Positive Column Of Glow Discharge Research Articles

Specificity of the electron energy distribution function in a low-pressure nitrogen plasma

In this work, self-consistent simulations of a glow discharge positive column in low-pressure nitrogen plasma are presented. The electron energy distribution function (EEDF) was calculated by solving the complete (i.e. nonlocal) Boltzmann kinetic equation for electrons in both the energy and coordinate (space) variables. The accuracy and range of applicability of the two limiting cases are considered when the kinetic equation is reduced to a dependence on only one variable: kinetic energy in the local approximation or total energy in the so-called totally nonlocal (Holstein–Tsendin) approximation. It is shown that the Holstein–Tsendin approximation, when electron spatial transport dominates the electron energy relaxation (i.e. the ratio between the typical plasma inhomogeneity characteristic length and the electron energy relaxation length ), can be used at low nitrogen pressures (when the parameter pR ⩽ 0.05 Torr). With a further increase in pressure, there is a large intermediate region where the EEDF is nonlocal in the sense that the full kinetic equation must be solved. So, even at pR ≈ 0.5 Torr, the EEDF in nitrogen plasma is nonlocal. Therefore, the use of a local approximation to find the EEDF, when all terms with spatial gradients and an ambipolar field can be discarded in the kinetic equation, requires careful verification. Particular attention should be paid to the periphery of the discharge volume, where the self-consistent ambipolar field inevitably exceeds the external electric field that heats the electrons and produces plasma.

Formation and destruction of striation plasmas in helium glow discharge at medium pressures

The striation plasmas are usually generated within a positive column of glow discharge, where rich and complex physical interactions are involved, especially, in the medium or high pressures. Along these lines, our work aims to thoroughly investigate the formation and destruction of helium striation plasmas at kPa level pressures. The characteristics of the helium striation plasmas, and especially the optical emission properties are explored. The emission lines of 706.52 nm and 391.44 nm related to the energetic electrons and the high-energy metastable helium atoms respectively, were focused on in this work. The formation of striation plasmas in a helium glow discharge, is mainly associated with the instability originating from the stepwise ionization of high-energy metastable state atoms, Maxwellization of the electron distribution functions and gas heating. Additionally, the destruction effect of helium striation plasmas is of great significance when a small amount of nitrogen or oxygen is mixed into the discharge plasmas. The reduction of the mean electron energy and the consumption of the high-energy metastable helium atoms are considered as the underlying reasons for the destruction of striation plasmas.

Features of the EEDF formation in the dusty plasma of the positive column of a glow discharge

In this paper, the formation of the electron energy distribution function (EEDF) in the argon dusty plasma of the positive column of glow discharge at low pressure is investigated. A model for calculating EEDF in the local approximation is adapted to find the nonlocal EEDF via the Holstein–Tsendin model. The results show that, contrary to the prevalent opinion in the literature, the presence of dust has little effect on the EEDF up to the limiting values of the density of dust particles that can be injected into the plasma for the considered conditions. It is also shown that, when obtaining the nonlocal EEDF, the spatial profiles of the axial (heating) and radial (ambipolar) fields should be chosen from a self-consistent solution. Additionally, the differences between the local and nonlocal EEDFs increase in the peripheral regions of the discharge due to a sharp decrease of fast electrons in the nonlocal case. Significant changes in the form of the nonlocal EEDF along the radius also lead to noticeable changes in other characteristics of the electrons in this area, especially for those with a large energy threshold (e.g. due to excitation, ionization).

Simulating glow discharge positive column parameters in neon

The nonlocal self-consistent model for the low temperature plasma parameters in a glow discharge positive column is presented. The model implies relaxation method for the solving of the nonlocal Boltzmann equation for electron energy distribution function, continuity equation for ions distribution and Poisson equation for radial electric field. Calculations are provided for a cylindrical discharge tube used in the Plasma Kristall-4 experiments for neon as a plasma forming gas for the gas pressures of 30-70 Pa and discharge currents of 0.5-2.5 mA. Axial electric field strength, electron temperature and electron density are calculated as functions of the discharge current and the gas pressure. The results are in good agreement with the data provided by other authors.

Ambipolar Trap for Dust Particles in a V-Shaped Homogeneous Positive Column of Glow Discharge at Low and Medium Pressures

The spatial distribution of dust particles in a low-pressure homogeneous positive column of a dc glow discharge in a right-angle curved (V-shaped) glass tube in different spatial orientations was observed and analyzed. It is found that in all cases, the ambipolar field prevents charged dust particles from falling on the wall of the glass tube. As a result, the design of the curved glass tube makes it possible to create in practice a simple and effective ambipolar trap and to implement the collection and control of dust particles in plasma.

