bluuebunny/crossref_metadata_2025_split huggingface dataset:
Plasmons and Instabilities in Quantum Plasmas
Authors: Bonitz M. , Binder R. , Scott D. C. , Koch S. W. , Kremp Dietrich 
Published: July 2007

AbstractCollective excitations in degenerate one‐, two‐ and three‐dimensional plasmas including quantum confinement effects are discussed within the rándom phase approximation (RPA). The results of the analytic continuation of the retarded dielectric function for these systems are presented.
Exploring Dense Plasma by Laser Compression. A simulation study
Authors: Aoki T. , Hüller S. , Meyer‐ter‐Vehn J. 
Published: July 2007

AbstractA series of hydrodynamic simulations is presented, related to laser compression of matter. In particular, low entropy compression of hydrogen is studied in order to reach the metallic phase transition. Anomalous hydrodynamic phenomena like shock splitting and rarefaction shocks occuring in the neighbourhood of the phase transition are investigated for a special configuration.
Interpolated Mean Spherical Approach to the Energy Equation of State of the Classical One‐Component Plasma Fluid
Authors: Kahlbaum Torsten , Dewitt Hugh E. 
Published: July 2007

AbstractWe present a fit formula for the excess internal energy of the one‐component plasma in the fluid phase that was obtained from the analytic solution of the mean spherical approximation for charged hard spheres in a uniform neutralizing background by utilizing a new relation for the effective packing fraction. Our results are in much better agreement to recent Monte Carlo data for strong coupling, Γ ≥ 1, than previous results from similar calculations, and extend down to the Debye limit, Γ → 0.
Electron Temperature Relaxation in Afterglow Plasmas: Diffusion Cooling
Authors: Trunec D. , Španěl P. , Smith D. 
Published: July 2007

AbstractWe have carried out a thorough theoretical analysis of the cooling and heating processes of the electron gas in Ne, Ar and Kr afterglow plasmas. Thus the rate of relaxation of the electron temperature, Te, is seen to be in good agreement with the experimental measurements when spatial gradients of Te in the early afterglow and heating of the electron gas by superelastic collisions between the electrons and metastable atoms are accounted for. At low pressures of the rare gases, pg, the phenomenon of diffusion cooling occurs in which Te relaxes to an equilibrium temperature, Tee, which is less than the gas temperature, Tg. This reduction in Tee below Tg is mirrored in a reduction in the ambipolar diffusion coefficient, Da, for the rare gas atomic ions and electrons. Thus the Da can be calculated as a function of pg using the values of Tee, and when this is done, properly accounting for the heating by metastable atoms, the calculated and experimental values of Da in all three rare gas afterglows are seen to be in agreement.
Theory of the plasma–sheath transition in an oblique magnetic field
Authors: Riemann K.‐U. 
Published: July 2007

AbstractBohm's criterion for the formation of a thin (λd → 0) sheath requires that the ions are pre‐accelerated in a quasineutral “presheath”. Usually the presheath mechanism is based on geometric ion current concentration, on ion friction (collisions), or on ionization. The present paper considers a presheath which depends essentially on magnetic deflection of the ion orbits. To this end a hydrodynamic model of the presheath accounting for an oblique magnetic field as well as for collisions and ionization is investigated. It is shown that the magnetic field alone is not sufficient to provide a presheath mechanism. The “magnetic presheath” is intrinsically controlled by elementary processes, and “compressed” by a strong magnetic field into a thin layer with a characteristic extension of the ion gyroradius ρi.
Effects of an Oblique Magnetic Field on Sheath Formation in the Presence of Electron Emission
Authors: Sato K. , Katayama H. , Miyawaki F. 
Published: July 2007

AbstractIt is found from kinetic analyses that an oblique magnetic field provides two presheath mechanisms. One is due to the ion polarization drift and another is due to the finite ion‐gyroradius effect. The secondary‐electron inflow is effectively diminished due to reflection by the Lorentz force and the emission coefficient is limited to a value less than 0. 8 by the space‐charge effect when the magnetic angle approaches to 90°.
Radial Electric Field Influence on Neoclassical Orbits in a Tokamak
Authors: Krasheninnikov S. I. , Yushmanov P. N. 
Published: July 2007

