bluuebunny/crossref_metadata_2025_split huggingface dataset:
Selection of the Time Parameters of Oscillating Impulse Voltages for On‐Site Testing of Gas Insulated Switchgears (GIS)
Authors: Hauschild W. , Schader W. , Mosch W. , Petzold K. 
Published: July 2007

AbstractGIS for operation voltages ≧ 245 kV can be tested with oscillating impulse voltages on site advantageously, because this H. V. test can be performed with easily mountable impulse generators. The IEC recommendation for on‐site testing of GIS which is now under discussion doesn't fix the time parameters of the oscillating impulse voltages, but these influence the breakdown behaviour of slightly non‐uniform fields with disturbances (sharpe edges, fixed or free‐moving particles) in SF2.For the mentioned GIS (≧ 245 kV) fixed disturbances are more dangerous than free‐moving particles. Therefore the breakdown voltages of model insulations with a disturbance at the H.V. electrode (needle with length l=0…5 mm) in SF6 (p20=0.1…0.4 MPa) were investigated at oscillating lightning (OLI) and oscillating switching (OSI) impulse voltages with different times to crest.From the results, which were compared with those at aperiodic lightning (LI) or switching (SI) impulse voltages, permissible time parameters for OLI and OSI can be derived. On the basis of these parameters an impulse generator was designed which enables on‐site testing for a wide range of the capacity of the tested GIS.
An Introduction to Quark—Gluon Plasmas
Authors: Wallis G. 
Published: July 2007

AbstractIt is tried to present the main features of quark‐gluon plasma physics to a possible reader not so familiar with quantum chromodynamics and its extension to high temperatures, merely by looking for some analogies to usual electrodynamic plasma phenomena: The electrons correspond to the quarks, the photons to the gluons, the electromagnetic coupling to the strong coupling. However, in contrast to the ionization processes or, more general, generation processes of electrically charged particles or holes, the change from the usual hadronized state of nuclear matter to the collective quark‐gluon plasma state is a first‐order phase transition. The possible existence of such quark matter in the cores of massive neutron stars, at ultrarelativistic heavy‐ion collisions and in the early state of the Universe are discussed in a verbal approximation.
The Formation of Dissipative Structures and Chaotic Beam Relaxation in the Strongly Dissipative Beam‐Plasma Instability
Authors: Kruscha K. J. G. , Leven R. W. 
Published: July 2007

AbstractNumerical solutions of a nonlinear system of equations describing the evolution of the strongly dissipative beam‐plasma instability are presented (time or space dependence of the unstable waves, the evolution of the beam distribution function and the corresponding phase space representations are given). Such an instability establishes if the linear growth rate of the unstable waves is small in comparison to the effective collision frequency of the electrons of the dissipative plasma. It is shown that after saturation of the instability there is an efficient energy transfer from the directed motion of the beam electrons to the thermal motion of the plasma electrons. Arguments are given that the strongly dissipative beam‐plasma instability is possibly the basic plasma heating mechanism which operates in the quasi‐stationary state of the beam plasma discharge. Self‐consistent initial conditions are used for the numerical calculations. Formation and evolution of dissipative structures (vortex structure, chaotic structure) were observed. A profound investigation of the chaotic or turbulent beam relaxation mechanism is presented. Such a relaxation mechanism develops in the case of the nonresonant dissipative instability (e.g. in resistive wall‐electron beam amplifiers). The method of investigation of dissipative structures presented in this paper (application of Shannon's information theory and results of the theory of dynamical systems with chaotic behaviour) can be extended to studies of other beam‐plasma systems within the framework of partial kinetic description.
High‐Frequency Electrical Conductivity and Dielectric Function of Strongly Coupled Plasmas
Authors: Meyer T. , Tkachenko I. M. 
Published: July 2007

AbstractUsing the frequency‐moments analysis of the electrical conductivity with quantum mechanical assumptions and with the help of sum rules a generalization of the Drude‐Lorentz theory of the electrical conductivity is given. For Coulomb‐systems (e.g. plasmas), a connection is formulated in this framework between the known static electrical conductivity and the high‐frequency conductivity. In this way, we are able to give an expression of the high‐frequency dielectric function.
Negative Ions in a Glow Discharge of Tetrafluoromethane
Authors: Meichsner J. , Poll H. U. , Wickleder K. H. 
Published: July 2007

