bluuebunny/crossref_metadata_2025_split huggingface dataset:
Electromagnetic Waves in Waveguide Partially Filled with Semiconductor Plasma
Authors: Ivanov S. T. , Alexov E. G. 
Published: July 2007

AbstractThe dispersion of electromagnetic waves in waveguides partially filled with semiconductor plasma is investigated for unmagnetized and for strongly magnetized plasma.The effects which may be useful for the plasma electronics are found: In such waveguides there exist a large number of slow waves with typical frequencies ω ≈ ωP/√ϵL. The filling at which the different modes at fixed phase velocity are maximum separated in wavelength is found. The thickness of the semiconductor layer at which this effect arises is about hundred micrometers and depends on the crystals' type. In addition to this, in strongly magnetized semiconductor plasma the maximum frequency separation of the typical plasma waves is found at fixed filling.Is it shown that in such systems there exist many surface waves which are of the slow wave type.In the case of strongly magnetized plasma coupling between nonsymmetrical EH‐ and HE‐ modes is shown to exist.
Negative Ions, Ozone, and Metastable Components in dc Oxygen Glow Discharge
Authors: Khvorostovskaya L. E. , Yankovsky V. A. 
Published: July 2007

AbstractIn a dc glow discharge in oxygen, the concentrations of minor components of O2(a1Δg), O2(b1 Σg), O3, O(1D), as well as nagative ions and electrons have been measured. Balance equations have been derived which describe satisfactorily the stationary concentrations of these components as functions of gas pressure and discharge current. For the first time, the rate constants of important aeronomical reactions (a) O− + O2(a1Δg) → O3 + e, (b) O2− + O2(a1Δg) → 2O2 + e and (c) e + O3 → O2− +O have been measured as functions of gas temperature T and mean energies of ions Ei and electron E6: Ka = (2.5 ± 0.5) · 10−9 · (T/300)4 ± 0.4· (Ei/0.04)−2.6 ± 0.4 cm3/s for T = 385−605 K and Ei = 0.10 − 0.66 eV; Kb = (1.0 ± 0.3) · 10−10 · (T/300)−2 ± 0.5 · (Ei/0.04)0.23 ± 0.05 cm3/s for T = 330−605 K and Ei = 0.09 + 1.5 eV; Kc for Ee = 0.8÷5 eV.
Barrier Discharge The Transferred Charge and Ozone Synthesis
Authors: Gibalov V. I. , Dřímal J. , Wronski M. , Samoilovich V. G. 
Published: July 2007

AbstractWe have undertaken an experimental investigation of the influence of the conditions of barrier discharge implementation such as: the discharge gap value, the type of gas, and the polarity and dielectric permittivity of the dielectric electrode on the value of charge transferred in a micro‐discharge. It is shown that the increase in the specific capacitance of the electrodes leads to proportional increase in the transferred charge value, reaching 100–200 nC in a discharge gap 1 mm, in air. In this case the amplitude and duration of a current pulse in the microdischarge reach, respectively, 10 to 15 A and 40 ns. It is also demonstrated that in air with increase in the discharge gap value one can observe a decrease in the efficiency of the ozone synthesis whereas in oxygen there exists a more complicated dependence: the maximum of efficiency is observed at a discharge gap value of 0.7 to 1.0 mm.
A Simple Theoretical Analysis of a Discharge Pumped XeCl‐Laser
Authors: Krause U. , Kleinschmidt J. 
Published: July 2007

AbstractA simple theoretical analysis of the discharge characteristics and the laser output performance of a discharge ‐ pumped XeCl‐laser is described. Validity of the model is confirmed by comparing the results with the measured time histories of the discharge voltage and current as well as with measured laser‐output‐energies. The model allows qualitative explanations with respect to the laser output energy in dependence on the total gas pressure, the concentrations of Xe and He as well as the load voltage of the power supply and the primary stored energy.
Two‐Fluid Theory of Presheath and Space Charge Sheath in Low Pressure Plasmas
Authors: Valentini H. ‐B. 
Published: July 2007

