bluuebunny/crossref_metadata_2025_split huggingface dataset:
Influence of Nonideality Effects on the Ionization and Recombination Coefficients of a Reacting Hydrogen Plasma
Authors: Bornat Th. , Schlanges M. , Kremp D. 
Published: July 2007

AbstractOn the basis of generalized quantum kinetic equations for chemically reacting systems which include many particle effects, the ionization and recombination coefficient of a dense hydrogen plasma are determined. Using a simple approximation for the continuum shift in the quasiparticle energies, nonideality effects are taken into account and lead to a nonlinear density dependence of the rate coefficients. In the case of thermodynamic equilibrium the rate equation yields a Saha equation for a nonideal plasma.
The non Linear Decay of the Fast Wave During ICRF Heating
Authors: Avinash K. , Core W. G. F. , Hellsten T. 
Published: July 2007

AbstractVarious non linear decay processes of the fast magnetosonic wave can take place, such as the non‐resonant decay of the fast wave into an Ion‐Bernstein wave and a quasi‐mode, or the resonant decay of the magnetosonic wave into two ion Bernstein waves. The relevance of these processes to the direct edge heating observed during ICRH is discussed.
Transport Coefficients in the Jet Boundary
Authors: Lowry C. G. , Harbour P. J. , Tagle J. A. 
Published: July 2007

AbstractLangmuir probes mounted in an antenna protection tiles have facilitated the comprehensive measurement of electron temperatures and densities in the JET scrape‐off layer (sol)2. The probes are close to the outside midplane and at radial positions of 15 and 28 mm behind the last closed flux surface. The data are from ohmic discharges with plasma currents between 1 and 5 MA and average electron densities between 8 × 1018 and 5 × 1019 m−3.Here we use these measurements in a simple diffusive model for the electrons to obtain empirical scalings of the transport coefficients with local parameters. The scalings are shown to be inconsistent with exponentially decaying profiles of electron temperature and density, such as are measured in the JET sol.In the apparent absence of a suitable model we are forced to scale directly the characteristic decay lengths in similar fashion. Finaally we use these dependences to campare models of global particle and power balance with the data.
Currents in Intersected Tokamak Flux Tubes
Authors: Hantzsche E. 
Published: July 2007

AbstractIn an elementary way the toroidal electric current in tokamaks is considered if the flux tube is intersected by limiters within the Scrape Off Layer (SOL). Simple sheath conditions are applied. The limiter space charge sheaths act as additional resistances, consuming partly the available voltage and diminishing the current density which is limited both by the plasma conductivity and by the ion saturation current of the sheaths. The difference between both potential drops at a limiter may rise up to the loop voltage (per flux tube circulation). Electron induced secondary electron emission has no influence at all on these results, which are applied to measured SOL plasma parameters in the TEXTOR tokamak as an example.
Impurity Transport Calculations for a Drift‐Dependent Tokamak Scrape‐Off Plasma
Authors: Brooks J. N. , Petravic M. , Kuo‐Petravic G. 
Published: July 2007

AbstractTwo dimensional calculations of impurity transport in a high recycling divertor scrape‐off region have been made with an updated version of the ZTRANS Monte Carlo computer code. The calculations use plasma parameters for the Doublet 3 divertor, as computed by the Planet Fluid Transport Code. The effects of electric field, particle drift velocities, and thermal forces are included in the calculations. For all impurity species studied, it is found that impurity transport is dominated by frictional forces, over most of the scrape‐off region. Light impurities, however, impinge substantially closer to the divertor plate center than do heavy impurities, which tend to impinge at the outer plate boundary.
Monte Carlo Modelling of Impurity Atom and Ion Transport Near A Limiter
Authors: Stangeby P. C. , Farrell C. , Wood L. 
Published: July 2007

AbstractA Monte Carlo code, LIM (Limiter Impurity), is used to track impurity atoms and ions toroidally/radially in the vicinity of a limiter. As an illustration of the use of LIM, two cases are analysed: physical sputtering and sublimation of carbon from the limiter. For the same total impurity production from the limiter, physical sputtering is found to be approximately three times more efficient at contaminating the plasma centre as sublimation. A number of further quantities, which can be compared with experiment, are computed: (a) the toroidal/radial shapes of the impurity clouds of successive ionization states, (b) the average impurity ion temperature in each cloud, (c) the ratio of the different charge states of the impurities returning to the limiter, their spatial distribution and impact energy, and (d) total radiated power.
Dynamics of Impurities in the Scrape‐Off Layer
Authors: Stangeby P. C. 
Published: July 2007

