bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of charged surfaces on the morphology of DNA condensed with multivalent ions
Authors: Besteman K. , van Eijk K. , Vilfan I. D. , Ziese U. , Lemay S. G.
Published: July 2007

DNA in solution can be condensed into dense aggregates by multivalent counterions. Here we investigate the effect of a nearby surface on the morphology of DNA condensates. We show that, contrary to what has often been assumed, interactions between DNA condensates and the surface can strongly influence the observed morphology. This limits the usefulness of surface probes such as atomic force microscopy for studying the morphology of condensates in bulk solution. Surprisingly, we find that the most negatively charged surface disturbs the condensate morphology most, suggesting that the microscopic mechanism resulting in DNA condensation is also responsible for the attractive force between DNA and the surface. © 2007 Wiley Periodicals, Inc. Biopolymers 87: 141–148, 2007.

This article was originally published online as an accepted preprint. The “Published Online” date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com
Tryptathionine bridges in peptide synthesis
Authors: May Jonathan P. , Perrin David M.
Published: July 2007

The tryptathionine linkage is a crosslink formed between tryptophan and cysteine. This feature is characteristic of the bicyclic peptides: the phallotoxins and the amatoxins. These peptides both bind to protein folds of their respective targets (F‐actin and RNA pol II, respectively) with extremely high affinities. Studies on these peptides have shown that the tryptathionine crosslink is essential for this binding affinity. Tryptathionines have been investigated for many years and several syntheses exist for their formation. In this review, we report on the various methodologies employed in tryptathionine synthesis, and discuss some of the advantages and disadvantages associated with each of them. © 2007 Wiley Periodicals, Inc. Biopolymers (Pept Sci) 88: 714–724, 2007.

This article was originally published online as an accepted preprint. The “Published Online” date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com
Population balance modeling of the conidial aggregation of Aspergillus niger
Authors: Lin P.‐J. , Grimm L.H. , Wulkow M. , Hempel D.C. , Krull R.
Published: July 2007

Numerous biotechnological production processes are based on the submerse cultivation of filamentous fungi. Process design, however, is often hampered by the complex growth pattern of these organisms. In the morphologic development of coagulating filamentous fungi, like Aspergillus niger, conidial aggregation is the first step of filamentous morphogenesis. For a proper description of this phenomenon it is necessary to characterize conidial populations. Kinetic studies performed with an in‐line particle size analyzer suggested that two distinct aggregation steps have to be considered. The first step of conidial aggregation starts immediately after inoculation. Both the rate constants of formation and disintegration of aggregates have been determined by measuring the concentration of conidia at the beginning of the cultivation and the concentration of particles at steady state during the first hours of cultivation. In contrast to the first aggregation step, where the collision of conidia is presumed to be responsible for the process, the second aggregation step is thought to be initiated by germination of conidia. Growing hyphae provide additional surface for the attachment of non‐ germinated conidia, which leads to a strong decrease in particle concentration. The specific hyphal length growth rate and the ratio of particle concentration to the growing adhesion hyphal surface are decisive matters of the second aggregation step. Both aggregation steps can be described by population dynamics and simulated using the program package PARSIVAL (PARticle SIze eVALution) for the treatment of general particle population balances. Biotechnol. Bioeng. 2008;99: 341–350. © 2007 Wiley Periodicals, Inc.
Effect of drying on the biological activities of a red microalgal polysaccharide
Authors: Ginzberg Ariel , Korin Eli , (Malis) Arad Shoshana
Published: July 2007

The red microalga Porphyridium sp. produces a polysaccharide exhibiting a variety of biological activities with potential for medical and cosmetic uses. For this reason, it is important that the drying process, which is the end point of production, should not destroy the natural characteristics of the material. The objective of this study was to evaluate the effect of drying at temperatures ranging from 40 to 140°C on the bioactivities of the polysaccharide. Drying the polysaccharide at temperatures above 90°C caused a significant decline in its biological activities (antiviral and anti‐cell proliferation) and reduced elasticity, viscosity, and intrinsic viscosity relative to lyophilized polysaccharide and to the starting product. The relationship between molecular weight and intrinsic viscosity indicated that the polysaccharide takes a rigid coil conformation, which stiffens as a result of drying. FTIR analysis revealed that drying caused both significant conformational alterations in the polymer chains and changes in the interaction between the polysaccharide and the glycoprotein to which it is noncovalently associated. Differential scanning calorimetry analysis of the water adsorbed on the charged groups of the polysaccharide showed that drying at higher temperatures increased the bound water content due to dissociation of the polymer chains. Thus, it is recommended that the polysaccharide be dried in a two‐step process in which free water is removed by convection and bound freezing water is removed by lyphophilization. Biotechnol. Bioeng. 2008;99: 411–420. © 2007 Wiley Periodicals, Inc.
FnTm2, a novel brain‐specific transcript, is dynamically expressed in the song learning circuit of the zebra finch
Authors: Agate Robert J. , Hertel Moritz , Nottebohm Fernando
Published: July 2007

