Positive Column Of Glow Discharge Research Articles

Glow Discharge Positive Column with Dust Particles in Neon

AbstractExperimental and numerical study of positive column of glow discharge in neon with dust particles is presented. The influence of dust structures on integral parameters was measured and simulated. Spatial distributions of electrons and electric field configuration in presence of dust cloud are represented. The reverse radial electric field direction is shown to appear within the dust cloud at high dust particle concentration. The current‐voltage characteristics of discharge in neon with and without dust particles are represented. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Positive column of glow discharge with dust particles

The effect of microparticles on the current-voltage characteristics (CVC) and on the distribution of plasma components in a positive column of a glow discharge in air is studied both experimentally and numerically. The analysis is carried out on the basis of a diffusion description of the plasma of a discharge and the description of flows of ions and electrons onto the surfaces of dust particles in the orbit motion limited approximation. The CVC change is found to be connected with an increase in the volumetric losses of the charge on particles and the drift of a substantial part of the free electrons onto the particles. The radial distributions of the plasma components, the radial electric field, and the charges of the particles are calculated. The effect of a dust cloud on the configuration of an electric field and the CVC of a positive column of a glow discharge is analyzed.

Parameters of the positive column of glow discharge with dust particles

We calculate the measured nonlocal parameters of the plasma of the positive column of direct current glow discharge in the presence of dust structures with different dust particle concentrations. The calculations are performed for typical conditions of the positive column of low-pressure glow discharge in air at which a collisional regime of maintaining discharge is achieved. The discharge plasma is described using the diffusion approximation; the flows to the surface of the dust particles are described in the orbital motion limited approximation. Calculation is carried out for micron-size particles with concentrations of up to 1011 m−3. The distribution of the dust component is assumed to be independent of the discharge parameters. Radial distributions of the plasma components and of the electric field component are obtained. The charges of dust particles for various concentrations and discharge parameters are calculated. It is demonstrated that for a certain particle concentration, the absorption efficiency of plasma particles becomes comparable with diffusion losses at the tube walls. The influence of the dust cloud on the electric field configuration at different dust particle concentrations in the cloud is analyzed. The current-voltage characteristics of the positive column of glow discharge are calculated. A higher discharge stability toward the perturbative action of dust particles at high discharge current values is demonstrated.

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.

Study of positive column of glow discharge in nitrogen by optical emission spectroscopy and numerical simulation

Nitrogen dc discharges are investigated at a constant pressure of 3 Torr and a variable discharge current of 17–100 mA. Optical emission spectroscopy is employed to detect the excited species at four axial positions far from the cathode (25, 75, 125 and 175 mm) and to determine the rotational and translational temperatures and the vibrational distribution functions (VDFs) of the B 3Πg and C 3Πu states of the nitrogen molecule. A semiempirical level-to-level collisional–radiative model is used for the modeling of the collisional and radiative processes and the processing of data. It provides detailed information on the processes occurring in the dc discharge, calculates the nitrogen emission spectra, predicts the translational and rotational temperatures, the VDFs in the ground and electronic excited B 3Πg (vB = 0–17) and C 3Πu (vC = 0–4) states together with the corresponding vibrational temperatures TV, TB and TC. Theoretical emission spectra and VDFs of the B 3Πg and C 3Πu states are also in good agreement with the experimental ones. The main processes responsible for the VDFs are also established.

Shock wave propagation in glow-discharge plasma in dry and humid air

We have experimentally studied propagation shock waves in glow-discharge plasma in dry and humid air. It is established that the structure of a pressure pulse behind a shock wave propagating across the positive column of glow discharge in both cases generally remains the same. At the same time, the wave velocity profile across the column exhibits a change in positions of the velocity peaks.

On the stability of a dc-driven oxygen discharge in cylindrical geometry

Starting from the hydrodynamic equations describing the positive column of glow discharges in oxygen, the stability of the homogeneous state is investigated. The model contains electrons, positive and negative ions as well as the metastable molecule O2(a1Δg) as a detachment partner. It is shown that the transition from the H-mode to the T-mode of a dc-driven oxygen discharge is caused by an attachment-induced ionization instability. The stability boundaries are calculated for selected values of the plasma parameters. The comparison of experimental data and theoretical predictions shows satisfactory agreement.

The effect of humid and dusty atmosphere on shock wave destruction in a glow-discharge plasma

The influence of air humidity and the dust present in air and nitrogen on the structure of a pressure momentum distribution behind a shock wave propagating across the positive column of glow discharge in these gases has been experimentally studied. Analysis of the experimental data provides information concerning the mechanism of shock wave degradation under such conditions.

Acoustic Instability in Inhomogeneous Gas-Discharge Plasma

The possibility of amplification of acoustic waves in inhomogeneous atomic dc gas-discharge plasma (positive column of glow discharge) is investigated theoretically. This amplification is caused by the transfer of thermal energy from electrons to colder electron gas under conditions of elastic electron-atom collisions. It is demonstrated that the inclusion of nonuniform distribution of equilibrium temperature, neutral gas concentration, and electron concentration over the plasma column cross section, similar to the case of uniform distribution, cannot result in acoustic instability and, consequently, in the interpretation of the experimental results in sound amplification in weakly ionized plasma. The dispersion equation for sound waves in inhomogeneous glow-discharge plasma is derived and numerically analyzed in detail. Comparison of the theoretical and experimental results enables one to identify the reasons for their discrepancy and to actually reveal the basic principles essential for constructing a theory which will make it possible to quantitatively and adequately describe the experimental data on the amplification of sound in weakly ionized atomic plasma.

The Sound Velocity Profile and the Effect of Weak Shock Wave Destruction in the Positive Column of Transverse Glow Discharge

The sound velocity profile in the direction across the positive column of glow discharge in air has been experimentally measured and theoretically calculated. The sound velocity exhibits a sharp local increase, which coincides in the experimental and theoretical profiles.

