Kinetic models of ESD spark resistance in atmospheric pressure gases*

Electrostatic discharge (ESD) can create hazards through the rapid breakdown of an air gap between charged objects. Sensitive devices within the discharge circuit can be exposed to short rise-time, high current pulses produced by the formation of a spark channel bridging the gap. The collapse in the electrical resistance of the channel occurs through the mechanisms of ionization degree increase and hydrodynamic expansion. Under the low temperature, atmospheric pressure conditions of the formation phase of the spark, the ionization can be in non-equilibrium with the gas temperature, thus requiring a kinetic approach to model the populations of charged species.

We present here a time-dependent model of the spark channel that includes collisional-radiative kinetics to calculate species populations, independent energy equations for the electrons and heavy species, and a simplified momentum equation for the channel expansion. Observable quantities predicted by this model include channel radius, discharge current, spark resistance, electron density, temperatures (electron and heavy species), and configuration-averaged line emission. This model is applied to ESD scenarios with series RLC circuits and spark gaps consisting of pure argon or nitrogen at atmospheric pressure. The results compare favorably with experiments conducted at Colorado School of Mines involving an enclosed spark gap chamber using those same gases.