bluuebunny/crossref_metadata_2025 huggingface dataset:
Spin-up from rest in a cylinder
Authors: Watkins William B. , Hussey R. G.
Published: March 2003

The problem of impulsive spin-up from rest of a fluid of kinematic viscosity ν in a closed cylindrical container is examined numerically and experimentally. The shape of the velocity profiles is found to depend upon a parameter α0=h (ν/Ω1/2/a2, where h is the height, a is the radius, and Ω is the angular speed of the container. When α0 is less than 0.005, the numerical profiles agree well with the solutions of Wedemeyer and Venezian, and the fractional spin-up time (the time to reach some fraction of solid body rotation) is proportional to h (ν/Ω)−1/2. When α0 is larger than 1, the numerical profiles agree well with the solution of the diffusion equation, and the fractional spin-up time is proportional to a2/ν. For intermediate values of α0, the numerical profiles agree well with experiment, and the dependence of the fractional spin-up time on Ω, ν, h, and a varies with α0, with radial position r, and with the dimensionless angular velocity W=v/rΩ, where v is the azimuthal velocity.
Slender streams with gravity: Outer asymptotic expansions. I
Authors: Geer James
Published: March 2003

A method is presented to determine the steady, three-dimensional, potential flow (neglecting surface tension) of a slender stream of fluid in the presence of gravity. Three basic flows are considered: jet flow (for which the bounding surface is entirely free); pipe flow (for which the bounding surface is entirely specified) and channel flow (for which the bounding surface is partially free and partially specified). The leading terms in the asymptotic expansions of these flows, which are called outer expansions, are presented. The leading terms in the pressure distribution for each of the three basic flows are also computed and several examples are presented.
Slender streams with gravity: Outer asymptotic expansions. II
Authors: Geer James
Published: March 2003

Higher order terms in the outer asymptotic expansions for flows of slender streams in the presence of gravity are computed. In particular, for the case of jet flow, higher order terms corresponding to a basic flow with either a circular or elliptical cross-sectional shape are discussed in detail and an inherent spatial instability (due to the effects of gravity) in the jet is discussed. Higher order terms for pipe flow and channel flow are also calculated and an example is presented. The pressure distribution within the flow is also computed and the effects of the pressure on the flow when a free surface is present is discussed.
Three-point method in the theory of homogeneous turbulence
Authors: Weinstock J.
Published: March 2003

A systematic method is presented, in some detail, for solving Navier–Stokes turbulence problems. This method is based on the use of a three-point (or triple) Green’s function G(3). A new set of covariant turbulence equations is thereby derived from the Navier–Stokes equation, without having to make any ad hoc assumptions; in fact, these equations simply constitute the first order terms of an expansion in a new ordering parameter R. The derived set of equations preserve Galilean invariance, and reduce to the direct-interaction approximation when certain definite terms are arbitrarily disregarded. It is the omission of these terms which is primarily responsible for the loss of Galilean invariance in several previous approximations. It is shown that random Galilean invariance is closely associated with a dependence of 〈G(3)〉 on the correlation length of the turbulence. A simple approximation is suggested which expresses 〈G(3)〉 in terms of a new (modified) single Green’s function. The modified Green’s function is random Galilean invariant, but does not involve an arbitrary constant as does the Green’s function used in the test-field model.
Continuum theory for the interaction of a weakly ionized gas with an emitting surface
Authors: Kalnavarns Juris , Bienkowski George
Published: March 2003

An asymptotic theory is formulated to describe the effects of surface electron emission on the behavior of a stationary, collision-dominated, weakly ionized gas in the vicinity of a spherical probe. Limits where an electron energy balance yields either constant or variable electron temperatures are examined. When the microscopic emission current is of the order of the product of the plasma random current and the small normalized sheath thickness associated with no emission and isothermal electrons, the theory, under certain restrictions, follows the corresponding no-emission formalism; the results, however, are different due to the altered surface boundary conditions. In particular, moderate emission can suppress the saturation behavior usually exhibited by the current-voltage characteristics at highly negative probe potentials. When the microscopic emission current is of the order of the plasma random current itself, even the overall structure of the flow field may exhibit significant variations. In the cold ion limit, at a given level of massive emission, the nonisothermal theory predicts a saturation of the electron current at highly negative probe potentials due to the divergence of the quasi-neutral potential drop, whereas the isothermal theory does not. When the ion and electron temperatures are of the same order of magnitude, the potential drop across the sheath becomes comparable to that across the quasi-neutral region.
Transport properties of a two-temperature argon plasma
Authors: Kannappan D. , Bose T. K.
Published: March 2003

Numerical computations have been performed using rigorous kinetic theory to determine the transport properties such as viscosity, thermal conductivity, electrical conductivity and electron diffusion coefficient, for an argon plasma at elevated electron temperatures (5000°K to 20 000°K) and pressures (10−3 atm to 103 atm) with the ratio of electron temperature to heavy particle temperature ranging from 1.0 to 3.0. The values for the transport properties for a plasma in thermal equilibrium could be obtained as a special case from the present scheme of calculations. Comparison with previous results for the special case of a plasma in thermal equilibrium shows good agreement.
Investigation of wave conversion in induced Thomson scattering
Authors: Johnston Shayne , Kulsrud Russell M.
Published: March 2003