AbstractThe Langmuir — probe measurements in a CF4— glow discharge reveal a large number of negative ions (1010cm−3) in the plasma between the planar C‐electrodes. Under special conditions the density of them exceeds the electron density at several orders of magnitude and sustains a quasi — electron free plasma. The ratio depends on the residence time of the molecular gas in the discharge reactor. It is due to dissociative electron attachment to highly molecular gas components arising from the plasmachemical conversion of CF4. F−and CF3−are the most important negative ions.
The Mathematical Modelling of the Switching Arc
Authors: Bergmann V. , Grams B. , Rother W. 
Published: July 2007

AbstractFor developing and optimizing of high‐voltage SF6‐puffer breaker a mathematical model of the switching arc is an important tool for the manufacturer. A physico‐mathematical model was build up to simulate the behaviour of the switching arc near current zero. To proof the model the influence of steepness of current and voltage, of the gas pressure and the position of the upstream electrode on the breaking capacity have been calculated. First work has been done to use the model to simulate the dielectric behaviour too. To minimize computer time and to get more informations on the integral model the characteristic functions have been calculated with the pm‐model. The result shows the influence of the steepness of the current before current zero.
Model of Non‐Laminar Low‐Temperature Plasma Flow with Intensive Self‐Mixing
Authors: Burnat M. , Kurowski S. , Penczek M. , Wierzbicki J. 
Published: July 2007

AbstractA new model of turbulence is presented. It consists in treating the turbulence as an essentially self‐mixing process. The mass, momentum and energy transport is assumed to proceed along interlacing curvilinear cones. A relevant mixing field is introduced. It consists in relating to each point of space an infinite set of instantaneous velocities momentums and energies.Into each transport equation a self‐mixing term of the proper form is introduced. The closure procedures for modyfied transport equations are also discussed.
Suspended Particles and the Gravitational Instability of Rotating Magnetised Medium
Authors: Chhajlani R. K. , Sanghvi R. K. 
Published: July 2007

AbstractThe effect of uniform rotation on the self gravitational instability of an infinite homogeneous magnetised gas particle medium in the presence of suspended particles is investigated. The equations of the problem are linearized and the general dispersion relation for such system is obtained. The rotation is assumed along two different directions and separate dispersion relation for each case is obtained. The dispersion relation for propagation parallel and perpendicular to the uniform magnetic field along with rotation is derived. The effect of suspended particles on the different modes of propagation is investigated. It is found that in presence of suspended particles, magnetic field, rotation and viscosity, Jeans' criterion determines the condition of gravitational instability of gas‐particle medium.
Elastic Scattering of Electrons by a Cut‐Off Coulomb Potential at Low Energies
Authors: Mihajlov A. A. , Djordjević D. , Vučić S. , Kraeft W. D. , Luft M. 
Published: July 2007

AbstractElastic scattering of electrons by cut‐off Coulomb potential Uc(r) is investigated, where Uc(r) = 0, for r > rc and Uc(r) = −1/r + 1/rc for r ≦ rc. This is first considered in terms of classical, and later quantum mechanical (partial wave) methods in the low energy range 0 ≦ ϵ ≲ 1/rc, where ϵ is the energy of the free electron. Scattering in this energy region displays a number of particular characteristics, such as back scattering, at certain energies. It can be concluded that some agreement does exist between the classical and quantum mechanical results.
Instationary Electric Fields, Ion Transport and Strong Density Fluctuations in Tokamaks with Dominant Anomalous Electron Transport
Authors: Wolschke S. 
Published: July 2007

