Current runaway in insulators affected by impact ionization and recombination

When impact ionization occurs, current runaway can arise in insulators, due to a regenerative effect between the rate of ionization and the rate of current injection at the cathode. Solving a set of conduction equations analytically, the critial field for current runaway F̄r was determined as a function of insulator properties, when the effect of impact ionizations is opposed by recombinations. Current transients were obtained by computer solutions for fields both smaller and larger than the critical field F̄r. The current transients can be used to determine the ionization coefficient and the recombination cross section. For fields larger than F̄r times to current runaway tr were found to decrease quasiexponentially with increasing field.