Nikolay Vagin

Mechanism of pulse discharge production of iodine atoms from CF3I molecules for a chemical oxygen?iodine laser

The pulsed chemical oxygen–iodine laser (COIL) development is aimed at many new applications. Pulsed electric discharge is most effective in turning COIL operation into the pulse mode by instant production of iodine atoms. A numerical model is developed for simulations of the pulsed COIL initiated by an electric discharge. The model comprises a system of kinetic equations for neutral and charged species, electric circuit equation, gas thermal balance equation and the photon balance equation. Reaction rate coefficients for processes involving electrons are found by solving the electron Boltzmann equation, which is re-calculated in a course of computations when plasma parameters changed. The processes accounted for in the Boltzmann equation include excitation and ionization of atoms and molecules, dissociation of molecules, electron attachment processes, electron–ion recombination, electron–electron collisions, second-kind collisions and stepwise excitation of molecules. The last processes are particularly important because of a high singlet oxygen concentration in gas flow from the singlet oxygen chemical generator. Results of numerical simulations are compared with experimental laser pulse waveforms. It is concluded that there is satisfactory agreement between theory and the experiment. The prevailing mechanism of iodine atom formation from the CF3I donor in a very complex kinetic system of the COIL medium under pulse discharge conditions, based on their detailed numerical modelling and by comparing these results both with experimental results of other authors and their own experiments, is established. The dominant iodine atom production mechanism for conditions under study is the electron-impact dissociation of CF3I molecules. It was proved that in the conditions of the experiment the secondary chemical reactions with O atoms play an insignificant role.

Influence of nitrogen oxides NO and NO2 on singlet delta oxygen production in pulsed discharge

The influence of nitrogen oxides NO and NO2 on the specific input energy (SIE) and the time behaviour of singlet delta oxygen (SDO) luminescence excited by a pulsed e-beam sustained discharge in oxygen were experimentally and theoretically studied. NO and NO2 addition into oxygen results in a small increase and decrease in the SIE, respectively, the latter being connected with a large energy of electron affinity to NO2. The addition of 0.1–0.3% nitrogen oxides was experimentally and theoretically demonstrated to result in a notable enhancement of the SDO lifetime, which is related to a decrease in the atomic oxygen concentration in afterglow. It was experimentally demonstrated that to get a high SDO concentration at the gas pressure 30–60 Torr for a time interval of less than ~0.5 s one needs to add not less than 0.2% nitrogen oxides into oxygen. The temperature dependence of the relaxation constant for SDO quenching by unexcited oxygen was estimated by using experimental data on the time behaviour of SDO luminescence.

Role of N2 molecules in pulse discharge production of I atoms for a pulsed chemical oxygen–iodine laser

A pulsed electric discharge is the most effective means to turn chemical oxygen–iodine laser (COIL) operation into the pulse mode by fast production of iodine atoms. Experimental studies and numerical simulations are performed on a pulsed COIL initiated by an electric discharge in a mixture CF3I : N2 : O2(3X) : O2(a 1Δg) flowing out of a chemical singlet oxygen generator. A transverse pulsed discharge is realized at various iodide pressures. The model comprises a system of kinetic equations for neutral and charged species, the electric circuit equation, the gas thermal balance equation and the photon balance equation. Reaction rate coefficients for processes involving electrons are repeatedly re-calculated by the electron Boltzmann equation solver when the plasma parameters are changed. The processes accounted for in the Boltzmann equation include direct and stepwise excitation and ionization of atoms and molecules, dissociation of molecules, electron attachment processes, electron–ion recombination, electron–electron collisions and second-kind collisions. The last processes are particularly important because of a high singlet oxygen concentration in gas flow from the singlet oxygen chemical generator. A conclusion is drawn about satisfactory agreement between the theory and the experiment.

Iodine atom production rates by electron impact versus post discharge reactions for pulsed COIL

Pulsed discharge is effective means to achieve high-peak lasing in COIL. Numerical model is developed for simulation of pulsed discharge in gas stream from the singlet oxygen generator mixed with CF3I. The model comprises a system of kinetic equations for neutral and charged species, electric circuit equation, and gas thermal balance equation. Sources of iodine atoms under discharge and post-discharge conditions are analyzed. The dominant source in the discharge is electron-impact dissociation of CF3I molecules. In post-discharge phase chemical reactions are identified giving notable input into I production. Deformation of laser pulse waveform observed experimentally is explained by influence of these reactions.

