Microwave and optical techniques for gas discharge studies

Summary Some recently developed microwave and optical techniques for studying fundamental processes in gas discharges are described. Microwave apparatus which measures the change of resonant frequency andQ of a cavity containing a gas discharge is used to determine the concentration of electrons and their rate of collision with gas atoms in the discharge. Time sampling techniques are used to reduce the statistical fluctuations in data obtained in very low intensity optical emission studies. These techniques have been employed in direct recording spectrographic and interferometric equipments which require orders of magnitude less exposure time than conventional photographic recording methods. Time sampling has also been applied to optical absorption techniques used to study metastable atoms, with a hundred-fold increase in detection sensitivity over previous methods. The use of these methods is illustrated by a brief discussion of studies of electron-ion recombination, conversion of singlet metastable atoms to triplet metastables by collisions with slow electrons, and the formation and decay of excited mercury molecules.     

Gas discharge breakdown as a function of frequency

Summary Breakdown voltages of glow discharges in Ne and Ne-A mixtures as a function of the frequency will be discussed. The variation of the breakdown voltage with rising frequency can be understood qualitatively from buildup times and the increase of pre-breakdown current caused by particles remaining from previous periods.Thanks are due to prof. dr H. B. Dorgelo and ir A. W. van. Wagensveld for discussions on the subject.     

Beaded structure of discharge during breakdown in a nonuniform field

Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 1, pp. 16–21, January–February, 1990.     

Corona discharge in a moving gas

Some aspects of the theory of corona discharges in a moving medium are considered. Two situations are analyzed: a corona discharge at a negative electrode under the condition that in the region of electrogasdynamic flow exterior and interior regions of the discharge can be distinguished, the motion of the gas being taken into account only in the exterior region, and corona discharge at a negative electrode under the condition that the effects of the motion of the gas are important in both the exterior and the interior regions of the discharge. For the first situation, a mathmatical generalization is proposed of the traditional model of the interior region, and dimensional and similarity methods are used to obtain functional relationships for the current—voltage characteristics of the discharge in the moving medium. The second situation is investigated for the example of a corona discharge between cylindrical electrodes through which gas is blown or sucked. In this case, the solution to the problem is found without dividing the flow region into exterior and interior regions of the discharge, a system of kinetic equations describing the flow in the complete interelectrode gap being used.     

Reduction of gas breakdown voltage with pulsed ionizing radiation

An algorithm is described for computer calculation of the dynamic breakdown voltage of a gas gap affected by a spatially uniform pulse of ionizing radiation. The algorithm is based on numerical integration of a system of nonlinear equations with integral boundary conditions. The program is used to calculate the breakdown voltage of an air gap affected by a bell-shaped ionizing pulse. It is shown that the relative reduction in breakdown voltage can amount to tens of percent for a radiation exposure dose rate P₀ 10⁸ R/sec.Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 6, pp. 52–60, November–December, 1973.     

Chemical reactions in non-equilibrium gas mixtures and mass action law breakdown

Strong deviation of chemical reaction rates from their equilibrium values in vibrationally non-equilibrium gas is shown. Performed analysis is based on a new approach for solving the generalized Boltzmann equation. It allows to overstep the limits of a traditional method, where the part of the collisional integral responsible for chemical reactions is assumed to be small (of the order of the Knudsen number). Another generalization consists in considering both the monomolecular and collisional reaction paths. The influence of non-equilibrium vibrational distributions, which are caused by the chemical reactions, on the chemical reactions themselves is studied. Strong correlation between parallel reactions (when one molecule reacts with a number of others) is shown. The situation when one reaction blocks another one is described. Such a behavior of the reaction rates means the mass action law breakdown.     

Pressure wave breakdown of a gas film in a liquid-filled slit

In [1–4] the results of investigating the breakdown of gas bubbles by medium-intensity pressure waves are presented and various bubble breakdown mechanisms are proposed. It is shown that breakdown may occur as a result of the formation of a cumulative jet on the boundary of the bubble or as a result of instability due to the relative motion of the bubble in the wave. In [5] experimental data on the pressure wave breakdown of a gas film in a liquid on a solid wall are reported. It is shown that at wave amplitudes p/p₀1 a liquid jet is formed at the edge of the gas film. The jet, traveling along the wall, strips off the film and carries it into the surrounding liquid. Below we investigate the pressure wave behavior of a gas film in a liquid-filled slit.Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No.5, pp. 175–178, September–October, 1992.     

