bluuebunny/crossref_metadata_2025 huggingface dataset:
Energy transfer of lower-hybrid-drift waves by Compton scattering
Authors: Diamond P. H. , Myra J. R.
Published: March 2003

A renormalized, energy-conserving theory of low-frequency, finite-Larmor-radius turbulence is applied to the determination of the nonlinear electron response to the lower-hybrid-drift instability. The theory predicts a transfer of energy from short wavelengths to long wavelengths by Compton scattering. The resulting amplitude of short-wavelength fluctuations is estimated.
Resonant ion transport in the ELMO Bumpy Torus
Authors: Hastings D. E. , Jaeger E. F. , Hedrick C. L. , Tolliver J. S.
Published: March 2003

Modeling the ELMO Bumpy Torus as a bumpy cylinder with toroidally induced vertical drift, neoclassical transport coefficients are obtained for resonant ions as integrals over the energy-dependent flux. A continuous approximation to this energy-dependent flux reduces to the correct results in the banana and plateau regimes and yields simple analytic formulas for the diffusion coefficients which agree well with numerical results.
Oblique instream streamline intersections
Authors: O’Brien V.
Published: March 2003

A class of eccentric cylinder solutions negates the Moore–Rott–Sears conjecture at steady instream dividing streamlines.
Nonintrinsic ambipolar diffusion in turbulence theory
Authors: Berk H. L. , Molvig K.
Published: March 2003

Ambipolar flow in a turbulent plasma is investigated by combining a WKB treatment of the waves with a turbulent collision operator resulting from either quasilinear theory or certain renormalized turbulence theories. If the wave momentum has a flow from outgoing waves, then particle diffusion is not intrinsically ambipolar, and the time variation of the electric potential profile is determined by the turbulent spectrum. However, in most cases of practical interest, as in the drift-wave problem, this effect is small; and in steady state, equal rates of stochastic diffusion are predicted for electrons and ions.
Monte Carlo calculation of resonant diffusion coefficients in the ELMO Bumpy Torus and the applicability of local diffusion theory
Authors: Tolliver J. S. , Jaeger E. F. , Hastings D. E. , Hedrick C. L.
Published: March 2003

A Monte Carlo calculation of resonant diffusion coefficients in the ELMO bumpy torus (EBT) is described and is shown to agree well with analytic theory in a regime where the assumptions of local, diffusive behavior are valid. Since present and future EBT devices do not fall into this regime, local diffusion theory may not be entirely applicable.
Calculation of parallel viscosity in the plateau regime
Authors: Shaing K. C. , Callen J. D.
Published: March 2003

A direct calculation of the parallel viscosity 〈B⋅∇⋅πa〉 in the plateau regime for a large-aspect-ratio, axisymmetric tokamak is presented.
Eigenfunction analysis of the beam–plasma instability with finite radial dimensions
Authors: Jones Michael E.
Published: March 2003

A linear eigenfunction analysis of the beam–plasma instability for an annular beam interacting with a plasma filling the space between the conductors of a coaxial transmission line is presented. The beam and plasma electrons are modeled by relativistic cold fluids and the dispersion relation is three-dimensional and fully electromagnetic. Particular attention is given to the radial eigenfunction structure and extensive numerical examples are presented. The behavior of the dispersion relation with various parameters is interpreted in terms of the infinite homogeneous theory. Simple analytic approximations for the dispersion relation for annular beams are given. Also, particle-in-cell simulation results are compared with the predictions of the linear analysis.
Local WKB dispersion relation for the Vlasov–Maxwell equations
Authors: Berk H. L. , Dominguez R. R.
Published: March 2003

A formalism for analyzing systems of integral equations, based on the Wentzel–Kramers–Brillouin (WKB) approximation, is applied to the Vlasov–Maxwell integral equations in an arbitrary-β, spatially inhomogenous plasma model. It is shown that when treating frequencies comparable with and larger than the cyclotron frequency, relevant new terms must be accounted for to treat waves that depend upon local spatial gradients. For a specific model, the response for very short wavelength and high frequency is shown to reduce to the straight-line orbit approximation when the WKB rules are correctly followed.
Particle simulations of ion-cyclotron turbulence in a mirror plasma
Authors: Cohen Bruce I. , Smith Gary R. , Maron Neil , Nevins William McCay
Published: March 2003

Particle–fluid hybrid simulations of electrostatic ion-cyclotron instabilities in a mirror plasma have been extended to include axial ion bouncing in a nonuniform magnetic field. This model admits unstable ion-bounce modes as well as drift-cyclotron and drift-cyclotron-loss-cone modes. Linear theory showed that ion-bounce modes were as difficult to stabilize as drift-cyclotron-loss-cone modes, but the ion-bounce modes saturated at very low levels in simulations. Simulations have also followed the self-consistent interaction of a mirror plasma with turbulent electric fields in the presence of warm plasma stream, ion drag on electrons, injection of energetic neutral beams, and transit losses. Driven by velocity diffusion due to the drift-cyclotron-loss-cone instability, the plasma evolved to a stable configuration. The wave turbulence was moderated by streaming plasma and axial electron dissipation, was insensitive to the energy width of the neutral beam, and decayed when the neutral beam was removed. The simulation results confirmed many of the predictions of quasilinear theory and theories of orbital stochasticity, and were in qualitative agreement with many (but not all) of the observations in the Lawrence Livermore National Laboratory 2XIIB experiment.
Reduction of radial losses in bumpy tori
Authors: Catto P. J. , Hazeltine R. D.
Published: March 2003

