bluuebunny/crossref_metadata_2025 huggingface dataset:
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

The 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

In 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

A 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

The 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

Evaporation 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.
Parametric Excitation of Electromagnetic Fields by two Pump Waves
Authors: Brodin G. , Lundberg J. , Stenflo L.
Published: July 2007

A collisionless plasma in the presence of two monochromatic electric fields is considered. By means of a kinetic analysis, a dispersion relation that governs the excitation of transverse electromagnetic fluctuations is derived and analysed.
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

This 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

A 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

Electron 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

We 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

The 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

The 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

Voraussetzungen, 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

Investigations 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

The 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

Finite 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

A 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

The 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

Starting 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

We 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

The 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

The 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

The 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.
Kinetic Study of the Emission of the First Negative System in an Argon‐Nitrogen Plasma at Atmospheric Pressure
Authors: Callède G. , Deschamps J. , Godart J. L.
Published: July 2007

Quantitative optical spectroscopy measurements of the emission spectra of the N(B2∑u,)ν′→X2∑gν″ transition (first negative system) in an Ar‐N2microwave discharge at atmospheric pressure have allowed determination of the rate coefficient of the production of Nmolecules in theB2∑u, state with vibrational level ν′ = 0.

The N(B2∑u, ν′) molecules are produced by the reactionmagnified imagein a surface‐wave‐induced microwave discharge (2450 MHz) sustained in an open‐ended dielectric tube. The rate coefficientK(T) has been obtained for ν′ν″ = 0 for different gas temperatures by varying the incident microwave power. TheK00(T) values are between 7.10−10and 4.10−10cm3s−1for the temperature range 2500 to 3450K.
Effect of Electron Velocity Distribution on the Heating of Core by Corona in a Spherical Pellet
Authors: Singh D. P. , Bredice F. , Giammanco F. , Vaselli M.
Published: July 2007

When a spherical plasma pellet is irradiated symmetrically from all sides by high power laser beams, hot electrons are produced at the plasma resonance layer. They move in the inward radial direction causing a counter‐streaming cold electron current flowing outwardly to maintain the charge neutrality. In general, the interaction between the hot electrons and the counter‐streaming cold background electrons leads to broadening of the velocity distribution of the latter. For a given heat flux, the electron velocity distribution constrained by the requirements for not supporting beam plasma instabilities, predicts a minimum electron velocity in the plasma ablation zone. These considerations affect the efficiency of heat transfer from the hot corona to the cold core. The purpose of this paper is to study the dependence of core‐corona coupling on the electron velocity distribution, laser wavelength and other plasma parameters in detail.
Numerical Modelling of Impurity Retention in the ITER Tokamak Scrape‐off Layer Plasma
Authors: Zagórski R.
Published: July 2007

The hydrogen plasma and carbon ions flows generated at the target plates in the ITER tokamak scrape‐off layer are numerically investigated. A 2D model of hydrogen plasma and impurity ions is presented. The model is based on the electron‐ion Braginski fluid equations [1] for hydrogen plasma and rate equations for impurities. Arbitrary level of impurity ions concentration is assumed. Recycling of hydrogen, sputtering and self sputtering of carbon atoms at the target plates are taken into account. Equations of the model are solved in the slab geometry using 2D‐multifluid numerical code EPIT [2]. Problems of impurity ions retention and radiation in the divertor volume are analyzed. Results of calculations for ITER tokamak boundary plasma are presented, showing that poor retention is likely at high impurity concentration in the divertor volume. The radiation power can be a significant part of ingoing energy.
Investigation of an Enhanced Glow Structure in a Low‐Pressure rf Discharge in Helium
Authors: Flohr R. , Schirmer H. , Piel A.
Published: July 2007

