bluuebunny/crossref_metadata_2025 huggingface dataset:
Initial condition dependence of the statistical properties of Burgers’ turbulence
Authors: Mizushima Jiro , Segami Akihide
Published: March 2003

Initial condition dependence of the statistical properties, especially the energy decay law, of Burgers’ turbulence is investigated using the modified zero-fourth cumulant approximation. It is shown that the power index of the energy decay varies from −0.67 to 1.2 on the initial conditions.
High-energy tail formation by a monochromatic wave in the magnetized plasma
Authors: Abe Hirotada , Momota Hiromu , Itatani Ryohei , Fukuyama Atsushi
Published: March 2003

High-energy tail formations due to the monochromatic wave in a magnetized plasma are studied numerically and analytically. By calculating the phase space trajectories of 10 000 particles, initially Maxwell-velocity-distributed, in the presence of a uniform magnetic field and a sinusoidal wave traveling closely in the perpendicular direction with the frequency of cyclotron harmonics, some properties of particle acceleration are clarified. The acceleration mechanism can be described by a modification of trapping theory and two types of stochastic acceleration. The behavior of the high-energy tail formation depends on the magnitude of ω/Ω. For small ω/Ω (ω/Ω≲10), the cyclotron harmonics resonance is very important. The ratio of the perpendicular wavelength to the average Larmor radius and the wave amplitude play an important role in determining the ratio of tail to the bulk portion.
The unsteady flux of heat and momentum from a flat plate
Authors: Lueck Rolf G.
Published: March 2003

The unsteady viscous fluid stress on a flat plate was computed numerically from a simplified unsteady momentum equation which is not restricted by a frequency parameter and compares favorably with the available (frequency restricted) calculations. The unsteady heat flux from the same plate is examined for three boundary conditions: (a) free-stream speed oscillations with a constant surface and free-stream temperature, (b) free-stream temperature oscillations with a constant surface temperature and constant free-stream speed, and (c) uniform surface temperature oscillations with a constant free-stream speed and temperature. The heat flux in response to speed oscillations has a maximum value at low frequencies and a larger bandwidth than the response to free-stream temperature oscillations. When the boundary layer is unsteady, the response of the heat flux to surface temperature oscillations is not comparable to either the response to speed oscillations or the response to free-stream temperature oscillations. The results have implications for the interpretation and calibration of constant temperature anemometer and constant temperature thermometer output signals in regions with small amplitude temperature and streamwise velocity fluctuations.
Boundary conditions for thin lubrication layers
Authors: Joseph Daniel D.
Published: March 2003

In certain circumstances, the effects of a thin lubrication layer may be accommodated by a slip flow boundary condition with the gradient of the tangential component of the velocity at the wall proportional to the square of the tangential component there.
Particle acceleration by an intense solitary electromagnetic pulse
Authors: Lai H. M.
Published: March 2003

A stationary charge, while left stationary after the passage of an intense electromagnetic pulse containing many waves, can be efficiently accelerated by a solitary pulse. Its relevance to the acceleration of particles in a magnetically insulated vacuum power transmission line is discussed.
Integral equation analysis of drift wave eigenmodes in a sheared slab geometry
Authors: Tang W. M. , Rewoldt G. , Frieman E. A.
Published: March 2003

The derivation of the appropriate form for the integral eigenmode equation governing both electron and ion drift waves of arbitrary radial wavelengths in a sheared slab is presented. The solutions to this equation provide useful information regarding the absolute stability of universal modes and ion-temperature-gradient driven modes for arbitrary wavelengths, and particularly for short wavelengths.
Nonlinear effects on the mode conversion of upper-hybrid waves
Authors: Shoucri Merit , Kuehl H. H.
Published: March 2003

A simple model is presented which is capable of describing the nonlinear field across the upper-hybrid resonance layer, its time evolution and mode conversion. In the electrostatic approximation, when the density gradient scale length is small compared with the incident wave wavelength, the fields are governed by a driven nonlinear Schrödinger equation. It is found that the nonlinearity due to the ponderomotive force produces an enhancement and a spreading of the Bernstein wave accompanied by a flattening of the density profile. Mode conversion efficiencies as high as 200% of those of the linear regime are reached. The model shows the importance of nonlinearity in the analysis of mode conversion in ionospheric and laboratory, as well as fusion plasmas.
Effect of a dc electric field on the trapping dynamics of a cold electron beam
Authors: Morales G. J.
Published: March 2003

The self-consistent modification of the trapping dynamics of a low density cold electron beam due to the external application of a dc electric field is considered. For dc fields smaller than the peak amplitude of the saturated beam-plasma instability, the beam energy remains clamped while the wave amplitude grows secularly. Large traveling potential wells appear and create strongly focused charge clumps. By considering the role of wave dissipation, an exact dynamic Bernstein–Greene–Kruskal equilibrium is found analytically. It consists of a singular charge clump which propagates through the medium at constant velocity even though a dc field is present. The numerical study of the basic equations shows that the system evolves asymptotically to this singular state. A variety of experimentally relevant properties associated with the trapping dynamics is investigated, including the stability of the dynamic nonlinear equilibrium to sideband growth.
Fluid theory of tearing instabilities
Authors: Hassam A. B.
Published: March 2003