Toroidal corrections to the fields in a bumpy torus cause the particle drift surfaces to depart from the magnetic flux surfaces, thereby resulting in transport and direct radial losses. Such losses can be reduced by choosing field structures such that the drift and flux surfaces remain close everywhere. A technique is presented for finding, analytically, such optimized fields in the near-axis, vacuum approximation.
An examination of hot-wire length corrections
Authors: Derksen R. W. , Azad R. S.
Published: March 2003

A comprehensive experimental examination is presented of the effect of hot-wire length for a single-wire probe. Specially constructed hot wires, with 2.5 μm and 5.0 μm nominal diameters and lengths from 0.3 mm to 2.8 mm, were used to measure the one-dimensional spectrum of the streamwise fluctuating velocity component u as well as the skewness and flatness of both u and du/dt. All measurements were made in air at Y+=150 (corresponding to Y/δ=0.1) in a boundary layer growing inside a pipe. The Reynolds number was 37 000 based on the velocity at the centerline and on the boundary-layer thickness. The longest wires exhibited some attenuation at the highest wavenumbers. This attenuation was found to roughly confirm the correction to the spectrum due to Wyngaard. A correction for the microscale λ, and thus dissipation, was examined and found to be correct to a fair degree (within 8%). This correction is based on the early work of Skramstad and of Frankiel, but with the integral scale of R11 (0, 0, r) assumed to equal the λ scale. The measurements of skewness and flatness did not indicate an experimentally discernible effect of the length of the hot wire.
Bandwidth effects in Brillouin scattering from inhomogeneous plasma
Authors: Mitchel G. R. , Johnston T. W. , Pépin H.
Published: March 2003

Convective Brillouin amplification in inhomogeneous, drifting plasmas is discussed. The bandwidth of the amplifier is a function of both wave damping and plasma inhomogeneity. For any given plasma model and source spectrum, the final amplified spectrum can be constructed, including the effects of inhomogeneity, drift, damping, and gain narrowing. Conversely, the shape of observed spectra of Brillouin scattering can be used to obtain information about conditions in the underdense plasma corona if it can be assumed that amplification is high enough that the final spectral bandwidth is amplifier dominated.
Self-consistent eigenvalue analysis of Rayleigh–Taylor instability in an ablating plasma
Authors: Takabe H. , Montierth L. , Morse R. L.
Published: March 2003

A mathematical method for a fully self-consistent treatment of the Rayleigh–Taylor instability is developed by solving the linearized fluid equations as an eigenvalue problem. The method is applied to analyze the instability in stationary ablating plasmas with strong inhomogeneity. A reduction of growth rate compared to the classical value is found. The importance of a self-consistent treatment of the Rayleigh–Taylor instability is shown by comparing the result with the growth rate estimated by approximate theoretical arguments.
Analysis of fast-ion velocity distributions in laser plasmas with a truncated Maxwellian velocity distribution of hot electrons
Authors: Kishimoto Yasuaki , Mima Kunioki , Watanabe Tsuguhiro , Nishikawa Kyoji
Published: March 2003

Fast-ion production in laser plasmas with a truncated Maxwellian velocity distribution of hot electrons is investigated by using a new numerical method, namely the systematic Newton’s iteration method which has been applied to nonlinear equations. The analysis of the temporal evolution of coronal plasma expansion discloses that the ion-front velocity approaches a constant value within thirty ion plasma oscillation periods, when the high-energy tail is truncated. In such a case, the maximum ion velocity is found to be proportional to the maximum energy of hot electrons. Consequently, the ion velocity distributions are steepened and truncated. Furthermore, it is found that the energy partition of the absorbed laser energy to fast ions is appreciably reduced when the maximum electron energy is below a few times the hot-electron temperature.
Diffusive separation of binary mixtures of CO2–H2 in a sonic-orifice expansion
Authors: McCay T. Dwayne , Price Linwood L.
Published: March 2003

The separation of binary gas mixtures of carbon dioxide and hydrogen in sonic-orifice-generated free jets is investigated over a source Reynolds number range of 100 to 3000 using the well-known electron beam fluorescence technique. The lighter species, hydrogen, is chosen as the minor species in order to examine the extent of the validity of Sherman’s first-order diffusive separation theory for large separation. The diffusive separation of mixtures containing approximately 2%, 5%, and 20% hydrogen in carbon dioxide is investigated by experimentally determining the relative number densities of the two species as a function of centerline axial distance within the free jets. Sherman’s diffusive separation theory is applied to the jets using axial Mach number profiles which were a combination of experimental and analytical results for γ=1.40 expansions. The γ=1.40 expansion is shown to approximate the CO2–H2 expansion quite well, and the calculated separation agrees remarkably well with the experimentally determined values.
Variational approach to the closure problem of turbulence theory
Authors: Qian J.
Published: March 2003

