bluuebunny/crossref_metadata_2025 huggingface dataset:
Vortex ring formation at tube and orifice openings
Authors: Pullin D. I.
Published: March 2003

The formation, at tube and orifice openings, of vortex rings generated by a piston moving with velocity proportional to time to some power m, is considered. The expansion of the axisymmetric generating flow about the circular forming edge is used in conjunction with the similarity theory of edge vortex growth to model the ring formation process. For large Reynolds numbers the ring diameter and circulation are not strongly dependent on the piston velocity profile. However, the ring viscous subcore shows peaks in the tangential velocity profile only if m < (π−ϑe)/(2π−ϑe), where ϑe is the edge forming angle.
Nonlinear effects of temperature on simple shear flows of heat conducting viscoelastic fluids
Authors: Dunwoody J. , Nunziato J. W.
Published: March 2003

The effect of temperature-dependent conductivity on the behavior of heat conducting viscoelastic fluids, such as oils and polymer melts, is considered for the case of steady, simple shear when the bounding plates are at fixed temperature. In particular, it is shown that if the thermal conductivity increases with temperature, then there exists a maximum plate width for which steady flows are possible. Furthermore, it is shown that, in general, there is a critical shear stress which also limits the possibility of steady flows. Finally, the possible nonuniqueness of solutions is discussed and our results are contrasted with those obtained by Joseph for Navier–Stokes fluids.
The polymorphic detonation
Authors: Rabie(a) R. L. , Fowles G. R. , Fickett W.
Published: March 2003

A simple thermodynamic system, having a single first-order phase transformation, is examined as an elementary explosive. The energy needed to support self-sustaining waves is stored in the volume change of the phase transformation. It is shown that this system can support the conventional viscous detonations as well as a set of unsteady eigenvalue detonations. Eigenvalue detonations have been discussed previously with respect to conventional explosives, but the very large reaction rates required to produce them are not thought to exist in nature. The occurrence of eigenvalue detonations in our system, for arbitrarily small reaction rates, is due entirely to the presence of an equilibrium coexistence surface connecting the two phases of the material, allowing mixed phase equilibrium states to be attained in a single shock process.
Explicit demonstration of epochal relaxation in a binary gas mixture
Authors: Fitzpatrick J. M. , Shizgal B.
Published: March 2003

The relaxation of a binary gas mixture is studied with a moment method of solution of the Boltzmann equation, valid for arbitrary mass ratios. In these calculations, the number densities of the two components are taken to be equal and the hard sphere interaction is assumed throughout. The explicit time dependence of the distribution functions is obtained and epochal relaxation is demonstrated and found to occur only for the disparate mass case.
A high Hartmann number rotating plasma
Authors: Brand G. F. , James B. W. , Walsh C. J.
Published: March 2003

Experimental measurements on a rotating argon plasma are presented which confirm that a flowing magnetohydrodynamic fluid may be divided into distinct core and boundary regions when the Hartmann number is large. Estimates of the rotational speed of the plasma are obtained by measuring the radial density profile.
Wave coupling effects in the nonlinear evolution of the beam-plasma instability
Authors: Throop A. L. , Parker R. R.
Published: March 2003

A formalism is presented which has been used to study the nonlinear evolution of the reactive beam-plasma instability in the presence of wave coupling. Special consideration is given to describing the energy of the unstable mode in deriving the coupled-mode equations, and this results in a four-wave model for the interaction. The results show that pump depletion can stabilize the linear instability, and also predict transitional behavior in saturation mechanisms which is observed experimentally.
Excitation of lower hybrid waves in a finite plasma
Authors: Decyk V. K. , Dawson J. M. , Morales G. J.
Published: March 2003

A computer simulation study of the launching of lower hybrid waves by external sources and their propagation in a finite but homogeneous plasma slab is presented. The study makes use of a two and one-half dimensional electrostatic particle code developed for simulation of bounded plasma. A number of antenna configurations are considered: a point source, two finite-length capacitor plates, and a phased array of capacitor plates. When the oscillating frequency does not match a bounded plasma resonance, one can observe resonance cones, energy absorption at the plasma surface, ion cyclotron modulation of the source, and energetic ions, depending on the parameters chosen. The excitation of a bounded plasma resonance is also considered. The nonlinear evolution of the resonance shows that wave-particle interactions and ponderomotive force effects play an important role. The possibility of controlling the electron temperature profile is discussed.
Theory of the striated corona in a theta pinch
Authors: Krall Nicholas A. , McBride John B. , Matteson Laura
Published: March 2003

The radial striations observed in the low density corona surrounding a theta-pinch-confined plasma are explained as due to an instability at the ion plasma frequency driven by plasma rotation in the corona. A nonlocal theory is used to find radially extended modes, as observed experimentally. The observed wavelength of the striations can then be used to deduce the density in this region; this density is in reasonable agreement with estimates from numerical models.
Diamagnetic frequency profile effects on toroidal drift waves
Authors: Horton Wendell , Choi Duk-In , Estes R. D.
Published: March 2003