Lowering of the breakdown potential of a gas under steady ionizing radiation

The problem of the lowering of the electric strength of a gas under steady external ionizing radiation is solved numerically. The right-hand branches of the Paschen curve for helium, argon, and xenon are calculated by the so-called ranging method using the standard Runge-Kutta program.     

Theory of nonequilibrium inductive high-frequency discharge in a gas flow

The global nonequilibrium flow in the discharge chamber of an induction plasma generator is modeled. The problem for an equilibrium discharge was considered in [2, 3]. Here, on the basis of a numerical solution of the combined system of Navier-Stokes, Maxwell, energy, ionization kinetics and electron-gas energy balance equations, the structure of the nonequilibrium discharge is analyzed and the results obtained within the framework of the local one-dimensional approach [1] and on the basis of global numerical modeling of the flow are compared. As distinct from [2, 3], in finding the electromagnetic field distribution in the discharge chamber the boundary-value problem for the two-dimensional Maxwell equations is solved.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 2, pp. 153–160, March–April, 1991.The author is grateful to V. V. Lunev and G. N. Zalogin for their constant interest and useful discussions.     

Surface waves on the positive column of a gas discharge

Summary The propagation of surface waves along a mercury vapour discharge is investigated theoretically and experimentally. The classical solution of the electromagnetic problem, involving Bessel functions, is compared with a numerical solution. A density profile is used to obtain the theoretical curve that fits measured values best. A surface wave launching device with a minimum of direct radiation is applied, giving a standing wave of pure circular symmetry along the discharge tube. There is no metallic screening tube.     

The corona ignition voltage of an electrical discharge in a gas

The corona ignition voltage of an electrical discharge in air of atmospheric pressure depends on the presence of (moisture) particles, which may increase the corona losses. A relation between the corona ignition voltage and the particle size when tested shows unexpected results. With the corona ignition voltage in air as observed by Rose and Wood our calculations do not give particle sizes of 50 m (as used by Rose and Wood), but sizes of about 1 Å corresponding to the diameters of the molecules of the component gases in air. Our conclusion is that these molecules align in a conductive channel from the axial wires to the particle considered. In this way the charge transfer from the axial wire to the particles may be explained.     

The rapid cooling of a hot gas discharge by liquid sprays

The cooling effect of liquid droplets introduced into a hot gas stream flowing in an adiabatic duct is analysed. The coupled interaction between the changes in the droplets and in the surrounding gas conditions is examined as a result of droplets vaporization. It was found that the use of liquid sprays as a rapid cooling process for a hot gas discharge is quite effective.     

A high-frequency high-pressure gas flow discharge as a slow combustion process

Induction heating of a gas flowing through a coil is widely used. but only ~e static case (induction heating of a substance at rest where all the heat is lost by conduction to the cooled walls) has been considered theoretically [3.,2]. An approximate theory is proposed here for eleetrodeless discharge, and the process is found to be analogous to flame propagation in a combustible mixture.I am indebted to M. I. Yakushin for many helpful discussions and to G. I. Barenblatt for interest in the work.     

Investigation of unsteady flow structure during discharge of a shock-heated gas

This paper examines the structure of the near-gasdynamic section of a jet discharging into a rarefied volume. The experimental part of the article deals with unsteady discharge of a high-temperature gas. Discharge from a slot and from a circular aperture is investigated for air, nitrogen, CO₂, and argon with nonuniformities from 20–200. Approximate relations are obtained to describe the motion of the front of a discharging substance in dimensionless coordinates and the associated perturbation along the flow axis. It is established that the time for a steady geometric structure to form in the gasdynamic section of the jet is greater than the values obtained from data available in the literature.Translated from Zhurnal Prikladnoi Mekhaniki i Teoreticheskoi Fiziki, No. 5, pp. 34–40, September–October, 1973.