A new method is proposed to solve the closure problem of turbulence theory and to drive the Kolmogorov law in an Eulerian framework. Instead of using complex Fourier components of velocity field as modal parameters, a complete set of independent real parameters and dynamic equations are worked out to describe the dynamic states of a turbulence. Classical statistical mechanics is used to study the statistical behavior of the turbulence. An approximate stationary solution of the Liouville equation is obtained by a perturbation method based on a Langevin–Fokker–Planck (LFP) model. The dynamic damping coefficient η of the LFP model is treated as an optimum control parameter to minimize the error of the perturbation solution; this leads to a convergent integral equation for η to replace the divergent response equation of Kraichnan’s direct-interaction (DI) approximation, thereby solving the closure problem without appealing to a Lagrangian formulation. The Kolmogorov constant Ko is evaluated numerically, obtaining Ko=1.2, which is compatible with the experimental data given by Gibson and Schwartz.
The calculation of nonlinear short-crested gravity waves
Authors: Roberts A. J. , Schwartz L. W.
Published: March 2003

A numerical method involving truncated Fourier series is presented for the calculation of properties of short-crested water waves. The method produces accurate results over much of the nonlinear regime. In the case of infinite water depth, calculated results include a representative wave profile and the variation in frequency and energy densities with wave steepness and planform skewness.
Filamentation instability in magneto plasmas
Authors: Kuo S. P. , Schmidt G.
Published: March 2003

It is shown that the filamentation of ordinary-mode pumps propagating at an arbitrary angle with respect to the magnetic field has to be magnetic field-aligned, but not for extraordinary-mode pumps. A general dispersion relation is derived including the effects of magnetic field and collisions, and the nonlinear effects of ponderomotive force, thermal focusing force, and the beating currents. Threshold field and growth rates are obtained and compared to the results of the unmagnetized and collisionless case. Applications of these results to ionospheric modifications are discussed.
Energetics and the resistive tearing mode: Effects of Joule heating and radiation
Authors: Steinolfson R. S.
Published: March 2003

Hydromagnetic theory is used to investigate the influence of Joule heating and temperature–dependent radiation on the linear development of the incompressible, resistive tearing instability in both force-free and neutral-sheet magnetic fields in a slab geometry. A temperature-dependent resistivity couples the energetics and the dynamics of the instability. Analytical expressions are derived for the growth rates utilizing, in separate analyses, the constant-Ψ and the long-wavelength (nonconstant-Ψ) approximations. The solutions indicate the occurrence of several modes in addition to the usual tearing mode. A number of the modes have relatively slow, complex growth rates. However, at large values of the magnetic Reynolds number S (S≳107, the actual value depending on the relevant parametric values), there are at least two modes with purely exponential growth (real, positive growth rates) when the radiative loss decreases with increasing temperature. One is the resistive tearing mode, and the other is a more rapidly growing mode with a growth rate resembling that of a thermal instability. If the radiation is neglected, the Joule heating alone also results in two modes with real, positive growth at large S. One mode is again the tearing mode, but, in this case, the second mode is a more slowly growing Joule-heating mode. Another point of departure from previous theoretical results is that, below a particular value of S (S≲106, the value once again being determined by the parameters), all the modes are generally stabilized.
Centrifugal isotope separation in zirconium plasmas
Authors: Krishnan M.
Published: March 2003

Centrifugal isotopic enrichment in a zirconium vacuum arc centrifuge is described. Peak, single-pass enrichments up to 1700% for 96Zr2+, 330% for 94Zr2+, 280% for 92Zr2+, and 50% for 91Zr2+ were measured, for a discharge current of 3.7 kA and magnetic field strength of 0.17 T. Such high enrichments are compared with predictions of a simple, two-fluid centrifuge model.
Nonlinear periodic solutions for the isothermal magnetostatic atmosphere
Authors: Low B. C. , Hundhausen A. J. , Zweibel Ellen G.
Published: March 2003

A set of analytical, periodic magnetostatic solutions is presented describing parallel filaments of diffuse, magnetized plasma suspended horizontally in equilibrium in a uniform gravitational field. The magnetic field has no component along the filament, and the temperature is uniform in space. The problem is two dimensional and reduces to solving the magnetostatic equation of Dungey in a nonlinear form. Different field topologies are associated with the same basic plasma structure, depending on the sign and strength of the field far above and below the array of parallel filaments. These equilibria are shown to be locally unstable against ideal magnetohydrodynamic perturbations having large wavenumbers along the plasma filaments. It is suggested that the system may be stabilized if there is a component of the magnetic field parallel to the plasma filaments.
Erratum: ‘‘Turbulent spots, wave packets, and growth’’ [Phys. Fluids 2
6, 1160 (1983)]
Authors: Chambers F. W. , Thomas A. S. W.
Published: March 2003

Erratum
A measurement of the two-dimensional structure of the flow in a coaxial shock tube
Authors: Howard J. , James B. W. , Law A. R.
Published: March 2003

An optical (633 nm) Michelson interferometer in which the length of the reference arm is varied by means of a pair of rotating mirrors, has been used to measure the phase shift produced in the probing beam during the propagation of transverse magnetohydrodynamic and ionizing shock waves in a coaxial electromagnetic shock tube. The measurements, which achieve a phase resolution of about 0.1 rad with a time resolution of 70 nsec, have been obtained at three chordal positions and are inverted by Abel transform to give a coarse picture of the two-dimensional electron density distribution in the tube. This distribution shows marked radial nonuniformity, indicating that 2-D effects are of considerable importance in determining the dynamics and structure of the transverse shock waves produced in a coaxial geometry.
Determination of laser intensity and hot-electron temperature from fastest ion velocity measurement on laser-produced plasma
Authors: Tan T. H. , McCall G. H. , Williams A. H.
Published: March 2003

