Air breakdown dynamics of preformed plasma channels

Summary form only given. A time-dependent air-plasma model based upon the Boltzmann equation for the electron energy distribution function, coupled with an extensive non-equilibrium air-chemistry kinetics was developed to study the breakdown dynamics of electric discharges in preformed plasma channels. Incorporated in the model are the species balance equations, nitrogen vibrational kinetics as well as the thermal balance equation. The temporal evolution of various nitrogen and oxygen species in ground and excited states, as well as electrons, atomic and molecular ions was obtained from the model. The electrical breakdown process was studied for different combinations of applied external electric field strengths (5-30 kV/cm) and different initial electron densities (10¹⁵-10¹⁷ cm^-3). The model predicts low plasma channel electric breakdown field of 5-10 kV/cm, with a delay time of hundreds of nanoseconds, when the electron density drops to ~10¹³-10¹² cm^-3. It was observed that a combination of factors such as increased ionization due to relaxation of the electron energy distribution function toward a Maxwellian distribution, strong electron detachment, and the gas heating dynamics contribute to the reduction of the breakdown field