bluuebunny/crossref_metadata_2025_split huggingface dataset:
CO2Laser Discharge Influenced by a Rotating Magnetic Field
Authors: Ose E. , Triebel W. , Schumann A. 
Published: July 2007

AbstractThis paper deals with experimental investigations of the effect of a rotating magnetic field on a diffusion cooled CO2laser discharge. Some properties relevant to laser activity are discussed, e.g. neutral gas temperature, magnetically driven gas rotation, pumping rate, and distribution of small signal gain within the discharge tube. By means of an intracavity method the radial distribution and the time behavior of the laser output power were measured.
On the Relaxation of the Energy Distribution Function of Light Particles in Heavy Gases
Authors: Braglia M. , Minari P. 
Published: July 2007

AbstractA stochastic approach to the thermalization problem of light particles in heavy gases is discussed which presents a number of advantages with respect to more conventional techniques. The procedure is used to study the relaxation of the distribution function in cold gases in two situations in which: i) only first order terms are retained and ii) second order terms are also included, with respect to the ratio m/M between light‐particle mass m and atomic mass M.
Modon Saturation in Collisional Driftwave Turbulence
Authors: Naulin V. , Spatschek K. H. 
Published: July 2007

AbstractThe nonlinear evolution of a collisional driftwave instability is considered. Based on the two‐fluid description with ion viscosity and electric resistivity effects, first two coupled equations are derived. Iterating the latter for nearly adiabatic behaviour and a two‐dimensional geometry, a one‐field description is found which properly takes into account the damping of structures. As demonstrated by numerical simulations, this solves an old problem of collisional driftwave turbulence, since in contrast to previous considerations the unlimited growth of self‐organized structures is stopped.
Study of the Nitrogen Arc under Reduced Pressure
Authors: Kaminska A. 
Published: July 2007

AbstractThe paper presents a model of arc in a d.c. vortex plasma torch which allows to determine distributions of temperature and plasma electron density in conditions of reduced pressure. The model makes it possible to elucidate voltage‐current characteristics of the arc at different pressures and its dynamic behaviour connected with the phenomenon of the electric arc root displacement. The experimental research also determined voltage‐current characteristics for different flow rates and pressures. The fluctuations of the arc current and the arc voltage were measured. The corresponding wave shapes were analysed by Fast Fourier Transform. The frequency variations with flow rate, arc current and pressure were studied and discussed.
Alfvén Pulses in the Ionospheric Waveguide
Authors: Shvartsburg A. B. , Stenflo L. 
Published: July 2007

AbstractExact explicit solutions, describing the propagation of wideband non‐sinusoidal waveforms in the ionospheric Alfvén waveguide by means of non‐separable electromagnetic fields, are presented. The dispersive modulation of these fields is shown to result in the formation of quasimonochromatic oscillations at the wings of the Alfvén pulses. The frequencies of these oscillations are close to the cut off frequencies of the waveguide.
Radiative Thermal Instability and Bifurcation
Authors: Bachmann P. , Sünder D. 
Published: July 2007

AbstractA radial hydrodynamic model is used to investigate the radiative thermal instability in the scrape‐off layer by applying a linear stability analysis of existing equilibrium states. Phase space trajectories are analyzed to derive conditions of their existence and bifurcation. Equilibrium profiles are calculated for the cases of homogeneous plasma temperature, plasma density and self‐consistency. Unstable perturbations, localized in the scrape‐off layer, may lead to a strongly radiating detached plasma belt.
Plasma‐Maser Instability of Bernstein Mode in Presence of Magnetohydrodynamic Turbulence
Authors: Saikia B. J. , Deka P. N. , Bujarbarua S. 
Published: July 2007

AbstractA theoretical study is made on the amplification mechanism of electrostatic Bernstein mode wave in presence of kinetic Alfven wave turbulence in a magnetized plasma on the basis of plasma‐maser interaction. It is shown that a test high frequency electrostativ Bernstein mode wave is unstable in the presence of low frequency kinetic Alfven wave turbulence. The growth rate of the Bernstein wave vanishes only in an unmagnetized plasma. Because of the universal existence of the kinetic Alfven waves in large scale plasmas, the results have potential importance in space and astrophysical radiation processes.
Modeling of Plasma‐Chemical Reactions in Gas Mixture of CO2 lasers. II. Theoretical Model and its Verification
Authors: Cenian A. , Chernukho A. , Borodin V. 
Published: July 2007

