bluuebunny/crossref_metadata_2025_split huggingface dataset:
Numerical Simulation of a DC‐Glow‐Discharge in an Electronegative Gas
Authors: Schmitt W. , Ruder H. , Köhler W. E. 
Published: July 2007

AbstractA one‐dimensional continuum model is presented for a dc‐glow‐discharge in an electronegative gas between parallel plates. It is based on the local balance equations for particle densities and fluxes of electrons, positive and negative ions, the local electron energy balance and the Poisson equation for the self‐consistent electric field. These equations are supplemented by suitably chosen boundary conditions and are solved by the finite difference procedure HEMODES (HEnyey Method Ordinary Differential Equation Solver) which, in particular, can successfully handle the singular point occuring if the inertia term in the ion momentum balance equation is taken into account. Since not all data needed within this treatment for the simulation of realistic electronegative gases were available, a fictitious argon‐like gas has been considered which nevertheless can demonstrate the characteristic features of such a discharge. In particular, the influence of variations of the attachment and the ion‐ion recombination coefficients on the physical variables has been studied.
Laser‐Induced Fluorescence on a Metastable and a Resonant Argon Ion Level
Authors: Schubert M. , Valentini H.‐B. 
Published: July 2007

AbstractLaser‐induced fluorescence on metastable and on resonant argon ion levels and spontaneous emission have been measured in two similar dc‐low pressure discharge configurations in dependence on gas pressure. Using a simple collision‐radiative model and various approximations a few results about pump rate ratios, electron temperatures, laser‐induced transition rates and relaxation rates from the metastable or resonant level are derived.
Stark Parameters of Several B II, C II and N III Spectral Lines
Authors: Djeniže S. , Popović L. Č. , Labat J. , Srećković A. , Platiša M. 
Published: July 2007

AbstractStark shifts and widths of ionized boron, carbon and nitrogen spectral lines have been measured in a low‐pressure pulsed arc plasma and compared with calculated values based on the modified semiempirical approach.
Determination of the Electron Density in an Argon Laser Plasma by Spectroscopy of the Hydrogen Hα and Hβ Lines
Authors: de Mos B. Becker‐ , Kessler B. , Seelig W. 
Published: July 2007

AbstractFrom measurements of the Hα and Hβ spectral line profiles in a plasma, a method is developed which allows to separate the contributions of Doppler and Stark broadening. This method is superior to the deconvolution of Voigt profiles, in particular, when the lines are of low intensity. The electron density in the plasma can be calculated from the Stark broadening.An example is the low pressure (p ≈ 1 hPa) arc discharge of argon ion lasers which is characteristised by electron densities of approximately 1014 cm−3 at heavy particle temperatures of about 104 K. These plasma parameters lead to a broadening of the Balmer Hα and Hβ spectral lines of hydrogen, which has a low concentration within the discharge area. The spectral lines are broadened due to the electron density dependent Stark effect and the temperature responsive Doppler effect. The results are consistent with predictions of the argon ion laser modelling.
Cathode Spot Phenomena in Low Current Vacuum Arcs on Arc‐Cleaned Electrode Surfaces. II. Spot Dynamics
Authors: Djakov B. E. 
Published: July 2007

AbstractPart II of the paper presents results of high temporal and spatial resolution experiments with vacuum arcs on pre‐arced surfaces. Immobile spots, continuous spot motion and spot position oscillations have been observed. Tentative explanations of these phenomena are offered.
Discontinuity of Plasma Flow Parameters
Authors: Soliman H. M. , Masoud M. M. 
Published: July 2007

AbstractThis paper is concerned with the study of the dynamics of the expanded dense plasma from a coaxial electrodes discharge device. Experimental investigations were carried out with hydrogen gas at 0.8 Torr base pressure. The condenser bank voltage was 12 KV, which corresponds to a capacitor bank energy of 4.5 KJ.The experimental results show that a shock wave is generated near the muzzle, and is separated from the plasma shell. The shock front velocity (Vs) and the plasma shell velocity (V1) decay within propagation up to 14 cm according to the relations, Vs ∞ Z−1 and V1 ∞ Z−2. At Z = 14 cm a discontinuity in the velocity curves occurs, where velocities of both the shock front and the plasma shell are increased. The distribution of the self‐induced axial magnetic field along the expansion chamber axis shows that at Z = 14 cm the magnetic field lines have a solitary form. Its value is decreased before Z = 14 cm according to Bz ∞ Z−1, but after Z = 14 cm as the relation Bz ∞ Z−3. The time evaluation of soft X‐ray consists of two different spikes.
On the Causes and Effects of Contaminations during rf Diode Deposition of Cr‐Si Alloys
Authors: Sobe G. , Schreiber H. , Weise G. , Heinrich A. 
Published: July 2007

