bluuebunny/crossref_metadata_2025 huggingface dataset:
Generation of Extra‐Ordinary Mode Radiation by an Electrostatic Pump in a Two‐Electron‐Temperature Plasma
Authors: Hasan Zehra , Guha S.
Published: July 2007

Coherent wave‐wave coupling can produce radiation with a high efficiency. Recently, there has been a great deal of interest in the study of electro‐magnetic wave generation in magnetized plasmas. We have investigated theoretically the effect of finite ion temperature on the parametric instability of an electro‐static upperhybrid pump into an X‐mode nonthermal radiation and low frequency ion waves in a two electron temperature plasma. The latter may include the lower‐hybrid, the electron‐acoustic and the ion‐cyclotron waves. The loss cone distribution existing permanently at low altitudes acts as a free energy source generating the upper‐hybrid waves. The upper‐hybrid waves can also be present because of a linear instability produced by runaway electrons. Nonlinear dispersion relation and the growth rates are derived for each case using the hydrodynamical model. We find extra numerical factor arising due to the ions of finite temperature in the growth rate expression. This study may be useful in magnetosphere, auroral ionosphere, solar wind, solar radio bursts, and laboratory plasmas where ion has finite temperature and electrons have two distinct energy distributions.
Comparison of Radial Helium Emission Line Profiles in Transverse and Longitudinal Hollow Cathode Discharges
Authors: Bergmann J. , Konieczka J. , Mizeraczyk J. , Schubert M.
Published: July 2007

Results of measurements of the radial distributions of intensities of the He I and He II spectral lines emitted by the transverse and longitudinal hollow cathode discharges direct current excited are presented. The results show that both hollow cathode discharges exhibit different excitation efficiency of the spectral lines. The metastable level 2s3S seems to be important for excitation of He I emission lines.
Kinetic Theory of Hot Carrier Screening
Authors: Morawetz K. , Kilimann K. , Kremp D.
Published: July 2007

The influence of high electric fields on the distribution function and following on the dielectric constant is considered in the framework of nonequilibrium Greenfunction technique. In the partial ionized H‐plasma additional plasma‐poles occur due to the field, which become field dependent. The existence of 2 maxima in the distribution function results in additional damping and turbulent regions.
Partially Ionized Hydrogen Plasmas in Strong Electric Fields
Authors: Kremp D.
Published: July 2007

A partially ionized hydrogen plasma is considered in high electric fields. The influence of the field on the electron distribution function is described by solving the Boltzmann‐equation in Fokker‐Planck approximation. Three‐particle processes like exitation are included. With the help of the distribution function the field — behaviour is seen and the macroscopic values like kinetic energy, conductivity and runaway‐electrons are calculated explicitly. The heating up of the plasma and the break down of the system are shown.
An Experimental and Theoretical Study of the Creation Plasma Process in dc Pulsed Discharges
Authors: Ballesteros J. , Hernández M. A. , Dengra A. , Colomer V.
Published: July 2007

An experimental study of the evolution along the creation process of the plasma parameters characterizing a dc pulsed Argon discharge has been developed. The diagnostic of these parameters is based on the I — V probe characteristic technique. The electron density evolution values so measured are in a good agreement with those obtained from a theoretical model of this process, so the validity of the assumptions involving the model are confirmed.
Kinetic Effects in the Scrape Off Layer
Authors: Chodura R.
Published: July 2007

The scrape off layer (SOL) of a confined plasma (Fig. 1a) is in many respects in a state far from, thermodynamic equilibrium:

The energy diffusing outward from the plasma core across the separatrix is condensed in the thin SOL to a strong energy flux along the magnetic field.

The recycling of cold neutrals from the limiter or divertor target gives rise to a strong temperature gradient from the hot midplane region to the relatively cold recycling zone.

For long mean free path length in the plasma relative to the extension of the recycling zone the thermalization in the recycling zone may be incomplete.

The potential gradient length in the sheath in front of the target is small as compared to the mean free path length; the velocity distributions of ions and electrons as determined by the electric field are far from being Maxwellians there.

