bluuebunny/crossref_metadata_2025_split huggingface dataset:
Radiative Divertor Modelling for ITER and TPX
Authors: Braams B. J. 
Published: July 2007

AbstractThe B2.5 code for two‐dimensional multi‐species fluid modelling of the tokamak edge plasma is described and is applied for a parameter study of the effect of impurity seeding in ITER and TPX. Our modelling indicates that ITER must operate at an edge density of about 6.0 × 1019/m3 and the extended performance TPX must operate at an edge density of about 5.0 × 1019/m3 in order to obtain a robust divertor solution based on impurity radiation from the edge plasma only at neon concentration below 0.6% or argon concentration below 0.4%. For both devices, a high‐recycling divertor solution relying on impurity radiation from core and edge together appears very credible.
Numerical Simulation of the ITER Gaseous Divertor with the B2.5 Code
Authors: Ohtsu S. , Tanaka S. , Braams B. J. 
Published: July 2007

AbstractNeon impurity behavior in the ITER gaseous target divertor was investigated numerically by a 2‐dimensional multifulid code (B2.5 code). The balance between neon gas puffing and particle pumping in the divertor region had a strong effect on electron energy cooling processes. With increasing puffing or decreasing pumping, the divertor plasma changed into a detached state. The electron cooling zone by neon impurity was distributed along the separatrix, while that by hydrogen and helium spread out from the striking point to the outer wall. A large flow circulation all over the edge region was driven by electron pressure gradient force. It was found that neon impurity flow in the private region had an important role for the electron cooling in the upstream region.
Transport theory in self‐similar variables for neutrals atoms in an edge plasma
Authors: Helander P. , Krasheninnikov S. I. 
Published: July 2007

AbstractA family of analytical solutions to the Botzmann equation is found describing neutral atoms penetrating into a hot plasma whilst undergoing charge‐exchange, ionization, and recombination. It is shown that if the neutral mean‐free path divided by the scale length of ion temperature variation is constant, it is possible to introduce self‐similar variables in the kinetic equation. Since the mean‐free path increases with increasing energy, a one‐sided, high‐energy tail arises in the neutral distribution. This tail may contribute significantly to the heat and particle fluxes, which are nonlocal in character. When this is the case, the fluid approximation of these quantities breaks down at arbitrarily short mean‐free paths.
Advances and Issues in the Finite Element Fluid Modeling of the Tokamak Scrape‐Off Layer
Authors: Zanino R. 
Published: July 2007

AbstractThe 2‐D 2‐fluid finite element code FELS has been coupled to the Monte‐Carlo code for neutrals EIRENE and to the flux‐surface fitted structured mesh generator Sonnet. A good agreement with the finite volume B2 code is demonstrated in an actual divertor geometry, provided the FELS mesh is sufficiently aligned and poloidally refined.
Experimental and Theoretical Study of the Inhomogeneous Electron Kinetics in the dc Column Plasma
Authors: Pfau S. , Rohmann J. , Uhrlandt D. , Winkler R. 
Published: July 2007

AbstractThe radial change of the electron velocity distribution function and of related macroscopic quantities of the electrons are studied theoretically and experimentally in the positive column plasma of a neon dc low pressure glow discharge. The theoretical investigations are based on the solution of electron kinetic equations. The measurements of electron kinetic quantities are performed by using a single probe technique with automated recording. To avoid the strict treatment of the complicated radially varying electron kinetics in the microphysical description of the column plasma, various simplifications of the appropriate inhomogeneous kinetic equation have been adopted in the past. Recently a strict solution approach of this complex kinetic problem could be developed. Using this strict solution approach and experimentally determined electron kinetic quantities the approximation quality, obtained by applying various simplified approaches to treat the electron kinetics as the conventional homogeneous approach, the nonlocal approach and the local field approximation, is illustrated and critically evaluated in this paper.
Reaction Kinetics and Chemical Quasi‐Equilibria of the Ozone Synthesis in Oxygen DC Discharges
Authors: Jacobs H. , Miethke F. , Rutscher A. , Wagner H.‐E. 
Published: July 2007