The physics of induced Thomson scattering is studied for the general case of coherent fields. The analysis is purely classical. A direct evaluation of the radiation emitted by a resonant particle leads to a classical interpretation of the wave-conversion process. The relation between induced scattering and spontaneous scattering is discussed in classical terms.
Conduction heat loss scaling in open field line geometries
Authors: Chu T. K. , Johnson L. C.
Published: March 2003

A scaling law governing the cooling of a finite-length column due to electron thermal conduction loss at the column ends, where the magnetic field lines are intercepted by a cold material wall, is derived. In addition to the electron temperature, both the electron number density and the magnetic field strength are allowed to vary along the field lines. It is shown that the cooling of the column is not very sensitive to moderate spatial variations of number density and magnetic field strength and is well represented by a characteristic cooling time given by τ0= (5/2) nL2/K0, where L is the column half-length and n and K0 are the number density and coefficient of thermal conductivity at the midplane.
Experimental study of the structure of isotropic turbulence with intermediate range of Reynolds number
Authors: Ling S. C. , Saad Alice
Published: March 2003

The energetic isotropic turbulence generated by a waterfall of low head was found to be developed in part through the unstable two-phase flow of entrained air bubbles. The resulting turbulent field had a turbulent Reynolds number of ≳2×104 and maintained a self-similar structure throughout the decay period studied. The present study may provide some insight into the structure of turbulence produced by the breaking waves over the ocean.
Theory of thermal slip along the spherical surface of a binary mixture of gases
Authors: Yalamov Yu. I. , Yushkanov A. A.
Published: March 2003

The thermal slip of a binary mixture of gases along a spherical surface having a small curvature is studied. The Boltzmann equation with a model collision integral is used. The thermal slip coefficient obtained coincides with the result derived earlier in the limiting case of the thermal slip of the binary mixture along a flat surface.
Slow flow of a fluid carrying a uniform current past an arbitrarily conducting porous sphere
Authors: Swarup Shanti
Published: March 2003

The problem of an arbitrarily conducting porous sphere moving slowly through a current-carrying, incompressible, and viscous fluid is studied. The effect of permeability on the flow has been studied analytically at low Reynolds number by means of matched asymptotic expansions. The drag force up to order Re is reduced by a factor 1+K/2, K being the permeability associated with the porosity of the sphere. Further, the permeability as well as the current tend to increase the length of eddies behind the porous sphere.
Influence of strong inhomogeneities and magnetic shear on microstability properties of the Tormac sheath
Authors: Gladd N. T. , Goren Y. , Liu C. S. , Davidson R. C.
Published: March 2003

Microstability properties of the Tormac sheath are discussed with particular emphasis on the influence of strong inhomogeneities and magnetic shear on the lower-hybrid-drift and mirror-drift-cone instabilities. It is found that magnetic shear can completely stabilize the lower-hybrid-drift instability (Maxwellian ions), and lead to a reduction in growth rate of the mirror-drift-cone instability (loss-cone ions). The persistence of the mirror-drift-cone instability (at a reduced growth rate) in the presence of moderate magnetic shear suggests that the addition of a cold plasma component (as in the 2X-IIB mirror experiment) may be desirable to further reduce the instability growth rate and suppress the associated anomalous transport.
Stimulated scattering in a plasma filling an optical cavity
Authors: Meyer J. , Myra J. R.
Published: March 2003

Stimulated scattering processes in a homogeneous plasma inside an optical cavity are studied theoretically. In particular, attention is focused on the Raman and Brillouin instabilities. The coupled equations for the wave amplitudes are solved subject to optical cavity boundary conditions, and it is shown that for a wide range of plasma lengths and cavity mirror reflectivities, the threshold values for instability are approximately those for the temporal problem (waves uniform in space, growth or decay in time). Sample results are calculated numerically for the Raman instability in a typical laboratory plasma. Finally, the physical significance of these results is discussed.
Coherent scattering of CO2 light from ion-acoustic waves
Authors: Peratt A. L. , Watterson R. L. , Derfler H.
Published: March 2003

Scattering of laser radiation from ion-acoustic waves in a plasma is investigated analytically and experimentally. The formulation predicts a coherent component of the scattered power on a largely incoherent background spectrum when the acoustic analog of Bragg’s law and Doppler shift conditions are satisfied. The experiment consists of a hybrid CO2 laser system capable of either low power continuous wave or high power pulsed mode operation. A heterodyne light mixing scheme is used to detect the scattered power. The proportionality predicted by the theory is verified by scattering from externally excited acoustic and ion-acoustic waves; continuous wave and pulsed modes in each case. Measurement of the ion-acoustic dispersion relation by continuous wave scattering is also presented.
Interference with, and excitation of ion-acoustic waves by laser light
Authors: Peratt A. L. , Watterson R. L.
Published: March 2003