AbstractA common explanation is given for ion transport and strong broadband density fluctuations in tokamaks as a result of large anomalous electron transport near dominant magnetic surfaces (resp. in small magnetic islands). The main mechanism is local density flattening connected with an anomalous electron transport induced instationary radial electric field, which forces the ions via polarization drift to follow the electrons. For the density flattening process an exact solution of the time‐dependent diffusion equation for a linear initial profile over the island width is used. From this we also derive an expression for a temporal growing radial electric field. This positive field reaches its maximum at the density plateau. Strong viscous diffusion or instability‐induced transport between high and low electric field regions may now reverse the density flattening. Therefore relaxation oscillations result which may also explain the observed strong density and potential fluctuations in tokamaks. Several details of recent measurements of impurity ion behaviour and density fluctuations in tokamaks may be better explained with the theory given here.
A Pair of Zakharov Equations with Collisional Damping and the Motion of Langmuir Soliton
Authors: Bhakta J. C. 
Published: July 2007

AbstractThe effects of collisional damping on high frequency Langmuir wave and low frequency ion‐acoustic wave have been investigated. It is found that the governing equations for the waves are a pair of Zakharov equations with a damping term in each equation. By using the treatment which consists of approximate solutions of the balance equations, a set of first order ordinary differential equations have been derived for the solution parameters in order to study the motion of Zakharov solitons in presence of damping. It has been shown that the width of the soliton remains constant throughout the motion.
Plasma Maser Theory of Whistler Waves in the Presence of Ion Cyclotron Turbulence
Authors: Khound R. N. , Sarma S. N. , Bujarbarua S. 
Published: July 2007

AbstractIn this paper we consider the plasma maser theory of whistler waves in the presence of ion cyclotron waves in a magnetized plasma. In a plasma with low frequency ion cyclotron turbulence and a high frequency test whistler wave, growth of the whistler wave takes place because of the turbulent bremsstrahlung interaction between the resonant electrons and the modulated electric fields. The growth rate of the whistler wave is calculated and the results discussed.
Gravitational Instability of a Rotating Viscous Finitely Conducting Plasma
Authors: Bhatia P. K. , Maheshwari S. L. 
Published: July 2007

AbstractThe gravitational instability of infinite homogeneous plasma has been studied to include simultaneously the effects of rotations, Hall currents, viscosity, finite electrical conductivity and the finite Larmor radius (FLR). Both the longitudinal, and transverse modes of wave propagation have been studied. It is found that the gravitational instability is determined by Jeans' criterion even in the presence of effects of rotation, Hall currents, FLR, viscosity and finite conductivity whether included separately or jointly.
Effect of Conductivity on Magneto‐Gravitational Instability of a Medium with Finite Larmor Radius and Suspended Particles
Authors: Chhajlani R. K. , Bariwal R. L. 
Published: July 2007

AbstractThe self‐gravitational instability of an infinite homogeneous magnetised and finitely conducting gas‐particle medium is considered to include the finite Larmor radius effect in the presence of suspended particles. The equations of the problem are linearized and from linearized equations a general dispersion relation for dusty‐gas is obtained. The dispersion relations are also obtained for propagation, parallel and perpendicular to the direction of uniform magnetic field. The Jeans, criterion is discussed for these two different directions of wave propagation. It is found that in the presence of finite Larmor radius corrections and suspended particles the condition of instability is determined by Jeans' criterion for a self gravitating, finitely conducting, magnetized gas‐particle medium.
On the Interaction of an Alternating Electrical Field with an Inhomogeneous Magnetized Plasma
Authors: Zoler D. , Burdujan I. 
Published: July 2007

AbstractIt is found out the form of the vectorial and isotropic cartesian component for the distribution function for electrons in an inhomogeneous plasma interacting with an alternative electric field, without being done any previous supposition on the temporal dependence of these quantities. For this purpose it is applied a method of succesive approximations for solving an integro‐differential equation for the isotropic component of the distribution function. The scalar and vector components of the plasma spherical harmonic expansion are calculated including transient and secular terms.Some particular quantities as time‐independent part of vectorial component of distribution function and of nonlinear conductivity were also obtained. Also corrected expressions for the transport coefficients in a electrical field, are obtained.
Effect of the State of the Cathode Surface on its Photoemission Properties
Authors: Fomin N. A. , Samtsov P. P. , Soloukhin R. I. 
Published: July 2007

AbstractThe results of experimental investigation of the effect of the state of the cathode surface on its photoemission properties are presented. It is found that the low‐pressure glow discharge treatment of the copper cathode surface in the air results both in a substantial shift of the photoeffect threshold to the long‐wave region of a spectrum and in a change of the quantum photoemission yield.
Electrical and Spectral Characteristics of a Heated Cathode Discharge in Metal Vapors
Authors: Musa G. , Baltog A. , Popescu A. , Betiu N. , Mustata I. 
Published: July 2007

