bluuebunny/crossref_metadata_2025_split huggingface dataset:
Impurity Driven Linear and Nonlinear MHD Cylindrical Waves in a Three Species Plasma
Authors: Singhal R. , Srivastava K. M. , Chhonkar R. P. S. 
Published: July 2007

AbstractThe propagation of axisymmetric linear and nonlinear dispersive waves in a three species plasma to include the thermoelectrostatic effects together with the dissipative effects of main ions has been discussed. The impurity driven MHD fluid modes have been examined when the electrostatic drift has been taken into account. We have discussed the linear propagation of dispersive cylindrical waves in the plasma system for different ion thermal phase number. The thermal force resulting from the collisions between main ion and impurity ion densities (i.e. αiI = 0) has been neglected. The shock waves and the soliton solutions are obtained for two different cases of the non‐collisional plasma and the non‐dissipative plasma.
Elektronenstrom zylindrischer Langmuirsonden bei Nichtmaxwellverteilungen
Authors: Johanning D. 
Published: July 2007

AbstractOne of the main assumptions of the conventional Langmuir probe theory is the demand for a Maxwellian distribution function.In this paper is tried to calculate probe currents for non‐Maxwellian electron energy distributions.The classical Langmuir formula for the orbital‐motion‐limited current of cylindrical probes is simplified. The new equation permits a very easy detailed examination of the effects of non‐Maxwellian electron energy distributions on the current‐voltage characteristics in the accelarating region for large probe voltages.It is shown that the electron current is independent of the form of the electron energy distribution, if the mean electronenergy Ē is constant.Variations of the mean energy change the probe current slightly.As examples currents are computed for two non‐Maxwellian distribution functions.
Spatial Characteristics of the Beam Plasma Discharge in Crossed Electric and Magnetic Fields
Authors: Gadeev K. K. , Denkevits A. V. , Ivanov A. A. , Nikiforov V. A. , Shapkin V. V. 
Published: July 2007

AbstractThe paper presents the results of the experimental investigation of the beam plasma discharge spatial structure in crossed fields induced by adding a high ionization potential gas to the discharge. Direct experimental evidence of the polarization mechanism of the radial current in a device with this type of discharge has been obtained.
The Electrical Conductivity of Plasma in Wide Range of Charge Densities
Authors: Kurilenkov Yu. K. , Valuev A. A. 
Published: July 2007

AbstractThe possibility of the existence of plasma oscillations in nonideal plasma and their role in effective “collision” frequency are analyzed. The simple formula for the electrical conductivity of nonideal plasma is obtained on the base of model considerations. An account is taken of a new scattering mechanism, namely, the collective plasma oscillations.
Perturbed Arcs in Turbulent Axial Gas Flow. III. Numerical Simulation of Stochastically Disturbed Arc Discharges
Authors: Rothhardt L. , Schumann A. 
Published: July 2007

AbstractStochastically perturbed arcs are modelled by means of a Mayr type differential equation, the thermal constant τ being stochastically controlled by Gaussian fluctuations of given dispersion and correlation time: 1/τ = 1/τ0 (1 + ζ). The ζ‐signals are taken from an electronic noise source by an appropriately equipped intelligent CAMAC crate, which further processes the whole simulation program.Special cases treated are 1. stationary (in the mean) arc, 2. freely decaying arc, and additionally, 3. thermal reignition of a decaying arc with stiff recovery voltage.
Electron Kinetics of Weakly Ionized HF Plasmas. II. Decoupling in the Fourier Hierarchy and Simplified Kinetics at Higher Frequencies
Authors: Winkler R. , Deutsch H. , Wilhelm J. , Wilke Ch. 
Published: July 2007

AbstractIn a preceding paper based upon the time dependent Boltzmann equation the electron kinetics of the weakly ionized HF plasma was investigated firstly by a time‐consuming direct treatment and secondly by the Fourier expansion for the established HF state. Continuing these investigations, the decoupling of the equation determining the period average of the isotropic distribution from the other equations of the system for the harmonics of the isotropic distribution is quantitatively studied for a neon plasma as a typical representative. In this way the applicability of a simplified approach for the electron kinetics in the HF plasma could be justified and a former estimate for a field frequency above which this kinetics can be used could be confirmed. The generalization of this simpler description to arbitrary HF fields and to HF plasmas in other gases is discussed. Employing this approach, the electron kinetics is systematically investigated for the HF plasma in Ne for wide ranges of the HF field amplitude and field frequency.
Amplification of Ion‐Acoustic Solitary Waves in a Vlasov‐Plasma. II. Existence of a Maximum Potential and Numerical Experiments
Authors: Bruhn B. , Leven R. 
Published: July 2007