Радиальное распределение концентрации плазмы в положительном столбе тлеющего разряда с пылевыми частицами

Радиальное распределение концентрации плазмы в положительном столбе тлеющего разряда с пылевыми частицами

Plasma Source for Bipolar Electron-Optical System

The paper presents the experimental study of pulsed plasma source with hollow cathode intended for bipolar electron-optical system with open-boundary plasma. The proposed configuration of the plasma source includes two ring-shaped discharge cells based on plasma thruster technology. The plasma source can operate both in a low-current high-voltage mode and a high-current low-voltage mode. The main attention is paid to the highcurrent mode which is similar to the glow discharge positive column. It is found that along with the discharge in closed electron drift the ignition of additional, non-self-sustained hollow cathode discharge with electron oscillation is possible, thus considerably reducing the voltage of the closed-drift discharge. Current–voltage characteristics of the high-current discharge are measured for these conditions. Using the double probe technique, the local plasma parameters are measured together with their spatial distribution in the discharge region. The maximum plasma density along the plasma source axis is (6.5–6.8)•1012 сm–3.

Noncontact diagnostics of remote anisotropic plasmas

A new noncontact method for diagnostics of nonequilibrium plasma that integrates technologies of optical-and-magnetic technique of the Hanley effect and those of probe investigations is proposed. The method mentioned has been experimentally tested in plasmas with cardinally dissimilar structure of the electron velocity distribution function. As a model plasma object the positive column of glow discharge has been studied and as a distant object a short low-voltage beam discharge. The following potentialities of this method were illustrated, viz. in the distant object the complete electron velocity distribution function was determined and the diagram of electron pressure angular anisotropy was constructed. Verification of the method accuracy was carried out using the technique of flat single-sided probe.

An analytical model of glow discharge positive column in axially symmetric channel with variable cross section

A model of glow discharge positive column in gas flow is considered in this paper. It is supposed the discharge is between the permeable mesh electrodes installed in the initial and end sections of axially symmetric channel. In general case the channel width changing along the stream is accounted. The positive column in gas flow is described by integro-differential system of equations with an approximation of constant gas flow density. The border conditions for gas ionization degree and temperature in the initial section of channel are given by any functions. An analytical solution of that system was obtained. The special cases of the boundary conditions are analyzed.

Influence of dust particles on spatial distributions of particles and fluxes in positive column of glow discharge

The research herein examined the results of numerical simulations of the positive column of a glow discharge in argon dusty plasma using COMSOL Multiphysics software under conditions similar to the project known as PK-4. Various scenarios dealing with formations of spatial distributions of densities and fluxes for charged particles were studied, and evaluations of the influence of dust particles on the discharge were obtained in a wide range of dust densities. Two extreme cases were distinguished: weak dust influence when the densities, fluxes and electric field profiles are not perturbed, and strong dust influence when all three density profiles (electrons, ions and charged dust) in the dust cloud are similar (parallel) to each other, resulting in all created charges in the dust cloud being lost inside the cloud. In such a case, the ambipolar field and the transport of charged particles are decreased in the dust cloud, and any ambipolar flux is almost absent within the cloud.

Theoretical simulation of hydrogen glow discharge in the positive column of plasma sources

Direct current (DC) glow discharge positive column has played an important role in the field of plasma material surface modification. In this kinetic study of hydrogen glow discharge in the positive column, it is found that electron energy distribution function (EEDF) obviously departs from Maxwell distribution. The EEDF tail moves to higher energy when the ratio between electric field E and density of neutral species N (E/N) increases and the tail moves toward higher energy if hydrogen atom proportion increases at the same E/N. It is also shown that electron temperature augments with the increase of E/N. Additionally, the dissociation ratio percentage of H2 rises with the increase of E/N.

The role of molecular ions in cryogenic dusty plasmas of dc discharge in neon

The diffusion-drift model of positive column of glow discharge in neon have been used to study the effect of molecular ions in the interaction of plasma with dust particles of micron size. Simulations have been carried out at a pressure of 20 – 100 Pa and gas temperature of 77 K. The electric field of the discharge, the concentrations of discharge components, including metastable atoms and molecular ions, and the charge of dust particles have been simulated.

Modeling of glow discharge in longitudinal gas flow in a plane channel of variable cross section

A two-dimensional model of glow discharge positive column in gas flow has been suggested in this paper. It is considered that the discharge maintained between the permeable mesh electrodes installed in the initial and end sections of the plane channel. In general case the channel width changing along the stream is accounted. The positive column in gas flow is described by integro-differential system of equations with an approximation of constant gas flow density. The border conditions for gas ionization degree and temperature in the initial section of channel are given by any functions. An analytical solution of that system was obtained and special cases of the boundary conditions analyzed.