AbstractInvestigations to the causes and effects of contaminants at the rf diode deposition of CrSi films in a non‐heated high vacuum apparatus were carried out comparing an oxygen‐free fusion target with an oxygen‐containing cermet target. The films of the fusion target contained considerable amounts of oxygen; analogously the oxygen concentration in the films was increased in the case of the cermet target. Moreover, hydrogen was found. The concentration of the contaminants decreased with the sputtering power, however the rate of incorporation increased. For high sputtering rates the contamination process was reproducible and independent of the plant conditioning; the deposited films were depth‐homogeneous. The reasons for this behaviour lie in water sources which are activated first of all by the discharge itself. The electrical properties found are explained by the contaminants and the deposition conditions.
Correlation Functions AND Thermodynamic Potentials FOR Nonideal Plasmas
Authors: Ebeling W. 
Published: July 2007

AbstractThe analytical structure of the binary correlation functions and the free energy of quantum plasmas is studied at low and moderate densities. By using the approach of Slater sums and effective potentials a systematic search of power law contributions to the binary correlations is given. The corresponding contributions to the free energy density up to the order O(n5/2) are calculated. The available analytical results from different theories developed with the Montroll‐Ward technique, the Greens function technique and the Feynman‐Kac technique are compared.
Kinetics of Plasma Flow in Recycling Region
Authors: Krasheninnikov S. I. , Chodura R. 
Published: July 2007

AbstractKinetics of plasma flow in tokamak SOL plasma recycling region for large ratio of Coulomb mean free path, λT, to neutral recycling length, LN, is considered. Such regimes are quite typical for both current tokamaks and ITER‐like reactor conditions and can not be treated by fluid approximation.
Effects of Rotation on Ideal Ballooning Modes
Authors: Sen S. 
Published: July 2007

AbstractThe stability of ideal ballooning modes in presence of a rigid toroidal rotation is revisited. Centrifugal forces induce poloidal asymmetry in the equilibrium pressure and affect the shape of the flux surfaces. Taking this two effects into account shows that the rigid rotation has a stabilising role on the the inner flux surfaces (for which r < Lp, where Lp is the pressure scale length). On the other hand, rotation is shown to have a destabilising role on the outer flux surfaces (for which r > Lp). However, the instability at the outer plasma is found to be terminated by a new stable zone which may be conjectured to be a “third” region of stability.
The Effect of the Anomalous Inertia, Viscosity and the Electric Field on the Transport Within the Sol in a Tokamak
Authors: Rozhansky V. , Tendler M. 
Published: July 2007

AbstractThe issue of transport on open field lines is addressed along the lines of the extended neoclassical theory invoking anomalous inertia and viscosity. Our studies suggest that tokamaks with divertors may benefit from a significant amplification of the radial electric field. It is shown that biasing of the scrape ‐ off layer (SOL) with respect to the grounded first wall results in fundamental phenomena affecting the performance of a divertor. Theoretical model appears to be consistent with experimental results obtained on TdeV.
A Simple Model for Impurity Production in Tokamaks
Authors: Zagorski R. , Romanelli F. 
Published: July 2007

AbstractA simple analytical model is presented for the plasma in the region outside the limiter which describes the impurity ions transport and production in the tokamak scrape‐off layer. The equations of the model are solved analytically in the test particle approximation for the simple SOL configurations. A discussion of the solutions for different plasma parameters and target materials is presented.
Benchmarking UEDGE with DIII‐D Data
Authors: Porter G. D. , Fenstermacher M. , Groebner R. , Leonard A. , Nguyen Q. , Rensink M. E. , Rognlien T. D. 
Published: July 2007

AbstractComparisons between a 2‐D fluid simulation of the SOL plasma of a diverted tokamak and experimental data from the DIII‐D are shown. It is concluded that a simple diffusive model for perpendicular transport is consistent with the data. Discrepancies in the simulation suggest that impurity radiation may be playing a significant role in the experiment, and that further work is required to understand hydrogen recycling at the divertor.
Nonlinear interactions of azimuthal surface waves in a magnetoactive plasma waveguide
Authors: Ostrikov K. N. , Osmayev O. A. 
Published: July 2007