AbstractThe effects of radial electric fields on neoclassical orbits in a tokamak are considered. It is shown that for high radial electric field shear, it is not possible to use local theory to describe neoclassical transport processes; this is due to a dramatic change of the particle orbit topology at a distance of the order of the particle orbit width. For the step‐like electrostatic potentials typical for the tokamak plasma periphery in the H‐mode, the trajectories of the particles can be either squeezed or expanded in the radial direction.
Finite Mean‐Free‐Path Effects in Tokamak Scrape‐Off Layers
Authors: Cohen Ronald H. , Rognlien Thomas D. 
Published: July 2007

AbstractWe address the problem of calculating the parallel electron heat conduction in a tokamak scrape off layer with non‐negligible mean free path. We develop a model distribution function based on pieces of Fokker‐Planck solutions, containing: a local Maxwellian at low energies, a modified Spitzer‐Härm distribution at energies below where the mean free path equals the distance to the nearest wall, a bounce‐averaged distribution at higher energies up to the confining potential energy, a filled‐in outgoing loss‐cone distribution at still higher energies, and finally an empty loss region at energies such that the mean free path exceeds the length of the field line. The model is compared with Monte Carlo simulations.
Scrape‐Off Layer Turbulence Theory
Authors: Cohen Ronald H. , Mattor Nathan , Xu Xueqiao 
Published: July 2007

AbstractA review is presented of recent developments in the theory of fluctuations in tokamak scrape‐off layers. A brief summary of typical experimental features is presented, followed by derivation of a flute‐mode dispersion relation including conducting‐wall, curvature, axial E × B shear and radial compression drives. Nonlinear results are reviewed, including arguments for and evidence of inverse cascading, penetration of SOL‐generated turbulence into the closed‐flux‐surface edge plasma, and large‐amplitude fluid excursions, comparable to observed SOL widths. Effects of divertor and limiter geometry, including x‐point effects, are discussed. The potential importance of atomic physics drives for radiative and gas‐target divertors is noted, as is the possibility that SOL turbulence originates in the core plasma. Consequences of SOL turbulence, including broadening of the SOL and dissipating parallel momentum (of potential importance for gas‐target divertors) are outlined, and the possibility of actively exciting turbulence to achieve these objectives is discussed.
The influence of Polarization Currents on the Edge Plasma Turbulence in Tokamaks
Authors: Nedospasov A. V. , Uzdensky D. A. 
Published: July 2007

AbstractThe nature of edge turbulence in tokamaks and stellarators is associated in literature with the dissipation by currents, flowing through the potential sheath near the surface (SD ‐ surface dissipation). There are two mechanisms for the instability: the flute instability due to the fluctuations of the Pfirsch‐Schlüter currents [1], and an instability due to the fluctuations of polarization currents [2], the latter mechanism taking place only when ▽Te ≠ 0. So far these two mechanisms were considered separately. In the present work the stability of plasma in the scrape‐off‐layer (SOL) of tokamak with a ring poloidal limiter is studied in linear approximation. Both magnetic field toroidicity effects and polarization current fluctuations are taken into account.
Reduction of Plasma Heat Flow by Sheath‐Presheath Modifications with Ponderomotive Force
Authors: Masuzaki S. , Takamura S. 
Published: July 2007

AbstractA r. f. induced directed force exerted by the application of r. f. voltage on the divertor plate or by introducing r. f. electric field in front of the plate is taken into account for the analysis on sheath‐presheath formation in a very simple manner. The ponderomotive force repels electrons coming to the divertor plate, which results in a reduction of the electron heat flow. The reduction of ionic impact energy to the plate is also expected even for presheath modification combined with positive divertor biasing as well as for successful sheath modification.
Finite Element Modelling of the Plasma Edge
Authors: Pütz Th. , Reiter D. , Wuttke M. W. 
Published: July 2007

AbstractAnalysis of particle‐ and energy‐transport in tokamak plasmas shows the importance of the scrape‐off layer (SOL) to achieve satisfying conditions for a burning plasma in a fusion reactor. To take into account the influence of complex geometrical features on transport, we developed a 2D‐fluid‐code based on a Finite Element Method (FEM). Because this numerical scheme needs no regular grid structure, one can deal much more accurately with the plasma flow in non simply connected domains and near limiter‐ or divertor‐plates, where the magnetic field is inclined to the target. This permits a geometrically and physically more realistic description of the interaction of plasma‐ and neutral‐particles. Results from a coupled calculation between the FEM‐code and a neutral‐gas Monte‐Carlo‐code (EIRENE) are discussed for the SOL of TEXTOR.
Numerical Modelling of Impurity Production in the FTU Tokamak Scrape‐Off Layer
Authors: Zagorski R. , Pericoli V. , Pieroni L. 
Published: July 2007