AbstractWe demonstrate a proof for the existence of a maximal potential for the higher nonlinear evolution equation (see part I). This maximum potential depends upon the plasma parameters and therefore upon the mechanism of instability too. The problems of the stability and of the asymptotic soliton solution are discussed. Finally we present different numerical results.
Experimental Study of Ion‐Acoustic Instability in Stratified Krypton and Xenon Plasma at High Pressures
Authors: Serapinas P. , Šimkus P. 
Published: July 2007

AbstractThe ion‐acoustic instability in gaseous discharge plasma in krypton and xenon at the pressures 0.4 to 2.5 Torr was found and studied. The necessary conditions for the instability existence were satisfied only in the ionisation wave region where electron density was about an order larger than average one. The detected noise amplitude and frequency dependence on the glow discharge plasma parameters was also investigated.
Density of fast electrons on the Axis of a Zylindrical Hollow‐Cathode Discharge
Authors: Handle F. , Lindinger W. , Howorka F. , Pahl M. 
Published: July 2007

AbstractFast electrons leaving a hollow cathode discharge axially through the orifice of a hole probe undergo ionizing collisions with the discharge gas in and behind the orifice. Ar++ ions produced in this way are used as a monitor for the density of fast electrons, Nef, on the axis of the negative glow of a cylindrical hollow cathode discharge. Data on Nef as dependent on the pressure of the Ar discharge gas and on the discharge current are obtained and an analytical expression for these dependences is found and discussed.
Schwingungsrelaxation und Gasaufheizung bei periodischem Betrieb der Impulslaser‐Gasentladung in Stickstoff
Authors: Wojaczek K. 
Published: July 2007

AbstractFür eine typische Impulslaser‐Gasentladung in ruhendem Stickstoff wird das zeitliche Verhalten der Schwingungstemperatur zwischen zwei Entladungsimpulsen rechnerisch untersucht, wobei eine verallgemeinerte Treanor‐Verteilung der Besetzung der Schwingungsniveaus zugrunde gelegt wird. Als Abbauprozesse der Schwingungsenergie werden Wandstöße, VV‐ und VT‐Prozesse berücksichtigt. Es ergeben sich Angaben über die Schwingungstemperatur zu Beginn jedes neuen Entladungsimpulses und über die Gastemperaturerhöhung gegenüber der Rohrwand in Abhängigkeit von der Folgefrequenz. Abschließend wird diskutiert, welche Einflüsse die erhöhten Schwingungs‐ und Gastemperaturen auf die Leistung des Stickstoff‐Impulslasers haben können.
Resonant Wave‐Particle Interaction in an Explosively Unstable Beam‐Plasma System. I. Derivation of a System of Nonlinear Equations and Numerical Evaluation of the Saturation Field Strength
Authors: Kruscha K. J. G. , Leven R. W. 
Published: July 2007

AbstractThe evolution of a resonant triplet of linearly stable electrostatic waves in a beam‐plasma system is considered. A set of nonlinear ordinary differential equations is derived, which allow an investigation of the explosive instability with minimum numerical expense. Our model is different from the well known single wave model in taking into consideration the nonlinear susceptibility of the plasma and in making use of the ponderomotive force description. Maximum values of the wave amplitudes are obtained numerically and it is shown that the saturation of the explosive instability is due to different trapping mechanisms of the beam electrons by the excited waves.
Fundamentals of a Technique for Determining Electron Distribution Functions by Multi‐Term Even‐Order Expansion in Legendre Polynomials 1. Theory
Authors: Winkler R. , Braglia G. L. , Hess A. , Wilhelm J. 
Published: July 2007