AbstractSeveral possible three‐wave and four‐wave interactions, namely decay and modulational instabilities of a specific type of surface waves‐azimuthal sufaces waves (ASW)‐in a magnetoactive plasma waveguide are considered. The studied ASW propagate in the azimuthal direction at the cylindrical waveguide wall‐plasma interface.
On Modulational Instability of Turbulent Spectra
Authors: Popel S. I. , Tsytovich V. N. 
Published: July 2007

AbstractThe character of the modulational instability of a Langmuir wave packet is usually assumed to be similar to that of the instability of a monochromatic pump Langmuir wave if the width of the packet is small when compared to the rate of the instability. This assumption has been confirmed only for the case corresponding to the “hydrodynamical” development of the modulational instability, i.e., for the case when the phase velocity of the modulational perturbations exceeds the ion thermal velocity. Here we consider the opposite case (when the phase velocity of the modulational perturbations is less than the ion thermal velocity) which corresponds to the “static” development of the instability. We demonstrate that the above assumption is valid for the situation considered.
Expansion Model of the Neutral Component in Vacuum Arc Spot Plasmas
Authors: Hantzsche E. 
Published: July 2007

AbstractPlasma generated by cathode spots in vacuum arcs expands towards the anode and the walls. In spite of a high degree of ionization (mostly), this plasma contains also a small but noticeable constituent of neutral atoms. Starting from the known analytical solution of a hydrodynamic model describing the plasma ions and electrons, the corresponding motion of neutrals is treated in a similar way. The results show: 1) The neutrals take part in the general plasma expansion; however, their final kinetic energy is lower (by about 50%) than the final energy of the ions. 2) The temperature of the neutrals also is lower than the ion temperature and decreases during expansion. 3) The acceleration of neutrals is caused partly by the pressure gradient, partly by interaction with the ions (friction); the forces diminish rapidly with increasing distance. Finally, the limitations of this approximate solution are discussed.
Optical Emission Diagnostics of an U‐Shaped Argon Stabilized d.c. Arc
Authors: Malović G. , Tripković M. , Holclajtner‐Antunović I. 
Published: July 2007

AbstractThe radial distribution of parameters has been measured by using the optical emission spectroscopy of an U‐shaped argon stabilized low current arc at atmospheric pressure. All the measurements reported here were performed from a side‐on observation direction by applying the Abel inversion routine. Radial distributions of apparent temperatures (Texc., Te, Ti, Tg) and of electron number density (ne) for the plasma were measured, with and without presence of KCl (spectrochemical buffer). The measured data of ne are compared to the theoretically calculated values of the equilibrium plasma composition. On the basis of the measured data, the validity of LTE concept is considered. It was found that deviation from LTE increases to the plasma periphery.
Temperature Dependence of the Rate of the Reaction N + H + Ar → NH + Ar
Authors: Deschamps J. , Godart J. L. 
Published: July 2007

AbstractThe rate constant for the 3 body atom recombination N + H + M with M = Ar has been measured over the temperature range 550 to 750 K in an Ar − N2 − H2 microwave flowing discharge. A temperature dependence for the rate constant is reported.
Ion Beam Driven Ion Cyclotron Double Layers
Authors: Sah O. P. , Goswami K. S. 
Published: July 2007

AbstractWe present here a self consistent theory of small amplitude double layers associated with electrostatic ion cyclotron waves in a plasma containing hot electrons, cold ions and traversed by an ion beam. It has been shown that compressive type of double layers solution exists when θb (beam temperature) < αb (beam concentration) < 1.
The Influence of Ion – Neutral Collisions in the Plasma Sheath on the Ion Current to an Electrostatic Probe: Monte Carlo Simulation
Authors: Trunec D. , Španěl P. , Smith D. 
Published: July 2007

AbstractWe have carried out Monte Carlo simulation of the motion of Ar+ ions in the space charge sheath surrounding a cylindrical Langmuir probe. From these simulations the percentage of ions crossing the sheath boundary that are collected by the probe have been determined and thus the ion currents to the probe have been calculated. It is shown that the collisions of ions with neutral helium gas atoms in the sheath increase the percentage of ions collected by the probe above that predicted by collisionless orbital motion limited current (OMLC) theory and that the exponent, χ, of the power law dependence, i+∼U, of the ion current, i+, on the probe voltage, Up, increases above the value 0.5 predicted by OMLC theory. The results of the simulations are compared with recent Langmuir probe measurements made in flowing afterglow plasmas.
UV Radiation of Low Pressure XeCl* and KrCl* Glow Discharges
Authors: Schwabedissen A. , Bötticher W. 
Published: July 2007

