K.S. Klopovsky

Experimental and theoretical investigation of oxygen glow discharge structure at low pressures

An experimental and theoretical investigation of the oxygen glow discharge structure at low pressures has been performed. Radial dependencies of the electron energy distribution function, the ambipolar plasma potential, and the negative ion concentration, as well as the axial electric field and the concentrations of atomic and singlet oxygen were measured. A new approach to the application of laser photodetachment method has been used to measure the negative ion concentration. It allows one to obtain information about fast processes after the photodetachment at low frequencies (/spl sim/100-200 Hz) by using the simplest modulation technique. A self-consistent model involving the electrodynamics and kinetics of the discharge was developed. The observed variations of the negative ion densities with current density and oxygen pressure were explained in the model frame by a dependence of the detachment rate constant of the O/sup -/+O/spl rarr/e+O/sub 2/ process on the effective ion temperature (k=1.9/spl middot/10/sup -10/-/spl radic/1100/T/sub i//sup eff/). It was shown that the feature of oxygen dc discharge at low pressures is a possibility to change the basic type of negative ions from the O/sup -/ to the O/sub 2//sup -/. This effect become more pronounced with decreasing current density.

Kinetics of metastable states in high-pressure nitrogen plasma pumped by high-current electron beam

An effective method for calculating the electron energy distribution function in a plasma pumped by an electron beam is suggested. The electron impact excitation rates of different N2 and Hg states are obtained. The evolution of populations of the N2 excited states and of the Hg radiative states in a N2-Hg mixture is considered. The characteristic time tau e of equilibrium establishment is shown to be strongly dependent on the pressure of the mixture. The variation of the N2(A3 Sigma ) population is found to be determined by the dynamics of the Hg emissions if the measurement time is longer than tau e.

Low pressure RF discharge in electronegative gases for plasma processing

Abstract An RF plasma discharge in oxygen has been investigated both experimentally and theoretically. The excited species in the oxygen plasma were detected by means of spontaneous luminescence spectroscopy. A self-consistent numerical model was developed for these discharges. The model was confirmed by several theoretical and experimental investigations. The spatial distribution over the discharge gap of both charged and neutral plasma components and their fluxes to electrodes have been calculated.

Study of singlet delta oxygen O 2 ( 1 δg) impact on H 2-O 2 mixture ignition in flow reactor : 2D modeling

Influence of electron excited singlet delta oxygen (SDO) molecules produced in direct current (DC) glow discharged plasma on the induction length decrease in the H2–O2 mixture has been studied via comprehensive two-dimensional (2D) numerical simulations. The sensitivity analysis of the induction length on SDO mole fractions and residual mole fractions of odd oxygen was carried out. The influence of the reaction H2 + O2(1Δg) → H + HO2 on the ignition length was found to be negligible due to the presence of residual odd oxygen in the oxidizer flow. Two stages specify the ignition time decrease for the studied conditions: (1) chain initiation in reactions with residual odd oxygen and (2) the following chain-branching enhancement due to reaction H + O2(1Δg) → O + OH. The last reaction is the key process for studied conditions when the concentration of SDO exceeds 4%. The estimated rate constant of this reaction was found to be about 2.5 · 10−13 cm3/s at 780 K. The quenching reaction H + O2(1Δg) → H + O2 does not affect the ignition length.

Specific features of the kinetics of H2-O2-O2(a1Δg) mixtures: I. formation and quenching of electronically and vibrationally excited (A′) molecules in H2-O2-O2(A1Δg) mixtures at a temperature of 300 K

Available data on the kinetic processes in H2-O2-O2(a1Δg) mixtures are analyzed theoretically, and the ranges in which the rate constants of these processes can vary are determined. The processes of energy transformation in an O2(a1Δg)-H2-H-HO2 system in the approximations of the fast and slow (in comparison with the vibrational relaxation time of the HO2 radical) quenching of the electronically excited state are considered. The experiments on the quenching of singlet delta oxygen (SDO) molecules O2(a1Δg) excited in a microwave discharge at a temperature of 300 K and pressure of 6 Torr in a lean hydrogen-oxygen mixture are simulated (by a lean fuel mixture is meant a mixture in which the ratio of the fuel to the oxidizer mass fraction is less than the stoichiometric ratio, which is 2: 1 for a hydrogen-oxygen mixture). It is shown that, over the experimental observation times, the SDO quenching frequency depends on the concentration of molecular hydrogen, the residual odd oxygen fraction in the gas flow, and the ratio between the rate constants of kinetic processes involving HO2 and HO2* radicals. Simulations of the microwave discharge and the transport of excited oxygen along the drift tube make it possible to determine the residual odd oxygen concentration in the gas flow. Recommendations on the choice of the rate constants for the O2(a1Δg) + HO2)A″, v3″ = 0) ↔ O2 + HO2*(A′, v3′ = 1), HO2*(A′v3′ ≤ 1) + O2(a1Δg) → HO2*(A′,v3′ ≥ 6) + O2, and HO2*(A′,v3′ ≤ 1) + O2(a1Δg) → H + O2 + O2 processes are given. It is shown that, in the case of slow quenching in a H2-O2-O2(a1Δg) mixture at a low temperature, the intensity of hydrogen oxidation is enhanced due to the reaction + HO2*(A′,v3′ ≤ 1) + O2(1Δ) → H + O2 + O2.

