Ionization processes in flowing liquid nitrogen cooled discharges in He-CO, He-CO-O₂mixtures

Abstract

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.

Direct Determination of Interface Trapped Charges

“…The present model might also be useful in studying CO(a 3 ) kinetics. As a matter of fact, CO(a 3 ) together with CO(X 1 , v) has been considered as a possible precursor if ionization [15]. Also, recent experiments on CO(a 3 ) formation in the optically pumped cell [13] suggest that the V-E transition CO(X 1 , v ∼ = 25) + CO → CO(a 3 , v ∼ = 0) + CO (10) may require the presence of some low-energy electrons, which presumably are incapable of direct impact excitation of the a 3 state.…”

Vibrational distributions of CO molecules in a dc discharge in the presence of molecular oxygen admixture

“…Our vision of the problem is as follows: the changes in the voltage and discharge current taking place for mixtures with small content of O 2 molecules are really the consequence of, but not a reason for, enlarged vibrational populations of CO. As it was demonstrated in [12,13] the increase in populations of high vibrational levels led to the increase in the ionization rate due to additional channels of ionization in which highly excited CO molecules took part. These processes result in lowering of the E/N parameter (E is the electric field strength, N the gas number density) and increasing effectiveness of vibration excitation in the discharge.…”

“…The typical values of the translational temperature were in the range (160 ± 20)-(320 ± 30) K for liquid nitrogen cooling. More detailed information about the translational gas temperature for mixtures He-CO and He-CO-O 2 experimental conditions is given in [12].…”

“…In our experiments, plasma emission from the region of about 3 mm size near the tube axis in the discharge positive column was recorded by an end-light fluorescence technique. The populations of individual vibrational levels were derived from the overtone emission intensities by the technique described in [12,13,19,20]. The spontaneous emission intensities from the fundamental (v → v − 1) band, the first (v → v − 2) and second (v → v − 3) overtone bands were registered.…”

“…It turned out that the VDF plateau is the highest one at the molecular oxygen concentration in the range 2-7% relative to CO concentration. The level of this plateau depends on the discharge current, gas mixture composition, gas temperature and flow rate (see for example [3,7,[11][12][13][14]). When the O 2 concentration amounted to approximately 10% of [CO] or greater, the decrease in vibrational populations of CO was detected for vibrational levels v > 17 in [1,4,7,14].…”