AbstractIn the paper we have modelled plasma‐chemical reactions in the CO2 low pressure, DC excited lasers. A good agreement of theoretical and experimental results has been achieved. It has been proved that neglect of reactions with electronic excited species or heterogeneous recombination leads to almost 50% overestimation of CO2 equilibrium conversion. The relation of CO2 equilibrium conversion to the reduced field E/N, pressure and current density depends on discharge conditions and mainly on the role played in discharge by ambipolar diffusion. This role decreases with an increase of the discharge diameter and of the mixture convection velocity. The CO2 equilibrium conversion increases with growth of E/N and j and with decrease of pressure for discharges in small, sealed‐off laser systems. The CO2 equilibrium conversion is not always a monotone function of p in large, convection cooled lasers. It does not depend so much on E/N as the electron temperature alone if conversions in different mixtures are compared.
Absolute Cross Sections for the Electron‐Impact Dissociation of CF4 and CHF3 into the CFx (x = 1−3) Neutral Radicals
Authors: Sugai H. , Toyoda H. , Nakano T. , Goto M. 
Published: July 2007

AbstractThe electron‐impact energy dependence of the dissociation cross sections of CF4 and CHF3 into the CFx (x = 1 − 3) free radicals was previously reported, in which the absolute values of the cross sections were tentatively estimated based on certain assumptions for the unknown ionization cross sections of the CF2 and CF radicals. These assumptions are no longer needed, since a complete set of absolute parent and dissociative ionization cross sections of CFx radicals has been reported recently by Becker and co‐workers. Based on these data, the absolute cross sections for the electron‐impact neutral dissociation of CF4 and CHF3 into CF3, CF2 and CF from the threshold up to 200–300 eV have now been accurately calibrated. Adjustments to the previously reported absolute cross sections of up to a factor of 16 were necessary.
Calculated Cross Sections for Double and Triple Ionization of Atoms by Electron Impact
Authors: Deutsch H. , Becker K. , Märk T. D. 
Published: July 2007

AbstractThe semi‐empirical Deutsch‐Märk (DM) formalism for the calculation of absolute cross sections for the single ionization of atoms has been extended to the calculation of cross sections for the double and triple ionization of ground state atoms. Detailed comparisons are made with available experimental data from threshold to 200 eV. In general, we find good agreement between the present calculations and the available experimental data. On that basis, we feel confident that the present formalism can be applied to predict double and triple ionization cross sections for those atoms, for which no experimental data are currently available, with an accuracy in the 30–50% range for impact energies where direct ionization processes dominate and where contributions from tightly bound inner shells can be neglected. This level of precision should be sufficient for modelling purposes and many other practical applications.
Enhanced Negative Ion Formation in ArF‐Laser‐Irradiated Methane: Possible Implications for Plasma Processing Discharges
Authors: Pinnaduwage L. A. , Martin M. Z. , Christophorou L. G. 
Published: July 2007

AbstractOberservation of enhanced electron attachment to ArF‐excimer‐laser irradiated methane is reported. Preliminary evidence is presented that laser‐excited superexcited states of CH4 (or other excited states to which these convert) are responsible for the observed enhanced electron attachment, and, that predominantly H− ions are produced via this process. The possible significance of this process for plasma processing discharges using CH4 and its mixtures is indicated.
The Effect of a Magnetic Field on the Hβ Line Emission from a T‐Tube Plasma
Authors: Mijatović Z. , Djurović S. , Pavlov M. , Kobilarov R. , Vujičić B. T. 
Published: July 2007

AbstractThe influence of a magnetic field on the emission of the Hβ line in a T‐tube plasma was investigated. Applied magnetic fields were 0.5 T and 2.1 T. The Hβ line profiles recorded under the same conditions in the presence and in the absence of the magnetic field were compared. We observed a small red‐shift of the lines emitted along the magnetic field lines. A qualitative explanation of this effect is given.
Nonlinear Interactions of the Surface Waves Propagating at the Plasma‐like Medium‐Metal Interface
Authors: Ostrikov K. 
Published: July 2007

