bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Rotation of Ions and Neutrals in a Cylindrical Magnetized Hollow Cathode Argon Arc
Authors: Timmermans C. J. , Lunk A. , Schram D. C. 
Published: July 2007

AbstractIn a magnetized hollow cathode arc rotational velocities of ions and neutrals and their temperatures were measured in axial and radial dependence. In comparison with theory experimental results give a detailed analysis of radial transport phenomena.
Cathode Erosion in Vacuum Arcs and Unipolar Arcs
Authors: Nürnberg A. W. , Bauder U. H. , Mooser C. , Behrisch R. 
Published: July 2007

AbstractThe cathode spots from vacuum arcs on 316 stainless steel are compared with the tracks found on the same material after exposure to the plasma of the tokamak TFR 600. Further the erosion yields of vacuum arc cathodes of 316 stainless steel and titanium are determined from experiments and the measured values are compared with theoretical estimates. The velocity of the arc is investigated as a function of the applied magnetic cross‐field. The scatter of both, the velocity data and the erosion yields is substantial. Improved experiments are planned.
Reaktionskinetische Vorgänge an der Grenzfläche zwischen nichtisothermem Plasma und Feststoff
Authors: Friedrich J. 
Published: July 2007

AbstractAn der Grenzfläche nichtisothermes reaktives Molekülgasplasma – Feststoff bilden sich ätzgasspezifische funktionelle Gruppen durch Anlagerung von Plasmaspezies als Vorstufe für Abbauvorgänge (chemische Abbaureaktionen und Sputterprozesse) oder für die Bildung von (Polymer‐) Schichten. Die z. B. bei verschiedenen Polymeren beobachteten langsam fortschreitenden Veränderungen der Struktur in oberflächennahen Schichten, bis etwa max. 100 μm, werden durch die energiereiche Plasma‐Vakuum‐UV‐Strahlung hervorgerufen. Die Bildung funktioneller Gruppen an der Feststoffoberfläche vollzieht sich sehr rasch. Daran schließt sich eine Periode der langsamen Penetration von Plasmaspezies in die obersten Feststoffschichten an (nm‐Bereich). Der Abbau der Feststoffe verläuft nur dann nicht zeitlich linear, wenn der Festkörper eine schichtartige Struktur besitzt.
On the Quantitative Treatment of the Growth Rate of Thin Polymer Films Produced in Glow Discharges
Authors: Deutsch H. , Schmidt M. 
Published: July 2007

AbstractAn extensive system of equations is derived to determine the growth rate of thin polymer films induced by an anisothermic plasma taking into account activation reactions as well as transport processes in the plasma volume and surface reactions. A survey of the literature on the quantitative treatment of plasma polymerization is given.
Investigations on Afterglows of Neon Gas Discharges
Authors: Steenhuijsen L. W. G. 
Published: July 2007

AbstractWe report on the experimental and numerical investigations on afterglows of neon gas discharges, which are performed at the Eindhoven University of Technology.The studied gas pressure range extends from 1 to 100 torr, the discharge current from 1 to 100 mA. The densities of the 1s‐levels are measured with the help of the selective excitation spectroscopy (fluorescence technique). In this way a great number of decay curves of the 1s‐densities have been measured in the afterglow of neon gas discharges. From these curves the diffusion coefficient of the metastable 1s‐atoms, the coefficients of atomic collisional transfer between the 1s5‐ and 1s4‐level, as well as the three body collision coefficient between metastable 1s5‐atoms and neon ground state atoms have been determined.Besides these experiments a numerical model of the neon afterglows has been developed. With this model the afterglow phenomena can be simulated and the influence of the particular processes on the whole afterglow can be studied conveniently. Comparison is made between the experimentally and numerically obtained decay curves.For the application of the numerical model a number of starting conditions, such as radial density profiles, gas temperature, (relative) densities of the 1s‐levels, have been measured. Results of these measurements are presented.Also with the help of the selective excitation spectroscopy the coefficients of atomic collisional transfer between the 2p‐levels have been measured in the afterglow. From these results, together with the measured (relative) intensities of the neon spectral lines in the afterglow the partial recombination coefficients for the 2p‐levels were calculated.
Physikalisch‐chemische Vorgänge beim Plasmaätzen mit fluorhaltigen Ätzgasen
Authors: Poll H. U. , Schlemm H. 
Published: July 2007

