Gas Discharge Physics Research Articles

Plasma electroradiolysis of aqueous solutions

Electroradiolysis of aqueous solutions, a process that is induced by the action of glow discharge on an electrolytic cathode, is considered. The results of investigation of systems of this type are summarized. The set of phenomena at the discharge plasma/electrolyte-cathode interface is treated in terms of radiation chemistry, plasma chemistry, emission electronics, and gas discharge physics. A new area of research, electroradiation chemistry of water and aqueous solutions, is presented.

A PIC based procedure for the integration of multiple time scale problems in gas discharge physics

A efficient PIC technique has been implemented to study the development of electrical discharges during long periods of time. Special motivation is provided by electrical pulsations that develop in very short times but whose repetition period is much longer. The method exploits the existence of different time scales in the electrical discharge to implement a long time-step particle pushing technique both at particle and at mesh levels. The development of a train of hundreds of Trichel pulses, which is a prohibitively long computation with a conventional PIC, has been used to test the validity of the method.

Physics of Electric Discharges in Atmospheric Gases: An Informal Introduction

A short account of the physics of electrical discharges in gases is given from the viewpoint of its historical evolution and application to planetary atmospheres. As such it serves as an introduction to the papers on particular aspects of electric discharges contained in this issue, in particular in the chapters on lightning and the discharges which in the last two decades have been observed to take place in Earth’s upper atmosphere. In addition to briefly reviewing the early history of gas discharge physics we discuss the main parameters affecting atmospheric discharges like collision frequency, mean free path and critical electric field strength. Any discharge current in the atmosphere is clearly carried only by electrons. Above the lower boundary of the mesosphere the electrons must be considered magnetized with the conductivity becoming a tensor. Moreover, the collisional mean free path in the upper atmosphere becomes relatively large which lowers the critical electric field there and more easily enables discharges than at lower altitudes. Finally we briefly mention the importance of such discharges as sources for wave emission.

Plasma Nanoscience: From Nature's Mastery to Deterministic Plasma-Aided Nanofabrication

Summary form only given. Plasma nanoscience is an emerging research area at the cutting edge of the physics of plasmas and gas discharges, nanoscience and nanotechnology, materials science and engineering, and structural chemistry. The existing approaches to fabricating exotic nanostructures and functional nanofilms are mostly process-specific and suffer from cost-inefficient trial and error practices. One of the reasons is that the ability to control the generation, transport, deposition, and structural incorporation of the building units of such films and structures, still remains elusive. On the other hand, the pioneering concept of deterministic plasma nanoscience is treated with extreme caution due to inherent chaotic nature of the plasma at the microscopic level. This contribution shows how to challenge one of the previously intractable problems of bridging nine orders of magnitude between the sizes of plasma nanofabrication facilities (~0.5 m) and self-organization of adsorbed building units on solid surfaces (~0.2 nm). One of the possibilities is to manipulate the ionic building blocks in the non-neutral layer of space charge that separates the plasma and solid surfaces and control self-organization of nanostructure building blocks on plasma-exposed surfaces and their insertion into the nanoassemblies. The results of advanced computer simulation allow one to obtain the microscopic topology of ion fluxes in the vicinity of selected functional nanostructures and the arrangement of adsorbed species into nanopatterns on solid surfaces. These results are linked, via the sheath parameters, to the building unit densities and energies in the plasma bulk and eventually to the process control parameters. On the other hand, the desired nanoassemblies can be engineered by using atomistic ab initio density functional theory approaches. Recent experimental and computational results obtained within the International Research Network for Deterministic Plasma-Aided Nanofabrication suggest the possibility of deterministic synthesis of conical nanotip structures for electron microemitter arrays, and are discussed in this talk. Finally, this talk reveals how the Nature's mastery works in the self-assembly of nanometre-sized particles in the Universe and of exotic nanoassemblies in laboratory plasmas

Similarity law for a homogeneous discharge in the presence of a strong field and analogues of the Stoletov constant for the pulsed regime