AbstractThe nonlinear three‐wave interactions of the surface waves (SW) which exist at the plasma‐like medium‐metal interface are considered. The studied SW are caused by collective phenomena in the plasma‐like medium and propagate across an external magnetic field which is parallel to the interface. The wave coupling coefficients are obtained in the most general form and are expressed through the second order nonlinear susceptibilities. The simple case when the plasma‐like medium allows a hydrodynamical description is considered as well. The conditions providing the most effective interaction between the waves are discussed and the analytical expressions describing the amplitude evolution of the SW under such interaction are given. The possibility of realization of a parametric generator based on the SW nonlinear interaction is discussed. The characteristic length of the nonlinear medium providing the effective interaction is estimated for several important cases.
Langmuir Probe Determination of Charged Particle Number Density in a Flowing Afterglow Plasma
Authors: Chudáček O. , Kudrna P. , Glosík J. , Šícha M. , Tichý M. 
Published: July 2007

AbstractExperimental study of the electron and ion density determined by Langmuir probe is presented. The probe data have been obtained on FALP apparatus for electron (and ion) number densities ranging from 1012 m−3 to 1016 m−3, at electron temperatures equal to room temperature and also roughly ten times higher and at neutral pressures from 60 Pa to 150 Pa.The number densities of electrons for all measured probe data have been deduced from the electron current to the probe at the space potential and also by means of OML method from the electron current measured for positive probe with respect to the space potential. In the paper it is shown that in the flowing afterglow plasma the values of the electron density determined according both methods are in a good agreement and it is possible to take them as the reference number density for comparison with apparent ion densities obtained from the ion current.The number densities obtained from the ion currents in the ion accelerating region (negative probe with respect to the space potential) according to different applicable probe theories have been compared with reference value. It is found that the best agreement between the number densities evaluated from the electron current and from the ion current gives the theory of ion collection by Tichý et al. [16], which takes into account the collisions of ions with neutrals in the space charge sheath around the probe provided that the conditions correspond to the OML regime.
The Conversion of NOx in a Corona Discharge with an Electrode Material Variation
Authors: Hensel K. , Morvová M. 
Published: July 2007

AbstractThe spatial and surface chemical products and effectiveness of NOx removal (abbreviated deNOx) under the corona discharge action at atmospheric pressure were investigated. The influence of high‐voltage electrode material on a discharge character and the heterogeneous influence of the electrode surface are also reported in the article. The qualitative analysis was performed using infrared absorption spectrometry. Special attention was paid to NO and NO2 calibration measurements.
Progress in Integrated 2‐D Models for Analysis of Scrape‐Off Layer Transport Physics
Authors: Rognlien T. D. , Braams B. J. , Knoll D. A. 
Published: July 2007

AbstractWe present the status of comprehensive two‐dimensional (2‐D) transport modeling for the tokamak scrape‐off layer (SOL) using the UEDGE and B2.5 codes. These codes are now able to integrate a variety of physics, including coupling of plasma and neutral transport leading to detachment, complicated divertor‐plate geometries, multispecies impurities, and currents and E × B drifts. These new models are outlined and the capabilities are illustrated by a number of examples that emphasize the importance of including the 2‐D geometry.
Phenomenology of Flute‐Like Perturbations in the Divertor Region
Authors: Cohen R. H. , Ryutov D. D. 
Published: July 2007

AbstractA very strong squeezing of the flux‐tube passing near the divertor X‐point should make impossible existence of flute‐like perturbations connecting the divertor plate and the median part of the SOL. On the other hand, some of the current experimental observations imply that such perturbations do exist. In the present paper we consider possible resolutions of this apparent paradox for some specific experimental situations: short divertor legs; presence of a cold plasma in the divertor legs; and excitation of the modes with small toroidal wave numbers.
SOL Studies for Finite‐β Helias Equilibria
Authors: Strumberger E. 
Published: July 2007

AbstractThe suitability of the island divertor concept developed for Wendelstein 7‐X is investigated for various finite‐β Helias magnetic fields with average β‐values up to 〈β〉 = 0.04. For this purpose, the magnetic field structures of these finite‐β fields, which have been computed with the NEMEC+MFBE code, are studied in detail in the edge region.
Kinetic Theory Analysis of Sheaths and Shocks
Authors: Ryutov D. D. 
Published: July 2007