Spatially resolved plasma induced emission spectroscopy (PIE) is applied to a symmetric parallel plate discharge in helium under rf excitation at 13.56 MHz. The optical emission features are studied in the pressure range of 10–360 Pa and power densities from 6 mW/cm3 to 90 mW/cm3. At pressures above 60 Pa and power densities exceeding 50 mW/cm3 the transition from the α‐ to the γ‐mode is observed, which, in helium, is accompanied by the formation of a disk‐shaped brightly luminous glow. A marked difference between the emission from levels of the triplet and singlet system of the helium atom occurs above this threshold of applied power. The spatial emission distribution of equivalent lines of the helium atom is rather different under pressure variation. Therefore the spatial distribution of the metastable levels is concluded to be substantially different between singlets and triplets. This effect is attributed to a rapid decrease of electron temperature and increase of electron density which is a characteristic of the transition between the two heating modes. Low temperature and high density of the electrons favour an overproportional growth of the associated 2 1S destruction rate, i.e., singlet to triplet conversion. A similar effect has been reported for a dc discharge by Lawler et al. [1].
A New Method for the Development of a Nonlinear Equivalent Circuit for a Gas Discharge
Authors: Unger H. , Weltmann K.‐D. , Deutsch H. , Wesch J. , Wilke C.
Published: July 2007

The behaviour of gas discharges can be modelled by equivalent circuits built on the basis of a theoretical description of the plasma. This paper introduces a method to develop a nonlinear equivalent circuit directly by means of the balance equations of the column plasma and by the help of the knowledge obtained from the design of the linear equivalent circuit. The linear network theory was used for the derivation. The circuit found in this way is similar to a derived linear equivalent circuit of the column plasma with two inertial factors (delayed effects) for a neon gas discharge described in previous papers.
Theory of Jovian Kilometric Radiation
Authors: Goswami K. S. , Saikia B. K. , Bujarbarua S. , Nambu M.
Published: July 2007

This report presents a theoretical model of extraordinary mode radiation in presence of low frequency whistler mode. We show that the generation mechanism of extraordinary mode emission in the presence of whistler mode is based on the plasma maser theory. Application of theoretical results to Jovian Kilometric radiation is examined.
The Use of Corona Discharge for Rubber Crush Drier Exhaust Control
Authors: Morvová M. , Morva I. , Kurdel M.
Published: July 2007

The rubber crush drier exhaust contains mainly styrene, ethylbenzene, cumene, diizopropylbenzene, alkylphenols, monocyclic terpenes and technological additives as stearic acid, oils an colophony. For possible application of d.c. corona discharge to control styrene in exhaust, the reaction of styrene with additives and air in various d.c. corona discharge tubes was studied. The change of styrene content in the gas phase was measured by IR absorption spectrometry. The decrease of styrene concentration was minimum 83% and reached the 98,9% efficiency. No aromatic compounds remain after corona discharge action in gas phase. The structure of solid products was specified with reflection IR absorption spectrometry and compared with a calibration polystyrene foil (300 μm). The main product has been of malein anhydride‐styrene copolymer character for a negative corona discharge and of phenol or quinone‐styrene copolymer character for a positive corona discharge.
On the Structure of Atoms in Strong Magnetic Fields
Authors: Lief E. P. , Weisheit J. C.
Published: July 2007

The problem of a multi‐electron atom in a strong magnetic field is treated within the framework of a new statistical model. Here, the charge density n is required to have axial symmmetry. The partial factorization ansatz, n(ϱ, z) = nϱ(ϱ) · nz(ϱ;z), when introduced into Kadomtsev's equation, leads to a second‐order, non‐linear partial differential equation for nz that is valid over an important range of field strengths. Analytical solutions for two limiting approximations are consistent with earlier qualitative studies. Some illustrative, numerical solutions for a less restrictive approximation reveal atomic structures analogous to accurate hydrogenic results, already in the literature.
Model for Ion Collision Rate and Kinetic Equation
Authors: Dufty James W.
Published: July 2007

A model for the collision rate of an impurity ion in a plasma is formulated by extending a corresponding model for velocity and electric field correlation functions. All dynamical effects of the plasma are represented by its electric field at the impurity, which is then given a simple stochastic description. The simplest example allows complete determination of the collision rate and solution to the associated kinetic equation.
Equation of State of High Density Argon Plasmas obtained by Ballistic Gas Compression
Authors: Kusch H. J. , Groth U. , Schapals S.
Published: July 2007

