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 --> CO+ + 2e. For He-CO-O2 MiXtUres, the reaction CO(v > 14) + CO*(I1-SIGMA) --> C2O2+ + e is proposed as the main ionization process. Such a mechanism allows us to explain the marked influence of a small 02 admixture on He-CO plasma parameters.