Measurements of the velocity of the fastest ion emitted by a CO2-laser-produced plasma were made, and it was found that the relationship between velocity and laser flux was given by Vi =5.7×106 φ1/6l for single-beam illumination. Comparison with computer simulation, ion velocity spectrum, and x-ray data indicate that the hot-electron temperature is given by Th =7.5×10−18 V2i. Measurements of emission from multiple-beam experiments and from experiments at 1.06 μm wavelength are also described. Some simple models are used for discussion and correlation of the data.
An experimental investigation of the quasisteady turbulent pulsating flow in a pipe
Authors: Shemer L. , Kit E.
Published: March 2003

Turbulent pulsating pipe flow is investigated at 3600<Re<9000 and a period of forcing 0.55 sec<T<5.5 sec. Velocities at the exit plane of the pipe and the pressure drop along the pipe are measured simultaneously and processed by a computer. The conditions of the quasisteady behavior of the flow are defined, and some conclusions regarding the details of the steady turbulent pipe flow are drawn from the nonsteady measurements.
Shock initiation of detonation in a dilute explosive
Authors: Fickett Wildon
Published: March 2003

The plane-shock initiation of detonation in the limiting case of small heat release is studied by a linear perturbation analysis, with a small parameter which is roughly the ratio of chemical to mechanical energy. The solution consists of three waves traveling at different velocities. One of these is a steady wave and two are transients. The wave shapes are simply related to the composition dependence of the reaction rate.
Steady Couette flow in a strong external field
Authors: Johnson E. A. , Stopford P. J.
Published: March 2003

Plane steady Couette flow at low Mach number is studied in the presence of an external force field. Force strengths may be so great that the gas is highly rarefied in one region of the flow but a continuum nearby. An approximate solution to the Boltzmann equation, of modified Liu–Lees type, is found to yield simple analytic expressions for flow velocity and shear stress. These predictions give correct results in both the continuum and rarefied limits, and show reasonable agreement with other more exact predictions in the limited regimes for which such predictions have been obtained. It is also shown that the predicted relation between flow and shear stress may be described by a simple generalized viscosity coefficient of the Cha–McCoy type which applies over the complete range of force strength and rarefaction.
Experimental and computational study of high-beta tokamak equilibria
Authors: Levinton F. M. , Grossman A. A. , Navratil G. A.
Published: March 2003

High-beta tokamak equilibria in Torus II are studied both experimentally and computationally. Electron temperature and density profile measurements from the multipoint Thomson scattering system and line-integrated density from a CO2 interferometer show that an equilibrium is obtained with a volume averaged beta of 10%. The peak electron temperature is 80 eV and the density is 1×1015 cm−3. A numerical computation of these equilibria is carried out using a 2-D, free-boundary, magnetohydrodynamic equilibrium code which is in good agreement with the experimental results.
Magnetohydrodynamics of laminar flow in slowly varying tubes in an axial magnetic field
Authors: McMichael J. M. , Deutsch S.
Published: March 2003

Laminar flow of a conducting fluid in round, straight tubes with axially varying radius, with a uniform magnetic field applied parallel to the tube axis, is treated theoretically as a regular perturbation problem at finite hydrodynamic Reynolds number, finite magnetic Reynolds number, and Hartmann numbers as large as O(α−1/2), where α is a small parameter characteristic of the slope of the tube wall. The first-order solution is examined numerically for local tube dilations and for local constrictions. Flow separation along both converging and diverging sections of the tube is discussed. Pressure, current density, and induced magnetic field distributions are also presented.
A uniform integral representation for geometric optics solutions near caustics
Authors: Hazak G. , Friedland L. , Bernstein Ira B.
Published: March 2003

Generalized Fourier integral (GFI) representation of geometric optics solutions for the field of dressed particles in inhomogeneous plasmas is applied to the problem of wave propagation near caustics: GFI is based on the replacement of plane waves, conventionally used in Fourier integrals for homogeneous plasmas, by a complete orthogonal set of ‘‘quasiplane’’ waves for the case of an inhomogeneous plasma. It is shown that the resulting integral provides a uniform asymptotic approximation to the exact solution of the wave equation.
Transport associated with the collisionless detrapping/retrapping orbits in a nonaxisymmetric torus
Authors: Shaing K. C. , Rome J. A. , Fowler R. H.
Published: March 2003

The differences among the various scalings in the transport calculations associated with the collisionless detrapping/retrapping orbits in a nonaxisymmetric torus are clarified. A simple random walk argument indicates that these differences are mainly due to an implicit assumption made about the retrapping rate of the toroidally trapped particles.
Axial particle density gradient in direct-current discharges
Authors: Ingold J. H. , Oskam H. J.
Published: March 2003