The equation of state of argon is evaluated from simultaneous p, V, T‐and number density determinations of high pressure plasmas produced in a ballistic compressor.
Dynamic screening effects on the shift and the shape of spectral lines
Authors: Günter Sibylle
Published: July 2007

A many particle theory has been applied to investigate collective effects on the shift and the shape of spectral lines. It is shown that the line shift becomes nonlinear with respect to the electron density if the energy distance of the radiators levels is in the order of magnitude of the electron plasma frequency. For weakly non thermal plasmas dips on the line profile occur near the electron plasma frequency.
Influence of the Plasma Kinetics on the Si/C Ratio of a‐SixC1‐x: H Thin Films Deposited by Reactive Magnetron Sputtering of a Si Target in Ar + CH4 Gas Mixtures
Authors: Statev Sv. , Ivanov I. , Petrov I. , Carlsson J. , Orlinov V.
Published: July 2007

Possible sources of silicon and carbon atoms built‐in amorphous hydrogenated silicon carbide thin films grown by reactive magnetron sputtering (RMS) in argon/methane gas mixtures are evaluated. It is found out that the plasma decomposition of methane molecules plays an essential role in providing of growing film surface by active hydrocarbon fragments, thus influencing significantly the film stoichiometry even though the methane partial pressure in the sputtering gas mixture is only 1.5–4.7%.
An Assessment of the Role of Atomic Processes for Dispersing the Power in a Divertor
Authors: Post D. , Hulse R. , Stotler D.
Published: July 2007

The present concepts for power and particle control in the next generation of tokamak experiments rely upon atomic processes to transfer the power and momentum from the divertor plasma to the divertor chamber walls. These concepts are being evaluated with sophisticated one‐ and two‐dimensional divertor models. We present a survey of some of the candidate atomic processes of impurity radiation, hydrogen radiation and atomic physics and molecular effects to aid the development of the models.
The Effect of Flow Reversal on Impurity Behaviour in Tokamaks
Authors: Stangeby P. C. , Elder J. D. , Reiter D. , Maddison G. P.
Published: July 2007

Results are reported for a study of impurity edge transport and core contamination in the presence of flow reversal of the DT plasma, using 2‐D plasma solutions for the ITER CDA configuration produced by the B2 fluid code, coupled to the EIRENE Monte Carlo neutral hydrogenic code and the DIVIMP Monte Carlo impurity neutral/ion code. The effect of different types of impurity source is considered, including (a) target sputtering, (b) wall sputtering, artificial injection (for radiative cooling), and core helium production.
2‐D Fluid Transport Simulations of Gaseous/Radiative Divertors
Authors: Rognlien T. D. , Brown P. N. , Campbell R. B. , Kaiser T. B. , Knoll D. A. , McHugh P. R. , Porter G. D. , Rensink M. E. , Smith G. R.
Published: July 2007

The features of the fully implicit 2‐D fluid code UEDGE are described. The utility of the code is demonstrated by showing bifurcations or multiple solutions of the tokamak edge plasma for both deuterium and impurity injection in the divertor.
Neutral Gas Transport Modeling with DEGAS 2
Authors: Stotler Daren , Karney Charles
Published: July 2007

We are currently rewriting the neutral gas transport code, DEGAS [1, 2], with a view to not only making it faster, but also easing the process of including new physics. The goal is to make adding new species and reactions relatively simple so that the code can be rapidly adapted to new divertor physics regimes. DEGAS 2 will also be optimized for coupling to fluid plasma codes, incorporating many of the techniques utilized in B2‐EIRENE[3–5]. Finally, it is our intention that DEGAS 2, like DEGAS, be well‐documented and easy to use. We will present model calculations including ionization and charge exchange which will illustrate the way reactions are included into DEGAS 2 and will demonstrate operation of the code.
Power Exhaust in ITER
Authors:   ITER Joint Central Team
Published: July 2007

