Anatoly P. Napartovich

Physics and engineering of singlet delta oxygen production in low-temperature plasma

An overview is presented of experimental and theoretical research in the field of physics and engineering of singlet delta oxygen (SDO) production in low-temperature plasma of various electric discharges. Attention is paid mainly to the SDO production with SDO yield adequate for the development of an electric discharge oxygen–iodine laser (DOIL). The review comprises a historical sketch describing the main experimental results on SDO physics in low-temperature plasma obtained since the first detection of SDO in electric discharge in the 1950s and the first attempt to launch a DOIL in the 1970s up to the mid-1980s when several research groups started their activity aimed at DOIL development, stimulated by success in the development of a chemical oxygen–iodine laser (COIL). A detailed analysis of theoretical and experimental research on SDO production in electric discharge from the mid-1980s to the present, when the first DOIL has been launched, is given. Different kinetic models of oxygen low-temperature plasma are compared with the model developed by the authors. The latter comprises electron kinetics based on the accompanying solution of the electron Boltzmann equation, plasma chemistry including reactions of excited molecules and numerous ion–molecular reactions, thermal energy balance and electric circuit equation. The experimental part of the overview is focused on the experimental methods of SDO detection including experiments on the measurements of the Einstein coefficient for SDO transition and experimental procedures of SDO production in self-sustained and non-self-sustained discharges and analysis of different plasma-chemical processes occurring in oxygen low-temperature plasma which brings limitation to the maximum SDO yield and to the lifetime of the SDO in an electric discharge and its afterglow. Quite recently obtained results on gain and output characteristics of DOIL and some projects aimed at the development of high-power DOIL are discussed.

Negative corona, glow and spark discharges in ambient air and transitions between them

Obtaining new information about different forms of self-sustained dc discharges that can be realized in pin-to-plane electrode geometry in ambient air is the goal of this paper. Experimental and numerical calculation data uncovering the physics of the temporal and spatial evolution of the negative corona and glow discharge (GD), with increase in current up to the transition to the spark, are presented. Special attention is paid to the properties of diffusive GD at atmospheric pressure, which is a necessary stage (steady-state or transient) preceding the spark and determining the threshold conditions of sparking.

Plasma-Assisted Combustion of Gaseous Fuel in Supersonic Duct

The field of plasma-induced ignition and plasma-assisted combustion in high-speed flow is under consideration. Nonequilibrium, unsteady, and nonuniform modes are analyzed as the most promising in reducing a required extra power. Numerical simulations of uniform, nonequilibrium, continuous, and pulse discharge effect on the premixed hydrogen and ethylene-air mixtures in supersonic flow demonstrate an advantage of such a technique over heating. At the same time, the energetic price occurs rather large to be scheme practical. A reduction of the required power deposition and mixing intensification in nonpremixed flow could be achieved by nonuniform electrical discharges. Experimental results on multielectrode discharge maintenance behind wallstep and in the cavity of supersonic flow are presented. The model test on hydrogen and ethylene ignition is demonstrated at direct fuel injection

A numerical simulation of Trichel-pulse formation in a negative corona

A new quasi-one-dimensional model for a negative corona in air is formulated allowing for the quantitative description of the mechanism of Trichel-pulse formation. Detailed analysis of the processes controlling pulse dynamics is made. Comparison with experiment for a short-gap corona demonstrates a reasonable agreement with the shape of the pulse and in the average characteristics of the negative corona.

Non-self-sustained electric discharge in oxygen gas mixtures: singlet delta oxygen production

The possibility of obtaining a high specific input energy in an electron-beam sustained discharge ignited in oxygen gas mixtures O2 :A r :C O (or H2) at the total gas pressures of 10–100 Torr was experimentally demonstrated. The specific input energy per molecular component exceeded ∼ 6k J l −1 atm −1 (150 kJ mol −1 ) as a small amount of carbon monoxide was added into a gas mixture of oxygen and argon. It was theoretically demonstrated that one might expect to obtain a singlet delta oxygen yield of 25% exceeding its threshold value needed for an oxygen–iodine laser operation at room temperature, when maintaining a non-self-sustained discharge in oxygen gas mixtures with molecular additives CO, H2 or D2. The efficiency of singlet delta oxygen production can be as high as 40%.

