bluuebunny/crossref_metadata_2025 huggingface dataset:
Stability of an unneutralized rigidly rotating electron beam
Authors: Wong H. Vernon , Sloan M. Lee , Thompson James R. , Drobot Adam T.
Published: February 2004

An unneutralized rigidly rotating electron beam is absolutely stable if the distribution function is a monotonically decreasing function of H0 −ωLLz and if (ρBωl/c) < 1, where HO and Lz are the single-particle energy and canonical angular momentum, ωL is the angular velocity, and ρB is the radius of an enclosing infinitely conducting cylindrical wall.
Hollow equilibrium and stability of a relativistic electron beam propagating in a preionized channel
Authors: Lee Edward P. , Pearlstein L. D.
Published: February 2004

A short pulse of relativistic electrons propagating along a preionized channel of high conductivity may assume a hollow equilibrium profile as a result of induced plasma currents. In this configuration the pulse is neutrally stable with respect to lateral expulsion from the channel by the induced currents. The properties of a thin hollow shell equilibrium are derived.
Occurrence of high-energy electrons and surface expansion in laser-heated target plasmas
Authors: Morse R. L. , Nielson C. W.
Published: February 2004

It is shown that limitations on collisionless electron thermal conduction place a lower limit on the range of energies of electrons in the surface of target plasmas which are heated by incident electromagnetic radiation, and that in cases of contemporary experimental interest these energies can be hundreds of keV. It is then shown that these high-energy electrons can cause a much faster expansion of plasma from the heated surface than would be predicted by a single fluid theory. Numerical simulations demonstrate both effects.
Parametric interactions among plasma waves propagating along a static magnetic field
Authors: Stone F. T. , Serafim P. E. , Levi E.
Published: February 2004

Parametric interactions among plasma waves propagating along an applied dc magnetic field are examined. The driving mechanism consists of either an ac electric field impressed transversely to the applied magnetic field, or bunches of particles injected with preferential phase. The physical system is composed of a (possibly infinite) number of cold beams. The equations are linearized with the effect of the induced first-order magnetic field included throughout. Six absolute instabilities are found to result from the coupling between two electronic modes of a cold plasma and three more result from a coupling between an electronic mode and the ion cyclotron branch. The extension to temperate plasmas is indicated. The instabilities become important in systems with high transverse velocity ν0⊥, since the growth rates calculated from coupling of modes go as ν0⊥/c or ν0⊥2/c2. These interactions may find application to fusion and microwave devices. In particular, those with the ions may be useful as energy transfer mechanisms.
Ratio of Reynolds shear stress to turbulence kinetic energy in a boundary layer
Authors: Rose William C. , Murphy John D.
Published: February 2004

Experimental values of the ratio of Reynolds shear stress to turbulence kinetic energy for a compressible boundary layer are presented. This ratio, for nonequilibrium compressible flows, is shown to be near the value of 0.15 obtained in equilibrium, incompressible flows.
Cylindrical Poiseuille flow and thermal creep of a rarefied gas
Authors: Kanki Tatsuo , Iuchi Satoru
Published: February 2004

The rarefied gas flow in a circular tube whose wall is nonuniform in temperature is analyzed using the Maxwell moment method, with special reference to thermal creep. The results obtained are in fair agreement with both Sone and Yamamoto's and the calculations worked out at the low Knudsen number by the elementary kinetic theory of gases.
Fluid motion caused by conical currents
Authors: Narain Jai Prakash , Uberoi Mahinder S.
Published: February 2004

Exact analytical solution for motion of an incompressible inviscid fluid and numerical solutions for viscous fluid flow caused by conical flow of current are given. Breakdown of viscous solutions at a critical value of current parameter depending on cone angle is discussed.
High-frequency conductivity of a magnetoplasma
Authors: Pytte A. , Baird A. M.
Published: February 2004

The conductivity is calculated with a convergent method requiring no cutoffs. The close collisions are treated quantum mechanically.
Negative pressure effect on the ordinary mode
Authors: Nambu Mitsuhiro
Published: February 2004

Based on the linearized Vlasov-Maxwell equations, it is found that, without macroscopic current, the ordinary mode instability can occur with the negative pressure of the electrons. These electrons reduce the critical number density of hot electrons for the onset of instability.
Inability of electron trapping to stabilize the ion acoustic instability
Authors: Manheimer Wallace M.
Published: February 2004

It is shown that electron trapping does not stabilize the ion acoustic instability in an unmagnetized two- or three-dimensional plasma. Specifically, it is shown that for nearly all resonant particles, the correlation time is much less than the trapping time.
Electromagnetic ion streaming instability
Authors: Vithal K. L. , Tandon J. N.
Published: February 2004

The instability of electromagnetic linearly polarized waves is discussed for a system composed of two identical counterstreaming ion beams in a uniform background of relatively stationary electrons.
Ion containment in axisymmetric mirrors in the presence of fluctuating electric fields
Authors: Catto Peter J.
Published: February 2004

