bluuebunny/crossref_metadata_2025_split huggingface dataset:
Shear Viscosity and Temperature Inequalities for Multi‐Species Plasmas
Authors: Suchy K. 
Published: July 2007

AbstractThe first coefficients in the orthogonal expansions of the velocity distribution functions with respect to Grad's tensorial (three‐dimensional) Hermite polynomials are shown to be proportional to ther‐modynamic fluxes, if the weight functions are local Maxwellians centered at the mean mass velocity and widened with a mean temperature. Balance equations for the stress tensors are established and reduced to linear algebraic systems under certain restrictions. Explicit solutions for the traces and the tracefree parts of the stress tensors are given.
Response of the Electron Kinetics on Spatial Disturbances of the Electric Field in Nonisothermal Plasmas
Authors: Sigeneger F. , Winkler R. 
Published: July 2007

AbstractAn efficient method for solving the inhomogeneous electron Boltzmann equation for a weakly ionized collision dominated plasma is represented. As a first application this method is used to investigate in a helium plasma the response of the electron velocity distribution function and of the relevant macroscopic quantities to the impact of spatially limited disturbances in the electric field. In addition to the field action elastic and (conservative) inelastic collisions of electrons with gas atoms are taken into account in the kinetic treatment. In this way the spatial relaxation behaviour of the electrons and their establishment into homogeneous plasma states could be studied on a strict kinetic basis. Unexpectedly large relaxation lengths in electron acceleration direction have been found at medium electric fields.
Density Distribution of Plasma Species in a Hollow Cathode Arc Discharge for Coating Application
Authors: Mönke D. , Scheibner H. , Mechold L. , Becker W. , Schrade F. 
Published: July 2007

AbstractThe plasma of a hollow cathode arc discharge (argon/titanium) was studied by emission spectro‐scopy and probe measurements. The behavior of the relative particle concentrations of the different heavy plasma components as well as the concentration and temperature of the electrons was determined as function of the vertical distance from the anode crucible.Abel‐inverted radial distributions of the relative level populations for TiI (neutral titanium), TiII (singly ionized titanium), Ar I and ArII are presented. Further measurements characterize the influence of the discharge current on the relative level population.
Electron Surface Cyclotron Waves in the Metallic Waveguide Structures with Two‐Component Filling
Authors: Girka V. O. , Girka I. O. , Kondratenko A. M. , Pavlenko I. V. 
Published: July 2007

AbstractThe dispersion properties of the slow electromagnetic surface waves propagating across external magnetic field in planar metallic waveguides with plasma and dielectric filling on the harmonics of the electron cyclotron frequency are studied in this paper. The external steady magnetic field is supposed to be directed perpendicularly to the waveguide wall. Dielectric layer separates semibounded plasma from the metallic wall. The analytical research is carried out using the kinetic description for plasma particles, the mirror reflection model for the interaction between particles and plasma boundary. Skin depth of the surface cyclotron waves (SCW) is much greater than electron Larmor radius. Effect of the following parameters of the waveguide structures: dielectric constant and thickness of the dielectric layer, plasma density value and number of the cyclotron harmonics, on the SCW dispersion is examined both analytically and numerically.
On Various Kinds of Dielectric Barrier Discharges
Authors: Müller S. , Zahn R.‐J. 
Published: July 2007

AbstractDielectric barrier discharges in Xe and Ne/Xe, He/Xe mixtures are investigated with regard to the ranges of existence of various discharge types over a wide range of parameters (total gas pressure p, electrode distance d, frequency f and mixture ratio X). The discharges were explained in more detail because of the bistable behaviour and the transfered charges, partly of the peak current and the maximum of the visible radiation pulse. The time behaviour of the discharge was observed, too. In this paper a distinction of various discharge types could be achieved by the similarity parameters f/p and pd. The charge carriers remaining in the volume and long‐living plasma species could be identified as essential mechanisms for the development of various types of discharges. The influence of space charges on the bistable behaviour could be shown indirectly.
Shock Waves due to Grain‐Charge Variation in Dusty Plasmas
Authors: Popel S. I. , Yu M. Y. , Tsytovich V. N. 
Published: July 2007