Influence of nitrogen oxides on singlet delta oxygen production in pulsed electric discharge for oxygen-iodine laser

Experimental and theoretical study of influence of nitrogen oxides NO and NO2 admixtures in oxygen containing gas mixture excited by pulsed electron-beam sustained discharge on input energy and time behavior of singlet delta oxygen (SDO) luminescence was carried out. Temperature dependence of the constant of SDO relaxation by unexcited molecular oxygen was estimated.

Parametric study of SDO production in MW discharge by titration with iodide

Admixing of iodide to the effluent of MW discharge in oxygen was used to measure yield of singlet oxygen generated. Singlet oxygen yield was evaluated using the equilibrium condition. The method was absolutely calibrated using a traditional chemical singlet oxygen generator.

Modelling coil with iodine atoms produced by pulsed electric discharge

The pulse mode of operation of the chemical oxygen iodine laser (COIL) is attractive for a large body of new applications. Pulsed electric discharge is most effective to turn COIL operation into the pulse mode by instant production of iodine atoms. Numerical model is developed for simulations of the pulsed COIL initiated by electric discharge. The model comprises a system of kinetic equations for neutral and charged species, electric circuit equation, gas thermal balance equation, and the photon balance equation. Reaction rate coefficients for processes involving electrons are found by solving the electron Boltzmann equation, which is recalculated in a course of computations when plasma parameters changed. The processes accounted for in the Boltzmann equation include excitation and ionization of atoms and molecules, electron-ion recombination, electron-electron collisions, second-kind collisions, and stepwise excitation of molecules. The last processes are particularly important because of a high singlet oxygen concentration in gas flow from the singlet oxygen chemical generator. Results of numerical simulations are compared with experimental laser pulse waveforms. The conclusion is drawn about satisfactory agreement of the theory with the experiment. The mechanisms of iodine atoms production in the pulsed discharge are identified.

Influence of chemically produced singlet delta oxygen molecules on thermal ignition of O2–H2 mixtures

Thermal ignition of the H2–O2 mixture with O2(a 1Δ g ) addition is studied experimentally and theoretically. The singlet delta oxygen was produced in a chemical generator. In this way, the competing chemical processes involving plasma produced chemically active O atoms and оzone (O3) were excluded. A satisfactory agreement is achieved between experimentally observed and numerically predicted values of the ignition time at the initial gas temperature (900–950) K and gas pressure (9–10) Torr. The percentage of the reactive channel in the binary collisions O2(a 1Δ g ) + H is evaluated on the level (10–20)% for the H2–O2 mixture.

Production of iodine atoms in a self-sustained pulsed electric discharge

Production of iodine atoms due to dissociation of iodides CF3I, CH3I, C2F5I, and C2H5I in a self sustained pulsed discharge has been investigated. The efficiency of iodide dissociation as well as a yield of excited iodine atoms has been measured for different experimental conditions.

Influence of nitrogen oxides NO and NO2 additives on singlet oxygen production in pulsed electron-beam sustained discharge

Influence of nitrogen oxides NO and NO2 on specific input energy (SIE) and time behavior of singlet delta oxygen (SDO) luminescence excited by pulsed e-beam sustained discharge in oxygen was experimentally and theoretically studied. NO and NO2 addition into oxygen results in small increase and decrease of SIE, respectively, the latter being connected with large energy of electron affinity to NO2. The addition of 0.1-0.3% nitrogen oxides was experimentally and theoretically demonstrated to result in notable enhancement of SDO lifetime, which is related to a decrease of atomic oxygen concentration in afterglow. There was experimentally demonstrated that for getting high SDO concentration at gas pressure 30-60 Torr for the time interval less than ~0.5 s one needs to add not less than 0.2% nitrogen oxides into oxygen. Temperature dependence of relaxation constant for SDO quenching by unexcited oxygen was estimated by using experimental data on time behavior of SDO luminescence.