bluuebunny/crossref_metadata_2025_split huggingface dataset:
Collisional Ionization of Excited State Neon in a Gas Discharge Plasma
Authors: Han X. L. , Wisehart V. , Conner S. E. , Su M.‐C. , Monts D. L. 
Published: July 2007

AbstractWe report the first case where it is possible to clearly identify and quantitatively characterize the dominant physical processes contributing to production of the optogalvanic effect (OGE) signal in a discharge plasma. This work concentrates on the simplest case where only two states are involved in the optical transition. The theoretical model with only four parameters is in excellent agreement with the experimentally obtained time‐resolved OGE waveforms. The collisional ionization rate in the upper state is twice as fast as that in the lower state although the two states are only separated by 1.94 eV. We conclude that the optogalvanic effect of the neon 640.22 nm transition is due primarily to the electron collisional ionization of the neon atoms. An alternative interpretation for the lengthening of the final state lifetime is also included (see Appendix).
Single‐ and Two‐Particle Energies and Thermodynamics of Dense Plasmas
Authors: Fehr R. , Kraeft W. D. 
Published: July 2007

AbstractSingle‐ and two‐particle states in dense plasmas differ significantly from those of ideal systems and have especially a finite lifetime. Both the bound states and the continuum edges of two‐particle states are controlled by “complex single‐particle energies”. Furthermore, the thermodynamics can be given by these quantities. For this reason we study the spectral weight function of the single‐particle Green's function and solve the equivalent dispersion relation self‐consistently in the Montroll‐Ward approximation of the self energy. We give results for the continuum edges of a hydrogen plasma and of a model electron‐hole plasma and discuss approximations for the equation of state.
The Particle and Heat Drift Fluxes and their Implementation into the EDGE2D Transport Code
Authors: Radford G. J. , Chankin A. V. , Corrigan G. , Simonini R. , Spence J. , Taroni A. 
Published: July 2007

AbstractThe various particle and energy drift fluxes are presented, and it is shown that the divergence‐free part of the diamagnetic terms do not contribute to the fluid equations. In particular, it is shown that the ∇TxB heat flux (the so‐called Hinton‐Staebler term) cancels exactly from the energy equation. The implementation of the drift fluxes into the EDGE2D code is described and some results of preliminary code runs indicated.
Propagation and Superposition of Cylindrical Rarefactive Waves in a Plasma
Authors: Hansen K. , Piel A. 
Published: July 2007

AbstractIn a collisionless quiet argon plasma, transient density cavities are formed by applying a large amplitude rf pulse to a cylindrical wire antenna. After the end of the pulse, the density cavity breaks up into cylindrical rarefaction waves. Due to the large depression of up to 50%, wave propagation is nonlinear. Numerical models based on a fluid‐description and a generalized Korteweg‐deVries‐equation are presented for the propagation and superposition of the cylindrical waves. The numerical findings are compared critically with the experiments.
Supersonic Jets with Periodic Structure due to Arc plasma Expansion into a Low pressure ambient
Authors: Djakov B. E. , Enikov R. , Oliver D. 
Published: July 2007

AbstractA supersonic plasma jet was produced by a d.c. arc plasma generator operated at normal pressure and connected to a low‐pressure (p∞ = 0.2‐50 kPa) chamber via cylindrical nozzle with diameter of 2.5 mm. The argon gas flow rate was G = 0.025 to 0.35 g.s−1. In some experiments current IE ≦ 30 A passed coaxially through the initial part of the jet. Photographic records of the jet and pressure measurements are in agreement with theoretical predictions by a simple one‐dimensional, gasdynamical model capable of self‐consistent calculations throughout the plasma source/jet system. Periodic jet structure is observed over a wide range of experimental conditions, incl. in highly under‐expanded flow. The jet expansion angle and Mach disc position vary with p∞, G and IE, but are nearly constant at different arcing currents.
Constraints for the Construction of Kinetic Theories
Authors: Dufty J. W. 
Published: July 2007