Zebra finch males learn their song by imitation, a process influenced by social variables. The neural pathways for acquisition and production of learned song are known, but the cellular and molecular underpinnings are not. Here we describe a novel gene named “FnTm2” (“Phantom 2”) that is predicted to encode a small protein (220 aa) with a single fibronectin type III domain and a single transmembrane domain. This gene shows great variability in its expression in song system neurons of the anterior forebrain pathway (AFP), a circuit that influences song discrimination and is necessary for normal song acquisition. AFP nuclei that express FnTm2 include the nucleus HVC (its Area X‐projecting neurons), Area X, and LMAN (core and shell). FnTm2 expression does not correlate with singing behavior like the immediate early gene ZENK. It is expressed variably during sleeping hours and is not dependent on an intact song circuit. FnTm2′s expression is sensitive to hearing, because in deafened birds its expression is substantially reduced in the core of LMAN. Furthermore, a comparison of FnTm2 expression between mice and zebra finches revealed a conserved pattern of expression in the “limbic system.” We suggest that FnTm2 may be sensitive to affective and/or attentional states and thus may provide insights on how social variables influence the production and discrimination of learned vocalizations. J. Comp. Neurol. 504:127–148, 2007. © 2007 Wiley‐Liss, Inc.
Factorization problem on the Hilbert‐Schmidt group and the Camassa‐Holm equation
Authors: Li Luen‐Chau
Published: July 2007

In this paper we solve the Camassa‐Holm equation for a relatively large class of initial data by using a factorization problem on the Hilbert‐Schmidt group. © 2007 Wiley Periodicals, Inc.
Experimental Investigation of Jet Stabilization in Near‐Axis Region of Plasma Reactor
Authors: Volchkov E. P. , Baldinov G. R. , Terekhov V. I. , Tkach Yu. N.
Published: July 2007

The paper presents the results of experimental investigations of aerodynamics and heat transfer in a vortex plasma reactor with gas jet injection along its axis. The process of mixing under quasi‐isothermal conditions (injection of slightly heated jet) and inhomogeneous conditions (injection of helium and argon) as well as with the injection along the axis of plasma jet is studied consistently. A detailed comparison of temperature fields and concentrations is presented for these conditions.

The process of jet expansion is shown to be defined mainly by three factors — centrifugal mass forces, buoyancy forces and initial velocity shift in a jet at the chamber inlet. The end flows contribute considerably to the process of jet mass transfer with peripheral flow.
Influence of Nonideality Effects on the Ionization and Recombination Coefficients of a Reacting Hydrogen Plasma
Authors: Bornat Th. , Schlanges M. , Kremp D.
Published: July 2007

On the basis of generalized quantum kinetic equations for chemically reacting systems which include many particle effects, the ionization and recombination coefficient of a dense hydrogen plasma are determined. Using a simple approximation for the continuum shift in the quasiparticle energies, nonideality effects are taken into account and lead to a nonlinear density dependence of the rate coefficients. In the case of thermodynamic equilibrium the rate equation yields a Saha equation for a nonideal plasma.
The non Linear Decay of the Fast Wave During ICRF Heating
Authors: Avinash K. , Core W. G. F. , Hellsten T.
Published: July 2007

Various non linear decay processes of the fast magnetosonic wave can take place, such as the non‐resonant decay of the fast wave into an Ion‐Bernstein wave and a quasi‐mode, or the resonant decay of the magnetosonic wave into two ion Bernstein waves. The relevance of these processes to the direct edge heating observed during ICRH is discussed.
Transport Coefficients in the Jet Boundary
Authors: Lowry C. G. , Harbour P. J. , Tagle J. A.
Published: July 2007

Langmuir probes mounted in an antenna protection tiles have facilitated the comprehensive measurement of electron temperatures and densities in the JET scrape‐off layer (sol)2. The probes are close to the outside midplane and at radial positions of 15 and 28 mm behind the last closed flux surface. The data are from ohmic discharges with plasma currents between 1 and 5 MA and average electron densities between 8 × 1018 and 5 × 1019 m−3.

Here we use these measurements in a simple diffusive model for the electrons to obtain empirical scalings of the transport coefficients with local parameters. The scalings are shown to be inconsistent with exponentially decaying profiles of electron temperature and density, such as are measured in the JET sol.

In the apparent absence of a suitable model we are forced to scale directly the characteristic decay lengths in similar fashion. Finaally we use these dependences to campare models of global particle and power balance with the data.
Currents in Intersected Tokamak Flux Tubes
Authors: Hantzsche E.
Published: July 2007

In an elementary way the toroidal electric current in tokamaks is considered if the flux tube is intersected by limiters within the Scrape Off Layer (SOL). Simple sheath conditions are applied. The limiter space charge sheaths act as additional resistances, consuming partly the available voltage and diminishing the current density which is limited both by the plasma conductivity and by the ion saturation current of the sheaths. The difference between both potential drops at a limiter may rise up to the loop voltage (per flux tube circulation). Electron induced secondary electron emission has no influence at all on these results, which are applied to measured SOL plasma parameters in the TEXTOR tokamak as an example.
Impurity Transport Calculations for a Drift‐Dependent Tokamak Scrape‐Off Plasma
Authors: Brooks J. N. , Petravic M. , Kuo‐Petravic G.
Published: July 2007

Two dimensional calculations of impurity transport in a high recycling divertor scrape‐off region have been made with an updated version of the ZTRANS Monte Carlo computer code. The calculations use plasma parameters for the Doublet 3 divertor, as computed by the Planet Fluid Transport Code. The effects of electric field, particle drift velocities, and thermal forces are included in the calculations. For all impurity species studied, it is found that impurity transport is dominated by frictional forces, over most of the scrape‐off region. Light impurities, however, impinge substantially closer to the divertor plate center than do heavy impurities, which tend to impinge at the outer plate boundary.
Monte Carlo Modelling of Impurity Atom and Ion Transport Near A Limiter
Authors: Stangeby P. C. , Farrell C. , Wood L.
Published: July 2007