AbstractExamples are given for three main processes determining the reactions in plasma etching:The interaction between plasma particles and the surfaces of solids;The conversion of the gas composition in the plasma;The transport phenomena of reaction products in the reactor and the vacuum system.In the glow discharge the behaviour of saturated and unsaturated perfluorocarbon gases is very similar. Both classes of compounds are converted in a few seconds in the homologous series of perfluoroalcanes up to products of high molecular weight. The main products are CF4, C2F6, C3F8. Unsaturated compounds lead to the deposition of thin polymer films on the walls and the electrodes, whereas saturated ones are only capable of producing films on the surface of the reaction vessel. The deposition results from the recombination of free radicals arising from the plasma interactions in the gas and at the surfaces. Vice versa sputtering of polymer fragments acts on the gas composition in the plasma. Conversion processes are controled by current density and gas pressure. The cathode fall region of the discharge is found to be the zone of the highest reaction activity.
Calculation of Recombination and Ionization Coefficients in Argon
Authors: Gleizes A. 
Published: July 2007

AbstractVarious methods for calculating electron‐ion recombination and ionization coefficients for argon (α and S) have been developed in the past. For given values of electron temperature and electron density, a large dispersion exists between the different results due to a great number of parameters. We have developed the method based on the collisional‐radiative model to calculate α and S for limited conditions (atmospheric pressure; strong resonance radiation absorption) in order to obtain realistic values applicable in real cases such as arc plasmas. Influences of resonance radiation absorption and atom‐atom collisions have been studied. The collisional‐radiative recombination coefficient has been compared with results obtained by other calculation methods: the best agreement occurs with the “bottleneck” model for high values of electron density and temperature. Finally the comparison with available experimental results shows a good agreement between our computed values and experimental values when experimental and theoretical conditions are analogous.
The Thermo‐Field Emission of Electrons in Arc Discharges
Authors: Hantzsche E. 
Published: July 2007

AbstractStarting from the conventional theory of thermo‐field emission of electrons from metal surfaces, the range of validity and the errors of several approximate emission formulae are examined that are additive or harmonic combinations of the limiting thermionic (Richardson) and field emission (Fowler—Nordheim) equations. An optimization of such kinds of equations results in the simple dependence (for example)

(iTF electron current density, T temperature, F field strength, k, A, B etc. are constants), or

(dependent on only one variable Y = T + β′F β′ = const.).If the emission equations are applied to arc cathodes, both T and F must be expressed as functions of the ion current (Ii) and the ion current density (ji); a simple interpolating formula of the electron current density je adapted to numerical results in the case of Cu cathodes becomes

(Ā, B̄, C̄: constants).
On the Conductance Theory of Plasmas
Authors: Kraeft W. D. , Blümlein J. , Meyer T. 
Published: July 2007

AbstractIn the framework of the linear response theory a quantumstatistical expression for the conductivity of nonideal plasmas is derived. In a simple approximation the influence of electron‐ion scattering and that of masses of equal magnitude on the conductivity is discussed; the latter is expressed in terms of transport collision frequencies.
Analysis of the Kinetic Properties and the Energy Budget of the Electrons in the ArHg Glow Discharge Plasma at Varying Partial Pressures and Discharge Currents
Authors: Winkler R. B. , Wilhelm J. , Winkler R. 
Published: July 2007

AbstractBy simultaneously solving the Boltzmann equation and the current balance for the electrons the energy distribution function, the electron concentration and resulting macroscopic electron quantities were calculated for the ArHg mixture plasma under conditions typical of fluorescent lamps. Besides the usual external parameters of such diffusion determined discharge plasmas measured values of the electric field strength were employed. The investigations were performed for independent variation of the partial pressures of Ar and Hg as well as of the discharge current in wide ranges of practical interest. The results obtained are discussed and compared with various energy distributions employed up to now and measured values of the electron concentration and temperature as well as with experimental results on the energy budget of this mixture plasma available in the literature.
Half‐Integer Harmonics Generation in Laser‐Produced Plasma
Authors: Bychenkov V. Tu. , Zozulja A. A. , Silin V. P. , Tikhonchuk V. T. 
Published: July 2007