The main features and engineering parameters of the ITER EDA design are described and the operating parameter space is surveyed. A key element in the design is the divertor which must exhaust the bulk of the power generated by α‐particles. At the fusion power levels envisioned, Pf⩾1500 MW, conventional divertors of the type developed in the CDA are unable to accommodate the resultant heat levels. The novel design being developed to address the power exhaust for ITER is described, as are the underlying physics concepts. Model calculations performed in support of the concept and the results of experiments aimed at establishing an empirical basis for its operation are reviewed.
Influence of Kinetic Effects on Particle and Energy Flows in the ITER Divertor
Authors: Batischev O. V. , Krasheninnikov S. I. , Sigmar D. J. , Sigov Yu. S. , Soboleva T. K.
Published: July 2007

A kinetic modelling of 1d collisional and 2d Vlasov magnetic SOL's using the W1 and W2 particle codes is presented. Deviation of the distribution function from the equilibrium one is shown, as well as the possibility of kinetic instability in diverted plasmas.
Numerical Simulation of Carbon Impurities In JT‐60U Experiment
Authors: Tanaka M. , Ueda N. , Suzuki Y. , Tsuji S. , Takizuka T. , Itoh S.‐I. , Itoh K.
Published: July 2007

Numerical simulation of the behavior of carbon impurity for the JT‐60U divertor experiment has been carried out. Two approaches are examined for the impurity model: (1) a full charge state model and (2) a single average ion model. The full model simulates fairly well the power loss due to the impurities. The amount of power loss obtained by the single average ion model disagrees with that of the full model.
Investigations on Plasma Assisted Surface Cleaning of Aluminum in an Oxygen Glow Discharge
Authors: Kersten H. , Behnke J. F. , Eggs C.
Published: July 2007

Aluminum plates which are contaminated with hydrocarbon containing compounds (oil, grease) were treated in an Ar‐, O2‐ and Ar/O2‐plasma generated by a dc‐discharge. Besides a variation of the macroscopic discharge parameters (power, pressure) also different modes (anomalous glow regime, hollow cathode regime) have been studied. In most cases the contaminated substrates served as cathodes of an anomalous glow discharge where the combined influence of chemically reactive radicals and energetic ions was very effective.

During the plasma process the discharge was monitored by means of power variation and optical emission spectroscopy. The spectral line intensities of several species (etchants and products) have been measured as functions of the process duration. Simultaneously the removal of the contamination layers was observed by means of in‐situ ellipsometry. The temporal change of the ellipsometric parameters ψ and δ during the cleaning process was taken as a measure for the state of the surface. The combination of spectroscopic and ellipsometric measurements which indicate the progress of the plasma treatment gave interesting results on the mechanisms at the surface. In addition, surface analysis was used to assess the quality of the substrates treated.
Coaxial Discharge and Transverse Magnetic Field
Authors: Soliman H. M. , El‐Kashaf G. M. , Masoud M. M.
Published: July 2007

The study deals with the effect of an applied transverse magnetic field on the dynamics and parameters of the focused and expanded plasma in a coaxial discharge. The experimental results were found with a 3 kJ Plasma focus device of a Mather geometry. The discharge takes place in hydrogen gas with base pressure of 0.5 Torr. The experiments are conducted with a 10 kV bank voltage, which corresponds to 100 kA peak discharge current with rise time 8 μs. Helmholtz magnetic coils are placed outside the expansions chamber to produce a transverse magnetic field with intensity 280 G perpendicular to the plasma expanded from the coaxial electrodes. The investigations have shown that the plasma flow along the expansion chamber axis is restricted when applying the externally transverse magnetic field and the maximum axial velocity of the expanded plasma is decreased by 33%. X‐ray probe has been used to measure the focused plasma electron temperature (Te). The experimental results and the calculations showed that Te is decreased from 2.2 keV to 800 eV with the application of a transverse magnetic field. The expanded plasma electron temperature and density have been measured by an electric double probe, the results cleared that the expanded plasma electron temperature is decreased by 2.6 times while its density is increased by 9 times, when a transverse magnetic field is applied.
Kinetic Description of Elastic Processes in Hydrogen‐Helium Plasmas
Authors: Bachmann P. , Reiter D.
Published: July 2007

