bluuebunny/crossref_metadata_2025_split huggingface dataset:
Parametric Study of Biased Scrape‐Off Layer
Authors: Parbhakar K. 
Published: July 2007

AbstractThe particle and energy balance equations in the scrape‐off layer (SOL) plasma are solved analytically in a rectangular domain. The parallel flow is supposed to be convective, whereas the cross field flow is assumed diffusive, with modifications due to a radial E field. When the energy balance equation is neglected we get a quadratic equation for λ, the e‐folding density scale length. The normalized e‐folding scale length λ/λ0 (λ0 = λ for E = 0) is a function of single parameter α (= eEλ0/2kT, where T is the plasma temperature, e the elementary charge and k is Boltzmann's constant), and monotonically increases with α. Taking the energy balance equation into account and neglecting R1 (the ionization rate), the quadratic equation is further simplified, and λ/λ0 again depends on a single parameter, determined by Q (the input power flux), D (the cross field diffusion coefficient), γ (the sheath transmission coefficient for energy) and np (the plate density). Now λ/λ0 decreases with Q and increases linearly with D, γ and np. The variation of λ/λ0 with E is estimated for TdeV and ITER. We find that, by a proper choice of parameters, biasing may be a very valuable tool to modify the SOL properties at modest E fields, provided the heat load on the divertor plate is not excessively large.
The Influence of Parasitic Capacities on Measurements of the Dynamic Behaviour of a Gas Discharge
Authors: Weltmann K.‐D. , Deutsch H. , Unger H. , Wilke C. 
Published: July 2007

AbstractMeasurements of the impedance behaviour of the positive column of a glow discharge are falsified by parasitic capacities. A model, which respects these capacities, was developed and tested by computer simulations and experimental data. Using this model it is possible to correct the influence of parasitic capacities on experimental measured impedance curves. The efficiency of this method is demonstrated on some measurements in a neon discharge.
Corrigendum Towards Finite Element Modeling of the Tokamak Scrape‐Off Layer
Authors: Zanino R. 
Published: July 2007

AbstractA term is missing in the weak form of the total parallel momentum balance given in [1], and this affects the results of [2]. We present here the correct balance, and the corresponding results which supersede those given in [2]. The results of [3], on the contrary, are essentially unaffected.
Densities and Life Time of Electrons in KrF* Laser Gas Mixtures During the X‐Ray Preionization
Authors: Müller T. , Neuber A. , Seelig W. 
Published: July 2007

AbstractThe homogeneity and stability of TEA‐Excimer laser discharges strongly depend on the preionization. A homogeneous discharge can only develope if it is ensured that the electron density exceeds a certain level at the moment of the ignition. The kinetic of these electrons during the preionization is analyzed theoretically by the use of the Boltzmann equation for x‐ray preionized KrF* laser systems. The time dependent velocity distribution of the electrons is calculated for different buffer gases and gas mixtures. The resulting electron densities and life times are discussed and compared with experimental investigations. It is quantitatively shown at the first time that the kind of the buffer gas has a decisive influence on the velocity distribution, density and life time of the preionization electrons.
Cathode Spot Phenomena in Low Current Vacuum Arcs on Arc‐Cleaned Electrode Surfaces I. Spot Size
Authors: Djakov B. E. 
Published: July 2007

AbstractCathode spots of vacuum arcs on pre‐arced surfaces have been studied using image converter photographs with suitable temporal and spatial resolution. Part I describes experimental details and presents observations of two coexisting spot modes: the smaller spots tend to move behind the larger spots. A possible relationship to the general classification scheme for arc cathode phenomena (Anders and Anders, 1989) is discussed.
A Method for the Ion Density Estimation from the Double Probe Data at Medium and Higher Pressures
Authors: Šicha M. , Tichý M. , Hrachový V. , David P. , David T. , Touš J. 
Published: July 2007

AbstractIn this article a method of estimation of the positive ion density from the double probe data is developed. In the presented method we suggest to use the single probe collisional model developed in [10]. The method itself can, however, use any ion/electron collection model and the pressure range of applicability of the method will then depend on the range of pressures within which the used particle collection model is valid. The application of the developed method is demonstrated on a sample of experimental double probe data and the ion density determined from these data is compared to the electron density estimated independently using the microwave diagnostic technique.
Interpretation of a Planar Langmuir Probe Current — Voltage Characteristic in a Strong Magnetic Field
Authors: Stanojević M. , Čerček M. , Gyergyek T. , Jelić N. 
Published: July 2007