A set of equations and resulting constraints are derived for ions contained in an axisymmetric mirror in the presence of a fluctuating electric field. These are in agreement with previous slab geometry results which imply that a confined distribution of particles still exists.
Theory of electron distributions for small field cancellation in the quiescent E layer of the astron
Authors: Humphries Stanley
Published: February 2004

A theory appropriate to the description of the stable astron E layer in experiments up to the present time is developed. When field cancellation is small and it can be assumed that the E layer is perturbed by collisions with a uniform background neutral gas, it is shown the axial and radial distributions are described by simple cylindrical diffusion equaitons. The model predicts loss rates of the E layer as well as self-consistent radial and axial density profiles.
Transport and particle scattering due to toroidal plasma modes
Authors: Coppi Bruno , Minardi Ettore
Published: February 2004

Electrostatic modes are shown to be excited, in two-dimensional plasma equilibrium configurations, with frequency and parity characteristics such as to significantly affect the orbits of trapped ions by proper mode-particle resonances in regimes where the single-particle collision mean free paths are considerably longer than the periodic particle excursions. In particular, new modes driven by the ion temperature gradient are shown to become unstable in the presence of trapped particles under less restrictive conditions and with considerably larger transverse wavelengths than the ion temperature gradient driven modes arising in a one-dimensional equilibrium configuration. The resulting enhancement in the transport of ion thermal energy across the magnetic field is discussed.
Electrostatic waves in a nonuniform plasma
Authors: Peratt A. L.
Published: February 2004

Approximate expressions describing the Tonks-Dattner and Buchsbaum-Hasegawa resonances (at the second electron cyclotron harmonic) in a warm nonuniform plasma are derived by means of a fairly easy analytic continuation technique. Connection formulas are developed for third-order electric field differential equations derived from kinetic theories and show the coupling of slow and fast waves in the vicinity of a linear turning point. The relatively simple field expressions predict traveling longitudinal waves possessing outwardly directed phase velocities. Internal plasma fields appreciably larger than the excitation field are found when the density nonuniformity supports even mode resonances. The field equations and expressions for the associated impedance variation are compared to numerical integration solutions and show striking similarity to experimental observations.
Low-frequency flute instabilities of a hollow cathode arc discharge: Theory and experiment
Authors: Ilić D. B. , Rognlien T. D. , Self S. A. , Crawford F. W.
Published: February 2004

The characteristics of two low-frequency electrostatic flute instabilities of a low-pressure hollow cathode arc discharge are reported. Mode I has azimuthal mode number m = 1, and occurs when the radial electric field is negative (directed inward) while mode II has m = −1 and occurs when the field is positive. The radial electric field is controlled by varying the potential of a secondary anode cylinder located close to the outer discharge radius. A linear perturbation analysis, based on the two-fluid equations, is given for a low-β, collisionless, cylindrical plasma column, immersed in a uniform axial magnetic field, having a Gaussian density profile and an arbitrary radial electric field profile. Reasonable correlation between theory and experiment is demonstrated for both modes, by comparing the calculated and measured frequencies, mode numbers, and also the eigenfunctions of the density and potential fluctuations. The instabilities are basically centrifugal flute modes, driven by E × B drift in the presence of a density gradient and modified by the velocity shear due to nonuniform E × B rotation.
Low-frequency hydromagnetic kink mode of a relativistic beam
Authors: Lee Edward P.
Published: February 2004

An analysis of the stability of the kink mode of a relativistic charged-particle beam propagating in a toroidally confined plasma is presented. The essential feature is the treatment of the beam as a distinct component of the system having finite velocity and inertia in addition to its current. To simplify the analysis, the plasma background is assumed to be a pressureless, uniform fluid obeying the laws of perfect magnetohydrodynamics while the beam is treated as a cold, rigid body. To simulate toroidal geometry, periodic boundary conditions are imposed in the axial direction of a straight, cylindrical volume. The walls of the cylinder have perfect conductivity. A strong solenoidal field is externally imposed, but the beam is the only source of the poloidal field. It is found that a modification of the stability condition of Kruskal and Shafranov applies; the onset of instability corresponds to the appearance of closed particle orbits rather than the more severe condition of closed field lines. The maximum rotational transform consistent with stability is ι/ 2π = 1 + (βz γmc2) / (e R 0 Bz).
Direct nonlinear coupling of electromagnetic waves and electrostatic waves in a plasma: experiment
Authors: Phelps David , Van Hoven Gerard , Rynn Nathan
Published: February 2004

Observations of direct nonlinear coupling between electromagnetic waves and electrostatic waves in the bulk volume of a plasma are reported and compared with the predictions of an accompanying physical theory. The experimental configuration consists of a cylindrical resonant cavity partially filled with a coaxial Q -machine plasma column. Experimental verification of the predicted interaction resonances is presented. The finite interaction length defined by the cavity modifies the theoretical wave number selection rule, imparting a “lineshape” to the resonance which is consistent with observations. Two of the three interacting waves are externally excited and their interaction causes a third wave to grow with distance. The direction of growth depends upon the resonance conditions and choice of excitation, while the rate of growth depends upon the pump level, coupling strength, and linear wave damping. Indirect measurements of the mode power levels are presented which verify in magnitude the theoretically predicted coupling.
Electrostatic instabilities driven by velocity gradients
Authors: Hirose A. , Alexeff I.
Published: February 2004

