bluuebunny/crossref_metadata_2025 huggingface dataset:
Magnetic Electron Drift Vortex Modes in General Equilibria
Authors: Stenflo L. , Yu M. Y. , Shukla P. K.
Published: July 2007

The equation and dispersion relation describing the magnetic electron drift vortex mode in a generalized equilibrium are presented. The results are useful for investigating related surface wave problems as well as for identifying the various forms of the magnetic electron drift vortex mode.
Nonlinearly‐coupled Langmuir and Ion‐Acoustic Waves
Authors: Shivamoggi Bhimsen K.
Published: July 2007

In a plasma acted on by an intense laser field, one encounters the problem of nonlinearly‐coupled Langmuir and ion‐acoustic waves. We use a generalized perturbation theory to discuss the nature of coupled oscillatory waves in this system, and the possibility of formation of an ionsheath.
A Probe Method for Determination of time Evolution of Metastable Atoms Density in a Flowing Afterglow Plasma
Authors: Pavlík J. , Glosík J. , Šícha M. , Tichý M. , Potoček P.
Published: July 2007

The Langmuir Probe Measurement of the electron density and electron temperature has been made in the argon flowing afterglow plasma. Furthermore the metastable and charged particle densities evolution in the afterglow plasma are investigated by means of a numerical solution of the set of balance equations. From the fitting of the results of these calculations to the experimental data obtained from Langmuir probe measurements it is possible to determine the evolution of the metastable atoms density in the flowing afterglow plasma.
Harmonics Analysis of the Electron Component of rf Bulk Plasmas. I. Theoretical Base
Authors: Voigt H.‐D. , Wilhelm J. , Winkler B.
Published: July 2007

rf discharges are increasingly used in low pressure plasma processing, i.e. for etching, film deposition and sputtering. The modelling of such discharges is a very complex task, especially dependent on discharge conditions, however of large importance for the insight into the main physical processes and thus for their control to improve the final results. One main important aspect is the determination of the electron velocity distribution function and of relevant rate and transport coefficients. The paper contributes to the treatment of this problem. In the first part a systematic Fourier expansion of the kinetic equation and of the consistent particle, energy and momentum balance equation is described. Then, a mathematical analysis of the resulting ordinary differential equation system for the coefficients of the Fourier expansion is performed. Based upon this we succeeded to develop a numerical approach to calculate the physical relevant solution of this system. By this approach in addition to the harmonics of the distribution function that of relevant macroscopic quantities, as transport coefficients and collision frequencies, can be determined. In the second part of this paper this method will be applied to investigate the bulk plasma of a rf discharge in molecular hydrogen.
On the Relationship Between Macroscopic and Microscopic Time Constants in gas Discharges
Authors: Wilke C. , Kablan N. , Deutsch H.
Published: July 2007

The complicated relationship between macroscopic and microscopic time constants in gas discharges was given on the basis of the theory of the positive column of glow discharges.
The Thermal Balance of Substrates During Plasma Processing
Authors: Kersten H. , Kroesen G. M. W.
Published: July 2007

In this paper an example is given for measurement and calculation of the energy influx towards a substrate during plasma processing in a supersonic reactor. From the results the energy transfer coefficients are obtained for several pressures. Also the evolution of the profile of the temperature is presented.
Langmuir Probe Determination of Charged Particles Density in an rf Discharge
Authors: Šícha M. , Špatenka P. , Tichý M.
Published: July 2007

The article presents results of probe measurements of the electron and ion densities in an argon rf discharge. The electron density is determined from the electron probe current at the space potential which is estimated by extrapolation of the linear part of the probe electron current dependence to the plasma potential. The plasma potential is calculated from the floating potential. The positive ion density is determined from the probe ion saturated current according to collisional KOPICZYNSKI and ZAKREWSKI model [1]. The agreement between the electron and ion densities is better than in the work of HOPKINS and GRAHAM [2], where the collisionless Lafram‐boise theory is used under similar conditions.
Arc Discharge in a Channel with Transparent Walls at Intense Flow Rates of a Plasma Forming Gas
Authors: Pustogarov A. V. , Karabut A. B. , Kucherov Ya. R.
Published: July 2007