AbstractThe properties of sheaths formed on the divertor plates have a strong influence on plasma behavior in the scrape‐off‐layer. What makes these properties quite different from those of „standard”︁ Debye sheaths is that the magnetic field in the SOL intersects divertor plates at a shallow angle. The survey covers the following issues of the sheath physics in an oblique magnetic field: sheath structure and particle trajectories; effect of diamagnetic and electric drifts on the current‐voltage characteristics of the sheath; effect of the surface „roughness”︁ and „waviness”︁ on sheath properties and plasma transport; possible role of the anomalous transport, etc. The second class of objects briefly discussed in the present survey are shock waves which can appear in the divertor region if the incoming plasma flow is supersonic. The outline of the kinetic theory of impurity retention by the shocks is presented.
Kinetic models of ELMs burst
Authors: Sigmar D. J. , Batishcheva A. A. , Batishchev O. V. , Krasheninnikov S. I. , Catto P. J. 
Published: July 2007

AbstractFluid descriptions can fail for fast processes such as Edge Localized Mode (ELM) [1] bursts because plasma transport properties may be affected by incomplete Maxwellization of plasma particles. In this case only kinetic plasma descriptions of ELMs can give qualitatively correct results. In the present work we propose three different models of ELM propagation in the scrape‐off‐layer (SOL). We also present the first results of the kinetic modeling of the propagation of ELM bursts along the magnetic field, towards the target in a SOL plasma. These simulations are performed with a 1D2V finite element Fokker‐Planck code ALLA [2] and with a 2D PIC code W2 [3].
Toroidal Wall Heat Flux and Conductivity Profiles due to Neutral 3D Turbulence in the Gas Blanket Regime for Divertors
Authors: Vahala G. , Vahala L. , Morrison J. H. , Krasheninnikov S. , Sigmar D. J. 
Published: July 2007

Abstract3D neutral fluid turbulence is considered within the gas blanket regime in front of the divertor plate. For 2D mean flows over toroidal cavities, it is shown that the turbulence leads to enhanced conductivity profiles as well as strongly increased heat flux to the toroidal walls. For ITER‐like divertors, these effects significantly lengthen the gas blanket regime to protect the target ‐ which under laminar conditions would not occur.
Plasma Recombination and Divertor Detachment
Authors: Krasheninnikov S. I. , Pigarov A. Yu. , Sigmar D. J. 
Published: July 2007

AbstractWe consider the influence on plasma recombination of the formation of negative and molecular ions in divertor plasma. We take into account different atomic processes (vibrational excitation of molecular hydrogen, electron dissociative attachment, ion conversion, charge exchange and dissociative recombinations, dissociation and ionization, etc.) and find the expression for the effective plasma recombination rate constant from a suitably reduced set of coupled rate equations. We estimate the influence of the recombination process on divertor plasma behavior and find that for AlcatorC‐MOD like parameters plasma recombination due to negative and molecular ions becomes significant in the temperature range below a few eV. We conclude that plasma recombination is a strongly contributing mechanism for the explanation of divertor plasma detachment in low temperature plasmas.
Simulation of an ITER‐Like Dissipative Divertor Plasma with a Combined Edge Plasma Navier‐Stokes Neutral Model
Authors: Knoll D. A. , McHugh P. R. , Krasheninnikov S. I. , Sigmar D. J. 
Published: July 2007

AbstractA combined edge plasma / Navier‐Stokes neutral transport model is used to simulate dissipative divertor plasmas in the collisional limit for neutrals on a simplified two‐dimensional slab geometry with ITER‐like plasma conditions and scale lengths. The neutral model contains three momentum equations which are coupled to the plasma through ionization, recombination, and ion‐neutral elastic collisions. The neutral transport coefficients are evaluated including both ion‐neutral and neutral‐neutral collisions.
Neutral Gas Transport Calculations for ITER
Authors: Grossman A. , Schmitz L. , Merriman B. , Najmabadi F. 
Published: July 2007

AbstractIn modeling the neutral transport in the edge plasma for tokamak divertor design, geometry can play as important a role as the plasma density and temperature profiles. We have developed a novel interface between the neutral transport code, DEGAS, and CAD images of the tokamak and magnetic field geometry, which provides an accurate representation of the wall geometry for neutral transport modelling. In addition to superior spatial resolution of the vessel geometry, the interface allows subset regions of special interest to be selected out for modeling and permits the wall geometry to be readily modified by point and click techniques. Neutral transport results for the two divertor geometries under consideration for ITER, the gas bag design and the v‐shaped target design, are presented.
Effects of Neutral Gas Collisions and an Expanding Magnetic Field on Plasma Flow in a Divertor Chamber
Authors: Sato K. , Kameda S. , Katayama H. , Miyawaki F. 
Published: July 2007