It is shown that cross-field gradients of guiding-center drift velocities can excite several high-frequency (ω > ωci ) electrostatic instabilities. The instabilities can enhance effective interelectron and/or electron-ion collisions which in turn destory the velocity gradients. In pulsed, turbulent heating experiments, this effect is expected to appear as anomalously rapid current penetration (anomalous skin effect).
Laminar interactions in high Mach number plasma flows
Authors: Clark R. W. , Denavit J. , Papadopoulos K.
Published: February 2004

The laminar interaction of counterstreaming plasmas in the presence of a magnetic field was studied by numerical simulation. The model is one-dimensional and is based on the Vlasov equation with straight orbits for ions (Ωi t ≪ 1). Electrons are treated as a massless, zero-termperature fluid maintaining charge neutrality with the ions, and a finite resistivity is assumed. Magnetic field and density profiles are determined for different Mach numbers, density ratios, and resistivities. Effects of various finite initial density profiles in the streaming plasma are investigated. The distribution function is examined to determine whether microinstabilities would develop in a turbulent model. The relevance of these results to the formation of magnetic pistons is discussed.
Oscillation center quasilinear theory
Authors: Dewar R. L.
Published: February 2004

A new formulation of the quasilinear theory of weakly turbulent plasmas is presented, which explicitly separates resonant and nonresonant wave-particle interactions from the outset. This is achieved by making a canonical transformation to “oscillation center variables” before attempting to solve the Vlasov equation. A systematic method of constructing the generating function to any order in the wave amplitude is presented, based on a variant of Hamilton-Jacobi perturbation theory. Momentum and energy split naturally into a wave and a particle component. The results are generalized to apply to weakly inhomogeneous plasmas, and verified by demonstrating momentum and energy conservation.
Toroidal effects on magnetohydrodynamic modes in tokamaks
Authors: Frieman E. A. , Greene J. M. , Johnson J. L. , Weimer K. E.
Published: February 2004

In order to investigate the effect of toroidal curvature on magnetohydrodynamic modes in tokamak configurations, stability criteria are derived by means of an expansion in the inverse aspect ratio. For a low-pressure system, βθ ∼ 1, with a nearly constant safety factor, q = qa(0) + …, the well known stability criterion for kink modes, relating qa to the ratio a / b of the plasma radius to that of a conducting wall, is determined in second order. Here, it is shown that toroidal effects modify this criterion favorably in fourth order when the vacuum region does not extend too far. Typically, it is found that improvement is achieved when b / a is less than 1.25 to 1.5. Interchange and ballooning effects are incorporated in the stability criteria.
Role of spontaneous magnetic fields in a laser-created deuterium plasma
Authors: Chase J. B. , LeBlanc J. M. , Wilson J. R.
Published: February 2004

Using numerical simulation, it was found that, with the inclusion of thermally-generated magnetic fields, about 3 × 104 neutrons are produced in 2 nsec and the electron temperature rose as high as 15 keV in a target heated by a 4-nsec, 80-J laser pulse.
Relating one-point concentration moments of a chemical reactant to the Lagrangian probability density
Authors: Riley James J.
Published: February 2004

Arbitrary one-point moments of the concentration of the chemical reactant in a turbulent flow are related to the Lagrangian position probability density. The results are extended to multicomponent reactions. Molecular diffusion effects are neglected in the analysis.
Temperature slip problem with arbitrary accommodation at the surface
Authors: Thomas J. R.
Published: February 2004

Elementary solutions for the linearized BGK model equation are used to calculate accurate values for the temperature slip coefficient with arbitrary accommodation at the surface. Results are compared to those of Loyalka and of Welander.
Effect of partial coherence on laser-driven plasma instabilities
Authors: Tamor S.
Published: February 2004

The two-fluid theory of laser-driven nonlinear plasma instabilities is reformulated to describe imperfectly coherent radiation. For a particular model of the laser noise, the modified dispersion relation is found and a simple estimate for the increase in stability threshold obtained.
Electrostatic surface modes of a toroidal plasma
Authors: Talmadge S. , Marshall T. C. , Schlesinger S. P.
Published: February 2004

A theoretical study has been made of the surface wave resonances of an electrostatic wave propagating on a plasma torus. These results are in satisfactory agreement with an experiment.
Collisional resistivity in low aspect ratio tori
Authors: Coppi B. , Sigmar D. J.
Published: February 2004

The electrical conductivity of a toroidal plasma in the long mean free path limit is evaluated for finite values of the aspect ratio by using physical arguments on the effect of trapped particles.
Determination of electron temperature of shock-heated plasma from microwave measurements
Authors: Singer A. , Minkowski J. M.
Published: February 2004

It is shown that the anomalous results reported for microwave measurements of electron temperature of shock-heated plasma in the range of Mach 9.7 to 10.4 were due to an incorrect model for relating the measured plasma parameters to the electron plasma temperature. A corrected model removes the anomaly.
Some exact solutions for the decay of streamwise vorticity
Authors: Sedney Raymond
Published: February 2004

