Nonlocal phenomena in the positive column of a medium-pressure glow discharge

Commercial CFDRC software () is used to self-consistently simulate the plasma of the positive column (PC) of a medium-pressure dc discharge in argon. The software allows simulations in an arbitrary 3D geometry by using Poisson’s equation for the electric potential and fluid equations for the heavy components and by solving a nonlocal kinetic equation for electrons. It is shown that, in calculating the electron distribution function, the local approximation is almost always inapplicable not only at relatively low pressures (pR<1 cm Torr), but also at relatively high pressures (pR<10 cm Torr), i.e., under the real conditions of a diffuse PC usually met in practice. The use of the local approximation in solving the kinetic equation for electrons leads to significant errors in determining the main parameters of the PC. A paradoxical effect has been revealed: the peaks of the profiles of the excitation rates shift from the discharge axis toward the periphery as the pressure increases from low to medium values (1 cm Torr<pR<10 cm Torr). It is shown that the effect is related to the nonlocal character of the electron distribution function.     

Simple analytic formulas for estimating the parameters of the positive column of a glow discharge in electronegative gases

Simple analytic expressions are analyzed for the plasma of the positive column of low- and moderate-pressure discharges in the case of detachment by neutral particles. These relations make it possible to easily and rapidly estimate the parameters of spatial distributions of charged particle concentrations in this plasma, as well as its energy parameters. For the first time, the conditions for applicability of these relations are determined and their accuracy is estimated.     

Crystallization of a dusty plasma in the positive column of a glow discharge

The formation of macroscopic ordered structures in the standing striations of a stationary glow discharge in Ne is observed. A Coulomb quasicrystal is formed by spherical glass particles with diameters of 50–63 μm and charge Z _p~7·10⁵ e. The interparticle distance is approximately 300 μm. This corresponds to a nonideality parameter Γ~5·10⁴, which leads to crystallization in the Yukawa model. The factors leading to the formation of a quasicrystal in the striations are discussed. Pis’ma Zh. éksp. Teor. Fiz. 64, No. 2, 86–91 (25 July 1996)     

Formulas for estimating the parameters of the positive column of a glow discharge in electronegative gases for finite ionic temperatures

Explicit simple but at the same time sufficiently exact explicit analytic expressions are obtained under the simplest assumption concerning the constancy of plasma-chemical processes in the plasma of the positive column of low- and moderate-pressure discharges in the case of detachment by neutral particles. These relations make it possible to rapidly estimate the geometrical parameters of spatial distributions of charged particle concentrations in this plasma, as well as its energy parameters, without resorting to numerical simulation. For the first time, the finiteness of ionic temperatures and the presence of ion diffusion are taken into account. It is shown that transverse stratification of the electronegative plasma into regions with different ionic compositions is a consequence of nonisothermality of the plasma.     

Study of glow discharge positive column with cloud of disperse particles

The study aims to describe plasma parameters changes induced by clouds of disperse micron size particles. Dust clouds were formed in the positive column of glow discharge in air at pressure 0.1-0.6 torr and current 0.1-3 mA. The simultaneous registration of discharge voltage and dust cloud parameters was carried out. Experimental results were simulated using diffusion model. The dust cloud is shown to smooth the radial electron concentration profile, increase electric field strength and electron temperature and stabilize the discharge. The cloud is demonstrated to be a trap for positive ions without increase of discharge current.     

Self-consistent hybrid model for a stratified positive column of a low pressure glow discharge

The stratification of a positive column of a low-pressure glow discharge in inert gases has been studied with the help of a self-consistent hybrid model. The model is based on the solution of a nonlocal kinetic Boltzmann equation for the electron distribution function, a nonstationary drift-diffusion equation for the ions, and the Poisson equation for the electric field. Spatial electron and ion density distributions and the electric field distribution in the positive column were obtained. The converged solution of the model gives a self-consistent resonant strata length L and the value and the form of the modulated plasma parameters. An unexpected surprising result was obtained: for a given potential drop in the positive column of a low-pressure glow discharge, a self-consistent spatially modulated striation-like electric field does not lead to the resonant increasing of the ionization frequencies in the discharge as compared with a constant electric field with the same potential drop. Usually, it was assumed that, in spatially modulated field distributions, all the parameters in a striated plasma will be more pronounced and have a resonant form. The text was submitted by the authors in English.     