A Monte Carlo code, LIM (Limiter Impurity), is used to track impurity atoms and ions toroidally/radially in the vicinity of a limiter. As an illustration of the use of LIM, two cases are analysed: physical sputtering and sublimation of carbon from the limiter. For the same total impurity production from the limiter, physical sputtering is found to be approximately three times more efficient at contaminating the plasma centre as sublimation. A number of further quantities, which can be compared with experiment, are computed: (a) the toroidal/radial shapes of the impurity clouds of successive ionization states, (b) the average impurity ion temperature in each cloud, (c) the ratio of the different charge states of the impurities returning to the limiter, their spatial distribution and impact energy, and (d) total radiated power.
Dynamics of Impurities in the Scrape‐Off Layer
Authors: Stangeby P. C.
Published: July 2007

Impurity modelling of the Scrape‐Off Layer, SOL, is reviewed. Simple analytic models are sometimes adequate for relating central impurity levels to edge plasma conditions and for explaining the patterns of net erosion/deposition found on limiters. More sophisticated approaches, which are also necessary, are categorized and reviewed. A plea is made for the acquisition of a more comprehensive data base of edge plasma properties since reliable impurity modelling appears to be dependent on more extensive use of experimental input.
Extension of Schottky's Theory to a Cylindrical Discharge Plasma Containing a Coaxial Rod
Authors: Voigt H.‐D. , Winkler R. , Wilhelm J.
Published: July 2007

The well known diffusion theory of the positive discharge column is extended considering a plasma which burns between two coaxial cylindrical walls. Recent experimental investigations carried out with the goal to enlarge the fluxes of ultraviolet radiation in fluorescent lamp tubes motivate such an extension. Indeed, an enhancement of the efficacy could be found installating a glass rod along the tube axis which acts as an additional recombination surface. In order to understand this effect also a description of the radial plasma behaviour, especially that of the electron density, and of the necessary charged particle production by ionization is of interest. The paper reports about such an extension, including a representation of a suitable numerical solution approach and a discussion of the results.
Increased Power Concentration and its Effects on the Discharge Parameters of the Low Pressure Hg‐rare Gas Positive Column. II. Variation of Tube Radius
Authors: Kreher J. , Steern W.
Published: July 2007

The reduction of the tube radius is an effective technique for enhancing power concentration. The increased wall losses are compensated by larger field strengths, which counteract the decrease in radiation efficiency with rising current density. The causal relationships are investigated for tube radii of 18‐4 mm at constant discharge current i = 200 mA and constant current density j = 1.2 mA/mm2 and for parameter variation of the field strength only. The measured efficiencies of the Hg‐resonance lines 254 and 185 nm and the electron energy distribution functions agree well with the calculated values. Moreover, the results of the model calculations provide information on the elementary processes involved, such as elastic losses, collisions of second kind, stepwise processes and Coulomb interaction. The results show that Hg‐rare gas discharge with tube radii R = 5–10 mm are no less suitable for light production than those with radii between 13 and 18 mm.
Equilibrium Properties of Ionic Mixtures: Derivation of Fluctuation Formulae from the Grand‐Canonical Ensemble
Authors: Suttorp L. G.
Published: July 2007

The grand‐canonical ensemble is used to derive fluctuation formulae for the particle densities, the pressure and the energy density of a multi‐component ionic mixture. As an intermediate step sum rules are established for the two‐particle Ursell functions.
Anomalous Electrical Conductivity of Weakly‐Collisional, Magnetoactive Plasma Excited by the Lower‐Hybrid‐Drift Instability
Authors: Belyi V. V. , Meister C.‐V.
Published: July 2007

In this paper the kinetic theory for a weakly‐collisional plasma immersed in a static magnetic field with no curvature is considered. In the plasma an electrostatic flute (kB = 0) instability is excited causing an anomalous wave‐particle collision frequency. In the special case of the lower‐hybrid‐drift instability a simple expression for this collision frequency is found containing the wave spectrum as a parameter.
Dense Plasma in Electrical Implosions of Refractory Metal Wires
Authors: Isakov V. P. , Mintsev V. B.
Published: July 2007

Peculiarities of the refractory metal wire implosions are investigated, when the high power currents (up to 106 A) flow through the conductor. It is found, that the surrounding dense air plasma achieves brightness temperature of 70000 K. About 75% of the applied electrical energy are converted into the optical radiation.
Statistical Theory of Bremsstrahlung in Plasma‐Molecular Systems
Authors: Klimontovich Yu. L. , Shevchenko A. Yu. , Yakimenko I. P. , Zagorodny A. G.
Published: July 2007

Different approaches to the statistical theory of bremsstrahlung in nonequilibrium plasma‐molecular systems are compared. The spectra of bremsstrahlung, as well as collision integrals and effective dissipation constants are calculated for such systems within the framework of both classical and quantum theory.
Stopping Power of Charged Particles I
Authors: Brouwer H. H. , Kraeft W. D. , Luft M. , Meyer T. , Schram P. P. I. M. , Strege B.
Published: July 2007

The stopping power of charged particles is determined in the random phase approximation using Lenard Balescu type collision integrals. The stopping power is closely related to other single particle properties such as self energy and quasi particle life time.