AbstractIn low pressure plasmas the transition between the presheath and the sheath is investigated taking into account solutions of a two‐fluid model in the whole plasma. The kinetic theory is reviewed only shortly. The hydrodynamic theory is described in detail. In addition, new results are given. Boundary conditions necessary for the hydrodynamic description are derived from the electron kinetics.The two‐fluid equations supplemented by the Poisson equation constitute a set of nonlinear differential equations with isolated singular points. In addition, this is a singularly perturbated problem if the space charge sheath is thin. Singular points occur if the ions or the electrons attain the corresponding sound speed. The mathematical problem can be split into a boundary value problem for subsonic ion velocities and in an initial value problem for the hypersonic range.Solutions are obtained by combination of analytical and numerical methods. The numerical integration involvesinstabilities in the subsonic range if simultaneously the plasma is collision dominated and the space charge density is very small in the interior. Several methods are given to reduce or to avoid these difficulties. It is shown that a magnetic field, directed parallel to the tube wall, can reduce the voltage drop across the sheath substantially. In a positive column the radial variation of the electron temperature is calculated by means of the two‐fluid model. Sheath criteria are discussed.
Trends in the Plasma Activated Deposition of Hard Coatings
Authors: Lunk A. 
Published: July 2007

AbstractPlasma assisted deposition of hard coatings is a well‐known technique to improve the properties of bulk materials. From a detailed knowledge of the wear mechanisms and the characteristic properties of the coated materials there can be deduced the requirements to the deposition technique. These requirements are discussed in relation to the plasma parameters and the plasma ‐ surface interaction for the plasma assisted physical vapour deposition and the plasma assisted chemical vapour deposition.
The Temperature Dependence of the Etch Rate of Si Measured by Ellipsometry
Authors: Haverlag M. , Kersten H. , Kroesen G. M. W. , de Hoog F. J. , Rutscher A. 
Published: July 2007

AbstractThe etching of Si wafers in an RF discharge in CF4 has been studied using single‐wavelength ellipsometry. The etch rate was measured as a function of surface temperature at two pressures. Only at high pressure (0,36 Torr) a small temperature effect was found. Furthermore, the existence of a modified top layer is suggested by the results of the measurements.
Harmonics Analysis of the Electron Component of rf Bulk Plasmas II. Electron Distribution Function and Relevant Macroscopic Quantities in H2
Authors: Voigt H.‐D. , Wilhelm J. , Winkler R. 
Published: July 2007

AbstractIn a preceding part of the paper, based on the Fourier expansion technique, a new method was developed to study the electron kinetics in weakly ionized, spatially uniform bulk plasmas of rf discharges in the established periodic state. Starting from the electron Boltzmann equation the Fourier expansion technique has been applied to the partial differential equation system for f and fA, the isotropic part and the first contribution to the anisotropy of the electron velocity distribution function, where both the distribution parts are the first two coefficients of the Legendre Polynomial expansion of the distribution function. In this part of the paper the new method will be applied to investigate the behaviour of the electron velocity distribution of the rf bulk plasma in molecular hydrogen and, in addition, of main macroscopic quantities.The study of the latter quantities will be possible since these are determined by appropriate energy space averaging over f and ft, respectively. Thus, a comprehensive harmonics analysis of the electron component of the rf H2 bulk plasma could be made in a wide rf field frequency range. This includes the determination of the harmonics contributions to the isotropic and anisotropic distribution and to relevant macroscopic quantities as dependent on the field frequency for the mentioned wide rf field frequency range as well as of the phase angles between the different harmonics. It could be proved that the so‐called 10‐term approximation is sufficient for the description. Further on the periodic alteration of important macroscopic quantities, as mean electron energy, power input from the rf field and power loss in collision processes etc., and their period averages will be investigated in this truncation order. The results obtained are discussed and could be especially interpreted within a physical concept based on a comparison of the rf field frequency with the lumped collision frequency for energy dissipation and that for impulse dissipation.
Theoretical Study of Two Dimensional Evolution of a Weak Gaussian Wave in a F Region Ionosphere Modified by a Strong Gaussian Wave
Authors: Laxmi V. N. , Srivastava M. P. 
Published: July 2007

AbstractA high power electromagnetic Gaussian beam is assumed to be incident on the F region ionosphere, which causes modification in the plasma temperature and density. Subsequently the evolution of a second Gaussian em beam in such modified F region inosphere has been studied numerically. The numerical calculations are carried out in a two dimensional grid space which covers a region of 80 km horizontally and 100 km vertically. It is seen that the second wave propagating through the modified plasma gets focused in the axial regions and gets filamented near its peak intensity point. Consequently the plasma gets irregularly structured and the resulting fluctuations in plasma temperature and density give rise to a pressure gradient force. This force inturn causes the formation of more number of filamentary structures about the axis in wave intensity and also amplifies the initially formed ones.
Space Charge Sheath Theory Including Dissociative Recombination
Authors: Teplanová K. 
Published: July 2007