The effect of laser light having Gaussian spatial and temporal variations upon ion-acoustic waves is investigated analytically. At high power densities this light can interfere with coherent propagating waves in addition to exciting waves streamers which propagate away from the perturbed region at the ion sound velocity.
Multiple-bounce and snowplow model expansions of exploding plasmas
Authors: Albritton James R.
Published: March 2003

Multiple-bounce and snowplow models are employed to analyze the expansion dynamics of the interface separating exploding sheet and line mass plasmas from constant external pressure fields. The snowplow model is shown to be a successively poorer approximation to the multiple bounce when comparing systems of increasing total interface curvature; specifically, planar, cylindrical, and spherical systems are investigated.
Torque-free rotation of a cylinder
Authors: Wood W. W.
Published: March 2003

Steady two-dimensional flow between two eccentric rotating circular cylinders is considered. The angular speed of an inner cylinder subject to zero net viscous torque is determined for small eccentricities and small Ekman numbers.
Some effects of end stoppering on a theta-pinch plasma
Authors: Dixon R. H. , Elton R. C. , Griem Hans R.
Published: March 2003

Experimental data are presented indicating improved homogeneity and stability of the luminous plasma in a hard core ϑ-pinch device equipped with quartz end-stopper disks.
Reduction of particle end losses from linear magnetic fusion devices
Authors: Sinnott T. , Ahlborn Boye
Published: March 2003

A cold gas blanket of density ρ1 reduces the plasma outflow velocity u5 because of the inertia of the cold gas and the establishment of an internal ablation front by absorption of power W (watt/cm2). u5 is calculated as function of ρ1 and W.
Drift wave eigenmodes in a torus are not localized by shear
Authors: Ross David W. , Miner William H.
Published: March 2003

The radial equations for the poloidal Fourier components of a drift wave in a torus are solved by a numerical finite element method. It is shown that in the trapped electron regime the solutions are not localized by shear.
Envelope soliton of random phase waves
Authors: Hasegawa Akira
Published: March 2003

The shape of the envelope soliton of random phase waves, which is considered to have an arbitrary form, is obtained using moment equations of the wave kinetic equation.
Parametric instabilities in the presence of space-time random fluctuations
Authors: Laval G. , Pellat R. , Pesme D. , Ramani A. , Rosenbluth Marshall N. , Williams E. A.
Published: March 2003

The effect of a finite bandwidth driver or of turbulence on the parametric instability is considered. First, exact equations are obtained for special values of the group velocity of the fluctuations V0, with bandwidth modeled by a Kubo–Anderson process. Next, a method which enables one to deal with the space-time problem for arbitrary V0 is given. For the averaged amplitudes it reduces to the Bourret approximation and for the correlation function it gives the kinetic equation for random phase waves. Convective and absolute instability thresholds are given. It is found that for absolute instabilities the threshold obtained from the averaged intensities is lower than the one obtained from the averaged amplitudes.
Steady-state convection with melting at a boundary
Authors: Heard William B.
Published: March 2003

A fluid is heated from below and cooled from above in such a way that a frozen layer overlies a convecting layer. The lower boundary of the fluid is maintained at a constant temperature while the upper boundary of the ice transfers heat to an ambient atmosphere according to Newton’s law of cooling. The Boussinesq equations for convection are used in the mean field approximation and with a one-mode, two-dimensional representation to determine the steady state of the system in the limit of very large Rayleigh number. The fluid-ice interface is corrugated and is a free boundary of the problem. The convective steady states are likely to bifurcate discontinuously from the conductive steady states. Analytical and numerical results are given for the temperature at the upper boundary of the ice, the mean depth of the fluid, and the amplitude of the corrugations.
Unstable normal mode for Rayleigh–Taylor instability in viscous fluids
Authors: Menikoff R. , Mjolsness R. C. , Sharp D. H. , Zemach C.
Published: March 2003

The character of the growth rates of the normal modes for Rayleigh–Taylor instability of superposed incompressible, viscous fluids is analyzed in terms of appropriately scaled dimensionless parameters and a particularly simple representation of the Rayleigh–Taylor dispersion relation. The chief feature that emerges is that the scaled growth rate is remarkably insensitive to the values of fluid densities and viscosities. To within a few percent, the physical growth rate depends only on the surface tension, the density-weighted average viscosity, and the effective acceleration. Approximate formulae for the most unstable wavenumber and the corresponding maximum growth rate are given.
Stability of a liquid film with respect to initially finite three-dimensional disturbances
Authors: Lin S. P. , Krishna M. V. G.
Published: March 2003

The nonlinear stability of a viscous liquid film flowing steadily down an inclined plane is studied in the phase plane. Explicit expressions of the critical points of the governing differential system are obtained. The nature of the critical points and the integral curves corresponding to various flow parameters, initial conditions, and disturbance characteristics are determined numerically. Based on the phase plane analysis and the numerical results, the following conclusions are reached: The film which is unstable according to linear theory may be stable with respect to a finite three-dimensional disturbance if the initial amplitude and the side-band width are sufficiently small. The particular values of the initial amplitude and the side-band width beyond which the film becomes unstable depend on the relevant flow parameters. The film which is stable according to linear theory is also shown to be stable with respect to three-dimensional small finite amplitude disturbances with finite bandwidths.
Kinetic theory boundary conditions for discrete velocity gases
Authors: Gatignol R.
Published: March 2003