Particle density gradients in the positive column of a dc discharge have been reported previously. An increase of the density at the cathode end of the discharge tube is due to the neutralization of ions at the cathode (cataphoresis), while a density increase at the anode end is caused by an imbalance of the momenta transferred by the electrons and ions to the neutral particles (electrophoresis). A general transport theory is presented which incorporates both effects. An approximate analytical solution shows that for a monoatomic gas, cataphoresis dominates electrophoresis when the ion mean free path for momentum transfer exceeds 2R/3 (R is tube radius). Numerical results are given for helium over a wide range of gas pressure.
Cross-field free electron laser instability for a tenuous electron beam
Authors: Davidson Ronald C. , McMullin Wayne A. , Tsang Kang
Published: March 2003

The free electron laser instability is investigated for a tenuous circulating electron beam propagating perpendicular to a uniform magnetic field B0êz and transverse wiggler field modeled by Bw  sin k0yêx in planar geometry. Unlike the rippled-field magnetron which operates at Brillouin flow, the present analysis assumes a low-density electron beam with ω2p ≪Ω2c. Making use of a macroscopic cold-fluid model for the electrons coupled with Maxwell’s equations for the fields, it is found that wave perturbations with ordinary-mode polarization (δE∥B0 and δB⊥B0) amplify with characteristic maximum growth rate Im(δω)=ωp (Ωw/2ck0) and emission frequency ωr =(1+βE)γ2Ek0VE. Here, Ωw =eBw/γEmc, βE =VE/C, γE =(1−β2E)−1/2, and VE =−cE0/B0, where E0 is the applied electric field across the anode–cathode gap. Depending on the size of Ωw/ck0, the characteristic exponentiation time ω−1p(Ωw/2ck0)−1 for the cross-field free electron laser instability can be relatively short in units of ω−1p.
Experimental observation of cavitons and rarefaction waves in laser-produced plasma
Authors: Briand J. , El Tamer M. , Adrian V. , Gomes A. , Quemener Y. , Kieffer J. C. , Dinguirard J. P.
Published: March 2003

A Wollaston’s prism interferometer and a 632.9 nm probe beam having a 10 psec (FWHM) pulse are used to detect the electron density profile instabilities in a 1.06 μm laser-produced plasma. Experimental observations of cavitons and rarefaction waves are presented and discussed for a laser irradiance of 1015 W/cm2.
Wave enhancement due to a static electric field
Authors: Tsunoda S. I. , Malmberg J. H.
Published: March 2003

The effect of an applied static electric field on beam electrons trapped by the wave in a traveling wave tube has been investigated experimentally. For sufficiently weak applied fields the wave power is enhanced. When the applied field is sufficiently strong the beam electrons are detrapped, and the wave power enhancement is destroyed. It is found that the beam space charge plays an important role in the detrapping process and acts to limit the wave power enhancement. In addition it is found that the wave power enhancement can be increased by increasing the rf input drive level. By launching waves near the saturation level, over 10 dB of wave power enhancement has been observed. These effects are predicted in a computer simulation, and there is good agreement between the results of the simulation and the experimental results.
Dynamical equations for the reversed field pinch
Authors: Strauss H.
Published: March 2003

Reduced magnetohydrodynamic (MHD) equations are derived for small amplitude fluctuations in reversed field pinches. Numerical solutions exhibit a dynamo effect with self-reversal of the magnetic field.
Quasi-one-dimensional nozzle flows of disparate mixtures
Authors: Mitra N. K. , Fiebig M. , Schwan W.
Published: March 2003

Quasi-one-dimensional inviscid flows of helium-argon mixtures are computed from a two-fluid flow model in a convergent divergent nozzle. Results show not only velocity and temperature slip but also critical mass flow rates larger than those predicted by isentropic one-dimensional flow.
Constant density acceleration of laser targets
Authors: Ahlborn B. , Kwan J. , Ng A. , Barnard A. J.
Published: March 2003

An analytical model is given to determine a stepped laser pulse that accelerates a target by a sequence of weak shocks and expansion waves so that the density loss in one expansion is recovered approximately in the succeeding shock wave. With ten steps and a maximum laser intensity of 8×1014 W/cm2, an Al target will be accelerated to about 2×107 cm/sec. Gaussian pulses are a fair approximation for the first few steps.
Reply to the comments by R. Jones
Authors: Matthieussent G.
Published: March 2003

A reply to the comments by R. Jones is made.
Numerical solutions for cavitating flow of a fluid with surface tension past a curved obstacle
Authors: Vanden-Broeck Jean-Marc
Published: March 2003

The problem of cavitating flow past a two-dimensional curved obstacle is considered. Surface tension is included in the dynamic boundary condition. The problem is solved numerically by series truncation. Explicit solutions are presented for the flow past a circle. It is shown that for each value of the surface tension different from zero, there exists a unique solution which leaves the obstacle tangentially. As the surface tension approaches zero, this solution tends to the classical solution satisfying the Brillouin–Villat condition. Vanden-Broeck considered the effect of surface tension on the cavitating flow past a flat plate and on the shape of a jet emerging from a reservoir. His results indicate that the velocity is infinite at the separation points. It is shown that these unbounded values of the velocity are removed when the thickness and finite curvature of the ends of the plate and of the ends of the walls of the reservoir are taken into account.
Heat transfer by high-frequency oscillations: A new hydrodynamic technique for achieving large effective thermal conductivities
Authors: Kurzweg U. H. , Zhao Ling de
Published: March 2003