AbstractA theory of current collection by a planar Langmuir probe in a strong magnetic field with the direction perpendicular to the probe surface based on the models of Stangeby (J. Phys. D: Appl. Phys. 15 (1982) 1007) and Stanojevic et al. (Contrib. Plasma Phys. 33 (1993) 241) is presented. Besides the possibility of deriving the plasma density, n0, the electron temperature, Te, and the cross‐field diffusion coefficient, D1, from the measured probe characteristic reported in the previous studies, experiments in a strongly magnetized D.C. discharge argon plasma showed the applicability of this theory also for deriving the ion temperature, Ti.
Doppler Broadening and Magnetic Field Effects on Some Ion Impurity Spectra Emitted in the Boundary Layer of a Tokamak Plasma
Authors: Hey J. D. , Lie Y. T. , Rusbüldt D. , Hintz E. 
Published: July 2007

AbstractExamples are presented of Doppler broadening measurements on singlet, doublet and triplet emission spectra from the following impurity ions found in the boundary layer of the TEXTOR tokamak: Cii, Ciii, Civ, Siii, and Siiii. The shapes of these spectral lines are significantly influenced by the confining magnetic field of some 2T, in some cases exhibiting an appreciable Paschen‐Back effect which complicates their appearance. It is shown that reliable values for the particular ion temperature can be obtained from the Doppler widths of the various Zeeman components, when the presence of the magnetic field is properly accounted for. Such temperatures derived from partially ionised impurity species should, however, be cautiously interpreted, as the ions in question probably do not exist for long enough in the particular ionisation stage to achieve thermal equilibrium with the background deuterons and protons. This interpretation of our results is supported by a simple one‐dimensional model of ionisation and collisional heating processes in the plasma boundary.
Some Properties of a Novel Far UV Xenon Excimer Barrier Discharge Light Source
Authors: Stockwald K. , Neiger M. 
Published: July 2007

AbstractElectrical and optical properties of dielectric barrier Xenon discharge lamps, selectively emitting Xe/172 nm vuv radiation from a multitude of transient discharge filaments have been investigated. The lamps used were uncooled and of the flat panel type with two dielectric quartz barriers and external metal electrodes. Such lamps can be considered as small scale models of much larger flat panel uv lamps. UV emission scales almost linearly with operating frequency below 10 kHz. Both uv emission and uv efficiency rise with increasing gap spacing. The specific 172 nm emission is in the range of 100 mW/cm2 for frequencies close to 100 kHz (no lamp cooling). External efficiency at high specific uv emission is close to 10%. Higher external efficiencies up to 20% are possible at lower frequencies of a few kHz, but at reduced specific uv flux.
Gravitational Instability of a Thermally Conducting Plasma in an Oblique Magnetic Field
Authors: Bhatia P. K. , Khan Aiyub 
Published: July 2007

AbstractThe combined influence of the effects of Hall currents, magnetic resistivity and viscosity have been studied on the gravitational instability of a thermally conducting homogeneous unbounded plasma in an oblique magnetic field. The solution has been obtained through the normal mode technique and the dispersion relation has been derived. It is shown that the Jeans' criterion for gravitational instability remains unchanged. Solving numerically the dispersion relation, the dependence of the growth rate of the gravitational unstable mode on the considered physical effects has been obtained for an astrophysical situation. For conditions prevailing in the magnetized collapsing clouds, the numerical calculations for the plot of growth rate against wave number has been obtained for several values of the parameters characterizing Hall currents magnetic resistivity viscosity thermal conductivity. It is found that magnetic resistivity and thermal conductivity have destabilizing influence while viscosity has stabilizing influence on the instability of the plasma of disturbance m(ϱ) = 9 × 10−3 kg.
Vibrational Population of Hydrogen Molecules Excited by an RF Discharge in an Expanding Thermal Arc Plasma as Determined by Emission Spectroscopy
Authors: Otorbaev D. K. , de Graaf M. J. , van de Sanden M. C. M. , Schram D. C. 
Published: July 2007

