bluuebunny/crossref_metadata_2025 huggingface dataset:
The effect of rigid sidewalls on nonlinear two-dimensional Bénard convection
Authors: Metzener P.
Published: July 2002

Consider a rectangular box filled with a fluid and heated from below. A two-dimensional model is used to describe the effects of rigid sidewalls. For some aspect ratios the linear theory cannot predict which mode is preferred; thus a study of the bifurcating solutions of the nonlinear problem around these special ratios is made. The stability of the steady solutions is discussed when the competing modes are either the one and two roll modes or the three and four roll modes. In the first case as the Rayleigh number is increased, the flow prefers either the one roll mode for almost all Prandtl numbers or a mixed mode for a small range of low Prandtl numbers. In the second the flow always prefers the four roll mode.
Mode conversion of a propagating to nonpropagating wave
Authors: Cairns R. A. , Lashmore-Davies C. N.
Published: July 2002

A previous theory that gives a simple expression for the transmission coefficient through a mode conversion region, in terms of the local wave dispersion properties, is examined further in the special case where a propagating wave interacts with a localized resonant response. For this case it is shown how the theory can be derived, starting from Maxwell’s equations and the plasma conductivity tensor, and a particular example is analyzed by way of illustration.
Parametric excitation of an ion-acoustic wave by an electron-cyclotron wave
Authors: Matsuda Kyoko
Published: July 2002

Parametric excitation of an ion-acoustic wave by a left circularly polarized wave of a frequency near the electron frequency in a high-density, quasi-isothermal plasma (Ti∼Te) has been studied. The instability may occur with realistic input power, and bulk ion heating is expected. It is also found that a higher ion temperature favors the instability.
A new formulation for the synchrotron absorption–emission coefficient in plasmas
Authors: Nassri A. , Heindler M.
Published: July 2002

Starting from single particle radiation theory for a relativistic Maxwell distribution of electrons, a new exact representation of the absorption coefficient for synchrotron radiation in a plasma which offers considerable numerical advantages is derived. For the propagation perpendicular to the magnetic field, the same results were obtained as with formulas derived from plasma kinetic theory, however, with considerably reduced effort in numerical evaluation. Performing the integration analytically, a representation is arrived at, without any restricting assumptions, by an infinite sum which is shown to converge very fast at all temperatures below several tens of keV and to reproduce the strong resonant behavior at low temperatures. For higher temperatures the discrete sum was replaced by an integral which is solved analytically, again without any restricting assumptions such as the usual kT/m0c2≪1. The superiority of these analytical representations even to the alternatives that have been previously published is shown.
Importance of radiation effects in ion-beam-driven inertial fusion target calculations: Compensation of range shortening by radiation transport in ion-beam-generated plasmas
Authors: Tahir N. A. , Long K. A.
Published: July 2002

In this paper computer simulation results showing that radiation can compensate for range shortening in ion-beam inertial fusion targets are presented. Simulation results of ablation, compression, ignition, burn, and hydrodynamic stability of a heavy ion-beam-driven, reactor-size, inertial confinement fusion (ICF) target including radiation transport are also reported. In this target design the fuel is protected against radiative preheat by a high-Z, high-ρ lead radiation shield, and the fuel is separated from the radiation shield by a low-Z, low-ρ lithium cushion. This avoids mixing of the lead from the radiation shield into the fuel at the end of the implosion. The target is driven by 10 GeV Bi++ ions, and it yields an output energy of ∼690 MJ for an imput energy of ∼4.56 MJ, so that the overall target gain is ∼152. The peak power in the input pulse is 500 TW.
Harmonic vortices in bounded plasmas
Authors: Yu M. Y.
Published: July 2002

Vortex solutions with azimuthal harmonics higher than the dipole are shown to exist for a class of nonlinear dynamical equations governing low-frequency motion in a magnetized cylindrically bounded plasma.
Ion-acoustic solitary waves in relativistic plasmas
Authors: Roychoudhury R. K. , Bhattacharyya Sikha
Published: July 2002

Using a pseudopotential approach, solitary wave solutions in a relativistic plasma have been found.
Direct observation of high frequency emissions from a critical velocity rotating plasma
Authors: Nickenig L. , Piel A.
Published: July 2002

The high frequency (hf) emission associated with the turbulent heating mechanism, which is part of the critical velocity effect, is measured directly for the first time. The emissions are found to occur in the steep density gradient in the front of so-called rotating ‘‘spokes,’’ as predicted by a model of the critical velocity effect in inhomogeneous plasmas. The spectral distribution of the waves and a lower bound for the absolute wave amplitude are obtained.
Viscous effects on wave propagation in a bubbly liquid
Authors: Miksis Michael J. , Ting Lu
Published: July 2002

The effects of viscosity on wave propagation in a bubbly liquid with a finite gas volume fraction are studied using the effective equations of Miksis and Ting [Phys. Fluids 29, 603 (1986)]. Both the linear and nonlinear versions of their equations are considered. For linear waves an exact solution of the microscopic problem is found. At finite Reynolds number the attenuation caused by viscosity is found. The Crespo wave speed and the Wood wave speed are shown to be the effective sound speed for the two limiting cases of infinite Reynolds number and zero Reynolds number, respectively. In the nonlinear case viscous effects are accounted for by using Levich’s method. This new nonlinear system of effective equations including the viscous effects is analyzed.
Radio frequency suppression of lower hybrid drift instability in a theta pinch
Authors: Laxmi V. N. , Tripathi V. K.
Published: July 2002