Dust particle trapping of ions in a dc glow discharge in neon

The distributions of an average concentrations of ions in a positive column of glow discharge were simulated in pure neon and in plasma with micron size dust particles on the base of the drift-diffusion model. Simulations indicate that ion concentration within the dust structure may few times exceed that in a dust-free discharge. The discharge parameters were resulting analyzed in increase of ion concentration. The dust trap was demonstrated to require less energy input in a discharge than an increase of discharge current.

Positive column of a glow discharge in neon with charged dust grains (a review)

The effect of charged micron-size dust grains (microparticles) on the electric parameters of the positive column of a low-pressure dc glow discharge in neon has been studied experimentally and numerically. Numerical analysis is carried out in the diffusion-drift approximation with allowance for the interaction of dust grains with metastable neon atoms. In a discharge with a dust grain cloud, the longitudinal electric field increases. As the number density of dust grains in an axisymmetric cylindrical dust cloud rises, the growth of the electric field saturates. It is shown that the contribution of metastable atoms to ionization is higher in a discharge with dust grains, in spite of the quenching of metastable atoms on dust grains. The processes of charging of dust grains and the dust cloud are considered. As the number density of dust grains rises, their charge decreases, while the space charge of the dust cloud increases. The results obtained can be used in plasma technologies involving microparticles.

Influence of dust void on neon DC discharge

The diffusion/drift model of the positive column of glow discharge in neon with fine dust particles was used to study the role of a dust cloud with a void in the interaction between plasma and dust particles in the range of neon pressure and discharge current where dust particles may form structures with cavities. The results represent the nonlocal effect of void size on plasma composition, configuration of electric field and on distributions of plasma components in discharge with voids in dust structures. Simulations show that the electric field strength and the metastable atom concentration inside the void are higher than in the discharge without dust particles, while electron concentration may be either higher or lower.

Direct current discharge with microparticles: The electrical characteristics and the plasma trap parameters

The electrical characteristics of the positive column of glow discharge were measured and simulated in pure neon and in plasma with micron size particles. The increment of the longitudinal electric field strength caused by the presence of dust structures was measured. Simulation was based on the diffusion-drift model of the positive column of glow discharge. Simulation was carried out using the measured values of dusty structure parameters and discharge characteristics. It was shown, that a dust structure maintained in a dc discharge represents a plasma trap for ions with ion concentrations more than three times higher than in a free discharge. The results can be used to calculate the traps for confinement of ions and dust particles in gas-discharge plasma.

Influence of dust particles on ionization and excitation in neon dc discharge

The influence of dust particles on the concentration of metastable neon atoms and ionization was investigated using the developed drift/diffusion model for plasma of positive column of glow discharge. The detailed de-excitation in neon was considered. In addition to usual plasma losses in dusty plasmas, the quenching of metastable atoms on dust particle surface was considered. The strong influence of dust particles on the ionization rate and concentration of metastable neon atoms in a positive column of glow discharge is shown to result from the change in the longitudinal electric field strength.

One-dimensional electromagnetic band gap structures formed by discharge plasmas in a waveguide

We demonstrate the ability to develop one-dimensional electromagnetic band gap structure in X-band waveguide solely by using the positive columns of glow discharges in neon at the middle pressure. Plasma inhomogeneities are distributed uniformly along a typical X-band waveguide with cross section of 23 × 10 mm2. It is shown that electron densities larger than 1014 cm−3 are needed in order to create an effective one-dimensional electromagnetic band gap structure. Some applications for using the one-dimensional electromagnetic band gap structure in waveguide as a control of microwave (broadband filter and device for variation of pulse duration) are demonstrated.

Effect of metastable neon atoms in a positive column of glow discharge with dust particles

The diffusion/drift model of the positive column of glow discharge in neon was used for the analysis of the role of neon metastable atoms in the interaction between neon plasma and dust particles. The radial profiles of electrons and metastable atoms were simulated in the typical range of neon pressure and discharge current where dust particles may form dense dust structures changing the plasma properties. The results showed the nonlocal effect of dust particles on the plasma composition. Within the dust structure, the metastable atom concentration was shown to be higher than in the discharge without dust particles at the same discharge parameters; the ratio of concentrations of metastable atoms and electrons may increase with increasing dust particle concentration in a certain range of discharge parameters. The partial contribution of metastable atoms to the ionization was found to be higher than their losses on the surface of dust particles and increased when the gas pressure was increased.