AbstractIn the absence of a small parameter for systematic many‐body analysis (e.g., strongly coupled systems), the construction of an appropriate kinetic theory description necessarily has an uncontrolled, phenomenological component. In this context it is useful to identify selective exact properties of the underlying microscopic description to serve as constraints for guidance in the construction of an approximate kinetic theory. We consider here three such properties: 1) exact local conservation laws; 2) exact stationary solutions; 3) exact relationship of one‐ and two‐ particle reduced density operators. The corresponding conditions on the kinetic description are identified, and a simple “mean field” approximation is indicated as an example.
Quasi‐classical Theory and Simulations of Hydrogen‐like Quantum Plasmas
Authors: Ebeling W. , Militzer B. , Schautz F. 
Published: July 2007

AbstractFirst the range of validity of a quasi‐classical approach is analyzed and analytical formulae for the thermo‐dynamical potentials are derived. Then a simple quasi‐classical model for the quantum molecular dynamics of hydrogen‐like plasmas is developed. The model is based on a quasi‐classical wave packet representation and leads to effective momentum‐dependent Hamiltonians. The quantum‐mechanical effects corresponding to the Pauli and the Heisenberg principle are modeled by constraints in the Hamiltonian. Monte Carlo and Molecular Dynamics calculations are carried out for electron‐, electron‐positron‐, and for hydrogen plasmas considering ensembles of 64 – 250 particles. A comparison with the analytical formulae shows reasonable agreement.
On the Theory of Ionization Rate in Superdense Plasmas
Authors: Iakubov I. T. 
Published: July 2007

AbstractThe diffusion theory in energy space is used to describe the step‐by‐step ionization in superdense plasma. The rate of ionization is obtained. The theory can be used under conditions when thermal ionization accompanies cold ionization. The ionization time in laser‐generated aluminum plasma is calculated.
Numerical Solution of the Quantum Landau Equation for Dense Plasmas
Authors: Kosse S. , Bonitz M. , Schlanges M. , Kraeft W. D. 
Published: July 2007

AbstractThe numerical solution of the quantum Landau kinetic equation for a dense electron gas is considered. Being one of the most simple kinetic equations, it still retains essential physical features of a correlated many‐particle system, such as selfconsistent static screening and Pauli blocking, and, at the same time, it is a good test case for the efficiency of numerical methods. Two schemes for the evaluation of the scattering rates and the collision integral are discussed. To illustrate our results, we present time‐dependent calculations i) for the relaxation of a nonequilibrium electron distribution function and ii) for the stopping of fast electrons.
Parametric Instability of Surface Waves on the Second Harmonic of Electron Cyclotron Frequency in a Plasma Layer
Authors: Girka V. O. , Sporov A. E. 
Published: July 2007

AbstractThe parametric instability of surface waves on the second harmonic of electron cyclotron frequency (SWCF) in a plasma filled dielectric wave guide is examined in a kinetic approximation. The studied surface waves are extraordinary polarized modes and propagate across the external steady magnetic field. The amplitude of the electrical pump wave is assumed to be small. Simple expressions for increments of the parametric instability of the SWCF are calculated. The otained results can be used in controlled fusion researches in order to avoid undesirable regimes of plasma periphery heating in that fusion devices which use the resonance electron cyclotron heating method.
The Development of Simplified Heat Flux Limiters for EDGE2D
Authors: Radford G. J. , Corrigan G. , Fichtmüller M. , Simonini R. , Spence J. , Taroni A. 
Published: July 2007

AbstractA theoretically based model for heat flux limiters is under development for the multi‐fluid code EDGE2D. Results show a strong reduction in the ion heat flux while that for the electrons is largely classical. A corresponding reduction in the thermal forces on impurities has lead to a small improvement in impurity retention.
Fluid modelling of edge plasmas with ion frictional forces allowing for arbitrary impurity abundances
Authors: Maddison G P , Helander P , Cornford S L 
Published: July 2007