A radially peaked diamagnetic frequency profile typical of some tokamak discharges is shown to lead to radial localization of the drift wave fields. A critical condition for the onset of shear stabilization is derived which balances the effects of toroidal mode coupling, the degree of peaking in ω*e(r), and the strength of the magnetic shear.
Kinetic theory of ion ring compression
Authors: Lovelace R. V.
Published: March 2003

A general kinetic theory is developed for the adiabatic compression of ion rings, and associated plasma, in an external magnetic mirror field Be(t). The single particle distribution function is shown to be given by f (ℋ,𝒫ϑ,t) =F (I,𝒫ϑ) during axisymmetric compression in the absence of instabilities and under conditions where the particle motion is ergodic in the poloidal (r,z) plane. Here, ℋ and 𝒫ϑ are the energy and canonical momentum of a ring ion; I (ℋ,𝒫ϑ) is an adiabatic invariant involving an average over the region of the poloidal plane accessible to a particle with constants ℋ and 𝒫ϑ; and F is an invariant function. A complete description of ring compression is obtained from F, which gives the ring current density Jbϑ, from an appropriate constitutive relation for the plasma response, which gives the plasma current density Jpϑ, and from Ampère’s law. The theory is valid for rings of arbitrary aspect ratio, the particle orbits are essentially unrestricted, and account is taken of ring particle evaporation. A general analysis is made of energy and angular momentum conservation during compression. In particular, the total power input and the power absorbed are derived in terms of the magnetic moment of the ring-plasma system, M (Be).
Magnetic focusing of intense ion beams
Authors: Maenchen J. , Wiley L. , Humphries S. , Peleg E. , Sudan R. N. , Hammer D. A.
Published: March 2003

Magnetic focusing of a uniform intense proton beam produced by a new magnetically insulated diode has been demonstrated using a single dipole coil. The new diode produces an intense (80 A/cm2 at 350 keV), low divergence (half-angle less than 4°), uniform proton beam that can be injected into a field-free vacuum drift region. Prompt space-charge neutralization by low energy electrons occurs almost immediately after the beam emerges from the diode. Experimental observations of the beam focal properties are in reasonable agreement with numerical calculations of the particle orbits and show that the protons follow essentially single particle trajectories. Calculations also show that for ion currents approaching the ion Alfvén current a net azimuthal diamagnetic current in the region of the dipole lens causes the beam defocusing. Finally, calculations and experimental observations indicate that the beam angular divergence may provide the most serious limitation on beam focusing for pellet fusion.
Magnetic mirror confinement of laser-produced LiH plasmas
Authors: Tomlinson R. G. , Fader W. J. , Polk D. H. , Stufflebeam J. H.
Published: March 2003

The results of measurement and analysis of the decay of mirror-confined lithium hydride plasmas are reported. The plasmas are produced by laser irradiation of a solid LiH particle suspended at the center of a mimimum-B magnetic field. In the initial state, the ratio of the Li3+ energy to H+ energy is 7 to 1, the mean energy of lithium ions is about 2000 eV, and the electrons are cold. In the subsequent decay of the mirror-confined plasmas from 3×1013 to 1012 cm−3, the H+ lifetime is sufficiently shorter than the lifetime of the Li3+ ions so that the plasma evolves to a lithium plasma. The density decay is faster than classical but quiescent for the first 250 μsec. After that time, there are sudden increases in the plasma decay rate and in the rf emission at the central cyclotron frequency of lithium ions, interpreted as evidence of the onset of the drift cyclotron loss cone instability. The quiescent behavior is correlated with the observation of optical radiation from the plasma between 70 and 250 μsec. The plasma luminosity is interpreted as evidence for the creation of cold plasma by ionization of cold neutral reflux from the walls of the baseball coil. A quasi-linear Fokker–Planck calculation of the ion distributions and the growth and damping of the drift cyclotron loss cone mode yielded results consistent with an explanation of the quiescent decay as the suppression of the instability by the cold plasma.
Stability of a current-carrying plasma sheet
Authors: Kutty A. P. G.
Published: March 2003

The dispersion relation for hydromagnetic waves on a planar plasma sheet carrying an asymmetric current has been shown to be the same as that for a symmetric current. The relevance of this result to experimental observations is discussed briefly.
Simulation of space-charge limiting current in relativistic electron beams
Authors: Sullivan D. J. , Roderick N. F.
Published: March 2003

A relativistic particle-in-cell simulation code has been used to study the space-charge limiting currents of a solid and an annular relativistic electron beam. The resulting limiting currents are significantly higher than that given by the widely used Bogdankevich–Rukhadze interpolation formula.
Vacuum propagation of solid relativistic electron beams
Authors: Thode Lester E. , Godfrey Brendan B. , Shanahan William R.
Published: March 2003

An investigation of equilibrium, stability, and space-charge- limiting current of a solid relativistic beam propagating along a finite external magnetic field has been carried out and compared with experiments. The concept of a rigid-rotor equilibrium is only approximately valid when the beam current is much less than the Alfvèn critical current. Typically, low-voltage beams rotate fastest at the beam edge whereas high-voltage beams rotate fastest near the beam axis. A limited investigation of the rigid rotor stability condition indicates, at worst, a weak instability may be present if the rigid-rotor equilibrium is artificially imposed, and no instability at all for a self-consistent equilibrium. Numerical solutions for the space-charge limiting current and relativistic factor on axis are presented and compared with two-dimensional, cylindrical, space- and time-dependent simulations. Analytical expressions for the limiting current are valid for ωc/ωb≳5, where ωc is the cyclotron frequency and ωb is the beam frequency. For external magnetic field strengths below this level, the limiting current increases monotonically with decreasing field strength until the beam collides with the drift tube. Expressions for foil scattering are also presented. The results are in good agreement with experiments.
Thomson scattering from an anisotropic plasma
Authors: Watt R. G. , Pietrzyk Z. A.
Published: March 2003