A fluid theory of tearing instabilities is presented. Recently derived fluid equations, which have the feature of describing adiabatic electron dynamics more completely than the usual transport equations, are employed for this theory. The temperature gradient driven self-filamentation of a plasma in a uniform magnetic field is described. Temperature gradient driven and magnetically driven ’’collisional’’ and ’’semicollisional’’ drift-tearing modes are also derived. A comparison with kinetic theories is made; the comparison suggests that the neglect of electron-electron collisions in kinetic theories of tearing may lead to an overestimate, of appreciable magnitude, of the relative importance of the temperature gradient free energy in driving tearing modes.
Solitary plasma hole via ion-vortex distribution
Authors: Schamel H. , Bujarbarua S.
Published: March 2003

The first analytical solution of the trapped ion-vortex state known since the early days of computer simulations is presented. It appears as a nonlinear saturated state of the ion-ion two-stream instability and represents, macroscopically, a plasma (ion) hole moving near the ion thermal velocity. Both electron and ion densities are locally depressed.
Some conservation properties of linearized particle codes
Authors: Cohen Bruce I. , Auerbach S. P. , Byers J. A. , Weitzner H.
Published: March 2003

Conservation laws are derived which are appropriate for use in linearized particle simulation codes. A continuity equation describing mass or charge conservation and an extended Poynting theorem describing energy flow are obtained for general curvilinear coordinate systems. These conservation equations are expressed in terms of quantities readily calculable in a particle code, serve to quantitatively assess the validity and precision of code results, and provide valuable insight into the physics being studied. A conserved quantity related to the system energy, rather than a Poynting theorem, is derived from a Lagrangian formulation. It is bilinear in first-order quantities but is not attractive for implementation as a diagnostic in a linearized particle simulation.
Resonant interactions of surface and internal gravity waves
Authors: Segur Harvey
Published: March 2003

A stably stratified, two-layer fluid system with a free surface admits resonant triads, including ones involving one surface and two internal waves.
Dispersion in disparate-mass gases: the breakdown of hydrodynamics
Authors: Johnson E. A.
Published: March 2003

It is argued that the initial sound dispersion predictions of Foch, Uhlenbeck, and Losa must be modified for gases with a long internal relaxation time. The disparate-mass mixture Xe-He is considered as a specific example.
Kinetic equation of a slightly relativistic plasma
Authors: Jones Roger D. , Pytte A.
Published: March 2003

A fully convergent kinetic equation, with no arbitrary cutoffs, is derived for a homogeneous, isotropic, slightly relativistic plasma. The equations is good to first order in the ratio of the electron thermal energy to the electron rest energy.
Linear stability of internal wave solitons in a deep stratified fluid
Authors: Chen H. H. , Kaup D. J.
Published: March 2003

The linear stability problem of the internal wave solitons described by the Benjamin–Ono equation has been solved. The wave functions corresponding to the continuum spectrum are stable, showing no reflection and no phase shift. There are two bound states associated with the soliton symmetries. The one associated with the translational invariance shows no growth; the other one associated with the scale invariance shows a secular instability growing linearly with time. The closure is also proven and, therefore, the completeness of these wave functions.
Vortex-edge interaction: Mechanisms for generating low frequency components
Authors: Rockwell D. , Knisely C.
Published: March 2003

For an impinging free shear layer having a fundamental instability frequency β, either a 0.5β component or components of ∼0.4β and ∼0.6β may be generated. Neither possibility results directly from vortex coalescence; instead, they are due to newly discovered patterns of vortex-edge interaction.
Microscopic flow regimes created when a paraffin drop strikes a solid plane
Authors: Merigoux R.
Published: March 2003

The microscopic flows created when a drop of melted paraffin strikes a solid plane obey strict laws. Two rings are left at the place of contact, the diameters of which, expressed by D/d, are a function of the speed and viscosity of the drop; i.e., the mechanical conditions of the collision. A study of D/d has revealed the existence of several regimes in the flows. The discontinuities appearing between these regimes can be explained by the orientation of the molecules creating local reductions in viscosity and sliding planes.
Effects of a linearly speed-dependent collision frequency on fluctuation spectrum and drift instabilities in partially ionized plasmas
Authors: Theimer O. , Behl Y. K.
Published: March 2003

The low frequency electron fluctuation spectrum of a hydrogenlike partially ionized plasma has been computed for various values of plasma parameters like electron-ion temperature ratio, the relative drift between electrons and ions, and the collision frequency. The fluctuation spectrum has been computed both for constant and for linearly speed-dependent collision frequencies; the comparison leads to the conclusion that while investigating the effects of collisions on the fluctuation spectrum, the speed dependence of the collision frequency must be explicitly taken into account.
Breaking of modulated ion beam in phase space
Authors: Ikezi H. , Folkes P.
Published: March 2003

The steepening and breaking of the velocity-modulated ion beam in phase space is observed experimentally. Depending on the range of velocity perturbation amplitude, three different types of beam evolution are identified. A simple theory which takes into account the ion-temperature effect explains the observed behavior of the beam.
Nonlinear stability problems in dissipative plasmas on two time scales
Authors: Hu Pung Nien
Published: March 2003