AbstractA 2D multifluid model for deuterium plasma and impurity ions has been applied to study the problem of the plasma and nickel ions transport in the FTU tokamak scrape‐off layer (SOL). The model is based on the electron‐ion fluid equations for background plasma and rate equations for impurities. An analytical model for neutrals is employed allowing to take into account recycling of hydrogen, sputtering and selfsputtering of nickel atoms at the target in a selfconsistent way with boundary plasma dynamics. Equations of the model are solved in the slab geometry using 2D ‐ multifluid code EPIT.Plasma parameters in the SOL are investigated under conditions when the physical sputtering at the target plate is the only mechanism of the impurity production. Calculations are performed for nickel ions in the simplified poloidal geometry of the FTU tokamak scrape‐off layer. The calculated results indicate the existence of a selfregulating mechanism limiting the electron temperature in the SOL below 30 eV.A comparison of the calculated results with the experimental data is also reported.
Arcing in ASDEX‐Upgrade
Authors: Juttner B. , Buchl K. , Weinlich M. ,   The Team of Asdex‐Upgrade
Published: July 2007

AbstractArc traces and luminous phenomena at the divertor tiles of ASDEX‐Upgrade were recorded, and experimentally modelled by artificially ignited arcs. At the graphite surfaces the arcs produced relatively immobile spots that were uniformly distributed in toroidal direction. To explain the latter effect, the behavior of flux tubes emanating from the arc spots is discussed. It is concluded that arcing should not be neglected in theoretical models that describe processes in high power machines.
The Physics of Bounded Plasma Systems (BPS's): Simulation and Interpretation
Authors: Kuhn S. 
Published: July 2007

AbstractThe dynamical behavior of a bounded plasma system (BPS) is, by definition, characterized by the simultaneous and self‐consistent interaction of the plasma itself, its material boundaries, and whatever external circuit(s) there may be. A full theoretical description of these systems, which are of relevance in a variety of fields (e.g., plasma technology), must involve (microscopic or macroscopic) evolution equations for the plasma, Maxwell's equations for the fields, boundary conditions for the plasma and the fields, and the external‐circuit equation(s). By “BPS simulation” we mean obtaining theoretical (including numerical) results from models accounting, at least conceptually, for all the basic features mentioned above.This paper is exclusively concerned with microscopic (i.e., kinetic and particle) BPS simulation. A very general system of basic equations for kinetic BPS simulation is proposed. With the PD (“plasma device”) codes from U.C. Berkeley [Birdsall, C. K., IEEE Trans. Plasma Sci. 19 (1991) 65], particle simulations of (1d, 3v) BPS's can now be routinely performed by everybody. Particular emphasis is laid on an alternative method called “trajectory simulation”, which has shown great potential for kinetic BPS simulation with high accuracy and resolution. From the point of view of nonlinear dynamics, BPS's are rather complex dissipative systems exhibiting, in particular, regular and chaotic attractor states. For their proper interpretation, an advisable (if not indispensable) first step is to carefully study relatively simple, but still representative “archetypal” BPS's, such as the Pierce diode [Godfrey, B. B., Phys. Fluids 30 (1987) 1553] and the single‐emitter plasma diode or “KDSI” [Crystal, T. L., et al., Phys. Fluids B 3 (1991) 244]. These systems and representative results obtained therewith are surveyed, and both recent developments and future perspectives of BPS physics are addressed.
Heating Mechanism of Self‐Interaction of Potential Surface Waves in a Warm Nonisothermal Plasma Bounded by Metal
Authors: Azarenkov N. A. , Ostrikov K. N. 
Published: July 2007

AbstractThe influence of electrons heating in the high‐frequency potential surface wave (SW) field on dispersion properties of the considered SW is studied in this paper. High‐frequency SW propagate at the interface between a warm nonisothermal plasma and a metal. The nonlinear dispersion relation for the SW is derived and investigated. The obtained results are valid in both semiconductor and gaseous plasmas in a weak heating approximation.
Propagation Characteristics of Wave Packet in Non‐Uniform Magnetic Fields
Authors: Maruyama T. , Togashi K. , Sato T. , Itagaki K. , Kitamura H. 
Published: July 2007