The general form of the scattered spectrum from a plasma in which the electrons and ions are allowed to have Maxwellian velocity distribution functions with temperatures in the three major directions unequal is calculated. The general structure is shown annd the possibility of measuring the direction of anisotropy in a plasma using this structure is discussed.
Structure and observable characteristics of laser driven ablation
Authors: Matzen M. Keith , Morse Richard L.
Published: March 2003

Numerical hydrodynamic-heat flow simulations of spherical ablation have been done with sufficient spatial resolution to show the details of the ablation front structure. These simulations show a continuous qualitative change in the velocity spectrum of expanding ions with increasing laser pulse length, ranging from approximately isothermal behavior from short pulse to ablative behavior from longer pulses. The ablative behavior is characterized by an energetic peak in the ion spectrum, a characteristic of ablation that is experimentally observable. The longer pulse cases are found to be in good agreement with the stationary flow model of ablation.
Localized trapped electron drift instability
Authors: Mahajan Swadesh M. , Ross David W.
Published: March 2003

The full electron dynamics in the collisionless drift wave radial equation is used to discover a class of drift modes which are localized by electron temperature gradients and are unaffected by the ion acoustic term. In the presence of a driving term, such as provided by trapped particles, these modes become strongly unstable.
Instabilities induced by over-reflection in stratified fluids in horizontal sheared motion
Authors: Pellacani C. , Tebaldi C. , Tosi E.
Published: March 2003

The destabilizing effect of the over-reflection mechanism in stratified fluids in horizontal sheared motion is considered. It is shown that the behavior of unstable modes, induced by the contemporary presence of jumps in both the mean horizontal velocity and the Brunt–Väisälä frequency located at different heights, can be interpreted in terms of successive reflections and over-reflections at the Brünt–Väisälä frequency jump and at the vortex sheet, respectively. A very good accord is obtained with the predictions of the linear theory of unstable modes with small associated growth rates.
Wall effects on cylinder drag at low Reynolds number
Authors: Stalnaker John F. , Hussey R. G.
Published: March 2003

Measurements were made of the terminal velocity of a slender circular cylinder moving transverse to its axis at low Reynolds number in a fluid bounded by a rectangular container. The measurements are compared to theoretical results in four limiting cases: (1) a cylinder of infinite length in an unbounded fluid, (2) a cylinder of finite length (but large length to diameter ratio) in an unbounded fluid, a cylinder of finite length moving midway between infinite plane parallel boundaries when (3) the boundary influence is strong, and (4) when the boundary influence is weak. The effects of other boundaries are shown to be small. Empirical correction terms are presented and the practical limitations of the theoretical solutions are discussed. The most important result is that when the boundary influence is strong, there is an unexpectedly large correction term due to the finite length of the cylinder. In these experiments the Reynolds number based on cylinder length ranges from 8.1 to 0.065 and the ratio of sidewall boundary separation to cylinder length ranges from 18 to 0.022.
Structure of a heavy ion shock in a weakly ionized gas
Authors: Williams Marc H. , Bienkowski George K.
Published: March 2003

The response of a heavy ion seed component to the passage of a plane shock in the neutral background gas has been analyzed. The translational equilibrium of the ion trace occurs in a region of effectively frozen ionization level and electron temperature where the ion behavior is controlled by a momentum balance of electrical, inertial, and collisional forces. Three distinct types of solutions are found to occur: quasi- neutral downstream relaxation at low electron temperatures; quasi-neutral upstream accommodation at high electron temperatures; and non-quasi- neutral damped electrostatic oscillations at intermediate electron temperatures.
Cold plasma wavebreaking in the presence of an electromagnetic driver
Authors: Speziale Thomas , Catto P. J.
Published: March 2003

Nonlinear electron plasma oscillations driven by an electromagnetic wave are investigated. An improved, self-consistent Lagrangian description of the resonant interaction is derived. The modifications to the simple capacitor plate or uniform electrostatic driver model previously employed are calculated and shown to have a negligible effect on the wavebreaking process for laser intensities I<1017 W cm−2 in the case of Nd lasers.
Stability properties of a cylindrical rotating P-layer immersed in a uniform background plasma
Authors: Uhm Han S. , Davidson R. C.
Published: March 2003