A general theory for treating nonlinear stability problems in dissipative plasmas is developed, based on a two-time method extended to a system of partial differential equations. Assuming small dissipation, the first-order system is identical to that for the usual linear stability problem in magnetohydrodynamics; dissipative and nonlinear effects appear on the slow time scale in higher-order systems. For modes with finite frequencies on the fast time scale, the amplitudes are evolving on the slow time scale and are governed by ordinary differential equations with coefficients depending on the global effects of the eigenfunctions in the first-order system. For modes with low frequencies or small growth rates, nothing changes on the fast time scale; waves and nonlinear effects interact with dissipative effects on the slow time scale, resulting in a higher-order equation. Several possible scalings for dissipation are studied and stability related criteria on the slow time scale are obtained. Ohmic heating effects are also discussed.
Stabilization of drift waves by lower hybrid waves of finite wavenumber
Authors: Liu C. S. , Tripathi V. K.
Published: March 2003

The lower hybrid waves of finite wavenumber k0 are shown to be able to quench the entire k spectrum of unstable drift waves in tokamak plasmas for k0 greater than k, where k0 is perpendicular to k. In relatively cold plasmas, where k0 may become less than k, one needs to invoke the ion damping to stabilize the whole spectrum. The analysis explains very well the experimental results of Gore, Grun, and Lashinsky on the suppression of whole drift wave spectrum in a Q machine by a lower hybrid electric field.
Two-dimensional Lagrangian calculation of a laser-heated solenoid
Authors: Makomaski A. H. , Pietrzyk Z. A.
Published: March 2003

A two-dimensional Lagrangian code is used to model a laser-heated solenoid. The results indicate important two-dimensional effects and the global behavior of the plasma is found to be different from the predictions of one-dimensional theories. Most of the laser energy transferred to the plasma appears in the form of internal energy, suggesting that the bleaching wave approach for reactor calculations is correct. The plasma parameters are significantly changed when the peak of the laser beam profile is flattened.
Mass-diffusion and boundary effects in Soret-driven convective instability
Authors: Velarde M. G. , Cordoba A.
Published: March 2003

The effect of a concentration-dependent mass diffusion coefficient and permeability of a boundary are considered in the linear stability analysis of a two-component liquid mixture heated from below.
Similarity and decay laws of momentumless wakes
Authors: Hassid Samuel
Published: March 2003

The decay laws of self-similar momentumless wakes are investigated using a simple turbulent energy-dissipation (k-ε) model. Agreement with existing data is shown to be generally good.
Measurements of fluid oscillations in isochronous containers
Authors: Weidman Patrick D. , Mamrol Andrew J.
Published: March 2003

An experiment was designed to measure the fluid oscillations in planar isochronous containers. Measurements of the resonant fluid response to forced oscillations provide direct experimental confirmation of the existence of these special containers.
Thermal instability of an internally heated fluid layer in a magnetic field
Authors: Yu C. P. , Shih Y. D.
Published: March 2003

The onset of thermal instability of an electrically conducting fluid layer subjected to volumetric heating and bounded between two rigid surfaces in the presence of a magnetic field is considered. The stability conditions are found for different thermal boundary conditions.
Transport of growing waves
Authors: Lin Dong L. , Tigner J. E.
Published: March 2003

Neglecting wave scattering, the steady-state wave energy density for waves which grow as they travel through the plasma medium has been calculated.
Experimental observation of plasma paramagnetism in a tokamak
Authors: Holly D. J. , Prager S. C. , Phillips M. W. , Sprott J. C.
Published: March 2003

The increase in the toroidal magnetic field of a tokamak due to plasma presence is measured experimentally and compared with predictions of an equilibrium code.
Comments on ’’Nearly extensional flows’’
Authors: Powell Robert L. , Schwarz William H.
Published: March 2003

By means of a counterexample it is shown that the consistency relations derived recently by Pountney and Walters for incompressible fluids undergoing steady and superposed motions are not valid in all nearly extensional flows.
Multiple time scale analysis of the g×B instability in a finite Larmor radius plasma
Authors: Janssen Peter A. E. M.
Published: March 2003

The evolution in time of the g×B instability in a collisionless finite Larmor radius plasma is considered in the flute approximation. The gravity constant g is increased above its neutral stable value such that there is only one slightly unstable mode according to linear theory. Hence, two times scales are present, and the multiple time scale method can be applied. As a result, a modulation in the amplitude of the unstable mode is obtained which for small dissipation gives limit cycle behavior. The steady-state oscillation is found to be stable.
Strong plasma turbulence and anomalous diffusion in a magnetic field
Authors: Okuda H.
Published: March 2003