AbstractFluid modelling of ion parallel transport in tokamak scrape‐off layers (SOLs) is generalized according to the descriptions of Hirshman and Hinton. A compact representation is implemented into the “B2” code, and initial test calculations performed for helium flow in COMPASS‐D divertor plasmas. Relation to other, higher‐order treatments of impurity fluxes is considered.
Two Alternative Approaches in the Kinetic Theory of Fully Ionized Plasmas
Authors: Klimontovich Yu. L. 
Published: July 2007

AbstractA brief review of two alternative descriptions of nonequilibrium processes in fully ionized plasmas is presented. The example of “Landau damping” is used to demonstrate that some fundamental problems remain unsolved in the kinetic theory of plasmas. They arise from inconsistent descriptions of the transition from the reversible equations of mechanics of charged particles and fields to the irreversible equations of continuous media in the theory of plasmas. These difficulties can be overcome through consistently defining the structure of continuous media and the characteristics of dynamic instability motion of particles. The procedure leads to generalized irreversible kinetic equations which provide the basis for a unified description of nonequilibrium processes in plasma on kinetic and hydrodynamic scales.
Stationary Regimes of Nonlinear Alfvén Oscillations in a Driven System with Discrete Spectrum
Authors: Markovskii S. A. 
Published: July 2007

AbstractDriven stationary Alfvén oscillations in a system with discrete spectrum are considered in the approximation of weak nonlinearity. The correction to the eigenfrequency of small oscillations, proportional to the square of their amplitude, is derived with the help of the perturbative approach. The dependence of the amplitude versus the frequency of the driving force is found to have two bifurcation points at which the amplitude exhibits finite variation under the action of infinitesimal deviation of the driver frequency. It is shown that the bifurcation is possible only when the unstable processes of interaction of the initial standing Alfvén wave with small perturbations are stabilized to the third order in the wave amplitude. Conditions of the stabilization, as a consequence of a finite length of the system or due to dissipation, of three‐ and four‐wave parametric instabilities are discussed.
A Possible Way for dc Discharge Simulation
Authors: Mustatā I. , Biloiu C. 
Published: July 2007

AbstractA method to obtain the dc electric field variation along the discharge gap in a fluid one‐dimensional, local ionisation case, is presented. The obtained dependence was used further to infer the other interesting parameters spatial distributions in the low pressure (1 Torr) discharge. These parameters could be, the current and charge densities, the ionisation source, the electric potential and so on.
Accurate First‐Principle Equation of State for the One‐Component Plasma
Authors: Brilliantov N. V. 
Published: July 2007

AbstractAccurate “first‐principle” expressions for the excess free energy Fex and internal energy of Uex of the classical one‐component plasma (OCP) are obtained. We use the Hubbard‐Schofield transformation that maps the OCP Hamiltonian onto the Ising‐like Hamiltonian, with coefficients expressed in terms of equilibrium correlation functions of a reference system. We use the ideal gas as a reference system for which all the correlation functions are known. Explicit calculations are performed with the high‐order terms in the Ising‐like Hamiltonian omitted. For small values of the plasma parameter Γ the Debye‐Huckel result for Fex and Uex is recovered. For Γ ≫ 1, these depend linearly on Γ in accordance with the Monte Carlo findings for the OCP. The MC data for the internal energy are reproduced fairly well by the expression for Uex obtained.
Studies of Silicon Erosion in Plasma‐Target‐Interaction from Optical Emission and Absorption Spectroscopy
Authors: Jentschke H. , Schumacher U. , Hirsch K. 
Published: July 2007

AbstractThe densities of eroded silicon from a target in interaction with a cylindrically symmetric plasma are determined from measurements of the transverse radiance and transmittance of Doppler broadened spectral lines with high spectral resolution. The transmission distributions, branching ratios, and the spectral line shapes, which depend on the optical depths of the emitting and absorbing particles along the line of sight, are investigated for particle density and temperature determination. First results on emission and transmission measurements of the Si I resonance multiplet spectral line branching ratios and line profiles (centered at 251 and 288 nm, respectively) for silicon as the erosion product from a C/C‐SiC target in a low temperature plasma jet give absorption coefficients, from which erosion rates can be deduced, which are in good agreement with the results from the emission spectroscopy and from the gravimetric measurements.
Evalution of Plasma Composition and Mobilities in Argon Plasma with Chlorine as Additive
Authors: Novaković N. V. , Milić B. S. , Stojilković S. M. , Gajić D. Ž. 
Published: July 2007