AbstractThe spatial distribution of ozone and of oxygen atoms was studied along the active and the passive zone of a dc discharge (positive column, pressure: p = (4 … 10) · 102 Pa, current: I = 2 … 50 mA, flow rate: F = 5 … 100 sccm) in flowing oxygen. The composition of the final output O2/O3‐mixture is controlled by relaxation processes in the passive reactor zone. It is affected sensitively by the total number density and the gas temperature in the afterglow. Steady states meaning reversible chemical quasi‐equilibria were observed and analysed extensively. Within a detailed kinetic model the formation of these equilibria can be explained quantitatively. The synthesis to ozone is controlled above all by the metastable O2 (a1Δg) species, which modify drastically the results for the basic mechanism, considering the O atoms in the 3P and 1D states.
Abel Inversion of Rotating Plasmas
Authors: Fussmann G. , Meyer H. , Pasch E. 
Published: July 2007

AbstractA new mathematical method is presented which allows a systematic construction of the radial profiles of emissivity, angular frequency, and temperature from a measured two‐dimensional intensity distribution function I(λ, x) whose spectral part is determined by line shift and line broadening due the Doppler‐effect. The suitability of the method is demonstrated by test calculations and application to experimental data.
Global Behavior of Field Line and Particle Diffusion in a Stochastic Magnetic Field
Authors: Wang Hai‐Da 
Published: July 2007

AbstractGlobal behavior of field line diffusion in a stochastic magnetic field is obtained. Stochastic motion of particles undergoing mutural random collisions in the stochastic magnetic field is studied for the whole time range. The field line as wel as the particle diffusion coefficients are calculated to the sixth order of the relative magnitude of the fluctuating magnetic field.
Decomposition of NO2 in Oxygen‐free NO2: N2 Gas Mixture by Back‐Corona Generated Plasma
Authors: Jaworek A. , Krupa A. , Czech T. 
Published: July 2007

AbstractThe back‐corona discharge has been successfully applied as a plasma source for decomposition of NO2 in the oxygen‐free gas mixture of N2:NO2. The paper reports a first attempt to use back‐corona discharge for noxious gas conversion. The preliminary results of laboratory experiments in a needle‐to‐plate reactor show that the De‐NOx processes in back‐corona discharge are similar to the dc streamer corona discharges generated in the same geometry. Both types of discharges convert NO2 to nitrogen, oxygen and also to N2O and NO. However, back‐corona discharge produces less NO, and is more efficient energetically in NOx decomposition than the dc streamer corona discharge.
Excitation of the Potential Relaxation Instability in a Weakly Magnetized Discharge Plasma by a Voltage Step
Authors: Gyergyek T. , Čerček M. , Stanojević M. 
Published: July 2007

AbstractAn instability is triggered in a weakly magnetized discharge plasma by the application of a positive voltage step to a planar collector immersed into the plasma column with its surface perpendicular to the magnetic field lines. Time developement of the plasma density after the application of the pulse is measured by a Langmuir probe. Radial and axial velocity of the plasma density perturbation are measured. Radial velocity is consistent with the increase of the plasma potential in the current channel. Axial velocity is very high. It is interpreted as phase velocity of radial quasiperiodic motion of the plasma in and out of the current channel. Response time of the collector current to the applied voltage step is measured versus different parameters. Experimental results are in agreement with a qualitative model presented in previous work [1] where the observed instability is modeled as a two dimensional potential relaxation instability (PRI). Minor improvements of the previous model are proposed. A rarefaction pulse that moves towards the collector is found as the initial stage of the instability.
Numerical Method and Composition at and out of Chemical Equilibrium in a Multitemperature Plasma. Application to a Pure Nitrogen Plasma
Authors: Andre P. 
Published: July 2007

AbstractThe disequilibrium between the temperatures (excitation, rotation, vibration, translation) in plasmas lead us to specific chemical potentials. Then, they are used to develop a mass action law in a multitemperature plasma. This mass action law enables us to determine the composition of a pure nitrogen mixture out of thermal equilibrium.The composition evolution versus time is determined from a kinetic method modified to take into account different temperature hypotheses.The composition and different thermodynamic properties of a pure nitrogen mixture are given at the chemical equilibrium, then versus time for various temperature hypotheses and thermal disequilibriums.
Calculation of the X‐Ray Absorption Fine Structure in Shock‐Compressed Matter
Authors: Frey H.‐D. , Meyer‐ter‐Vehn J. 
Published: July 2007

