bluuebunny/crossref_metadata_2025_split huggingface dataset:
Weak Ion Acoustic Double Layers in a Warm Plasma
Authors: Sutradhar Das S. , Bujarbarua S. 
Published: July 2007

AbstractThe analytic solutions of the weak ion acoustic double layers in warm unmagnetized and magnetized plasma have been presented with the fluid equation for ions and an arbitrary equation of state for the hot electrons. It has been shown that double layers solutions exist for both magnetized and unmagnetized plasmas when two Boltzmann model for electrons are considered. The potential, the thickness and the velocity of such type of double layers have been calculated and compared with those for the cold plasma.
Exchange‐Correlation Potentials for Hydrogen at any Degeneracy
Authors: Stolzmann W. , Kraeft W. D. , Fromhold‐Treu I. 
Published: July 2007

AbstractNumerical values of the exchange‐correlation contributions of the pressure, the free energy and the chemical potential are obtained for hydrogen at any degree of degeneracy. The evaluations are performed with the RPA‐dielectric function for the Montroll‐Ward contribution by integration over real frequencies. The influence of the proton degeneracy is analyzed for increasing degeneracy of the electrons. A comparison with the correlation part of the free energy and of the chemical potential without proton degeneracy is given.
Effects of Non‐Ideality and Non‐Equilibrium in the Cathode Spot Plasma of Vacuum Arcs
Authors: Anders S. , Anders A. 
Published: July 2007

AbstractThe cathode spot plasma of a metal vapour arc in vacuum is non‐ideal (electron density ne ∼ 1025–1027 m−3, temperature T ∼ 1–5 eV, plasma parameter Γ = 0.6−0.1). The fast expansion of the spot plasma into the ambient vacuum leads to a non‐equilibrium charge state distribution (“frozen” state of ionization). The calculations presented show that the freezing of the different charge states appears at different distances from the spot, therefore at different plasma densities and temperatures. In this way, specific proportions of the ion species are produced which do not agree with any equilibrium state. The freezing of the charge states occurs near the cathode spot (γ = 5–50 μm, γ — distance from the spot centre) where the plasma is weakly non‐ideal (Γ = 0.2–0.6).
Kinetic Current‐Convective Instability in Hot Electron Plasma
Authors: Khalil Sh. M. , Sayed Y. A. , Zaki N. G. 
Published: July 2007

AbstractThe kinetic current‐convective instability excited in a hot electron plasma, i.e. for Te ≫ Ti, is investigated in the linear stage. Density and temperature of plasma components have gradients along the x‐direction.In the absence of longitudinal current (u = 0) and homogeneous temperature the instability is also excited with maximum growth rate much exceeding that obtained in the case of u ≠ 0. Gradual increasing of the ion temperature over that of the electrons and a large density gradient leads to reduce the instability in the linear stage.
80 Ev Imaging of Laser Produced Plasmas for Different Z Materials at 1.06, 0.53 and 0.26 μM
Authors: Benattar R. , Godart J. L. 
Published: July 2007

AbstractThe VUV emissions (155 Å) of laser produced plasma on massive plane targets with different Z numbers are recorded according three laser wavelengths with a pinhole camera associated with a multilayered mirror.The 2D dimensions of these VUV images are compared with the sizes of the focal spots through the 1 Kev pinhole image sizes recorded at the same laser intensity (51014 W/cm2, 600 ps). The lateral and axial dimensions of the VUV emissions of Al, Cu, Au plasmas are analyzed and give informations on the radiations‐hydrodynamic behavior of Laser heated plane targets with respect to the wavelength of the incident laser.
Conductivity and Cross Sections for Partially Ionized Cesium and Sodium Plasmas
Authors: Arndt S. , Sigeneger F. , Bialas F. , Kraeft W.‐D. , Luft M. , Meyer T. , Redmer R. , Röpke G. , Schlanges M. 
Published: July 2007

AbstractThe electroconductivity of partially ionized cesium and sodium plasmas is calculated within the frame of the Chapman‐Enskog method. The composition of the plasma and the transport cross section for electron‐electron and electron‐ion scattering were evaluated in previous papers (Redmer et al. [1], Sigeneger et al. [2]). This paper is mainly devoted to the influence of neutrals on the electroconductivity. Therefore, the total and transport cross section for electron‐atom scattering are determined numerically. The results for the cross sections and the conductivity are compared with experiments and other theoretical approaches.
Mutual Focusing of Electromagnetic Waves in the Ionospheric Plasma
Authors: Laxmi V. N. , Srivastava M. P. 
Published: July 2007

AbstractA one dimensional analysis has been carried out to study the interaction of two co‐axial electromagnetic waves propagating vertically at close frequencies in the F‐region ionosphere. Coupled equations for the beam width parameters of the two interacting waves have been set up to determine the intensities in the axial direction. Two cases have been examined, i one of the em beams is assumed to be weak so that its influence on the medium as well as on the other beam is neglected, ii) the two beams are of comparable intensities so that they mutually influence each other. In the first case the axial intensity of the weak beam grows at the expense of the other one which is strong. Whereas in the other situation mutual influence results in the focusing of both the beams.
Initiation of Gas Discharges in Plasma Displays Assisted by Electron Emission of Thin Insulators
Authors: Röpcke J. , Zimdahl T. , Schlott D. , Glaefeke H. 
Published: July 2007