AbstractA new type of discharge in pure metal vapors like copper or titanium is described. A stable discharge is produced between a heated cathode and the anode which has a melted spot on its surface due to the electron bombardment. The spectral characteristics prove that the discharge take place in the vapors of the anode material continuously evaporated from the melted spot on the anode. The discharge has a similar behaviour as the low voltage arc.
Experimental Study of Non‐Equilibrium Ionization in a Supersonic CO Flow
Authors: Blaha J. , Labuda S. A. , Maštovský J. , Rothhardt L. 
Published: July 2007

AbstractExperimental results are presented on ionization processes in the vibrationally non‐equilibrium flow of CO preliminarily heated by a shock wave and adiabatically cooled in the supersonic nozzle with a flow Mach number of M = 3.9.It is shown that for a wide range of flow stagnation temperatures, the value of the recorded semi‐self‐maintained current considerably exceeds the one due to thermal gas ionization in the plenum chamber.
Coupling Between the Discharge Plasma Instability and the Laser Oscillation in a He—Cd Laser
Authors: Cristescu C. P. , Popescu I. M. , Preda A. M. , Podoleanu A. 
Published: July 2007

AbstractThe investigation of the output of a He–Cd laser with electrically floating hollow electrodes shows that the discharge plasma instability plays an important role in the generation of the population inversion. The experimental evidence is presented and a qualitative interpretation is given by considering the plasma instability as equivalent to a radio frequency component of the discharge voltage.
Methods for the Numerical Calculation of the Plasma Potential from Measured Langmuir Probe Characteristics
Authors: Seifert W. , Johanning D. , Lehmann H.‐R. , Bankov N. 
Published: July 2007

AbstractIn a previous paper the results of the Langmuir probe experiment carried out on board of two INTERKOSMOS satellites have been described. The experiences have shown that the usage of high quality algorithms for analyzing the current‐voltage‐characteristics is necessary to yield real physical parameters.The key problem is the determination of the plasma potential. This paper reviews the different methods to determine the plasma potential especially under the circumstances of computer application. The test of the well developed methods shows, that for the evaluation of the applied methods a number of different factors, discussed in the following sections of this paper, has to be taken into account. The used test data are model values or real measurements obtained by the satellite missions IK‐10, IK‐18 and BULGARIA‐1300.The computer procedures have been realized as FORTRAN‐subroutines for the BESM 6 and ES 1040.
Desaktivierung angeregter He‐Atome (31P1, 31S0, 41S0, 51S0, 61S0) durch Rb‐Atome
Authors: Kasjanenko S. W. , Talmatschov J. A. , Krause U. 
Published: July 2007

AbstractTotal collisional depopulation rates for He(n1S0) (3 ≦ n ≦ 6), He(31P1) in thermal collisions with Rb have been measured using the transient‐decay method. The measured quenching cross‐sections increase from 4.3 · 10−10 cm2 to 24 · 10−14 cm2 with increasing n from 3 to 6.Comparison of experimental results with theoretical estimations shows that the main processes of quenching depend on n. He‐atoms in the n = 3, 4 states are mainly quenched by Penning ionisation and higher excited states by collisional l‐mixing.
The Electrical Conductivity of Break Arcs: A Diffusion Dominated Phenomenon
Authors: Vogel N. , Cebulla H. 
Published: July 2007

AbstractThe current‐conducting channel near the cathode of metal vapour ares is described theoretically by a diffusion model. Time resolved measurements of voltage and current during opening of electric contacts are used to determine channel radius and plasma conductivity. Channel radii of the order of 1–10 μm are deduced, leading to conductivities of the metal vapour plasma of the order of 105 Ω−1 cm−1. This is considerably higher than the classical conductivity according to Spitzer.
On the Transversal Diffusion of Electrons in a Gas in an Electric Field
Authors: Braglia G. L. , Diligenti M. 
Published: July 2007