AbstractThe interpretation of the author's previously given results regarding the space charge sheath model between an infinite low temperature plasma composed of electrons, single charged ions and their parent gas and the planar floating wall is extended supposing dissociative recombination instead of the less probable radiative one while the normalized numerical results remain the same.
Atomabsorption von Barium in Leuchtstofflampen
Authors: Drawert S. , Riemann M. , Jordanov W. 
Published: July 2007

AbstractEvaporation of emitter material from electrodes of fluorescent lamps has been measured by means of atomic absorption of Ba. A hollow‐cathode discharge lamp served as background radiator. The arrangement is briefly described. Spot resolved measurements has been done in preheating and in discharge regimes. Essential results are dependence on evaporation rate and filament structure, evaporation and arising of cathode spot in discharge, and diminished evaporation regarding preheating.
Growth of a Gaussian Laser Ripple on a Gaussian Beam in a Collisionless Magnetoplasma and its Effect on the Excitation of Ion‐Acoustic Wave
Authors: Singh A. , Singh T. 
Published: July 2007

AbstractThis paper presents an investigation of the growth of a radially symmetrical ripple, superimposed on a Gaussian laser beam in a collisionless magnetoplasma. Here we have presented the effect of magnetic field and the intensity of the laser beam on the growth of ripple in some detail. The effect of presence of ripple on the excitation of an ion‐acoustic wave is also investigated. Coupling of a weak ion‐acoustic wave with main laser beam is through modified background density. Interesting feature of the analysis is that the combined effect of increased intensity of the laser beam and magnetic field is observed to suppress the growth of the ripple as well as the excitation of the ion‐acoustic wave.
Electron Energy Distribution and Optical Characteristics of a Hollow Cathode Discharge
Authors: Khvorostovskaya L. E. , Yu. Potekhin I. , Khvorostovsky S. N. 
Published: July 2007

AbstractA model is proposed for the formation of the electron energy distribution in a hollow cathode discharge. On the basis of this model, an integral equation has been derived to calculate the electron distribution function over the entire cathode cavity volume. The equation holds true for both the isotropic distribution, and the case when the local distribution function is anisotropic. Solutions of the kinetic equation obtained are presented, for electron energies over 2–3 eV and up to the cathode fall potential. It is shown that the electron energy distribution function in this interval determines the optical characteristics of the hollow cathode discharge. A comparison is given of the calculated and measured radiation powers for the cases of the hollow cathode discharge in xenon and carbon dioxide. The discrepancy between the theoretical and experimental data does not exceed 20%.
Electron Energy Distribution Functions in CO2 Laser Mixture: The Effects of Second Kind Collisions from Metastable Electronic States
Authors: Colonna G. , Capitelli M. , Debenedictis S. , Gorse C. , Paniccia F. 
Published: July 2007

AbstractElectron energy distribution functions (eedf) in CO2 laser discharge (He—CO2—N2—CO mixture) have been calculated by solving the Boltzmann equation in the presence of given concentrations of excited (vibrational and electronic) states. The results show a well structured eedf as a result of second kind collisions coming from metastable electronic states of N2 and He as well as a strong dependence of rate coefficients for CO2 dissociation and for the ionization of the different species.
Generation and Radiation of Waves at Combined Frequencies in a Warm Inhomogeneous Plasma Layer
Authors: Khalil S. H. M. , Mohamed B. F. 
Published: July 2007

AbstractWe investigate generation and radiation of waves at combined frequencies from an arbitrary inhomogeneous, isotropic plasma layer, when electromagnetic waves are obliquely incident on it to interact with a surface wave at the plasma boundary. This interaction has been described for both S‐ and P‐polarized waves. We consider a warm plasma layer with thickness very small as compared to the wavelengths of oscillations. It is shown that generated waves are strongly amplified, compared to cold plasma, when phase velocities of generated waves approaches the electron thermal velocity. Waves are not emitted when P‐polarized waves are incident perpendicular onto the plasma layer.
Nonlinear Evolution of a Gaussian Wave Perturbation in the Presence of a High Power Electromagnetic Plane Wave in the F Region Ionosphere
Authors: Laxmi V. N. , Srivastava M. P. 
Published: July 2007