A lower hybrid pump wave with frequency close to the lower hybrid frequency (ω1/2cω1/2ci) is a potential candidate for the suppression of lower hybrid drift instability in a theta pinch. The coupling is a four-wave parametric process involving lower hybrid sidebands. It introduces an effective damping on the drift mode causing suppression of the latter at modest pump powers. The longer wavelength modes are more strongly affected than the shorter ones.
Diffusion with varying drag: The runaway problem. II
Authors: Rollins David , Corngold Noel
Published: July 2002

Diffusion driven by a constant field, and opposed by a velocity-dependent diffusion coefficient that decreases to zero at large velocity, leads to the phenomenon of ‘‘runaway.’’ It is studied here in the case of a one-dimensional velocity space, when the Fokker–Planck equation is equivalent to an interesting Schrödinger equation. The runaway current is extracted from the smallest eigenvalue, after the equation has been solved by the method of matched asymptotic expansions. There is discussion of connections between our approach, the conventional approach, and the classical two-dimensional results.
A model for fully developed turbulence
Authors: Canuto V. M. , Goldman I. , Chasnov J.
Published: July 2002

A model for stationary, fully developed turbulence is presented. The physical model used to describe the nonlinear interactions provides an equation for the turbulent spectral energy function F(k) as a function of the time scale for the energy fed into the system, n−1s. The model makes quantitative predictions that are compared with the following available data of a different nature. (a) For turbulent convection, in the case of a constant superadiabatic gradient and for σ≪1 (σ≡Prandtl number), the convective flux is computed and compared with the result of the mixing length theory (MLT). For the case of a variable superadiabatic gradient, and for arbitrary σ, as in the case of laboratory convection, the Nusselt number N versus Rayleigh number R relation is found to be N=AσR1/3 as recently determined experimentally. The computed Aσ deviates 3% and 8% from recent laboratory data at high R for σ=6.6 and σ=2000. (b) The K–ε and Smagorinsky relations. Four alternative expressions for the turbulent (eddy) viscosity are derived (the K–ε and Smagorinsky relations being two of them) and the numerical coefficients appearing in them are computed. They compare favorably with theoretical estimates (the direct interaction approximation and the renormalization group method), laboratory

data, and simulation studies. (c) The spectral function, transfer term, and dissipation term. The spectral energy function F(k), the transfer term T(k), and the dissipation term νk2F(k) are computed and compared with

laboratory data on grid turbulence. (d) The skewness factor S̄3 is computed and compared with laboratory data. The turbulence model is extended to treat temperature fluctuations characterized by a spectral function G(k). The main results are (e) when both temperature and velocity fluctuations are taken into account, the rate ns(k), that in the first part was taken to be given by the linear mode analysis, can be determined self-consistently from the model itself; (f) in the inertial-convective range, the model predicts the well-known result G(k)∼k−5/3; (g) the Kolmogorov and Batchelor constants are shown to be related by Ba=σt Ko, where σt is the turbulent Prandtl number; and (h) in the inertial-conductive range the model predicts G(k)∼k−17/3 for thermally driven convection as well as for advection of a passive scalar, the difference being contained in the numerical coefficient in front. The predicted G(k) vs k compare favorably with experiments for air (σ=0.725), mercury (σ=0.018), and salt water (σ=9.2).
Relativistic electron motion in the presence of cyclotron resonant electromagnetic waves
Authors: Hafizi B. , Aamodt R. E.
Published: July 2002

The relativistic collisionless motion of magnetically trapped electrons under the influence of rf wave with frequency near an integral multiple of their ambient synchrotron frequency is studied analytically. A Hamiltonian formalism is used to determine the phenomena of losing or maintaining local resonance and the accumulation or dispersion of the electrons in the magnetic well as they heat. Sustenance of resonance is shown to be markedly dependent on the index of refraction of the wave; it is also shown that the inherently relativistic detrapping effect can be important even for low energies and can be enhanced by low energy collisions.
Statistical closure approximations and the fluctuation-dissipation theorem for drift-wave interaction
Authors: Koniges A. E. , Leith C. E.
Published: July 2002

The statistical dynamics of a truncated (three-wave) model for drift-wave interaction are studied using numerical simulation in order to determine appropriate turbulence modeling approaches. The nonlinear dynamical equation is integrated for a Gaussian ensemble of initial states, and time-lag correlation functions and infinitesimal response functions are computed. The fluctuation-dissipation relation, an assumption of many statistical closure approximations, is shown to be qualitatively valid for statistical steady states of the system. Guided by the ensemble results, a Markovian turbulence model is selected and investigated.
Gyroresonant absorption from congruent reduction of an anisotropic pressure fluid model
Authors: Friedland Lazar
Published: July 2002

