bluuebunny/crossref_metadata_2025 huggingface dataset:
Parametric Excitation of Hybrid Modes in Multispecies Plasmas
Authors: Asthana Meenu , Guha S.
Published: July 2007

Nonlinear decay of an electromagnetic wave into lower‐hybrid and upper‐hybrid wave in a plasma containing two types of ions and two temperature electrons has been analytically investigated. Hydrodynamical model of the plasma is used. Nonlinear dispersion relation and growth rates are calculated for parametric decay, modulational and filamentation instabilities. As an application of the investigation growth rates are calculated for typical parameters of both laboratory and space plasmas. Effect of addition of second species of electrons and ions is discussed.
Diffusion in Turbulent Magnetoactive Plasmas
Authors: Meister C.‐V. , Nikutowski B. , Schindler K. , Arendt U.
Published: July 2007

A Langevin equation for charged particles in a plasma with ion‐acoustic turbulence is developed from first principles in consistency with kinetic theory.
Influence of the Argon Pressure at dc Magnetron Sputtering on Contaminations in CrSi Thin Films
Authors: Sobe G. , Schreiber H. , Weise G. , Heinrich A.
Published: July 2007

This paper deals with the influence of process parameters, especially of argon pressure, power, and target‐substrate spacing on impurity content and properties of Cr‐Si thin films deposited by dc magnetron sputtering in a non‐heated high vacuum apparatus. The results confirm the well‐known fact that in such a unit by means of a magnetron pure films can be produced without any difficulties. However, this has proved to be possible only in the case of low argon pressure being preferentially employed in magnetron sputtering. Boosting the argon pressure yields drastic film contaminations by oxygen and hydrogen, which are caused by a reinforced release of adsorbats from the apparatus walls under these operating conditions. A high argon pressure effects simultaneously a change in the film microstructure resulting together with the contaminants in modified electrical properties.
Monte Carlo Simulation of Helium Transport in the Vicinity of Divertor Plate
Authors: Deng B. Q. , Xie Zh. Y. , Shi H. W. , Abou‐gabal H. H. , Emmert G. A.
Published: July 2007

A Monte Carlo code “1DHET” has been utilized for simulating the transport of neutral helium near divertor flat pumping target plate. The dominant atomic processes of electron impact ionization and elastic scattering by plasma ions are included. The thermal and streaming motion of the ions along the magnetic field is taken into consideration. Calculations show that the probability of neutral helium turning back to the target plate will increase by 45% if the divertor edge plasma density is smoothly raised up to 4.7 times higher at the divertor plate than that at 7cm apart inward as compared with the ordinary outward decreasing density profile while keeping temperature profile fixed. The temperature decreases smoothly from 40 eV at z = 7 cm to 3 eV at the plate. The effects of angle between the magnetic field and the target plate, the temperature of plate, edge plasma sheath potential and different target materials on the probability of helium particles scattered back to the plate are studied.
Quantum Statistical Equation of State for Nonideal Dense Plasmas
Authors: Kremp D. , Kraeft W. D. , Schlanges M.
Published: July 2007

An equation of state is derived on the basis of Green's function technique. The formation of bound states is accounted for and the possibility of phase transitions is discussed. The latter is of special interest if it is connected with the vanishing of bound states at high densities, it is then a Mott phase transition.
Calculation of Absolute Outer‐Shell Electron Impact Ionization Cross Sections
Authors: Deutsch H. , Märk T. D.
Published: July 2007

The recently developed semiempirical DM‐approach for the calculation of electron impact single ionization cross sections is applied here to the ionization of the rare gases (Ne, Ar, Kr and Xe) via ejection of an outer s‐shell electron. The results obtained are compared with previous experimental and theoretical s‐shell ionization cross section functions.
Field Line Mapping and Edge Modeling for Helias Configurations
Authors: Strumberger E.
Published: July 2007

Tracing magnetic field lines between divertor plates and characterizing them according to their lengths shows that an ordered‐layer structure of the field lines in the edge region of Helias stellarators prevails. Because of the layer structure these field lines are used as coordinate lines for plasma edge modeling: in a first attempt, the temperature, density and velocity along the field lines are calculated by solving simple 1D particle and energy transport equations along 3D field lines. Combining these 1D calculations with complementary Monte Carlo methods, which allow simulation of transport across the field lines, yields a 3D scrape‐off layer description encompassing parallel and cross‐field transport.
The Role OF Electric Field IN SOL Plasma
Authors: Rozhansky V.
Published: July 2007

A natural electric field in SOL plasma is discussed. It is shown that the potential difference between the relatively hot plasma in SOL and cold plasma near the divertor plates is of order of 2Teh/e, where Teh is the hot plasma temperature. The radial dependence of electron temperature produces the outward directed positive electric field perpendicular to the magnetic surfaces and poloidal E×B drifts.
Kinetics of Tokamak Edge Plasmas: Progress and Problems
Authors: Krasheninnikov S. I.
Published: July 2007

Influence of kinetics effects on plasma transport in the tokamak edge are reviewed. Problems of electron and ion kinetics along and across magnetic field lines, plasma‐neutral interaction and the kinetics of the radiation in dense edge plasmas are considered.
Kinetic Theory of the Lorentz Gas
Authors: Chen Qun , Bernstein Ira B.
Published: July 2007