AbstractOn the basis of our recent investigations concerning the mathematical structure of the hierarchy which results from the Legendre polynomial expansion of the electron velocity distribution function in Boltzmann's equation a new technique for solving this equation in multi‐term even‐order approximation is presented. This method is, even if more complex, the logical generalization of the well known technique for solving Boltzmann's equation by backward integration in the conventional two‐term approximation. A weakly ionized, spatially homogeneous and stationary plasma with elastic and exciting electron‐atom collisions is considered acted upon by a dc electric field.The technique, presented in detail, determines the distribution function in even order 2l of the expansion at the end by l‐fold backward and 2l‐fold forward integration of the hierarchy and by continuous connection of the resulting non‐singular parts of the general solutions at low and high energies at an appropriate connection point. A first application of this method is made on a model gas for the even orders from 2 to 10 and under conditions with distinct anisotropy in the velocity space due to intensive exciting collisions. The converged macroscopic quantities and the corresponding first coefficients of the distribution expansion itself are compared with very accurate Monte Carlo simulations under the same conditions where a perfect agreement between the results obtained with both techniques was found confirming the high accuracy of the new technique to be presented.
Propagation and Absorption of ECR Waves in a Low Temperature Toroidal Plasma of Small Size and Magnetic Field
Authors: Someşan M. L. 
Published: July 2007

AbstractThe propagation and absorption of ECR waves in a tokamak plasma with small size and low values of the electron temperature and the toroidal magnetic field is studied numerically. The cold plasma dispersion equation is solved and ray tracing calculations are performed to find the accessibility conditions and the optimal angle of wave launching for maximal ECR absorption. Absorption coefficients are computed in the high density approximation.
High‐Velocity Projectile‐Stabilized z‐Pinch
Authors: Winterberg F. 
Published: July 2007

AbstractA high current z‐pinch can be stabilized by a thin long projectile accelerated to a few km/sec, if the projectile is shot through the core of the pinch. Furthermore, as a result of the thermomagnetic Nernst effect both the heat conduction and radiation losses at thermonuclear temperatures are sufficiently small. The stabilized pinch configuration can therefore be used for the controlled release of large amounts of thermonuclear energy from a dense plasma. The needed projectile velocity of a few km/sec can be already reached with chemical propulsion.
Numerical Study of the Instability in a Maxwellian Beam‐Plasma System II. Many Wave Regime
Authors: Bodrow W. , Leven R. W. , Koch B. P. 
Published: July 2007

AbstractThe relaxation of the beam‐plasma system with several preliminarily excited unstable waves in its spectrum is investigated on the basis of computer simulations. The nature of the waves and particles interaction during the instability development is analysed. It is shown that the destroying of the amplitude oscillations of the single wave after saturation in the presence of additional waves is caused by the well known effect of resonance overlapping. A chaotization of the motion of the beam particles occurs even in the case when the amplitudes of the neighbouring waves are small.
Investigation of the Beam Plasma Discharge in Electronegative Gases Using the Second Derivative of Langmuir Probe Characteristics
Authors: Klagge S. , Maass M. , Serov A. 
Published: July 2007

AbstractThe distribution of the charge carriers is measured and the influence of the attachment processes on the electron energy distribution function is demonstrated for beam plasma discharges in SF6, CF4 and O2 with the aid of the second derivative of Langmuir probe characteristics. The structuration of the plasma into regions of predominating negative ions and regions of predominating electrons is determined by the the established radial Te‐profile. The dimension of the quasi electronfree plasma changes significantly as well at transition from the turbulent heating mechanism into the electron impact plasma generation as by occuring low‐frequency instabilities. With increasing n−/ne a deficit of low energetic electrons appears in the electron energy distribution parallel to the formation of the negative ion peak. The saturation currents at ne/n−=0 yield the mass ratios between negative and positive ions.
Deuterium and Impurity Flux Measurements in the Boundary Plasma of T‐10
Authors: Grote H. , Hildebrandt D. , Strusny H. , Kotai E. , Manuaba A. , Paszti F. 
Published: July 2007

AbstractTime resolved measurements of deuterium and impurity fluxes in the boundary layer of T‐10 tokamak were carried out using carbon strips as deposition probes. Analysing these probes by RBS and ERD deuterium impact energies of 25–40 eV could be estimated from the saturation behaviour of deuterium in carbon. The high impurity concentration level and it's time behaviour give indications for local impurity producing sources playing an important role for the impurity transport in the near wall plasma.
Ionization Cross Sections of Gas Molecules for Plasma Chemistry
Authors: Deutsch H. , Schmidt M. 
Published: July 2007