AbstractThis work is devoted to the determination of the vibrational population of hydrogen molecules in the ground and excited electronic states from the analysis of visible spectra of the H2 molecules excited by an RF discharge in an expanding thermal arc plasma. Comparison of the experimental results on relative electron‐impact excitation cross sections for the transition H2(X1Σ, υ0 = 0)→ H2(d3IIu, υ′) with other experiments, and with calculations based on the Franck‐Condon principle, shows good agreement. This means, that for plasma under investigation: 1) in the ground electronic state H2(d3IIu,υ′), only the lowest vibrational level with υ0 = 0 is significantly populated, and 2) direct electron exictation of H2(d3IIu, υ′, υ′) state from the ground state H2(X1Σ, υ0 = 0) dominates.
Investigation of the Plasma of a Magnetron Discharge during Titanium Deposition
Authors: Adler F. , Kersten H. , Steffen H. 
Published: July 2007

AbstractIn the present work the deposition of titanium layers using a planar‐magnetron sputtering system is performed. To optimize the sputtering process and to improve the layer quality the plasma has been monitored in front of the target and near the substrate. The plasma was studied by means of Langmuir‐probe diagnostics and optical emission spectroscopy (OES). The internal plasma parameters (ne, kB Te) and the relative power dependence of the neutral densities (nTi) at the target as well as at the substrate have been determined as functions of discharge power and pressure.It was found that the plasma densities increase with power and pressure and reach a maximum at a certain gas pressure (0.8 Pa) connected with a maximum of the energy influx and a maximum of the mass density of the deposited films.
Investigations about the Influence of the External Circuit Elements on the Propagation of Ionization Waves in the Positive Column of a Neon Glow Discharge
Authors: Weltmann K.‐D. , Bräuer T. , Deutsch H. , Wilke C. 
Published: July 2007

AbstractOur investigations have been motivated by former works of Michel and Achterberg [1]. They described the important influence of the external circuit elements and connected therewith the mechanism of feedback (Barkhausen k · v ≧ 1). The properties of external and self‐excited moving striations (threshold current, fundamental frequency) are strongly influenced by the feedback. This paper demonstrates the differences occuring either a voltage or a current source in the external circuit is used in order to perturb the discharge and to realize different degrees of feedback by changing the external resistor Rext. of the discharge. It is shown the impact on the fields of existence of self excited striations in a non driven discharge. Furthermore our investigations yield differences in the width of Arnol'd tongues [2] of periods one and two in the perturbed discharge depending on a varied degree of feedback. Last not least its influence on the behaviour of quasiperiodic and chaotic states is demonstrated. The investigations permit first information concerning the sensivitity of one parameter variation (feedback controll by external resistor) which might be used e.g. for a stabilization of unstable periodic orbits (controlling chaos).
Electron and Heavy Particle Energy Redistributions in Glow Discharges in Gas Mixtures
Authors: Nagpal R. , Garscadden A. 
Published: July 2007

AbstractA review is presented on the contemporary modelling efforts describing the coupled electronic and heavy particle excited state kinetics in glow discharges in gas mixtures. The dramatic effects of the heterogeneous collisional interactions between the electronic/vibronic states of the gas mixture constituents on the dissociation, ionization, gas heating, discharge impedance and power loading are described and discussed. A template construct of a collisional model of molecular gas mixtures where the electron kinetics are obtained from the collisional Boltzmann transport equation, and the vibrational kinetics are governed by a system of vibrational master equations, is described in detail. Three test cases are discussed: (i) Ar − Cl2, (ii) N2 − O2, and (iii) N2 − H2. The generic guidelines that are derived from the analysis of the above mixtures are that: (a) There is a strong coupling between the dissociation and the ionization balances in gas mixtures. It is cautioned that for most conditions, even in pure molecular gases, neither channel can be studied independently of the other. (b) In molecular gas mixtures, the heterogeneous collisional interactions between the metastable excited electronic states play important roles in determining the discharge characteristics. (c) The calculations assuming constant E/N and constant electron density in gas mixtures can lead to inconsistent and misleading conclusions on the throughput of these discharges.
Negative Ions in Low Pressure Discharges
Authors: Stoffels E. , Stoffels W. W. , Vender D. , Haverlag M. , Kroesen G. M. W. , de Hoog F. J. 
Published: July 2007