AbstractResults of numerical evaluation of equilibrium compositions and mobilities in plasmas formed in the mixtures of argon and chlorine are given. The temperature dependence of the number densities of the components and their mobilities in function of temperature for low‐pressure (from0, 1 kPa to 1,0 kPa) and low‐temperature (from 500 K to 5 000 K) argon plasmas with 20% and 30% of added chlorine are evaluated. It is assumed that the system is kept under constant pressure and that a corresponding state of local themodynamical equilibrium is attained in it. A previously derived expression for the modified Debye radius, offering the possibility to treat the plasmas considered as weakly non‐ideal in the whole temperature range, is used and the cut‐off at the Landau length rather than of the smallest of ionic radii is introduced. This alteration in the evaluatin procedure brings different change in the final numerical results for all the relevant quantities.It is found that the equilibrium plasma composition depends considerably on the presence of chlorine in the whole temperature range for both pressures; the addition of chlorine significantly enhances number densities of all relevant charged constituents. This fact influences of the electron and ion collision frequencies and their mobilities too.
Debye‐Hückel Free Energy for a weakly Nonideal Plasma with Helium‐like Bound States
Authors: Lehmann H. 
Published: July 2007

AbstractIn plasmas with helium‐like bound states electrostatic screening inside the atom gives rise to deviations from the Debye‐Hückel chemical potential. Assuming a variational solution for the ground state of the helium‐like atom the corresponding Free Energy is explicitely given. The result provides a simple means to describe the forming of bound states in consistency with the surrounding plasma and surpasses in this sense perturbation theories.
Kinetics of Langmuir Turbulence: An Equation for the Two‐time Correlation Function
Authors: Erofeev V. I. 
Published: July 2007

AbstractThe two‐point correlation function is reduced to expansion in terms of the two‐time correlation function with improved accuracy. The ideas reported extends the applicability area for calculations typical to the weak plasma turbulence theory on the “strong plasma turbulence”. Some implications of the results obtained for the dynamics of Langmuir turbulence are discussed.
Quasiclassical Theory and Molecular Dynamics of Two‐Component Nonideal Plasmas
Authors: Ebeling W. , Norman G. E. , Valuev A. A. , Valuev I. A. 
Published: July 2007

AbstractA simple model of two‐component plasmas based on pseudopotentials and quasi‐classical dynamics is derived from Planck's model. In the framework of this model bound states are treated quantum‐mechanically and free pair states are treated in a quasi‐classical way. The statistical thermodynamics, structure factors and conductance of the model are investigated by molecular dynamics simulations.
Experimental Study of Planar Langmuir Probe Characteristics in Electron Current‐Carrying Magnetized Plasma
Authors: Stanojević M. , Čerček M. , Gyergyek T. 
Published: July 2007

AbstractExperimental study of planar Langmuir probe characteristics in a magnetized plasma with an electron current along the direction of the magnetic field shows that the usual procedure for determination of the electron temperature and plasma density, which is applicable in a current‐free magnetized plasma, gives erroneous results for these plasma parameters. When this procedure is applied on the characteristics measured at two opposite orientations of the probe collecting surface with respect to the direction of the electron drift, different values of the electron temperature are obtained. These virtual electron temperatures and corresponding plasma densities calculated from the measured ion saturation currents are higher and/or smaller than the exact local electron temperature and plasma density. Calculation of particular averages of these quantities is proposed as a possible way to obtain correct results for the local electron temperature and plasma density. These averages are used in the approximate evaluation of the electron drift velocity from the electron saturation currents measured at the two orientations of the probe collecting surface.
Compilation of Cross Section Data of Elementary Processes of HCI Applicable for Plasma Modeling
Authors: Efremov A. M. , Svetsov V. I. , Balashov D. I. 
Published: July 2007