Determination of the relaxation length of electron temperature in the positive column of a glow discharge

This paper presents a formula (14) for determining the reciprocal value of the relaxation length of the temperature of electrons,a ₁, by means of the phase shift of directly measurable curves, of the deviation of the intensity of radiated light and the concentration of the electrons from the equilibrium state. Furthermore, the average values of this phase shift are given as measured in Ne and He in the region of artificially excited moving striations as well as in the wave of stratification anda ₁ is calculated by means of (14).     

Radial distribution of plasma density in the positive column of thehigh-current stationary glow discharge

A model is presented which describes the radial distributions of the plasma density, electric potential, current density, and magnetic field in the positive column of a stationary glow discharge not in contact with the longitudinal walls of the discharge chamber. In this model, the compression of the positive column is provided by the azimuthal magnetic field created by the discharge current. The value of, the discharge current is obtained for the case where charged-particle diffusion is balanced by the actions of the radial electric field and the magnetic pinch effect. The radial distributions of plasma parameters are also calculated for the case of high-current glow discharges where charged-particle diffusion can be ignored     

The influence of acoustic waves on the positive column of a glow discharge with standing striations

The influence was investigated of low-frequency standing acoustic waves on the positive column of a glow discharge in air and nitrogen in a regime in which spontaneous formation of standing striations readily occurs. Experimental information is presented proving that an acoustic wave of sufficient energy propagating along the discharge axis has a great influence on physical processes creating standing striations in a molecular gas.In conclusion the author would like to thank Prof. J. Kracík for his support and his interest in this work and Mr. P. Slovák for his assistance with the experimental work.     

Positive column of a glow discharge in a ternary mixture

The positive column of a glow discharge in a ternary mixture is considered. It is assumed that there is a primary gas, to which are added two gases (vapors) which are completely responsible for the ionization processes. The primary gas serves as a background determining such characteristics as the mobility and the diffusion coefficient of the atoms, ions, and electrons. The axial ion current in the discharge leads to an axial redistribution of the impurity atoms. This phenomenon, called cataphoresis, was considered first in [1] for a binary mixture. In the present paper axial cataphoresis is considered in a ternary mixture.     

Calculation of the parameters of excimer light sources on the basis of a positive column glow discharge

We calculate the concentration of plasma and gas-temperature components in a contracted filament of a glow capillary discharge (R = 0.75 mm) in xenon for pressures of P = 100 and 400 Torr and currents of I = 6–15 mA for cases of with and without cryogenic cooling of the discharge. We find that the gas temperature in the channel of the glow discharge has a value of 1000–2000 K, the concentration of xenon excimers attains a maximum at the boundary of the filament with a value of 10¹⁰–10¹¹ cm⁻³, and the efficiency of electric energy transformation into excimer radiation energy has a value of 0.1–5%.     

Theoretical foundation of a proposed new method of the optical diagnostics of positive column plasma in glow discharge

An integral equation has been constructed which describes the image of cylindrically symmetric, longitudinally homogeneous transparent systems radiating in the optical region. As a base, the construction of the three-dimensional impulse response of a point light source was used. If an experiment is arranged so that it can be described by such an equation, radial variations of atomic concentration in different levels may be determined (e.g., in the positive column of the glow discharge).     

Coaxial (tubular) glow discharge in electronegative gases

The positive-column plasma of a low- and medium-pressure electronegative glow discharge initiated in the gap between two coaxial cylindrical tubes has been considered (the current is directed along the tube axis). It is assumed that the gas mixture contains halogens, and ion diffusion is not negligibly weak. It is found that the coaxial discharge is characterized by plasma separation into three coaxial regions with different compositions in the direction transverse to the current. It has been shown that the ionization and excitation frequencies of atoms are higher than in the purely cylindrical case, even for a small (0.05–0.15) ratio of the radii of the inner and outer walls. An asymptotic analysis of the continuity equations yields analytic expressions that make it possible to rapidly and easily estimate the geometrical parameters of the spatial distributions of charge particle concentrations, as well as energy parameters of the plasma for the radii ratio that exceed 0.3. The conditions for the applicability of analytic relations and their accuracy are established from a comparison of the results of analytic and numerical calculations.