The electrostatic stability properties of a rotating, charge-neutralized P-layer are investigated within the framework of a hybrid (Vlasov-fluid) model in which the layer ions are described by the Vlasov equation, and the layer electrons and the uniform background plasma are described as macroscopic, cold fluids. It is assumed that the P layer is thin, with radial thickness (2a) much smaller than the mean radius (R0), and that ν≪1, where ν is Budker’s parameter for the layer ions. Electrostatic stability properties are calculated for perturbations about a weakly diamagnetic P layer with rectangular density profile, described by the equilibrium distribution function f0b= (nbR0/2πmi) δ[H−VzPz−mi (V20−V2z)/2]δ (Pϑ−P0), where H is the energy, Pϑ is the canonical angular momentum, Pz is the axial canonical momentum, and nb, R0, Vz, V0, and P0 are constants. The stability analysis is carried out including the effects of a uniform background plasma, and weak self-magnetic fields. Although a slow rotational P layer (P0≳0) is found to be stable, it is shown that a fast rotational P-layer (P0<0) is unstable for sufficiently high background plasma density (ω2p≫ω2ci). The typical instability growth rate is a substantial fraction of the ion cyclotron frequency.
Two-dimensional transport of tokamak plasmas
Authors: Hirshman S. P. , Jardin S. C.
Published: March 2003

A reduced set of two-fluid transport equations is obtained from the conservation equations describing the time evolution of the differential particle number, entropy, and magnetic fluxes in an axisymmetric toroidal plasma with nested magnetic surfaces. Expanding in the small ratio of perpendicular to parallel mobilities and thermal conductivities yields as solubility constraints one-dimensional equations for the surface-averaged thermodynamic variables and magnetic fluxes. Since Ohm’s law E +u×B =R′, where R′ accounts for any nonideal effects, only determines the particle flow relative to the diffusing magnetic surfaces, it is necessary to solve a single two-dimensional generalized differential equation, (∂/∂t) ∇ψ. (∇p − J×B) =0, to find the absolute velocity of a magnetic surface enclosing a fixed toroidal flux. This equation is linear but nonstandard in that it involves flux surface averages of the unknown velocity. Specification of R′ and the cross-field ion and electron heat fluxes provides a closed system of equations. A time-dependent coordinate transformation is used to describe the diffusion of plasma quantities through magnetic surfaces of changing shape.
Continuous magnetohydrodynamic spectrum in axially symmetric rotating plasmas
Authors: Hellsten T. A. K. , Spies G. O.
Published: March 2003

The continuous magnetohydrodynamic spectrum is investigated for axially symmetric equilibria in which the plasma rotates toroidally in a purely poloidal magnetic field. The flow continuum is given by a simple algebraic expression, while the Alfvén- and cusp continua (which are coupled through the Coriolis force) are given by the eigenvalues of a fourth-order non-self-adjoint problem in ordinary differential equations along magnetic field lines. It is shown that these continua are stable if the entropy does not increase along the field lines away from the rotation axis, but that the cusp continuum may turn unstable otherwise.
Weissenberg effect in Newtonian liquids
Authors: Bobrovsky B. Z. , Shlien D. J. , Brosh A. , Kleinstein G.
Published: March 2003

A Newtonian liquid was observed to climb up a rotating shaft whose tip was initially just in contact with the liquid surface. This phenomenon occurred when the rotation speed was increased above a certain threshold. An energy transfer mechanism is suggested as a possible explanation.
Comparison of two computation methods for vibrational nonequilibrium flows
Authors: Brun R. , Zappoli B. , Zeitoun D.
Published: March 2003

Nozzle flows are investigated assuming either a strong or a weak vibrational nonequilibrium. The corresponding vibrational temperature evolutions are found to be in disagreement due to the fact that both methods are probably not appropriate for computing the entire flow.
Nonlinear development of an electromagnetic filamentation instability
Authors: Montgomery David , Liu C. S.
Published: March 2003

A simplified model of an electromagnetic filamentation instability that arises when two counterstreaming electron beams pass through a uniform ion background is treated by statistical mechanical techniques borrowed from fluid turbulence theory. Accumulation of magnetic energy at long wavelengths is predicted, as observed in the numerical simulations of Lee and Lampe.
Stable equilibrium statistical states for spheromaks
Authors: Vahala George , Vahala Linda
Published: March 2003

Incompressible nondissipative magnetohydrodynamic turbulence is treated for spherical systems. From the absolute equilibrium expectation values of the fields one can investigate those initially quiescent states for which no large mean square velocity will develop. This stable state is force-free and gives rise to the Hill vortex structure for the magnetic flux surfaces.
Generation of interfacial gravity waves by submerged regions of fluctuating hydrodynamical motions and fluid inhomogeneities
Authors: Liu J. T. C.
Published: March 2003

The problem of interfacial gravity wave generation by submerged regions of vorticity and fluid inhomogeneities is formulated via the Boussinesq form of the momentum equation and the continuity equation for an incompressible fluid. The velocity vector is split into an irrotational (ambient) and a rotational (source) contribution. With the source contributions presumed known, the Bernoulli function is then solved from a Poisson equation in terms of an integral over the region of source vorticity and inhomogeneities. This then enters into the interfacial gravity wave problem in the form of a dynamical condition in the usual manner. The theory is applied to a linearized, small-amplitude study of unconvected sources in a medium which is stationary in the mean. The gravity wave ripples in the far field are estimated. While the phase factor can be interpreted in terms of one familiar in deep-water waves, the amplitude function is obtained in terms of the spectrum of the source region. An analogy with simple unsteady sources is drawn.
Spectral variance estimation and the analysis of turbulence data
Authors: Helland K. N. , Rosenblatt M.
Published: March 2003