Plasma diffusion in the presence of strong turbulence has been studied by means of analytic theory and numerical simulations. First, diffusion and turbulent fluctuation spectra in the presence of convective cells are studied using a two-dimensional guiding center model and a two-fluid model retaining ion inertia. It is shown that for these models, turbulent diffusion takes place which dissipates a density gradient and is associated with the inverse cascades of the fluctuations transferring the electric field energy toward the long wavelength modes. Second, particle diffusion associated with drift wave turbulence using full dynamic ions and Debye shielding electrons is considered. It is shown that diffusion and the inverse cascades are much slower in this model compared with those found for convective cell turbulence. This difference arises from the fact that the mode coupling coefficient for inverse cascade is much smaller for the drift wave turbulence compared with the turbulence associated with the convective cells.
Lower-hybrid-drift instability in field reversed plasmas
Authors: Huba J. D. , Drake J. F. , Gladd N. T.
Published: March 2003

The nonlocal structure of the lower-hybrid-drift instability is investigated in a reversed field configuration. The calculation includes electromagnetic effects and ∇B electron orbit modifications, which must be considered in the high β region of the current sheet. The eigenmodes are trapped in a potential well centered symmetrically on either side of the neutral layer at ‖x‖∼λ (λ is the scale length of the current sheet). The fundamental mode is well localized away from the neutral line with a half-width Δx∼ (λ/ky)1/2<<λ, where ky∼Ωe(Ti/me)1/2 for the fastest growing mode. Higher order modes, however, have growth rates comparable to the fundamental mode and are much more global. In the cold electron limit (Te=0), the higher order modes with ∂/∂x∼ky can propagate throughout the entire sheet. In the warm electron limit (Te≠0), the electron ∇B drift-wave resonance damps the mode and prevents the penetration of the mode closer than ‖x‖p∼λ (Te/2Ti) 1/2 of the neutral line. The effects of this instability on magnetic energy dissipation and its role in the Los Alamos field reversed theta pinch are discussed.
Nonlinear converging resonance cones
Authors: Wilson J. R. , Wong K. L.
Published: March 2003

The trajectory modification of a focused resonance cone due to ponderomotive force effects was investigated in the Princeton L-3 device. A single ring pulsed at f0∼50 MHz (flh<<fo<<fpe, fce ) launches a converging resonance cone in an argon plasma with ne∼109–1010, B∼400 G–1 kG, and Te∼1–3 eV. At high driving power the strong localized electric fields modify the density through the ponderomotive force on the electrons, leading to a modification of the resonance cone trajectory. The cone is seen to bend in toward the axis and the focus moves toward the ring in agreement with the recent theory. When the rf is modulated, the density perturbation at the focus propagates radially outward and excites ion-acoustic waves. The wave dispersion relation was verified in He+, Ne+, Ar+, and Kr+ plasmas. Electron heating was observed which is consistent with collisional heating.
Quasi-linear theory of shear Alfvén waves driven by a bump-on-tail distribution
Authors: Migliuolo S.
Published: March 2003

A magnetized plasma in a shearless slab geometry is considered. The plasma ions have a distribution, in velocity space, of the bump-on-tail type. The plasma is assumed to be spatially homogeneous. Shear Alfvén waves can be destabilized via wave-ion resonances near the bump. A quasi-linear theory describing the saturation of the unstable wave is developed for the case where a single mode description is appropriate.
Stabilization of the Alfvén-ion cyclotron instability in inhomogeneous media
Authors: Tajima T. , Mima K.
Published: March 2003

Stabilization criteria for the Alfvén-ion cyclotron instability due to anisotropic temperature in inhomogeneous high β plasmas are obtained. A wave equation is derived appropriate to describe the essential aspects of this fluid-type instability in inhomogeneous media. The dispersion relation is obtained with the help of the associated Legendre functions. The critical β for stabilization is a sharply increasing function of the inhomogeneity strength of the system: the critical system length Lc is approximately proportional to β−1/2. Under the equilibrium configuration the stability criteria for the mirror mode instability and the present mode are compared, and it is found that those for the mirror mode are more stringent for moderate to large β.
Inhibition of the trapped ion mode by drift wave fluctuations
Authors: Horton Wendell , Choi Duk-In , Terry Paul , Biskamp Dieter
Published: March 2003

The influence of a spectrum of drift wave fluctuations on the trapped ion mode is investigated and shown to inhibit the onset of these modes. The stochastic damping of the trapped ion mode becomes comparable to the linear growth rate when the drift wave spectrum is described by previous theoretical models.
Energy stability theory of decelerating swirl flows
Authors: Neitzel G. P. , Davis Stephen H.
Published: March 2003

An infinite circular cylinder, filled with viscous, incompressible fluid, is rotating as a solid body. At time t=0 the angular velocity ω (t) of the cylinder is decreased in a prescribed fashion. The resulting swirl flow is susceptible to centrifugal instabilities. The method of energy is used to determine sufficient conditions, R<RG, where R is a Reynolds number, such that rotationally symmetric disturbances of arbitrary amplitude decay to zero with time. Both impulsive and smooth angular velocity histories of the container are considered. The analysis further provides a lower bound t+ on the onset time before which all disturbances must decay to zero, for R≳RG. If the final state (as t→∞) also corresponds to solid body rotation (e.g., when the cylinder is brought to rest), then the analysis simultaneously provides an upper bound t‡ on the decay time after which all disturbances decay zero, for R≳RG. In this case centrifugal instabilities are confined to times t in the interval t+<t<t‡.
Solitary-wave interaction
Authors: Bona Jerry L. , Pritchard W. G. , Scott L. Ridgway
Published: March 2003

