Radial Distribution of Plasma Concentration in a Positive Glow Discharge Column with Dust Particles

Russian Physics Journal - The work considers the influence of dust structures on the positive column of a glow discharge. A formula describing the radial distribution of ions in the case of an...     

Modelling of the Positive Column in an Argon-Hexamethyl-disiloxane dc Glow Discharge

A model is presented of the positive column of a dc glow discharge in argon with small admixtures of hexamethyldisiloxane (HMDS). The axial electric field, the ion production rates for direct-, stepwise-, pair-, and Penning ionization, the densities of metastable Ar atoms and of electrons, and the wall current of HMDS ions are calculated in dependence on HMDS admixture and discharge current density. For the calculations particle balance equations were used for a diffusion determined plasma in a mixture of two gaseous components. The reaction rates for the electron collision processes were determined applying the electron distribution function calculated for pure argon. Taking into account PENNING ionization of HMDS molecules by metastable argon atoms the decrease of electric field for increasing HMDS admixtures is according to the experimen-tally measured values. Also ion wall currents and electron densities are compared with experimen-tal values for thin film formation rate and results of probe measurements.     

Electron Attachment and Detachment Processes in Electronegative Gases

Selected results of recent studies on electron attachment (especially to excited molecules) and detachment processes in electronegative gases are presented and discussed and their relevance to modern technologies is indicated.     

Ambipolar Diffusion in Direct-Current Positive Column with Variations in Radius of Discharge Tube

The ambipolar diffusion and argon ion mobility as functions of the reduced electric field and pressure times the tube radius are investigated in a weakly ionized non-uniform glow discharge plasma system. In particular, the variable cross section at the same discharge tube on the ambipolar diffusion coefficient shows a more noticeable effect than the effects from the ion mobility. As the diffusion length A increases, the ambipolar diffusion Da increases. However, it decreases as the discharge current is increased.     

Charged Particle Distribution near the Shock Front in a Glow Discharge

The charged particle distribution near the front of a shock wave propagating in the glow discharge plasma has been investigated. It has been found that the ion concentration before the front varies nonmonotonically. Behind the shock front, the charged particle concentration varies smoothly in contrast to the neutral component density.     

Increased Power Concentration and its Effects on the Discharge Parameters of the Low Pressure Hg-rare Gas Positive Column. II. Variation of Tube Radius

The reduction of the tube radius is an effective technique for enhancing power concentration. The increased wall losses are compensated by larger field strengths, which counteract the decrease in radiation efficiency with rising current density. The causal relationships are investigated for tube radii of 18-4 mm at constant discharge current i = 200 mA and constant current density j = 1.2 mA/mm² and for parameter variation of the field strength only. The measured efficiencies of the Hg-resonance lines 254 and 185 nm and the electron energy distribution functions agree well with the calculated values. Moreover, the results of the model calculations provide information on the elementary processes involved, such as elastic losses, collisions of second kind, stepwise processes and Coulomb interaction. The results show that Hg-rare gas discharge with tube radii R = 5–10 mm are no less suitable for light production than those with radii between 13 and 18 mm.     

Influence of the Anode of a Non-Self-Sustained Glow Discharge with a Hollow Cathode on the Spatial Distribution of Plasma Concentration

Russian Physics Journal - The results of investigation of the influence of geometrical dimensions, shape and position of the anode of a high-current non-self-sustained glow discharge with a hollow...     

Electron Kinetics in the Cathode Region of a Glow Discharge and in Hollow Cathodes

On the basis of an improved cascade model a multi-group theory for studying the electron kinetics in the cathode region of a glow discharge and in hollow cathodes is developed. The secondary electrons newly created by ionization are taken into account. The electrons are divided in groups with respect to the interval where they were created or where they made an inelastic collision. The inelastic collisions and the forward scattering are assumed to dominate. The mean energies of two neighbouring groups are taken to be different by the ionization energy or by parts of it. For the flux densities of the various electron groups a set of ordinary first order differential equations and corresponding boundary conditions are obtained and solved for He. These formulae are valid for any electric potentials. The results relatively well agree with those of Monte Carlo simulations. The first Townsend ionization coefficient differs substantially from that resulting from the Townsend formula. The velocity distribution function spatially varies and contains several groups of fast electrons. Using the detour factor the angular scattering can be included in the calculations.     

Investigations about the Influence of the External Circuit Elements on the Propagation of Ionization Waves in the Positive Column of a Neon Glow Discharge

Our investigations have been motivated by former works of Michel and Achterberg [1]. They described the important influence of the external circuit elements and connected therewith the mechanism of feedback (Barkhausen k · v ≧ 1). The properties of external and self-excited moving striations (threshold current, fundamental frequency) are strongly influenced by the feedback. This paper demonstrates the differences occuring either a voltage or a current source in the external circuit is used in order to perturb the discharge and to realize different degrees of feedback by changing the external resistor R_ext. of the discharge. It is shown the impact on the fields of existence of self excited striations in a non driven discharge. Furthermore our investigations yield differences in the width of Arnol'd tongues [2] of periods one and two in the perturbed discharge depending on a varied degree of feedback. Last not least its influence on the behaviour of quasiperiodic and chaotic states is demonstrated. The investigations permit first information concerning the sensivitity of one parameter variation (feedback controll by external resistor) which might be used e.g. for a stabilization of unstable periodic orbits (controlling chaos).     