The results of an asymptotic analysis for the variance of power spectra and the real and imaginary parts of complex cross spectra are presented. The formulae for the spectral variances do not require an assumption of jointly Gaussian probability density functions for the time series and, therefore, are of special importance to the analysis of turbulence data. The variances computed from the asymptotic formulae compare favorably with directly estimated variances for power spectra and a third-order cross spectrum which appear in the study of spectral energy transfer in turbulent flows. The asymptotic variance formulae can be useful tools for the design of experiments which require estimation of power and cross spectra.
Stability properties of an anisotropic guiding center plasma and relation with the Suydam function
Authors: Choe Joon Y. , Davidson R. C.
Published: March 2003

The effect of pressure anisotropy on the equilibrium and stability properties of an unstable guiding center plasma and the dependence of associated stability properties on the Suydam function S are examined. An explicit solution of the guiding center plasma equilibrium equation is obtained as a function of the anitsotropy parameter α≡P∥/P⊥ (assumed constant), and the maximum growth rates for internal kink modes are numerically computed for the entire permissible range of α. For a typical tokamak field configuration with shear in straight cylindrical geometry, it is found that the maximum growth rate is a monotonically increasing function of α. A detailed parameter study of equilibrium and stability properties is presented. The dependence of stability properties on the Suydam function S is investigated by correlating maximum growth rates with the magnitude of S, and by examining the ratio of consecutive eigenvalues for each set of the parameters. The numerical analysis shows that, even though the Suydam function occurs naturally in studies of marginal stability, the maximum growth rate (except for a narrow range of α) is a monotonically decreasing function of S.
Twisting modes
Authors: Strauss H. R. , Hazeltine R. D. , Mahajan Swadesh M. , Ross David W.
Published: March 2003

New electromagnetic modes with odd magnetic field parity, the twisting modes, are described. These are closely related to the m=1 tearing modes, but are much more localized and are not restricted in azimuthal mode number. Unstable modes are found in the hydrodynamic and adiabatic electron dynamical regimes.
Finite beta effects on the drift-cyclotron instability
Authors: Gladd N. T. , Huba J. D.
Published: March 2003

The local dispersion equation for the drift-cyclotron instability is derived and solved in order to examine the effects of finite beta associated with (a) transverse electromagnetic perturbations (δB≠0), and (b) resonant and nonresonant ∇B orbit modifications of both electrons and ions. Moreover, a formalism is chosen which allows consideration of variable density gradients, (me/mi)1/2≲rLi/LN≲1, on the ions. A detailed numerical study of the effects of finite beta on the general dispersive character and unstable spectrum is presented as well as a consideration of the effects of finite beta on the most rapidly growing mode. It is found that finite beta, in general, increases the frequency and reduces the growth rate but does not completely stabilize the drift-cyclotron instability. The transition of the drift-cyclotron instability into the lower-hybrid-drift instability which occurs for rLi/LN≃ (me/mi)1/4 is also discussed.
Nonlinear evolution of lower hybrid waves
Authors: Karney Charles F. F. , Sen Abhijit , Chu Flora Y. F.
Published: March 2003

The two-dimensional steady-state distribution of lower hybrid waves is governed by the complex modified Korteweg–deVries equation, vτ+vξξξ+(‖v‖2v)ξ=0, where v is proportional to the electric field and ξ and τ are two spatial coordinates. The equation is studied numerically. Two types of solitary waves can arise; one is a constant phase pulse, whereas the other is an envelope solitary wave. These solitary waves are not solitons. The occurrence of the constant phase pulses points to the possibility of internal reflections due to scattering off ponderomotive density fluctuations. This necessitates solving the equation as a boundary value problem. With typical fields for lower hybrid heating of a tokamak, it is found that large reflections can occur close to the edge of the plasma.
Variational calculation of drift wave eigenvalues
Authors: Ross David W.
Published: March 2003

The validity of the variational calculation of drift wave eigenvalues in plasmas with magnetic shear is reaffirmed by means of a rotation in the complex x plane. Recent criticism of the method is thereby refuted.
Streak mode interferometric study of plasma focus
Authors: Hamada Fumio , Shimoda Katsuji , Hirano Katsumi
Published: March 2003

A streak mode interferometer system with nanosecond time resolution is developed. Using the system, the macroscopic behavior of plasma in collapse and pinch phase is observed continuously, and the time variation of the spatial distribution and the line density of electrons are obtained.
Energy stability of a natural convective flow in a horizontal annular space
Authors: Mojtabi Abdelkader , Caltagirone Jean-Paul
Published: March 2003

The conditions for global asymptotic stability are determined by energy theory. The basic flow is obtained using the perturbation method. The results are compared to those obtained by the linear theory and to those derived from various experimental investigations.
Incompressible magnetohydrodynamic flow with heat transfer between inclined walls
Authors: Choi S. H. , Wilhelm H. E.
Published: March 2003

