Studies of plastic insulators under shock conditions

As experiments done with explosively driven switches and magnetic flux compression generators become complex, the details become increasingly important. In most experiments the detonation of explosives is done through layers of material that include metal and plastic, which may retard the detonation, and at the same time the insulating materials must maintain their integrity at high voltages. We have initiated some small-scale experiments that use a few hundred grains of explosives to study effects on shocked materials. These studies look at effects on detonation through various materials as a function of their thickness, and will be compared with hydrodynamic computer modeling done with the MESA2D code. Another related series of experiments observed the voltage breakdown of insulators under shock conditions. In this set of experiments insulators made of polyethylene, Teflon and Mylar were placed between two electrodes and exposed to 120 kV during a shock. The timing of the shock was determined from light produced at a flash gap. Photo-diodes coupled to optical fibers were used to transmit the signals to the diagnostic bunker. A Pearson probe was used to monitor the current at the insulator during the breakdown. The timing of the breakdown relative to the shock arrival time was recorded. The breakdown data as a function of materials and geometry are provided in this report. Also, these data are compared with computer simulations that may suggest material conditions at the time of insulator failure.