Ionization processes in flowing liquid nitrogen cooled discharges in He-CO, He-CO-O2 mixtures

Discharges in He-CO, He-CO-O2 mixtures are studied in the range of experimental parameters typical of the action of a high-power CO laser with fast gas flow and liquid N2 cooling. Gas and vibrational temperatures, their radial profiles, CO vibrational population and E/N values are measured. The values of E/N are also calculated by solving the electron balance equation. Comparison of the measured and calculated data shows that the dominant ionization process in He-CO mixtures is the reaction CO+e to CO++2e. For He-CO-O2 mixtures, the reaction CO( nu >14)+CO*(I1 Sigma ) to C2O2++e is proposed as the main ionization process. Such a mechanism allows one to explain the marked influence of a small O2 admixture on He-CO plasma parameters.