AbstractThe interaction of a high power electromagnetic plane wave of uniform intensity with a weak electromagnetic Gaussian wave has been studies analytically. The two waves propagate vertically with almost the same frequency in the F region ionosphre. It is seen that the Gaussian wave acquires an oscillatory structure due to the nonlinear coupling of the strong plane wave and the weak Gaussian wave and the amplitude of these fluctuations grows with height. The growth, however, occurs only above a certain altitude z0, which is determined by the plasma and wave parameters.
On the Nonlinear Processes During Generation of Current Drive
Authors: Popel S. I. , Tsytovich V. N. 
Published: July 2007

AbstractThe manifestations of the induced scattering effects in the generation process of current driven by lower‐hybrid (LH) waves are studied taking into account the radiative‐resonant interactions. The influence extent of the LH wave modulational instability on current drive is estimated. It is shown that the induced scattering of LH waves on plasma particles leads to a change of the LH waves spectrum and through this leads to an essential influence on fast electrons generation rate and the steady‐state current drive. The modulational instability of LH waves can provide a “spectral gap” filling in the case of sufficiently strong LH wave pumping.
Theoretische Modelle des katodischen Brennflecks von Bogenentladungen. Teil I: Grundlagen
Authors: Hantzsche E. 
Published: July 2007

AbstractVoraussetzungen, theoretische Grundlagen, Ergebnisse und allgemeine Erfahrungen bei numerischen Modellrechnungen für quasi‐stationäre katodische Brennflecken von (Vakuum‐)Bögen werden zusammenfassend dargestellt. Die Ergebnisse beziehen sich hauptsächlich auf Kupfer als Katodenmaterial und umfassen alle wesentlichen physikalischen Größen des Katodenflecks (der Katoden‐Oberfläche und teilweise des katodennahen Plasmas), sie beschreiben mögliche Existenz‐Zustände im Parameterraum. Insbesondere wird auch die Abhängigkeit dieser Ergebnisse von verschiedenen Änderungen der Parameter und Gleichungen untersucht. Mehrere Beispiele werden dargestellt und interpretiert. Der Einfluß der Rauhigkeit der Katodenoberfläche ist in jedem Fall beriicksichtigt worden. Schließlich werden die Gül‐tigkeits‐Beschränkungen des Modells diskutiert, und vor allem wird die große Bedeutung nichtstatio‐niirer (z B. explosiver) Prozesse im Brennfleck betont, obgleich solche Prozesse aukrhalb des Rahmens dieses Modells liegen.Die Arbeit wird in zwei Teilen veröffentlicht. Dieser erste Teil umfaßt eine Einführung in verschiedene Gesichtspunkte der Brennfleck‐Modellierung, die Diskussion physikalischer Prozesse in den Katoden‐Brennflecken und die Entwicklung entsprechender Gleichungen, die für das Modell benötigt werden.
Topology of Divertor Field Line Mapping in Helias Configurations
Authors: Strumberger E. 
Published: July 2007

AbstractInvestigations of various vacuum magnetic fields of Helias configurations allowed a divertor concept to be developed. Here, the structure of the magnetic field lines between the plasma surface, i.e. the last closed magnetic surface, and the plasma facing surfaces of the helical troughs is investigated. Magnetic field lines, starting at the helical troughs, are traced until they end at the troughs. The resulting mapping is studied in detail.
On Electrostatic Coupling in ICRH at the Plasma Edge
Authors: Alava M. J. , Heikkinen J. A. 
Published: July 2007

AbstractThe mechanisms leading to a concomitant coupling of electrostatic (ES) waves in ion cyclotron range fast wave heating experiments are studied. Mode conversion at the lower hybrid resonance and direct coupling to ES waves due to the misalignment of the antenna Faraday shields are considered as sources of intense ES waves in the edge plasma. Ion acceleration by wave trapping is suggested as a mechanism that restricts the amplitude of the parasitic modes and creates energetic ions.
Towards Finite Element Modeling of the Tokamak Scrape‐Off Layer
Authors: Zanino R. , Paolini M. , Russo A. 
Published: July 2007