The steady state kinetic equation for the Lorentz gas, where μ=ex · v/v, has been solved numerically. Analytic approximations have been developed for f(z, v, 0) in the limits of mean‐free‐path long and short compared with the system size. These have been shown to be good, and to provide a useful starting point for the numerical procedure employed, which iterates on f(x, v, 0). Their success suggests that counterpart approximations may work well for more complicated steady state kinetic problems of interest in the physics of the edge in proposed controlled fusion reactors, the diffusion of neutrons, the Brownian motion of heavy molecules, and the structure of shocks. It has also been demonstrated that the determination of f(z, v, 0) can be reduced to the solution of a one dimensional integral equation.
Monte Carlo Simulation of Edge Ion Dynamics in the Presence of Collisions and a Radial Electric Field
Authors: Kurki‐Suonio T. K. , Alava M. J. , Sipilä S. K. , Heikkinen J. A.
Published: July 2007

The dynamics of ions in the vicinity of the last closed flux surface in tokamaks is a topic of current interest because of its significance to the first wall and divertor surfaces as well as to the LH‐transition. In the presence of a radial electric field, the ion trajectories and the structure of the ion phase space are altered. The fields can have secondary effects e. g. through the radial current resulting from the direct ion orbit loss. A Monte Carlo method for studying the edge ion behaviour is presented here. The direct ion orbit loss of the main plasma ions is analyzed under various plasma conditions, and the effect of boundary conditions on direct ion orbit loss is studied.
The Electron Temperature Gradient Instability in Presence of a Limiter with Tilted Plates
Authors: Farina D. , Pozzoli R. , Ryutov D.
Published: July 2007

The analysis of the electron temperature gradient instability in the scrape‐off layer is generalized to the case of non‐orthogonal intersections of the magnetic field with the wall surface, a situation which is most typical for a tokamak with a limiter.
Surface Dissipation Effects in Tokamak Poloidal Divertor Plasmas: Pfirsch ‐ Schlüter Currents and Space Potential Distribution
Authors: Bogomolov L. M. , Sychev V. N.
Published: July 2007

A simple model to describe the influence of surface dissipation (i. e. the end losses) on SOL plasma potential in poloidal divertor tokamak is presented. The model takes into account the topology of divertor configurations and basic characteristics of magnetic lines near separatrix.
Fluid Simulation of Beryllium Transport in the ITER Gaseous Divertor
Authors: Knoll D. A. , Campbell R. B. , McHugh P. R.
Published: July 2007

The transport of either intrinsic or injected impurities will play a crucial role in the energy loss mechanisms in the ITER gaseous/cold plasma target divertor. Both 1‐D and 2‐D multi‐charge state fluid codes are used to model the transport of beryllium in the ITER SOL. Our major conclusion is that in order to model the containment of impurities, the background flow field must be known in detail. Comparing 1‐D and 2‐D solutions, hydrogen flow reversal plays an important role in the entrainment process. Further, the flow of particles from the core plasma also has a strong impact on the resultant entrainment of the impurities in both 1‐D and 2‐D. It is imperative that those components of poloidal velocity due to ExB and diamagnetic drifts be included in the models.
Finite Element Fluid Modeling of a Poloidal Divertor
Authors: Zanino R. , Russo A.
Published: July 2007

The finite element fluid code FELS, which includes an unstructured stretched triangular mesh generator, works now in a realistic (computed or measured) magnetic geometry, as can be provided by any Grad‐Schlüter‐Shafranov solver. Steady state plasma profiles are shown for a portion of the scrape‐off layer in an ASDEX‐Upgrade shot, with significant recycling and model geometry of wall and divertor plate.
Comments on the Self‐focusing of Surface Plasma Waves
Authors: Stenflo L. , Bratukhin A. G. , Gradov O. M.
Published: July 2007

An electrostatic wave propagating on a semi‐infinite plasma is considered in order to estimate the self‐focusing length for surface waves.
Kinetic Nonlinear Buneman's Instability in Field‐Free Isothermal Collisonal Plasma
Authors: Khalil Sh. M. , Sayed Y. A.
Published: July 2007

A nonlinear dispersion relation is derived and solved for a 1‐D electron‐ion two‐stream (Buneman) instability excited in an isothermal field‐free plasma. The major nonlinear mechanism is the qualilinear modification of the background distribution function. We take into consideration the effect of Coulomb collisions which describes the broadening of the Cherenkov interaction of waves with particles. Nonlinear effects seem to lead, in field‐free plasma, to the increase in the current velocity and consequently, to the growth of the instability and a rapid turbulent heating of plasma electrons. The methods used here to solve the Vlasov's kinetic equation may also be used to investigate other types of current micro‐instabilities in plasmas.
Simple Physical Model of Generation of the Low‐Pressure Radio Frequency Supersonic Plasma Jet
Authors: Šicha M. , Bárdoš L. , Tichý M. , Soukup L. , Jastrabík L. , Baránková H. , Soukup R. J. , Touš J.
Published: July 2007