A method of generating a class of exact solutions for three-dimensional boundary layer flows is presented. These are solutions to the initial value problem for steady, incompressible flow. In one type the history upstream of the initial plane is known; in a second type this history is not known. A power law pressure gradient exists in the streamwise direction but the cross flow decays under zero cross pressure gradient. The essential restriction for obtaining exact solutions is that all quantities not depend on the cross stream coordinate. The solutions are obtained as expansions in terms of eigenfunctions. The cross flow and the streamwise vorticity decay algebraically with powers that depend on the pressure gradient and eigenvalues. An S-shaped initial profile has a decay rate approximately twice as great as a C-shaped initial profile; the former requires a few hundred boundary thicknesses to decay appreciably. The decay rate is only mildly dependent on the streamwise pressure gradient. These results of physical interest in three-dimensional boundary layer flows are obtained without extensive numerical calculations.
Numerical investigation of unsteady boundary-layer separation
Authors: Telionis D. P. , Tsahalis D. Th. , Werle M. J.
Published: February 2004

A numerical scheme of integration is devised to integrate the unsteady laminar boundary-layer equations with partly reversed flows. The neighborhood of the vanishing skin friction which has been considered up to now as the location of separation, is found to be nonsingular while a typical Goldstein-type of a traveling singularity is discovered farther downstream. This singularity is interpreted according to the theory of Sears and Telionis as unsteady boundary-layer separation. The features of the flow in the neighborhood of the singularity are investigated.
Multipoint distribution calculation of the isotropic turbulent energy spectrum
Authors: Fox Ronald L.
Published: February 2004

A solution for the dynamical behavior of the energy spectrum for a homogeneous isotropic fluid is obtained from the equations for the turbulent multipoint distribution functions. The calculated spectrum shows reasonable agreement with experimental data.
Sound amplification from controlled excitation reactions
Authors: Bauer H.-J. , Bass H. E.
Published: February 2004

The possibility of acoustic amplification in a gas subjected to an external means of overpopulating internal energy levels has been explored theoretically. The basic concept that the temperature variation of the sound wave controls the flow of energy from the source to translation must take into account the internal structure of the gas. When the gas is pumped optically, the strong temperature dependence of the collisional de-excitation rate constants is included in addition to the temperature and pressure dependence of the optical absorption coefficient considered by others. The resulting attenuation or amplification of sound has been calculated both for a two-level and a multilevel gas. For illustrative purpose, a 90% CO-10% H2 numerical example has been developed. This example demonstrates that sound amplification should be experimentally observable.
Ion kinematics in a plasma focus
Authors: Gary S. Peter , Hohl Frank
Published: February 2004

The results of numerical integrations of three-dimensional equations of motion of ions subject to given electric and magnetic fields are presented. The fields represent those which may exist in the pinch phase of the plasma focus, although here they depend only on the radial coordinate. The ions initially have Maxwellian velocity distributions, and their trajectories are interpreted in terms of single-particle constants of the motion. Two models of the axial electric field Ez are considered. For strong Ez away from the axis, there is a cyclotron acceleration which leads to ion heating. For positive Ez on the axis, ions within a Larmor radius of the axis undergo very efficient acceleration; the results for this new model are in general agreement with experimental results.
Structure of turbulent line vortices
Authors: Saffman P. G.
Published: February 2004

A theory is given to explain the observed dependence on Reynolds number of the decay of turbulent line vortices. It is argued that the turbulent vortex has a triple structure. There is an outer region for r > r 1 (r1 is the radius of maximum tangential velocity) with a logarithmic distribution of circulation, and for r < r1 an inner region and viscous core in both of which the motion is close to solid body rotation. It is predicted that r1 ∼ (νΓ 1 t2)1/4, where Γ1 is the circulation at r1. Further, Γ1 /Γ0 is predicted to be a slowly decreasing function of Γ0/ν, where Γ0 is the strength of the vortex. The development of an overshoot of circulation in the outer region is discussed, and the axial velocities produced by growth of a trailing vortex are calculated.
Asymptotic analysis of turbulent channel flow for mean turbulent energy closures
Authors: Bush William B. , Fendell Francis E.
Published: February 2004

The Reynolds time-averaged equations are adopted for fully turbulent two-dimensional flow of an incompressible fluid through a channel with plane smooth walls. Closure is effected by means of so-called second-order methods based on the conservation of mean turbulent kinetic energy. In particular, generalizations of the turbulent shear flow models due to Bradshaw and co-workers and to Spalding and co-workers, are adopted as representative of recent differential closure models. The models are treated in the limit of large turbulent Reynolds number by means of limit-process expansions. The principal division of the flow is into a relatively thick defect layer near the center of the channel (in which the channel half-width characterizes the layer thickness, the velocity may be linearized about its centerline speed, and the Reynolds stress dominates the Newtonian stress to lowest order), and the relatively thin viscous sublayer near the wall (in which a viscous length scale is appropriate, the velocity is small relative to the centerline speed, and the Reynolds and Newtonian stresses are of comparable magnitude). Certain previously unnoticed constraints on the closure models are revealed by the analysis.
Some small scale properties of boundary layer turbulence
Authors: Antonia R. A.
Published: February 2004