AbstractUsing the recently tested formula of Gryzinski electron impact ionization cross sections for several molecules are calculated. The additivity rule and the statistical approach by Fitch and Sauter are discussed. With new experimental ionization cross sections it is possible to derive the regression coefficients also for P, As, B, and Si, which are presented together with the previously obtained values as a function of the atomic number. It appears to be possible to obtain coefficients for other atoms by interpolation. First attemps to determine regression coefficients also for 20 and 35 eV electron energy are discussed.
A Note on the Monte Carlo Simulations of Non‐Equilibrium Electron Energy Distributions
Authors: Braglia G. L. 
Published: July 2007

AbstractThe Monte Carlo method is an important approach for finding solutions of the electron Boltzmann equation in a gas in a field under conditions which are particularly difficult to be treated by analytical techniques. For this reason several expedients have been invented to reduce the computer time and make the simulations sufficiently fast and accurate. In this paper it is shown how the most significant expedients can be extended and used to simulate electron motions in non equilibrium situations.
Numerical Analysis of Symmetrical Waves Dispersion in a Nonisothermal Plasma Waveguide in a Magnetic Field
Authors: Nikolov N. A. , Dankov P. I. 
Published: July 2007

AbstractDispersion equations of a nonisothermal plasma waveguide in a constant external magnetic field are derived, when the magnetic field intensity tends to infinity. The plasma electrons' thermal velocity are taken in mind. A numerical analysis of dispersion equations for the E‐ (TH‐) and H‐ (TE‐) waves is made. In the high‐frequency range it shows the possibility of the slow E‐waves exciting with a higher frequency than the electron Langmuir frequency. In the range near to the ion Langmuir frequency it shows the existence of waves with an anomalous dispersion. These waves are named low‐frequency backward E‐waves and it is shown, that in some frequency ranges they change the group velocity sign. The dispersion is investigated also in respect to the waveguide plasma filling.
Multiphoton Excitation and Ionisation in the 9–12 eV Region of O2 by a 1.06 μm Glass Laser
Authors: Godart J. 
Published: July 2007

AbstractIn this letter we report results of a selective multiphoton excitation of O2 in the 9–12 eV region by a neodymium glass laser. The main feature of this experiment is the major presence of the ion specie O2+ in the interaction volume with the values 10 ± 1 for the nonlinear interaction order. This result can be interpreted as a double mechanisms namely: a one step process, the direct absorption from the ground state or a two step process via an intermediate resonant state which has been attributed as the second (B′3Σu−, v′=2) state of O2 located at 10.56 ± 0.03 eV. The probability of multiphoton formation of O2+ for a flux value of 1,5 × 1012 W/cm2 is equal to 2 × 107±1 sec−1.
Effect of Hall Current on the Magnetogravitational Instability of Anisotropic Plasma with Generalized Polytrope Law
Authors: Chhajlani R. K. , Purohit P. 
Published: July 2007

AbstractThe effect of Hall current on the propagation of small perturbations through self gravitating anisotropic collisionless pressure plasma with generalized polytrope law is investigated. The poly‐trope law for pressure components parallel and perpendicular to the direction of magnetic field is utilized in the analysis. The effect of Hall current and finite conductivity is introduced in the generalized Ohm's law. Using the polytrope law and Ohm's law dispersion relations are obtained from linearized perturbation equations for wave propagation along and perpendicular to the direction of magnetic field. The dispersion relations incorporating polytrope indices are able to represent the Chew, Goldberger and Low approximation with double adiabatic equation of state for the anisotropic pressure and the magnetohydrodynamic set of equations with isothermal equation of state for the isotropic pressure. The effect of Hall current, finite conductivity and polytrope indices is discussed on the well known hose and gravitational instability. It is found that Jeans' criterion depends on polytrope indices and the condition of gravitational instability is determined for different special cases of interest.
Sudden Jumps, Hysteresis, and Negative Resistance in an Argon Plasma Discharge. I. Discharges with No Magnetic Field
Authors: Bosch R. A. , Merlino R. L. 
Published: July 2007