Recent experiments with high density divertor plasma operation in tokamaks and future tokamak design projects have revived interest in the much earlier work on elastic collision processes between neutral and charged components in hot plasmas. In revisiting these papers, we employ classical methods to calculate deflection functions, cross sections and collision rates for the most important of such elastic collision processes. A phyiscally motivated cut‐off procedure for the model interaction potential function is introduced. An algorithm for implementation of such processes into kinetic Monte Carlo neutral gas transport models is described, which accurately accounts also for possible singularities in the deflection function. Data fits for the relevant quantities are provided for hydrogenic and helium species. The relevance of elastic neutral‐ion collisions is illustrated by a numerical simulation of an ITER relevant divertor model.
Plasma Phase Transition in Fluid Hydrogen‐Helium Mixtures
Authors: Schlanges M. , Bonitz M. , Tschttschjan A.
Published: July 2007

The composition and the equation of state for a binary mixture of dense partially ionized hydrogen and helium are investigated on the basis of quantum statistical theory. Theoretical evidence for the existence of a hydrogen‐like and helium‐like plasma phase transition is found. Critical data for the phase transitions are given for the whole range of the mixing parameter.
Nonstationary and Quasi‐stationary Treatment of Distribution Anisotropy in the Temporal Relaxation of an Energetic Electron Group
Authors: Winkler R. , Braglia G. L. , Wilhelm J.
Published: July 2007

A relaxation study of an electron group in collision dominated weakly ionized plasmas has been performed. The study is based on the two‐term approximation of the Legendre polynomial expansion of the electron velocity distribution in the nonstationary Boltzmann equation. To overcome the limitation of the conventional quasi‐stationary treatment of the distribution anisotropy, a very efficient solution approach of the nonstationary kinetic equation in two‐term approximation has been developed which allows for a strict nonstationary treatment of the distribution anisotropy. By using this approach the temporal evolution of the isotropic and anisotropic distribution of the electrons has been investigated for a model plasma, which involves typical features of an inert gas plasma. A comparison of the results with corresponding ones obtained by applying the conventional approach under various parameter conditions clearly indicates a pronounced falsification of the real relaxation course by the latter approach.
A Barrier Discharge Reactor with Ferroelectric Electrodes I. Influence of thickness and surface area of electrodes
Authors: Opalińska T. , Szymański A.
Published: July 2007

A study aimed at finding a way of scaling‐up a small laboratory reactor employing an electric discharge with a dielectric barrier was carried out. The dielectric used was ferroelectric ceramic material of a high permittivity (ϵ above 1000) comparing to glass (ϵ ≈︁ 3–10), which is generally used. The main component of the ceramics was BaTiO3. The advantage of using this type of ceramics is related to a considerable increase in power density without the need of increasing voltage which supplies the system.

The influence of the thickness and surface of ferroelectric electrodes on the macroscopic characteristics of the discharge and efficiency of chemical process was investigated. Ozone synthesis from oxygen was the reaction under consideration.

A new structure of the reactor was proposed comprising a series of parallelly spaced thin ceramic plates. High electric permittivity of the ferroelectric ceramics enables such „sandwich”︁ structure to be supplied by only two edge ceramic electrodes.
Self‐Consistent Model of a Positive Column in an Inert Gas Discharge at Low Pressures and Small Currents
Authors: Behnke J. , Golubovsky Yu. B. , Nisimov S. U. , Porokhova I. A.
Published: July 2007