AbstractThe positive column of low pressure DC glow discharges in Xe/Cl2 and Kr/Cl2 gas mixtures has been investigated with respect to its UV radiation power and radiative efficiency for a wide range of parameters (total gas pressure: 1–30 mbar, current 10–30 mA, partial pressure of Cl2: 1–33%). Also the radial distribution of the particle number densities of XeCl* (B) and KrCl* (B) has been determined by absolutely calibrated emission spectroscopy. Optimum UV (190–350 nm) output and efficiency has been found in gas mixtures with a relative Cl2 partial pressure of 2–3% and total gas pressure of 12–18 mbar. At these parameters, the UV radiation power per column length is greater than 40 Watt/m with a radiative efficiency of 15–18%. These discharges could be used for UV induced photochemical processes.
Cross‐Sections, Rate Constants and Transport Coefficients in Silane Plasma Chemistry
Authors: Perrin J. , Leroy O. , Bordage M. C. 
Published: July 2007

AbstractThis paper presents a critical review of the basic data concerning the physics and chemistry of low pressure SiH4 glow discharges used to deposit hydrogenated amorphous silicon films (a‐Si:H). Starting with an updated table of thermochemical data, we analyze the gas‐phase elementary processes consisting of i) electron‐molecule collisions, ii) ion‐molecule collisions, iii) neutral‐neutral collisions, iv) other electron and ion collisions involving electron‐ion and ion‐ion recombination, electron attachment on radicals and detachment of anions, and v) cluster growth kinetics in dusty plasmas. Experimental data or theoretical estimates are given and discussed in terms of cross‐sections, collision and reaction rate constants, and transport coefficients. We also analyze the surface processes and reaction probabilities of ions, radicals and molecules.
Particle simulation of the plasma‐wall transition in presence of drifts perpendicular to the wall
Authors: Bergmann A. , Chodura R. 
Published: July 2007

AbstractThe flow of a non‐uniform collisionless plasma towards an absorbing wall is modelled with one‐ and two‐dimensional particle simulations. The influence on the plasma flow of the E × B and diamagnetic drift motion perpendicular to the wall is studied.
Power Balance in the ITER Plasma and Divertor
Authors: Post D. E. , Braams B. , Mandrekas J. , Stacey W. , Putvinskaya N. 
Published: July 2007

AbstractIt is planned to use atomic processes to spread out most of the heating power over the first wall and side walls to reduce the heat loads on the plasma facing components in ITER to ∼ 50 MW. Calculations indicate that there will be 100 MW in bremstrahlung radiation from the plasma center, 50 MW of radiation from the plasma edge inside the separatrix and 100 MW of radiation from the scrape‐off layer and divertor plasma, leaving 50 MW of power to be deposited on the divertor plates. The radiation losses are enhanced by the injection of impurities such as Neon or Argon at acceptably low levels (∼0.1 % Argon, etc.)
Particle in Cell Simulation on Thermoelectron Emission from Hot Target Plate
Authors: Ohno Noriyasu , Shimizu Eri , Takamura Shuichi 
Published: July 2007

AbstractA space charge effect on thermoelectron emission current from an electron‐emissive target plate in plasmas has been investigated by using a self‐consistent particle in cell simulation code. Comparison between the conventional Child‐Langmuir's formula for the space charge limited current and the simulation results shows that we should employ αλD (λD : Debye length; α ∼ 2.6 in helium plasma, α ∼ 2.0 in hydrogen plasma) as the effective sheath thickness in the Child‐Langmuir's formula. The sheath voltage is found to be constant, independent of plasma density in the space charge limited condition. This can be clearly explained by the Stangeby's formula for a sheath voltage including the thermoelectron emission current determined by the above‐mentioned modified Child‐Langmuir's formula.
Bifurcation and Relaxation Oscillations in Divertor Plasmas
Authors: Bachmann P. , Sünder D. , Wenzel U. 
Published: July 2007