In this part I, numerical evaluations are given for equal masses (of test and target particles).
Hollow Cathode Effect in a Long Perforated Cylindrical Cathode with External Coaxial Anode
Authors: Iova I. , Ciobotaru D. , Cosma B. , Dima G.
Published: July 2007

The paper presents the main characteristics of transverse mode HCE glow discharges in spectral pure helium and neon and in a He/Ne mixture in a long perforated cylindrical cathode with an external coaxial anode. At optimum values of gas pressure, when HCE gets its climatic stage, the compact negative glow evenly “fills” the cathode cavity with maximum amplifications of current and radiation.
Stimulated Brillouin Scattering of Whistler Waves by Electron‐Acoustic Wave in a Two‐Electron Temperature Plasma
Authors: Guha S. , Asthana M.
Published: July 2007

Stimulated Brillouin Scattering has been investigated in a two‐electron‐temperature plasma and it is found that the growth rate can be controlled by injecting hot electrons in the plasma. For typical values of the magnetosphere plasmas the values of growth rates for different concentrations of hot to cold alectrons are calculated.
Radiation Efficiency and Kinetic Calculations for the Positive Column in Hg/Ar Mixtures II. Impact of Tube Radius and Current Density
Authors: Kreher J. , Bartolomäus G. , Wilhelm J. , Stern W.
Published: July 2007

In a preceding part of the paper, based on experimental methods and on a corresponding kinetic model, especially the impact of the effective life times of the 63P1 and 61P1 Hg resonance levels on the main properties of the low pressure Hg‐–Ar positive column has been studied. In the presented second part these investigations, which have been performed under the aspect of their application in fluorescent lamps, will be continued. They are related to the effects of tube radius and discharge current density. New fluorescent lamps have reduced tube radii from R = 18 to 13 mm and compact lamps down to R = 5 mm. Thus it is of interest to study the electron distribution function and main macroscopic properties of such low pressure discharge plasmas, where the latter properties are obtained by adequate energy space averaging. At first, results are reported and discussed which are related to the dependence of main plasma parameters on the Hg partial pressure when reducing the discharge tube radius for constant discharge current i and argon pressure pAr. Starting from the electron distribution function the particle and energy budget will be studied in detail, especially of course the change of the ultraviolet radiation output from both Hg resonance levels 63P1 and 61P1 and, in addition, of visible radiation. Then, to understand the effect of the discharge current density, as a representative example two cases with different values of R, i and PAr but with equal current density have been investigated and discussed. Altogether the investigations made will shed light upon the complex relations in the mentioned mixture plasma and give hints to select suitable parameter values which can be useful to improve light sources.
Generation of Electromagnetic Wave in Two‐Electron‐Temperature Plasmas
Authors: Guha S. , Sarkar Ruby
Published: July 2007

It is shown that in a two‐electron‐temperature plasma a finite amplitude upper‐hybrid wave can parametrically decay into an electrostatic electron acoustic wave (EAW) and a left handed circularly polarized (LHCP) electromagnetic wave propagating along the magnetic field. The electromagnetic oscillating two stream instability is also discussed in the same system. The role of second electron component is discussed with its application in lab plasma as well as in space plasma.
Hydrodynamic Effects on Thermalisation of Dense Core with Surrounding Corona in Laser‐Imploded Z‐Layered Plasma Target
Authors: Singh D. P. , Harith M. A. , Palleschi V. , Vaselli M.
Published: July 2007

Plasma ablation effect on the heat transfer from the superthermal corona to the inner cold dense core in the case of Z layered plasma target is analysed. Thermalisation of core with the surrounding corona depends on the laser wavelength, the ‘flux‐limit’ parameter, width of Z layer and the mean electron temperature of the overlapping region between the core and the corona. The presence of Z layer reduces the electronic mean free path and consequently the width of the plasma ablation zone. Considering the self‐regulation condition for the heating of plasma target, the dependence of core‐corona coupling on the “flux‐limit”, the laser and plasma parameters has been studied.
Modelling of Secondary Electron Impact on the Self‐Consistent RF Bulk Plasma Description
Authors: Winkler R. , Capitelli M. , Gorse C. , Wilhelm J.
Published: July 2007

The impact of a secondary electron beam, generated at the electrodes and accelerated in the sheaths, on the self‐consistent treatment of the electron behaviour in an rf bulk plasma has been investigated by a parametric study. Source of electrons in the plasma are collisional ionization and secondary electron injection.

Electrons are lost by ambipolar diffusion to the electrodes of a parallel plate rf discharge configuration. The non‐stationary Boltzmann equation is used to determine self‐consistently the rf field amplitude necessary for maintaining the steady‐state rf bulk plasma as well as the time resolved behaviour of the electron energy distribution function and of all contributions to the electron particle and power balance, at given source rate and energy distribution of secondary electron injection.
Periodically Self‐Excited Moving Striations in a Low‐Temperature Gas Plasma
Authors: Ammelt E. , Willebrand H. , Purwins H.‐G.
Published: July 2007

A new nonlinear effect in a low temperature gas plasma has been found and investigated experimentally. At a critical value of the discharge current in a special glow discharge system the positive column constricts and striations evolve spontaneously. On a large time scale the pattern seems to consist of standing striations. At higher temporal resolution the striations turn out to be moving ones which are modulated by high amplitude oscillations of the total electric current and of the voltage observed at the device. In addition phenomena like period doubling and irregular behaviour occur.
Note on the E × B Instability
Authors: Kildal A.
Published: July 2007

