bluuebunny/crossref_metadata_2025 huggingface dataset:
Excitation of the Potential Relaxation Instability in a Weakly Magnetized Discharge Plasma by a Voltage Step
Authors: Gyergyek T. , Čerček M. , Stanojević M.
Published: July 2007

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

The disequilibrium between the temperatures (excitation, rotation, vibration, translation) in plasmas lead us to specific chemical potentials. Then, they are used to develop a mass action law in a multitemperature plasma. This mass action law enables us to determine the composition of a pure nitrogen mixture out of thermal equilibrium.

The composition evolution versus time is determined from a kinetic method modified to take into account different temperature hypotheses.

The composition and different thermodynamic properties of a pure nitrogen mixture are given at the chemical equilibrium, then versus time for various temperature hypotheses and thermal disequilibriums.
Calculation of the X‐Ray Absorption Fine Structure in Shock‐Compressed Matter
Authors: Frey H.‐D. , Meyer‐ter‐Vehn J.
Published: July 2007

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

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

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

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

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

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

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

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

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

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

A Monte Carlo simulation code is described that is suitable for modelling low‐pressure glow discharges that possess cylindrical symmetry, but are of otherwise completely variable geometry. In this single‐particle simulation in 3 space and 3 velocity dimensions, an entire discharge including the cathode fall can be modelled with or without magnetic fields of arbitrary shape. Electric and magnetic fields are given externally and are not adjusted self‐consistently. Collision processes are modelled in great detail, and cathode sputtering phenomena are also included in the simulation.

This simulation code is applied to hollow cathode discharges with and without superimposed magnetic fields and to a Penning discharge. Exemplary results are shown that include density profiles of cathode‐sputtered atoms, energy distribution functions of electrons and cathode sputtering effects for a Penning discharge. Comparisons to results from experiment and other simulations are given.
Scattering Cross Sections and Electrical Conductivity in Fully Ionized Hydrogen Plasma
Authors: Nurekenov Kh. T. , Baimbetov F. B. , Redmer R. , Röpke G.
Published: July 2007

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

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

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

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

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

Detailed edge plasma modeling in the presence of moving fronts requires adaptive meshes. We use an adaptive anisotropic triangular mesh generator for solving a steady state 2‐D anisotropic nonlinear conduction problem with strongly nonlinear sinks. This equation can be thought of as a simplified scalar model of energy transport in a scrape‐off layer (SOL) plasma, under the action of ionization and/or impurity losses. The problem is solved with finite elements using a triply nested loop of iterations.
Investigation of the Radiation Mechanism of Microwave Excited Cluster Lamps
Authors: Heintel M. , Neiger M. , Scholl R.
Published: July 2007

Experimental and theoretical investigations towards a better understanding of the radiation mechanisms in WO2Br2‐discharges, so‐called “cluster lamps” are presented. The main purpose of the investigation is to find out whether a major part of the continuum emitted from these discharges, which in the past has been interpreted as thermal cluster radiation, could also originate from molecular band radiation, in particular from triatomic molecules in colder discharge regions. Comparing emission spectra of WO2Br2‐discharges from different plasma regions, using lamps operated at different vapor pressures and power levels (i.e. non‐LTE and LTE‐discharges), we conclude that by far the major part of the strong continuum radiation emitted from WO2Br2 lamps is indeed thermal radiation of hot tungsten cluster particles. WO— (below 550 nm) and WO2‐molecular radiation (above 650 nm), which is superimposed on the cluster continuum, also contribute to the total radiation output, but to a lesser degree. A crude model for WO2 molecular emission is presented. Unfortunately, the WO2 emission component greatly impedes proper fitting of the measured cluster continuum to a thermal cluster model.
Modal and Focusing Properties of Plasma Based Waveguides for X‐Ray Beams
Authors: Kukhlevsky S. V. , Kozma L.
Published: July 2007