AbstractSeveral aspects of negative ions in low pressure discharges are treated. The elementary processes, in which negative ions are produced and destroyed, are summarized. The influence of negative ions on plasma operation is analyzed in terms of transport equations. It is shown that diffusion, electric field, power input, plasma stability and plasma boundary layer are strongly affected by the presence of negative ions. Finally, an overview is given of experimental techniques for the detection of negative ions. Some typical results in low pressure discharges are presented.
CH3 and CH Densities in a Diamond Growth DC Discharge
Authors: Menningen K. L. , Childs M. A. , Toyoda H. , Ueda Y. , Anderson L. W. , Lawler J. E. 
Published: July 2007

AbstractA highly sensitive multi‐element optical absorption technique is used to measure the absolute column density of both CH3 and CH radicals in a dc hollow cathode plasma‐assisted chemical vapor deposition (CVD) system with CH4 and H2 used as the input gases. The plasma gas temperature is determined at different spatial points using the H2 emission spectrum near 460 nm. The spatial maps of the temperature and the radical densities provide information on the chemical processes taking place in the discharge. The CH3 and CH radical density measurements made in the dc discharge system are compared with similar measurements made in a hot filament CVD system. The [H]/[H2] ratio is derived from the CH3 and CH densities using an analysis based on partial thermodynamic equilibrium of the single carbon hydrocarbon abstraction reactions.
Ionization Cross Sections of Silane and Disilane by Electron Impact
Authors: Krishnakumar E. , Srivastava S. K. 
Published: July 2007

AbstractPartial ionization cross sections for silane and disilane by electron impact have been measured for electron energies in the range of threshold to 1000 eV using a crossed beam geometry and employing a pulsed electron beam and a pulsed ion extraction technique. The cross sections were normalized by using the relative flow technique. For ease of use in various plasma modeling we have fitted the cross sections to an empirical formula.
Field Calculations for Permanent Magnets used for Glow Discharges
Authors: Heise C. , Kock M. 
Published: July 2007

AbstractIf a permanent magnet has both a homogeneous polarization inside the material and a linear demagnetization characteristic in external fields, its magnetic field can be expressed using a surface pole model. For magnets satisfying these conditions and, in addition, having a rectangular shape, the fields at any given point in space can be calculated analytically. An algorithm for this calculation is presented in a form that can easily be implemented into a computer program. In our experiments we used Nd2Fe14B magnets to support low pressure glow discharges by magnetic fields. The magnets can be seen as composed of elementary magnets with rectangular shape, for which the magnetic field distribution is calculable. We present results of field calculations for various configurations of permanent magnets that we used in hollow cathode and Penning discharges.
A Comprehensive 2‐D Divertor Data Set from DIII‐D for Edge Theory Validation
Authors: Fenstermacher M. E. , Allen S. L. , Hill D. N. , Leonard A. W. , Lasnier C. J. , Petrie T. W. , Wood R. D. , Brooks N. H. , Buchenauer D. A. , Carlstrom T. N. , Cuthbertson J. W. , Doyle E. J. , Evans T. E. , Garbet P.‐M. , Harvey R. W. , Hyatt A. W. , Isler R. C. , Jackson G. L. , James R. A. , Jong R. A. , Klepper C. C. , Mahdavi M. A. , Maingi R. , Meyer W. H. , Moyer R. A. , Nilson D. G. , Porter G. D. , Rhodes T. E. , Schaffer M. J. , Staebler G. M. , Stambaugh R. D. , Stockdale R. E. , Thomas D. M. , Tugarinov S. , Wade M. R. , Watkins J. G. , West W. P. , Whyte D. G. 
Published: July 2007

AbstractA comprehensive set of experiments has been carried out on the DIII‐D tokamak to measure the 2‐D (R,Z) structure of the divertor plasma in a systematic way using new diagnostics. Measurements cover the divertor radially from inside the X–‐point to the outer target plate and vertically from the target plate to above the X–‐point. Identical, repeatable shots were made, each having radial sweeps of the X–‐point and divertor strike points, to allow complete plasma and radiation profile measurements. Data have been obtained in ohmic, L–‐mode, ELMing H–‐mode, and reversed BToperation (ΔB drift away from the X–‐point). In addition, complete measurements were made of radiative divertor plasmas with a Partially Detached Divertor (PDD) induced by D2 injection and with a Radiating Mantle induced by Impurity injection (MI) using neon and nitrogen. The data set includes first observations of the radial and poloidal profiles of the X‐point, inner and outer leg plasmas in PDD and RMI radiative divertor operation. Preliminary data analysis shows that intrinsic impurities play a critical role in determining the SOL and divertor conditions.
Implementation into B2 of a 21‐moment description for the parallel transport
Authors: Bergmann A. , Igitkhanov Yu. , Braams B. , Coster D. P. , Schneider R. 
Published: July 2007

