Insulator and electrode mass erosion and surface voltage holdoff recovery for transient, high current surface discharges

Several polymeric insulator materials commonly used as sidewall insulators in electromagnetic accelerators were subjected to repetitive (from ~0.1 to 1 discharge per second), high current (from ~100 to 300 kA peak or ~100 to 300 kA/cm), transient (~20 μs pulse width) surface discharges. The insulator materials tested include the thermosetting polymers G-9, G-10, and G-11 (i.e., fiberglass reinforced melamine and epoxy) and the thermoplastic polymers Lexan (i.e., polycarbonate) and Delrin (i.e., polyacetyl). Empirical scaling relationships are given that relate the amount of insulator and electrode (i.e., molybdenum) mass erosion to the total amount of arc energy transferred. Scaling relationships are also given for the lifetime of the given polymer as a function of the initial discharge current. The lifetime of an insulator material is defined as the number of discharges required to reduce the initial surface holdoff voltage to its half-power level for three consecutive discharges and is a useful parameter when specifying insulator materials to be used in high-power switching devices