A formalism of the self‐consistent solution of the kinetic equation and the field equation is described for the positive plasma column in an inert gas discharge. The model considers the presence of electrons trapped in the potential well transfering the discharge current and of free electrons which reach the walls in a free diffusion regime supporting the required ionization level in the discharge. The calculations have been carried out for neon. In the model application range the comparison is made with experimental data of axial fields, wall potentials, wall currents and in some cases with distribution functions. A good correspondence takes place.
New Developments in Plasma Edge Modeling with Particular Emphasis on Drift Flows and Electric Fields
Authors: Baelmans M. , Reiter D. , Weynants R. R.
Published: July 2007

This paper reviews the present status of 2‐dimensional plasma edge codes with respect to simulation of electric fields and drift flows. Starting from experimental results and based on available simple analytic theories, different features of important mechanisms in the edge of a tokamak plasma are discussed and their availability in advanced numerical codes is established.
Self‐consistent Core‐Edge Nonlinear Transport Simulations with CORSICA 2
Authors: Tarditi A. , Cohen R. H. , Craddock G. G. , Crotinger J. A. , Porter G. D. , Rognlien T. D. , Shestakov A. I. , Smith G. R.
Published: July 2007

The coupled core‐edge nonlinear transport code CORSICA 2 is introduced and the structure of its iterative coupling algorithm is briefly discussed. Selected application results are reported that reproduce equilibria in DIII‐D discharges with plasma profiles initialized from the experimental data. Simulations for an L‐H transition and for a gas puffing experiment in DIII‐D plasmas are presented.
Simulation of the Alcator C‐Mod Divertor with an Improved Neutral Fluid Model
Authors: Wising F. , Knoll D. A. , Krasheninnikov S. I. , Rognlien T. D. , Sigmar D. J.
Published: July 2007

We have simulated detachment in Alcator C‐Mod, using an improved neutral fluid model. It features a parallel neutral momentum equation, fully coupled to the ions, allowing parallel plasma momentum to be converted into neutral momentum, which is dispersed to the material walls due to the high neutral viscosity. The simulations reproduce the pervasive experimental feature that the plasma detaches gradually, starting at the strike point, while always remaining attached above the nose of the divertor channel. The strike point heat flux and current drop by an order of magnitude as 0.5% of carbon is introduced to induce partial detachment. The plate temperature remains at or above about 1 eV all the way out to the divertor nose, in agreement with the experimental data.
Theory and Modelling of Time Dependent Phenomena in the Plasma Edge
Authors: Coster D. P. , Schneider R. , Neuhauser J. , Braams B. , Reiter D.
Published: July 2007

Recent work, both theoretical and computational, in the modelling of time‐dependent phenomena (Edge Localized Modes (ELMs)) in the plasma edge is reviewed.
Tokamak Edge Transport Theory
Authors: Hazeltine R. D. , Catto Peter J.
Published: July 2007

Kinetic equations commonly used to study the plasma core of a tokamak do not allow a balance between parallel ion streaming and radial diffusion and are, therefore, inappropriate in the plasma edge. Standard core tokamak transport orderings allow large divergence‐free flows in flux surfaces, but only weak radial flows. Alternate orderings are required in the edge region where radial diffusion must balance large parallel ion flows to divertor target plates or limiters. Similarly, core transport formulae cannot be extended to the edge region without qualitative alteration. Here we address the necessary changes by considering a large parallel flow ordering appropriate for the scrape‐off layer of a tokamak. By deriving and solving a novel kinetic equation, we construct distinctive transport laws for an impure, collisional edge plasma. We find in particular a surprising form for parallel transport in the scrape‐off layer, in which the parallel flow of particles (and heat) are driven by a combination of the conventional gradients, as well as viscosity terms and new terms involving products of radial derivatives of the parallel mean velocity with density and temperature gradients. The new terms are not relatively small, and could affect understanding of limiter and divertor operation.
Impurity driven current‐convective turbulence in the SOL plasma
Authors: Nedospasov A. V.
Published: July 2007

In this paper the diffusion coefficient for Impurity driven Current‐Convective Turbulence (ICCT) in the SOL plasma is obtained. The experimental verifications of the developed model are discussed.
3D Fluid Simulations of Turbulence in Detached Scrape‐off‐Layer Plasmas
Authors: Xu X. Q. , Cohen R. H.
Published: July 2007