AbstractThe multifluid edge plasma code B2 is improved by implementing a new description for the parallel heat flux, thermal force, and viscous momentum flux obtained by a 21‐moment approximation. An exact transformation to a set of only two equations for each isotope is used. Hence there is only a moderate increase of the computational time. The new code provides a more accurate treatment of the parallel transport, in particular the impurity transport, valid for any impurity concentration.
Effect of Perpendicular Transport on Edge Plasma Energy Loss due to Impurity Radiation
Authors: Krasheninnikov S. I. , Knoll D. A. 
Published: July 2007

AbstractWe consider the effect of perpendicular energy transport in the low temperature divertor region on impurity radiation loss from the SOL plasma. We show that the perpendicular energy transport results in enlargement of the volume with relatively low temperature and a very high density of the plasma. High plasma density causes a strong energy loss due to impurity radiation peak in this low temperature region. For low Z impurity the energy transport due to plasma convection and neutrals also can strongly influence the volume of low temperature region.
Reduced Two‐Field Equations and Anomalous Transport Scaling in Low‐Temperature Plasmas
Authors: Spatschek K. H. , Eickermann Th. 
Published: July 2007

AbstractAfter a review of more or less systematic approaches for normal as well as anomalous particle transport phenomena across a magnetic field, simplified macroscopic models are discussed. A reduced two‐field model for collision‐dominated low‐temperature plasmas is presented. Although it looks similar to its high‐temperature analogue (known as the Hasegawa‐Wakatani equations), it has significant peculiarities which are discussed in detail. Some basic results following from the reduced two‐field model, e.g. anomalous transport scaling close to the onset of collisional driftwave instability, are discussed.
Time Integrated Measurements of the Spectral Line Emission of a Neon Pinch Plasma Radiation Source in the 0.9–1.4 nm Wavelength Range
Authors: Grieser M. , Roth M. , Eckrich H. , Michel L. , Seelig W. 
Published: July 2007

AbstractTime integrated measurements of the line emission of hydrogen‐like and helium‐like neon from a dense plasma focus device were performed. Relative intensities of Lyman‐series emission from Ne X were measured end‐on and side‐on showing strong deviation from thermal equilibrium and indicating substantial population inversion between levels n = 5 and n = 2.
Investigations of the Cathode Spot Dynamics in a Vacuum Arc Coating Process
Authors: Ellrodt M. , Kühn M. 
Published: July 2007

AbstractInfluence of cathode materials (Ti, Al, Cu, TiN), ambient gases (Ar, N2, p = 0.1‐1 Pa) and the arc current itself on the motion and the velocity of cathode spots in an arc coating process have been investigated with the help of a new high speed framing camera. It was found, that the cathode material causes different spot currents but in general the spot arrangement and the motion on the surface are similar. Surface contaminations due to ambient gases affect this dynamics in several ways. Insulating layers like AIN can drastically increase the instantaneous spot velocity, for example from <5 m/s on Al up to 170 m/s on AIN contaminated areas. TiN layers with a high conductivity increase the spot mobility at first. But at nearly completely contaminated surfaces (simulated by a TiN cathode), the mobility is strongly decreased. The values change from an average velocity of 6.3 m/s with a diffusion constant of 54 cm2/s (Ti, 0.01 Pa) to 2 m/s and 6.4 cm2/s at TiN.The course of the instantaneous spot velocity during the spot splitting phase was investigated too. The instantaneous spot velocity of each of the two new spots originated from the starting spot is relatively high (30–40 m/s) within the first 50 μs. The cathode material and the ambient gases are of slight influence in this phase. The movement is directed. In the further development the instantaneous spot velocity is decreasing to values under 5–10 m/s. The motion is now more and more random. Additionally it could be proved, that the lower stability limit for a stable discharge is strongly connected with the spot current, which depends on discharge conditions.