The arc discharge was studied in a transparent channel at an intense flow rate of nitrogen, hydrogen, air, carbon dioxide in the current range 100–1500 A. The internal diameter of the porous channel varied from 10 to 34 mm, the length ‐ from 50 to 150 mm, the air and nitrogen flow rates ‐ from 0.05 to 1.5 kg/s, hydrogen ‐ from 0.005 to 0.05 kg/s. The electric field strength in the arc channel reached a value of 300 V/cm for N2 and 500 V/cm for H2. The effect of plasma thermochemical non‐equilibrium was discovered.
Approximate Solution of the Saha Equation — Temperature as an Explicit Function of Particle Densities
Authors: Sato M.
Published: July 2007

The Saha equation for a plasma in thermodynamic equilibrium (TE) is approximately solved to give the temperature as an explicit function of population densities. It is shown that the derived expressions for the Saha temperature are valid approximations to the exact solution. An application of the approximate temperature to the calculation of TE plasma parameters is also described.
Hydrodynamic Theory of Low‐Pressure Multi‐Component Discharges with Neutral Gas Depletion
Authors: Shapiro D. A. , Valentini H.‐B.
Published: July 2007

A hydrodynamic description of a low‐pressure discharge with singly and doubly‐charged positive ions in the high ionization regime is given. Modified hydrodynamic equations are used to include the neutral gas depletion by ionization processes under free‐flight conditions. Analytical formulas for the concentrations of the two species of ions at the discharge axis are derived.

Numerical results for the radial drift velocities, the radial distributions of the densities and the neutral gas temperature are presented. The nature of the dip in the density profile of the singly‐charged ions and the decrease in their radial drift velocity near the axis with increasing degree of ionization are discussed.
Spectroscopic Detection of Oxygen in Nitrogeneous Gas Mixtures
Authors: Ross W. , Berger D. , Erbs H. , Gündel H. , Kornejew P. , Volkmann H.
Published: July 2007

A pulsed high‐frequency discharge was used to excite a non‐LTE (local thermal equilibrium) plasma with a high specific power density sufficiently high to dissociate oxygen and gaseous oxides. If traces of hydrocarbons were present in the gas mixture, in the spectrum the Violet system of CN appeared with a long radiation decay time. The CN bands are excited preferentially by inelastic collisions with metastable nitrogen molecules (A3σ). These levels can be efficiently depopulated by competing impact with atomic oxygen. By measuring the radiation signal during the radiation decay a dynamic range of 6 was achieved for a variation of the oxygen content between 1 and 100 ppm.

The measured radiation decay of the violet CN 0–0‐bands at 388 nm was simulated by a simple model of rate equations valid in the time region where diffusion processes may be neglected.
Investigation of Gas Degradation in CO2  N2 Pulse Discharges I. Long Term Behaviour of Pulsed Laser Discharges in CO2 — N2 Gas Mixtures
Authors: Rudolph R. , Bisin P. , Berger D. , Francke K.‐P.
Published: July 2007

The correlation between the plasma resistance and the laser output parameters has been investigated in pulsed CO2 — N2 discharges. The strong increase of the discharge resistance during gas degradation can be explained on the basis of strong attaching gas components. In degraded mixtures a supression of discharge instabilities together with the restoration of the laser pulse energy is possible by increasing the reduced electric field E/N temporarily.
Investigation of Gas Degradation in CO2–N2 Pulse Discharges II. Origin and Influence of Highly Attaching Species
Authors: Rudolph R. , Bisin P. , Berger D.
Published: July 2007

The mechanism of plasma resistance increase found in sealed CO2—N2 discharges has been analyzed. From the various species occuring in such discharges only oxides of nitrogen seem to be suitable candidates. Indeed the degradation process can be simulated by adding a certain amount of N2O. The failure in detection of these contaminants in naturally degraded mixtures suggests the involvement of complex molecular species depending strongly on the discharge conditions.
Kinetic Buneman Instability in a Homogeneous Hot Electron Plasma
Authors: Khalil S. H. M. , Mohamed B. F.
Published: July 2007

The development of Buneman kinetic instability in plasma with hot electrons and cold ions is investigated in the quasilinear approximation at current velocites close to the instability threshold values. It is shown that the contribution of electron's dielectric permeability in the dispersion equation is negligible and that quasilinear theory has in general stabilizing effect.
The Nonstationary Behaviour of the Electron Current Density in the Weakly Inonized Plasma at High Field Frequencies
Authors: Gundermann S. , Winkler R.
Published: July 2007