In this paper, we present 3D simulations of scrape‐off‐layer (SOL) turbulence in detached plasmas. The nonlinear evolution of edge turbulence in the electrostatic limit is described by a four‐field model of the reduced Braginskii equations in a model x‐point geometry, including drives for the (1) conducting‐wall mode, (2) Kelvin‐Holmhotz mode, (3) curvature‐driven mode, (4) ▽xv∥‐driven mode, and (5) axial shear mode. In a detached plasma with Te0/Ted = 50 and Ne0/Ned = 0.2, and without magnetic shear, we find that a conducting‐wall‐like mode is the dominant drive even if turbulence drive from the sheath is small.
Fokker‐Planck Simulation of Electron Transport in SOL Plasmas with ALLA Code
Authors: Batishcheva A. A. , Batishchev O. V. , Krasheninnikov S. I. , Sigmar D. J. , Shoucri M. M. , Shkarofsky I. P.
Published: July 2007

The recently developed Fokker‐Planck code ALLA [1] permits us to simulate the temporal evolution collisional edge plasmas in 1D in space, IV in velocity space. It was used to simulate the SOL parallel electron flow in Alcator C‐Mod (PFC MIT) and TdeV (CCFM) tokamaks. Plasma parameters are taken as „best guesses”︁ from available detachment experimental data [2,3]. We show that the actual electron distribution function is asymmetric in the direction parallel to the magnetic field and its tail starts to departure from the Maxwellian at energies around 2T. This feature can substantially affect probe measurements and modify reaction rates and plasma transport properties.
Effect of the Dynamics of the Impurity Distribution over the Ionization States on the Radiative Plasma Instabilities and Shock Wave Structure
Authors: Krasheninnikov S. I. , Morozov D. Kh. , Sigmar D. J. , Herrera J. J. E. , Soboleva T. K.
Published: July 2007

We show that conventional quasistationary (coronal, or improved coronal) approximation for the energy loss due to the impurity radiation in practice can never be applied to the investigations of the impurity radiation driven instabilities in the edge plasmas due to relatively slow evolution of the impurity population over ionization states. We show that taking into account the effect of the evolution of the impurity population over ionization states results in a very significant change of the growth rates of the radiative driven instabilities and the structure of the shock wave in the radiative plasmas and leads to the strict conditions for the existence of the shock wave.
Simulation of Detachment in ITER‐Geometry Using the UEDGE Code and a Fluid Neutral Model
Authors: Wising F. , Knoll D. A. , Krasheninnikov S. I. , Rognlien T. D. , Sigmar D. J.
Published: July 2007

We have simulated detachment in ITER, with the UEDGE code coupled to a Navier‐Stokes neutral model, for realistic toroidal geometry and plasma parameters, with a heat flux of 100 MW into the outboard SOL. For a fixed fraction of carbon, corresponding to Zeff∼2.5 in the SOL, the power to the outer plate is reduced by more than 90%, the peak plate temperature is reduced to about 1 eV, and the total ion saturation current drops by 85%. Volume recombination plays an important role in removing the current. Bifurcated solutions and marfe‐like structures below the X‐point have been found under certain conditions.
1D Fluid Regime of Plasma‐Neutral Interaction and Divertor Detachment
Authors: Soboleva T. K. , Krasheninnikov S. I.
Published: July 2007

We show that self consistent decrease of both plasma flux and neutral ionization in current tokamaks is only possible when neutrals can be treated in a short mean free path approximation. We investigate these fluid regimes of plasma‐neutral interaction with 1D fluid equations employing a neutral viscosity term to treat the neutral interaction with the divertor plate. We have found that plasma flux onto the target starts to decrease at a very low heat flux coming into the hydrogen recycling region, when the temperature near the target drops below 1 eV, which seems lower than observed in the experiments. We conclude that the neutral‐neutral collisions, 2D effects of plasma‐neutral interaction, and plasma recombination processes can play a very important role in divertor plasma detachment.