Heat transfer between two fluid reservoirs maintained at different temperatures and connected to each other via a capillary bundle is examined when the fluid within the capillaries is oscillated axially. Very large effective axial heat conduction rates, exceeding those possible with heat pipes by several orders of magnitude, are found to be achievable. A laminar hydrodynamic theory is developed to describe the phenomenon and to show that the enhanced heat conduction is one involving radial heat transfer across very thin Stokes’s boundary layers existing in these flows. Experimental measurements using water as the working fluid show effective thermal diffusivities up to 17 900 times those existing in the absence of oscillations. Since the process involves no net convective mass transport, it offers considerable promise as a means for the rapid removal of heat from radioactive fluids.
Resistive fluid turbulence and energy confinement
Authors: Connor J. W. , Taylor J. B.
Published: March 2003

The invariance properties of the underlying equations under scale transformations provide information about plasma transport. By applying this argument to specific models, in which the magnetic configuration and the physical mechanism of transport are identified, this information can be sufficient to completely determine the transport coefficients in a turbulent plasma. In this way the electron energy transport due to resistive fluid turbulence is examined in tokamak and reversed field pinch configuration. The resulting confinement times have interesting implications for the performance of the two systems.
Stabilization of an axisymmetric tandem mirror cell by a hot plasma component
Authors: Berk H. L. , Rosenbluth M. N. , Wong H. Vernon , Antonsen Thomas M.
Published: March 2003

A hot plasma component formalism is used for a symmetric tandem mirror cell to relate the precessional mode, well known from Astron experiments, to more standard magnetohydrodynamic (MHD) modes. The l=1 mode can be stabilized by conducting walls, while the higher l modes can be stabilized by finite Larmor radius. Such a configuration is free of remnant dissipative instabilities because all perturbations are positive energy excitations when stability is achieved. OFF
Nonlinear slowly varying standing waves on deep water
Authors: Roskes G. J.
Published: March 2003

The existence of nonlinear, slowly varying standing waves on deep water is discussed from the point of view of weakly nonlinear slowly varying multiphase interactions.
Electrostatic structure of the rotational discontinuity II: Shock pair solutions
Authors: Wang Dong-Jian , Sonnerup B. U. Ö.
Published: March 2003

The structure of one-dimensional rotational discontinuities in a collision-free plasma is analyzed. The plasma consists of cold streaming ions, isothermal streaming electrons, and electrostatically trapped warm electrons or ions. Allowances for large deviations from charge neutrality are made. By properly adjusting the trapped particle population, the rotational discontinuity can acquire a width comparable to or greater than the ion inertial length. Its structure then consists of an approximately charge neutral region of helical magnetic field sandwiched between a reversible electrostatic shock pair in which large deviations from charge neutrality occur. The discontinuity has left-hand (ion) polarization for positive potentials, φ>0, and right-hand (electron) polarization for φ<0. The magnetic field magnitude is constant throughout the discontinuity and the plasma state is identical on its two sides.
Laser-Doppler measurements of bubble dynamics
Authors: Brankovic A. , Currie I.G. , Martin W.W.
Published: March 2003

Laser-Doppler anemometry is applied to study the dynamics of small-diameter carbon dioxide and air bubbles rising in a quiescent liquid. Primary data include bubble velocity and diameter as functions of position above a generating nozzle. Direct observation of decreasing bubble diameter provides instantaneous mass transfer results for carbon dioxide bubbles, presented in terms of Sherwood versus Reynolds and Peclet numbers. The range of velocity measured is 1.0 to 35.0 cm/sec, and the range of diameter measured is 0.07 to 1.20 mm, corresponding to a Reynolds number range from less than unity to over 500. Bubble oscillations, observed through direct diameter measurements, are recorded for bubbles with initial diameter greater than 0.80 mm. Fourier transforms of the instantaneous diameter profiles result in a frequency of oscillation of about 10 Hz for most test runs. Drag studies indicate that bubbles with Reynolds number greater than 40 follow correlations developed for fluid spheres with attached boundary layers and wakes. Transition from solid-sphere to fluid-sphere drag behavior is observed for increasing Reynolds number in the range 10 to 40.
Reduction of turbulent skin friction by microbubbles
Authors: Madavan N. K. , Deutsch S. , Merkle C. L.
Published: March 2003

Measurements of the effect of microbubbles on a zero pressure gradient turbulent boundary layer generated on the test section wall of a water tunnel are described. Microbubbles are created by injecting air through a 0.5 μm sintered stainless steel plate immediately upstream of a floating element drag balance. At the downstream edge of the balance the length Reynolds number is as high as ten million. Integrated skin friction reduction of greater than 80% is observed. The drag balance results are confirmed by measurements with a surface hot-film probe. For the case in which buoyancy tends to keep the bubbles in the boundary layer, the skin friction data are shown to collapse when plotted against the ratio of air to water volume flow rate. The effects of buoyancy on skin friction reduction are also documented.
Radio frequency stabilization of electrostatic interchange modes
Authors: McBride John B.
Published: March 2003

It is shown theoretically that long-wavelength, rf fields in the ion cyclotron frequency range can stabilize low-frequency, electrostatic interchange modes. Stabilization does not require specified gradients in the spatial distribution of rf energy. This offers an appealing alternative to ponderomotive stabilization of curvature driven modes, and may help explain recent observations on the Phaedrus tandem mirror experiment.
Intense solitary laser pulse propagation in a plasma
Authors: Shukla P. K. , Yu M. Y. , Tsintsadze N. L.
Published: March 2003