AbstractImpurity modelling of the Scrape‐Off Layer, SOL, is reviewed. Simple analytic models are sometimes adequate for relating central impurity levels to edge plasma conditions and for explaining the patterns of net erosion/deposition found on limiters. More sophisticated approaches, which are also necessary, are categorized and reviewed. A plea is made for the acquisition of a more comprehensive data base of edge plasma properties since reliable impurity modelling appears to be dependent on more extensive use of experimental input.
Extension of Schottky's Theory to a Cylindrical Discharge Plasma Containing a Coaxial Rod
Authors: Voigt H.‐D. , Winkler R. , Wilhelm J. 
Published: July 2007

AbstractThe well known diffusion theory of the positive discharge column is extended considering a plasma which burns between two coaxial cylindrical walls. Recent experimental investigations carried out with the goal to enlarge the fluxes of ultraviolet radiation in fluorescent lamp tubes motivate such an extension. Indeed, an enhancement of the efficacy could be found installating a glass rod along the tube axis which acts as an additional recombination surface. In order to understand this effect also a description of the radial plasma behaviour, especially that of the electron density, and of the necessary charged particle production by ionization is of interest. The paper reports about such an extension, including a representation of a suitable numerical solution approach and a discussion of the results.
Increased Power Concentration and its Effects on the Discharge Parameters of the Low Pressure Hg‐rare Gas Positive Column. II. Variation of Tube Radius
Authors: Kreher J. , Steern W. 
Published: July 2007

AbstractThe reduction of the tube radius is an effective technique for enhancing power concentration. The increased wall losses are compensated by larger field strengths, which counteract the decrease in radiation efficiency with rising current density. The causal relationships are investigated for tube radii of 18‐4 mm at constant discharge current i = 200 mA and constant current density j = 1.2 mA/mm2 and for parameter variation of the field strength only. The measured efficiencies of the Hg‐resonance lines 254 and 185 nm and the electron energy distribution functions agree well with the calculated values. Moreover, the results of the model calculations provide information on the elementary processes involved, such as elastic losses, collisions of second kind, stepwise processes and Coulomb interaction. The results show that Hg‐rare gas discharge with tube radii R = 5–10 mm are no less suitable for light production than those with radii between 13 and 18 mm.
Equilibrium Properties of Ionic Mixtures: Derivation of Fluctuation Formulae from the Grand‐Canonical Ensemble
Authors: Suttorp L. G. 
Published: July 2007

AbstractThe grand‐canonical ensemble is used to derive fluctuation formulae for the particle densities, the pressure and the energy density of a multi‐component ionic mixture. As an intermediate step sum rules are established for the two‐particle Ursell functions.
Anomalous Electrical Conductivity of Weakly‐Collisional, Magnetoactive Plasma Excited by the Lower‐Hybrid‐Drift Instability
Authors: Belyi V. V. , Meister C.‐V. 
Published: July 2007

AbstractIn this paper the kinetic theory for a weakly‐collisional plasma immersed in a static magnetic field with no curvature is considered. In the plasma an electrostatic flute (kB = 0) instability is excited causing an anomalous wave‐particle collision frequency. In the special case of the lower‐hybrid‐drift instability a simple expression for this collision frequency is found containing the wave spectrum as a parameter.
Dense Plasma in Electrical Implosions of Refractory Metal Wires
Authors: Isakov V. P. , Mintsev V. B. 
Published: July 2007

AbstractPeculiarities of the refractory metal wire implosions are investigated, when the high power currents (up to 106 A) flow through the conductor. It is found, that the surrounding dense air plasma achieves brightness temperature of 70000 K. About 75% of the applied electrical energy are converted into the optical radiation.
Statistical Theory of Bremsstrahlung in Plasma‐Molecular Systems
Authors: Klimontovich Yu. L. , Shevchenko A. Yu. , Yakimenko I. P. , Zagorodny A. G. 
Published: July 2007

AbstractDifferent approaches to the statistical theory of bremsstrahlung in nonequilibrium plasma‐molecular systems are compared. The spectra of bremsstrahlung, as well as collision integrals and effective dissipation constants are calculated for such systems within the framework of both classical and quantum theory.
Stopping Power of Charged Particles I
Authors: Brouwer H. H. , Kraeft W. D. , Luft M. , Meyer T. , Schram P. P. I. M. , Strege B. 
Published: July 2007