The paper presents a simple theoretical model of the breakdown of the supersonic plasma jet generated by the hollow cathode discharge inside the nozzle in the low pressure RF plasma‐chemical reactor. Through the nozzle which is drilled in the RF electrode the working gas flows to the reactor chamber. If at the outlet of the nozzle the gas flow is supersonic the well defined plasma jet is created inside the reactor chamber. The results of our model are in qualitative agreement with experimental data.
The Influence of Collisions in the Space Charge Sheath on the Ion current Collected by a Langmuir Probe
Authors: Spanel P. , Smith D. , Chudacek O. , Kudrna P. , Tichy M.
Published: July 2007

The current/voltage characteristics of a cylindrical Langmuir probe have been studied in Ar+/electron afterglow plasmas in helium carrier gas under truly thermal conditions at 300 K using our flowing afterglow/Langmuir probe (FALP) apparatus. The orbital motion limited (oml) ion and electron current regions of the probe characteristics have been explored over a wide range of the reduced probe voltage (up to ∼ 100) and over a wide range of electron (ne) and ion (n+) number densities (1.6 × 107 to 1.5 × 1010 cm−3) at a constant pressure of the He carrier gas of 1.2 Torr. The observed increase of the probe ion currents above those predicted by collisionless oml theory, resulting in an apparent increase of the measured ion number density above ne in the plasma, is explained by the enhancement in the ion current collection efficiency due to collisions of ions with neutral gas atoms in the space charge sheath surrounding the probe. The continuous change in the exponent, χ, of the power‐law dependence,i+ ∞ V of the ion current, i+, on the probe voltage, Vp from 0.5 at the highest n+ (smallest sheath) towards 1.0 at the lowest n+ (large sheath) indicates that the ion current collection from the plasma changes from the oml current regime at the high n+ to the continuum regime at the low n+ when the ions undergo multiple collisions with the helium atoms in the space charge sheath and thus “drift” towards the probe.
High‐Frequency Backward Waves in Longitudinally Magnetized Gyrotropic Waveguides
Authors: Alexov E. G.
Published: July 2007

Backward waves in waveguides completely filled with magnetoactive plasma (gaseous or semiconductor plasma) have been investigated numerically. It is shown that two types of backward waves exist in such waveguides: cyclotron backward waves and waveguide HE‐modes. While the cyclotron modes are backward waves at arbitrary system parameters (plasma density, magnetic field and waveguide radius), the waveguide backward waves appear only at certain values of there parameters. In addition the cyclotron backward waves can propagate at arbitrary wave‐number kz and at arbitrary phase velocity. The backward waveguide modes exist only at limited values of kz and of phase velocities.
Collisional Ionization of Excited State Neon in a Gas Discharge Plasma
Authors: Han X. L. , Wisehart V. , Conner S. E. , Su M.‐C. , Monts D. L.
Published: July 2007

We report the first case where it is possible to clearly identify and quantitatively characterize the dominant physical processes contributing to production of the optogalvanic effect (OGE) signal in a discharge plasma. This work concentrates on the simplest case where only two states are involved in the optical transition. The theoretical model with only four parameters is in excellent agreement with the experimentally obtained time‐resolved OGE waveforms. The collisional ionization rate in the upper state is twice as fast as that in the lower state although the two states are only separated by 1.94 eV. We conclude that the optogalvanic effect of the neon 640.22 nm transition is due primarily to the electron collisional ionization of the neon atoms. An alternative interpretation for the lengthening of the final state lifetime is also included (see Appendix).
Single‐ and Two‐Particle Energies and Thermodynamics of Dense Plasmas
Authors: Fehr R. , Kraeft W. D.
Published: July 2007

Single‐ and two‐particle states in dense plasmas differ significantly from those of ideal systems and have especially a finite lifetime. Both the bound states and the continuum edges of two‐particle states are controlled by “complex single‐particle energies”. Furthermore, the thermodynamics can be given by these quantities. For this reason we study the spectral weight function of the single‐particle Green's function and solve the equivalent dispersion relation self‐consistently in the Montroll‐Ward approximation of the self energy. We give results for the continuum edges of a hydrogen plasma and of a model electron‐hole plasma and discuss approximations for the equation of state.
The Particle and Heat Drift Fluxes and their Implementation into the EDGE2D Transport Code
Authors: Radford G. J. , Chankin A. V. , Corrigan G. , Simonini R. , Spence J. , Taroni A.
Published: July 2007

The various particle and energy drift fluxes are presented, and it is shown that the divergence‐free part of the diamagnetic terms do not contribute to the fluid equations. In particular, it is shown that the ∇TxB heat flux (the so‐called Hinton‐Staebler term) cancels exactly from the energy equation. The implementation of the drift fluxes into the EDGE2D code is described and some results of preliminary code runs indicated.
Propagation and Superposition of Cylindrical Rarefactive Waves in a Plasma
Authors: Hansen K. , Piel A.
Published: July 2007

In a collisionless quiet argon plasma, transient density cavities are formed by applying a large amplitude rf pulse to a cylindrical wire antenna. After the end of the pulse, the density cavity breaks up into cylindrical rarefaction waves. Due to the large depression of up to 50%, wave propagation is nonlinear. Numerical models based on a fluid‐description and a generalized Korteweg‐deVries‐equation are presented for the propagation and superposition of the cylindrical waves. The numerical findings are compared critically with the experiments.
Supersonic Jets with Periodic Structure due to Arc plasma Expansion into a Low pressure ambient
Authors: Djakov B. E. , Enikov R. , Oliver D.
Published: July 2007