Without appeal to trial functions an instability criterium for the inhomogeneous plasma slab is derived. The growth rate for the flute type instabilities is expressed in terms of the density perturbation n1. When n1 is put equal to the trial function used by SIMON (1963), a growth rate which differs somewhat from that of Simon is found. The reason for the discrepancy is pointed out.
Experimental Observation of Simultaneously Existing Moving and Standing Patterns in a Gas‐Discharge System
Authors: Willebrand H. , Matthiessen K. , Niedernostheide F.‐J. , Dohmen R. , Purwins H.‐G.
Published: July 2007

In a quasi 1‐dimensional lateral gas‐discharge system we observe experimentally sub‐ and supercritical bifurcations from a spatially homogeneous to an inhomogeneous distribution of the current density. Among other results we find for the first time the simultaneous existence of a nontrivial nonstationary pattern (travelling waves) with a nontrivial stationary pattern (periodic filaments) in a laterally extended dc‐driven gas‐discharge system.
Model of the Linearized Collision Operator for Plasmas with Temperature Anisotropy
Authors: Meister C.‐V.
Published: July 2007

A model kinetic operator is proposed, describing the relaxation of the first sixteen hydrodynamic moments of a two‐component plasma with temperature anisotropy with respect to an external magnetic field. The analytical expression given for the model, taking into account only density, velocity, and temperature relaxation, is more exact than a corresponding Bhatnagar‐Gross‐Krook model.
Effect of Finite Spectral Width on the Modulational Instability of Langmuir Waves described by a Nonlinear Schrödinger Equation
Authors: Roy P. C.
Published: July 2007

By using the two‐point space correlation function an equation for the power spectral density for a random Langmuir field has been derived. The dispersion relation for a monochromatic wave is regained for a delta spectrum. For a Gaussian spectrum, the maximum growth rate is less than that for a monochromatic wave. For a “meander spectrum”, the growth rate is increased with the width of the spectrum in the first stage then decreased for further increase of the width.
Theoretische Modelle des katodischen Brennflecks von Bogenentladungen
Authors: Hantzsche E.
Published: July 2007

Voraussetzungen, theoretische Grundlagen, Ergebnisse und allgemeine Erfahrungen bei numerischen Modellrechnungen für quasi‐stationäre katodische Brennflecken von (Vakuum‐)Bögen werden zusammenfassend dargestellt. Die Ergebnisse beziehen sich hauptsächlich auf Kupfer als Katodenmaterial und umfassen alle wesentlichen physikalischen Größen des Katodenflecks (der Katoden‐Oberfläche und teilweise des katodennahen Plasmas), sie beschreiben mögliche Existenz‐Zustände im Parameterraum. Insbesondere wird auch die Abhängigkeit dieser Ergebnisse von verschiedenen Änderungen der Parameter und Gleichungen untersucht. Mehrere Beispiele werden dargestellt und interpretiert. Der Einfluß der Rauhigkeit der Katodenoberfläche ist in jedem Fall beriicksichtigt worden. Schließlich werden die Gül‐tigkeits‐Beschränkungen des Modells diskutiert, und vor allem wird die große Bedeutung nichtstatio‐niirer (z B. explosiver) Prozesse im Brennfleck betont, obgleich solche Prozesse aukrhalb des Rahmens dieses Modells liegen.

Die Arbeit wird in zwei Teilen veröffentlicht. Dieser zweite Teil umfaßt die Anwendung der Modellgleichungen auf die numerische Berechnung von Brennfleck‐Parametern, die Diskussion der Ergebnisse und einige Gesichtspunkte für Weiterentwicklungen in der Theorie katodischer Brennflecken.
Development of Divertor Concept for Optimized Stellarators
Authors: Nührenberg J. , Strumberger E.
Published: July 2007

Development of Divertor Concept for Optimized Stellarators. 1. Stellarator optimization. 2. Configurational aspects. 3. Field line tracing for investigation of diversion properties. 4. Simplified SOL models: one‐dimensional estimates and Monte Carlo simulations. 5. Divertor troughs. 6. Discussion and outlook.
Fokker‐Planck Modelling of Edge Plasma Near the Neutralizer Plate in a Tokamak
Authors: Abou‐Assaleh Z. , Matte J. P. , Johnston T. W. , Marchand R.
Published: July 2007

We have modelled the transport of particles and energy through a tokamak SOL near the neutralizer plate. The electron kinetic/ion fluid code FPI and a two‐fluid code were employed for this study. Because of the electron time scale, it would lake a very long time to reach steady state with the kinetic code. We have therefore developed a hybrid technique, using both codes in alternation, to reach a full equilibrium compatible with electron kinetics. When it is used in the stand‐alone mode, the two‐fluid code's results are closest to FPI if a heat flux limiter f=0.2 is used. The electron distribution function is very non‐Maxwellian near the plate.
Longitudinal Ion Transport Coefficients in Magnetized D‐He and H‐C Plasmas
Authors: Claaßen H. A. , Gerhauser H. , Sayed Y. A.
Published: July 2007