Self-similar flows of viscous, incompressible, electrically conducting fluids and of heat in a diffuser with an azimuthal magnetic field and plane walls (at constant temperature) are analyzed by analytical and numerical methods. Velocity distributions for pure outflows and temperature distributions are presented for various invariance parameters I1=ϑ0R1/2, I2= (H2−4)/R, and Prandtl numbers 𝒫 where ϑ0 is the duct angle, R is the Reynolds number, and H is the Hartmann number. In the approximation of constant fluid properties, the onset of flow separation is independent of the heat transfer, and separation is inhibited for I2⩾2/3 if R ≫ 1. The theory is applicable to proper incompressible fluids such as liquid metals (small Prandtl numbers), in which self-similar velocity and temperature fields can be realized.
Finite beta trapped electron fluid mode
Authors: Strauss H. R.
Published: March 2003

It is shown that finite plasma beta can destabilize relatively long wavelength trapped electron fluid ballooning modes, which are the electromagnetic generalization of the electrostatic ’’ubiquitous’’ mode.
Structure of laser-induced normal modes in finite inhomogeneous plasma
Authors: Fuchs Vladimir
Published: March 2003

An analytic treatment of the problem of normal modes resulting from the decay of an electromagnetic pump wave propagating in a strongly inhomogeneous finite plasma is presented. Asymptotic solutions of the Weber equation and, alternatively, the WKB method, are applied to formulate dispersion relations which agree. Simple formulae for the complex growth rate pm = ρm±iΩm are obtained as functions of the coherence length κ−1/2 (κ being the wavenumber mismatch gradient), the plasma length L, and the basic gain length L0. Where numerical results are available, they agree with the eigenvalues from the formulae to within 10% or better. The mth mode appears if, and only if, the inequality amL0<κ−1/2<bmL holds, where am and bm are certain eigenvalues which, respectively, increase and decrease with m. The first part of the inequality determines the threshold pump intensity, whereas the second part defines a starting length.
Wavebreaking amplitudes in warm, inhomogeneous plasmas
Authors: Kruer William L.
Published: March 2003

The effect of plasma temperature on reducing the wavebreaking amplitude of resonantly driven fields in a spatially inhomogeneous plasma is shown. A simple theory is developed, and some applications to laser plasma interactions are given.
Growth of the two-dimensional mixing layer from a turbulent and nonturbulent boundary layer
Authors: Browand F. K. , Latigo B. O.
Published: March 2003

The effect of the initial boundary layer upon the downstream growth of the turbulent mixing layer between two streams is studied experimentally. Two conditions are carefully documented; in one case the boundary layers at separation are laminar and in the other case one boundary layer is made turbulent with a trip wire. When the boundary layer is turbulent; the lateral length scale, ϑ, characterizing the thickness of the mixing region, grows more slowly. At 400–500 initial momentum thickness downstream, the growth rate relaxes toward, but does not meet, the growth rate of the untripped mixing layer. The lateral distributions of the turbulence quantities, when scaled with the local lateral thickness, achieve the same form at distances beyond approximately 800 initial momentum thicknesses.
The Kolmogoroff r2/3 law
Authors: Dickey T. D. , Mellor G. L.
Published: March 2003

The Kolmogoroff r2/3 law has been rederived from high wavenumber universal spectra and an additive constant has been obtained as a function of α, the empirical constant in the r2/3 law. The value of α is uncertain. However, values determined from both structure function data and spectral density data have been collected and plotted as a function of Reynolds number. Although the results may be of more general interest, the original motivation for this study was to provide a diagnostic tool for evaluating the turbulent energy dissipation rate from correlation data (much as wall shear stress is evaluated from velocity profile data using the law of the wall). The technique for this procedure is illustrated.
Thermal diffusion and convective stability: The role of uniform rotation of the container
Authors: Antoranz J. C. , Velardea) M. G.
Published: March 2003

The stability of a horizontal, two-component fluid layer subjected to a vertical temperature gradient is investigated in the case of a container rotating with uniform speed. Rotation generally plays a stabilizing role, and quantitative results are given for its influence on the instability driven by the coupling of buoyancy forces to the Soret effect. The results found may be useful to experimentalists measuring the Soret effect by the thermogravitational method.
Velocity field measurements of a laminar thermal
Authors: Shlien D. J. , Brosh A.
Published: March 2003

Tracer particle path photographs of a rising isolated laminar thermal injected from a small source are presented. The presence of a velocity wake was clearly observed. The streaks of the tracers were sufficiently clear to deduce the velocity and vorticity fields. There is some indication that the velocity field approached a similarity state after an initial development distance. The vorticity distribution, calculated from the velocity field, was diffuse with no evidence of a distinctive core. Near the symmetry axis, the vorticity varied almost linearly with the radial coordinate and was independent of the axial coordinate. In the far field, the vorticity decreased monotonically.
Ultra-high-speed filming of atomizing jets
Authors: Reitz R. D. , Bracco F. V.
Published: March 2003