AbstractThe stopping power of charged particles is determined in the random phase approximation using Lenard Balescu type collision integrals. The stopping power is closely related to other single particle properties such as self energy and quasi particle life time.In this part I, numerical evaluations are given for equal masses (of test and target particles).
Hollow Cathode Effect in a Long Perforated Cylindrical Cathode with External Coaxial Anode
Authors: Iova I. , Ciobotaru D. , Cosma B. , Dima G. 
Published: July 2007

AbstractThe paper presents the main characteristics of transverse mode HCE glow discharges in spectral pure helium and neon and in a He/Ne mixture in a long perforated cylindrical cathode with an external coaxial anode. At optimum values of gas pressure, when HCE gets its climatic stage, the compact negative glow evenly “fills” the cathode cavity with maximum amplifications of current and radiation.
Stimulated Brillouin Scattering of Whistler Waves by Electron‐Acoustic Wave in a Two‐Electron Temperature Plasma
Authors: Guha S. , Asthana M. 
Published: July 2007

AbstractStimulated Brillouin Scattering has been investigated in a two‐electron‐temperature plasma and it is found that the growth rate can be controlled by injecting hot electrons in the plasma. For typical values of the magnetosphere plasmas the values of growth rates for different concentrations of hot to cold alectrons are calculated.
Radiation Efficiency and Kinetic Calculations for the Positive Column in Hg/Ar Mixtures II. Impact of Tube Radius and Current Density
Authors: Kreher J. , Bartolomäus G. , Wilhelm J. , Stern W. 
Published: July 2007

AbstractIn a preceding part of the paper, based on experimental methods and on a corresponding kinetic model, especially the impact of the effective life times of the 63P1 and 61P1 Hg resonance levels on the main properties of the low pressure Hg‐–Ar positive column has been studied. In the presented second part these investigations, which have been performed under the aspect of their application in fluorescent lamps, will be continued. They are related to the effects of tube radius and discharge current density. New fluorescent lamps have reduced tube radii from R = 18 to 13 mm and compact lamps down to R = 5 mm. Thus it is of interest to study the electron distribution function and main macroscopic properties of such low pressure discharge plasmas, where the latter properties are obtained by adequate energy space averaging. At first, results are reported and discussed which are related to the dependence of main plasma parameters on the Hg partial pressure when reducing the discharge tube radius for constant discharge current i and argon pressure pAr. Starting from the electron distribution function the particle and energy budget will be studied in detail, especially of course the change of the ultraviolet radiation output from both Hg resonance levels 63P1 and 61P1 and, in addition, of visible radiation. Then, to understand the effect of the discharge current density, as a representative example two cases with different values of R, i and PAr but with equal current density have been investigated and discussed. Altogether the investigations made will shed light upon the complex relations in the mentioned mixture plasma and give hints to select suitable parameter values which can be useful to improve light sources.
Generation of Electromagnetic Wave in Two‐Electron‐Temperature Plasmas
Authors: Guha S. , Sarkar Ruby 
Published: July 2007

AbstractIt is shown that in a two‐electron‐temperature plasma a finite amplitude upper‐hybrid wave can parametrically decay into an electrostatic electron acoustic wave (EAW) and a left handed circularly polarized (LHCP) electromagnetic wave propagating along the magnetic field. The electromagnetic oscillating two stream instability is also discussed in the same system. The role of second electron component is discussed with its application in lab plasma as well as in space plasma.
Hydrodynamic Effects on Thermalisation of Dense Core with Surrounding Corona in Laser‐Imploded Z‐Layered Plasma Target
Authors: Singh D. P. , Harith M. A. , Palleschi V. , Vaselli M. 
Published: July 2007

AbstractPlasma ablation effect on the heat transfer from the superthermal corona to the inner cold dense core in the case of Z layered plasma target is analysed. Thermalisation of core with the surrounding corona depends on the laser wavelength, the ‘flux‐limit’ parameter, width of Z layer and the mean electron temperature of the overlapping region between the core and the corona. The presence of Z layer reduces the electronic mean free path and consequently the width of the plasma ablation zone. Considering the self‐regulation condition for the heating of plasma target, the dependence of core‐corona coupling on the “flux‐limit”, the laser and plasma parameters has been studied.
Modelling of Secondary Electron Impact on the Self‐Consistent RF Bulk Plasma Description
Authors: Winkler R. , Capitelli M. , Gorse C. , Wilhelm J. 
Published: July 2007