AbstractDense plasma modifications of X‐ray absorption fine structure (EXAFS) are investigated theoretically for shock‐compressed, strongly‐coupled plasma in the region of 1–5 times solid density and 1–20 eV temperature. The analysis includes explicit calculations (1) of the ion pair distribution functions to account for large amplitude thermal motion, (2) of the photoelectron scattering and phaseshift by solving the Schrödinger equation in the ion potential, and (3) of the photoelectron mean free path describing inelastic scattering on degenerate electrons of the plasma environment within Lindhard theory. Results are given for the K‐edge of aluminum. The fine structure survives for temperatures up to 20 eV, but only in a range of 50–100 eV above the edge. Position and amplitude of the first minimum may be used to extract information on plasma temperature and density, and a practical scaling relation is derived for future experiments.
Quantum Kinetic Equations: Correlation Dynamics and Selfenergy
Authors: Bonitz M. , Binder R. , Köhler H. S. 
Published: July 2007

AbstractThe derivation of non—Markovian quantum kinetic equations is reconsidered in the framework of density operators. Conventional derivations use for the decoupling of the BBGKY‐hierarchy the assumption of vanishing three—particle correlations g123 = 0. This yields non—Markovian kinetic equations with infinite memory depth. We discuss a different closure relation to the hierarchy, which overcomes this difficulty without assumptions on weakening of initial correlations and in fact corresponds to the inclusion of selfenergy effects (beyond Hartree—Fock).
Self Energy and Two Particle States in Dense Plasmas
Authors: Kraeft W.‐D. , Fehr R. 
Published: July 2007

AbstractSingle and two particle properties in dense plasmas are investigated in the framework of Green's functions. For this reason, the self energy is considered in Vs and T‐matrix approximations. Here, especially off‐shell T‐matrices have to be considered. Thermodynamic functions and the Mott transition are briefly discussed.
Debye‐Onsager‐Relaxation‐Effect beyond Linear Response and Antiscreening in Plasma Systems
Authors: Morawetz K. 
Published: July 2007

AbstractThe quantum kinetic equation for charged particles in strong electric fields is derived and analyzed with respect to the particle flux. It is found that the applied electric field is screened nonlinearly. The relaxation field is calculated completely quantum mechanically and up to any order in the applied field. The classical limit is given in analytical form. In the range of weak fields the deformation of the screening cloud is responsible for the Debye‐Onsager relaxation effect. The result beyond linear response presented here allows to investigate a field regime where no screening cloud is present. The descreening field is determined as a function of thermal energy density of the plasma. For stronger fields the moving charge is accelerated by accumulated opposite charges in front of the particle. This can be understood in analogue to the accoustic Doppler effect. A critical field strength is presented up to which value a thermalized plasma is possible. The range of applicability of the treatment is discussed with respect to applied field strength and space gradients.
Diffusion and Heat Transport in a Dense Partially Ionized Plasma
Authors: Ohde T. , Bonitz M. , Bornath T. , Schlanges M. 
Published: July 2007

AbstractBalance equations for the density, momentum and energy of a dense plasma are derived on the basis of quantum kinetic theory. The influence of many—body effects on ionization/recombination reactions, diffusion and thermal conductivity are discussed. It is shown that (microscopic) many—particle effects lead to nonlinear macroscopic relaxation behaviour. For illustration, we solve the coupled density—temperature balance equations for a dense partially ionized hydrogen plasma.
Quantum Kinetics of Plasma and Radiation — a Nonequilibrium Green's Function Approach
Authors: Tamme D. , Henneberger K. 
Published: July 2007

AbstractA microscopic description of an electron‐ion plasma coupled to the quantized electromagnetic field as an interacting many‐body system far from equilibrium is given, generalizing results of DuBois [1] to include two‐particle correlations. As applications (1) light propagation through a partially ionized plasma is investigated including modifications of transition energy and ‐matrix element as well as dephasing and scattering due to Coulomb interaction, and (2) a T‐matrix approximation for the one‐particle selfenergy and for the polarization 4‐tensor is developed enabling a consistent treatment of two‐particle correlations in the nonlinear optical and transport properties of plasmas.
Electromagnetic Forces on Plasma Particles in the Presence of Resonant and Nonresonant Plasma Turbulence
Authors: Vladimirov S. V. , Nambu M. 
Published: July 2007