AbstractNonlinear electrostatic wave structures in plasmas containing variable‐charge dust grains, Boltz‐mann electrons, and inertial ions are investigated. The charge variation is assumed to be caused by electron and ion currents at the grains. It is found that intense shock waves can exist. The dissipation in such shock waves originate from the process of dust charging.
Analytical Results for the Boltzmann Equation
Authors: Toepffer C. , Cercignani C. 
Published: July 2007

AbstractThe manifold of solutions of the Boltzmann equation in the relaxation time approximation for particles in a constant field is obtained in closed form. The Green's function for the infinite domain and the moments of the probability distribution are calculated explicitly. A generalized drift‐diffusion equation with local temperatures is obtained by matching moments. The Green's function for the finite domain is derived for vanishing equilibrium temperature β → ∞ in a ballistic regime of large momentum gain between collisions.
Strict Kinetic Treatment of the Electron Response to Spatial Field Disturbances in Nonequilibrium Plasmas
Authors: Petrov G. , Winkler R. 
Published: July 2007

AbstractIn generalization of former approaches for the simplified solution of the inhomogeneous electron Boltzmann equation a higher order solution technique has been developed. This technique is based on a multi‐term expansion of the electron velocity distribution function and allows a strict study of the electron kinetics in plasmas acted upon by space‐dependent electric fields. This solution technique is used to investigate the response of the plasma electrons to spatially limited disturbances of the electric field in weakly ionized plasmas of helium and mercury. By solving the kinetic equation with increasing order of the multi‐term expansion the convergent solution of the kinetic problem and thus the strict spatial behaviour of the velocity distribution and of significant macroscopic properties of the electrons has been determined and analysed. Furthermore, the impact of higher order terms of the expansion has been revealed and the falsification of the velocity distribution and of related macroscopic properties has been evaluated when instead of the multi‐term solution the simpler two‐term solution of the kinetic equation is used.
Cross‐Field Diffusion by Charge Changing Processes
Authors: Fussmann G. 
Published: July 2007

AbstractThe particle transport induced by ionization, recombination and charge exchange processes in magnetically confined plasmas is analyzed. For ions with charge numbers Z ≧ 2 a random walk is caused by the fluttering of the gyro‐radius as a result of successive recombination and ionization events. The corresponding diffusion coefficient, however, is very small and may be neglected even in the case of high‐energy alpha particles being produced in fusion plasmas. Single and neutral particles are subjected to joint transport across the magnetic field due to their unimpeded motion during the short atomic phases. It is found that this mechanism is more important than classical transport over a wide temperature and density range. The corresponding diffusion coefficient D1 = f(Te)Ti/mine is independent of the magnetic field strength and shows an electron temperature dependence which can be expressed in terms of the rate coefficients for ionization, recombination and charge exchange. The latter effect leads to a strong reduction of the diffusion process in hydrogen plasmas. Diffusion coefficients comparable with anomalous values of about 1m2/s are therefore reached only for cool (divertor) plasmas with T < 5eV.
Effective Radiative Lifetimes
Authors: Lange H. , Leipold F. 
Published: July 2007

AbstractMeasurements of trapped decay rates for the xenon 146.9 nm resonance transition in the positive column of low current xenon discharges are reported. These rates, also called “effective lifetime of resonance photons”, were measured in contrast to other authors in an active discharge by means of a laser produced disturbance in the density of the 6s[3/2]1‐xenon resonance atoms at the discharge axis. The 146.9 nm radiation resulting from this temporary overpopulation was measured and then analysed for the determination of the trapped decay rates. The dependence of the measured quantities of tube diameter is discussed. A comparision with decay rates obtained by other experimental methodes and simulations of resonance radiation trapping shows good agreement.
The Scaling of the Edge Temperature in Tokamaks Based on the Alfven Drift ‐ Wave Turbulence
Authors: Kerner W. , Igitkhanov Yu. , Janeschitz G. , Pogutse O. 
Published: July 2007

AbstractThe stability analysis of Alfven drift type modes leads to a threshold condition for the L‐H transition. This condition yields the scaling for the edge temperature, which is in agreement with the experimental results.
Poloidal Pressure Gradients, Divertor Detachment and Marfes
Authors: Schaffer M. J. 
Published: July 2007