In the atomization regime, a liquid jet breaks up into droplets of diameter much smaller than the nozzle exit diameter, within the nozzle or immediately upon entering the chamber gas. The mechanism of atomization is currently unknown. The initial emergence and breakup details of liquid jets at the onset of injection were recorded, apparently for the first time, by an ultra-high-speed framing camera (up to 106 frames/sec). Liquid pressure and viscosity, gas pressure and density, and the nozzle internal geometry were varied. The nozzle exit diameter, the liquid surface tension and density, and the gas and liquid temperatures were not varied significantly. Intact length, spray angle, penetration rate, and quasi-steadiness of the breaking jet are discussed. It is concluded that within the tested range, liquid cavitation or aerodynamic surface wave growth, augmented by liquid cavitation and/or boundary layer velocity profile relaxation phenomena, could explain the observed experimental trends adequately.
Laboratory double layers
Authors: Coakley Peter , Hershkowitz Noah
Published: March 2003

Strong electric potential double layers (eφ/Te≳10) are produced in the University of Iowa’s triple plasma device. The electron beam which results from acceleration by the double layer maintains its identity with little heating until it reaches the end of the chamber. Structure of the double layers is seen to depend upon the characteristics of the free and trapped particle species. A three-dimensional mapping for double layers is shown. A density criterion model for the stability of double layers is also presented.
Staircase model for magnetohydrodynamic spectrum and global instabilities in the Elmo bumpy torus
Authors: Nelson D. B. , Spies G. O.
Published: March 2003

In the staircase model a continuous equilibrium is approximated by a discontinuous one with jump surfaces separating regions of constant pressure, density, and magnetic rotation number. The dispersion relation, giving the growth rates or frequencies of eigenmodes of the linearized motion as solutions of a finite matrix eigenvalue problem, is derived for arbitrary axisymmetric straight staircase equilibria with no azimuthal magnetic field and with weak, long, and thin periodic mirrors. This relation is shown to describe global modes accurately, thus being well suited to obtaining their dependence upon the pressure and density profile with minimal numerical effort. Application to hollow pressure profiles typical of the Elmo bumpy torus yields global instabilities with growth rates too large to be compatible with observations, indicating that kinetic effects must be invoked to explain even the large-scale behavior of this device.
Volume forces in weakly ionized plasmas
Authors: Ecker G. , Kaschuba K. , Riemann K.-U. , Schumacher A.
Published: March 2003

The force which is exerted on the neutral gas in the plasma column of a gas discharge (electrophoresis) is calculated by kinetic theory. The calculation refers to rare gas discharges at medium pressures where charge exchange is the dominant collision process, conditions which are met in most of the corresponding experimental investigations. The analysis makes the various contributions to the electrophoresis effect transparent and reveals their physical background. In particular, the strong influence of velocity correlations due to a non-Maxwellian ion distribution function, even for small E/p values, is demonstrated.
Instantaneous direction of the velocity vector in a fully developed turbulent channel flow
Authors: Kreplin Hans-Peter , Eckelmann Helmut
Published: March 2003

In a fully developed turbulent channel flow, the angular deviation of the actual velocity components from the mean stream was instantaneously measured. Probability density distributions of these deviations were calculated.
Kelvin–Helmholtz-like instability of a shear layer subject to free boundary conditions
Authors: Mjolsness R. C.
Published: March 2003

For free boundary conditions a shear layer with linear velocity profile supports irrotational disturbances, one mode being unstable when its wavelength λ≳2.619 times the thickness h of the shear layer. For long wavelengths the dispersion relation of the mode approaches the Kelvin–Helmholtz form.
New two-pole approximation for the plasma dispersion function Z
Authors: Martín Pablo , González Miguel Angel
Published: March 2003

A new two-pole approximation for the plasma dispersion function Z (s) is obtained by a modified Padé (1/2) approximant. It gives a better agreement than the known two-pole approximation. It also has the advantage that the same poles are used for Z (s) and its derivative Z′ (s).
Electron density measurement using the Stark profiles of AlXII lines
Authors: Datla R. U. , Griem Hans R.
Published: March 2003

Single shot photographic spectra of helium-like resonance lines of AlXII were obtained from a low inductance vacuum spark. The space- and time-averaged electron density determined from the Stark profile analysis of the 1s2−1s4p, 1s2−1s5p, and 1s2−1s6p singlet lines is 4×1021–7×1021 cm−3.
Location of the eddy viscosity maximum in smooth pipe flow
Authors: Neumann J.
Published: March 2003

Nikuradse found from his measurements of turbulent flow in smooth pipes that the eddy viscosity maximum occurs midway between the pipe wall and the center line. It is shown that a velocity-defect law for a similar flow leads to the same result.
Resistive drift-Alfvén waves in sheared magnetic fields
Authors: Catto Peter J. , Rosenbluth Marshall N. , Tsang K. T.
Published: March 2003

A new class of resistive drift-Alfvén modes is discovered. The new modes are believed to be the generalization of shear-Alfvén waves to sheared magnetic fields. In addition, the finite β (plasma over magnetic pressure) corrections to the electrostatic dissipative drift wave are evaluated.
Current-driven drift modes in sheared magnetic field
Authors: Gladd N. T. , Liu C. S.
Published: March 2003

The radial eigenmode problem for current-driven drift modes in a plasma slab with sheared magnetic field is solved including the full electron dynamics and effects of electron temperature gradient and electron-ion collisions. Particular attention is given to the eigenmode structure and comparisons with the universal drift mode are made. The threshold current for the onset of current-driven drift mode is found to be close to that predicted by analytic theory and not greatly affected by electron temperature gradient or collisionality.
Fundamental radiative instability of accelerated plasmas
Authors: Buschauer Robert , Benford Gregory
Published: March 2003