AbstractIn this current work an cross section data for HCI elementary processes were calculated on the base of calculated and experimental data comparison on electrons drift rate and Townsend coefficients of dissociative attachment. Cross sections data of HCI electronic excitation are obtained for the first time.
Computer Simulation of High Power Ion Beams Interaction with Matter
Authors: Fortov V. E. , Skvortsov V. A. 
Published: July 2007

AbstractWhen high‐power ion beams (HPIB) collides with matter, it generates plasma with parameters of a wide range, staring with those well mastered in physics and gas discharge technologies and ending with those appropriate to such natural systems as star nucleus and thermonuclear systems in feasible power projects based on the controlled inertial thermonuclear synthesis. We are interested in a fairly wide range of beam power densities (from 1 GW/cm2 to 10 TW/cm2). This paper describes one mathematical model in one dimension (a plane geometry is assumed) and one model in two dimensions (r‐ and z‐coordinates). The models are completed by wide‐ range equations of state for real matter (construction materials) and supplemented with additional equations describing rheological, thermophysical, and optical properties of solid media under consideration (in various phase states from solid to plasma, including states of a strongly nonideal plasma). On the base of the continual approach, mechanical destruction of materials due to tensile strain generated by rarefaction waves is taken into account. 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 intensities I > 10 GW/cm2 (in the two‐ dimensional model based on the large‐particle technique) heat transfer, including radiational processes, is considered. Opportunities offered by contemporary computer simulation techniques in the field of interaction between HPIB and matter are demonstrated, in particular, a possibility of simulating hypervelocity impact with the help of HPIB has been shown and the necessary conditions have been determined. The results of our computer simulation may be interesting from the viewpoint of some technological applications of HPIB, for example, pulsed destruction and strengthening of construction materials, pulsed ion implantation and etc. [1].
In Situ Characterisation of Polymer Surfaces and Thin Organic Films in Plasma Processing
Authors: Meichsner J. 
Published: July 2007

AbstractIn situ sampling techniques are presented for investigation of plasma surface modification of polymers and plasma polymerisation. FTIR spectroscopy (infrared absorption reflection spectroscopy ‐ IRRAS, and attenuated total reflection ‐ ATR) are properly used for characterisation of the changes in the molecular structure of thin polymer films (polystyrene, polyethylene) due to low pressure plasma treatment. The thin films were prepared by dip or spin coating procedures. In the case of plasma polymerisation a novel fibre‐ATR technique is applied to investigate the plasma polymerisation process in the plasma bulk. Results are exemplary shown for plasma polymerisation of styrene. Ellipsometric measurements allowed the characterisation of the thin plasma modified top polymer surface layer or thin deposited plasma polymer films by their refractive index and thickness. It was shown that the applied surface plasmon ellipsometry is very sensitive with respect to the usual ellipsometry for investigation of polymer surface modification. The in situ microgravimetry by means of electronic vacuum microbalance permitted to measure the change of the sample mass in the order of 1 μg during the plasma treatment. The first steps in plasma modification (concurrence between the incorporation of plasma particles and the material etching) were studied.
Parametrical Instability of Surface Type X‐modes Immersed into a Nonmonochromatic Pumping Electric Field
Authors: Girka V. O. , Lapshin V. I. , Yu. Puzirkov S. 
Published: July 2007

AbstractParametrical excitation of surface type X‐modes (STXM) at the second harmonic of electron cyclotron frequency by nonmonochromatic external alternating electric field is under consideration. STXM are the eigenmodes of a planar magnetoactive plasma waveguide structure consisting of a metal wall with dielectric coating and uniform plasma filling. An external steady magnetic field is applied along the plasma interface, so it is perpendicular to the group velocity of the considered extraordinarily polarized waves. Influence of the plasma waveguide parameters on the parametrical instability of the STXM is studied. External alternating electric field is assumed to consist of two fields with different amplitudes and frequencies. A theoretical investigation is carried out using kinetic equation for plasma particles under the conditions of weak plasma spatial dispersion and small amplitudes of external electric fields. The obtained results can be useful for research in branch of edge plasma physics.