It is demonstrated that the similarity relationships (breakdown curves), which establish a dependence of the field strength divided by the pressure on the product of the pressure and the delay time of the breakdown, are realized upon the uniform breakdown of the gas gap in the presence of both rectangular and triangular voltage pulses, which is interesting for the physics of gas and plasma discharges, and remain valid for strong fields. The breakdown criterion is described with a two-valued curve such that the effective multiplication of electrons in gas becomes possible in the presence of both weak and strong fields and at small products of the pressure and the pulse time. An analogue of the Stoletov effect, which corresponds to a maximum in the current with respect to pressure at a given voltage pulse, is demonstrated for the pulsed discharge. The analogues of the Stoletov constant are calculated for non-self-sustained pulsed discharges in various gases. The minimum delay time of the breakdown is also determined by these constants.

Dynamics of formation of the pulsed electrical breakdown of highly overvoltaged gas gaps in the subnanosecond range

The mechanisms of the initiation of pulsed electrical breakdown of gas gaps in the subnanosecond range are of great interest for gas-discharge physics. Recently developed voltage-pulse generators make it possible to form high-voltage pulses with 200-ps-wide fronts and to apply voltages much higher than the static-breakdown voltage to a gas gap. Under these conditions, field emission from a cathode with the subsequent explosion of microinhomogeneities on its surface begins to make an increasing contribution to the initiation of breakdown [1]. Moreover, for high ratios of the electric field to pressure at the stage of breakdown delay and the initial stage of commutation, the energy gained by some free electrons per unit path can be higher than the energy lost in inelastic collisions. This regime is called the regime of the continuous acceleration of electrons, and these electrons are named fast or runaway electrons [1]. Fast electrons intensely ionize the gas medium in the interelectrode gap, and the breakdown formation time can decrease sharply in comparison to the classical streamer mechanism [2]. When fast electrons are decelerated on an anode, x rays are emitted [3‐6] and initiate secondary electrons and new avalanches. Since these processes are short-term and overlap in time, it is very difficult to analyze the dynamics of the initiation of subnanosecond gas breakdown. It is also worth noting that the regime of the continuous acceleration of electrons was analyzed primarily theoretically, because the corresponding experiments are complicated. The existence of fast electrons has been experimentally proved in only a few works [3‐6]. Experimental data related to the effect of continuously accelerated electrons on the E p

Travelling-wave-sustained discharges

The paper presents a review on recent development in modelling and diagnostics of diffusion-controlled gas discharges produced in the fields of travelling waves as well as on their instabilities, with a stress on the results obtained in the Plasma and Gas-discharge Physics Group at Sofia University. Directed to basic features of the discharge, the discussion is on argon discharges with unmagnetized and magnetized plasma production.

Features of the transport of sputtered atoms during Ta2O5 film deposition onto substrates of complicated configuration

The possibility of obtaining Ta2O5 films with homogeneous properties on the surface of substrates possessing complicated shapes was studied. In the deposition systems employing point molecular sources of a vapor flow, the problem is solved by using various planetar manipulators ensuring complicated rotations of the substrates in a vacuum chamber; in the case of magnetron sputtering, a more technological method can be realized based on the controlled transport of sputtered particles in the target-substrate drift space. The transport of sputtered particles is described using various models and static modeling techniques, which can be also of interest for solving numerous applied problems in the physics of gas discharge. The results were used to optimize the technology of Ta2O5 film deposition onto large-size substrates of complicated configurations.

Properties of a catalytically active pulsed microwave discharge at atmospheric pressure

A pulse-periodic pseudocorona microwave discharge at atmospheric pressure [4] is of interest from both the fundamental and applied standpoints. This phenomenon attracts attention as a complicated object for investigation in the field of gas-discharge physics. For practice, this type of discharge is important by virtue of its catalytic properties in the chemical processes of hydrocarbon conversion with participation of plasma [1–3]. The effect of discharge-plasma catalytic activity in the process of thermal decomposition of methane into hydrogen and carbon consists in a significant (by several times) increase in the degree of preheated-methane decomposition under the action of discharge plasma. In this case, the microwave energy introduced into the system in the form of plasma represents a small fraction (smaller than 20%) of the thermal energy required for heating the methane. The process occurs mainly owing to accumulated thermal energy, so that the energy cost for the additional decomposition of methane molecules under the action of plasma, as compared with the energy introduced only in the plasma form, turns out to be lower than the enthalpy inherent in the process [3].

