Behavior near the current zeros of an alternating-current cascade arc in argon

A model describing an arc plasma in argon is developed and predictions are compared with data from an ac cascade arc experiment. The model accounts for nonequilibrium effects such as ambipolar diffusion to the confining wall, differing species temperatures, and finite reaction rates. Dissociative recombination of electrons with the argon ionic dimer is accounted for, as well as multistep ionization and three-body recombination. The model contains no free parameters and is based on experimental data only at the level of collision cross-sections and reaction rates. The model successfully explains experimental features near current zero in the ac arc, where the ionic dimer plays an important role.