Investigation of the Beam Plasma Discharge in Electronegative Gases Using the Second Derivative of Langmuir Probe Characteristics

The distribution of the charge carriers is measured and the influence of the attachment processes on the electron energy distribution function is demonstrated for beam plasma discharges in SF₆, CF₄ and O₂ with the aid of the second derivative of Langmuir probe characteristics. The structuration of the plasma into regions of predominating negative ions and regions of predominating electrons is determined by the the established radial T_e-profile. The dimension of the quasi electronfree plasma changes significantly as well at transition from the turbulent heating mechanism into the electron impact plasma generation as by occuring low-frequency instabilities. With increasing n_?/n_e a deficit of low energetic electrons appears in the electron energy distribution parallel to the formation of the negative ion peak. The saturation currents at n_e/n_?=0 yield the mass ratios between negative and positive ions.     

Current Distribution Over the Hollow-Cathode Surface for a Low-Pressure Glow Discharge

Russian Physics Journal - The results of an investigation of a low-pressure hollow-cathode glow discharge are presented for the conditions where the cathode cavity depth is comparable with the...     

Kinetics of the Electron Component in the Turbulent Electron-Beam Discharge Plasma in Diatomic Gases and Comparison of some Macroscopic Properties between the Plasmas of the Beam and the Glow Discharge

The present paper is devoted to the investigation of the kinetics of the electron component in the stationary beam discharge plasma in molecular nitrogen. Using the Boltzmann equation with the inclusion of the elastic and the main inelastic binary collisions and also the Coulomb interaction between the charged particles we have calculated the energy distribution function and some macroscopic quantities of the electrons within a large range of parameters. Using our earlier results for the beam discharge plasma in hydrogen, also the dependence of the macroscopic quantities on the kind of molecular gas is discussed. Finally, the comparison of some macroscopic properties of the beam and the glow discharge plasma was performed under the condition of equal power input per volume unit in both types of plasmas in nitrogen.     

The Measurement of Current Column Plasma Parameters in the Glow Discharge at Increased Pressure

Results of the probe and thermocouple measurements of the constricted stationary glow dis charge in nitrogen and air at pressures up to 60 Torr are given. It was shown that the main energy processes in the column are the heating of the gas and its vibrational excitation. The balance of charged particles is determined by the electron-ion recombination and the stepwise ionization through metastable levels of nitrogen molecules. The results obtained can be used in the numerical simulation of a moving filament during the current constriction in the glow discharge.     

On the Anomaly of the Electrical Field Strength in the Magnetized Positive Column of Glow Discharges at Small Currents

The axial electrical field strength in the positive column of glow discharges at small currents in noble gases passes through a maximum with the increase of an axially directed magnetic field. This maximum is explained of the contrary processes of extension of the radial profiles of the electron energy and the concentration of the metastable atoms on the one hand and the decrease of the ambipolar diffusion losses on the other hand. Using the results of measurements of metastable atom concentrations, the electrical field strength is calculated as a function of magnetical induction with the aid of a set of balance equations. The radial and axial distribution of the electrons is checked by probe measurements. The methods for measuring the concentration of the excited atoms and the electrons are described.     

Negative Ions in a Glow Discharge of Tetrafluoromethane

The Langmuir — probe measurements in a CF₄ — glow discharge reveal a large number of negative ions (10¹⁰ cm^?3) in the plasma between the planar C-electrodes. Under special conditions the density of them exceeds the electron density at several orders of magnitude and sustains a quasi — electron free plasma. The ratio depends on the residence time of the molecular gas in the discharge reactor. It is due to dissociative electron attachment to highly molecular gas components arising from the plasmachemical conversion of CF₄. F^? and CF₃^? are the most important negative ions.     

Features of Transient Processes in DC Microdischarges in Molecular Gases: From a Glow Discharge to an Arc Discharge with a Unfree or Free Cathode Regime

JETP Letters - A unified self-consistent model is formulated to describe a discharge gap, electrodes, and the formation of the parameters of dc microdischarges in molecular gases at atmospheric...     

离子分子束源的浓度调制光谱研究

建立了一套交流放电产生离子分子束源的装置,以N₂为例,束流中N＋₂的发射谱强度远大于N₂的发射谱强度,N+₂(B)/N₂(C)高达6∶1。根据其发射谱,对交流放电过程和浓度调制光谱进行了测量研究,并计算了离子分子激发态振动温度和转动温度,分别为3 310和282 K。