AbstractExperimental observations on a wave packet in a positive column of helium discharge with magnetic fields are reported. The wave packet is a kind of ionization wave and is created by applying voltage pulses to a mesh grid. When an axial non‐uniform magnetic field is applied to a positive column, the plasma parameters change inhomogeneously near the magnetic coil. So various characteristics (amplitude, frequency, wavelength and so on) of the wave packet are changed at the both sides of the coil. The wavelength of the wave making up the wave packet varies continuously with a magnetic field. On the contrary, its amplitude and frequency vary remarkable near the magnetic coil, as a strong magnetic field is applied.
Magnetogravitational Instability of Anisotropic Plasma with Finite Ion Larmor and Generalized Polytrope Law
Authors: Chhajlani R. K. , Parihar A. K. 
Published: July 2007

AbstractThe effect of finite ion Larmor radius corrections on the propagation of small perturbations through self gravitating, anisotropic system with generalized polytrope law is investigated. The polytrope laws are considered for the pressure components in parallel and perpendicular directions to the magnetic field. The polytrope model proposed by Abraham‐Shranuer can be reduced to CGL equations with double adiabatic equations of state and MHD set of equations with isothermal equation of state. The effects of FLR and polytrope indices are discussed on the gravitational, firehose and mirror instability. The critical Jeans wave numbers are found to depend on polytropic indices and derived for CGL and MHD cases. The FLR corrections are found effective in shorter wave length region and produce stabilizing influence. The condition of mirror instability is uninfluenced by FLR but dependent on polytropic indices.
A Study of the Gas Flow in the RF Low‐Pressure Supersonic Jet Plasma Chemical System
Authors: Tichý M. , Šicha M. , Bárdos L. , Soukup L. , Jastrabík L. , Kapoun K. , Touš J. , Mazanec Z. , Soukup R. J. 
Published: July 2007

AbstractWe present results of the experimental study of the gas flow in the RF low‐pressure supersonic‐jet plasma‐chemical reactor. The flow is investigated by using photography with subsequent digital picture processing. The results of the investigations yield valuable data for the physical model of the plasma‐jet system.
Electron Impact Ionization and Fragmentation of Metal‐Organic Compounds Used in Plasma Assisted Thin Film Deposition Techniques
Authors: Basner R. , Schmidt M. , Deutsch H. 
Published: July 2007

AbstractMeasurements of the total and selected partial cross sections for the electron impact ionization of cyclopentadienyltrimethylplatinium (C5H5)Pt(CH3)3 [CpPtMe3], bismethylcyclopentadienylruthenium (CH3C5H4)2Ru [(MeCp)2Ru], and bismethylcyclopentadienylferrum (CH3C5H4)2Fe [(MeCp)2Fe] in the energy range from threshold up to 90 eV are presented. A double focussing mass spectrometer with an improved ion extraction system to avoid the discrimination of fragment ions with excess energy was used. The following values for the total single ionization cross sections σ at an impact energy of 70 eV and for the ionization energies (EI) were determined: σ = (13.7 ± 2.5) 10−16 cm2, EI = 7.6 ± 0.5 eV [CpPtMe3], σ = (23.2 ± 4.2) × 10−16 cm2, EI = 7.5 ± 0.5 eV [(MeCp)2Ru], σ = (20.2 ± 3.6) × 10−16 cm2, EI = 8.1 ± 0.5 eV [(MeCp)2Fe]. The results are compared with known mass spectra of the Pt‐ and Fe‐compound. Schemes for the fragmentation and ion formation processes in the ion source are discussed. The fragment ion composition as a function of the ion source temperature was investigated. The production rate of pure metal ions is small. The measured total single ionization cross sections when compared with calculations using two additivity rules were found to be lower than the calculated values.
Relative Cross Sections for Electron‐Impact Dissociation of SF6 into SFx (x = 1−3) Neutral Radicals
Authors: Iio M. , Goto M. , Toyoda H. , Sugai H. 
Published: July 2007

