The role of excited electronic states in ambient air ionization by a nanosecond discharge

Abstract

The mechanism of air ionization by a single nanosecond discharge under atmospheric conditions is studied using numerical simulations. The plasma kinetics are solved with ZDPlasKin and the electron energy distribution function is calculated with BOLSIG+. The model includes the excited electronic states of O and N atoms, which are shown to play the main role in plasma ionization for ne > 10 16 cm -3 .For electric fields typical in nanosecond discharges, a non-equilibrium plasma (Te > Tgas) is formed at ambient conditions and remains partially ionized for about 12 nanoseconds (ne < 10 16 cm -3 ). Then, the discharge abruptly reaches full ionization (ne ≈ 10 19 cm -3 ) and thermalization (Te = Tgas ≈ 3 eV) in less than half a nanosecond, as also encountered in experimental studies. This fast ionization process is explained by the electron impact ionization of atomic excited states whereas the fast thermalization is induced by the elastic electron-ion collisions.

Jetting axial flow induced by nanosecond repetitively pulsed discharges in quiescent ambient air

“…It was suggested in [32], that the ionization rate in nanosecond discharges can be significantly accelerated by considering the direct electron impact on the ionization and dissociation from the excited N * 2 states. Later, it was found [37] that by considering additional ionization channels from eight states of N and three states of O-atoms, the transition time to a fully ionized plasma regime can be reduced to 0.5 ns, which is in a good agreement with the experimental data.…”

“…From the spectra shown in figure 9, it can be seen that the intense emission lines are located near 500 nm, corresponding to the transitions from N + ( 3 S, 3 P 0 , 3 F 0 ). According to the kinetic mechanisms suggested by Minesi and Laux [37][38][39], N + is the dominant ion after transition to the LTE regime. Approximately 70% of the electrons are produced by electron-impact ionization of the N * excited states.…”

“…It was recently shown that ionization from the electronically excited states of atoms and molecules plays a major role in the transition to the LTE regime on nanosecond and subnanosecond time scales [32,37]. It was suggested in [32], that the ionization rate in nanosecond discharges can be significantly accelerated by considering the direct electron impact on the ionization and dissociation from the excited N * 2 states.…”

“…To retrieve the key concept of plasma behavior, we used a synthetic profile of a constant electric field of 15 ns in duration with a 2 ns front rise time, as suggested in [37]:…”

Effects of plasma kinetic modeling on performance characterization of plasma actuators for active flow control

“…Concerning reactions, bimolecular and trimolecular nitrogen-oxygen processes, ions reactions and nitrogen oxides reactions complete the chemistry dataset whose reaction rate constants are added for each one. The electron cross-section data were retrieved from the LXCat website [34] using Phelps and Pancheshnyi databases [35].…”