A supersonic plasma jet was produced by a d.c. arc plasma generator operated at normal pressure and connected to a low‐pressure (p∞ = 0.2‐50 kPa) chamber via cylindrical nozzle with diameter of 2.5 mm. The argon gas flow rate was G = 0.025 to 0.35 g.s−1. In some experiments current IE ≦ 30 A passed coaxially through the initial part of the jet. Photographic records of the jet and pressure measurements are in agreement with theoretical predictions by a simple one‐dimensional, gasdynamical model capable of self‐consistent calculations throughout the plasma source/jet system. Periodic jet structure is observed over a wide range of experimental conditions, incl. in highly under‐expanded flow. The jet expansion angle and Mach disc position vary with p∞, G and IE, but are nearly constant at different arcing currents.
Constraints for the Construction of Kinetic Theories
Authors: Dufty J. W.
Published: July 2007

In the absence of a small parameter for systematic many‐body analysis (e.g., strongly coupled systems), the construction of an appropriate kinetic theory description necessarily has an uncontrolled, phenomenological component. In this context it is useful to identify selective exact properties of the underlying microscopic description to serve as constraints for guidance in the construction of an approximate kinetic theory. We consider here three such properties: 1) exact local conservation laws; 2) exact stationary solutions; 3) exact relationship of one‐ and two‐ particle reduced density operators. The corresponding conditions on the kinetic description are identified, and a simple “mean field” approximation is indicated as an example.
Quasi‐classical Theory and Simulations of Hydrogen‐like Quantum Plasmas
Authors: Ebeling W. , Militzer B. , Schautz F.
Published: July 2007

First the range of validity of a quasi‐classical approach is analyzed and analytical formulae for the thermo‐dynamical potentials are derived. Then a simple quasi‐classical model for the quantum molecular dynamics of hydrogen‐like plasmas is developed. The model is based on a quasi‐classical wave packet representation and leads to effective momentum‐dependent Hamiltonians. The quantum‐mechanical effects corresponding to the Pauli and the Heisenberg principle are modeled by constraints in the Hamiltonian. Monte Carlo and Molecular Dynamics calculations are carried out for electron‐, electron‐positron‐, and for hydrogen plasmas considering ensembles of 64 – 250 particles. A comparison with the analytical formulae shows reasonable agreement.
On the Theory of Ionization Rate in Superdense Plasmas
Authors: Iakubov I. T.
Published: July 2007

The diffusion theory in energy space is used to describe the step‐by‐step ionization in superdense plasma. The rate of ionization is obtained. The theory can be used under conditions when thermal ionization accompanies cold ionization. The ionization time in laser‐generated aluminum plasma is calculated.
Numerical Solution of the Quantum Landau Equation for Dense Plasmas
Authors: Kosse S. , Bonitz M. , Schlanges M. , Kraeft W. D.
Published: July 2007

The numerical solution of the quantum Landau kinetic equation for a dense electron gas is considered. Being one of the most simple kinetic equations, it still retains essential physical features of a correlated many‐particle system, such as selfconsistent static screening and Pauli blocking, and, at the same time, it is a good test case for the efficiency of numerical methods. Two schemes for the evaluation of the scattering rates and the collision integral are discussed. To illustrate our results, we present time‐dependent calculations i) for the relaxation of a nonequilibrium electron distribution function and ii) for the stopping of fast electrons.
Parametric Instability of Surface Waves on the Second Harmonic of Electron Cyclotron Frequency in a Plasma Layer
Authors: Girka V. O. , Sporov A. E.
Published: July 2007

The parametric instability of surface waves on the second harmonic of electron cyclotron frequency (SWCF) in a plasma filled dielectric wave guide is examined in a kinetic approximation. The studied surface waves are extraordinary polarized modes and propagate across the external steady magnetic field. The amplitude of the electrical pump wave is assumed to be small. Simple expressions for increments of the parametric instability of the SWCF are calculated. The otained results can be used in controlled fusion researches in order to avoid undesirable regimes of plasma periphery heating in that fusion devices which use the resonance electron cyclotron heating method.
The Development of Simplified Heat Flux Limiters for EDGE2D
Authors: Radford G. J. , Corrigan G. , Fichtmüller M. , Simonini R. , Spence J. , Taroni A.
Published: July 2007

A theoretically based model for heat flux limiters is under development for the multi‐fluid code EDGE2D. Results show a strong reduction in the ion heat flux while that for the electrons is largely classical. A corresponding reduction in the thermal forces on impurities has lead to a small improvement in impurity retention.
Fluid modelling of edge plasmas with ion frictional forces allowing for arbitrary impurity abundances
Authors: Maddison G P , Helander P , Cornford S L
Published: July 2007

Fluid modelling of ion parallel transport in tokamak scrape‐off layers (SOLs) is generalized according to the descriptions of Hirshman and Hinton. A compact representation is implemented into the “B2” code, and initial test calculations performed for helium flow in COMPASS‐D divertor plasmas. Relation to other, higher‐order treatments of impurity fluxes is considered.
Two Alternative Approaches in the Kinetic Theory of Fully Ionized Plasmas
Authors: Klimontovich Yu. L.
Published: July 2007