The interaction of solitary-wave solutions of a model equation for long waves in dispersive media is examined numerically. It is found that the waves do not emerge from the interaction unscathed. Instead, two new solitary waves, having slightly different amplitudes from the original waves, together with a small dispersive tail are generated as a result of the interaction.
Closure relations for the pressure-strain correlation of turbulence
Authors: Speziale Charles G.
Published: March 2003

The modeling of the pressure-strain correlation of turbulence is examined. It is found that most of the closure relations that have recently been proposed are not form invariant under a change of frame while the pressure-strain correlation can be proven to be invariant under this group of transformations. On this basis, it is highly unlikely that any of these expressions will be of general use since they ignore basic invariance requirements. The most complete representation for the pressure-strain correlation that is properly invariant is obtained for the general class of closures where the correlation is taken to be a function of the Reynolds stresses, mean velocity gradients, and a master length scale of turbulence. Rational approximations to this form are discussed.
Interchange stability of axisymmetric field reversed equilibria
Authors: Sparks L. , Finn J. M. , Sudan R. N.
Published: March 2003

Axisymmetric field reversed equilibria are obtained by solving the Grad–Shafranov equation, with pressure on the magnetic axis and pressure on the separatrix specified as independent parameters. A stability criterion assuming unfavorable curvature is evaluated for various pressure profiles.
Ideal magnetohydrodynamic stability of tokamak plasmas
Authors: Copenhaver C.
Published: March 2003

Variational theory is used to derive a generalized Euler equation and a new energy functional which are convenient for analytical studies of ideal magnetohydrodynamic stability in tokamaks. This generalized Euler equation, which is an explicit function of the magnetic surface coordinate ψ only, represents an infinite set of equations coupled together by poloidal m mode coupling. In the infinite aspect ratio limit, the toroidal curvature and mode coupling terms disappear and an infinite set of uncoupled Euler equations for the diffuse linear pinch (Hain–Lüst equation) for each m value results. The continuous spectra are discussed for the circular toroidal case. In this case, the equations are further specialized to three modes (m, m−1, m+1) and in the marginal stability limit reduce to known results. Analytically eliminating the m−1 and m+1 modes for arbitrary current profiles provides results on limiting β poloidal for tokamaks.
Location of the interference structure near the lower oblique (whistler) resonance cone
Authors: Storey L. R. O. , Thiel J. , Boswell R. W.
Published: March 2003

By numerically solving the dispersion relation for electrostatic waves in a Maxwellian magnetoplasma with stationary ions, it is shown that above a certain frequency fα the interference structure may be either inside or outside the resonance cone, depending on the distance from the source.
Reply to comments of P. Bradshaw
Authors: Raj R.
Published: March 2003

In reply to Bradshaw, Raj notes that the wall effect is represented by the tensor Cir divided by R, the disturbance from the wall, not by Cir itself; he further disputes the claim that his Eq(2) omits the viscous contribution. (AIP)
Comments on ’’Analysis of spherical imploding shocks’’
Authors: Lazarus Roger B.
Published: March 2003

It is asserted that Fujimoto and Mishkin’s article is incorrect in its claim for a pressure extremum at or behind the shock for all values of γ and in its claim for an analytical form for the similarity exponent. (AIP)
Reply to the comments by Roger B. Lazarus
Authors: Mishkin Eli A.
Published: March 2003

It is claimed that because the pressure, density and velocity, behind the shock front, must be well behaved analytical functions the pressure must have an extremum. The claim by Lazarus of circular reasoning is refuted. (AIP)
Reply to the comments by K. Itoh and S. Inoue
Authors: Catto Peter J. , Rosenbluth M. N. , Tsang K. T.
Published: March 2003

The assertion by Itoh et al. of the stability of the collisional shear Alfvén wave, based on a quadratic form derived by them, is accepted. The difficulties involved are claimed to result, not from an incorrect expansion, but from difficulties in matching of inner and outer solutions. (AIP)
Kinetic description of coupled transverse oscillations in an intense relativistic electron beam-plasma system
Authors: Uhm Han S. , Davidson Ronald C.
Published: March 2003

The stability properties of an intense relativistic electron beam propagating through a collisionless background plasma are investigated within the framework of the Vlasov–Maxwell equations. It is assumed that νj/γj<<1, where j=b,e,i denote beam electrons, plasma electrons, and plasma ions, respectively, and νj and γjmjc2 are Budker’s parameter and the characteristic energy, respectively, of the plasma component j. The analysis is carried out for the class of rigid-rotor equilibrium distribution functions in which all particles of plasma component j have the same value of energy in a frame rotating with angular velocity ωj and the same value of axial canonical momentum. From the stability analysis for coupled transverse oscillations between the beam electrons and the plasma electrons, it is found for a low density beam (ω2pb/ω2cb≲0.5) that perturbations with azimuthal harmonic numbers l⩾2 are the most unstable modes. Moreover, the fundamental mode (l=1) is completely stabilized whenever the conducting wall is sufficiently close to the plasma boundary. The ion resonance stability properties are also investigated, including the interaction of the beam electrons with the plasma ions. It is shown that the instability domain for the ion resonance instability extends to large values of axial wavenumber kz for high harmonic numbers l.
Rotational temperatures in nonequilibrium free jet expansion of nitrogen
Authors: Coe D. , Robben F. , Talbot L. , Cattolica R.
Published: March 2003