AbstractThe impact of a secondary electron beam, generated at the electrodes and accelerated in the sheaths, on the self‐consistent treatment of the electron behaviour in an rf bulk plasma has been investigated by a parametric study. Source of electrons in the plasma are collisional ionization and secondary electron injection.Electrons are lost by ambipolar diffusion to the electrodes of a parallel plate rf discharge configuration. The non‐stationary Boltzmann equation is used to determine self‐consistently the rf field amplitude necessary for maintaining the steady‐state rf bulk plasma as well as the time resolved behaviour of the electron energy distribution function and of all contributions to the electron particle and power balance, at given source rate and energy distribution of secondary electron injection.
Periodically Self‐Excited Moving Striations in a Low‐Temperature Gas Plasma
Authors: Ammelt E. , Willebrand H. , Purwins H.‐G. 
Published: July 2007

AbstractA new nonlinear effect in a low temperature gas plasma has been found and investigated experimentally. At a critical value of the discharge current in a special glow discharge system the positive column constricts and striations evolve spontaneously. On a large time scale the pattern seems to consist of standing striations. At higher temporal resolution the striations turn out to be moving ones which are modulated by high amplitude oscillations of the total electric current and of the voltage observed at the device. In addition phenomena like period doubling and irregular behaviour occur.
Note on the E × B Instability
Authors: Kildal A. 
Published: July 2007

AbstractWithout appeal to trial functions an instability criterium for the inhomogeneous plasma slab is derived. The growth rate for the flute type instabilities is expressed in terms of the density perturbation n1. When n1 is put equal to the trial function used by SIMON (1963), a growth rate which differs somewhat from that of Simon is found. The reason for the discrepancy is pointed out.
Experimental Observation of Simultaneously Existing Moving and Standing Patterns in a Gas‐Discharge System
Authors: Willebrand H. , Matthiessen K. , Niedernostheide F.‐J. , Dohmen R. , Purwins H.‐G. 
Published: July 2007

AbstractIn a quasi 1‐dimensional lateral gas‐discharge system we observe experimentally sub‐ and supercritical bifurcations from a spatially homogeneous to an inhomogeneous distribution of the current density. Among other results we find for the first time the simultaneous existence of a nontrivial nonstationary pattern (travelling waves) with a nontrivial stationary pattern (periodic filaments) in a laterally extended dc‐driven gas‐discharge system.
Model of the Linearized Collision Operator for Plasmas with Temperature Anisotropy
Authors: Meister C.‐V. 
Published: July 2007

AbstractA model kinetic operator is proposed, describing the relaxation of the first sixteen hydrodynamic moments of a two‐component plasma with temperature anisotropy with respect to an external magnetic field. The analytical expression given for the model, taking into account only density, velocity, and temperature relaxation, is more exact than a corresponding Bhatnagar‐Gross‐Krook model.
Effect of Finite Spectral Width on the Modulational Instability of Langmuir Waves described by a Nonlinear Schrödinger Equation
Authors: Roy P. C. 
Published: July 2007

AbstractBy using the two‐point space correlation function an equation for the power spectral density for a random Langmuir field has been derived. The dispersion relation for a monochromatic wave is regained for a delta spectrum. For a Gaussian spectrum, the maximum growth rate is less than that for a monochromatic wave. For a “meander spectrum”, the growth rate is increased with the width of the spectrum in the first stage then decreased for further increase of the width.
Theoretische Modelle des katodischen Brennflecks von Bogenentladungen
Authors: Hantzsche E. 
Published: July 2007

AbstractVoraussetzungen, theoretische Grundlagen, Ergebnisse und allgemeine Erfahrungen bei numerischen Modellrechnungen für quasi‐stationäre katodische Brennflecken von (Vakuum‐)Bögen werden zusammenfassend dargestellt. Die Ergebnisse beziehen sich hauptsächlich auf Kupfer als Katodenmaterial und umfassen alle wesentlichen physikalischen Größen des Katodenflecks (der Katoden‐Oberfläche und teilweise des katodennahen Plasmas), sie beschreiben mögliche Existenz‐Zustände im Parameterraum. Insbesondere wird auch die Abhängigkeit dieser Ergebnisse von verschiedenen Änderungen der Parameter und Gleichungen untersucht. Mehrere Beispiele werden dargestellt und interpretiert. Der Einfluß der Rauhigkeit der Katodenoberfläche ist in jedem Fall beriicksichtigt worden. Schließlich werden die Gül‐tigkeits‐Beschränkungen des Modells diskutiert, und vor allem wird die große Bedeutung nichtstatio‐niirer (z B. explosiver) Prozesse im Brennfleck betont, obgleich solche Prozesse aukrhalb des Rahmens dieses Modells liegen.Die Arbeit wird in zwei Teilen veröffentlicht. Dieser zweite Teil umfaßt die Anwendung der Modellgleichungen auf die numerische Berechnung von Brennfleck‐Parametern, die Diskussion der Ergebnisse und einige Gesichtspunkte für Weiterentwicklungen in der Theorie katodischer Brennflecken.
Development of Divertor Concept for Optimized Stellarators
Authors: Nührenberg J. , Strumberger E. 
Published: July 2007