AbstractBecause the radiation power density from a marfe scales approximately as the square of its plasma pressure, and since increased radiation would aid divertor detachment for high power tokamaks, this paper identifies regions that might permit locally increased plasma pressure in steady state. The magnetic and dynamic (flow) constraints of magneto‐hydrodynamics (MHD) are examined for self‐consistent locally increased pressure equilibria, in both the magnetically open tokamak scrape‐off layer (SOL) and the closed surfaces just inside the last closed flux surface. In most tokamak geometries it is difficult to recycle particles at a sufficient rate to sustain high pressure marfes, but they might be possible near a divertor X‐point.
Time‐dependent modelling of impurity transport in the jet core and divertor plasma
Authors: Taroni L. Lauro , Corrigan G. , Simonini R. , Spence J. , Springmann E. , Taroni A. , Andrew P. , Giannella R. , Harbour P. J. , Horton L. D. , Ingesson L. C. , Lawson K. , Maggi C. F. , Monk R. D. , O'mullane M. , von Hellermann M. 
Published: July 2007

AbstractThe analysis of the contamination of the plasma by a puffed recycling impurity, such as neon, is intrinsically time‐dependent and requires simultaneous time‐dependent modelling of both the core region and the SOL and divertor region. To this end, a new code, combining core and edge codes, has been developed: its main features will be described and its application to the analysis of an L‐mode discharge in which neon was puffed will be shown.
Modeling of neutral plasma in a divertor in the fluid‐kinetic transition
Authors: Karney C. F. F. , Stotler D. P. , Braams B. J. 
Published: July 2007

AbstractThe neutrals in a tokamak divertor in the so‐called “detached” mode of operation may be in a kinetic regime (long mean free path) in some regions and in a fluid regime (short mean free path) elsewhere. For example, a kinetic description is necessary in the thin ionization front, while the cold neutrals in front of the divertor plate are adequately described by fluid equations. The paper describes a way to model this by coupling existing Monte Carlo neutral transport and plasma fluid codes. This is explored with a simple analytical model.
Lattice Boltzmann Representations of Neutral Gas Hydrodynamics
Authors: Krasheninnikov S. I. , Catto Peter J. 
Published: July 2007

AbstractLattice Boltzmann prescriptions attempt to replace continuous Navier‐Stokes equations with kinetic equations on a discrete lattice on which particles are only allowed to move to other lattice sites during each time step. We employ a Grad procedure to find the constraints which must be satisfied to model a monatomic gas in a long scale length limit. A non‐invariant form of the equilibrium function allows us to reduce the number of sub‐lattices which are needed to compensate for non‐physical lattice effects and recover the exact Navier‐Stokes equations.
Hydrogen Equation of State and Plasma Phase Transition
Authors: Beule D. , Ebeling W. , Förster A. , Juranek H. , Redmer R. , Röpke G. 
Published: July 2007

AbstractWe combine equations of state valid for the dense, neutral fluid and the dense, fully ionized plasma to obtain a new equation of state for the intermediate region where partial dissociation and ionization occur. A region of thermodynamic instability is found which is known as plasma phase transition. Hugoniots curves are calculated and compared with experiments and other theories.
Electrical Conductivity in Dense Hydrogen Fluid and Metal Plasmas
Authors: Redmer R. , Röpke G. , Beule D. , Ebeling W. 
Published: July 2007

AbstractRecent shock‐wave experiments on fluid hydrogen have shown that a transition from nonconducting to metallic‐like conductivity occurs at Mbar pressures. On the other hand, a transition from metallic to non‐metallic conductivities has been observed in aluminum and copper plasmas at about 0.1 solid state density using the rapid wire evaporation technique. The equation of state and composition of both shock‐compressed hydrogen and expanded metals are calculated within a partially ionized plasma model. The conductivity is determined in linear response theory taking into account all relevant scattering processes of free electrons on T matrix level. Reasonable agreement with the experiments is found.
Bloch Equations in Dense Plasmas
Authors: Schepe R. , Tamme D. , Henneberger K. 
Published: July 2007