AbstractAt present many efforts are done for the development of colour plasma displays (PD). One main problem is to secure a reliable ignition, provided by a suitable concentration of starting particles in the discharge cells (priming). In this paper a new priming method is proposed using the exoelectron emission (EEE) of thin insulators. The influence of the EEE on the ignition behaviour of ac PD cells is investigated and compared with direct measurements of the afteremission of MgO, Al2O3 and MgAl2O4. Auger electron spectroscopy (AES), residual gas mass spectra and Ar+ etching are additionally used methods.
Pulsed Operation of High‐Pressure‐Sodium Discharge Lamps
Authors: Günther K. , Kloss H.‐G. , Lehmann T. , Radtke R. , Serick F. 
Published: July 2007

AbstractResults of spectral and photometric measurements are presented for pulsed operated high‐pressure‐sodium lamps. Choosing for the colour temperature a value of 3000 K, the output spectrum was optimized with respect to colour rendition and lamp efficacy taking the pulse parameters, the sodium mole fraction, and the cold spot temperature as quantities to be varied. For the nominal rating of 70 W a maximum lamp efficacy of 70 lm/W and a colour rendering index of 40 can be obtained. Further improvements of the colour rendition require an enhanced sodium vapour pressure which can be achieved by operating the lamp at rised cold spot temperature.
Stark Broadening Regularities within Successive Ionization Stages in Krypton and Xenon
Authors: Purić J. , Djeniže S. , Labat J. , Srećković A. , Platiša M. 
Published: July 2007

AbstractOn the basis of existing experimental and theoretical results on Stark widths of neutral and multiply ionized states of krypton and xenon, we have indicated existence of certain regularities of Stark broadening for ns‐np types of transitions. These regularities were used to estimate the Stark widths of spectral lines from KrIV and XeI spectra that have not yet been measured or calculated.
Low Temperature Dry Etching of Graphite Anodes in Hydrogen Glow Discharges
Authors: Nawra J. , Pfau S. , Resztak A. , Richter Th. , Rutscher A. 
Published: July 2007

AbstractTo discribe the temperature dependence of the etching rate of graphite in a hydrogen glow discharge a model is discussed taking into accout the transition from CH4 to CH as the main etching product with increasing temperature.
On the Relaxation of Energetic Electrons in Plasmas
Authors: Braglia M. , Winkler R. , Wilhelm J. 
Published: July 2007

AbstractThe impact of individual collision processes on the relaxation of the velocity distribution function of a group of electrons, initially localized in a narrow region at relatively high energies, has been studied. By having recourse to solutions of the non‐stationary Boltzmann equation and to corresponding Monte‐Carlo simulations, the temporal behaviour of electrons in CO2 plasmas, both in the absence and the presence of an external dc field, has been investigated. A microphysical interpretation of observed relaxation phenomena, based on the data relevant to the individual collision processes, is also given.
Collisional — Radiative Model of Helium Plasma. I. Description of the Model
Authors: Slavík J. 
Published: July 2007

AbstractWe present a collisional‐radiative model of helium plasma with explicit inclusion of metastable state influences and give results of numerical calculations of population coefficients and effective reaction rates (generalization of effective ionization and recombination coefficients for the case when metastable states are not explicitly included) for a large region of electron densities and temperatures for optically thin and thick helium plasma. The model is described in this paper.
Collisional — Radiative Model of Helium Plasma. II. Global Population Coefficients
Authors: Slavík J. 
Published: July 2007

AbstractWe present results of our calculation of global population coefficients based on a collisional — radiative model of the helium plasma. The results are given for 23P, 21P, 33S, 31S, 33P, 31D, 33D, 31P, 43 and 41 states of helium atoms. We consider electron densities from 107 to 1018 cm−3 and electron temperature from 1 to 10 eV. The electron distribution function is considered to be Maxwellian and the plasma to be radiatively thin.
Parametric Excitation of Hybrid Modes in Multispecies Plasmas
Authors: Asthana Meenu , Guha S. 
Published: July 2007

AbstractNonlinear 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.
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

AbstractThis 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

AbstractA 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

AbstractAn 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

AbstractThe 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

AbstractTracing 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

AbstractA 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.
Kinetic Theory of the Lorentz Gas
Authors: Chen Qun , Bernstein Ira B. 
Published: July 2007

AbstractThe 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

AbstractThe 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

AbstractThe 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

AbstractA 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

AbstractThe 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

AbstractThe 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.
Kinetic Nonlinear Buneman's Instability in Field‐Free Isothermal Collisonal Plasma
Authors: Khalil Sh. M. , Sayed Y. A. 
Published: July 2007

AbstractA 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

AbstractThe 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

AbstractThe 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

AbstractBackward 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.