The distributions across a smooth wall layer of the skewness and flatness factor of the first-order time derivatives of u and ν, the longitudinal and normal velocity fluctuations, respectively, and of uν, the Reynolds shear stress fluctuations, are compared with the corresponding distributions in a boundary layer over a rough wall. Both the smooth and rough wall boundary layers are nearly self-preserving under zero pressure gradient conditions. Although the probability density of the square of ∂u / ∂t, the time derivative of u, is reasonably represented by the log-normal distribution, the skewness and flatness factor of ∂u / ∂t in the inner region of the layers are found to remain approximately constant for a turbulence Reynolds number R λ range 150-450.
Experimental investigation of Rayleigh-Taylor instability
Authors: Ratafia M.
Published: February 2004

Taylor instability is investigated in a series of experimental runs at an Atwood number of 0.095 (density ratio of 1.22). The fluids used are octyl alcohol and water. The expected bubble and spike formation is observed, and, for the first time, the spike is seen to flatten and curl over due to Kelvin-Helmholtz instability. The results are compared with the analytical, numerical, and empirical findings of others.
Theory for radiatively driven harmonic acoustic waves in a confined gas
Authors: Chapman Gary T. , Compton Dale L. , Vincenti Walter G.
Published: February 2004

A detailed theoretical study is made of radiatively driven acoustic waves inside a closed cylindrical tube. The formulation accounts for all the essential phenomena for a gas in vibrational equilibrium—namely, gas motion, longitudinal and radial viscous dissipation, longitudinal and radial heat conduction, and radiative transfer with spectral detail included. An approximate expression is derived for the pressure response. This solution is applicable to arbitrary spectral distribution of the radiative absorption coefficient, under conditions attainable in the laboratory. The solution includes both tuned and untuned acoustic conditions as well as the spectrophone limit—that is, the condition where the length of the tube is much smaller than the length of the acoustic wave. The influence of spectral detail on the pressure response is illustrated by an example that employs a single Lorentz profile to represent an absorption band.
Experiments on radiatively driven harmonic acoustic waves in a confined gas
Authors: Compton Dale L. , Chapman Gary T. , Baganoff D.
Published: February 2004

Measurements are presented of the acoustic pressure resulting from the periodic absorption and emission of radiative energy by an infrared-active gas contained in a closed, cylindrical tube. The acoustic waves are generated by means of an external, sinusoidally time-modulated blackbody source. The pressure measurements are for both resonant and nonresonant conditions at acoustic frequencies from about 60 to 600 Hz. Comparison of the measurements with predictions shows that the response is due primarily to the modified-classical acoustic wave, but that a small contribution from the so-called radiation-induced wave can be measured in certain of the tests. Strong effects of vibrational nonequilibrium, similar to those observed previously in spectrophone studies, were found in some of the tests. Generally, the agreement between theory and experiment is satisfactory and provides verification of the basic physical and mathematical models of the theory.
Electron and ion momentum transfer from plasma electrical conductivity in a magnetic field
Authors: Albares D. J.
Published: February 2004

The electrical conductivity of a partially to strongly (Coulomb collision-dominated) ionized dc plasma in a dc magnetic field was investigated at low frequency by two experimental methods, one utilizing the Hall effect and the other a plasma interaction with an induced solenidal electric field. Electron-ion and electron-atom momentum transfer collision frequencies and ion mobility in the magnetic field (ion slip) were inferred. The helium abnormal negative glow plasma was used at pressures of 0.5 to 2.5 Torr, electron densities of 1 to 32 × 1017m−3 and temperature ≈ 600 °K; the magnetic field ranged up to 675 G. The data support Shkarofsky's theory of partial ionization. When ion motion becomes dominant, the resulting ion mobility is 75% larger that He+ mobility in helium taken from drift tube measurements. This disagreement suggests that further theoretical work on ion mobility in a plasma is needed.
New dispersion relation for a strongly magnetized degenerate electron plasma with anisotropic pressure
Authors: Canuto V. , Chou Chih Kang
Published: February 2004

A new dispersion relation for an unbounded degenerate electron plasma imbedded in a superstrong magnetic field is derived on the basis of the Canuto-Chiu equation of state. The properties of the various types of waves are discussed for two density regimes of astrophysical interest. Propagation parallel and perpendicular to the magnetic field are examined in detail.
Observation of the beam-plasma interaction below threshold
Authors: Conrad J. R. , Diaz C. J. , Walsh J. E.
Published: February 2004

The wave spectrum of longitudinal electrostatic fluctuations of a beam-plasma system has been studied in the regime below the threshold for exponentially growing waves. The observed wave spectrum consists of a series of triplets, one set for each natural mode of the magnetized, cylindrical, axially bounded plasma column. The lineshape and intensity of the triplets are in good agreement with a simple theory based on the linearized dispersion relation.
Observation of free-streaming electrons in plasmas
Authors: Kawai Y. , Nakamura Y. , Itoh T. , Kawabe T.
Published: February 2004