Boundary conditions are investigated for a model gas composed of identical particles with velocities restricted to a given finite set of vectors. A possible model of the gas surface interaction is given and an H theorem for a gas in a vessel is obtained. Then, the steady Couette flow between two parallel plates is studied. The model with four coplanar velocities is used and the velocity set has arbitrary orientation. The exact kinetic solution is compared with the solutions of the associated Navier–Stokes problems.
Saturation of the cyclotron decay instability
Authors: Sperling J. L.
Published: March 2003

The cyclotron decay instability results from the nonlinear interaction of a magnetosonic wave with two electrostatic ion-cyclotron waves in a multispecies plasma. A saturation mechanism for the instability is the nonlinear ion-cyclotron damping process involving the interaction of electrostatic ion-cyclotron and hydromagnetic-acoustic turbulence with a nonlinear plasma response near an ion-cyclotron frequency. Strong nonlinear ion heating can be a consequence of the saturation particularly if electron Landau damping is reduced by quasi-linear diffusion or trapping.
Collisional effects on trapped electron instabilities
Authors: Tsang K. T. , Callen J. D. , Catto P. J.
Published: March 2003

The effects of collisions on dissipative trapped electron instabilities are evaluated by distinguishing between the perpendicular and parallel electron velocity components when calculating trapped and untrapped electron contributions. The growth rate is obtained for all regimes of collisionality and reduces to previous results in appropriate limits. It is shown that the dominant effect of finite collisionality is to determine the number of trapped and untrapped electrons and that collisional broadening removes the resonant electron response only for collision frequencies greater than or equal to ten times the wave frequency, νe≳10ω. For such large νe/ω, ion-ion collisions are found to exert a far stronger stabilizing influence than broadening.
Effect of electron-ion collisions on the nonlinear state of the relativistic two-stream instability
Authors: Thode Lester E.
Published: March 2003

The analysis outlines conditions for the hydrodynamic interaction, including foil scattering and beam self-magnetic field effects. For the hydrodynamic interaction, the oblique coupling coefficient model is extended to include the effect of a finite electron-ion collision rate on the nonlinear state. Partial numerical simulation results are found to be in agreement with the model. Limitations due to temperature inhomogeneity along the deposition length and to increased deposition length are also discussed. It is found that an intense relativistic electron beam can couple its energy via the two-stream instability to a high density 1017–1020 cm−3 plasma. It is required that the plasma be fully ionized, with an initial electron temperature of ≳10 eV for 1017 cm−3, 10–20 eV for 1018 cm−3, 15–50 eV for 1019 cm−3, and ∼100 eV for 1020 cm−3.
Energy stability limit for rotation-modified plane Poiseuille flow
Authors: Jankowski Daniel F. , Squire David R.
Published: March 2003

The energy theory of hydrodynamic stability is applied to the flow between two parallel horizontal plates caused by a constant reduced pressure gradient in a system rotating about a vertical axis.
Entrance region heat transfer with axial conduction in a cylindrical tube: Constant wall heat flux
Authors: Barr B. J. , Wiginton C. L.
Published: March 2003

An analysis is made of the temperature profile for fully developed laminar flow in a circular duct with constant wall heat flux, considering axial conduction. A series solution is assumed and the resulting nonorthogonal eigenfunctions are used in two ways to determine the full series coefficients.
Exit region central source flow between finite closely spaced parallel co-rotating disks
Authors: Bogy D. B. , Fromm J. E. , Talke F. E.
Published: March 2003

Laminar source flow between co-rotating disks can often be adequately described by boundary layer equations. However, when the disk spacing and rotation speed are large (small Ekman number) and the source strength is small (small Rossby number), recirculation occurs near the edges of the disks and the boundary layer equations cannot correctly describe the flow there. The flow is studied in the vicinity of the disk edges for swirl Reynolds number of order 106 using approximate equations that are valid in a small region far from the rotation center. Numerical solutions are obtained by finite differences for three values of the Ekman number E and several values of the Rossby number ε. The Ekman numbers chosen give flows between the disks characterized by linearized theory, boundary layer theory, and rotating flow theory with Ekman layers.
Measurements in a wall jet over a convex surface
Authors: Alcaraz E. , Charnay G. , Mathieu J.
Published: March 2003

A plane wall jet over a convex surface with constant radius is studied experimentally. Classical and intermittent properties of the flow are analyzed. The distribution of the Reynolds shear stress is examined and the contributions of the two centers of turbulent production are emphasized, especially in the region where the mean velocity is a maximum. All the terms included in the turbulent kinetic energy budget and in the Reynolds stress equation are measured or evaluated. Two interfaces are considered: the first one located in the edge region of the jet, the second one in the inner part located in the vicinity of the ordinate where the velocity is a maximum. Also, two intermittency factors are determined. Accordingly, conditional mean velocities can be measured. Results indicate that the wall region seems strongly dependent on the jet region.
Application of photon correlation techniques to the measurement of flow with a sinusoidal perturbation
Authors: Barnes F. H. , Daudpota Q. I. , Greated C. A. , Grant I.
Published: March 2003