Modal and focusing properties of the plasma based waveguide having a parabolic profile of the electron density are treated for x‐ray beams with the ray‐transfer and paraxial‐envelope equations. Conditions on the single mode, multimode and leaky mode propagation in straight and tapered plasma channels are evaluated. The near‐ and far‐field patterns of these modes are calculated. The main result is that the mode structure is guide length and wavelength dependent, resulting in the guide length and wavelength dependent conditions for the guiding and focusing. The modal analysis finds its application in the field of x‐ray lasers, extremly high harmonic generation and x‐ray beam focusing, in which it may be helpful to design guides for optimum beam propagation. Futhermore, the mode properties are extremly simple and provide an idealised model for the real plasma waveguides.
Highly Ionised Carbon in Capillary Discharge Plasma
Authors: Föurster A. , Beule D. , Conrads H. , Ebeling W.
Published: July 2007

Spectroscopic data indicate that fully ionised carbon ions occur in capillary discharge experiment using a polyethylene tube. On the basis of the simultaneously obtained data for electron density and temperature we calculate the charge‐state distribution. The theoretical model takes into account several dense plasma effects and yields the detailed composition of the polyethylene plasma over time. For typical densities of the discharge plasma a temperature of ≥ 30eV/kB is shown to be sufficient to generate a substantial amount of fully ionised carbon.
Shock‐Compression Experiments and Reflectivity Measurements in Deuterium up to 3.5 Mbar using the Nova Laser
Authors: Collins G. W. , Celliers P. M. , Gold D. M. , Da Silva L. B. , Cauble R.
Published: July 2007

We report on measurements of the equation of state and optical reflectivity at 1064 nm wavelength of a high pressure shock front propagating through a sample of liquid deuterium. We find that the shock front reflectivity increases from a low value (< 3.5%) to a saturation level of 65% in the pressure range of 0.22 ‐ 0.55 Mbar. The pressure range where this metallization transformation takes place coincides with the pressure range where high compressibilities were observed on the principal Hugoniot.
Model for Shock‐Compressed Liquid Deuterium
Authors: Ross M.
Published: July 2007

The equation of state of dense liquid deuterium has been calculated using a model in which the Helmholtz free energy is approximated as the composition average of the free energy of pure molecular and metallic hydrogen. The composition is determined by free energy minimization. Calculations for shock‐compressed liquid deuterium are in good agreement with experiments to a pressure of 2.1 Mbar. At about 1 Mbar and 20000 K, liquid deuterium is 90 % dissociated and is a nearly liquid degenerate metal. The model predicts that molecular dissociation will lead to negative values of (∂P/∂T)v in the range 4000 K to 10 000 K and volumes below 7 cm3/mol. This feature suggests the formation of covalently bonded species in the partially dissociated mixture.
Generalized Kadanoff–Baym Theory for Non–Equilibrium Many–Body Systems in External Fields. An Effective Multi–Band Approach
Authors: Bonitz M. , Kwong N. H. , Semkat D. , Kremp D.
Published: July 2007

The Kadanoff‐Baym approach (two‐time nonequilibrium Green's functions approach) is extended to charged particle systems in external fields. It is shown that its combination with an effecive multi‐band picture

This concept was first presented at the German Physical Society (DPG) Spring meeting, Regensburg, March 1998 [1].

yields a powerful theoretical and numerical method to describe correlated many‐body systems in nonequilibrium.
Wave Packet Molecular Dynamics Simulations of Hydrogen Near the Transition to a Metallic Fluid
Authors: Knaup M. , Reinhard P.‐G. , Toepffer Ch.
Published: July 2007

Recent multiple‐shock experiments of hydrogen at very high pressures show a transition from nonconducting to metallic behaviour at about 140 GPa and a temperature of approximately 3000 K [1].

We simulate hydrogen at various densities and temperatures in the region of this transition. As a theoretical tool we employ “Wave Packet Molecular Dynamics” simulations. This method was originally used by Heller for a description of the scattering of composite particles like simple atoms and molecules [2]; later it was applied to Coulomb systems by Klakow et al. [3]. From the simulations we can extract for example energies, pressure, structure information like pair‐correlations and auto‐correlation functions of current and velocity as well as the resulting transport coefficients.