The excitation and propagation of electron waves in a plasma have been studied experimentally in a low-density and large-volume plasma. For frequencies larger than the electron Langmuir frequency, an electron plasma wave was observed which is predicted by the linear theory for a Maxwellian plasma. For smaller frequencies, free-streaming electron or ballistic signals are observed. For frequencies close to the electron Langmuir frequency, both the electron plasma wave and the free-streaming electron are excited and show interference patterns. These observations are compared with the theoretical predictions. The effect of a sheath formed around a transmitter on the free-streaming electron is also discussed.
Interference structure near the resonance cone
Authors: Kuehl H. H.
Published: February 2004

The interference structure near the resonance cone of an oscillating point charge in a warm magnetized plasma is investigated theoretically, using the quasistatic approximation and neglecting ion motion. Depending on the frequency and plasma parameters, the interference structure appears inside, outside, or on both sides of the resonance cone. For frequencies less than both the plasma and cyclotron frequencies, the structure lies inside the resonance cone except for frequencies near the cyclotron frequency where the amplitude is small because of cyclotron damping. For frequencies between the upper-hybrid frequency and the larger of the cyclotron and plasma frequencies, the structure lies outside the resonance cone provided the frequency and angle are sufficiently removed from the upper-hybrid frequency and 90°, respectively. A simple expression for the angular interference spacing is derived.
Equilibrium of a toroidal plasma inside two concentric conducting shells
Authors: Hosea J. C. , Bobeldijk C.
Published: February 2004

The equilibrium analysis appropriate to tokamak geometry is extended to the case of two conducting shells surrounding the plasma column: a thick outer shell generally used in tokamaks to equilibrate the plasma hoop and pressure forces and a thin inner shell corresponding to the vacuum vessel or liner. Analytic expressions are derived for selected cases to demonstrate the influence of βθ + l i/2 and Bv on the increment of displacement omitted by the thin casing solution for the outer shell under conditions for which the inner shell has no influence. For quickly changing equilibria, the inner shell (vessel) plays a significant role and its effect on the equilibrium position as well as on magnetic probe measurements of this position and βθ + li /2 are derived.
Hot-electron plasma in the levitated spherator
Authors: Okabayashi M. , Voitsenya V. , Ripin B. , Schmidt J. , Yoshikawa S.
Published: February 2004

In the hot-electron plasma experiment of the levitated spherator, it is found that hot electrons initially trapped in the mirror section are diffused out by electron-neutral collisions resulting in the establishment of the equilibrium between the trapped hot electrons and circulating hot electrons. The confinement time reaches 6 sec at the neutral pressure of 2 × 10−7 Torr, which is about one-third of the classical decay time across the magnetic field. The time dependence of the density of the circulating hot electrons is in good agreement with the numerical calculations based on the Fokker-Planck equation. However, the existence of circulating hot electrons is sensitive to the magnetic field error of 1%. The establishment of the inductive current of the hot electron plasma is also investigated.
Stability of a finite β, l =2 stellarator
Authors: Freidberg J. P.
Published: February 2004

The stability of an infinitely long, high β, l = 2 stellarator is investigated. The calculation is carried out by using the new scyllac expansion in the sharp boundary ideal magnetohydrodynamic model. It is found that for any given size l = 2 field and mode number m, an infinite but discrete set of wavenumbers k exist for which the plasma is unstable to all β; that is, the critical β equals zero. These modes can be described as long wavelength interchanges. Thus, with regard to sharp boundary stability, l = 2 is less desirable than l = 1 for the basic scyllac field, and in addition does not offer any particular advantage over l = 0 as a sideband field required for toroidal equilibrium in the l = 1 configuration. configuration.
Electron spatial distributions and loss rates in experimentally achieved astron E-layers
Authors: Humphries Stanley
Published: February 2004

Experimental results are presented which show that stable astron E layers achieved to date can be described by a diffusion theory based on collisions with the background gas. The E layer is found to be primarily composed of the fundamental radial and axial modes. Time-resolved measurements of the radial density distribution are described. Decay rates are shown to be approximately classical. Axial decay rates can sometimes be strongly influenced by self-forces resulting in a linear rather than exponential decay of a fundamental mode E layer. The rapid initial decay of neutralized E layers during multiple pulse experiments is explained in terms of the theory by the presence of high order axial modes of injection.
Helicity cascades in fully developed isotropic turbulence
Authors: Brissaud A. , Frisch U. , Leorat J. , Lesieur M. , Mazure A.
Published: February 2004

Based on total helicity conservation in inviscid incompressible flows, the existence of simultaneous energy and helicity cascades is envisaged.
Spatial stability of incompressible two-dimensional Gaussian wake in steady viscous flow
Authors: Wazzan A. R. , Okamura T. T. , Keltner Gerlina
Published: February 2004

Linear spatial stability characteristics of a Gaussian wake in two-dimensional, steady viscous, incompressible flow are calculated. The results are in good agreement with the measurements of Sato and Kuriki in the linear region of a wake from a flat plate.
An exact solution of Euler's equations for the motion of a gas on a rotating sphere with gravity
Authors: Moses H. E.
Published: February 2004