A system of Maxwell, multifluid momentum and anisotropic pressure equations for a weakly inhomogeneous magnetized plasma is written in a special Hermitian form. A recently developed congruent reduction technique, for extracting embedded, multidimensional, pairwise mode conversion events, is applied in studying the electron gyroresonant absorption problem. The mode conversion from an electromagnetic mode to a fluid pressure mode near the fundamental and second harmonic gyrofrequency is interpreted as gyroresonant absorption. The transmission coefficient is found in an arbitrary three-dimensional plasma and magnetic field geometry, demonstrating the potential of the approach for systematically reducing the order in general multicomponent wave propagation problems in nonuniform plasmas.
Study of a collisionless, curvature and rotationally driven, trapped particle instability
Authors: Scarmozzino R. , Sen A. K. , Navratil G. A.
Published: July 2002

The Columbia Linear Machine [Plasma Phys. 24, 185 (1982)] has been redesigned to enter the parameter regime of the collisionless, curvature driven, trapped particle instability. The changes that were made reduced the neutral collisionality by over a factor of 2 and the Coulomb collisionality by an order of magnitude, and increased the curvature drive by nearly an order of magnitude. With the new machine configuration, a strong (ñ/N≳60%), coherent, m=1 fluctuation is observed which is identified as a collisionless, curvature and rotationally driven, trapped particle instability. The mode is localized strongly to the region of trapping. The radial structure of the mode is broad and the mode exhibits magnetohydrodynamiclike body motion of the plasma column. Furthermore, the mode displays the expected parametric dependences of increasing mode amplitude with increasing mirror ratio and rf power and decreasing mirror cell length. A theory whose predictions are in fair agreement with the experiment has been developed for the mode in the presence of a dc radial electric field. Preliminary experiments designed to test the concept of charge overshoot stabilization of trapped particle modes show results consistent with that idea. A measurement of the growth rate of the instability has been made and is in fair agreement with the theoretical prediction.
The measurement of shear-induced diffusion in concentrated suspensions with a Couette device
Authors: Nadim Ali
Published: July 2002

A novel theoretical scheme is presented, which permits measurements of the so-called shear-induced diffusivity in concentrated suspensions to be made based upon long-time data collected in a two-cylinder Couette device. For this purpose the motion of a single (labeled) suspended particle is analyzed as the suspension, which fills the region between the two concentric cylinders, is sheared by rotating the outer cylinder. As the particle samples all radial coordinates as a result of its lateral self-diffusivity caused by collisions with other suspended particles, its azimuthal coordinate increases. For long times, a Taylor–Aris-type dispersion analysis shows that both the mean angular position 〈θ〉 and the mean square deviation 〈(θ−〈θ〉)2〉 of the labeled particle grow linearly in time. The two coefficients that govern these linear growths are the mean angular velocity Ω̄* and twice the mean angular dispersivity D̄*θ, which are calculated herein as functions of the cylinder radii, particle size, rotation speed, and the shear-induced diffusivity. Measurements of the latter of these, based upon the outlined long-time data, can thus be made more accurately than those previously possible on the basis of short-time analyses that neglected the presence of the walls of the Couette device and its curved geometry.
NMR imaging studies of stratified flows in a horizontal rotating cylinder
Authors: Jeong E.-K. , Altobelli S. A. , Fukushima Eiichi
Published: July 2002

NMR imaging was used to study the flow of pairs of density stratified, immiscible fluids in a horizontal, rotating cylinder. Mixtures of oil and water, oil and ethyl alcohol, and air and water were studied in the regime of slow rotation in which stratification was maintained. Two types of NMR experiments were performed. A NMR tagging method was used to visualize the flow fields, and a phase method was used to measure detailed, quantitative two-dimensional velocities far from the ends of the cylinder. The difference of the spin-lattice relaxation times of the liquids was exploited to discriminate between the fluids. Both NMR experiments showed that the flows were composed of boundary layers rotating with the cylinder, interfacial currents, and slowly counter-rotating internal regions.
The effect of three-dimensionality on a laminarizing boundary layer
Authors: Webster D. R. , Eaton J. K.
Published: July 2002

Measurements of highly accelerated turbulent boundary layers with and without mean cross-flow are presented and compared. The accelerated mean longitudinal velocity profiles suggest that the Reynolds shear stress, u′v′, is greater in the two-dimensional case than in the three-dimensional case. The measured normal longitudinal Reynolds stress, u′u′, is greater in the three-dimensional accelerated boundary layer case. The measurements indicate that the Reynolds stress tensor components decouple in the three-dimensional case; hence, the three-dimensionality alters the characteristic of nondecoupling observed in highly accelerated two-dimensional boundary layers.
The generation of edge waves by a wave-maker
Authors: Liu Philip L.-F. , Yeh Harry H.
Published: July 2002

A theory is developed to describe the generation of edge waves on a uniform beach by a wave-maker. The theory is based on the linear shallow-water equations. The wave-maker is a vertical plate spanning between the shoreline and the paddle axis offshore, and oscillates periodically in the alongshore direction. It is found theoretically that only propagating modes exist; the evanescent modes are always accompanied by incoming waves from offshore and are not permissible in this case. For each propagation mode the cross-shore variation is described by the Laguerre polynomial with an exponentially decaying amplitude. Laboratory experiments are performed and experimental data are compared with theoretical solutions. Since the viscous damping is ignored in the theory, the wave amplitudes for the experimental data are usually lower than the theoretical predictions. However, the cross-shore variations of the wave form are predicted well by the theory. Furthermore, from both theoretical and experimental data, it is shown that wave fields are dominated by the Stokes edge-wave mode in the low frequency range, f<0.5 Hz.
Experiments on capillary-gravity waves of solitary type on deep water
Authors: Longuet-Higgins Michael , Zhang Xin
Published: July 2002