A brief review of two alternative descriptions of nonequilibrium processes in fully ionized plasmas is presented. The example of “Landau damping” is used to demonstrate that some fundamental problems remain unsolved in the kinetic theory of plasmas. They arise from inconsistent descriptions of the transition from the reversible equations of mechanics of charged particles and fields to the irreversible equations of continuous media in the theory of plasmas. These difficulties can be overcome through consistently defining the structure of continuous media and the characteristics of dynamic instability motion of particles. The procedure leads to generalized irreversible kinetic equations which provide the basis for a unified description of nonequilibrium processes in plasma on kinetic and hydrodynamic scales.
Stationary Regimes of Nonlinear Alfvén Oscillations in a Driven System with Discrete Spectrum
Authors: Markovskii S. A.
Published: July 2007

Driven stationary Alfvén oscillations in a system with discrete spectrum are considered in the approximation of weak nonlinearity. The correction to the eigenfrequency of small oscillations, proportional to the square of their amplitude, is derived with the help of the perturbative approach. The dependence of the amplitude versus the frequency of the driving force is found to have two bifurcation points at which the amplitude exhibits finite variation under the action of infinitesimal deviation of the driver frequency. It is shown that the bifurcation is possible only when the unstable processes of interaction of the initial standing Alfvén wave with small perturbations are stabilized to the third order in the wave amplitude. Conditions of the stabilization, as a consequence of a finite length of the system or due to dissipation, of three‐ and four‐wave parametric instabilities are discussed.
A Possible Way for dc Discharge Simulation
Authors: Mustatā I. , Biloiu C.
Published: July 2007

A method to obtain the dc electric field variation along the discharge gap in a fluid one‐dimensional, local ionisation case, is presented. The obtained dependence was used further to infer the other interesting parameters spatial distributions in the low pressure (1 Torr) discharge. These parameters could be, the current and charge densities, the ionisation source, the electric potential and so on.
Accurate First‐Principle Equation of State for the One‐Component Plasma
Authors: Brilliantov N. V.
Published: July 2007

Accurate “first‐principle” expressions for the excess free energy Fex and internal energy of Uex of the classical one‐component plasma (OCP) are obtained. We use the Hubbard‐Schofield transformation that maps the OCP Hamiltonian onto the Ising‐like Hamiltonian, with coefficients expressed in terms of equilibrium correlation functions of a reference system. We use the ideal gas as a reference system for which all the correlation functions are known. Explicit calculations are performed with the high‐order terms in the Ising‐like Hamiltonian omitted. For small values of the plasma parameter Γ the Debye‐Huckel result for Fex and Uex is recovered. For Γ ≫ 1, these depend linearly on Γ in accordance with the Monte Carlo findings for the OCP. The MC data for the internal energy are reproduced fairly well by the expression for Uex obtained.
Studies of Silicon Erosion in Plasma‐Target‐Interaction from Optical Emission and Absorption Spectroscopy
Authors: Jentschke H. , Schumacher U. , Hirsch K.
Published: July 2007

The densities of eroded silicon from a target in interaction with a cylindrically symmetric plasma are determined from measurements of the transverse radiance and transmittance of Doppler broadened spectral lines with high spectral resolution. The transmission distributions, branching ratios, and the spectral line shapes, which depend on the optical depths of the emitting and absorbing particles along the line of sight, are investigated for particle density and temperature determination. First results on emission and transmission measurements of the Si I resonance multiplet spectral line branching ratios and line profiles (centered at 251 and 288 nm, respectively) for silicon as the erosion product from a C/C‐SiC target in a low temperature plasma jet give absorption coefficients, from which erosion rates can be deduced, which are in good agreement with the results from the emission spectroscopy and from the gravimetric measurements.
Evalution of Plasma Composition and Mobilities in Argon Plasma with Chlorine as Additive
Authors: Novaković N. V. , Milić B. S. , Stojilković S. M. , Gajić D. Ž.
Published: July 2007

Results of numerical evaluation of equilibrium compositions and mobilities in plasmas formed in the mixtures of argon and chlorine are given. The temperature dependence of the number densities of the components and their mobilities in function of temperature for low‐pressure (from0, 1 kPa to 1,0 kPa) and low‐temperature (from 500 K to 5 000 K) argon plasmas with 20% and 30% of added chlorine are evaluated. It is assumed that the system is kept under constant pressure and that a corresponding state of local themodynamical equilibrium is attained in it. A previously derived expression for the modified Debye radius, offering the possibility to treat the plasmas considered as weakly non‐ideal in the whole temperature range, is used and the cut‐off at the Landau length rather than of the smallest of ionic radii is introduced. This alteration in the evaluatin procedure brings different change in the final numerical results for all the relevant quantities.