AbstractA divertor plasma is treated using a kinetic model to evaluate impurity control effects of an expanding magnetic field and effects of plasma‐neutral collisions on power transmission in a divertor chamber. Cold ions of fuel and ionized impurities are effectively trapped in the divertor chamber by the electrostatic potential caused by magnetic expansion if the ionization rate is smaller than an upper limit. Plasma‐neutral collisions remarkably reduce the impact energy of ions reaching the divertor plates through removal of energetic ions and through reduction of the potential drop in the divertor chamber.
Modelling of Scrape‐Off Layer Biasing Experiments
Authors: van Schoor M. , Baelmans M. , Weynants R. R. 
Published: July 2007

AbstractBased on the extended B2‐code a method has been developed to simulate electrode as well as divertor biasing experiments. To improve the convergence speed of the code a new implicit discretisation scheme for the potential equation based on the Braginski equations was implemented, incorporating viscosity and pressure gradient effects in the expression for the radial current.The organisation of the article is as follows: In a first paragraph a short introduction about the B2‐code and the additional equations that determine the electric field and the currents is given. Paragraph 2 deals with electrode and divertor biasing. Some results are shown. Next, a new discretisation scheme to improve the previous one is discussed.
Review of the experimental verification on the enhancement of edge turbulence by biasing
Authors: Nedospasov A. V. 
Published: July 2007

AbstractWell‐known the theoretical studies deal with two mechanisms of turbulence suppression by the shear of the poloidal rotation velocity and due to the plasma shift to inner board over a time shorter than the inverse increment. In paper1 the possibility of increasing the level of edge turbulence by a limiter current was pointed out. The enhancement of the turbulence is possible due to the variation of the sheath potential at the plasma‐ surface boundary provided that the positive current flows to the surface. In this brief review a new experimental results which were obtained by biasing in different tokamaks are discussed. The earlier observations of turbulence changing with biasing were considered in1. For instance, an increase of the flow potential fluctuations in the SOL up to e/Tc > 3 was observed in TEXTOR.
Transverse Conductivity and Theory of a Probe in a Magnetized Plasma
Authors: Rozhansky V. , Ushakov A. , Voskoboynikov S. 
Published: July 2007

AbstractThe I‐V characteristics in a fully ionized plasma are calculated for the probes larger than the ion gyroradius. The shape of the characteristics is crucially effected by the transverse conductivity caused by the perpendicular ion viscosity.
Two‐Dimensional Divertor Modeling and Scaling Laws
Authors: Catto Peter J. , Krasheninnikov S. I. , Connor J. W. , Knoll D. A. 
Published: July 2007

AbstractTwo‐dimensional numerical models of divertors contain large numbers of dimensionless parameters that must be varied to investigate all operating regimes of interest. To simplify the task and gain insight into divertor operation, we employ similarity techniques to investigate whether model systems of equations plus boundary conditions in the steady state admit scaling transformations that lead to useful divertor similarity scaling laws. A short mean free path neutral‐plasma model of the divertor region below the x‐point is adopted in which all perpendicular transport is due to the neutrals. We illustrate how the results can be used to benchmark large computer simulations by employing a modified version of UEDGE which contains a neutral fluid model.
Massively Parallel Fokker‐Planck Code ALLAp
Authors: Batishcheva A. A. , Batishchev O. V. , Krasheninnikov S. I. , Sigmar D. J. , Koniges A. E. , Craddock G. G. , Djordjevic V. 
Published: July 2007

AbstractThe recently developed for workstations Fokker‐Planck code ALLA simulates the temporal evolution of 1V, 2V and 1D2V collisional edge plasmas [1]. In this work we present the results of code parallelization on the CRI T3D massively parallel platform (ALLAp version). Simultaneously we benchmark the 1D2V parallel vesion against an analytic self‐similar solution of the collisional kinetic equation[2]. This test is not trivial as it demands a very strong spatial temperature and density variation within the simulation domain.