It is shown that capillary-gravity waves of solitary type on deep water can be generated by the resonant excitation of a water surface at a speed close to the phase-speed of free waves. This speed depends upon the wave amplitude. When the source of excitation is removed, the waves are shown to propagate as free solitary waves, damped by viscosity.
Resonant–triad interaction in a wall jet
Authors: Likhachev Oleg
Published: July 2002

The subharmonic nonlinear route to transition in a wall jet with respect to the Craik resonant–triad instability is considered theoretically. The general technique based on linear stability theory, allowing one to reveal the resonant triads in a parametric space, was developed and successfully implemented for both the boundary layer and the wall jet. The analysis showed that only resonant interaction between inner instability modes occurring in the vicinity of the wall is prospective for an experimental observation. The detailed calculations were performed for the particular case of the resonant triad consisting of components which all become neutral at the same downstream location. At a sufficiently large initial amplitude of the two-dimensional (2D) Tollmien–Schlichting wave imposed on the basic flow, the rapid emergence of its 3D subharmonics occurs within a few wavelengths of the fundamental. It follows from the present results that a wall jet is very sensitive to the three-dimensional wavy perturbations propagating in a narrow band of wave angles around θ=58°.
Numerical study of generalized interfacial solitary waves
Authors: Michallet H. , Dias F.
Published: July 2002

In a two-fluid system where the lower fluid is bounded below by a rigid bottom and the upper fluid is bounded above by a free surface, two kinds of solitary waves can propagate along the interface and the free surface, classical solitary waves characterized by a solitary pulse or generalized solitary waves with in addition nondecaying oscillations in their tails. In this paper, we present numerical solutions of generalized solitary waves. Since generalized solitary waves cannot be obtained as the continuous limit of long waves, we in fact compute generalized long waves. The effects of capillarity are neglected. The solutions depend on four dimensionless parameters, the layer thickness ratio, the density ratio, the Froude number, and the dimensionless amplitude of the oscillations in the far field. If the amplitude of the oscillations is varied while the other three parameters are kept fixed, two limiting cases are conjectured. As the amplitude of the oscillations decreases towards zero, it reaches a minimum nonzero value, which is exponentially small. On the other hand, as the amplitude of the oscillations is increased, the generalized solitary wave eventually becomes a periodic wave. In other words, the oscillations in the far field grow as large as the solitary pulse.
Electromagnetic radiation from the photoelectron plasma induced by an arbitrary photon pulse incident on a planar emitting surface in vacuum
Authors: Dietz David
Published: July 2002

The electromagnetic radiation field produced by the cloud of accelerating electrons induced at a planar photoelectron emitting surface in vacuum by a photon pulse of an arbitrary time profile incident upon that surface is derived analytically in the nonrelativistic, small-spot-size regime, this derivation providing scaling relations for the radiated fields explicit in the pulse and surface parameters. Electron cloud dynamics is discussed and integral expressions for the electric and magnetic fields at large but finite (i.e., ‘‘finitely remote’’) distances from the cloud are derived. The fields are calculated by directly summing contributions over individual electron trajectories, using exact small-spot retarded times, rather than by the usual technique of first forming the electron charge and current densities and integrating them. The resulting integral representations of the finitely remote fields are correct to first order in v/c, and are valid for all time and for somewhat spatially extended charge clouds. These finitely remote fields are then used to compute asymptotic radiation fields in the limit of the field point going to infinity in a suitable fashion; from these, asymptotic radiation quantities in which all the integrations have been fully carried out are then derived. Illustrations of the general results for some sample pulses (constant, linear ramp, triangular, parabolic, and sin2) are provided.
Generalized electron fluid equations in the presence of laser irradiation
Authors: Epperlein E. M. , Short R. W.
Published: July 2002

Generalized fluid models have become increasingly popular for incorporating kinetic effects in hydrodynamic studies of laser–plasma interactions. However, their transport coefficients depend on the source of the thermal perturbation, which leads to difficulties, since both inverse-bremsstrahlung heating and pdV work drive these perturbations. Treating these sources separately using a model with two energy equations is proposed. Tested against electron Fokker–Planck simulations, this model reproduces both Landau damping of ion-sound waves and the correct response to inverse bremsstrahlung.
Pulsating mode in peniotron backward wave oscillations
Authors: Lin A. T. , Lin Chih-Chien
Published: July 2002

A sustainable pulsating mode in peniotron backward wave oscillations can be excited if parameters are properly chosen, such that at some instant of time the reduction in beam energy resulting from the electron–wave interaction is to such an extent that its cyclotron harmonic line intersects with the waveguide dispersion curve in the positive kz region. The generation of the forward traveling self-oscillating mode eliminates the residual backward traveling wave, which is very essential in establishing relaxation oscillation. As a result, the time evolution of the output wave becomes self-pulsating.
Method for computing the attenuation coefficient of electromagnetic waves in anisotropic plasma columns
Authors: Ghanashev I. , Zhelyazkov I.
Published: July 2002

