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

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 n(e) > 10(16) cm(-3). For electric fields typical in nanosecond discharges, a non-equilibrium plasma (T-e > T-gas) is formed at ambient conditions and remains partially ionized for about 12 nanoseconds (n(e) < 10(16) cm(-3)). Then, the discharge abruptly reaches full ionization (n(e) approximate to 10(19) cm(-3)) and thermalization (T-e = T-gas approximate to 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.

Automated summary

Numerical simulations were used to study the mechanism of air ionization by a nanosecond discharge under atmospheric conditions. The model showed that excited electronic states of O and N atoms play a key role in plasma ionization.