In this work we show the equation of state and proton‐proton pair correlation functions for a constant electron number‐density n = 2.016 × 1029m−3 (rs = 2). We compare our results with other theoretical approaches: Path Integral Monte Carlo simulations of Magro et al. [5], Tight Binding Molecular Dynamics calculations of Lenosky et al. [7], and analytical approaches via dissociation model by Nagel et al. [8] and the linear mixing model by Ross [9].
The Long‐wavelength Limit of the Dielectric Function for Dense Plasmas
Authors: Reinholz H. , Redmer R. , Röpke G. , Wierling A.
Published: July 2007

The dielectric function of a system of charged particles is investigated for arbitrary degeneracy within a linear response theory. This approach allows for inclusion of collisions, thus going beyond the RPA and treating the electrical conductivity in consistency with the dielectric function. A general expression for the collision integral in the whole (k, w) plane is presented. Special attention is given to the long‐wavelength limit deriving a frequency‐dependent collision term. In the limit k = 0 and w = 0, the Ziman formula for the electrical conductivity in metallic systems is reproduced. By inspection of the high‐frequency limit, it is shown that the third moment of the response function is in accordance with the well‐known third moment sum rule.
Thermodynamic Properties of Dense Plasma of Shock—Compressed Metals
Authors: Gryaznov V. , Iosilevski I. , Fortov V. E.
Published: July 2007

Quasi‐chemical representation (“Chemical Model”) was extrapolated for description of thermodynamic properties of plasma of shock compressed extra‐foam nickel and iron samples. Modified Coulomb correction [High Temperature, 18 (1980) 447], was generalised for the case of multiply ionised partially degenerated hot dense plasmas. Intensive short‐range repulsion of heavy particles (atoms and ions) and electron degeneracy was taken into account in combination with simplified form of “Cold Additive”. Satisfactory agreement of theory and experiment was obtained for nickel and iron Hugoniots. This agreement proved to be valid when the approximation was extrapolated into the region of extra‐dense plasma of highly compressed solid iron.
Relaxation of Background Electrons and Ions in Plasma Crystals
Authors: Chutov Yu. , Schram P.
Published: July 2007

The Liouville equation is considered for the statistical system consisting of identical constructureless free particles and grains initially. It relaxes then due to a collection of the particles by the grains. Dusty plasmas are particular cases of this system. The free and collected particles are considered as a common sub‐system which is described by the common whole distribution function. It is shown that this sub‐system is described by the complex integral‐differential equation which can be expected to lead to Non‐Markovian kinetics.

Computer modeling shows that background electrons and ions can be non‐ideal components of relaxing dusty plasmas in plasma crystals due to the intensive charge exchange of electrons and ions with dust particles even in the cases where their numbers in the Debye cube are large. The selective collection of electrons and ions by dust particles causes their deviation from the initial equilibrium as well as the non‐equilibrium evolution of the self‐consistent electric potential and electric charge of dust particles.
Kinetic Theory for the OCP Crystal
Authors: Dufty J. W.
Published: July 2007

The problem of formulating a kinetic theory for systems with possible broken symmetry is considered. It is shown that to a large extent fluid and crystal phases can be treated on a common ground, with the primary differences occuring via the continuum fields of hydrodynamics or elasticity.
Molecular Dynamics Simulations of the Dynamics of Correlations and Relaxation in an OCP
Authors: Zwicknagel G.
Published: July 2007

The short time dynamics of the transition from an initial nonequilibrium state to an equilibrium state is investigated for an OCP by molecular dynamics (MD) simulations. Two different initial configurations are considered which allow to study either the build‐up of binary correlations or the relaxation of the single particle distribution. For a weakly coupled plasma the observed time scale for relaxation is much longer than the characteristic time for the correlation build‐up while the two time scales become equal for nonideal plasmas with Γ > 0.5.
Conductivity Measurements of Nonideal C Plasmas
Authors: Haun J. , Kunze H.‐J.
Published: July 2007