AbstractThis paper presents a contribution to bifurcation phenomena in scrape‐off layer modelling. The bifurcations are caused by the non‐monotonic temperature behaviour of the radiation characteristics of plasma impurities. Low‐frequency relaxation oscillations observed in divertor plasmas of the ASDEX Upgrade tokamak are analyzed and computed using a simple model for the dynamics of the impurity density and the electron temperature. The corresponding model equations are a special case of a general system of transport equations whose stability is analyzed. Bifurcations are calculated by solving autonomous and parametrically driven model equations.
Alfvén Waves in Non‐Stationary and Non‐Uniform Media: An Exactly Solvable Model
Authors: Stenflo L. , Shvartsburg A. B. , Weiland J. 
Published: July 2007

AbstractThe modulation of Alfvén waves interacting with a non‐uniform and non‐stationary plasma is considered. The waveforms are allowed to change rapidly. We examine our phenomena by means of exact analytical solutions of the MHD equations in the presence of large amplitude disturbances of the magnetic field and plasma density. In contrast to the WKB approach, we do not have to use limiting assumptions regarding the variations of the background medium. We show that the large amplitude time and space disturbances lead to a new cut‐off frequency for Alfvén wave propagation. A rapid reshaping of the Alfvén waveform can also obstruct the resonant interactions between the waves and the plasma particles.
A Linear Model for the Interpretation of Optical Emission Spectroscopy Measurements in Low Pressure DC Magnetron Sputtering
Authors: Schulte J. , Sobe G. , Reiss G. 
Published: July 2007

AbstractFor a balanced dc magnetron discharge a linear model for the formation of excited and ionized species is presented. The consideration is based on collisional kinetic theory and a correlation of discharge current with ionization rates, and leads to normalized rate coefficients. The electron energy distribution changes according to the determining external parameters, but needs neither to be known in detail nor to be of Maxwellian type. The model calculations are consistent with measurements done by optical emission spectroscopy (OES) on the magnetron sputtering of aluminium in argon discharges. The dependences of optical emission intensities on discharge current and on argon pressure show that both, excited argon atoms as well as excited argon ions, are generated from neutral argon by direct, fast electron impact. It is additionally shown that at least for low argon pressure the excitation of aluminium atoms is also caused by direct electron impact.
Stochastic Magnetic Field Structure in the Edge Region of W7‐X
Authors: Strumberger E. 
Published: July 2007

AbstractThe topology of stochastic magnetic fields in the edge region of Wendelstein 7‐X (W7‐X) is investigated for fields with volume‐averaged β‐values of 〈β〉 = 0. 2 and 4% inside the last closed magnetic surface (LCMS) and rotational transform values of i > 1 in the edge region. The Kolmogorov lengths of flux tubes are determined and compared with the corresponding connection lengths to an outer limiting surface.
Finite Beta Electro‐Magnetic Effects at the Edge and the Role of the Scrape‐off Layer in the L‐H Transition
Authors: Chankin A. V. , Matthews G. F. 
Published: July 2007

AbstractMagnetic induction becomes important when the skin‐depth equals the wavelength of the electrostatic drift turbulence: \documentclass{article}\pagestyle{empty}\begin{document}$ C/\sqrt 4 \pi \sigma \omega = K_ \bot ^{ - 1} $ \end{document}. It is predicted that this suppresses the longwave perturbations responsible for the bulk of the turbulent transport, providing an explanation for the L‐H transition. Since k⟂ρs ≪ 1 at the edge (ρs ‐ ion Larmor radius), this may occur at rather low β, typical of the separatrix parameters. The above equality is used to derive thresholds for the L‐H transition: β ≈ (k⟂ρs)2(me/mi)in the collisionless skin‐depth limit of very low density plasmas and \documentclass{article}\pagestyle{empty}\begin{document}$ T^3 _e \sim B^2 L_ \bot Z_{eff} /\sqrt m $\end{document} (L⟂‐perpendicular decay length) in the collisional skin‐depth limit of medium to high density plasmas. The latter is in a broad agreement with experiment, pointing to a possible role of low temperature collisional plasma (which is in the SOL) in the physics of the L‐H transition.
Long Mean Free Path Modifications of Electron Heat Conduction
Authors: Catto Peter J. , Yeoh Kim‐Ee 
Published: July 2007

AbstractThe Spitzer‐Härm parallel electron heat conductivity begins to fail even at surprisingly large values of collisionality because the energy squared dependence of the mean free path results in contributions from electrons not satisfying the short mean free path expansion. Self‐similar solutions of model problems are employed to demonstrate that exponentially small, non‐expandable modifications that cannot be retained in conventional treatments are the cause of the departure of heat transport from its Spitzer‐Härm value.