Thus the follwing topics will be discussed in this paper:

Parallel transport (electron heat flow, ion viscosity)

Recycling

Sheath structure (grazing incidence of magnetic field, secondary electrons).

Boundary conditions for fluid models

Numerical illustrations for these kinetic effects are given from a 1d particle‐in‐cell code including Coulomb collisions [1].
Not treated are kinetic effects connected with instabilities, perpendicular transport, neutrals and impurities.magnified image
Heat transmission through plasma sheath with energetic electrons
Authors: Shiraishi K. , Takamura S.
Published: July 2007

An electrostatic sheath formation on carbon and molybdenum target plates for plasmas with electrons of two different temperatures is analyzed by a simple formulation including the effect of secondary electron emission from the target plate. A modified Bohm criterion is given in terms of effective electron temperature which defines the ion sound velocity in two component plasmas. Hot electrons and the associated secondary electrons greatly modify the charge balance in the sheath. They change the sheath voltage and consequently the heat transmission characteristics. A critical amount of hot electrons for sharp increase in the sheath voltage is given by a simple formula.
Multidimensional and Multifluid Plasma Edge Modelling: Status and New Directions
Authors: Vold E. L.
Published: July 2007

The plasma boundary in magnetic confinement devices is observed in experiments and in computations to contain radial and poloidal variations in plasma potential, strong radial electric fields and large poloidal drift flows in addition to the parallel flow toward the plasma sheath boundaries and the particle recycling from the walls. The global power balence is largely influenced by impurity radiation and thus by impurity transport in the edge region. The behavior of the edge region is related to global confinement in ways not yet fully known and motivates further improvements in edge plasma modelling.

General multifluid transport equations are reviewed in the context of the current status of plasma edge modelling. It is assumed that the macroscopic transport in the plasma edge region is suitable for a moments description, or fluid model. Progress is well established in computational treatments of the standard paradigm including classical parallel and anomalous cross‐field flux coupled to neutrals in analytic or Monte Carlo steady state computations. Formulation of momentum diffusivities and curvature drift in toroidal coordinates are considered. New directions include defining the dominant influence of drifts and non‐ambipolar flows, improving coupled plasma‐neutral transport calculations, and treating impurity flow in full multifluid models. Calculation of the plasma potential driving the E × B drift in the scrape‐off layer can be extended inside the last closed flux surface by conserving the divergence of the plasma currents. Coupled plasma‐neutral fluids using a neutral diffusion approximation show promise for recycling calculations. Impurity transport based on full multifluid treatment along the field lines has shown good agreement with divertor experiments.

Advanced topics for the near future include plasma core‐edge transport coupling and eventually the direct solution of coupled momentum equations rather than the presently assumed cross‐field ‘anomalous’ flux functions. In the edge region, plasma sheath boundary conditions are a significant sink for plasma particles and heat; a small coupling between the momentum components in the plasma edge can be sufficient to drive an ‘anomalously’ large efflux from the core plasma.
Sensitivity of Divertor Operating Conditions on Plasma Parameters in a Next Step Device
Authors: D'haeseleer W. D. , Pacher H. D. , Pacher G. W.
Published: July 2007

Divertor power loads and electron temperatures, obtained numerically using the Braams Plasma Edge Code, B2, are reported and interpreted for the parameter range of a Next Step device. A guideline for terminating a B2 run is proposed: the power balance should follow a ‘strict’ exponential decay when the plasma is approaching its final state. Evidence is presented that erroneous solutions can be obtained if this is not the case. A comparison of results for imposed core density (at fixed plate porosity) and imposed core particle flux (with plate porosity adjusted to match this flux) is made. It is found that external pumping has no effect as long as the flux removed at the divertor plate stays in the range of a few tenths of a percent. We document the effect of an adhoc fluxlimiter. It is shown that similar ‘low’ plasma temperatures can be obtained without a flux limiter, by a small increase of the upstream density, and that the scaling relations are unaffected.
Propagation of Multidimensional Ion‐Acoustic Waves in Multicomponent Plasmas with Negative Ions
Authors: Das G. C. , Sen K. M.
Published: July 2007