We report measurements of the conductivity of nonideal C‐plasmas. They are produced by evaporating a carbon‐wire placed in a capillary within some hundred nanoseconds. Homogeneity of the plasma is obtained by the use of a ‘pre‐heating‐system’ which heats the wire before the main discharge. This way the initial resistivity of the wire is decreased, the discharge time is shortened. The reproducibility of the plasma is enhanced, the growth of instabilities is reduced. The conductivity is measured during 1 ms of the discharge. The particle density is of the order of 1022 cm−3 while the electron temperature is varying between 8000 K and 25000 K, the electron density is about 1018 cm−3. The temperature is measured spectroscopically by fitting a Planck curve to the spectrally resolved emission profile. The results are compared with theories from Spitzer, Ziman and the SESAME‐data.
Current Jumps and Hysteresis in a Single‐ended Q‐Machine in Connection with the Electrostatic Ion‐Cyclotron Instability
Authors: Avram C. , Schrittwieser R. , Sanduloviciu M.
Published: July 2007

We report on an investigation in a single‐ended Q‐machine where the current‐voltage characteristic of a small collector showed some interesting new features. The most interesting of these was a sudden jump of the current at the onset of the electrostatic ion‐cyclotron instability. This jump was also accompanied by hysteresis. Besides that, the characteristic showed another trivial type of hysteresis that was only due to a temporary covering of the collector by alkaline metal from the plasma. The former phenomenon could be an indication that the well‐known nonlinear potential structures that appear periodically in front of the collector during a cycle of a high‐amplitude electrostatic ion‐cyclotron instability, are related to inelastic collisions of accelerated electrons with alkaline vapour present in the plasma column.
A Comparative Study of Single and Double Langmuir Probe Techniques for RF Plasma Characterization
Authors: Castro R. M. , Cirino G. A. , Verdonck P. , Maciel H. S. , Massi M. , Pisani M. B. , Mansano R. D.
Published: July 2007

In this study, the plasma density and electron temperature of Radio Frequency (RF) plasmas were determined by three types of Langmuir probes, namely a conventional double probe, a single probe with RF choke and a single probe with RF choke and compensating electrode. The same plasmas were characterized by the three probes, each performing three measurements per plasma condition, in order to determine the precision of the measurement results. After performing a comparative analysis, which looked at the precision and the accuracy of these results, the conclusion is that the double probe, which has already the advantage of the simplest construction, yields the most reliable results for both capacitively and inductively coupled RF plasmas. The single probe with RF choke and compensating electrode has a similar precision as the single probe without compensating electrode, but its accuracy is better.
Quasiclassical Statistical Thermodynamics and New Padé Approximations for the Free Charges in Strongly‐Coupled Plasma
Authors: Ebeling W. , Stolzmann W. , Förster A. , Kasch M.
Published: July 2007

HNC equations in combination with effective quasi‐classical potentials are used to calculate correlation functions and the thermodynamic properties of the free charges in semi‐classical non‐degenerate quantum plasmas. The interactions of the free particles are taken into account via effective potentials obtained from the Slater sum method. Analytical formulae reproducing the known limits and the HNC‐results are constructed. Finally quantum effects are included as corrections by using known analytical results. This method is used to develope new Padé approximations for the subsystem of the free charges in mass‐symmetrical as well as for mass‐unsymmetrical hydrogen‐like plasmas. The most essential result of our investigations is, that in the classical limit the scaling properties correspond to the OCP, e.g. the thermodynamic functions follow for large coupling strength Γ a Berlin‐Montroll‐Rosenfeld asymptotics via a Γ + b Γv + c ln Γ + d. Including quantum effects, the coefficients depend on the temperature, e.g. the slope a(T) increases with decreasing T converging to the classical limit. The new formulae are compared with earlier variants.
The Ponderomotive Force on a Charge q, Moving in an Electromagnetic Field
Authors: Kildal A.
Published: July 2007