Previous work [Yu, Shukla, and Tsintsadze, Phys. Fluids 25, 1049 (1982)] on intense laser pulse propagation in plasmas is generalized to include nonlinear ion motion which can be of importance in the slow plasma response.
Perpendicular distribution of electrostatic electron cyclotron radiation under low-density plasma conditions
Authors: Lembège B.
Published: March 2003

The electrostatic potential distribution Φ of a point source antenna is studied numerically within the range 1<Ω<2 under low-density plasma conditions, i.e., where Ωp <2; Ω and Ωp are, respectively, the monochromatic frequency of the source and the plasma frequency normalized to the electron gyrofrequency. The whole study is performed for the direction of radiation R⊥ perpendicular to the magnetostatic field B0. Two electrostatic modes, respectively, the cyclotron harmonic mode h and the main mode m, are shown to contribute essentially to the total potential Φ so that Φ=Φh+Φm. The results obtained within the range 1<Ω<Ωp are similar to those under dense plasma conditions [B. Lembège, Phys. Fluids 26, 1780 (1983)]; in particular only the mode h has a low damped part in its dispersion curve and mainly governs the behavior of the total potential Φ. However, both modes have a low damped part in their respective dispersion curves for Ωp<Ω<Ωuh; Ωuh is the upper hybrid frequency normalized to the electron gyrofrequency. As a consequence, the amplitude of ‖Φ‖ exhibits a complicated pattern which varies according to the value of R⊥. Additionally, it appears that both modes are continuously defined within the propagation plane, when Ω passes through the frequency Ωuh. Within the range Ωuh<Ω<2 the amplitude of the total potential has a no-null finite value (the opposite of what would be expected). A more general discussion is presented concerning the behavior of ‖Φ‖ when Ωp varies.
Drift-ideal magnetohydrodynamics
Authors: Hassam A. B. , Lee Y. C.
Published: March 2003

The ideal magnetohydrodynamic equations are extended to include the frequency range ω≲ωd and ωci≲ω, where ω is the frequency of interest, ωd denotes any equilibrium drift frequency, and ωci is the ion cyclotron frequency. Such a frequency range is of interest in stability considerations for the ELMO Bumpy Torus and the tandem mirror fusion devices. Relative simplicity is attained by restricting the domain of validity of the equations to the collisional limit and the cold ion limit. The resulting equations are linearized and a normal mode analysis is performed to obtain the flute-like modes of the system. Application is made to the straight field line case and to a z pinch with no axial field. In the high-frequency limit (ωd≪ω), the usual ideal magnetohydrodynamic modes are recovered. In the low-frequency limit (ω≪ωd), an interchange-type instability is identified in the z-pinch case.
Production of hot electrons by two-plasmon decay instability in uv laser plasmas
Authors: Villeneuve D. M. , Keck R. L. , Afeyan B. B. , Seka W. , Williams E. A.
Published: March 2003

Hot electron emission from a uv laser produced plasma with incident intensities 8×1013–2×1015 W/cm2 was measured by means of an electron spectrometer. Because of the small hot electron population, the self-consistent target potential due to escaped electrons may be considered for the first time in the data reduction. The total energy in hot electrons of temperature 50 keV is shown to be ≲10−3 of the incident laser energy. The target potential ≲80 kV. The hot electron temperature is essentially independent of intensity, the angular distribution of electron emission shows a weak polarization asymmetry, and the intensity threshold of hot electron production is 5×1013 W/cm2, all consistent with the two-plasmon decay instability being responsible for heating the electrons. The predicted spectrum of plasma waves is such that the accelerated electrons should be directed into the plasma almost parallel to the laser axis. Because only a small fraction of these electrons are reflected backwards to the detector, the x-ray yield is a factor of 20 higher than the escaped electrons would indicate.
Resonant triads and direct resonance for Kelvin–Helmholtz waves
Authors: Ma Yan-Chow
Published: March 2003

It is shown that resonant triads exist for Kelvin–Helmholtz waves. The loci of various triad modes in wavenumber space are discussed in detail. In most cases of interest one of the three triad modes lies very close to the Kelvin–Helmholtz cutoff wavenumber and hence direct resonance occurs. Evolution equations are first derived in wavenumber space and then transformed into physical space. Interactions among various triad modes occur on a much faster time scale and the amplitudes of various modes are much larger than the amplitudes for a regular triad. The stability of a plane wavetrain subject to perturbations from resonant triad modes is examined.
Gas motion in front of a completely absorbing wall
Authors: Bergstro/m T. , Ytrehus T.
Published: March 2003

The one-dimensional motion of a gas due to a completely absorbing boundary is examined by means of a four-moment solution of the nonlinear Boltzmann equation. Definite nonzero values for the density, temperature, and the pressure in the gas at the boundary are computed, and a distinct structure of an expanding Knudsen layer flow is revealed. The gas velocity towards the boundary is found to be weakly supersonic.
The collapse of minute gas bubbles in a dilute polymer solution
Authors: Shima A. , Tomita Y. , Ohno T.
Published: March 2003