AbstractFinite elements provide a natural and flexible method for two‐dimensional fluid modeling of the tokamak scrape‐off layer. Here we present the first results obtained with the FELS code [1] on an unstructured grid, for the case of a toroidal limiter.
Radial density profiles in a poloidal divertor modelled by diffusion across a region with variable connection length
Authors: Loarte A. 
Published: July 2007

AbstractA simple model to describe the diffusion of particles in the scrape‐off layer of a poloidal divertor tokamak is presented. This model takes into account the basic magnetic characteristics of an open poloidal divertor and provides analytical expressions for the plasma density profiles at the divertor target, that are used to fit the experimental measurements in JET.
Monte‐Carlo Calculations of Electron Transport Coefficients in H2. First Simulations of the Townsend‐Huxley Experiment
Authors: Braglia M. 
Published: July 2007

AbstractThe aim is to get additional evidence to assist in resolving the discrepancy between swarm‐derived, theoretical and beam‐measured vibrational cross sections for the case v = 0→1. Good agreement between Monte‐Carlo and experimental transport data is obtained with the swarm‐derived cross sections. However, some simulations relevant to the Townsend‐Huxley experiment call into question the accuracy of the characteristic energies used in swarm analyses. Possible reasons of the observed discrepancies between Monte‐Carlo and experimental data and expected implications even on the accuracy of the cross sections in H2 are discussed.
Strong Turbulence of Drift‐Waves in Hamiltonian Canonical Description
Authors: Zhang W. , Spatschek K. H. 
Published: July 2007

AbstractStarting with a Hamiltonian formulation of the Hasegawa‐Mima equation, the statistical theory of strong turbulence of nonlinear drift‐waves in plasmas is developed. The procedure is based on the direct‐interaction‐approximation (DIA).
Hysteresis and Transition to Chaos in a Thermionic Plasma Discharge
Authors: Timm R. , Piel A. 
Published: July 2007

AbstractWe report a period‐doubling route to chaos in a modulated unmagnetized low pressure thermionic argon discharge. The bifurcation cascade has many similarities to a noisy logistic map. The non‐modulated discharge shows strong hysteresis in the current voltage characteristic. Two distinct discharge states are identified by spatial plasma potential measurements and compared with the classification for higher pressures.
Pressure Dependence of the Mean Electron Energy in the Bulk Plasma of an RF Discharge in Argon
Authors: Seeböck R. J. , Köhler W. E. , Römheld M. 
Published: July 2007

AbstractThe pressure dependence of the mean electron energy 〈ϵ〉 was investigated in discharges in Ar experimentally by sampling the plasma potential with an ion mass spectrometer, and theoretically by solving the electron Boltzmann equation for the bulk plasma. Both results show a decrease in 〈ϵ〉 with increasing pressure in the regime between 0.2 and 40 Pa although this behaviour is much more pronounced in the experimental results. The results are compared to those of single‐probe measurements of other authors. In one case they are in good agreement [10], while there is a discrepancy in another case [11]. Possible reasons for this behaviour are discussed. The advantage of the mass spectrometric sampling method is, that it is absolutely non‐invasive, so that also in sensitive processes no contamination will occur.
Aspect of K‐dV Solitons Studied with Different Stretching Co‐ordinates
Authors: Das G. C. , Singh Kh. Ibohanbi , Singh S. Surachandra 
Published: July 2007

AbstractThe present study focusses on the conspicuous properties of the temporal and spatial K‐dV solitary waves obtainable by the use of different stretching co‐ordinates. Singularities are observed in solitary waves which are due to the presence of negative ions and multiple electron‐temperatures in the plasmas. It is discussed how those situations are tackled by the derivation of modified K‐dV equations to describe the evolution of propagating solitons. Moreover, the soliton profiles admit the interactions of negative ions and multiple electron‐temperatures, which are playing the role of creating the steepness in soliton profiles. Simultaneously more solitary waves follow therein resembling the evolution of experimentally observed soliton characteristics and finally indicating the possible interest to put forth for experimental plasma investigations.
On the Evolution of Resonant Waves in Closed Plasma Systems
Authors: Vladimiroy S. V. , Yu M. Y. , Popel S. I. 
Published: July 2007

AbstractThe evolution of resonant waves in closed turbulent plasma systems is considered. It is shown that the effect of the system's nonstationarity on the evolution of the resonant waves should be considered together with the nonlinear interactions of the same order. The case for which the plasma‐maser effect is significant in the presence of the nonstationarity is investigated.