AbstractJumps and hysteresis in discharge current are produced in a low‐pressure (10−5 – 10−4 Torr). magnetic field free, thermionic argon plasma discharge by varying discharge voltage, neutral pressure, or filament temperature. This behavior can be attributed to a region of negative differential resistance in the voltage versus current characteristic of the discharge. A model is presented in order to understand the physical processes leading to this negative resistance.
[Russian Text Ignored]
Authors: [Russian Text Ignored]  , [Russian Text Ignored]  , [Russian Text Ignored]  
Published: July 2007

AbstractThis work is devoted to the investigation of physical processes in a non‐equilibrium plasma of a binary mixture of inert gases. The degree of radial separation of the mixture was found to increase with increasing pressure of buffer gas and discharge current and to decrease with growing partial pressure of the admixture. The correlation of the radial and axial types of separation was shown experimentally. The kinetics of population of the metastable states He(23S) and Xe(3P22) and of charged particles was investigated using an impulse regime. The time for the establishment of the stationary state of the radial distribution of the components was found to be several times less than the time of reestablishment of the homogeneous distribution of the atomic component after switching off the discharge impulse. The phenomenon of a decreasing effective diffusion length of the discharge was found. This effect has essential influence on the time for the establishment of the stationary state of radial cataphoresis.
An Efficient Spectroscopic Control — Technique of the Parameters of Thermic Plasmas Produced under the Condition of a Variable Current
Authors: Halenka J. , Janus H. 
Published: July 2007

AbstractThe spectroscopic diagnostics has been carried out as an example for an argon plasma from Maecker‐Shumaker type electric arc supplied by periodic variable current. It is shown that the time‐dependent runs of intensity of the plasma light may be determined using an ordinary oscilloscope. We have stated that the electron concentration Ne in the plasma is the most sensitive quantity to the current pulsations. In the percentage, Ne variations at the arc axis are approximately the same as the current ones.
Two Dimensional Megagauss Magnetic Field Variation Along Axial and Radial Direction of Laser Axis for a Plasma Produced due to Laser Irradiation on the Surface of a Wire Target
Authors: Jha L. N. , Srivastava M. P. 
Published: July 2007

AbstractThe variation of megagauss magnetic field in two dimensions for a cylindrical target plasma produced by lasers irradiation on the surface of a cylindrical wire has been solved analytically making use of Hankel and Fourier transforms. The results have been compared with the experiments of RAVEN et al. (1978).
Theoretical Studies of the Laser Induced Plasma Profile Near the Critical Density Region for an Adiabatic Plasma Model
Authors: Paikaray R. , Srivastava M. P. 
Published: July 2007

AbstractA theoretical study of the variation of density and flow velocity due to pondermotive force, near critical density region of a laser – produced plasma, obeying an adiabatic pressure law is reported. The ion‐continuity, momentum and wave equations are solved in a steady state. The density and flow velocity as a function of incident laser intensity are calculated and plotted for both underdense and overdense regions for adiabatic exponent γ = 4/3, 5/3, 2. The velocity decreases and density increases in the overdense region and velocity increase and density decreases in the underdense region with the increase of larger power at sonic point. It is found that the velocity is subsonic in the overdense region and supersonic in the underdense region. The nature of variation is similar to the isothermal model.
A Note on Second Harmonic Resonance of a Magneto‐Acoustic Wave in Planar Plasma‐Filled Waveguide
Authors: Gosh B. , Das K. P. 
Published: July 2007

AbstractThe second harmonic generated by non‐linear self interaction of a magneto‐acoustic wave in a planar plasma‐filled waveguide is a freely propagating mode. Coupled‐mode equations for resonant nonlinear interaction of this second harmonic mode with the fundamental mode are derived. Using these equations the possibility of generation of the second harmonic is analysed.
On the State of Ionization, Non‐Ideality and Electric Conductivity of the Cathode Plasma of Vacuum Arcs
Authors: Anders S. 
Published: July 2007

AbstractThe cathode spot plasma of a metal vapour are in vacuum has a high density (1025–1028 m3) with a relatively low temperature (1–5 eV), therefore it is strongly non‐ideal. The degree of ionization α and the electric conductivity σ of such plasmas are discussed, considering that non‐ideality. The burning voltage of the arc UB is estimated with the help of σ‐values, obtained from theories and measurements for non‐ideal copper plasmas. It is shown, that a high current density of the cathode spot of j = 1012 A/m2 is not in contradiction to a low burning voltage UB = 20–30 V, but these values give a consistent picture of the spot processes.