It is found that the equilibrium plasma composition depends considerably on the presence of chlorine in the whole temperature range for both pressures; the addition of chlorine significantly enhances number densities of all relevant charged constituents. This fact influences of the electron and ion collision frequencies and their mobilities too.
Debye‐Hückel Free Energy for a weakly Nonideal Plasma with Helium‐like Bound States
Authors: Lehmann H.
Published: July 2007

In plasmas with helium‐like bound states electrostatic screening inside the atom gives rise to deviations from the Debye‐Hückel chemical potential. Assuming a variational solution for the ground state of the helium‐like atom the corresponding Free Energy is explicitely given. The result provides a simple means to describe the forming of bound states in consistency with the surrounding plasma and surpasses in this sense perturbation theories.
Langmuir Paradox
Authors: Gorgoraky V. I.
Published: July 2007

Published data on the impact ionization of rarefied gases by electrons are analysed where from a simple explanation of the Langmuir paradox follows. This approach gives likewise an opportunity to explain some other anomalous phenomena observed when ionizing gas atoms or molecules by an electron impact.
Kinetics of Langmuir Turbulence: An Equation for the Two‐time Correlation Function
Authors: Erofeev V. I.
Published: July 2007

The two‐point correlation function is reduced to expansion in terms of the two‐time correlation function with improved accuracy. The ideas reported extends the applicability area for calculations typical to the weak plasma turbulence theory on the “strong plasma turbulence”. Some implications of the results obtained for the dynamics of Langmuir turbulence are discussed.
Quasiclassical Theory and Molecular Dynamics of Two‐Component Nonideal Plasmas
Authors: Ebeling W. , Norman G. E. , Valuev A. A. , Valuev I. A.
Published: July 2007

A simple model of two‐component plasmas based on pseudopotentials and quasi‐classical dynamics is derived from Planck's model. In the framework of this model bound states are treated quantum‐mechanically and free pair states are treated in a quasi‐classical way. The statistical thermodynamics, structure factors and conductance of the model are investigated by molecular dynamics simulations.
Experimental Study of Planar Langmuir Probe Characteristics in Electron Current‐Carrying Magnetized Plasma
Authors: Stanojević M. , Čerček M. , Gyergyek T.
Published: July 2007

Experimental study of planar Langmuir probe characteristics in a magnetized plasma with an electron current along the direction of the magnetic field shows that the usual procedure for determination of the electron temperature and plasma density, which is applicable in a current‐free magnetized plasma, gives erroneous results for these plasma parameters. When this procedure is applied on the characteristics measured at two opposite orientations of the probe collecting surface with respect to the direction of the electron drift, different values of the electron temperature are obtained. These virtual electron temperatures and corresponding plasma densities calculated from the measured ion saturation currents are higher and/or smaller than the exact local electron temperature and plasma density. Calculation of particular averages of these quantities is proposed as a possible way to obtain correct results for the local electron temperature and plasma density. These averages are used in the approximate evaluation of the electron drift velocity from the electron saturation currents measured at the two orientations of the probe collecting surface.
Compilation of Cross Section Data of Elementary Processes of HCI Applicable for Plasma Modeling
Authors: Efremov A. M. , Svetsov V. I. , Balashov D. I.
Published: July 2007

In this current work an cross section data for HCI elementary processes were calculated on the base of calculated and experimental data comparison on electrons drift rate and Townsend coefficients of dissociative attachment. Cross sections data of HCI electronic excitation are obtained for the first time.
Computer Simulation of High Power Ion Beams Interaction with Matter
Authors: Fortov V. E. , Skvortsov V. A.
Published: July 2007

When high‐power ion beams (HPIB) collides with matter, it generates plasma with parameters of a wide range, staring with those well mastered in physics and gas discharge technologies and ending with those appropriate to such natural systems as star nucleus and thermonuclear systems in feasible power projects based on the controlled inertial thermonuclear synthesis. We are interested in a fairly wide range of beam power densities (from 1 GW/cm2 to 10 TW/cm2). This paper describes one mathematical model in one dimension (a plane geometry is assumed) and one model in two dimensions (r‐ and z‐coordinates). The models are completed by wide‐ range equations of state for real matter (construction materials) and supplemented with additional equations describing rheological, thermophysical, and optical properties of solid media under consideration (in various phase states from solid to plasma, including states of a strongly nonideal plasma). On the base of the continual approach, mechanical destruction of materials due to tensile strain generated by rarefaction waves is taken into account. In modeling the action of ion beams of moderate intensity (I < 10 GW/cm2) on metal targets, elastoplastic properties are taken into account, and in describing the action of ion beams with intensities I > 10 GW/cm2 (in the two‐ dimensional model based on the large‐particle technique) heat transfer, including radiational processes, is considered. Opportunities offered by contemporary computer simulation techniques in the field of interaction between HPIB and matter are demonstrated, in particular, a possibility of simulating hypervelocity impact with the help of HPIB has been shown and the necessary conditions have been determined. The results of our computer simulation may be interesting from the viewpoint of some technological applications of HPIB, for example, pulsed destruction and strengthening of construction materials, pulsed ion implantation and etc. [1].
In Situ Characterisation of Polymer Surfaces and Thin Organic Films in Plasma Processing
Authors: Meichsner J.
Published: July 2007