AbstractHalf integer (3/2ω0, 1/2ω0) harmonics generation under oblique incidence of the pump‐wave on the spatially inhomogeneous plasma is theoretically investigated. Harmonics generation is connected with the two‐plasmon convective instability excitation near the quarter‐critical density. Harmonics spectra and intensities depend essentially on the pump wave polarization. In particular, significant harmonics spectra broadening arises under the p‐polarized pump wave.
On the Solution of the Electron Boltzmann Equation in Higher Order Legendre Polynomial Expansion
Authors: Winkler R. , Wilhelm J. , Hess A. 
Published: July 2007

AbstractThe paper deals with the mathematical structure of the general solution and the selection of the physical relevant solution of the hierarchy resulting from the electron Boltzmann equation by the Legendre polynomial expansion for a weakly ionized plasma with elastic and exciting collisions and under the action of an electric field. At first the properties of the general solution for the two and four term approximation of the distribution function are analyzed and then the study is extended to arbitrarily even order of the hierarchy using the theory of weakly and strongly singular differential equation systems for the investigation of the solution behaviour of the truncated hierarchy at small and at large energies, respectively. In this way, especially the free parameters of the non‐singular part of each general solution, which is obtained for small and large energies and is of interest for the construction of the desired solution, could be found, and the procedure for their final determination is explained. A first illustrative example is given of the application of these studies for the determination of the velocity distribution function of the electrons in four term approximation for a model plasma.
Initiation and Sustainment of Unipolar Arc Discharges by a Microsecond Pulse Plasma
Authors: Ivanov V. A. , Jüttner B. , Pursch H. , Siemroth P. 
Published: July 2007

AbstractUnipolar arcs have been produced by contacting metal surfaces with microsecond pulse plasmas. Plasma temperature Te, density ne and potential (with respect to ground) were controlled in the limits 7–12 eV, 1018–1019 m−3, 20–40 V, respectively, and the influence of these parameters on arc current amplitude (50–500 A) and ignition probability has been investigated. It was found that the ignition is the most limiting process requiring surface contaminations as well as the transport of net currents to the surface. The amplitude of the current was proportional to neTe1/2.
The Ratio of Lateral Diffusion Coefficient to Mobility for Electrons in CO2 Laser Mixtures
Authors: Braglia G. L. , Romanò L. , Roznerski W. 
Published: July 2007

AbstractA Townsend‐Huxley apparatus has been used to measure the lateral diffusion coefficient to mobility ratio D/μ in two gas mixtures of special interest when modeling h.p. CO2 lasers. The results are compared with the corresponding theoretical values obtained with the conventional two‐term theory in order to assess the limits of the theoretical predictions and have indications on the accuracy of the available cross sections.
Stability of a Rotating Compressible Stratified Plasma in the Presence of Hall Currents and Magnetic Resistivity
Authors: Adeniyan A. , Bhatian P. K. 
Published: July 2007

AbstractThe dynamic instability in a horizontal layer of a rotaing compressible plasma of variable density has been investigated to examine the influence of the simultaneous presence of the effects of Hall currents and finite magnetic resistivity. The linearized stability analysis has been carried out through the normal mode technique. By making use of the existence of a variational principle which is shown to characterize the problem, proper solutions have been obtained for a semiinfinite plasma in which there is an exponential density gradient along the vertical. The dispersion relation obtained has been solved numerically and it is found that both the resistivity and the Hall currents have a destabilizing influence as the growth rate of the unstable disturbances increases with increasing values of the parameters characterizing these effects. On the other hand, the Coriolis forces are found to have a stabilizing influence for in this case the growth rate decreases with increasing rotation.
Nonlinear Resonant Interaction of Two Longitudinal Waves and a Transverse Wave in a Hot Magnetized Plasma
Authors: Das K. P. 
Published: July 2007

AbstractBy Whitham's method of averaged Lagrangian and using Low's form of Lagrangian, coupled mode equations and coupling coefficients are derived for resonant nonlinear interaction of two longitudinal and one transverse wave in a magnetized plasma, in which the later wave propagates along the external uniform magnetic field. The limiting form of these coupling coefficients are obtained when the external magnetic field vanishes.
Abscheidung von Glimmpolymerschichten in einem weiten Metallrezipienten und Untersuchungen zur Struktur
Authors: Möller W. , Schmidt M. , Seefeldt R. , Wilberg R. 
Published: July 2007