AbstractIn this paper we discuss pulsed laser excitation, which is nearly resonant with an atomic transition in a partially ionized plasma. The dynamics of particles and the external laser field is microscopically described by a Green's function approach on the one‐ and two‐particle level. Particularly for the (1s → 2p) transition of hydrogen the influence of the particle density, laser intensity and detuning on the polarization dynamics is discussed. Treating the collision integral with the Lipavsky ansatz allows to determine the relaxation times T1 and T2 for the inversion and the polarization. These relaxation times vary from the ps scale (in the low‐density case) to the fs region (at high densities). Considering the pulse duration in comparison with the relaxation times, the Markovian limit is valid for moderate and high densities, whereas the low‐density case requires a non‐Markovian computation.
Nonequilibrium Two‐Particle Dyson Equation
Authors: Bornath Th. , Schlanges M. , Kremp D. 
Published: July 2007

AbstractThe two‐particle problem within a nonequilibrium many‐particle system is investigated in the framework of real‐time Green's functions. A nonequilibrium Dyson equation is given for the two‐time two‐particle Green's function. The two‐particle self‐energy in this equation consists of two qualitatively different parts: one part is local in time, whereas the other part is a two‐time quantity having thus a dynamical character. The latter part of the self‐energy can be expressed in terms of multi‐particle Green's functions.
Dielectric Properties of Dense Femtosecond Laser Produced Plasmas
Authors: Kingham R. , Theobald W. , Hässner R. , Sauerbrey R. , Fehr R. , Gericke D. O. , Schlanges M. , Kraeft W.‐D. , Ishikawa K. 
Published: July 2007

AbstractThe XUV optical properties of dense plasmas are investigated experimentally and theoretically. We calculate the dielectric function of a dense carbon plasma including effects of higher density. These dielectric functions are then used together with transmission measurements of high‐order harmonics through dense foil plasmas to obtain the initial electron density and temperature.
Electron Dynamics and Anderson Localization in Wigner Formulation of Quantum Statistical Mechanics
Authors: Filinov V. S. , Lozovik Yu. E. , Filinov A. V. , Zacharov I. E. 
Published: July 2007

AbstractThe new numerical approach for consideration of quantum dynamics and calculations of the average values of quantum operators and time correlation functions in the Wigner representation of quantum statistical mechanics has been developed. The time correlation functions have been presented in the form of the integral of the Weyl's symbol of considered operators and the Fourier transform of the product of matrix elements of the dynamic propagators. For electrons in disordered systems of scatterers the numerical results have been obtained for series of the average values of the quantum operators including position and momentum dispersions, average energy, energy distribution function as well as for the frequency dependencies of tensor of electron conductivity and permittivity according to quantum Kubo formula. Zero or very small value of static conductivity have been considered as the manifestation of Anderson localization of electrons in 1D case.
Scattering Rates and Stopping Power for Strongly Coupled Plasmas
Authors: Schlanges M. , Kosse S. , Gericke D. O. 
Published: July 2007

AbstractOn‐ and off‐shell scattering rates for strongly coupled plasmas are calculated in T‐matrix approximation to study the relevance of strong correlations between the plasma particles. Thermodynamic equilibrium as well as nonequilibrium plasmas are considered. On the basis of the calculated scattering rates, the stopping power is determined for ion beams in dense plasmas. These results are compared with molecular dynamic simulations. For the full T‐matrix approach, a good agreement is found for low beam velocities.
Using the Dielectric Function for Diagnostics of Laser‐Induced Plasmas
Authors: Wierling A. , Sorge S. , Röpke G. 
Published: July 2007

AbstractWe present an approach to the dielectric function of dense plasma based on a generalized linear response theory. The relation of this approach to the Drude model as well as to the random phase approximation is discussed. It is shown, that the dielectric function presented here obeys certain exact known properties such as sum rules. Using the dielectric function, the absorption coefficient for electro‐magnetic wave interacting with dense targets is calculated. Regions for the applicability for simplified models are given. Implications for the diagnostics of laser‐induced plasmas are pointed out.
Electron Distribution Function in a Nonideal Plasma in Strong Electric and Laser Fields
Authors: Starostin A. N. , Aleksandrov N. L. , Konchakov A. M. , Okhrimovskyy A. M. , Shchipka M. V. 
Published: July 2007