Based on analytical formulae derived in ref./1/, longitudinal ion viscosities, heat conductivities and thermal diffusion ratios in magnetized D‐He and H‐C plasmas are calculated within Grad's 21‐moment approximation. Calculations taking full account of the finite mass ratio m+/mZ between hydrogen (deuterium) and impurity ion mass are compared with those for m+/mz≫ 1. As is to be expected, the largest discrepancies between exact and approximate results (with respect to the mass ratio) arise for D‐He plasmas. It turns out that the approximate formula for the impurity ion heat conductivity has to be extended to remove some hitherto existing deficiencies already mentioned in ref. /1/.
Simulation of Tokamak Divertor Plasmas including Cross‐Field Drifts
Authors: Rognlien T. D. , Milovich J. L. , Rensink M. E. , Kaiser T. B.
Published: July 2007

The effects of plasma currents and cross‐field drifts on single null tokamak divertor operation are simulated using a fully implicit 2‐D fluid code. Equations solved are those for particle continuity, parallel momentum, electron energy, ion energy, electrostatic potential, and neutral gas diffusion. The core and scrape‐off layer regions are separated by a magnetic separatrix, both of which are included in the simulation. The core plasma is poloidally periodic, and the inner and outer private flux regions are properly connected. The code utilizes a fully implicit method‐of‐lines scheme to advance the variables in time with a Krylov technique or a direct Newton iteration with a numerical Jacobian. Results are presented on the effects of currents and cross‐field drifts for DIII‐D single‐null parameters.
Magnetischer Teilcheneinschluß in Synchrotrons und Tokamaks
Authors: Schamel H.
Published: July 2007

Inhomogene Magnetfelder bilden die Grundlage des Teilcheneinschlusses in Speicherringen und Fusionsanlagen. Eine Diskussion der Teilchenbewegung in diesen Feldern fördert neben typenspezifischen Eigenheiten manche Gemeinsamkeit, wie den störenden Einfluß der Arnold‐Diffusion zutage.
Transport Analysis of Low Density Discharges on JET
Authors: Dnestrovskij A. Yu. , Yushmanov P. N.
Published: July 2007

Energy and particle balance of plasma in discharges with low density on JET is investigated. Self‐consistent transport analysis accounting bulk and edge plasma phenomena is carried out. It is shown that large difference between the ion edge temperature and the electron one could be the result of the influence of the secondary electron emission from the limiter in low density discharges.
Numerical Simulation of a DC‐Glow‐Discharge in an Electronegative Gas
Authors: Schmitt W. , Ruder H. , Köhler W. E.
Published: July 2007

A one‐dimensional continuum model is presented for a dc‐glow‐discharge in an electronegative gas between parallel plates. It is based on the local balance equations for particle densities and fluxes of electrons, positive and negative ions, the local electron energy balance and the Poisson equation for the self‐consistent electric field. These equations are supplemented by suitably chosen boundary conditions and are solved by the finite difference procedure HEMODES (HEnyey Method Ordinary Differential Equation Solver) which, in particular, can successfully handle the singular point occuring if the inertia term in the ion momentum balance equation is taken into account. Since not all data needed within this treatment for the simulation of realistic electronegative gases were available, a fictitious argon‐like gas has been considered which nevertheless can demonstrate the characteristic features of such a discharge. In particular, the influence of variations of the attachment and the ion‐ion recombination coefficients on the physical variables has been studied.
Laser‐Induced Fluorescence on a Metastable and a Resonant Argon Ion Level
Authors: Schubert M. , Valentini H.‐B.
Published: July 2007

Laser‐induced fluorescence on metastable and on resonant argon ion levels and spontaneous emission have been measured in two similar dc‐low pressure discharge configurations in dependence on gas pressure. Using a simple collision‐radiative model and various approximations a few results about pump rate ratios, electron temperatures, laser‐induced transition rates and relaxation rates from the metastable or resonant level are derived.
Stark Parameters of Several B II, C II and N III Spectral Lines
Authors: Djeniže S. , Popović L. Č. , Labat J. , Srećković A. , Platiša M.
Published: July 2007

Stark shifts and widths of ionized boron, carbon and nitrogen spectral lines have been measured in a low‐pressure pulsed arc plasma and compared with calculated values based on the modified semiempirical approach.
Determination of the Electron Density in an Argon Laser Plasma by Spectroscopy of the Hydrogen Hα and Hβ Lines
Authors: de Mos B. Becker‐ , Kessler B. , Seelig W.
Published: July 2007

From measurements of the Hα and Hβ spectral line profiles in a plasma, a method is developed which allows to separate the contributions of Doppler and Stark broadening. This method is superior to the deconvolution of Voigt profiles, in particular, when the lines are of low intensity. The electron density in the plasma can be calculated from the Stark broadening.

An example is the low pressure (p ≈ 1 hPa) arc discharge of argon ion lasers which is characteristised by electron densities of approximately 1014 cm−3 at heavy particle temperatures of about 104 K. These plasma parameters lead to a broadening of the Balmer Hα and Hβ spectral lines of hydrogen, which has a low concentration within the discharge area. The spectral lines are broadened due to the electron density dependent Stark effect and the temperature responsive Doppler effect. The results are consistent with predictions of the argon ion laser modelling.
Cathode Spot Phenomena in Low Current Vacuum Arcs on Arc‐Cleaned Electrode Surfaces. II. Spot Dynamics
Authors: Djakov B. E.
Published: July 2007

Part II of the paper presents results of high temporal and spatial resolution experiments with vacuum arcs on pre‐arced surfaces. Immobile spots, continuous spot motion and spot position oscillations have been observed. Tentative explanations of these phenomena are offered.
Discontinuity of Plasma Flow Parameters
Authors: Soliman H. M. , Masoud M. M.
Published: July 2007

This paper is concerned with the study of the dynamics of the expanded dense plasma from a coaxial electrodes discharge device. Experimental investigations were carried out with hydrogen gas at 0.8 Torr base pressure. The condenser bank voltage was 12 KV, which corresponds to a capacitor bank energy of 4.5 KJ.