Equations of motion of a single charged particle are derived to second order in E where E is an electromagnetic field. By averaging over the wave‐period we find the ponderomotive force on the particle. This force may lead to a transport of matter as is also the case in ordinary hydrodynamics. There the effect is called acoustic streaming. We also suggest that the well‐known Landau damping may be considered as beeing due to a ponderomotive force.
Ion Temperature Measurement in the Edge Region of SINP Tokamak by a Retarding Field Analyser
Authors: Raychaudhuri S.
Published: July 2007

Based on the principle of retarding field analyser an ion energy analyser has been developed for the measurement of ion temperature in the edge plasma region of the SINP tokamak. This has been used to determine the dependence of the ion temperature on the safety factor q in the normal q region (q=2 to 4), plasma current, plasma electron temperature and also the Spitzer resistivity.
Thermal Plasmas for Material Processing
Authors: Henne R.
Published: July 2007

Plasma technologies have undoubtedly gained high importance due to their outstanding properties and they have found a large field of scientific and technical applications. Thermal plasmas with temperatures of around 10,000 K and more are particularly suitable for material processing, e.g. for melting, cutting, welding or coating. They are also of increased interest in waste destruction or material synthesis. Following some remarks about the definition of “thermal plasmas” and their generation some representative examples of applications are described in more detail together with considerations about the relevant technical and economic importance at present and potentially in future.
Effects of Energetic Electrons on Collector and Source Potentials in a Finite Ion Temperature Plasma
Authors: Čerček M. , Gyergyek T. , Stanojević M.
Published: July 2007

Formation of the potential in a two‐electron‐temperature plasma region facing a floating collector was studied theoretically with a kinetic plasma‐sheath model and by electrostatic particle simulation. The electrons were described by truncated full Maxwellian velocity distribution functions and the ions by an accelerated half‐Maxwellian velocity distribution function. The collector potential and the plasma source sheath or presheath potential drop were evaluated as functions of the hot to cool electron temperature ratio and the hot electron density ratio using Vlasov and Poison equations. The results showed that the presheath potential drop varied continuously with electron composition ratio for lower values of the electron temperature ratio, while for higher values in a narrow composition ratio range, triple values of the potential were found. Of the two physically acceptable values, the lower was characterized by the cool electrons and the higher by the hot electrons. It is anticipated that a current‐free double layer structure is formed in the plasma system between these two potential regions. The collector floating potential, as a function of electron composition ratio, is mainly dominated by the hot electrons, since already a small value of hot electron current is sufficient to compensate the ion saturation current. In order to complete the theoretical investigation we also study the hydrogen plasma system with the XPDP1 particule‐in‐cell simulation code composed at Berkeley. At certain plasma parameter values formation of a double layer structure was observed. The potential Values on the upper and lower side of the double layer, as well as that of the collector floating potential, corresponded very well to the calculated values. On the upper side the plasma was composed of ions, accelerated through the source sheath potential drop, and electrons consisting of cool full Maxwellian and hot truncated full Maxwellian populations. On the lower side only hot electrons and ions additionally accelerated through the double layer were found.
The design and installation of the Cleveland, Ohio point‐to‐multipoint CATV fiber‐optic transport system
Authors: Brinkerhuff William C.
Published: July 2007

Analog fiber‐optic transmission system use is becoming commonplace and widespread for point‐to‐point CATV programme channel trunking applications. Owing to improvements in single‐mode fiber, device technologies and availability of single‐mode optical splitter/couplers, it is now technically and economically feasible to implement point‐to‐multipoint CATV trunking systems.

This paper will describe the Cleveland, Ohio point‐to‐multipoint fiber‐optic transport system design, the pros and cons of analog FM versus digital systems, the fiber plant and the end‐to‐end performance of the installed fiber‐optic system.