Speeding Up Fluid Models for Gas Discharges by Implicit Treatment of the Electron Energy Source Term

Numerical fluid models are widely used in gas discharge physics. A typical discharge model comprises continuity equations and drift–diffusion equations for reactive particle species, a balance equation for the electron energy, and Poisson's equation for the electric field. When this system of equations is integrated numerically with respect to time, the explicit evaluation of coupled quantities necessitates strong time step restrictions, resulting in an enormous slowdown of the calculation. The strongest time step restriction arises from an explicit treatment of the coupling between the charged particle transport and the space charge field. In order to circumvent this constraint several implicit and semi-implicit techniques have been developed. When one uses these techniques, however, the explicit handling of the dependence of electron energy source term on the electron mean energy becomes limiting for the time step. In this work we present a technique for the implicit treatment of the electron energy source term, based on linearization with respect to the electron mean energy. This approach makes it possible to increase the time step by several orders of magnitude, thus giving a tremendous speedup of the calculation. Test results are provided for some typical cases, covering a wide range of numerical conditions.

The plasma discharge mechanism in wire chambers in the regime of large gas gain

The results of studies of wire chambers with gas gain corresponding to streamer production in the electronavalanche are reviewed. The dynamics of the development of an avalanche and its transformation into plasma production are demonstrated experimentally for the first time. Some qualitatively new features appear which allow the determination of the necessary conditions for streamer formation and growth toward the cathode. The results of these studies can be used to develop techniques for physics experiments and in gas-discharge physics.

Reply To "Comments On "The Time Evolution Of The Resistances And Inductances Of The Discharges In A Pulsed Gas Laser Through Its Current Waveforms'"

The physics of a pulsed gas discharge introduces adequate restrictions into the mathematical problem for the definition of the time evolution of the resistance and inductance. These restrictions permit the determination of the above-mentioned parameters uniquely. In a previous paper, 1 we had published a method for finding the time evolution of the resistance and inductance of a pulsed discharge. According to this method, the elaboration of the current waveforms through the integrodifferential equations of the system leads to the revelation of the time history of the resistance and inductance. However, two objections in our method have arisen in a paper by Friedman. According to the first objection, the definition of the time evolution of the resistance and inductance through the oscillograms of the current and voltage is not one-valued, but it has a set of solutions. As a verification, the author of the above Comments gave an example (an - - circuit) of various temporal dependencies of inductance and resistance corresponding to the identical current and voltage oscillograms. The set of solutions and consisted of the fundamental solutions plus oscillatory terms with frequencies multiples of the fundamental frequency of the system. Two restrictions were established by the author of the above Comments for the choice of the functions and : the physical restriction, that is, and , should be positive, and the mathematical restriction, that is, when , the inductance is

Nonequilibrium plasma produced by microwave nanosecond radiation: parameters, kinetics, and practical applications

The results of the investigation of nonequilibrium plasma produced by powerful microwave nanosecond radiation is reviewed. Nanosecond microwave discharge is a new branch of gas discharge physics. At present, this type of discharge is intensively investigated. Interesting properties and peculiarities of such a discharge and various its applications are discussed, first of all for the creation of an artificial ionized layer (AIL) in the earth's atmosphere. The laboratory experiments performed and the new effects which appear in nanosecond microwave discharge are briefly summarized. Different applications of AIL are analyzed on the basis of the experimental modeling.