In situ sampling techniques are presented for investigation of plasma surface modification of polymers and plasma polymerisation. FTIR spectroscopy (infrared absorption reflection spectroscopy ‐ IRRAS, and attenuated total reflection ‐ ATR) are properly used for characterisation of the changes in the molecular structure of thin polymer films (polystyrene, polyethylene) due to low pressure plasma treatment. The thin films were prepared by dip or spin coating procedures. In the case of plasma polymerisation a novel fibre‐ATR technique is applied to investigate the plasma polymerisation process in the plasma bulk. Results are exemplary shown for plasma polymerisation of styrene. Ellipsometric measurements allowed the characterisation of the thin plasma modified top polymer surface layer or thin deposited plasma polymer films by their refractive index and thickness. It was shown that the applied surface plasmon ellipsometry is very sensitive with respect to the usual ellipsometry for investigation of polymer surface modification. The in situ microgravimetry by means of electronic vacuum microbalance permitted to measure the change of the sample mass in the order of 1 μg during the plasma treatment. The first steps in plasma modification (concurrence between the incorporation of plasma particles and the material etching) were studied.
Parametrical Instability of Surface Type X‐modes Immersed into a Nonmonochromatic Pumping Electric Field
Authors: Girka V. O. , Lapshin V. I. , Yu. Puzirkov S.
Published: July 2007

Parametrical excitation of surface type X‐modes (STXM) at the second harmonic of electron cyclotron frequency by nonmonochromatic external alternating electric field is under consideration. STXM are the eigenmodes of a planar magnetoactive plasma waveguide structure consisting of a metal wall with dielectric coating and uniform plasma filling. An external steady magnetic field is applied along the plasma interface, so it is perpendicular to the group velocity of the considered extraordinarily polarized waves. Influence of the plasma waveguide parameters on the parametrical instability of the STXM is studied. External alternating electric field is assumed to consist of two fields with different amplitudes and frequencies. A theoretical investigation is carried out using kinetic equation for plasma particles under the conditions of weak plasma spatial dispersion and small amplitudes of external electric fields. The obtained results can be useful for research in branch of edge plasma physics.
Relaxing Phenomena in Negative Corona Discharge: New Aspects
Authors: Rahel J. , Pavlik M. , Holubcik L. , Sobek V. , Skalny J. D.
Published: July 2007

Two theories, explaining the time dependence of the negative corona discharge current in air, are confronted with new experimental results. The influence of the ozone concentration on the discharge current was experimentally confirmed in dry air and in mixtures of nitrogen with oxygen. Assuming that only the dissociative electron attachment to ozone molecule is a process being responsible for a reduction of the electron component in the total mean discharge current, the mean value of the electron attachment rate constant k = (3 ‐ 5.5) × 10−9 cm−3 s−1 was derived from the measured dependence of the discharge current on the ozone concentration. The calculated value of the rate constant k corresponds to the dissociative attachment of electron to ozone molecule via process e + O3 → products (O− or O−2 negative ions).
Density Measurements from the Asymmetry of the Lyman ζ Line in a Vacuum Spark Lithium Discharge
Authors: Podder N. K. , Clothiaux E. J. , Oks E.
Published: July 2007

A lithium spectrum is obtained form vacuum spark discharges using a grazing‐incidence flat‐field spectrometer. Hydrogen‐like lines up to Lyman η are identified in the spectrum. The spectrum is analyzed, and it is found that the experimental line widths increase along the Lyman series. An asymmetry between the blue and red wings appears in the profile of the Lyman ζ line, and becomes significant in the profile of the Lyman ϵ line. A relatively new method is used to estimate an electron density of 1 ± 0.4 × 1018cm−3 from the experimental degree of asymmetry between the blue and the red wings of the Lyman ζ line. This result is compared with an analysis of the experimental widths of two optically thin lines, namely, Lyman δ and Lyman ζ. In this analysis an electron density of 1.2±0.5 × 1018cm−3 is deduced. The principal quantum number of Lyman η (n=8) is used in the Inglis‐Teller formula for the last line seen before the merging of the lines with the continuum, and the estimated electron density is found to be 2.0 × 1018cm−3 for the lithium plasma. Thus, it is demonstrated that the new method employing the asymmetry of the lineshapes in dense plasmas yields results consistent with the analysis of the widths of the lines. However, it requires obtaining the profile of just one spectral line, which is a great advantage. The reference data on the Stark broadening of the Lyman ζ line is also tabulated, which was previously unavailable in the literature.
An Experimental Study of Noble Gas Isotope Separation by DC ArcDischarge
Authors: Akatsuka H. , Ohtsuki N. , Ezoubtchenko A. N. , Suzuki M.
Published: July 2007

Experiments are undertaken on the isotope separation by DC discharge through a narrow capillary of gaseous neon, argon and krypton of natural isotopic abundance. It is confirmed that the heavier isotopes become enriched in the region of cathode, and the lighter isotopes in that of anode. The effect on the obtainable separation factor brought by differences in experimental conditions is examined by changing the capillary tube diameter, tube length, discharge current and discharge pressure. The separation factor improves with increasing the tube length and the discharge current, and with decreasing the discharge pressure and the tube diameter. Ion density and electron temperature are measured in the positive column to compare the present experimental results with existing theories. The order of the isotope enrichment factor is well explained by the theory of the ion diffusive friction force onto isotopically different neutral molecules, together with the theory of the ionization degree of the different isotopic species.
The ‘leaky bucket’ policing method in the ATM (asynchronous transfer mode) network
Authors: Niestegge Gerd
Published: July 2007