AbstractDiscrepancies between Monte Carlo and Boltzmann calculations of electron drift and diffusion in gases have recently led some authors to call into question the same definition of diffusion coefficient perpendicular to the electric field. In this paper we report new results which confirm the observed discrepancies but at the same time we will show that the Monte Carlo results are consistent with more rigorous calculations based on theories of higher order than the first.
Zur Eindeutigkeit eines neuen Differenzmeßverfahrens für die sehr genaue Bestimmung der Resonatorgüte und der Resonanzfrequenz von Mikrowellenresonatoren
Authors: Gundermann S. 
Published: July 2007

AbstractIt is possible to improve the resolving power at the determination of the resonance frequency and the cavity Q by the timed modulation af a plasma loading the resonator. By this we get a higher exactness for the determination of the plasma parameters. The resonance curves obtained by aid of the differences of the output signals of the resonator result from the solutions of a nonlinear system of equations. The existence and uniqueness of the solutions are discussed in some special cases.
A Study of Small Amplitude Ion Acoustic Double Layers in a Multi‐Species Unmagnetized Plasma
Authors: Sharma N. K. , Goswami K. S. , Bujarbarua S. 
Published: July 2007

AbstractWe report here analytic solutions for weak ion acoustic double layers in an unmagnetized multi‐species plasma having two electron components, each described by a Boltzmann distribution, and two ions of different masses, each described by usual fluid equations. The velocity and the width of the double layers for different amplitude has been studied.
Self‐Interaction of Electron Plasma Waves in a Planar Plasma‐Filled Waveguide
Authors: Ghosh B. , Das K. P. 
Published: July 2007

AbstractNonlinear behaviour of electron plasma waves propagating in a planar plasma‐loaded waveguide immersed in an infinite magnetic field is analysed including finite temperature and mobile ion effects. It is shown that the wave becomes modulationally unstable if the wavenumber exceeds certain critical value Kc, which decreases with rise of temperature. The growth rate of instability is calculated and is found to increase with the rise of temperature.
Nonlinear Theory of the Plasma Wave Excitation in a Bounded Beam‐Plasma System
Authors: Kruscha K. J. G. 
Published: July 2007

AbstractThe excitation of symmetric and antisymmetric plasma waves by a beam layer that moves within a homogeneous plasma enclosed by a metallic wall was dealt with theoretically. Investigations were carried out for the magnetic field free case and for a magnetized electron beam. In the latter case, the beam electrons are assumed to be unable to move in the perpendicular direction. The theoretical model bases upon an extension of the well known single wave theory to a two‐dimensional beam‐plasma system. Special emphasis should be paid to the fact that the perpendicular wave profile of the excited waves was determined self‐consistently. Energy and momentum balance equations are derived for this system. The theoretical method outlined in this paper which is based on a Green's‐function technique can be extended easily to three‐dimensional systems or to beam‐plasma systems with other boundary conditions. The main features of the saturation process of the basic unstable wave types are discussed. Several interesting effects were found in the magnetic field free case: (i) numerical solutions describe an increasing steepening of the wave amplitudes in perpendicular direction near the center of the system for the symmetric potential wave; (ii) for the antisymmetric wave, a smoothing tendency was found in the development of the perpendicular wave potential profile; (iii) spatial separation of the slow and fast beam electrons was observed; (iv) it is shown for the antisymmetric potential wave type that, under certain conditions, a very efficient beam particle retardation mechanism occurs which is connected with a strong reduction of the formation of a fast particle group; (v) generally it was shown that the conversion of the kinetic energy of the beam electrons into the plasma wave energy may be more effective as compared with the case of the magnetized beam.
Excitation of Convective Cells by Nonlinear Interaction of Interchange Mode
Authors: Majumdar D. 
Published: July 2007

AbstractConvective Cell formation due to nonlinear interaction of interchange mode is studied using multiple time and space scales. Basic interchange mode equation is modified to obtain nonlinear localized structure with modulational perturbation in the drift direction and periodic boundary condition for the perturbation in the direction of the density gradient. To study modulational instability we have deduced nonlinear evolution equation for the first order perturbation from third order secularity elimination condition. Modulational instability, which is responsible for localized structure, is studied in two limits of the dispersion relation.