Application of the photon correlation technique to the measurement of sinusoidally perturbed fluid flows is described. An expression is derived for the shape of the count correlation function in terms of mean flow velocity and perturbation amplitude. Measurements have been made both in the wake behind a circular cylinder and with a mechanical flow simulator. These show that perturbation amplitudes can be measured by direct visual observation of the correlation displays. Maximum entropy transformation and curve fitting techniques are also described which produce results of higher accuracy.
Numerical modeling of the implosion heating experiment
Authors: Hamasaki S. , Krall N. A.
Published: March 2003

The results of a numerical modeling of the Los Alamos implosion heating experiment, based on self-consistent inclusion of turbulent effects is presented and the simulation results along with the experimental measurements are analyzed. The computer simulation shows very strikingly the mechanisms involved in the experimentally observed plasma motion. The structure of the density profile is explained and the implosion and diffusion of the magnetic field seen in the experiment are reproduced in the simulation.
Structure and scaling laws of laser-driven ablative implosions
Authors: Gitomer S. J. , Morse R. L. , Newberger B. S.
Published: March 2003

A stationary, spherical flow model gives the form of laser-driven ablation fronts and scaling laws for the dependence of implosion parameters on laser wavelength, pusher atomic number, and other input quantities.
Numerical simulations of one-dimensional solitons
Authors: Pereira N. R. , Sudan R. N. , Denavit J.
Published: March 2003

Numerical simulations of (i) the propagation and interactions of one-dimensional Langmuir solitons and (ii) their generation from random fluctuations by an external pump field are presented. The results of particle simulations are compared with computations based on Zakharov’s fluid model. Those computations establish that Langmuir solitons are reasonably long lived entities in one dimension and are accurately described by Zakharov’s equations, provided that resonant particle interactions are taken into account by the inclusion of a damping term. The power spectrum of the electron field fluctuations resulting from the generation of many solitons by an external pump field is compared with the theory of Kingsep, Rudakov, and Sudan.
Normal modes of a loss cone plasma slab with steep density gradient
Authors: Gerver M. J. , Birdsall C. K. , Langdon A. B. , Fuss D.
Published: March 2003

The electrostatic flute-like normal modes were found for a collisionless loss cone plasma in a uniform magnetic field with density varying sinusoidally in one direction in space. A local method, appropriate to kL≫1, where k is the wavenumber and L is the scale length, and a nonlocal method, appropriate to kL≲1, where both used; the ion Larmor radius ai was not assumed to be small. The usual drift cone mode was found when ai≪L; other instabilities were found for ai≳L. In principle, the methods could be applied to other configurations of plasma.
Shear stabilization of lower hybrid drift instabilities
Authors: Krall N. A.
Published: March 2003

Magnetic shear is shown to stabilize the lower hybrid drift wave when the shearing distance is Ls<Ln (ai/Ln+Ln/ai), where Ln≡dln n/dx is the density gradient scale length and ai is the ion gyroradius.
Non-Gaussian probability distributions for a vortex fluid
Authors: Lundgren T. S. , Pointin Y. B.
Published: March 2003

A system of N two-dimensional vortices interacting in a bounded region can be described by the statistics of the coordinates of the vortices or by the statistics of the Fourier coefficients of the vorticity field. It is shown that both descriptions give equivalent results. A high energy expression for the probability distribution function of the Fourier coefficients is derived and shown to be non-Gaussian; it has at least two, and in some cases a continuum of, equal height maximum points corresponding to distinct, but equally probable, equilibrium states. Other stationary points previously thought to be metastable states are shown to be saddle points of the distribution function and hence unstable.
Neoclassical transport of a multispecies toroidal plasma in various collisionality regimes
Authors: Hirshman S. P. , Sigmar D. J.
Published: March 2003

Continuously valid expressions for the neoclassical transport coefficients are analytically calculated for a multispecies plasma in the low to intermediate collision frequency regimes. The modification of the transport problem which results when a single heavy impurity ion species is in the collisional regime is presented. Consistent with the detailed balancing principle, a qualitative change in the magnitude of the long mean-free-path particle flux is shown to arise whenever there is more than a single collisionless species. A novel calculation of the bootstrap current permits the computation of a complete set of transport coefficients throughout the various collisionality regimes.
Influence of canonical angular momentum spread on the synchrotron radiation spectrum for a relativistic plasma
Authors: Tsakiris G. D. , Davidson R. C.
Published: March 2003