Rotational nonequilibrium was investigated in hypersonic free jet expansions of nitrogen using the electron beam fluorescence technique. The results confirm the conclusion of previous investigations that a dipole excitation model, with an assumed Boltzmann energy distribution, is not consistent with the measured line intensities. This discrepancy was examined quantitatively and found to be independent of density and source Knudsen number (except at number densities greater than 1016 cm−3). The effect was attributed to interactions with the ejected (ionized) electron and a new excitation model was developed and shown to be consistent with the measurements throughout the flow conditions explored. The resulting rotational temperatures were compared to a simplified relaxation model of the jet and indicate a rotational collision number of 1.9.
Measurement of translational temperature in nitrogen with the electron beam fluorescence technique
Authors: Coe D. , Robben F. , Talbot L. , Cattolica R.
Published: March 2003

The electron beam fluorescence technique was applied to nitrogen for the purpose of measuring the velocity distribution function in a nonequilibrium free jet expansion of a molecular species. This was accomplished by measuring the Doppler broadening of a single rotational line in the N+2 first negative band with a Fabry–Perot interferometer. It was found that the rotational lines of this band have an inherent line width equivalent to about 70 °K translational temperature. Because of the magnitude of this additional broadening, accurate determination of the translational temperature was not possible at the low temperatures in the free jet. A correction for the additional broadening is proposed which allows application of the technique to flows at higher temperature.
Sudden expansion of gas-solid two-phase flow in a pipe
Authors: Tomita Y. , Tashiro H. , Deguchi K. , Jotaki T.
Published: March 2003

Momentum transfer from particles to gas in the decelerated flow of suspensions is confirmed experimentally in a sudden expansion of the pipe by using different particles, when a flux Richardson number, approximately evaluated at the expansion, exceeds 0.002.
Partial chemical equilibrium in fluid dynamics
Authors: Ramshaw John D.
Published: March 2003

An analysis is given for the flow of a multicomponent fluid in which an arbitrary number of chemical reactions may occur, some of which are in equilibrium while the others proceed kinetically. The primitive equations describing this situation are inconvenient to use because the progress rates ω̇s for the equilibrium reactions are determined implicitly by the associated equilibrium constraint conditions. Two alternative equivalent equation systems that are more pleasant to deal with are derived. In the first system, the ω̇s are eliminated by replacing the transport equations for the chemical species involved in the equilibrium reactions with transport equations for the basic components of which these species are composed. The second system retains the usual species transport equations, but eliminates the nonlinear algebraic equilibrium constraint conditions by deriving an explicit expression for the ω̇s. Both systems are specialized to the case of an ideal gas mixture. Considerations involved in solving these equation systems numerically are discussed briefly.
Numerical solutions for unsteady laminar boundary layers behind blast waves
Authors: Liu S. W. , Mirels H.
Published: March 2003

Numerical solutions are obtained for plane (σ=0) and axisymmetric (σ=1) laminar boundary layers induced by blast waves of the form xs∼t2/(σ+3), where xs is the distance of the blast wave from the blast origin; t is time; and σ̄ is 0, 1, or 2 for plane, cylindrical, and spherical waves, respectively. Explicit dependence on time is eliminated by a similarity transformation. The entire region between the shock (x=xs) and the blast origin (x=0) is considered, except for a small region near x=0 where the equations are singular. Numerical results are presented for ideal air with σ̄=0, σ=0; σ̄=1, σ=0; σ̄=1, σ=1; and ⩽=2, σ=1. Wall shear and heat transfer are found to increase with ξ=1 −x/xs at a rate faster than that indicated by previous solutions for the flow directly behind the shock (ξ2<<1). The results are applicable in the laminar boundary layer region, p∞xs?O (10−1) atm-cm, where p∞ is ambient pressure.
Simulation of lower-hybrid heating in a nonuniform plasma slab
Authors: Decyk Viktor K. , Morales G. J. , Dawson J. M.
Published: March 2003

A computer simulation study of the excitation of lower hybrid waves by external sources and the associated plasma heating is presented. A plasma slab with a nonuniform density profile is modeled with a two and one-half dimensional electrostatic particle code. Both a finite-length electrostatic antenna and a single wave exciter are considered. The frequency is chosen so that a wave conversion layer exists in the plasma. It is found that a narrow sheath is formed at the plasma edge and the dominant effect is surface electron heating within that region. Ponderomotive force effects as well as the nonlinear generation of harmonics and subharmonics also occur. A low amplitude lower hybrid wave is observed to be excited by the sources and propatates to the wave conversion layer where it is absorbed.
Longitudinal baffling in Faraday generators
Authors: Elkins Rush E. , Trovillion Thomas A. , Lindgren E. Rune
Published: March 2003