AbstractInvestigations are reported of growth rate, chemical structure (IR‐spectroscopy, mass‐spectrometry), thermal stability, surface structure (scanning electron microscopy) of thin polymeric films grown in a gas (Ar‐hexamethyldisiloxane‐mixture) discharge with a heated cathode, which is situated in the centre of a cylindrical metallic vessel (l = 50 cm, 2r = 30 cm).The discharge conditions are the following: I = 0,25 – 4 A, U = 30 – 100 V, p = 6 – 40 Pa, argon flow rate = 3,8 · 10−5 mol/min, Ar/HMDS = 1 : 0,7 – 1 : 2,4.The growth rate changes from 2 to 18 nm/min, depending on the discharge conditions. The reproducibility of the growth rate shows deviations smaller than 10%. The films consist of a highly cross linked polymeric material and are stable up to 260°C, the solubility in n‐hexane being smaller than 2%. The surface of the thin film (d ∼ 102 nm) is smooth. Corrosion resistance to soda lye (0,2% NaOH) has been proved.
Investigation About Stepwise Excitation Cross Sections in Rare Gases
Authors: Behnke J. F. , Deutsch H. , Scheibner H. 
Published: July 2007

AbstractStepwise excitation cross sections of the rare gases helium, neon and argon were obtained by an indirect method resting on the combination of experimentally determined excited species number densities of the rare gas atoms in the positive column of a low pressure glow discharge with the results of the theory of the positive column and electron kinetics. Furthermore a semiempirical expression of the excitation functions basing on the analysis of the Born‐approximation and modifications as well as a formula of Vainstein is offered.
Formation of ac Discharges Between Glass Insulated Electrodes in Ne+1% N2 Mixtures. III. Discharge Development and Space Charge
Authors: Lange H. , Stern W. 
Published: July 2007

AbstractThe investigation of the optical space‐time‐structure of the discharge development was made for various values of pD (1,3 kPacm, 33,4 kPacm) by means of the variation of the electrode distance for two gas pressures. The broadening of the bistable region with growing electrode distance can be explained by the effect of the positive space charge as a virtual anode. Thus the space charge memory is dependent on the value of pD. If the space charge breakdown takes place, a light front moves from the anode to the cathode, its velocity, varying from 3 · 104 cm/s to 8 · 105 cm/s. In the volume an optical structure develops which is analogous to that of a medium pressure glow discharge. If the time between successive discharge pulses is too short, then the decay of the positive space charge is incomplete and there is no Townsend phase. The process depends, via the ion drift velocity, on the electrode distance.
Lichtenberg Figures on Dielectrics in Gases and in Vacuum
Authors: Anders A. 
Published: July 2007

AbstractA review is given first on Lichtenberg figures on dielectrics in gases. The problem of Lichtenberg figures at low gas pressures (p<1 Pa) is raised. Experiments are reported about the latter. The results are discussed by the help of models of vacuum flashover on dielectrics.
Fundamentals of a Technique for Determining Electron Distribution Functions by Multi‐Term Even‐Order Expansion in Legendre Polynomials. 2. Comprehensive Investigation of a Model Plasma
Authors: Winkler R. , Braglia G. L. , Hess A. , Wilhelm J. 
Published: July 2007

AbstractApplying the new technique for finding the converged solution of the Boltzmann equation in a weakly ionized plasma, which was developed in the first part of this paper, a comprehensive study of the electron velocity distribution function for a model plasma with elastic and exciting collisions is performed by solving the Boltzmann equation with increasing order of approximation. The purpose of this investigation is that of calculating the isotropic distribution f0, the first contribution f1 to the anisotropy of the velocity distribution, the important macroscopic quantities and, more generally, that of studying the total anisotropy as well as the changes of all these quantities when the approximation degree is enlarged beyond the 2 terms of the conventional Lorentz approximation. By varying some parameters of the model plasma, that is the electric field strength, the magnitude of the excitation cross section and the excitation threshold, the main features of plasmas in inert as well as molecular gases are modelled and the impact of these parameters on the mentioned quantities is analysed. Some of the converged results are compared with results of corresponding Monte Carlo simulations.The approximation degree required to find the converged values of isotropic distribution, main macroscopic quantities and electron distribution in the velocity space (and thus its real anisotropy) is estimated by solving the Boltzmann equation over wide parameter ranges.
Pressure Ionization of Atoms in Plasmas
Authors: Ebeling W. , Richert W. 
Published: July 2007