AbstractThe energy dependence of the partial cross sections of electron‐impact dissociation of SF6 into the neutral radicals SF, SF2 and SF3 is measured from the threshold to 200 eV. This measurement is accomplished by appearance mass spectrometry in a dual electron beam device. The dissociation products SF4 and SF5 are below the detection limit of the present system. The threshold energies for neutral dissociation into SF3, SF2 and SF are measured to be 16.0, 19.5 and 22.0 eV respectively. The surface loss probability of each radical and the electron‐impact nitrogen dissociation are examined to evaluate the relative dissociation cross section. However, the absolute cross section cannot be assigned for lack of the ionization cross sections for the SFx radicals.
The Influence of the Gas‐Temperature on the Behaviour of the Positive Column of a Neon Glow Discharge and its Description by a Nonlinear Equivalent Circuit
Authors: Weltmann K.‐D. , Unger H. , Deutsch H. , Wilke C. 
Published: July 2007

AbstractThe concentration of metastable atoms can significantly be influenced by changing the gas temperature [1]. Starting from a set of balance equations, consisting of the balance equation for the electrons, the balance equation for excited atoms and the current balance equation the impedance behaviour is calculated in dependence on the gas temperature. Based on a theoretical description of the discharge plasma a nonlinear equivalent circuit representing the behaviour of the positive column at higher gas‐temperatures (250 K – 500 K) is developed. The circuit posseses only positive parameters for the reactances which can be calculated by means of the elementary processes occuring in the discharge plasma. Experimental investigations of the static current/voltage characteristic and the impedance behaviour support the proposed circuit model.
Gas Density Distributions and Reduced Field Strenghts of the Positive Column of Low Pressure XeCl* Glow Discharges
Authors: Tiedtke K. , Schwabedissen A. , Schröder G. , Bötticher W. 
Published: July 2007

AbstractInterferometric measurements of radial gas density distributions have been performed on the cylindrical positive column of DC low pressure glow discharges (LPGD) in pure Xe and Xe/Cl2 gas mixtures. Absolute gas temperatures have been measured by thermocouples. In the mixtures, the gas temperature is several hundred Kelvin above the temperature in pure Xe. Additionally, the radial distribution of the gas density in the mixtures cannot be described by Bessel profiles, which would result from Schottky's diffusion theory. Combined with field strength measurements, radial profiles of E/N (electric field strength/neutral density) have been determined. Results of this work will be useful for model developments of LPGD in rare‐gas/Cl2 mixtures but also for the general understanding of the positive column in attaching gases.
Analysis of Neoclassical Edge Plasma Transport with Gyroviscosity and Inertia
Authors: Rogister A. , Antonov N. 
Published: July 2007

AbstractIt is shown that the ambipolarity constraint which results from neoclassical transport theory with gyroviscosity and inertia sets lower limits on the edge density and/or temperature and/or Zeff gradients. Toroidal momentum co, respectively counter,‐injection reduces, respectively increases these lower bounds. Generally speaking, co, respectively counter,‐injection increases, respectively reduces, the rotation velocities. The theory has so far been developed for the high collisionality regime only.
Kinetic Modelling of Detached and ELMy SOL Plasmas
Authors: Batishchev O. V. , Xu X. Q. , Byers J. A. , Cohen R. H. , Krasheninnikov S. I. , Rognlien T. D. , Sigmar D. J. 
Published: July 2007

AbstractKinetic modelling of parallel plasma and heat flows in the scrape‐off‐layer (SOL) is presented. Detached [1–4] and attached regimes are studied. A kinetic Edge Localized Mode (ELM) [5] model is simulated by temporally varying the incoming heat power from the core. Deviations of the plasma distribution functions from Maxwellian are observed. Our simulations are performed using the collisional PIC code W1 [6], which employs a non‐stationary 1D2V fully kinetic model of a high recycling SOL plasma.
Radiative Power Exhaust from ITER
Authors: Mandrekas J. , Stacey W. M. , Kelly F. A. 
Published: July 2007

AbstractRadiative plasma power exhaust from the core, mantle, and SOL/divertor regions has been evaluated for ITER, with emphasis upon establishment of a radiative mantle by impurity seeding in the SOL. The simulations investigated different seeded impurities, compatibility with the H‐mode, and sensitivity to different impurity pinch velocities. An analytic stability analysis of the radiative mantle is also presented.
Global Modeling of Impurity Production and Transport in a Limiter Tokamak Plasma
Authors: Zanino R. , Ferro C. 
Published: July 2007

AbstractA global model for impurity production and transport in a limiter tokamak plasma has been developed by coupling an iterative simplified model of the scrape‐off layer with a main plasma impurity transport code. The predictions of the global model are compared with experimental results from the Frascati Tokamak Upgrade with poloidal inconel limiter.