A numerical integration scheme for finite Faraday generators shows that no efficiency gain is accomplished by inserting insulating baffles parallel to the flow along the insulating walls of the generator duct. The computations confirm Shercliff’s analysis but differ from that of Yakhot and Levin.
Nonlinear cross-field ion acoustic instability and plasma heating
Authors: Jones R. , Barrett P. J.
Published: March 2003

The spatial growth of the cross-field ion acoustic instability, generated by ion drift across a weak magnetic field, is followed into the nonlinear domain. With increasing distance the initially broad noise spectrum becomes substantially broader by strong mode coupling; this is accompanied by heating of both the ions and the electrons. Wave saturation can be accounted for by the rise in electron temperature. The observed spatial heating rates are consistent with a simple modified quasi-linear model.
Simulation of drift-cone modes
Authors: Cohen Bruce I. , Maron Neil
Published: March 2003

Simulations of the drift-cone instability in a uniform magnetic field have shown agreement with the nonlinear theory of Myer and Simon (but only for a single mode and a weakly unstable, partially filled loss-cone velocity distribution) and with a theory that invokes ion trapping and a simple free-energy argument (for a spectrum of modes and for severe loss-cone distributions). These simulations have been performed with a particle-fluid hybrid code.
Formation of double layers
Authors: Leung P. , Wong A. Y. , Quon B. H.
Published: March 2003

Experiments on both stationary and propagating double layers and a related analytical model are described. Stationary double layers with eΔφ/kTe≳1 were produced in a multiple plasma device, in which an electron drift current was present. An investigation of the plasma parameters for the stable double layer condition is described. The particle distribution in the stable double layer establishes a potential profile, which creates electron and ion beams that excite plasma instabilities. The measured characteristics of the instabilities are consistent with the existence of the double layer. Propagating double layers are formed when the initial electron drift current is large. The slopes of the transition region increase as they propagate. A physical model for the formation of a double layer in the experimental device is described. This model explains the formation of the low potential region on the basis of the space charge. This space charge is created by the electron drift current. The model also accounts for the role of ions in double layer formation and explains the formation of moving double layers.
Persistence of magnetohydrodynamic stability in field reversed pinches against microinstability
Authors: Hamasaki S. , Krall N. A. , McBride J. B.
Published: March 2003

The question of the persistance of magnetohydrodynamic stable profiles in reversed field Z pinches is addresses, considering the probability of enhanced transport due to various microinstabilities. It is found that Suydam’s criterion for magnetohydrodynamic stability usually requires sufficient magnetic shear to prevent microinstabilities throughout most of the radial profiles.
Laser-plasma interaction and ablative acceleration of thin foils at 1012–1015 W/cm2
Authors: Ripin B. H. , Decoste R. , Obenschain S. P. , Bodner S. E. , McLean E. A. , Young F. C. , Whitlock R. R. , Armstrong C. M. , Grun J. , Stamper J. A. , Gold S. H. , Nagel D. J. , Lehmberg R. H. , McMahon J. M.
Published: March 2003

The interaction physics and hydrodynamic motion of thin-foil targets irradiated by long, low-flux Nd-laser pulses (3 nsec, 1012–1015 W/cm2) are studied experimentally and compared with theoretical models. Laser light absorption is high (80%–90%) and thin-foil targets are accelerated up to 107 cm/sec with good (20%) hydrodynamic efficiency in the 1012–1013 W/cm2 range. These results agree with a simple rocket ablation model. Details of thermal heat flow, both axially (related to ablation depth) and laterally (related to beam uniformity requirements), are also presented.
Theory of electron cyclotron resonance heating of tokamak plasmas
Authors: Ott Edward , Hui Bertram , Chu K. R.
Published: March 2003

A theoretical study of tokamak plasma heating by electron cyclotron resonance is presented. The density limitations imposed by accessibility are first reviewed. Then, the predictions of linear theory (including relativistic effects on the wave absorption) are examined via solutions of the ray equations in a toroidal tokamak equilibrium. These solutions indicate quite favorable characteristics for large tokamaks. Finally, the possibilities of scattering of the incident heating wave by existing drift-wave-type fluctuations and excitation of parametric instability are examined; it is tentatively concluded that parametric instabilities should not be important in typical situations of interest.
Stability of long, thin axisymmetric mirror machines
Authors: Weitzner Harold
Published: March 2003

The guiding center plasma model is used in the long, thin approximation to study the stability of axisymmetric mirror machines. A special case of an energy principle of Newcomb is derived and applied to the problem. It is shown that within the approximation there exist stable axisymmetric mirrors for plasma betas less than some positive number. The magnetic fields used have a weak singularity at one point on the very outer edge of the plasma. The fields are continuous, but the gradients of the field become infinite. The possibilities of eliminating such a singularity are discussed.
Simulations of the ZT-S reversed field pinch
Authors: Sgro A. G.
Published: March 2003

The implosion and approach to equilibrium of ZT-S reversed field pinch is studied numerically using the Los Alamos Scientific Laboratory one-dimensional hybrid code ’’aurora.’’ The effects of classical and anomalous transport, impurity radiation, ion-electron thermal equilibration, and wall emission of plasma are considered in the calculations. Simulations of the implosion which assumed classical transport do not agree with the measurements. However, an accurate simulation of both the magnetic field and electron temperature evolution is obtained with anomalous transport and 0.7% oxygen impurity. As equilibrium is approached, the anomalous terms in the transport coefficients decrease and the values of these coefficients become closer to their classical values.
Mean field equations of Bénard convection
Authors: McDonough J. M. , Catton I.
Published: March 2003