Based upon former studies concerning the nonstationary electron kinetics in collision dominated, weakly ionized plasmas the phase delay between the ac electric field component and the resultant ac electron current density has been analysed, theoretically and experimentally, under the specific conditions of a microwave field superimposed to a dc discharge plasma column. The complex plasma conductivity and thus the phase delay has been calculated by solving an appropriate electron kinetic equation. The same quantities have been experimentally determined by using the microwave cavity which operates with different resonator modes. A comprehensive comparison between calculated and measured quantities for different neon discharge plasmas leads to a complete confirmation of the theoretical expectations.
Potential Surface Waves in a Warm Nonisothermal Plasma Bounded by Metal
Authors: Azarenkov N. A. , Ostrikov K. N.
Published: July 2007

The dispersion properties of potential surface waves (SW), propagating at a warm nonisothermal plasma‐metal boundary across the external magnetic field are studied in this paper. The existence of potential SW is shown to be possible in frequency ranges, where electromagnetic SW do not exist. The influence of transverse plasma density inhomogeneity on dispersion properties of the SW considered is studied as well.
Optical Emission Diagnostic of a Low Pressure Planar Microwave Discharge for Plasmachemical Deposition
Authors: Röpcke J. , Ohl A.
Published: July 2007

Low pressure microwave plasmas are of growing interest for plasmachemical applications since they have special and in some cases unique advantages with respect to other plasma excitation methods. Subject of this paper are spatially resolved measurements of the optical emission of a special planar microwave plasma source utilized to investigate different plasmachemical processes. The optical emission spectroscopy (OES) is used as a tool to get information concerning the spatially distribution of reactive atom and molecule concentration by actinometry and concerning the neutral gas temperature by measurements of Doppler line broadening. The results refer to hydrocarbon containing hydrogen plasmas which gas pressures above 100 Pa. Surprisingly measurements confirm an earlier developed simplified two layer model consisting of a preferentially physically active plasma layer near the microwave window followed by a preferentially chemically active decaying region. They give evidence that this model is more adequate to the real physical situation as assumed until now.
The Application of Moment Equations to Scrape off Layer Plasmas
Authors: Radford G. J.
Published: July 2007

A set of 21 moment fluid equations has been applied to two aspects relevant to scrape off layer plasma transport codes. The first of these is the provision of classical parallel transport coefficients, particularly for impurity plasma ions. Although more general results have been obtained, those only for a low impurity density common ion temperature plasma are presented. The results reflect the coupling between heat and particle fluxes and a coupling of the main ion fluxes into the impurity fluxes. The second application is in response to the problem of nonphysical values for classical viscosities and heat fluxes in regions with large gradients. The basic five moment description of the Braginskii equations has been extended to a full thirteen moment approximation. The new equations are given and some preliminary numerical results from a one dimensional code are discussed.
Parametric Study of Biased Scrape‐Off Layer
Authors: Parbhakar K.
Published: July 2007

The 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

Measurements 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

A 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

The 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

Cathode 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.
OCP Reference Theory of Dynamic Structure Factor of Expanded Liquid Metals
Authors: Trigger S. A. , Allahyarov E. A. , Schram P. P. J. M.
Published: July 2007

We present a theoretical formula and calculations of the dynamic structure factor (DSF) of expanded liquid metals on basis of the pseudopotential theory and the OCP approximation.
Plasma Behaviour of Colloidal Crystals
Authors: Schram P. P. J. M.
Published: July 2007

Longitudinal and transverse waves in colloidal crystals are excited by Brownian motion. The theory of dispersion relations including the influence of counter—ionic diffusion is discussed and confronted with experimental results.
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

In 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

A 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

Examples 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

Electrical 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

The 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

This 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

In 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

Our 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

A 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

Several 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

A 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

Partial 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

If 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

A 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

The 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

We 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

After 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

Time 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

Influence 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.
Ion‐ion Correlations in Dense Plasma Derived from a Quasimolecular Thomas‐Fermi Model
Authors: Frey H.‐D. , Meyer‐ter‐Vehn J.
Published: July 2007

Ion‐ion correlation functions of shock‐compressed, strongly coupled aluminum plasma with 1–5 times solid density and 1–20 eV temperature are calculated by using a quasimolecular Thomas‐Fermi model to determine the interaction potential between ions and by solving the Ornstein‐Zernike equation together with the Percus‐Yevick and, alternatively, the hypernetted chain aproximation. The results are checked by Monte‐Carlo simulations and are compared with other independent calculations taken from the literature.
Dissociation and Thermodynamics in Dense Hydrogen Fluid
Authors: Bunker A. , Nagel S. , Redmer R. , Röpke G.
Published: July 2007