The influence of canonical angular momentum spread on the incoherent synchrotron radiation spectrum Il(ω) is calculated for a relativistic low-density (ω2p/ω2c≪1) plasma column that rotates about an axis of symmetry aligned parallel to a uniform magnetic field B0êz. The analysis is carried out for the class of spatially nonuniform Vlasov equilibria described by f0e(x,p) =const×F1(H/mc2)exp{−(Pϑ −P0)2/2Δ2}δ (pz), where P0 and Δ are positive constants, H is the energy, Pϑ is the canonical angular momentum, and pz is the axial momentum. A detailed parameter study is presented which shows that Il(ω) exhibits a sensitive dependence on canonical angular momentum spread Δ. For Δ=0, and smooth energy distribution F1(H/mc2), the lth harmonic spectrum Il(ω) is characterized by a sudden onset of emission for ω⩽lωc/γ0, where ωc=eB0/mc and γ20=1+2ωcP0/mc2. For sufficiently large Δ, however, there is a continuous onset of emission for ω⩽lωc. The analysis also reveals a strong dependence of electron density profile ne0(r) on canonical angular momentum spread Δ. In particular, small Δ corresponds to a hollow beam equilibrium, whereas sufficiently large Δ corresponds to an electron density profile peaked on axis.
Electrostatic ion cyclotron instabilities driven by parallel ion beam injection
Authors: Yamada M. , Seiler S. , Hendel H. W. , Ikezi H.
Published: March 2003

The detailed identification of two instabilities driven by an ion beam injected parallel to the confining magnetic field, a resonant ion cyclotron instability, and a nonresonant ion cyclotron drift wave driven by the density gradient of the beam, is reported. Experimental results are in good agreement with numerical calculations based on the kinetic Vlasov equations. Quasi-linear velocity space diffusion of the beam ions by wave-particle interaction is observed, demonstrating enhanced energy transfer. The relevancy of these results to tokamak neutral beam injection heating is discussed.
Parametric interactions in an inhomogeneous medium of finite extent with abrupt boundaries
Authors: Chambers Frank W. , Bers Abraham
Published: March 2003

The exact analytic forms of the dispersion relation and the spatial normal mode patterns for the one-dimensional parametric interaction in an inhomogeneous medium of finite extent are derived, and the results of calculations based upon them are displayed. The unstable modes that persist when the finite extent of the interaction region is increased are shown to be localized near the abrupt boundaries of the region. These localized modes exist even when only one abrupt boundary is present. The significance of the growing normal modes in a finite length interaction is evaluated in relation to the saturated growth that is found when the interaction length is unbounded.
Laminar-flow equilibria and limiting currents in magnetically focused relativistic beams
Authors: Reiser M.
Published: March 2003

A self-consistent theory of laminar-flow equilibria in magnetically focused relativistic beams propagating inside a conducting tube that confines both the electric and the magnetic self-fields is presented. In the differential equations describing the equilibrium state, the canonical angular momentum, pϑ, defined by conditions at the source, uniquely determines the possible solutions. Three cases, pϑ=0 (magnetically shielded source), pϑ=const (hollow beam with immersed source), and pϑ∝r2 (solid beam with immersed source) are discussed. The case pϑ=0 is examined in some detail and an exact analytical expression for the limiting current is derived, which is compared with approximate formulae reported in the literature. It is shown that higher currents can be achieved by injecting the beam from a magnetically shielded source as compared with an immersed source.
Vlasov equilibria of cylindrical relativistic electron beams of arbitrary high intensity
Authors: Gratreau P. , Giupponi P.
Published: March 2003

Self-consistent equilibria of cylindrical beams are studied in the Vlasov framework with the assumption of a uniform canonical axial momentum for the particles. The study is restricted to beams of circular cross section without azimuthal currents, but not necessarily without axial magnetic field. Attention is focused on beams with intensities much higher than Alfvén’s limit, which are shown to progress slowly along the axis and to flow predominantly in their external sheath.
Plasma heating with a rotating relativistic electron beam. I. Return current processes
Authors: Molvig Kim , Rostoker Norman
Published: March 2003

An advantageous configuration for plasma heating with a relativistic beam utilizes an annular beam rotating about a guide magnetic field. The return current processes for such a configuration are considered. For the parameters expected to prevail in an experiment, the plasma response can be described as magnetic diffusion or critically damped magnetosonic waves, these being equivalent. Equations for the axial and angular return currents are derived and take the form of decoupled diffusion equations. The effects of pulse shape, boundary conditions, etc. are then treated. The drag force on the beam resulting from the interaction is greatly enhanced and leads to a stopping length reduction by the factor (1/2)(v∥/c)3 as compared with nonrotating beams. The implications of these effects for a plasma heating application are discussed.
Plasma heating with a rotating relativistic electron beam. II. Magnetosonic wave emission
Authors: Molvig Kim , Rostoker Norman
Published: March 2003

The magnetosonic wave emission by an intense relativistic electron beam rotating within a plasma is calculated. This process follows the trapping of the beam in the plasma, and results in a transfer of approximately half the beam energy to the plasma ions. A nonlinear theory is given in accord with beam and plasma parameters of fusion interest. It is shown that dissipation balances the nonlinearity to produce a shock-type flow resembling that of the linear theory. The primary nonlinear modification is an adjustment of the wave speed to vs=vAMs, where v2A =B20/4πnmi and Ms=1+B̃/B0 is the mach number (B̃ is the wave field, B0 is the applied field). Estimates are made of power radiated to the waves and the resultant ion energies for some typical experimental parameters.
Oscillation modes of a laser-produced plasma expanding into a uniform magnetic field
Authors: Chang C. T. , Hashmi M.
Published: March 2003