We made an attempt to study the propagation of multidimensional ion‐acoustic waves in multicomponent plasmas that include negative ions by deriving a Kodomtsev‐Petviashvili (K‐P) equation. The negative ions, as expected, introduce the precursor on the propagation because of which the need arises to derive a modified K‐P equation with higher order non‐linearity. We have examined a number of solitons like waves and supported the results by numerical simulation. The results reveal the existence of compressive and rarefactive solitary waves which are comparable with those of one‐dimensional solitary waves in plasmas with negative ions except that multidimensional propagation of ion‐acoustic waves is more involved than unidirectional propagation.
Experimental Analysis of a Low Frequency Instability in a Magnetized Discharge Plasma
Authors: Gyergyek T. , Čerček M. , Jelič N. , Stanojevič M.
Published: July 2007

In the paper we present the results of an investigation of a low frequency (30‐100 kHz) instability in a weakly magnetized discharge plasma. The instability is triggered by a disc electrode which terminates the magnetized plasma column and is biased above the plasma potential. Frequency dependence on various parameters, e.g. electrode diameter, electrode bias, neutral gas pressure and plasma density is measured. Space and time dependence of the plasma potential and density in the perturbed region during one period of the electrode current oscillation are measured. During the phase of the current decrease a potential structure moves in axial direction from the edge of the perturbed region towards the electrode. During the phase of current saturation the motion of ions is mostly radial. The observed phenomenon is approximately modeled as a two dimensional potential relaxation instability (PRI).
Investigation of Chaotic States in a Neon Gas Discharge by Estimation of Dimensions and Correlation Functions
Authors: Weltmann K.‐D. , Deutsch H. , Unger H. , Wilke C.
Published: July 2007

Investigations in a periodically driven neon glow discharge show that the occurrence of bestabilities can lead to chaotic states. These states are caused by wave phenomena. Characterizing this behaviour by means of the autocorrelation and the crosscorrelation function without the knowledge of the power spectra can imply false interpretations. These are due to the different dissipation of the fluctuations synchronous with the phase‐shifted excitation. It is demonstrated that much information obtained from a large set of data is needed for a reliable evaluation of the dynamics of chaotic states.
Nonlinear Surface Waves in a Strongly Inhomogeneous Plasma
Authors: Lundberg J.
Published: July 2007

A nonlinear Schrödinger equation which governs the slow modulation of high‐frequency surface waves is derived. This evolution equation is obtained from a nonlinear dispersion relation, derived for a weakly nonlinear semi‐infinite cold plasma, where effects of the finite transition layer are taken into account. The fact that the surface wave frequency coincides with the local plasma frequency somewhere inside the transition layer results in a strongly peaked electric field and a significant modification of previously derived dispersion relations assuming a sharp boundary. The consequences of the weakly nonlinear assumptions are discussed.
Collisionless Currents for Cylindric Probes in a Plasma with non‐Maxwellian Distribution of the Electron Energy
Authors: Rohmann J. , Klagge S.
Published: July 2007

The radial model developed by Allen, Boyd, Reynolds and Chen [1, 2] for the ion collection of Langmuir probes is extended to describe the case of a non‐Maxwellian distribution of the electron energy. Assuming standard distributions, showing with respect to the Maxwell distribution an increasing deficite of fast electrons as the parameter k of the distribution increases, the electron‐retarded current characteristic, the potential distribution and the density profiles for electrons and ions in the probe sheath, ion‐current characteristics as well as graphs for the ion‐density determination are calculated for different k. It is shown, that the application of the Chen model (k = 1) in plasma with k > 1 leads only to a small error in the ion‐density measurement.
ηi‐Mode Related Properties of Collisionless Anisotropic Plasmas
Authors: Korn J. , Schamel H.
Published: July 2007

An extended eigenvalue problem for collisionless electrostatic driftwaves in cylindrical and slab geometry is discussed and solved in local approximation. The fact of a minimum threshold for the ITG instability (ηi‐mode) is used to get a unique concept for profile determination.
Rate Coefficients for Dense Hydrogen and Alkali Plasmas
Authors: Bornath Th. , Ohde Th. , Rietz V. , Schlanges M.
Published: July 2007

