bluuebunny/crossref_metadata_2025_split huggingface dataset:
Gravitational Instability of a Two‐Component Viscous Plasma with Finite Conductivity Flowing Through a Porous Medium with Fir Corrections
Authors: Vaghela D. S. , Chhajlani R. K. 
Published: July 2007

AbstractThe gravitational instability of a two component plasma is studied to include the simultaneous effects of collisions, gyroviscosity, finite conductivity, viscosity and porosity of the medium within the framework of two‐fluid theory. From linearized equations of the system, using normal mode analysis, the dispersion relations for parallel and perpendicular directions to the magnetic field are derived and discussed. For longitudinal wave propagation it is found that the value of critical JEANS' wave number increases with increasing density and decreasing temperature of the neutral component. For transverse wave propagation the value of critical JEANS' wave number depends on gyroviscosity, ALFVÉN number, ratio of sonic speeds and densities of the two component and porosity of the medium. It is observed that the effect of magnetic field and porosity is suppressed by finite condutivity of the plasma and similarly the effect of gyroviscosity is removed by viscosity from JEANS' expression of instability.For both the directions instability is produced when the velocity perturbations are considered parallel to wave vector. The damping effect is produced due to collisional frequency, permeability of the porous medium and viscosity. The density of the neutral component and porosity of the medium tends to destabilize the system while an increased value of FLR corrections leads the system towards stabilization.
Study of Dynamics of Plasma Produced due to Self‐Focussed Laser Beam on a Cylindrical Target
Authors: Vyas P. , Srivastava M. P. 
Published: July 2007

AbstractThe variation of density and flow speed of ions in a laser produced plasma as function of the intensity of the wave for different beam width parameter is studied. It is found that self‐focusing of the beam increases the density and decreases the velocity in the overdense region whereas it decreases the density and increases the velocity in the underdense region.
Non‐Equilibrium Heating of Molecular Gases
Authors: Pustogarov A. V. , Karabut A. B. , Yegorov V. E. , Kucherov Y. A. R. 
Published: July 2007

AbstractThe results of non‐equilibrium heating of air, carbon dioxide, nitrogen in a plasmatron with porous arc channel at intense gas blow are presented. The investigations are performed in the current range 100–500 A, at the gas pressure being higher than atmospheric. The deviation from the equilibrium conditions in the flow behind the plasmatron for air and carbon dioxide is evaluated by reaction products of nitrogen oxides synthesis and carbon dioxide conversion outputs. It is shown that these processes have non‐equilibrium mode and it can explained by an increased products output. For nitrogen the excess of the vibrational temperature Tv over the translational T is defined by the laser probe method (at T = 1500 K Tv = 3000 K).
Untersuchungen des Starkeffektes bei Hohen Feldstärken
Authors: Jäger H. , Windholz L. 
Published: July 2007

AbstractDer vorliegende Artikel befaßt sich mit dem statischen Starkeffekt bei Feldstärken oberhalb von einigen hundert kV/cm. Im Vordergrund stehen dabei Untersuchungen von nicht wasserstoffähnlichen atomaren Systemen. Nach einer Beschreibung der heute verwendeten apparativen Anordnung zur Realisierung derartiger Felder wird anhand der Ergebnisse von Untersuchungen an Edelgasatomen (vorzugsweise Neon) gezeigt, wie sich auf der Basis umfangreicher experimentell gewonnener Daten allgemein gültige ‘Regeln’ über die meist sehr komplizierten Verhaltensweisen von Starkeffekt‐Niveaus aufstellen lassen. Des weiteren wird gezeigt, wie die gemessenen Verschiebungen über weite Feldstärkebereiche hin in relativ einfacher Form analytisch beschrieben und dokumentiert werden können. Darüberhinaus wird auf das Problem einer brauchbaren Nomenklatur für die Starkeffekt‐Niveaus hin‐gewiesen und vorgeschlagen, dafür jeweils einen Satz geeigneter Quantenzahlen zu verwenden. Dies setzt allerdings eine adäquate theoretische Beschreibung der jeweiligen Starkeffektzustände voraus.
Ion Flux from the Cathode Region of a Vacuum Arc
Authors: Miller H. Craig , Kutzner J. 
Published: July 2007

AbstractThis paper reviews the properties of the cathode ion flux generated in the vacuum arc. The structure and distribution of mass erosion from individual cathode spots and the characteristics of current carriers from the cathode region at moderate arc currents are described. An appreciable ion flux (∼10% of total arc current) is emitted from the cathode of a vacuum arc. This ion flux is strongly peaked in the direction of the anode, though some ion flux may be seen even at angles below the plane of the cathode surface. The observed spatial distribution of the ion flux is expressed quite well as an exponential function of solid angle. The ion flux is quite energetic, with average ion potentials much larger than the arc voltage, and generally contains a considerable fraction of multiply‐charged ions. The average ion potential and ion multiplicity increase significantly for cathode materials with higher arc voltages, but decrease with increasing arc current for a particular material.The main theories concerning ion acceleration in cathode spots are the potential hump theory (PH), which assumes that all ions are created at the same potential, and the gas dynamic theory (GD), which assumes that all ions are created with the same flow velocity. Experimental data on the potentials and energies of individual ions indicates that these theories in their original forms are not quite correct, however extensions or modifications of the PH and GD theories seem very likely to be able to predict correct values for the charge states, potentials, and energies of individual ions.
Effects of Finite Magnetic Field and Ion Motion on Solitary Space Charge Waves
Authors: Ghosh B. 
Published: July 2007

AbstractA KDV equation is derived to describe the weakly nonlinear behaviour of electron plasma waves propagating along a plasma‐filled cylindrical waveguide immersed in an external strong but finite axial magnetic field. Solution of the KDV equation shows that the soliton properties depend significantly on the strength of external magnetic field as well as on ion motion.
Thermal Effects on K‐dV Solitons Existing at the Critical Density of Negative Ions in Ion‐Beam Plasmas
Authors: Das G. C. , Ibohanbi‐singh K. H. 
Published: July 2007

AbstractIon‐acoustic solitons in a generalized multicomponent plasma are studied through the derivation of Korteweg‐de Vries (K‐dV) equation. The negative ions and ion‐beams play quantitatively various roles on the existence of solitons in the plasma. Especially, the critical density introduced by the negative ions exhibits the existence of a large amplitude soliton in plasmas and due to which a derivation of a modified K‐dV (mK‐dV) equation is needed. By taking the higher order nonlinearity in the plasma, the transition of the K‐dV equation to the mK‐dV equation is also shown. Moreover, various models of the plasma due to the non‐isothermality are also considered in the discussions. Further study closely related to the stability of the soliton is made and yields the salient features of the solitons.
Generation of Extra‐Ordinary Mode Radiation by an Electrostatic Pump in a Two‐Electron‐Temperature Plasma
Authors: Hasan Zehra , Guha S. 
Published: July 2007

AbstractCoherent 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

AbstractResults 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

AbstractThe 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

AbstractA 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

AbstractAn 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

AbstractThe 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

AbstractAn 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

AbstractThe 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

AbstractDivertor 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

AbstractWe 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

AbstractIn 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

AbstractInvestigations 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

AbstractA 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

AbstractThe 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

AbstractAn 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.
Two Particle Bound States in Dense Plasmas
Authors: Arndt S. , Seidel J. , Kraeft W. D. 
Published: July 2007

AbstractBound 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

AbstractMolecular 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

AbstractExact 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

AbstractThis 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.