2D gasdynamic simulation of the kinetics of an oxygen-iodine laser with electric-discharge generation of singlet oxygen

The kinetic processes occurring in an electric-discharge oxygen-iodine laser are analyzed with the help of a 2D (r, z) gasdynamic model taking into account transport of excited oxygen, singlet oxygen, and radicals from the electric discharge and their mixing with the iodine-containing gas. The main processes affecting the dynamics of the gas temperature and gain are revealed. The simulation results obtained using the 2D model agree well with the experimental data on the mixture gain. A subsonic oxygen-iodine laser in which singlet oxygen is generated by a 350 W transverse RF discharge excited in an oxygen flow at a pressure P = 10 Torr and the discharge tube wall is covered with mercury oxide is simulated. The simulated mixing system is optimized in terms of the flow rate and the degree of preliminary dissociation of the iodine flow. The optimal regime of continuous operation of a subsonic electric-discharge oxygen-iodine laser is found.

Specific features of the kinetics of H2-O2-O2(a1Δg) mixtures: II. Quenching of O2(a1Δg) excited in a discharge behind the shock front at temperatures of 500–1020 K

Results of experiments on the quenching of singlet delta oxygen (SDO) O2(a1Δg) in lean hydrogen-oxygen mixtures at temperatures of 500–1020 K and pressures of 26–90 Torr behind the shock front are analyzed theoretically. The processes affecting SDO quenching are simulated taking into account the temporal characteristics of the experiment and various mechanisms of energy transformation in an O2(a1Δg)-H2-H-HO2 system. It is demonstrated that the approximations of both fast and slow (in comparison with the vibrational relaxation time of the HO2 radical) quenching of the electronically excited state of the radical are in good agreement with the experimental data on the effective rate constant of SDO deexcitation at temperatures of up to 700 K. It is shown that the available data on the kinetics of reactions involving SDO in H2-O2-O2(a1Δg) mixtures overestimate the SDO quenching rate in comparison with the experimental results obtained at temperatures above 850 K. The decrease in the rate constant of the reaction H + O2(a1Δg)→ products by one order of magnitude makes it possible to match the simulation results to the experimental data. The existence of the processes restoring SDO in the presence of atomic hydrogen that are not considered in the current models of the H2-O2-O2(a1Δg) kinetics is supposed.

Nonlocal Effects in Stationary and Non-Stationary Discharges

In this report effects of EDF non-locality in stationary and non-stationary discharges are studied using kinetic approaches. Applicability of two-term approach in RF discharges, in positive column of a DC discharge and in plasma display panel (PDP) cell discharge is analyzed. Effective algorithm of self-consistent modeling of stationary and non-stationary discharges is proposed. The necessity of adequate description of negative ion kinetics and transport is demonstrated in the course of the experimental and theoretical investigations of discharges in electronegative gases.

Numerical simulation of the effect of atomic oxygen impurity on the formation of population inversion during axisymmetric mixing of iodine and excited oxygen flows

We have performed a parametric analysis of the influence of the percentage fraction of atomic oxygen in the O2:O2(1Δ):O flow on the formation of population inversion for a laser transition in iodine atoms and the temperature regime at an elevated pressure of P = 5 Torr in a system with axisymmetric injection of a I2: He mixture to the flow of oxygen excited by an electric-discharge singlet oxygen generator.

Numerical simulation of the mixing kinetics of an iodine-containing flow and the oxygen flow excited in the electric-discharge oxygen-iodine laser

A parametric analysis has been carried out to discover how the concentration of atomic oxygen in the O2: O2 (1Δg): O flow and the degree of predissociation and concentration of molecular iodine in the I2: He mixture affect the temperature regime and the formation of the inverse population at the atomic iodine laser transition at elevated pressures of P = 5–10 Torr in a simulated system with the axial injection of an I2: He mixture in the EDSOG-excited oxygen flow.