A new and efficient method for calculating the attenuation coefficient of weakly damped electromagnetic waves traveling along wave-guiding structures partially or entirely filled by a lossy anisotropic dielectric, in particular cold axially magnetized plasma, is proposed. The structure cross-section geometry can be arbitrary and any nonradiating mode can be considered. In the case of plasma columns, they might be transversely inhomogeneous. Having obtained the attenuation coefficient, it is straightforward to find out the axial structure of plasma columns sustained by the waves themselves. The method is applied to azimuthally symmetric and dipolar waves in cylindrical plasma columns and it is found to reproduce all known theoretical results within its applicability.
Comment on ‘‘Nonlocal theory of a whistler pumped free electron laser’’ [Phys. Plasmas 1, 1025 (1994)]
Authors: Shoucri Magdi
Published: July 2002

In a recent paper [Phys. Plasmas 1, 1025 (1994)], the coupling of a whistler mode to a beam mode and a high-frequency electromagnetic mode was studied. It is the purpose of the present Comment to show that in that paper, the identification of a whistler mode in a waveguide (in the linear dispersion relation), as a transverse magnetic (TM) mode (Ez mode) is incorrect, and that the calculated relativistic beam contribution to the dispersion relation is also incorrect.
Bifurcated transition of radial transport in the HIEI tandem mirror
Authors: Sakai O. , Yasaka Y.
Published: July 2002

Transition to a high radial confinement mode in a mirror plasma is triggered by limiter biasing. Sheared plasma rotation is induced in the high confinement phase which is characterized by reduction of edge turbulence and a confinement enhancement factor of 2−4. Edge plasma parameters related to radial confinement show a hysteresis phenomenon as a function of bias voltage or bias current, leading to the fact that transition from low to high confinement mode occurs between the bifurcated states. A transition model based on azimuthal momentum balance is employed to clarify physics of the observed bifurcation.
The radiating regime of Lagrangian frame two-plasmon decay
Authors: Rappaport H. L. , Brodin G.
Published: July 2002

The two-plasmon decay instability in an abruptly bounded plasma, one for which all wavelengths are large compared with the plasma density gradient scale length, is investigated for p-polarized radiation in the absence of surface waves. Spatially dependent growth rate profiles and spatially dependent transit layer magnetic fields due to non-linear surface currents are reported. When the perturbation wave number parallel to the boundary is less than the pump frequency divided by twice the speed of light, energy radiates from the plasma boundary. It is proposed that these emissions may serve as an experimental signature for this mode.
On the existence of toroidal magnetohydrodynamic equilibria with poloidally closed magnetic field lines
Authors: Kaiser R. , Salat A. , Tataronis J. A.
Published: July 2002

The present work explores the existence of nonaxisymmetric toroidal magnetohydrodynamic equilibria when all lines of force of the magnetic field close after a single revolution about a given magnetic axis. It is assumed that the magnetic axis is a closed curve with arbitrary curvature and zero torsion, implying that it is constrained to lie in a plane surface. In addition, it is assumed that the closed magnetic field lines lie in planes that are orthogonal to the magnetic axis. Subject to these conditions, the existence of toroidal magnetic surfaces, F(r)=const, is explored. The governing equilibrium equations of magnetohydrodynamics place a constraint on the function F(r) in the form of two nonlinear partial differential equations that must be simultaneously satisfied. It is demonstrated that this is not always possible without axisymmetry. Two specific cases where toroidal magnetic surfaces do not exist are identified: (I) isodynamic configurations, which implies that the magnetic field strength is constant on each magnetic surface, and (II) configurations with ‘‘bumpy’’ surfaces, which implies that the size but not the geometrical shape of the poloidal section containing the closed field lines depends on s.
A hierarchy of empirical models of plasma profiles and transport
Authors: Imre Kaya , Riedel Kurt S. , Schunke Beatrix
Published: July 2002

Two families of statistical models of increasing statistical complexity are presented that generalize global confinement expressions to plasma profiles and local transport coefficients. The temperature or diffusivity is parameterized as a function of the normalized flux radius, ψ̄, and the engineering variables, u=(Ip,Bt,n̄,q95)°. The log-additive temperature model assumes that ln[T(ψ̄,u)] =f0(ψ̄)+fI(ψ̄)ln[Ip] +fB(ψ̄)ln[Bt] +fn(ψ̄)ln[n̄]+fq ln[q95]. The unknown fi(ψ̄) are estimated using smoothing splines. The Rice selection criterion is used to determine which terms in the log-linear model to include. A 43 profile Ohmic dataset from the Joint European Torus [P. H. Rebut, et al., Nucl. Fusion 25, 1011 (1985)] is analyzed and its shape dependencies are described. The best fit has a predictive error of 153 eV, which is 10.5% percent of the typical line average temperature. The average error is less than the estimated measurement error bars. The second class of models is log-additive diffusivity models, where ln[χ(ψ̄,u)]=g0(ψ̄) +gI(ψ̄)ln[Ip]+gB(ψ̄)ln[Bt]+gn (ψ̄)ln[n̄]. These log-additive diffusivity models are useful when the diffusivity varies smoothly with the plasma parameters. A penalized nonlinear regression technique is recommended to estimate the gi(ψ̄). The physics implications of the two classes of models, additive log-temperature models and additive log-diffusivity models, are different. The additive log-diffusivity models adjust the temperature profile shape as the radial distribution of sinks and sources. In contrast, the additive log-temperature model predicts that the temperature profile depends only on the global parameters and not on the radial heat deposition.
On the stability conditions of a stationary argon plasma at atmospheric pressure conditions
Authors: Gordillo-Vázquez F. J. , Cotrino J.
Published: July 2002