AbstractIt is shown that the main physical reason leading to the ionization of the atoms in plasmas at high densities (pressures) is the Pauli exclusion principle for the electrons which is responsible for the big spatial extension of atoms. Especially for the example of hydrogen the theory is extended to include those effects. Spatial and energetic variants for the definition of the species atom are discussed. The quantum theory of bound states in plasmas is compared with the classical theory of ion association in electrolytes.
Energy Selecting Action of Limiters on Particle Fluxes Penetrating into the SOL‐Plasma
Authors: Hildebrandt D. 
Published: July 2007

AbstractA simple model of the penetration of particle effluxes from the core plasma into the SOL‐plasma of tokamaks is proposed. The assumptions made are free streaming of particles parallel to the magnetic field and anomalous particle transport perpendicular to the toroidal field with a constant radial velocity. The model has been proved for measured particle fluxes of Li which was injected into the core plasma of the tokamak T‐10. The dependence of the Li‐particle flux on the minor radius as well as toroidal asymmetries in the SOL‐plasma can be explained by the results of the calculations.
Effects of Higher‐Order Terms on the Nonlinear Propagation of Electron Acoustic Waves
Authors: Sarma S. N. , Kalita M. K. , Bujarbarua S. 
Published: July 2007

AbstractThe contribution of higher‐order terms on the nonlinear propagation of electron acoustic waves has been investigated, using the reductive perturbation technique. A modified KdV equation for the first order perturbed potential and a linear inhomogeneous equation for the second order perturbed potential have been derived. The soliton width and amplitude have been calculated.
Diagnostics of Pulsed Discharge Plasma in Electrolyte
Authors: Radovanov S. B. , Tripković M. R. , Holclajtner‐Antunović I. D. 
Published: July 2007

AbstractTwo experimental methods are applied to determine electron temperature: the method of calculating temperature from the slope of the continuum's relative intensity, and the Boltzmann plot of the relative line intensity of oxygen OII, in a pulsed discharge in an electrolyte (PDE). Electron density is determined using the electron impact widths of magnesium ionic lines.
Quasi‐Classical and Classical Cross Sections for the Scattering of Electrons on the Coulomb Cut‐Off Potential
Authors: Mihajlov A. A. , Dimitrijević M. S. , Djordjević D. , Luft M. , Kraeft W. D. 
Published: July 2007

AbstractThe elastic scattering of electrons on the cut‐off Coulomb potential Uc(r) = −1/r + 1/rc, for r ≦ rc and Uc(r) = 0, for r > rc, has been considered. It has been shown that for ε > 0.5/rc (ε is the energy of free electrons in atomic units) the analytical quasi‐classical expressions describe quite well the behaviour of transport, differential and total cross sections for elastic scattering. It has been shown moreover, that in the energy range considered, transport cross section could be determined with practically the same accuracy already by means of classical, analytical expressions. Born approximations show larger deviations from exact quantum calculations.
Gravitational Instability of Fluid of Finite Electrical and Thermal Conductivity Flowing through Porous Medium
Authors: Vaghela D. S. , Chhajlani R. K. 
Published: July 2007

AbstractIn view of the importance of porosity in astrophysical context the problem of gravitational instability of fluid of finite electrical and thermal conductivity flowing through porous medium is studied. Equations of the problem are stated and from them linearized perturbation equations are derived. Dispersion relations are obtained and Jeans' criterion of instability is discussed taking properties of the medium in different combinations for parallel and perpendicular directions to the magnetic field. Thermal conductivity modifies the Jeans' expression. Magnetic field and porosity of the medium also modify the Jeans' expression in case of wave propagation in perpendicular direction to the magnetic field but finite electrical conductivity neutralizes the effect of porosity on Jeans' criterion of instability.