The oscillation mode of a laser-produced plasma expanding into a uniform transverse magnetic field is seen to depend on the similarity parameter, N= (8πρ0)1/2U0/B0.
Stimulated Compton scattering of electromagnetic waves off plasma ions
Authors: Lin A. T. , Dawson J. M.
Published: March 2003

The threshold and growth rate for backscattering processes in which electromagnetic waves are backscattered off bunches of plasma ions are given. Multiple backscattering processes are observed in computer simulations as the saturation mechanism of the instability.
Reynolds stress and joint probability density distributions in the u-v plane of a turbulent channel flow
Authors: Wallace James M. , Brodkey Robert S.
Published: March 2003

The joint probability density distributions, p (u,v), of the u and v turbulence components are presented for nine positions across a fully developed turbulent channel flow. These distributions were determined by using 512 000 pairs of u and v values at each position and thus enable comparison of the relative character between the distributions. To show the contribution to the Reynolds stress, −ρuv̄ at each point in the u-v plane, the distributions of uv p (u,v) were determined. These distributions show the relative contributions to uv̄ as a function of position across the channel. Finally, the distributions of p (u,v) are compared with those of uv p (u,v). The most probable pairs of velocities do not produce the largest contribution to uv̄.
Rayleigh–Taylor modes in constant-density incompressible fluids accelerated by radiation pressure
Authors: Krolik Julian H.
Published: March 2003

The behavior of linear perturbations in an incompressible fluid undergoing acceleration by radiation pressure is examined. A general formalism is developed, and explicit results are given for several examples in which the equilibrium density is a constant. In that case, the sign of the derivative of the local radiative acceleration by the optical depth determines the stability of the short wavelength normal modes. Long wavelength perturbations can be overstable independent of the shorter wavelength behavior. When an external gravity is introduced, a transition, continuous in the strength of that external gravity, back to the ordinary Rayleigh–Taylor instability appears.
Linearized gyro-kinetic equation with collisions
Authors: Catto P. J. , Tsang K. T.
Published: March 2003

A like particle collision operator is derived for arbitrary values of the product of poloidal wavenumber times gyroradius by employing an ordering in which gyroradius corrections are retained in lowest order and the radial dependence appropriate for sheared magnetic fields is included. In addition, neoclassical, drift, finite β (plasma pressure/magnetic pressure), and unperturbed toroidal electric field modifications are considered.
Generation of coherent Cerenkov radiation with an intense relativistic electron beam
Authors: Walsh J. E. , Marshall T. C. , Schlesinger S. P.
Published: March 2003

Theoretical predictions and preliminary experimental results for a microwave source consisting of a dielectric loaded waveguide and an intense relativistic electron beam are compared.
Spectroscopic observations of internal disruptions and m=1 oscillations in Doublet IIA
Authors: Brooks Neil H.
Published: March 2003

Sawtooth-like oscillations in the line emission of impurity ions have been observed on Doublet IIA which agree in phase and frequency with fluctuations in the soft x-ray signal caused by internal disruptions.
Induced wave scattering at low phase velocities
Authors: Choi Duk-In , Horton Wendell
Published: March 2003

By considering the induced wave scattering of low phase velocity waves, the breakdown point of the small amplitude expansion forming the basis of weak turbulence theory is investigated in detail. A possible observation of the transition point from the weak turbulence theory to the renormalized turbulence theory by comparing the calculation and the particle simulation is suggested.
One- and two-species equilibria for magnetic insulation in coaxial geometry
Authors: Bergeron Kenneth D.
Published: March 2003

A cold-fluid, self-consistent model of electron and ion flow in coaxial cylindrical geometries is applied to the problem of magnetically insulated diodes. The one species, nonrelativistic problem is studied to determine in what configurations and parameter domains equilibria corresponding to magnetic insulation exist. It is proved that when the outer electrode is the cathode, equilibria always exist. For an inner cathode, whether or not equilibria exist and whether they are unique depends on whether the field is azimuthal or longitudinal and on the ratio of the radii. The two-species relativistic problem is then analyzed with the help of a computational routine which integrates the cold-fluid differential equations and searches the parameter space for the point corresponding to space charge limited emission. As the critical field is approached from above, the resulting values of ion current show an enhancement over the single species prediction by a factor which increases with voltage and with anode radius. Patterns of nonexistence of equilibria similar to those observed for the one-species, nonrelativistic case are also found.
Growth of streamwise vorticity in unstable boundary layers
Authors: Nelson G. , Craik A. D. D.
Published: March 2003

The Lin–Benney mechanism for generation of secondary flow is reconsidered for the case of interaction among waves of equal frequency but differing downstream wavenumbers. This complements recent work of Antar and Collins.
Local equilibrium solutions for a stress-transport turbulence model
Authors: Naot D.
Published: March 2003

Local equilibrium solutions for a stress-transport turbulence model are given for the general case of turbulent plane flow. Turbulence is assumed to be in local equilibrium where the production balances the dissipation. The three-dimensional fluctuations are induced by a two-dimensional mean flow. The solution specifies the principal Reynolds stresses as well as the principal coordinate system as functions of the model coefficients and the mean velocity gradients. A hypothesis of a maximum third invariant is made and used to derive the model coefficients. A possible application of the solution as boundary conditions for the calculation of developing boundary layers is also outlined.
Multiphase mechanics of single component two-phase flow
Authors: Soo S. L.
Published: March 2003