The behavior of matter at high pressures is studied for a better understanding of planetary interiors and the structure and evolution of stars, or for inertial confinement fusion. Especially, the phase diagram of hydrogen and helium as the most abundant elements in the universe has been studied both theoretically and experimentally up to ultra‐high pressures in the Mbar region where metallization is expected to occur. While static high‐pressure experiments in diamond anvil cells give no evidence for metallic conduction in solid hydrogen up to 250 GPa, recent dynamic shock‐wave experiments in fluid hydrogen have demonstrated metallization for the first time at 140 GPa and 3000 K. The equation of state, possible phase transitions, and the structural properties of fluid hydrogen at ultra‐high pressures as well as of hydrogen plasma at elevated temperatures are of special interest. We use here analytical calculations and Monte Carlo simulations to determine the pair distribution functions in partly dissociated hydrogen. The equation of state and the degree of dissociation are calculated. The gradual transition from molecular to atomic hydrogen occurs due to pressure dissociation. Furthermore, we show the influence of dissociation on the proton‐proton pair distribution function.
Introduction in Quantum Theory of Open Systems
Authors: Klimontovich Yu. L.
Published: July 2007

In this paper we try to define the author's position with respect to some fundamental problems of quantum theory.
The Interplay of Electron‐Phonon and Electron‐Electron Scattering within the Two‐Time Green's Function Description
Authors: Köhler H. S. , Binder R.
Published: July 2007

We present numerical results for electron‐phonon and electron‐electron scattering in optically excited electron plasmas in bulk semiconductors. Our results are based on the full two‐time Green's function approach. They include quantum mechanical memory and correlation effects because the scattering integrals are generalizations of the conventional Boltzmann scattering integrals. The interplay of two different scattering mechanisms is studied and compared to results where only one scattering mechanism is present.
Lenard—Balescu—type Kinetic Equation for Composite Particles in Dense Quantum Plasmas
Authors: Schlanges M. , Bornath Th.
Published: July 2007

A kinetic equation for the distribution function of two—particle bound states in dense quantum plasmas is derived in the framework of the real—time Green's function technique. Using a generalized V5‐approximation Lenard—Balescu—type collision integrals are derived taking into account elastic, inelastic and reactive three—particle processes with dynamically screened interaction. An extended random phase approximation is discussed for the polarization function.
To the Theory of Colloidal Plasmas
Authors: Schram P. P. J. M. , Trigger S. A.
Published: July 2007

The problem of the microscopic effective pair interaction is discussed for two‐ and many‐macroion colloidal plasmas. For a crystallized state of colloids with charged particles the melting curve and the minimal charge for crystallization is considered analytically for a DLVO‐type of effective potential. The damping of longitudinal waves is investigated for infinite and finite sizes of colloidal crystals.
Debye Length in a Neutral‐beam‐heated Plasma
Authors: Wolle B.
Published: July 2007

The scale length for an effective shielding of a charged particle in a plasma is the Debye length, which is for Maxwellian velocity distributions determined by the ratio of the temperature to the density. However, fusion plasmas heated by neutral‐beam injection (NBI) exhibit highly non‐Maxwellian slowing‐down velocity distributions. In this case, the evaluation of the characteristic shielding distance from these velocity distributions requires the solution of Fokker‐Planck‐Poisson equations. In this paper, the effect of NBI slowing‐down velocity distributions on the shielding distance are discussed. Analytic expressions for the Debye length of a neutral‐beam‐heated plasma are given. The results are compared to the Maxwellian case.
Modelling Efforts on the Helical Near Field Divertor of the Dynamic Ergodic Divertor (DED) for TEXTOR‐94
Authors: Eich Th. , Finken K. H. , Kaleck A.
Published: July 2007

As a first step for the modelling of the plasma‐wall interaction of the proposed Dynamic Ergodic Divertor (DED) of TEXTOR‐94, the topology of the magnetic field lines of the divertor is analysed. Despite the strong ergodization, the magnetic field lines intersecting the wall in one poloidal turn form continuous sets. These sets are visualised by a 2‐D imaging technique; the field lines of each set of starting values is traced one poloidal turn clockwise and ctr. clockwise, marking those lines intersecting the wall. An overlay of the marked starting points defines areas with properties of a scrape‐off layer and areas with field lines ending on one side in the ergodic layer and one side on the wall. The edge plasma can be described by a 2‐D model; the model treats a part of the plasma as that of a conventional scrape‐off layer and another part with “half open” field lines connecting the divertor target plate with the ergodic layer. Calculations of the power flux distribution in the DED‐near field divertor are presented.
Scrape‐Off Layer Turbulence Theory and Simulations
Authors: Xu X. Q. , Cohen R. H.
Published: July 2007