The experimental results show that a shock wave is generated near the muzzle, and is separated from the plasma shell. The shock front velocity (Vs) and the plasma shell velocity (V1) decay within propagation up to 14 cm according to the relations, Vs ∞ Z−1 and V1 ∞ Z−2. At Z = 14 cm a discontinuity in the velocity curves occurs, where velocities of both the shock front and the plasma shell are increased. The distribution of the self‐induced axial magnetic field along the expansion chamber axis shows that at Z = 14 cm the magnetic field lines have a solitary form. Its value is decreased before Z = 14 cm according to Bz ∞ Z−1, but after Z = 14 cm as the relation Bz ∞ Z−3. The time evaluation of soft X‐ray consists of two different spikes.
On the Causes and Effects of Contaminations during rf Diode Deposition of Cr‐Si Alloys
Authors: Sobe G. , Schreiber H. , Weise G. , Heinrich A.
Published: July 2007

Investigations to the causes and effects of contaminants at the rf diode deposition of CrSi films in a non‐heated high vacuum apparatus were carried out comparing an oxygen‐free fusion target with an oxygen‐containing cermet target. The films of the fusion target contained considerable amounts of oxygen; analogously the oxygen concentration in the films was increased in the case of the cermet target. Moreover, hydrogen was found. The concentration of the contaminants decreased with the sputtering power, however the rate of incorporation increased. For high sputtering rates the contamination process was reproducible and independent of the plant conditioning; the deposited films were depth‐homogeneous. The reasons for this behaviour lie in water sources which are activated first of all by the discharge itself. The electrical properties found are explained by the contaminants and the deposition conditions.
Correlation Functions AND Thermodynamic Potentials FOR Nonideal Plasmas
Authors: Ebeling W.
Published: July 2007

The analytical structure of the binary correlation functions and the free energy of quantum plasmas is studied at low and moderate densities. By using the approach of Slater sums and effective potentials a systematic search of power law contributions to the binary correlations is given. The corresponding contributions to the free energy density up to the order O(n5/2) are calculated. The available analytical results from different theories developed with the Montroll‐Ward technique, the Greens function technique and the Feynman‐Kac technique are compared.
Kinetics of Plasma Flow in Recycling Region
Authors: Krasheninnikov S. I. , Chodura R.
Published: July 2007

Kinetics of plasma flow in tokamak SOL plasma recycling region for large ratio of Coulomb mean free path, λT, to neutral recycling length, LN, is considered. Such regimes are quite typical for both current tokamaks and ITER‐like reactor conditions and can not be treated by fluid approximation.
Effects of Rotation on Ideal Ballooning Modes
Authors: Sen S.
Published: July 2007

The stability of ideal ballooning modes in presence of a rigid toroidal rotation is revisited. Centrifugal forces induce poloidal asymmetry in the equilibrium pressure and affect the shape of the flux surfaces. Taking this two effects into account shows that the rigid rotation has a stabilising role on the the inner flux surfaces (for which r < Lp, where Lp is the pressure scale length). On the other hand, rotation is shown to have a destabilising role on the outer flux surfaces (for which r > Lp). However, the instability at the outer plasma is found to be terminated by a new stable zone which may be conjectured to be a “third” region of stability.
Boundary Conditions at the Vessel Walls being in Contact with a Hot Plasma
Authors: Behrisch R. , Naujoks D.
Published: July 2007

The main atomic processes occuring at the solid wall during plasma wall interaction are presented. The data are based on experimental results obtained under laboratory and plasma conditions and/or by computer simulations.
The Effect of the Anomalous Inertia, Viscosity and the Electric Field on the Transport Within the Sol in a Tokamak
Authors: Rozhansky V. , Tendler M.
Published: July 2007

The issue of transport on open field lines is addressed along the lines of the extended neoclassical theory invoking anomalous inertia and viscosity. Our studies suggest that tokamaks with divertors may benefit from a significant amplification of the radial electric field. It is shown that biasing of the scrape ‐ off layer (SOL) with respect to the grounded first wall results in fundamental phenomena affecting the performance of a divertor. Theoretical model appears to be consistent with experimental results obtained on TdeV.
A Simple Model for Impurity Production in Tokamaks
Authors: Zagorski R. , Romanelli F.
Published: July 2007

A simple analytical model is presented for the plasma in the region outside the limiter which describes the impurity ions transport and production in the tokamak scrape‐off layer. The equations of the model are solved analytically in the test particle approximation for the simple SOL configurations. A discussion of the solutions for different plasma parameters and target materials is presented.
Benchmarking UEDGE with DIII‐D Data
Authors: Porter G. D. , Fenstermacher M. , Groebner R. , Leonard A. , Nguyen Q. , Rensink M. E. , Rognlien T. D.
Published: July 2007

Comparisons between a 2‐D fluid simulation of the SOL plasma of a diverted tokamak and experimental data from the DIII‐D are shown. It is concluded that a simple diffusive model for perpendicular transport is consistent with the data. Discrepancies in the simulation suggest that impurity radiation may be playing a significant role in the experiment, and that further work is required to understand hydrogen recycling at the divertor.
Nonlinear interactions of azimuthal surface waves in a magnetoactive plasma waveguide
Authors: Ostrikov K. N. , Osmayev O. A.
Published: July 2007