When treating a two-phase system, the need to account for the fact that the phases of the mixture sharing the same space are mutually exclusive gives rise to the formulation with each phase following its own center-of-mass frame of reference together with inertial coupling. The lack of detailed knowledge of the virtual mass effect limits the formulation to a dilute suspension of the disconnected phase. The significance of the inertial coupling term due to the choice of frame of reference is noted.
Resonance cones in a warm magnetized bounded plasma
Authors: Grabbe Crockett L.
Published: March 2003

The resonance cone structure in a warm bounded slab magnetoplasma has been obtained in the electrostatic approximation for small electron and ion temperatures and a large magnetic field. It is found that the conducting boundaries act as perfect mirrors as in the cold plasma case; the cones reflect off the boundaries without any distortion of shape. The thermal effects produce the shifting of the maximum of the potential and the appearance of an interference structure inside each cone as in unbounded plasma theory. The amount of the shift is a uniformly increasing function of the axial distance from the source of each cone, while the spatial frequency is a uniformly decreasing function of that distance. Because of the spreading, there is significant interference between nearby cones, so the total potential is more complicated than in the unbounded case. The solution is first obtained for a homogeneous plasma and studied, and then extended to the inhomogeneous plasma. The effects of Landau and collisional damping are included.
Study of trapped electron instabilities driven by magnetic curvature drifts
Authors: Ross David W. , Tang W. M. , Adam J. C.
Published: March 2003

The trapped electron instability in tokamaks is investigated numerically for a range of physical parameters in which the large aspect ratio expansion is not valid. The frequency and growth rate are determined as functions of ε=r/R, εt= (R dlnTe/dr)−1, ηe =dlnTe/dlnn, and b= (k⊥ρi)2/2. In particular, the relationship of the usual drift wave, driven by trapped electron Landau resonances or collisions, to a nonresonant mode described by Coppi and Rewoldt is studied. It is verified that the latter, on the one hand, is obtained as a continuation of the former to large b, and, on the other hand, has a qualitatively different behavior. For sufficiently small εt, and for normal density gradients (ηe⩾0), the mode can reverse and propagate in the ion diamagnetic direction. Explicit criteria for this to happen are derived, and the scaling of the resulting growth rates for large b is obtained. In the collisionless limit, these nonresonant growth rates can exceed those of the usual drift waves. It is therefore necessary to consider the effects of collisions, particularly those of the ions, whose effect increases as νib. By means of a simple model, it is shown that the electron collisions have a small damping effect, which cannot stabilize the large b modes. The ion collisions can, however, reduce the growth rates of the large b modes below those of the drift waves. A criterion for this is derived and compared with the numerical results.
Induced gyroresonant emission of extraordinary mode radiation
Authors: Freund H. P. , Wu C. S.
Published: March 2003

Induced amplification of extraordinary-mode electromagnetic waves in a magnetized plasma is investigated. The analysis is performed for a plasma which consists of two components: a relatively dense species of thermal plasma and a diffuse population of suprathermal electrons characterized by a loss cone-type distribution. The excitation mechanism is primarily due to the interaction of the electromagnetic waves with the energetic electrons via the relativistic cyclotron resonance which arises because of the momentum dependence of the gyrofrequency. The present study is particularly concerned with waves propagating perpendicularly and nearly perpendicularly with respect to the external magnetic field, since it is expected that for these cases the cyclotron damping due to thermal electrons is vanishingly small and the growth rates are a maximum. The results indicate that excitation occurs primarily for frequencies near the first two gyroharmonics. Although the model under consideration is largely motivated by the study of planetary radio emissions, the physical mechanism is of interest in its own right.
Time and space resolved neutron measurements on a dense plasma focus
Authors: Pecorella F. , Samuelli M. , Messina A. , Strangio C.
Published: March 2003

The time and space resolved neutron emission from a Filippov type dense plasma focus is measured with scintillation detectors associated with collimators, giving a one or two dimensional resolution. Axial and radial neutron emission distributions are obtained. Arguments are presented for the existence of two mechanisms producing the main neturon yield that takes place 100 nsec after the maximum compression. The former, belonging to a thermonuclear plasma (ne=3×1017 cm−3, Ti=7−8 keV, V=20 cm3) located in a region between 1 and 3 cm above the anode, lasts for about 40 nsec and accounts for 70% of the main neutron emission. The latter, due to beam-target interactions, takes place mainly near the cathode wall and produces about 20% of the main neutron output. A third neutron emission, uniformly distributed along the axis of the machine, is also present, accounting for 10% of the main neutron yield.
Evolution of finite amplitude whistler wave
Authors: Shukla P. K. , Yu M. Y. , Tagare S. G.
Published: March 2003

The coupling of a large amplitude electron whistler wave with ion density perturbations is considered. It is shown that this coupling leads to the formation of supersonic whistler solitons. The properties and existence criteria of the latter are discussed in detail.