The stability of the general analytical solutions of a collisional-radiative model, for nonequilibrium, partially ionized, steady-state argon plasma, is examined. The model includes three atomic energy levels: the ground level, one excited level, and the continuum. A Maxwellian electron distribution function is also assumed. This model was previously considered by Braun and Kunc [Phys. Fluids 30, 671 (1987)]. All the rates for collisional-radiative processes and diffusion losses are expressed as analytical functions. The model is solved for the electron and excited atom densities in two plasma regimes, with and without diffusion losses. Transitions between these two possibilities are also discussed.
Thomson scattering measurements of ion-acoustic waves driven by ion-acoustic decay instabilities
Authors: Mizuno K. , Sleaford B. , Narihara K. , Drake R. P. , Estabrook K. , Villeneuve D. M.
Published: July 2002

A large angle, multichannel ultraviolet Thomson scattering diagnostic was developed to study ion-acoustic waves in laser-produced high-density plasma. The time evolution of the spectral density function of the ion-acoustic wave (IAW) was measured by the scattering system. When a weak IAW was excited, the measured spectrum had a well-defined narrow peak, which was consistent with plasma parameters predicted by computer simulations assuming an electron transport flux limit of 0.1. The spectrum of the IAW was quite different, and broad, when it was excited strongly.
Kinetic Alfvén mode and kinetic magnetosonic mode from a fluid description
Authors: Beach Glenn J. , Lau Y. Y.
Published: July 2002

The dispersion relations for the classical electromagnetic modes in a uniform, magnetized, monoenergetic plasma, are reconstructed from a fluid approach. Under study are the Alfvén waves (parallel propagation) and the magnetosonic waves (perpendicular propagation). This fluid theory accounts for finite Larmor radius effects to all order, and is shown to yield identical results from the Vlasov formulation.
Field enhancement due to anomalous skin effect inside a target
Authors: Ma Guo-bin , Tan Wei-han
Published: July 2002

A new method based on Fourier transformation to study the skin effects is presented. Using this method, the field amplitude in plasma is represented in terms of electric conductivity, and the normal and anomalous skin effects are described through one formula by omitting the plasma dispersion or not. The results are in agreement with other publications [e.g., J. P. Matte and K. Aguenaou, Phys. Rev. A 45, 2558 (1992)] for equivalent parameters. But for deeper positions inside a target, which have not been studied by others, it is found that the field amplitude is considerably enhanced due to an anomalous skin effect, even for constant collision frequency. In addition, the skin absorptions and some calculations on an anomalous skin effect for different collision frequencies are also presented.
Analytic solution for plasma dynamics in a small, pulsed bore
Authors: Sheridan T. E.
Published: July 2002

An analytic solution is found to the nonlinear, ordinary differential equation describing the decay of a plasma inside a small cylindrical bore following the application of a negative voltage pulse. The maximum values of the ion flux, velocity, and impact energy together with the average impact energy are calculated. The time-averaged ion energy distribution function is derived.
Classical electron-ion scattering in strongly magnetized plasmas. I. A generalized Coulomb logarithm
Authors: Geller David K. , Weisheit Jon C.
Published: July 2002

In a strongly magnetized plasma, where the electron cyclotron radius is less than the Debye length, the Rutherford scattering formula is expected to break down. In this paper, analytic expressions are developed for classical, small-angle scattering of electrons and ions in strong magnetic fields. Numerical evaluation of these expressions shows quantitatively how strong B fields can significantly inhibit electron deflections. The influence of the field on transport phenomena is then explored—in particular, a generalized Coulomb logarithm which includes the effects of a magnetic field is formulated and computed for a wide range of trajectory pitch angles. This generalized Coulomb logarithm is used to illustrate how a strong field influences the effective electron-ion cross section, the electron velocity diffusion coefficient, and the (parallel) electrical and thermal resistivity in a variety of astrophysical and terrestrial plasmas.
Ideal magnetohydrodynamic instabilities with low toroidal mode numbers localized near an internal transport barrier in high-βp mode plasmas in the Japan Atomic Energy Research Institute Tokamak-60 Upgrade
Authors: Takeji S. , Kamada Y. , Ozeki T. , Ishida S. , Takizuka T. , Neyatani Y. , Tokuda S.
Published: July 2002

Local steep pressure gradient generated near an internal transport barrier drives a radially localized magnetohydrodynamic (MHD) instability with low toroidal mode number (n) in the high-βp mode plasma in the Japan Atomic Energy Research Institute Tokamak-60 Upgrade (JT-60U) [Y. Koide et al., Phys. Plasmas 4, 1623 (1997)]. The instability occurs in the βp regime lower than that for the βp-collapse and its growth rate is of the order of the ideal MHD instability. By a linear analysis of ideal MHD stability, low n modes localized near the internal transport barrier are found to be destabilized in the situation that the bootstrap current driven by the steep pressure gradient reduces the local magnetic shear (s≲0) where the safety factor is right close to an integer value.
Pulsed sheath dynamics in a small cylindrical bore with an auxiliary electrode for plasma immersion ion implantation
Authors: Zeng X. C. , Liu A. G. , Kwok T. K. , Chu P. K. , Tang B. Y.
Published: July 2002

