Transient behavior of drift and ionization in atmospheric pressure nitrogen discharge

Abstract

Fluid models are frequently used to describe a non-thermal plasma, such as a streamer discharge. The required electron transport data and rate coefficients for the fluid model are parametrized using local field approximation in first-order models and local-mean-energy approximation in second-order models. We performed Monte Carlo simulations in nitrogen gas with step changes in the E/N (reduced electric field) to study the behavior of the transport properties in the transient phase. During the transient phase of the simulation, we extract the instantaneous electron mean energy, which is different to the steady-state mean electron energy, and the corresponding transport parameters and rate coefficients. Our results indicate that the mean electron energy is not a suitable parameter for mobility/drift of electrons due to the large difference in momentum relaxation and energy relaxation. However, the high-energy threshold rates, such as ionization, show a strong correlation to mean electron energy. In second-order models where the energy-balance equation is solved, we suggest that it would be appropriate to rather use the local electric field to find electron drift velocity in gases such as nitrogen, and the local mean electron energy to determine the ionization and excitation rates.