AbstractDevelopment of Divertor Concept for Optimized Stellarators. 1. Stellarator optimization. 2. Configurational aspects. 3. Field line tracing for investigation of diversion properties. 4. Simplified SOL models: one‐dimensional estimates and Monte Carlo simulations. 5. Divertor troughs. 6. Discussion and outlook.
Fokker‐Planck Modelling of Edge Plasma Near the Neutralizer Plate in a Tokamak
Authors: Abou‐Assaleh Z. , Matte J. P. , Johnston T. W. , Marchand R. 
Published: July 2007

AbstractWe have modelled the transport of particles and energy through a tokamak SOL near the neutralizer plate. The electron kinetic/ion fluid code FPI and a two‐fluid code were employed for this study. Because of the electron time scale, it would lake a very long time to reach steady state with the kinetic code. We have therefore developed a hybrid technique, using both codes in alternation, to reach a full equilibrium compatible with electron kinetics. When it is used in the stand‐alone mode, the two‐fluid code's results are closest to FPI if a heat flux limiter f=0.2 is used. The electron distribution function is very non‐Maxwellian near the plate.
Longitudinal Ion Transport Coefficients in Magnetized D‐He and H‐C Plasmas
Authors: Claaßen H. A. , Gerhauser H. , Sayed Y. A. 
Published: July 2007

AbstractBased on analytical formulae derived in ref./1/, longitudinal ion viscosities, heat conductivities and thermal diffusion ratios in magnetized D‐He and H‐C plasmas are calculated within Grad's 21‐moment approximation. Calculations taking full account of the finite mass ratio m+/mZ between hydrogen (deuterium) and impurity ion mass are compared with those for m+/mz≫ 1. As is to be expected, the largest discrepancies between exact and approximate results (with respect to the mass ratio) arise for D‐He plasmas. It turns out that the approximate formula for the impurity ion heat conductivity has to be extended to remove some hitherto existing deficiencies already mentioned in ref. /1/.
Simulation of Tokamak Divertor Plasmas including Cross‐Field Drifts
Authors: Rognlien T. D. , Milovich J. L. , Rensink M. E. , Kaiser T. B. 
Published: July 2007

AbstractThe effects of plasma currents and cross‐field drifts on single null tokamak divertor operation are simulated using a fully implicit 2‐D fluid code. Equations solved are those for particle continuity, parallel momentum, electron energy, ion energy, electrostatic potential, and neutral gas diffusion. The core and scrape‐off layer regions are separated by a magnetic separatrix, both of which are included in the simulation. The core plasma is poloidally periodic, and the inner and outer private flux regions are properly connected. The code utilizes a fully implicit method‐of‐lines scheme to advance the variables in time with a Krylov technique or a direct Newton iteration with a numerical Jacobian. Results are presented on the effects of currents and cross‐field drifts for DIII‐D single‐null parameters.
Magnetischer Teilcheneinschluß in Synchrotrons und Tokamaks
Authors: Schamel H. 
Published: July 2007

AbstractInhomogene Magnetfelder bilden die Grundlage des Teilcheneinschlusses in Speicherringen und Fusionsanlagen. Eine Diskussion der Teilchenbewegung in diesen Feldern fördert neben typenspezifischen Eigenheiten manche Gemeinsamkeit, wie den störenden Einfluß der Arnold‐Diffusion zutage.
Transport Analysis of Low Density Discharges on JET
Authors: Dnestrovskij A. Yu. , Yushmanov P. N. 
Published: July 2007

AbstractEnergy and particle balance of plasma in discharges with low density on JET is investigated. Self‐consistent transport analysis accounting bulk and edge plasma phenomena is carried out. It is shown that large difference between the ion edge temperature and the electron one could be the result of the influence of the secondary electron emission from the limiter in low density discharges.