Near-diffraction-limited coherent emission from large aperture antiguided vertical-cavity surface-emitting laser arrays

We demonstrate that in-phase mode operation with a near-diffraction-limited beam can be realized in large aperture (up to 100 elements) antiguided vertical-cavity surface-emitting laser (VCSEL) arrays. A selective etching process with two-step metalorganic chemical vapor deposition is used for fabrication of the antiguided VCSEL array structures. Modal discrimination is enhanced by intentionally choosing a GaAs cap thickness so as to introduce suitable loss to array interelement regions. Far field patterns indicate in-phase mode operation from both triangular and rectangular geometry antiguided VCSEL arrays, which is in good agreement with theory.

Experimental and theoretical study of the transition between diffuse and contracted forms of the glow discharge in argon

The constriction of the positive column of a glow discharge in argon was studied both experimentally and theoretically. In experiments the direct current discharge was maintained in a cylindrical glass tube of 3?cm internal diameter and 75?cm length. The voltage?current U(I) characteristics of the discharge were measured at a gas pressure P from 1 to 120?Torr in a wide range of discharge currents. At P > 20?Torr the measured U(I) characteristics display the classical hysteresis effect: the transition from the diffuse to the contracted discharge form (with increasing current) occurs at a current higher than that for reverse transition (with decreasing current). It was also found that in some cases the so-called partially contracted form of the discharge is realized, when the diffuse and contracted forms coexist in the discharge tube.To calculate the plasma parameters under experimental conditions a 1D axial-symmetric discharge model for pure argon was developed. The details of the model are described and the results of simulations are presented. In particular, the electric field strength E in the positive column was calculated as a function of the discharge current. Theoretical E(I) characteristics are compared with those derived from the experiment. For the first time, the detailed kinetic model without the usage of fit parameters predicts the hysteresis effect in pure Ar with parameters of diffuse and constricted forms of the discharge in good agreement with the experiment.

Non-thermal plasma instabilities induced by deformation of the electron energy distribution function

Non-thermal plasma is a key component in gas lasers, microelectronics, medical applications, waste gas cleaners, ozone generators, plasma igniters, flame holders, flow control in high-speed aerodynamics and others. A specific feature of non-thermal plasma is its high sensitivity to variations in governing parameters (gas composition, pressure, pulse duration, E/N parameter). This sensitivity is due to complex deformations of the electron energy distribution function (EEDF) shape induced by variations in electric field strength, electron and ion number densities and gas excitation degree. Particular attention in this article is paid to mechanisms of instabilities based on non-linearity of plasma properties for specific conditions: gas composition, steady-state and decaying plasma produced by the electron beam, or by an electric current pulse. The following effects are analyzed: the negative differential electron conductivity; the absolute negative electron mobility; the stepwise changes of plasma properties induced by the EEDF bi-stability; thermo-current instability and the constriction of the glow discharge column in rare gases. Some of these effects were observed experimentally and some of them were theoretically predicted and still wait for experimental confirmation.

Discharge production of the singlet delta oxygen for an iodine laser

The properties and kinetics of singlet delta oxygen (SDO) metastables in discharge plasma, which are important for the development of the discharge excited oxygen-iodine laser, are discussed. A short description is given of available experimental activity in the development of SDO generators. Specific requirements to the SDO discharge generator are reported. The capability of different kinds of discharge to meet these requirements is evaluated. Issues are discussed which are important for the study of SDO kinetics in more detail, including processes involving individual electronic-vibrational states.

Phase-locking of a multicore fiber laser by wave propagation through an annular waveguide

Abstract Out-of-phase supermode with adjacent modes was selected in a multicore fiber (MCF) laser phase-locked by field propagation inside an annular waveguide (AW), which was butt coupled to the MCF. The individual emitters (microcores) were placed on a ring with a radius of 131 μm . The AW had a ring radius of 130 μm and a ring thickness of 25 μm . In this all-fiber system the radiation of the circular laser array was directly launched into the guiding ring of the AW. The emitted field distribution was reproduced by constructive multimode interference while propagating over the AW. This realized mutual coherence between the individual microcores. Numerical simulations of the field-propagation in the AW are presented. The influence of the ring thickness as well as the influence of geometrical parameter variations on the phase-locking properties of the system is investigated numerically.