The multichannel FM/FDM fiber‐optic system deployed by The Ohio Bell Telephone Company (OBT), an Ameritech company, was manufactured and installed by Catel Telecommunications, Inc. of Fremont, California.
Admission control over mixed traffic in ATM networks
Authors: Lombardo A. , Palazzo S. , Panno D.
Published: July 2007

The new techniques for broadband ISDNs, such as ATM, will provide flexible and efficient allocation and bandwidth for communication services. These services may have very different traffic statistics and performance requirements. Therefore, criteria to decide about acceptance of new connection requests into the network must take into account which traffic and performance class connections belong to. This paper proposes a decision rule for admission control over mixed traffic which consists of connections possibly referring to different classes of traffic and performance. The rule, which is derived by approximate analysis, is based on the concept of maximum use of an ATM link. It is shown that it can be applied to a wide range of telecommunication services.
Dynamic capacity management in the BISDN
Authors: Burgin John
Published: July 2007

Use of virtual paths (VPs) in the broadband ISDN (BISDN) presents network operators with the ability to make processing intensive resource management decisions for flows of traffic instead of individual connections. Altering the amount of capacity assigned to different VPs provides the ability to reconfigure the network dynamically to respond to changes in traffic demand. This paper studies the dynamic behaviour of some algorithms for assigning capacity to VPs for a range of time‐varying offered traffic inputs.
An approach to controlling congestion in ATM networks
Authors: Eckberg A. E. , Luan D. T. , Lucantoni D. M.
Published: July 2007

Determining approaches to congestion and flow control, especially real‐time components in an overall strategy, is recognized as one of the fundamental challenges facing broadband ‘packet‐based’ information transport, as, for instance, in the case of BISDN/ATM, In this paper we summarize basic issues underlying this subject, and describe a particular approach to achieving a multilayer broadband congestion, flow and error‐control architecture, based on a ‘core’ congestion control strategy that we term bandwidth management. The modular and layered nature of this control architecture is described, and shown to lend itself to a structured approach to characterizing the control architecture performance.
CATV fibre‐optic supertrunking: A comparison of parameters and topologies using analog and/or digital techniques
Authors: Borelli Vincent R. , Gysel Hermann
Published: July 2007

Fibre‐optic supertrunking has a well‐established place in larger CATV networks. Supertrunks have to be transparent to the quality of the transmitted TV signals and they have to have a negligible impact on the system reliability of the total network. At least 60 dB (weighted) video SNR has to be achieved and down times of less than one hour per year per fibre are desirable. AM on fibre can achieve these goals only in shorter supertrunks. FM and digital modulation techniques with a higher loss budget than AM are well suited for high transmission quality as well as for redundant supertrunk topologies, achieving excellent system availability numbers at the expense of increased equipment complexity.
Cable television on fibre in stand‐alone networks and in systems combined with telephony
Authors: Edwards Terry
Published: July 2007

This paper presents details of dedicated cable television systems (stand‐alone cable TV), and combined cable TV/telephony systems, based upon the economic implementation of optical fibre technology. The factors that determine the choice of these two approaches are described and examples are given based upon systems designed by Raynet Corporation. Techno‐economic issues are debated and the need for effective future‐proofing is emphasized. In particular, the critical choice between fibre to the last amplifier (FTTLA) and fibre to the curb (FTTC) is discussed. Architectures are described for trunk and distributed systems and performance characteristics are given for a specific network, optical elements and electro‐optic interfaces. Detailed considerations relating to future developments conclude the paper.
Potential applications of sonet in BISDN customer premises network management
Authors: Kramer M. , Lo C. N. , Salloum H. R. , Wolff R. S.
Published: July 2007

Future broadband customer premises networks (CPNs) may employ synchronous optical network (SONET) transmission, carrying asynchronous transfer mode (ATM) cells, to interconnect intrapremises stations. This prospect, driven by current standardization efforts in ANSI T1 committees and CCITT, can lead to ubiquitous and cost‐effective, high‐speed interfaces capable of supporting a variety of services. Similar to the way they will support operations functions for SONET network elements in future broadband public networks, the embedded overhead channels in the SONET frame structure can assist in management of the CPN. In this paper, we suggest means of supporting CPN management in the functions of network configuration, fault location and notification, and performance monitoring, by taking advantage of the SONET overhead capabilities.
Head of the line arbitration of packet switches with combined input and output queueing
Authors: Iliadis Ilias
Published: July 2007

