kV/cm for short pulse duration (50 to 100 nsec). Other materials, such as fuse silica, have also shown values as high as 175 kV/cm. These values have been accomplished with a straight dielectric wall stack of thin wafers. Such values make the lamination and stacking technique an excellent candidate for applications where bipolar pulses and low inductance restrict the use of the J.C. Martin standard 450 design. We report experimental results of similar stacked insulator configurations using cross-linked polystyrene thin wafers of 0.010-inch and 0.020-inch thick and SS 304 0.0005-inch thick. The voltage used for testing is produced by a triggered Marx generator capable of 400 kV output with a rise time of 25 nsec and a pulse length of about 1.5 /spl mu/sec. A voltage ring-up gain of about 20% is reported as the peak voltage and the RC line extension crossover as the averaged voltage. The results of testing different layer densities and different metal locations are described in this paper. We also describe the preparation and cleaning techniques that we have used, including plasma cleaning and pre-testing glow discharges.