The simplest nontrivial solution for the motion of a gas on a rotating sphere with gravity is given. It is believed that it is the first exact solution on the rotating sphere.
Sufficient condition for magnetohydrodynamic stability against axially symmetric perturbations
Authors: Dobrott D. , Chu M. S.
Published: February 2004

A less stringent sufficient condition than that previously given is obtained for magnetohydrodynamic stability against arbitrary fluid displacements which vary in the cross-sectional plane of an axially symmetric equilibrium. An example illustrates the use of the new condition.
Experimental determination of the spectral index of a turbulent plasma from digitally computed power spectra
Authors: Smith D. E. , Powers E. J.
Published: February 2004

Digitally implemented power spectra techniques are used to determine the spectral index of the turbulent plasma while simultaneously verifying the existence of a linear relationship between k and ω which is necessary to compare theory and experiment.
Electron cyclotron heating as inverse cyclotron radiation
Authors: Shohet J. L.
Published: February 2004

Microwave heating of a plasma is developed as an inverse emission process. Heating rates based on this theory show close agreement with those based on particle motion or conductivity. Thus, well-known emission theories provide a basis for determining heating rates.
Toroidal magnetohydrodynamic equilibrium with toroidal flow
Authors: Strauss H. R.
Published: February 2004

Toroidal, axisymmetric, ideal magnetohydrodynamic equilibrium with toroidal flow is examined.
Nonlinear stabilization of oscillating two-stream instability
Authors: Nishikawa K. , Lee Y. C. , Kaw P. K.
Published: February 2004

It is shown that the basic nonlinear effect associated with the oscillating two-stream instability is a downshift of the natural frequencies of electron plasma waves. As a result, conversion of this instability to a decay instability can take place.
Radiated noise from turbulent boundary layers in dilute polymer solutions
Authors: Barker Steven J.
Published: February 2004

Measurements of radiated noise and wall-pressure fluctuations in a turbulent boundary layer in water are described. A comparison is made between results obtained in pure water and in dilute solutions of drag-reducing polymers. A new experimental geometry was developed to obtain these measurements. The experiment consisted of a spiral-shaped plate which was rotated about its central axis in a stationary fluid, generating a turbulent boundary layer upon its inner surface. This boundary layer is shown to resemble that upon a flat plate in a uniform free stream. Wall-pressure fluctuations under the boundary layer were measured with piezoelectric transducers mounted flush in the wall of the spiral plate. Noise radiated from the boundary layer was measured with a stationary transducer located outside of the boundary layer. All measurements were made as a comparison between water and dilute polymer solutions. It is shown that polymer additives cause significant reductions in both the radiated noise and wall pressure spectra. These reductions are greatest at high frequencies, corresponding to Strouhal numbers greater than one.
Integrodifferential equation for passive scalar diffusion in nonuniform random velocity fields
Authors: Thiebaux M. L.
Published: February 2004

The time evolution integrodifferential equation for the ensemble mean of an advected passive scalar is derived for a general ensemble of compressible flows. Eulerian one-point, n -time velocity correlation functions and their spatial derivatives are required in the equation. The equation is applied to a case for which an exact solution is already known, and the validity of certain formal operator manipulations is demonstrated. A simple closure is discussed and the results are compared with other established results. Suggestions for further studies are made.
Space-time correlations of the transverse velocity fluctuation in pipe flow
Authors: Sabot J. , Renault J. , Comte-Bellot G.
Published: February 2004

Memory times are smaller for transverse velocity components than for longitudinal components. For the former less downstream-upstream asymmetries are apparent in the optimal space-time isocorrelation contours.
Nonlinear stability of cylindrical vortex enclosing a central jet of light or dense fluid
Authors: Narain Jai Prakash , Uberoi Mahinder S.
Published: February 2004

A nonlinear analysis of the inviscid stability of a cylindrical vortex enclosing a central jet of light or dense fluid is presented. A uniformly valid second-order expansion is obtained using the method of multiple time scales. For a stagnant core surrounded by a potential vortex, the axisymmetric mode remains stable to various scales of disturbances independent of core density. For asymmetric modes, the nonlinear effects make the stagnant core vortex sheet more unstable in second order for a given value of the core density. A central jet of any finite density always has a destabilizing effect on the jet-vortex system undergoing any mode of deformation. A jet of any velocity tends to increase the unstable growth rates with increasing order of perturbations. The surface tension has a stabilizing effect with increasing order of perturbations. The frequency of oscillation becomes amplitude dependent in various orders of perturbations. The cylindrical surface departs significantly from its initially perturbed sinusoidal form and assumes an asinusoidal form.
Unsteady multiple boundary layers on a porous plate in a rotating system
Authors: Debnath Lokenath , Mukherjee Sukla
Published: February 2004