The new asynchronous transfer mode (ATM) will be used for the information transport in the future broadband network. An important function of the ATM network is bandwidth enforcement or policing. The so‐called ‘leaky bucket’ algorithm can be used to monitor and enforce the bit rate of a constant bit rate (CBR) connection. The parameters of the ‘leaky bucket’ algorithm depend on the bit rate of the connection and on the cell delay jitter. Sugestions for setting the parameters of the ‘leaky bucket’ algorithm are provided in this paper. Furthermore, a ‘dual leaky bucket’ algorithm is proposed to police the traffic parameters of a variable bit rate (VBR) connection. The ‘dual leaky bucket’ approach could also be used to define a VBR bearer service in the future broadband network.
An architecture for integrated networks that guarantees quality of service
Authors: Lazar Aurel A. , Temple Adam , Gidron Rafael
Published: July 2007

A generic architecture for integrated networks that guarantees quality of service is described. The network has a mesh topology and a switching architecture structured according to the concept of asynchronous time sharing. This concept is based on a multiclass network model and asynchronous algorithms for allocating network resources. There are three traffic classes for transporting user information and a fourth class for network management and control. Resource allocation is resolved through time‐sharing and space‐partitioning algorithms.
Subscriber premises' network architectures in a broadband ATM environment
Authors: de Vleeschouwer A.
Published: July 2007

In future broadband networks residential and business users will be distinguished, each with their own characteristic requirements. Whereas business users almost exclusively need interactive switched services, the huge number of residential users, on the country, mainly aim at entertainment services, either switched or distributed, at a low, possibly fixed, price. Based on the user requirements a twotier SPN architecture is derived, consisting of a TDN (terminal distribution network) and a BBN (broadband backbone network).

Alternative structures for TDN are analysed and compared. A passive tree solution is found to be most suitable for the above‐mentioned needs. Although the physical appearance may be quite different, all the given examples have a number of elements in common. This enables common components to be developed.

Inside the SPN, especially the residential SPN, the absence of any channel aggregate in ATM is of great advantage. Only the total available bandwidth imposes a restriction on the set up of new calls. This is very important, because SPN encounters a wide variety of user needs, together with a relatively small amount of users. In order to preserve the advantages of ATM in the subscriber area, it is essential to bring ATM down to the terminal.
R‐net: A high speed fibre optics network with reservation access protocol
Authors: Al‐Wakeel Sami S. , Ilyas Mohammad
Published: July 2007

This paper proposes and describes R‐net, a network with a new reservation access protocol that is very suitable for implementation with optical fibre in high speed local area networks. In the operation of R‐net, a framing structure with variable length is superimposed on the network bus to bound the network medium access delay which is a highly desirable feature for real time applications. As long as the frame length constraint is not violated, the performance of R‐net network is not limited by operating data rate, and the utilization can be set to unity by choosing the appropriate network parameters. The proposed network has the advantage of efficient throughput approaching unity for most practical configurations, bounded delay, and at normal load, the network protocol has fair access for all nodes and allows dynamic bandwidth allocation between the nodes connected to the network bus. A performance (delay and utilization) comparison between R‐net and Expressnet is also presented.
Implementation of multipoint connections in an ATM switching network
Authors: Knorr Rudi , Wild Thomas
Published: July 2007

This paper presents the problems in the implementation of multipoint connections at switching level using the example of an ATM switching network. By choosing the proper routeing mechanism and the appropriate architecture of the switching element, a switching network can gradually be adapted to an increasing share of multipoint traffic. The first section describes the problems with the handling of multipoint connections within a multiple stage connection oriented switching network. In particular this refers to the routeing of the cells through the switching network. Several alternatives on this issue are discussed. Both, the selected approach based on a differentiated self‐routeing mechanism and the corresponding cell format are introduced. In the second part of this article several switch architectures are compared in respect of their multipoint capability. It is demonstrated that at present the most promising solution are switching elements based on the principle of central buffering. A single chip solution using this concept is employed in the presented switching network.
Initial deployment of fibre in the local network for narrowband use in Spain: Technology, engineering and cost
Authors: de la Iglesia R. Diaz
Published: July 2007

This paper covers: (1) the field trials, with fibre in the local network systems, being conducted in Spain and intended for delivery telephone‐based services to residential customers; (2) the technical and functional requirements of these types of system intended for commercial (regular) deployment to be started around late 1993/early 1994, and (3) the most relevant initial deployment scenarios and persubscriber investment aspects.

The field trials are located in Madrid and in Barcelona: their rationale, technical characteristics and the lessons learned so far are described.

Such trials are providing insight into what requirements and objectives are anticipated to be needed should such new technology be an actual alternative to copper‐based subscriber loops. The requirement for such fibre in the local network systems intended for regular deployment in the near term are indicated, including technical and functional requirements of the optical line terminals (OLTs) (at local exchanges) and optical network units (ONUs) (located near customer premises); transmission requirements and optical distribution network (ODN) requirements and design aspects. For starting regular deployment, three preferred scenarios are identified. The chief parameters affecting persubscriber investments are illustrated including the number of fibres per ONU, and the number of users being served from each ONU. It is shown that in order to achieve cost parity with copper loop (which requires an initial investment of between $600 and $800) a capacity of some 60 narrowband (64 kb/s) channels per ONU should be required.