AbstractUsing a two‐term approximation to the kinetic equation, the generalized electron energy and momentum distribution which governs the electron transport and rate properties in nonideal plasma is analyzed. A class of general solutions of the equation is found in the model case which is widely used in semiconductor plasma. An equation that generalizes the well‐known Zeldovich‐Raizer quantum kinetic equation in the case of nonideal plasma is deduced. Explicit nonequilibrium solutions of this equation for the electron energy and momentum distribution function in a strong laser field are constructed.
Screening Enhancement of Thermonuclear Reactions in High Density Stars
Authors: Dewitt H. , Slattery W. 
Published: July 2007

AbstractThe screening function for zero separation for two reacting nuclei in a strongly coupled OCP plasma is obtained using new very accurate Monte Carlo OCP fluid simulation data by two methods. The first method obtains H(0), the screening function at x = 0, from the difference of free energies before and after the reaction. The second method is direct fitting of the Widom expansion in powers of x2 to the MC data for the pair distribution function, g(x). The two methods agree to 0.2%.
Modelling of Sunspot Equilibrium Considering Stratification and Temperature Gradients
Authors: Meister C.‐V. 
Published: July 2007

AbstractBasing on the Schlüter‐Temesváry similarity condition for the magnetic flux in sunspot regions, on experimental horizontal profiles for the absolute value of the magnetic induction, and, for the first time, also on horizontal and vertical hydrodynamic momentum balances, analytical expressions for horizontal and altitudinal dependencies of the magnetic induction and the kinetic pressure of the sunspot plasma are derived.
Kinetics of the Charging Process in Dusty Plasmas
Authors: Trigger S. A. , Schram P. P. J. M. 
Published: July 2007

AbstractOn basis of the kinetic equations for dusty plasmas we consider the charging equation for grains. We suggest the local charge approximation, in which the distribution function of the charge variable is a delta‐function, so that the charge becomes a function of position and time. We also simplify the kinetic equations and analyze the influence of the charging process on the dielectric function and wave spectra.
Computer Simulation of High Power Ion Beams Interaction with Matter
Authors: Fortov V. E. , Skvortsov V. A. 
Published: July 2007

AbstractWe are interested in a fairly wide range of high‐power ion beams (HPIB, with intensities from 1 GW/cm2to 10 TW/cm2). In modeling the action of ion beams of moderate intensity (I< 10 GW/cm2) on metal targets, elastoplastic properties are taken into account, and in describing the action of ion beams with intensitiesI> 10 GW/cm2heat transfer, including radiation processes, is considered. Computer simulations based on a system of hydrodynamic equations are supplemented with wide‐range equations of state, corresponding correlations for the calculation of the beam energy loss in the matter, parameters of energy transfer (coefficients of electronic, ionic, and radiative thermal conductivity, coefficients of optical radiation absorption), kinetics of generation and development of microcracks in solids when pulse loads are large. A possibility of simulating hypervelocity impact with the help of HPIB has been shown and the necessary conditions have been determined.
A Comparative Study for the Equation of State of Dense Fluid Hydrogen
Authors: Juranek H. , Redmer R. , Röpke G. , Fortov V. E. , Pyalling A. A. 
Published: July 2007

AbstractRecent developments in shock‐wave experimental techniques have allowed the 100 GPa range to be probed. Driven by a two‐stage gas gun (Livermore, USA) or chemical explosives (Chernogolovka, Russia), the multiple shock‐wave technique has been applied to determine the equation of state and the electrical conductivity of dense hydrogen and deuterium fluids. In single shock wave experiments driven by the NOVA laser, the principle Hugoniot curve of deuterium was determined. Interesting effects such as dissociation and the transition to metallic‐like conductivities occur under these conditions. The equations of state applied so far to analyze the experimental data are compared and a new semi‐empirical equation of state is given.
Semiclassical Dynamics and Time Correlations in Two‐Component Plasmas
Authors: Ortner J. , Valuev I. , Ebeling W. 
Published: July 2007

AbstractThe semiclassical dynamics of a charged particle moving in a two‐component plasma is considered using a corrected Kelbg pseudopotential. We employ the classical Nevanlinna‐type theory of frequency moments to determine the velocity and force autocorrelation functions. The constructed expressions preserve the exact short and long‐time behavior of the autocor‐relators. The short‐time behavior is characterized by two parameters which are expressable through the plasma static correlation functions. The long‐time behavior is determined by the self‐diffusion coefficient. The theoretical predictions are compared with the results of semiclassical molecular dynamics simulation.