A single‐stage non‐blockingN × Npacket switch is considered. Data units may be stored before switching at the inputs as well as after switching at the outputs. Some output buffering capacity is intended to achieve high throughput, whereas an additional input buffering capacity keeps losses due to input‐buffer overflow reasonably low. The paper studies the impact on performance of the head of the line arbitration policy, i.e. the sequence which is used to transfer data units from the heads of input queues to each output queue. The investigation is based on two performance measures: the average delay and the maximum throughput of the switch. Closed‐form expressions for the FCFS, LCFS and the ROS policies are obtained. The result of the average delay with the FCFS policy leads to a lower bound, and that with the LCFS policy to an upper bound for the average delay, corresponding to an arbitrary symmetric policy which does not use information related to the state of the input queues. It is shown that the maximum throughput does not depend on the head of the line arbitration policy. It depends only on the output‐buffer size and the packet‐size distribution. The cases of fixed and exponentially distributed packet sizes are studied. The effects of asymmetric policies which result in different behaviours of some of the input queues is also considered.
Analysis of a discrete‐time queue with integrated bursty inputs in ATM networks
Authors: Zhang Zhensheng
Published: July 2007

In this paper, we carry out an exact analysis of a discrete‐time queue system with a number of independent Markov modulated inputs in ATM networks, using a generating function approach. We assume that the queueing system has an infinite buffer with M servers. The cell arrival process is characterized by a number of independent Markov modulated geometrical batch arrival processes. We first obtain the generating function of the queue‐size distribution at steady‐state in vector form, then derive an expression for the average queue‐size in terms of the unknown boundary probabilities. To obtain those unknown probabilities, we use the technique proposed in Reference 1. This involves decomposing the system characteristic function to evaluate the roots and solving a set of linear equations. One of the contributions of this paper is presented in Lemma 1, which characterizes the property of the underlying eigenvalues. For one special case of at least M‐1 cell arrivals during one slot at one Markov state and of at least M arrivals at all other states, the determination of the unknowns is straightforward. If every Markov modulated arrival process can be further decomposed into a number of i.i.d. two‐state, or three‐state, or even four‐state Markov modulated arrival processes, then each root can be obtained separately using an iterative algorithm. Numerical results are presented to validate the proposed traffic models against actual traffic measurements.
Architecture design for ATM statistical multiplexers
Authors: Chao H. Jonathan , Liew Soung C.
Published: July 2007

Both high‐speed packet switches and statistical multiplexers are critical elements in the ATM (asynchronous transfer mode) network. Many switch architectures have been proposed and some of them have been built, but relatively fewer statistical multiplexer architectures have been investigated to date. It has been considered that multiplexers are a special kind of switches which can be implemented with similar approaches. The main function of a statistical multiplexer, however, is to concentrate traffic from a number of input ports to a comparatively smaller number of output ports; ‘switching’ in the sense that a cell must be delivered to a specific output port is often not required. This implies that the channel grouping design principle, in which more than one path is available for each virtual circuit connection, can be applied in the multiplexer. We show that this technique reduces the required buffer memory and increases the system performance significantly. The performances of three general approaches for implementing an ATM statistical multiplexer are studied through simulations with various bursty traffic assumptions. Based on the best performing approach (sharing output channels and buffers), we propose two architecture designs to implement a scalable statistical multiplexer that is modularly decomposed into many smaller multiplexers by using a novel grouping network.
Performance evaluation study of signal design and equalization options for high‐bit‐rate digital subscriber line transceivers
Authors: Krzymien Witold A. , Bilodeau Thomas D.
Published: July 2007

This paper analyses different equalization, coding and signal constellation alternatives for the proposed high‐bit‐rate (800 kb/s) digital subscriber loop transmission interface. The simulation results presented in the paper demonstrate that bit rates above 1000 kb/s at acceptably low bit‐error rates (≤ 10−7) are feasible, if baseband transceivers with appropriate equalization and simple trellis coding are used. It is also shown that baseband transmission and Tomlinson precoding provide a significant performance advantage over bandpass transmission and decision‐feedback equalization, respectively.