Collisional-radiative ionization and recombination model for high-temperature air and its application to discharges

A collisional-radiative (C-R) model for high-temperature air is developed. Ionization and recombination coefficients are presented for electron temperatures between 1.0 and 3.0 eV and electron densities between 1016 and 1019 cm−3. For an assumed airlike mixture of 80% nitrogen and 20% oxygen, these results are compared with C-R coefficients of nitrogen and oxygen plasmas developed separately and show little difference. The inclusion of charge-exchange effects does not alter the coefficients. Saha decrements for air are used to delineate the onset of local thermodynamic equilibrium (LTE) for the above conditions. These thresholds are compared to other criteria and show some difference. Finally, ratios of spectral line intensities are presented in terms of the Saha decrements as a means of diagnosing high-temperature air discharges, such as lightning channels, without requiring LTE.