The temporal evolution of the plasma sheath in a small cylindrical bore with an auxiliary electrode is calculated for zero-rise-time voltage pulses. The ion density, flux, dose, ion energy distribu-tion, and electric field are determined by solving Poisson’s equation and the equations of ion motion and continuity using finite difference methods. Our results indicate that the implantation time is about halved and slightly more than 50% of the ions possess impact energy higher than the maximum achieved when an auxiliary electrode is absent. The resulting ion flux, ion current, as well as ion energy distribution, are also determined.
Self-similar implosions and explosions of radiatively cooling gaseous masses
Authors: Basko Mikhail , Murakami Masakatsu
Published: July 2002

A self-similar solution of the gas dynamics equations with heat conduction, which describes homologous contraction and expansion of gaseous masses with a free external boundary, is investigated in detail. As a primary application, implosion of deuterium–tritium (DT) fuel in inertial confinement fusion targets is considered. For strongly non-adiabatic implosions the self-similar solution predicts that the flow pattern should approach an asymptotical regime in which it ceases to depend on the initial entropy. For DT masses relevant to inertial confinement fusion (ICF) this regime begins to dominate at αUim≳6×108 cm/s, where α=p/pdeg is the fuel isentrope parameter, and Uim is its implosion velocity. The solution has also a branch which describes an asymptotical regime of explosive expansion after an ultra-fast initial heating to a strongly radiating state.
Comment on “A new mathematical approach for finding the solitary waves in dusty plasma” [Phys. Plasmas 5, 3918 (1998)]
Authors: Verheest Frank , Hereman Willy , Malfliet Willy
Published: July 2002

It is argued that in their recent paper Das and Sarma use a method derived by Malfliet without mentioning his work. Quite to the contrary, they claim to have developed the method themselves (some 5 years later) with their co-workers. Moreover, Das and Sarma use expansions without checking their validity and applicability, show little insight into the theory of integrable or nonintegrable evolution equations and claim to be among the pioneers in dusty plasma research whereas they came late to the field.
Generalization of a special class of time-dependent solutions of the two-dimensional magnetohydrodynamic equations to arbitrary pressure profiles
Authors: Neukirch Thomas , Priest E. R.
Published: July 2002

It is shown that a special class of time-dependent solutions of the ideal two-dimensional magnetohydrodynamic equations, which has been found for pressure profiles with exponential dependence on the flux function, can be generalized to pressure profiles with arbitrary dependence on the flux function. Particular properties of the solution class are vanishing plasma acceleration and an adiabatic index γ=1. It is also shown that the plasma temperature does not have to be uniform in space as assumed in the derivation for the exponential solution class, but that it can vary across field lines. This allows a much wider range of solutions than previously thought, because any numerical or analytical solution of the time-independent Grad–Shafranov equation can be transformed into a time-dependent solution of the magnetohydrodynamic equations.
Nonparabolic subband structure of Ga0.47In0.53As-InP quantum wells
Authors: Yamada Syoji , Taguchi Akihito , Sugimura Akira
Published: July 2002

Nonparabolic subband structure of GaInAs-InP quantum wells is studied theoretically. The dispersion relations for electron, light hole, and split-off hole subbands are obtained using the envelope function approximation taking into account band nonparabolicity. Reported experimental electron effective mass values and photoluminescence energies for wide quantum wells are resonably explained by the present theory. The experimental photoluminescence energies, for the well width less than 50 Å, differ significantly from the calculated results.
HgTe-CdTe superlattice band-gap enhancement due to interdiffusion
Authors: Schulman J. N. , Chang Yia-Chung
Published: July 2002

The effect of interdiffusion on the band gap of the HgTe-CdTe superlattice is calculated. Two simple models of the form of the interdiffusion are assumed: linear compositional grading, or shrinkage of HgTe layer widths due to Hg diffusion. A two-band model is used to solve for the electronic energy levels using parameters obtained from bulk data. Comparison with tentative experimental data implies that some effective shrinkage of the HgTe layers occurs.
Transmission electron microscopy study of periodic amorphous multilayers
Authors: Cheng Ruguang , Wen Shulin , Feng Jingwei , Fritzsche H.
Published: July 2002

Transmission electron micrographs of a multilayer film consisting of 360 alternating layers of plasma deposited hydrogenated amorphous silicon and silicon nitride show that each 28-Å-thick layer is remarkably flat and uniform. Within the first 1000 Å near the glass substrate the regular growth of the layers is disturbed by instabilities which resemble dislocations in the layering. Electron microscopy of compositional layering may prove to be an important tool for studying the growth mechanism during plasma deposition.
High-frequency elastic waves in random composites via the Kramers–Kronig relations
Authors: Brauner Neima , Beltzer Abraham I.
Published: July 2002

A theory is presented for determination of the high-frequency behavior of random composites, based on the Kramers–Kronig relations. The results show explicitly the radical influence of the type of inclusions on the strongly dynamic response of materials.
Ridge waveguide distributed feedback lasers with electron beam defined gratings
Authors: Temkin H. , Dolan G. J. , Logan R. A. , Kazarinov R. F. , Olsson N. A. , Henry C. H.
Published: July 2002