Some mathematical aspects of the mean field approximation are considered; and it is shown that, in general, only single-α solutions are consistent with assumptions used to derive the mean field equations.
Nonlinear analysis of laminar boundary layer flow over a periodic wavy surface—Part II: Long waves
Authors: Bordner Gary L.
Published: March 2003

The previous analysis of laminar, incompressible flow over a periodic wavy surface is extended to include wavelengths which are large compared with the mean boundary-layer thickness. These larger wavelengths produce a stronger coupling between the outer inviscid flow and the viscous disturbance sublayer and, as a result, require the complete solution of the elliptic inviscid equations. The analysis is refined to allow for a net thickening of the mean boundary layer with increasing wave amplitude. Computer-generated solutions are presented for sinusoidal waves of varying amplitude and wavelength, including cases with local flow separation.
Examination of group-velocity criterion for breakdown of vortex flow in a divergent duct
Authors: Tsai Chon-Yin , Widnall Sheila E.
Published: March 2003

A group-velocity criterion for vortex breakdown implied by wave trapping theory is applied to vortex flows in a slightly divergent duct that exhibits breakdown. The group velocities for both symmetric (n=0) and nonsymmetric (n=±1) modes of wave propagation are calculated for the experimental data. It is found that the flow ahead of the breakdown region is always supercritical and stable to these modes of disturbances. However, the flow field behind the breakdown region may be either supercritical or subcritical to the modes n=0 and n=1, and always supercritical to mode n=−1. The flow field behind this breakdown region is unstable to the asymmetric mode disturbance (n=1) for a finite range of wavenumbers. The calculated frequencies of the unstable disturbances are in good agreement with the frenquencies obtained from the experimental measurements.
Effect of a chemical inhomogeneity on steady-state detonation velocity
Authors: Engelke Ray
Published: March 2003

The detonation behavior of the liquid explosive, nitromethane, sensitized by the liquid organic base, diethylene triamine, has been studied experimentally. The work to be described complements earlier work concerning the effect of physical impurities on steady detonation behavior. By interpretation of detonation-velocity measurements, the following three goals are reached: (1) The evidence that physical inhomogeneities (usually voids) produce the downward concave region of the diameter-effect curves of condensed high explosives is enhanced; (2) the hypothesis that homogeneous materials have linear diameter-effect curves is placed on a firmer basis; and (3) the experimental evidence indicates that the sensitizing material has altered the effective chemical kinetics and consequently, has produced an explosive with a shorter one-dimensional reaction zone. A remarkably small amount of the chemical impurity produces a significant reduction of the nitromethane failure diameter; e.g., addition of one molecule of the amine to 5500 molecules of nitromethane reduces the failure diameter by 43%. A discussion is given which attempts to relate this high sensitivity to a molecular isomer of nitromethane (the ’’aci’’ form) whose presence is favored in basic solutions.
Stability of shear flow in a magnetized plasma
Authors: Lau Y. Y. , Liu C. S.
Published: March 2003

By studying the eigenmode solutions and by calculating the evolution of an initial wavelet, it is shown that Alfvén waves in a magnetized plasma are stable even if the plasma possesses a longitudinal flow velocity v0 with a strong shear, provided the maximum flow velocity is less than twice the Alfvén speed. This result is discussed in the light of recent neutral beam injection experiments in tokamaks.
Particle stochasticity due to magnetic perturbations of axisymmetric geometries
Authors: Mynick H. E. , Krommes John A.
Published: March 2003

The quasi-linear theory of collisionless test particle diffusion in stochastic magnetic fields is extended to include the effects of finite gyroradius ρ and particle drifts (including magnetic trapping). A canonical framework is used, in which both the criterion for onset of stochasticity and the diffusion tensor scale with field-particle coupling coefficients gl. The gl contain all the information about the unperturbed orbit of a given particle and the perturbation fields with which the particle interacts. The modification of transport due to finite ρ and drifts is thus found by comparison of the gl including these effects to their driftless, ρ→0 limit. It is found that runaway electron confinement is substantially improved over earlier, driftless estimates, and that trapped particles in microturbulence ought not be stochastic. The perturbations from proposed ripple injection schemes are large enough to induce stochasticity for certain classes of particles.
Classical collisional theory of beam-driven plasma currents
Authors: Hirshman S. P.
Published: March 2003

A variational calculation of the current produced in a plasma by fast beam particles is presented. A new energy polynomial expansion of the classical Spitzer function is obtained and used to derive an accurate analytic expression for the beam-driven current j∥, which includes the effects of electron-electron collisions and is valid for all values of v̄b=vb/ve and effective charge Z̄. This analytic result is in excellent agreement with previous numerical calculations. An accurate rational form for the beam-driven current as a function of beam velocity is obtained by patching the large and small v̄b asymptotic expansions of j∥.