Collapse times of minute gas bubbles in both water and a dilute polymer solution were measured precisely by means of the streak schlieren method. It was found that when the bubble becomes smaller in size, the collapse time in a polymer solution is shortened in comparsion with it in water due to the relaxation effect.
Distortion of turbulence approaching a plate held normal to the flow
Authors: Huot J. P. , Rey C. , Arbey H.
Published: March 2003

An experimental study of the characteristics of the turbulent field upstream of a flat plate placed normal to the mean flow was performed when the integral scale of turbulence is small with respect to the characteristic dimension of the obstacle. Measurements of the turbulence intensities u′1 and u2, the spectrum E11( f̃) taken at different distances from the plate, and the pressure spectrum θpp( f̃) measured at the stagnation point are given in the framework of a comparison with Hunt’s theory.
Improved derivation of shear stabilization of the universal mode in slab geometry using asymptotic techniques
Authors: Briguglio S. , Romanelli F.
Published: March 2003

The problem of the stability of the universal mode in a sheared magnetic field is considered using the method of matched asymptotic expansions, which, among the analytical approaches, can perhaps provide the clearest physical insight. An eigenvalue equation is derived predicting marginal stability in the limit in which previous papers using the same technique find instability. The discrepancy is explained by showing that the analysis used therein is applicable only in the stability regime.
Ballooning and interchange stability of an ion ring confined plasma
Authors: Sparks L. , Sudan R. N.
Published: March 2003

High toroidal mode number, magnetohydrodynamic perturbations of a plasma confined in an axisymmetric field-reversed geometry with no toroidal field can be stabilized by the presence of a ring of energetic, large-orbit ions. Analytical and numerical studies reveal that high-β plasma stability against ballooning and interchange modes improves as the ring current profile becomes more peaked. The equations of motion for incompressible mode perturbations in the vicinity of the vortex point are solved analytically to obtain the ballooning stability condition F>(1+‖ε‖)/2, where F is the fraction of the current density carried by the ring ions and ε is the flux surface ellipticity. Higher-order corrections to the eigenfrequencies due to compressional effects are obtained in the limit of circular flux surfaces. Modeling the ring as an exponential rigid rotor, an iterative procedure is used to obtain optimal values of Ep/ Eb, the ratio of the total energy of the confined plasma to the total ring energy. Magnetohydrodynamically stable equilibria are found with Ep /Eb ≲2.
Electron cyclotron heating in rf current-driven tokamak plasmas
Authors: Fidone I. , Giruzzi G. , Granata G. , Meyer R. L.
Published: March 2003

Wave absorption near the electron cyclotron gyrofrequency by the current-carrying energetic tail in tokamak plasmas is investigated. It is shown that by the proper choice of the angle of propagation, strong wave damping occurs for wave frequencies much less than the central electron cyclotron frequency and that the extraordinary mode can be launched from the low magnetic field side of the torus. It is also found that wave absorption is weakly dependent on the perpendicular temperature of the resonant particles.
Elimination of stochasticity in stellarators
Authors: Hanson James D. , Cary John R.
Published: March 2003

A method for optimizing stellarator vacuum magnetic fields is introduced. Application of this method shows that the stochasticity of vacuum magnetic fields can be made negligible by proper choice of the coil configuration. This optimization is shown to increase the equilibrium β limit by factors of two or more over that of the simple, ‘‘straight’’ coil winding law. This method is general and ought to be applicable to other systems in which stochasticity (1) presents a problem, yet (2) is affected by the design parameters.
Simulation studies on line-tying stabilization of spheromak tilting instability
Authors: Hayashi Takaya , Sato Tetsuya
Published: March 2003

The stabilization mechanism of the spheromak tilting instability is investigated by means of a 3D magnetohydrodynamic simulation. Evidence that line-tying can completely suppress a tilting instability is observed. It is also found that the stabilization effect of an induction current induced on a conducting wall is weaker than the line-tying effect.
Wave excitation and fast ion generation in a double plasma device
Authors: Honzawa Tadao
Published: March 2003

Wave excitation and fast ion generation in a double plasma device are studied experimentally. Results show how a compressive density perturbation, propagating as a wave, is formed in the target plasma when a positive potential pulse is externally applied. Further, it is shown that fast ions are generated in a narrow plasma region close to the sheath near the grid because of reflection by the wave front during propagation of the wave.
Neutrally buoyant anisotropic particles for flow visualization
Authors: Matisse P. , Gorman M.
Published: March 2003

Anisotropic flakes dispersed in certain liquids are shown to remain suspended for periods of the order of months. Such particles represent an ideal flow visualization technique, especially for thermally driven flows such as Rayleigh–Bénard convection.
Measurements of vertical overturns in a stably stratified turbulent flow
Authors: Itsweire Eric C.
Published: March 2003

The vertical overturns occurring behind a biplane grid placed in a continuously stratified water channel were measured with a high-speed vertical density profiler. The resulting scale (LT)rms, known as the Thorpe scale is compared to the Ozmidov scale LR=(ε/N3)1/2 and the Eulerian turbulent scale l=2ρ′/(dρ̄/dz). For buoyancy-dominated or stratified turbulence, l and (LT)rms are linearly related, but when all turbulent overturning events have ceased, (LT)rms is shown to decay at a faster rate. Vertical displacements larger than the Ozmidov scale are observed implying that some previously turbulent scales have become fossil turbulence.