Boltzmann simulations of AC-PDP gas discharges

The AC-plasma display panel (AC-PDP), capable of producing real-time, high-resolution, full-color video images is a fairly recent technology. The operation of these devices is dictated by the physics of low-temperature gas discharges. We have developed a fully self-consistent, Boltzmann-Poisson numerical simulation for the operation of an idealized AC-PDP picture element. A key component in the operation of the AC-PDP is a dielectric layer on each of the pixel electrodes. These dielectric layers provide each pixel with a memory capability. This allows a pixel, once addressed, to remain in an on-state until it is specifically re-addressed into an off-state. This ability leads to "write", "sustain", and "erase" duty cycles for each pixel. In this paper, we will present a brief introduction to AC-PDP construction and operation and present detailed simulation results for the "write" and "sustain" operations of a picture element.

Application of direct methods to solve difference problems of gas-discharge physics

Application of direct methods to solve difference problems of gas-discharge physics

Discharges in air from point electrodes in the presence of dielectric plates-experimental results

The effect of a dielectric plate on characteristics of discharges in air from a point electrode was investigated experimentally. Experiments have been carried out with either 250/2500 mu s switching impulse, or DC voltage applied to the point electrode in the presence of a Plexiglas, (PMMA) dielectric plate. The dielectric plate was charged positively, irrespective of the polarity of the applied impulse voltage. The breakdown probability was measured for different crest voltages. The spatial distribution of the accumulated charge was measured for positive and negative impulse voltages. With DC applied voltages, the charge accumulated on the dielectric plate had the same polarity as the corona ions migrating from the point electrode. The repetition rate and charge content of Trichel pulse corona was measured for points stressed by negative DC voltage. The repetition rate and charge content were measured for positive onset streamer pulses. All measurements are discussed in the light of gas-discharge physics. >

Discharge development from positive point electrodes in air as influenced by a nearby dielectric surface

The interaction between discharges taking place in the stressed air volume of a point-to-point gap and the charge accumulating on a nearby dielectric surface due to these discharges is studied. For the discharge to be confined to one point-electrode of the gap, the tip radius of that electrode is chosen to be much smaller than that of the other electrode. Experiments were carried out with 250/2500 mu s switching impulse or DC voltage applied to the point electrode in the presence of a dielectric plate from Plexiglas (PMNA). The breakdown probability was measured for different crest voltages of the applied impulse. The spatial distribution of the accumulated charge on the dielectric plate was measured. The repetition rate and charge content of onset streamer pulses were measured in the presence of the dielectric plate with the point stressed by a positive DC voltage. All the measurements are discussed in the light of gas discharge physics. >

Pressure and frequency dependence of ion bombardment energy distributions from rf discharges

Experimental measurements of the energy distribution and flux of ions bombarding an electrode of a parallel-plate rf reactor were performed in argon, neon, and a 95% helium-5% argon mixture using a hemispherical retarding grid energy analyzer. Quadrupole mass analysis was performed to identify the ions which were bombarding the electrode. Frequencies from 2.5 to 20 MHz and pressures from 0.025 to 1.6 Torr were studied. For a given amplitude of the applied rf potential, the ratio of the frequency of the applied rf potential to the reactor gas pressure was found to be the critical parameter in determining the shape of the measured ion bombardment energy distributions. The total ion flux to the electrode surface was found to be proportional to the square of the frequency and insensitive to the reactor gas pressure, for a fixed amplitude of the applied rf potential. These results are discussed with reference to the physics of rf gas discharges.

Statistics of Ignition Processes in ac Plasma Displays

AbstractThe statistics of the ignition behaviour of discharge cells in ac plasma displays and interaction processes occurring between several ignited cells are described and interpreted with a view to basic problems of gas discharge and solid state physics. For the statistical evaluation of ignition lag values recorded by means of a computer controlled equipment the Laue distribution is used.

Ignition Processes in ac Plasma Displays

AbstractThe ignition behaviour of discharge cells in ac plasma displays, their ignition statistics and interaction processes occurring between several ignited cells are described and interpreted with a view to basic problems of gas discharge and solid state physics. Ac plasma displays of three different sizes were investigated: PAF 58, 90 and PAF 128.