Analysis of dusty plasma in the positive column of glow discharges

The radial distributions of ions, electrons and dust particles in the positive column of glow discharges are investigated in a triple-pole diffusion model. The dust particles are mainly trapped in the region around the column axis where the electrostatic potential is the highest. The presence of the dust particles results in the ion density increasing and the electron density decreasing in the dust-trapped region. The dust-trapped region is wider for a higher dust temperature or a smaller particulate radius. The ions and electrons in the dust-free region away from the column axis are in ambipolar diffusion.

Chaos control and taming of turbulence in plasma devices

Chaos and turbulence are often considered as troublesome features of plasma devices. In the general framework of nonlinear dynamical systems, a number of strategies have been developed to achieve active control over complex temporal or spatio-temporal behavior. Many of these techniques apply to plasma instabilities. In the present paper we discuss recent progress in chaos control and taming of turbulence in three different plasma “model” experiments: (1) Chaotic oscillations in simple plasma diodes, (2) ionization wave turbulence in the positive column of glow discharges, and (3) drift wave turbulence in a magnetized plasma column. Depending on the physical mechanism of the specific instability in each case, an appropriate control strategy is chosen out of a variety of different approaches; in particular discrete feedback, continuous feedback, or spatio-temporal open-loop synchronization. Electric control fields are externally applied to the plasma device and the chaotic or turbulent state is stabilized by only weak perturbations of the plasma equilibrium. The success of this approach is demonstrated in both experiment and numerical simulation and the actual effect of the applied control fields is investigated.

Hopf bifurcations in balance equations of glow discharges

Starting from the hydrodynamic equations describing the positive column of glow discharges in inert gases, the instability of the axially homogeneous state is investigated. Dirichlet boundary conditions at the ends of the positive column are chosen. Stimulated by experiments, the influence of metastable atoms and of the outer circuit is taken into consideration by additional equations. Center manifold and normal form theories are used to characterize the codimension-one bifurcations. Depending on the current, the length of the positive column and the resistance of the outer circuit supercritical and subcritical Hopf bifurcations are found. The importance of the results with respect to the experiments on the ionization instability in a neon discharge is discussed. {copyright} {ital 1997} {ital The American Physical Society}

Experimental stark shifts of several HeI and ArI spectral lines

Stark shifts of four HeI and six ArI spectral lines have been measured in a linear pulsed arc plasma, superimposed to the glow discharge positive column plasma in helium and argon-helium mixture, respectively. The measured values were compared to the existing data calculated, according to the various theoretical approaches.

Modelling of Noble Gas-SiH4 Gas Mixture Glow Discharge Positive Column Plasmas

Numerical modelling of He-SiH4, Ne-SiH4 and Ar-SiH4 gas mixture glow discharge positive column plasmas is conducted for the gas pressure from 0.1 to 30 Torr, the percentage silane gas mixture in a noble gas from 0.01 to 10%, and the electron density from 109 to 1013 cm-3. The results show that the plasma parameters significantly depend on the combination of the choice of the noble gas and the silane mixture fraction.

Experimental and theoretical study of the CF4 DC glow discharge positive column

An experimental and theoretical study of the positive column of the CF4 DC glow discharge is presented. It includes the experimental determination of the reduced electric field Ez /N and the electron impact excitation rate constant KAr of the line ( lambda =750.3 nm, epsilon th=13.5 eV) of the actinometric addition (Ar) in CF4 plasma for a wide range of parameters (pressure p=0.2-2.3 Torr, current density j=4-35 mA cm-2). All experimental values of the reduced electric field can be described within the limits of experimental error by the universal dependence Ez/N on r0N (r0=0.9 cm, the discharge tube radius). Also the experimental dependence of kAr on Ez/N has been obtained. These results have been used to test different theoretical models of the CF4 discharge positive column. Comparison of the experimental and calculated values of Ez /N and KAr has shown the validity of the theoretical model developed in this work. This model takes into account the large negative ion concentration in the positive column and predicts its division into regions of ion-ion plasma (in the centre) and electro-ion plasma (near the tube wall). The model also accounts for the effect of non-locality of the electron energy distribution function. It has been shown that this effect can be accounted for by solving the Boltzmann equation for the EEDF in the spatially non-uniform case. The incorrectness of the notion of ambipolar diffusion in the plasma of a strongly electronegative gas with high negative ion concentrations has been reaffirmed.

Electron Energy Distribution Function in Fluctuating Plasmas

A method is proposed for detecting the electron energy distribution function (EEDF) of periodically fluctuating plasmas by averaging the time-resolved EEDF. The method is applied to detect the EEDF for externally excited and self-excited ionization waves in He positive columns of glow discharges. Good agreement is obtained between the EEDFs with and without the externally excited ionization wave.

On the Relationship Between Macroscopic and Microscopic Time Constants in gas Discharges

AbstractThe complicated relationship between macroscopic and microscopic time constants in gas discharges was given on the basis of the theory of the positive column of glow discharges.

Mechanism of the ozone formations in a near liquid nitrogen temperature medium pressure glow discharge positive column

Abstract

A numerical model for the positive column of a glow discharge in a glass flow at low and moderate Reynolds numbers

A two-dimensional numerical model of the medium pressure (0.1<or=p<or=10 Torr) flowing glow discharge positive column plasma has been constructed. The axial and radial plasma density distributions and the degree of ionisation required to sustain the positive column have been calculated for a steady state ambipolar diffusion-controlled discharge acting over a finite portion of an infinite cylinder in which there is laminar gas flow. The influence of volume recombination, discharge region length and the gas flow velocity has been investigated.