Several possible three‐wave and four‐wave interactions, namely decay and modulational instabilities of a specific type of surface waves‐azimuthal sufaces waves (ASW)‐in a magnetoactive plasma waveguide are considered. The studied ASW propagate in the azimuthal direction at the cylindrical waveguide wall‐plasma interface.
On Modulational Instability of Turbulent Spectra
Authors: Popel S. I. , Tsytovich V. N.
Published: July 2007

The character of the modulational instability of a Langmuir wave packet is usually assumed to be similar to that of the instability of a monochromatic pump Langmuir wave if the width of the packet is small when compared to the rate of the instability. This assumption has been confirmed only for the case corresponding to the “hydrodynamical” development of the modulational instability, i.e., for the case when the phase velocity of the modulational perturbations exceeds the ion thermal velocity. Here we consider the opposite case (when the phase velocity of the modulational perturbations is less than the ion thermal velocity) which corresponds to the “static” development of the instability. We demonstrate that the above assumption is valid for the situation considered.
Expansion Model of the Neutral Component in Vacuum Arc Spot Plasmas
Authors: Hantzsche E.
Published: July 2007

Plasma generated by cathode spots in vacuum arcs expands towards the anode and the walls. In spite of a high degree of ionization (mostly), this plasma contains also a small but noticeable constituent of neutral atoms. Starting from the known analytical solution of a hydrodynamic model describing the plasma ions and electrons, the corresponding motion of neutrals is treated in a similar way. The results show: 1) The neutrals take part in the general plasma expansion; however, their final kinetic energy is lower (by about 50%) than the final energy of the ions. 2) The temperature of the neutrals also is lower than the ion temperature and decreases during expansion. 3) The acceleration of neutrals is caused partly by the pressure gradient, partly by interaction with the ions (friction); the forces diminish rapidly with increasing distance. Finally, the limitations of this approximate solution are discussed.
Optical Emission Diagnostics of an U‐Shaped Argon Stabilized d.c. Arc
Authors: Malović G. , Tripković M. , Holclajtner‐Antunović I.
Published: July 2007

The radial distribution of parameters has been measured by using the optical emission spectroscopy of an U‐shaped argon stabilized low current arc at atmospheric pressure. All the measurements reported here were performed from a side‐on observation direction by applying the Abel inversion routine. Radial distributions of apparent temperatures (Texc., Te, Ti, Tg) and of electron number density (ne) for the plasma were measured, with and without presence of KCl (spectrochemical buffer). The measured data of ne are compared to the theoretically calculated values of the equilibrium plasma composition. On the basis of the measured data, the validity of LTE concept is considered. It was found that deviation from LTE increases to the plasma periphery.
Temperature Dependence of the Rate of the Reaction N + H + Ar → NH + Ar
Authors: Deschamps J. , Godart J. L.
Published: July 2007

The rate constant for the 3 body atom recombination N + H + M with M = Ar has been measured over the temperature range 550 to 750 K in an Ar − N2 − H2 microwave flowing discharge. A temperature dependence for the rate constant is reported.
Ion Beam Driven Ion Cyclotron Double Layers
Authors: Sah O. P. , Goswami K. S.
Published: July 2007

We present here a self consistent theory of small amplitude double layers associated with electrostatic ion cyclotron waves in a plasma containing hot electrons, cold ions and traversed by an ion beam. It has been shown that compressive type of double layers solution exists when θb (beam temperature) < αb (beam concentration) < 1.
The Influence of Ion – Neutral Collisions in the Plasma Sheath on the Ion Current to an Electrostatic Probe: Monte Carlo Simulation
Authors: Trunec D. , Španěl P. , Smith D.
Published: July 2007

We have carried out Monte Carlo simulation of the motion of Ar+ ions in the space charge sheath surrounding a cylindrical Langmuir probe. From these simulations the percentage of ions crossing the sheath boundary that are collected by the probe have been determined and thus the ion currents to the probe have been calculated. It is shown that the collisions of ions with neutral helium gas atoms in the sheath increase the percentage of ions collected by the probe above that predicted by collisionless orbital motion limited current (OMLC) theory and that the exponent, χ, of the power law dependence, i+∼U, of the ion current, i+, on the probe voltage, Up, increases above the value 0.5 predicted by OMLC theory. The results of the simulations are compared with recent Langmuir probe measurements made in flowing afterglow plasmas.
UV Radiation of Low Pressure XeCl* and KrCl* Glow Discharges
Authors: Schwabedissen A. , Bötticher W.
Published: July 2007

The positive column of low pressure DC glow discharges in Xe/Cl2 and Kr/Cl2 gas mixtures has been investigated with respect to its UV radiation power and radiative efficiency for a wide range of parameters (total gas pressure: 1–30 mbar, current 10–30 mA, partial pressure of Cl2: 1–33%). Also the radial distribution of the particle number densities of XeCl* (B) and KrCl* (B) has been determined by absolutely calibrated emission spectroscopy. Optimum UV (190–350 nm) output and efficiency has been found in gas mixtures with a relative Cl2 partial pressure of 2–3% and total gas pressure of 12–18 mbar. At these parameters, the UV radiation power per column length is greater than 40 Watt/m with a radiative efficiency of 15–18%. These discharges could be used for UV induced photochemical processes.