AbstractNonlinear forces on plasma particles in the presence of a test nonresonant wave and resonant plasma wave turbulence are calculated. The important feature of the considered nonlinear effect is that the forces due to the nonresonant test wave act on the plasma particles in the absence of linear and nonlinear resonances between the wave and the particles. Although in a closed plasma‐wave system the process is balanced by the quasilinear interaction between the plasma resonant turbulence and plasma particles (leading to nonstationarity and inhomogeneity of the system), in open systems the effect can be significant.
Interaction of Electrons with Atoms in Ground and Excited States; Potential of Interaction, Momentum Transfer Cross‐Sections
Authors: Ignjatović L. J. M. , Mihajlov A. A. 
Published: July 2007

AbstractIn this paper the potential of the electron‐atom interaction was presented which may be useful both in the case of the ground state of an atom with one optical electron and in the case of the excited state of any atom, and which is given by expressions suitable for operational use. The presented potential is used in calculating the transport cross sections for the elastic electron scattering on the atoms of H, Li and Na respectively, in the ground and excited states.
Experimental Evidence of Periodic Pulling in a Weakly Magnetized Discharge Plasma Column
Authors: Gyergyek T. , Čerček M. , Stanojević M. 
Published: July 2007

AbstractDynamics of the PRI oscillations coupled to the externall harmonic oscillation is studied experimentally in a weakly magnetized discharge plasma column. Two characteristical phenomena, which are: synchronization and periodic pulling are observed. Experimental findings are compared to the approximate analytical and numerical solutions of the Van der Pol equation with the harmonic external force term: \documentclass{article}\pagestyle{empty}\begin{document}$ \frac{{d^2 n}}{{dt^2 }} - (\alpha - \beta n^2)\frac{{dn}}{{dt}} + \omega _0^2 n = A\omega _0^2 \cos (\omega _e t) $\end{document}. Relevance of the Van der Pol model for the PRI oscillations is confirmed.
Langmuir Probe Diagnostics of a Low Temperature Non‐Isothermal Plasma in a Weak Magnetic Field
Authors: Kudrna P. , Passoth E. 
Published: July 2007

AbstractThis article presents measurements by a cylindrical Langmuir probe in the plasma of a DC cylindrical magnetron discharge át the pressure 1.5 Pa that aim at the experimental assessment of the influence of a weak magnetic field to the estimation of the electron density when using conventional methods of probe data interpretation. The probe data was obtained under the presence of a weak magnetic field in the range 1.10−2−5.10−2 T. The influence of the magnetic field on the electron probe current is experimentally assessed for two cylindrical probes with different radii, 50 μm and 21 μm. This assessment is based on comparison of the values of the electron density estimated from the electron current part with the values of the positive ion density estimated from the positive ion current part of the probe characteristic respectively by assuming that at the magnetic field strengths used in the present study the probe positive ion currents are possible to be assumed as uninfluenced by the magnetic field. For interpretation of the probe positive ion current two theories are used and compared to each other: the radial motion model by Allen, Boyd and Reynolds [10] and Chen [11] and the model that accounts for the collisions of positive ions with neutrals in the probe space charge sheath that we call Chen‐Talbot model [8]. At lower magnetic field 3 · 10−2 T the positive ion density values interpreted by using the Chen‐Talbot model [8] are in better agreement with the values of electron density compared to those obtained by using the theory [10,11]; therefore the model [8] is used for calculation of the positive ion density from the probe data at higher magnetic fields. The comparison of the positive ion and electron density values calculated from the same probe data at higher magnetic fields shows that up to the magnetic field strength 4 . 10−2 T with the probe 100 μm and up to 5 . 10−2 T with the probe 42 μm in diameter respectively the decrease of the magnitude of the electron current at the space potential due to the magnetic field does not exceed the error limits that are usual for Langmuir probe measurements (absolute error ±20%).
Full‐dimensional Monte Carlo simulation of glow discharges with superposed magnetic fields
Authors: Heise C. , Lemke K. , Kock M. 
Published: July 2007