Significant investigations in the area of scrape‐off layer (SOL) turbulence theory and simulations are reviewed. The paper begins with description and derivation of the various models investigating specific linear modes as well as a discussion of the regions of validity. Special attention is given to various low‐frequency electromagnetic drift‐types modes in an x‐point divertor geometry, which are generally believed to be relevant under normal operating conditions for current and future large fusion devices. The anomalous transport from simulations and from mixing length estimates are discussed and compared with results infered from experiments. Studies of mechanisms for the L‐H transition due to turbulent transport in the SOL, and its impact on the H‐mode power threshold, are also surveyed.
Comparisons of physical and chemical sputtering in high density divertor plasmas with the Monte Carlo Impurity (MCI) transport model
Authors: Evans T. E. , Finkenthal D. F. , Loh Y. S. , Fenstermacher M. E. , Porter G. D. , West W. P.
Published: July 2007

The MCI transport model was used to compare chemical and physical sputtering for a DIII‐D divertor plasma near detachment. With physical sputtering alone the integrated carbon influx was 8.4 × 1019 neutrals/s while physical plus chemical sputtering produced an integrated carbon influx of 1.7 × 1021 neutrals/s. The average carbon concentration in the computational volume increased from 0.012% with only physical sputtering to 0.182% with both chemical and physical sputtering. This increase in the carbon inventory produced more radiated power which is in better agreement with experimental measurements.
Experimental Study of Atmospheric Pressure Glow Discharge
Authors: Trunec D. , Brablec A. , Šťastný F.
Published: July 2007

The atmospheric pressure glow discharge (APGD) is a new type of the discharge discovered by OKAZAKI et al. [1] recently. The APGD can be used in practical application (e.g. ozone generation), but the phenomena occurring in the discharge are not fully understood. We studied the APGD driven at 50 Hz, applied voltage up to 5 kV and burning in helium, argon and nitrogen. We used a planar configuration of discharge cell: metal electrode ‐ dielectric plate (1 mm thick) ‐ discharge gap (1.5 mm thick) ‐ dielectric plate ‐ metal electrode. Between the metal electrode and the dielectric plate a fine metal mesh was placed. For each gas we recorded the time dependence of power supply voltage and the time dependence of charge transferred through the discharge. We recorded also the discharges by the CCD camera with a video recorder. The same measurements were done in case of the discharge cells without the metal mesh. The metal mesh changes the discharge significantly. In the case of discharge cell with the mesh we can observe a homogeneous discharge and only one peak in the discharge current per half cycle of applied voltage while in the case of the discharge without mesh we observed individual micro‐discharges and many pulses in the current per half cycle. This effect is most obvious in helium.

In order to explain the observed phenomena we calculated the electric field in the discharge cell for APGD and propose a possible explanation of APGD. It has been found that the mesh does not influence the electric field in the discharge gap. Thus we propose that the mesh could influence the discharge by its electrical resistance, which is higher than the resistance of the metallic electrode.
Optical Properties of Laser‐Produced Plasmas
Authors: Fehr R. , Schlanges M. , Kraeft W.‐D.
Published: July 2007

The interaction of high intensity femtosecond laser pulses with matter allows the production of plasmas with high electron densities. This enables the study of basic plasma physics in regimes relevant to astrophysics, atomic physics, or in strongly correlated plasmas. Much of the understanding of such plasmas depends on the knowledge of the optical properties. The diagnostic requires theoretical models for the interpretation of experimental data. We study the dielectric function and the electric conductivity in the framework of a generalized Drude model. The required collision frequencies are taken in Born and strong coupling (T‐matrix) approximations. Furthermore, we try to give an estimation of the influence of nonlinear, high frequency effects of the electrical field. In order to describe the temporal evolution of the plasma, we determine the composition of the plasma solving Saha's equation. Therefore we investigate different approximations for the effective ionization energy including Padé formulas for the correlation part of the chemical potential.