An initial value investigation is made of the motion of an incompressible, homogeneous, viscous fluid bounded by a porous plate with uniform suction or blowing. Both the plate and the fluid are in a state of solid body rotation with constant angular velocity about the z axis normal to the plate, and additionally a nontorsional oscillation of a given frequency is superimposed on the plate for the generation of an unsteady flow in the rotating system. By using the Laplace transform technique, an exact solution of the three dimensional Navier-Stokes equations for unsteady flow is obtained. The structure of the associated multiple boundary layers is determined. Effects of uniform suction (or blowing) and rotation on the flow phenomena are analyzed. Several known results of interest are found to follow as particular cases of the solution of the problem considered.
New kind of boundary layer over a convex solid boundary in a rarefied gas
Authors: Sone Yoshio
Published: February 2004

A boundary layer whose thickness is of the order of the mean free path squared divided by the radius of the curvature of the boundary is proposed to exist at the bottom of the kinetic boundary layer (or Knudsen layer) when the boundary is convex in shape.
Magnetically induced instability in shock-heated argon
Authors: Hardy R. H. S.
Published: February 2004

Observations of a highly structured discharge and current instability in unseeded shock heated argon flowing through a region of large transverse magnetic field are presented and analyzed. The experimental results are related to an extension of the theory of electrothermal (ionization) instability in partially ionized gases in which the presence of multiply charged ions is taken into account.
Hot plasma in contact with a cold wall
Authors: Chu M. S.
Published: February 2004

The effect of a cold wall on a hot plasma with initial uniform temperature and strong magnetic field parallel to the wall is studied. For physical values of thermal conductivity, resistivity, and electron-ion equilibration coefficients, the full set of one-fluid, two-temperature equations is solved numerically. These results are then compared with analytic self-similar solutions. The dynamic behavior of the plasma is presented. The total energy loss to the wall per unit area is evaluated and may be approximated rather well by an analytical expression derived from the fundamental equations.
Application of a consistent kinetic equation to an inhomogeneous plasma
Authors: Heitowit Ezra D. , Liboff Richard L.
Published: February 2004

A consistent kinetic model is developed for investigating wave propagation in a two-component fully ionized, inhomogeneous, low-pressure plasma with collisions. A Gross-Krook-type model is developed with arbitrary parameters determined by the method of Morse [Phys. Fluids 7,2012 (1964)]. The collision terms of the model satisfy all conservation requirements to a consistent order. A different ordering for the cross-collision frequencies emerges compared to that of some earlier BGK models. The kinetic equations developed are used to obtain a dispersion relation for electrostatic waves in a plasma slab geometry which includes the effects of temperature fluctuations. The gravitational flute mode is investigated, and the present model predicts a larger growth rate for the collisional instability of this mode than earlier BGK models.
Effect of magnetic shear on convective plasma transport
Authors: Okuda Hideo , Dawson John M.
Published: February 2004

The effect of magnetic shear on convective plasma transport is investigated both by analytic theory and by computer simulations. It is found that the convective diffusion coefficient increases linearly with the shear length until it saturates at the value for close field lines; after this it is constant. It is essentially independent of B for ωpi > ωci.
Experimental determination of the nonlinear interaction in a one dimensional beam-plasma system
Authors: Gentle K. W. , Lohr J.
Published: February 2004

Recent theories have shown that the instability driven by a cold, weak electron beam in a one-dimensional plasma is stabilized when the unstable wave grows to an amplitude sufficient to trap the electron beam. Quantitative measurements of the instability confirm every prediction of the theory: the maximum wave amplitude, monochromaticity of the unstable mode, harmonic content of the mode, and wavelength of the slow oscillation in wave amplitude. The electron beam goes through the same patterns in phase space and time-averaged f(v) as predicted. Both scaling and absolute magnitudes agree with theory.
Model of kink modes and their feedback stabilization
Authors: Lowder R. S. , Thomassen K. I.
Published: February 2004

The kink modes of a cylindrical plasma carrying a uniform current are described in terms of the perturbed currents and fields arising from a helical displacement of the plasma. This description gives the well-known dispersion and stability relations, and illustrates the stabilizing role of feedback magnetic fields.
Plasma instability at an X-type magnetic neutral point
Authors: Baum P.J. , Bratenahl A. , Kao M. , White R. S.
Published: February 2004

Time-resolved measurements of temperatures, density, and other parameters which describe the plasma at the X-type neutral point of the double inverse pinch laboratory discharge device are reported. Turbulent resistivity develops in this experiment without the usual application of an external electric field. The electric field is generated by field line reconnection or magnetic flux transfer. Various conductivity mechanisms are examined including binary collisions, space charge current limitation (Alfv́en-Carlqvist instability), and other current driven instabilities. The evidence suggests that the ion-acoustic instability is responsible for the observed current cutoff and turbulent conductivity. However, this instability must be driven well above its normal threshold. The competing effects of electron runaway and wave-particle interactions are discussed.
Convergence of strong turbulence theory
Authors: Thomson J. J. , Benford Gregory
Published: February 2004

The orbital diffusion view of plasma turbulence differs from the usual treatment of particle motion, in that the “free” particle propagator is changed to a renormalized propagator. This new propagator contains information about the perturbing effects of the self-consistent field. It is shown that the perturbation series formed with this new propagator converges rigorously. Physical effects included in the perturbation series are discussed.