AbstractA Monte Carlo simulation code is described that is suitable for modelling low‐pressure glow discharges that possess cylindrical symmetry, but are of otherwise completely variable geometry. In this single‐particle simulation in 3 space and 3 velocity dimensions, an entire discharge including the cathode fall can be modelled with or without magnetic fields of arbitrary shape. Electric and magnetic fields are given externally and are not adjusted self‐consistently. Collision processes are modelled in great detail, and cathode sputtering phenomena are also included in the simulation.This simulation code is applied to hollow cathode discharges with and without superimposed magnetic fields and to a Penning discharge. Exemplary results are shown that include density profiles of cathode‐sputtered atoms, energy distribution functions of electrons and cathode sputtering effects for a Penning discharge. Comparisons to results from experiment and other simulations are given.
Scattering Cross Sections and Electrical Conductivity in Fully Ionized Hydrogen Plasma
Authors: Nurekenov Kh. T. , Baimbetov F. B. , Redmer R. , Röpke G. 
Published: July 2007

AbstractThe cross sections for the scattering of charged particles in hydrogen plasma are determined within the partial wave method. The scattering phase shifts δi are obtained from a numerical solution of the Schrödinger equation using an effective potential that takes into account also three‐particle correlations. The resulting scattering cross sections are compared with the respective Born approximation and those obtained for the usual Debye potential which represents only two‐particle correlations. Furthermore, the electrical conductivity of fully ionized hydrogen plasma is determined within the Chapman‐Enskog method and compared with available experimental data and other theoretical approaches up to the nonideal region.
Methane Conversion in the Flowing Afterglow of a Dinitrogen Microwave Plasma: Initiation of the Reaction
Authors: Legrand J.‐C. , Diamy A.‐M. , Hrach R. , Hrachova V. 
Published: July 2007

AbstractThe reaction of methane in the nitrogen afterglow is studied by combination of direct measurements and computer experiment. The experimental data were obtained by optical emission spectroscopy of the discharge, by gas chromatography of resulting stable products and by probe diagnostics of charged species in afterglow plasma. The simulation was based on a macroscopic kinetic approach covering 24 species and 61 reactions with input data given by the afterglow experiment. In the present stage of the modelling the initiation of methane conversion was studied. It was found that, contrary to active discharge, in the afterglow plasma the active neutral species (mainly excited dinitrogen molecules) are most important for the dissociation of methane into CHx and H radicals.
Modelling of JET H‐mode plasmas with type I ELMS
Authors: Taroni A. , Corrigan G. , Lingertat J. , Parail V. , Springmann E. 
Published: July 2007

AbstractA model previously developed to simulate JET L‐mode and ELM free H‐mode discharges has been upgraded to take into account type I ELMs. Features of the new model and results of simulations are discussed and compared to JET experimental results.
A Scrape‐off Layer Based Density Limit for JET ELMy H‐modes
Authors: Borrass K. , Lingertat J. , Schneider R. 
Published: July 2007

AbstractDuring a density ramp‐up JET ELMy H‐modes typically show a saturation of the core density which may even be followed by a decrease (density limit). At the limit the discharge detaches between ELMs and a recently proposed edge based detachment limit for the separatrix density applies. In this paper a simple picture is proposed for the relation between separatrix and core density which allows us to derive the corresponding limit for the core density. The empirical evidence from JET is discussed and compared with the model predictions. It is shown that the resulting limit for the line averaged density coincides in size and scaling with the empirical Greenwald limit.
Modelling drift effects on the limiter SOL of low density plasmas in W7‐AS
Authors: Feng Y. , Sardei F. , Grigull P. 
Published: July 2007

AbstractThe plasma transport in the limiter SOL of W7‐AS is modelled, including the classical drifts. The effects of these drifts on the plasma distribution in the SOL are studied. Model results are compared to measurements.
Adaptive Anisotropic Finite Elements for Edge Plasma Modeling
Authors: Zanino R. , Subba F. 
Published: July 2007

AbstractDetailed edge plasma modeling in the presence of moving fronts requires adaptive meshes. We use an adaptive anisotropic triangular mesh generator for solving a steady state 2‐D anisotropic nonlinear conduction problem with strongly nonlinear sinks. This equation can be thought of as a simplified scalar model of energy transport in a scrape‐off layer (SOL) plasma, under the action of ionization and/or impurity losses. The problem is solved with finite elements using a triply nested loop of iterations.