On the basis of quantum statistical theory, collisional rate coefficients are calculated for nonideal hydrogen and alkali plasmas. A brief discussion is given for plasmas in strong electric fields.
Two Particle Bound States in Dense Plasmas
Authors: Arndt S. , Seidel J. , Kraeft W. D.
Published: July 2007

Bound state energies and continuum edges are calculated for densities up to the Mott density with the help of an effective wave equation for two particle states in (dense) hydrogen plasmas derived in the framework of the Green's function method. The dielectric function describing the surrounding medium is used in Random Phase Approximation.
Molecular Dynamic Simulations of Strongly Coupled Plasmas
Authors: Zwicknagel G. , Klakow D. , Reinhard P.‐G. , Toepffer C.
Published: July 2007

Molecular dynamic computer simulations are used to investigate strongly coupled plasmas. We present some aspects of the simulation technique and some results concerning the stopping power of heavy ions in electron plasmas and the three‐body recombination in two‐component plasmas. Furthermore we briefly discuss the developement of a wave‐packet simulation technique to account for quantum corrections.
Analytic Properties of The OCP Ionic Mixtures in the Strongly Coupled Fluid State
Authors: Dewitt Hugh E.
Published: July 2007

Exact results for the Madelung constants and first order anharmonic energies are given for the inverse power potentials with the Coulomb potential as the softest example. Similar exact results are obtained using the analysis of Rosenfeld on the Γ →∞ limit for the OCP internal energy, direct corelation function, screening function, and bridge functions. Knowing these exact limits for the fluid phase of the OCP allows one to determine the nature of the thermal corrections to the strongly coupled results. Solutions of the HNC equation modified with the hard sphere bridge function give an example.
Electron transport with ion demixing
Authors: Deutsch C. , Leger D.
Published: July 2007

This paper is devoted to a systematic investigation of linear transport properties in strongly coupled binary ionic mixtures of pointlike ions interacting solely through Coulomb interactions. The basic formalism rests upon suitable extensions of the Boltzmann‐Ziman equation. Calculations are performed within binary ionic mixture (BIM) and polarized BIM (PBIM) frameworks respectively. We emphasize out the electron electric resistivity behavior investigated in the vicinity of critical ion demixing.
Plasmons and Instabilities in Quantum Plasmas
Authors: Bonitz M. , Binder R. , Scott D. C. , Koch S. W. , Kremp Dietrich
Published: July 2007

Collective 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.
Excess Electron Coupled With Dense Gases and Liquid
Authors: Iakubov I. T.
Published: July 2007

A pseudo—potential theory is developed of electron states in dense highly polarized media. Electron mobility, the bottom of the conduction zone and an effective mass are calculated and compared with experimental data.
Exploring Dense Plasma by Laser Compression. A simulation study
Authors: Aoki T. , Hüller S. , Meyer‐ter‐Vehn J.
Published: July 2007

A 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

We 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

We 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

Bohm'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

It 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

The 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

We 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

A 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

The 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

A 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

Analysis 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

A 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

Arc 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

The 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

The 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

Experimental 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

The 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

We 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

Measurements 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

The 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

The 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

Interferometric 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

It 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

Kinetic 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

Radiative 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

A 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.
Radiative Divertor Modelling for ITER and TPX
Authors: Braams B. J.
Published: July 2007

The 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

Neon 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.
Divertor Plasma Detachment: Present Status of Understanding
Authors: Krasheninnikov S. I.
Published: July 2007

We consider the main features of plasma detachment and try to find the most natural way to explain them. In general, we focus more on the qualitative analysis of the problem, illustrating the physics of the processes, rather than discussions of particular solutions of the plasma transport equations.
Neutral Atom Transport
Authors: Stacey W. M. , Thomas E. W. , Mandrekas J. , Evans T. M. , Rubilar R.
Published: July 2007

Summaries of recent and ongoing work on two neutral particle transport methods and of an evaluation and sensitivity analysis of the D data are presented.
Transport theory in self‐similar variables for neutrals atoms in an edge plasma
Authors: Helander P. , Krasheninnikov S. I.
Published: July 2007

A 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

The 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

The 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

The 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

A 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

Global 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

The 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.