We describe a ridge waveguide distributed feedback laser operating at λ=1.5 μm. The ridge waveguide has been formed by liquid phase epitaxial overgrowth over a dielectric-defined narrow stripe. Second order diffraction gratings have been written using electron beam writing and transferred by reactive ion milling. cw threshold currents of these lasers vary from 80 to 150 mA and single mode operation over a temperature range of 60 °C has been demonstrated. Even under 1-GHz modulation the Bragg mode intensity is at least 3000 times greater than that of the residual Fabry–Perot modes.
Direct observation of an enhanced concentration of the principal deep level EL2 at single dislocations
Authors: Stirland D. J. , Brozel M. R. , Grant I.
Published: July 2002

Regions of low dislocation density (∼5×102 cm−2) in 2-mm-thick {001} wafers from indium doped, liquid encapsulated Czochralski grown, 2-in-diam. GaAs ingots have been examined by transmission infrared microscopy. Discrete dislocations were located and identified by their etching behavior in the calibrated A/B etchant. Comparison of identical regions before and after etching showed that increased absorption at 1 μm occurred at the sites of each dislocation. The results demonstrate directly that enhancement of [EL2], the concentration of the deep donor level EL2, occurs at single dislocations.
Single longitudinal mode operation of long, integrated passive cavity InGaAsP lasers
Authors: Matsuda K. , Fujita T. , Ohya J. , Ishino M. , Sato H. , Serizawa H. , Shibata J.
Published: July 2002

We propose a new 1.3-μm wavelength InGaAsP laser—the integrated passive cavity (IPC) laser—and demonstrate its device performances compared with conventional lasers fabricated under similar procedures. The long IPC laser (3.55-mm-long passive cavity), as well as the short IPC laser, exhibited single frequency oscillation even just above the threshold, and the maximum ratio of longitudinal main to submode exceeded 30 dB. They also showed favorable effects in the oscillation frequency stabilization.
3-pJ, 82-MHz optical logic gates in a room-temperature GaAs-AlGaAs multiple-quantum-well étalon
Authors: Jewell J. L. , Lee Y. H. , Warren M. , Gibbs H. M. , Peyghambarian N. , Gossard A. C. , Wiegmann W.
Published: July 2002

Various pulsed logic functions (nor, xor, etc.) are performed in a high-finesse nonlinear Fabry–Perot étalon containing GaAs-AlGaAs multiple quantum wells at room temperature. Input pulses with energies less than 3 pJ incident on the device produced contrasts greater than 5 : 1 in the nor gate, and relaxation times of about 5 ns allowed us to operate the gates at 82 MHz. Thermal stability was demonstrated in the nor gate even though the device was poorly heat sunk.
Stop-cleaved InGaAsP lasers for monolithic optoelectronic integration
Authors: Antreasyan A. , Chen C. Y. , Logan R. A.
Published: July 2002

We report a novel technique for locally cleaving the mirrors of semiconductor lasers without cleaving the entire substrate. The stop-cleaving technique involves the etching of holes on a substrate prior to the conventional cleaving procedure. The presence of the hole prevents the propagation of the cleavage plane along the entire substrate. The technique permits the fabrication of lasers with cleaved mirrors without imposing any limitation on the size of the substrate; thus, it is suitable for monolithic optoelectronic integration. InGaAsP lasers (λ=1.3 μm) with stop-cleaved mirrors have been fabricated and have threshold currents comparable to those with conventionally cleaved mirrors.
Fabrication and performance characteristics of InGaAsP multiquantum well double channel planar buried heterostructure lasers
Authors: Dutta N. K. , Napholtz S. G. , Yen R. , Brown R. L. , Shen T. M. , Olsson N. A. , Craft D. C.
Published: July 2002

We report the fabrication and performance characteristics of InGaAsP double channel planar buried heterostructure (DCPBH) lasers with multiquantum well active layers emitting at 1.3 μm. These lasers have threshold currents in the range 40–50 mA at 30 °C, external differential quantum efficiencies of ∼50% at 30 °C, and T0 values ∼160–180 K in the temperature range 10–60 °C. Under optical pumping the measured T0 are in the range 100–150 K. The lasers operate in a single transverse mode up to high powers (>10 mW/facet), can be modulated at ∼2 Gb/s, and exhibit less frequency chirping than similar lasers with conventional active layers. The observed high T0 and smaller chirp make DCPBH multiquantum well lasers potentially attractive for system applications.
Studies of orientation of carbon by core electron energy loss spectroscopy
Authors: Cheung T. T. P.
Published: July 2002

Orientation ordering of graphite layers on surfaces of carbon has been investigated using electron energy loss spectroscopy. The ordering is monitored by the orientation dependence of the line shape of the carbon K edge. The effects of ion sputtering on the orientation ordering are also examined.
New method of measuring relaxation times in semiconductors
Authors: Mukherjee P. , Sheik-Bahaei M. , Kwok H. S.
Published: July 2002

A new method of measuring relaxation times of free carriers in semiconductors is proposed and demonstrated. It is based on the pulse duration dependence of free-carrier absorption through the sample. This method has been demonstrated with GaAs and InSb.