Counterstreaming plasmas are well known to be electrostatically unstable and produce charge bunches. A single plasma moving along a curved trajectory is also electromagnetically unstable; i.e., a bunching perturbation is driven by the radiation fields. This relativistic instability is discussed and a physical picture of its origin is given. Calculations are made of when the instability can be quenched by a spread in velocities among the plasma particles. Laboratory relativistic beams rotating in a magnetic field are unstable to this mode, with growth times comparable to their cyclotron frequency, and only relatively large energy spreads Δγ/γ⩾0.2 will stabilize it. Recently observed coherent radiation may result from such bunching of beam electrons.
Velocity space ring-plasma instability, magnetized, Part II: Simulation
Authors: Lee Jae Koo , Birdsall C. K.
Published: March 2003

The ring-plasma instability arising due to two-energy component ions of a homogeneous plasma in a uniform magnetic field is studied through use of electrostatic and electromagnetic simulations, treating the ring ions as particles and the target plasma (ions and electrons) as linearized fluids. Simulation results verify very closely the predictions of the linear Vlasov theory and provide extensive information on nonlinear features such as beam spreading, slowing down, and saturation, some of which are in agreement with analytic explanations. This nonlinear evolution occurs before Coulomb collisions take place, and may be considered as the initial condition for Fokker–Planck calculations. The justification for using a linearized fluid is also discussed.
Energy flow and absorption along resonance cones near the lower hybrid
Authors: Grabbe Crockett L.
Published: March 2003

Macroscopic and microscopic forms of the energy conservation theorem for quasi-static waves are applied to determine the approximate power flux density and rate of energy absorption along the resonance cones near the lower hybrid resonance, both for the incoming cone and the outgoing converted ion thermal cone. It is found that for the incoming cone excited by a point gap source, there is almost as much power flux and absorption along each of the first few secondary peaks as along the main peak, so that the channel along which most of the energy flow and absorption occurs extends the width of several peaks of the cone. On the outgoing cone, the power flow and absorption is more concentrated on the main peaks than for the incoming cone. Nonlinear ponderomotive force effects are found to be more important, in general, for this cone than the incoming cone unless substantial absorption occurs in the mode conversion region. An asymptotic relationship is found connecting the power absorbed to the power flux and the spatial damping rate of the potential of the resonance cones.
Behavior of the three fluctuating velocity components in the wall region of a turbulent channel flow
Authors: Kreplin Hans-Peter , Eckelmann Helmut
Published: March 2003

Measurements of the three fluctuating components of the velocity and of the two components of the wall shear stress fluctuations have been made in a fully developed turbulent channel flow at Re=7700 using hot-film probes. These measurements include rms values, skewness and flatness factors, and probability density functions. Although the wall region is emphasized here, information for the whole channel half-width is also given.
Vorticity dynamics in spin-up from rest
Authors: Benton Edward R.
Published: March 2003

Impulsively started spin-up from an initial state of rest for incompressible fluid in a circular cylinder is examined from the viewpoint of the vorticity field. Existing theoretical models of this flow are thought to have implausible vorticity dynamics.
Transport coupling theory for multicomponent nonequilibrium chemically reacting boundary layers
Authors: Tambour Yoram
Published: March 2003

A general analysis of thermodynamic coupling effects in flames and other nonequilibrium gas-phase chemically reacting multicomponent boundary-layer flows is presented. Changes in characteristic diffusion time relative to characteristic reaction time due to thermal-diffusion, diffusion-thermo- and multicomponent-diffusion effects are considered and a new generalized gas-phase Damkohler number which encompasses these effects is defined. Using a transformed total enthalpy-concentration field and the newly defined Damkohler number, compressible laminar reacting boundary layers were analyzed and compared with other available analyses for simpler specific cases. The applicability of the present theory is demonstrated by new solutions for the problem of combustion of injected premixed fuel. Comparison between these results and uncoupled solutions reported in the literature indicate that thermodynamic coupling effects are significant, especially when Damkohler numbers are smaller than unity.
Neoclassical transport in plasmas containing ions with multiple charge states
Authors: Boley C. D. , Gelbard E. M. , Hirshman S. P.
Published: March 2003

It is shown that in the calculation of the Spitzer function and the Pfirsch–Schlüter transport coefficients for a multispecies tokamak plasma, a considerable analytic simplification occurs for the case of ions with multiple charge states. The number of coupled integrodifferential equations to be solved can be reduced from the total number of species (each charge state constitutes a distinct species) to the number of ions with different nuclei. The solutions are expressed in terms of quantities characterizing a system of interacting electrons and ion aggregates.
Cylindrical and spherical Korteweg–deVries solitary waves
Authors: Ko K. , Kuehl H. H.
Published: March 2003

Solitary wave solutions for the dimensionally modified Korteweg–deVries equation appropriate to symmetric ion acoustic waves in both cylindrical and spherical geometrics are presented. Expressions are given for the amplitude, velocity, width, and energy. The energy in the main body of the solitary wave continually decreases due to energy transfer to the trailing structure. The solutions are verified by comparison with a numerical integration of the differential equation.