bluuebunny/crossref_metadata_2025 huggingface dataset:
Finite length thermal equilibria of a pure electron plasma column
Authors: Prasad S. A. , O’Neil T. M.
Published: March 2003

The electrons of a pure electron plasma may be in thermal equilibrium with each other and still be confined by static magnetic and electric fields. Since the electrons make a significant contribution to the electric field, only certain density profiles are consistent with Poisson’s equation. The class of such distributions for a finite length cylindrical column is investigated. In the limit where the Debye length is small compared with the dimensions of the column, the density is essentially constant out to some surface of revolution and then falls off abruptly. The falloff in density is a universal function when measured along the local normal to the surface of revolution and scaled in terms of the Debye length. The solution for the shape of the surface of revolution is simplified by passage to the limit of zero Debye length.
Stability criteria for current-driven drift wave eigenmodes
Authors: Ross David W. , Mahajan Swadesh M.
Published: March 2003

Eigenmodes of current-driven collisionless electrostatic drift waves in a sheared magnetic field are re-examined in the light of the recent discovery that their non-current-driven counterparts are stable. Conditions for instability are determined from numerical finite difference and variational solutions of the slab model differential equation. It is found that three stringent conditions are required for instability: (1) very weak shear, (2) low ion temperature, and (3) very large parallel drift velocity. For Ln/Ls=0.02 and Ti/Te=0, the instability threshold is ud/cs=0.85, where Ln and Ls are the density and shear scale lengths, respectively, ud is the drift velocity, and cs is the sound speed. For larger shear and finite ion temperature the critical drift velocity is even larger. It is concluded that drift wave fluctuations in tokamaks cannot be described in terms of these eigenmodes.
Negative plasma potentials produced by supplemental electron emission
Authors: Hershkowitz Noah , Ze Frederic , Kozima Hideo
Published: March 2003

A detailed investigation of the effects of supplemental electron injection into a multi-dipole argon plasma is presented. It is shown that an increase in the density of non-ionizing electrons produced by a space-charge-limited filament leads to the creation of negative plasma potentials that confine ions and result in ion heating. A model is given which shows that the requirement of charge neutrality predicts many of the experimental results.
Re-examination of strongly flux limited thermal conduction in laser produced plasmas
Authors: Gitomer S. J. , Henderson D. B.
Published: March 2003

Laser interaction experiments on plastic foils at 1.06 μm and 10.6 μm wavelengths have been re-examined using the LASNEX hydrodynamics code modified to include ponderomotive force effects and realistic hot electron generation. The data for a wide range of experiments have been accurately modeled without invoking an anomalous limit on the electron heat flux.
Test particle correlation by a whistler wave in a nonuniform magnetic field
Authors: Vomvoridis J. L. , Denavit J.
Published: March 2003

Computer simulations of the correlation in phase of test electrons in a monochromatic whistler wave propagating along a nonuniform external magnetic field are presented. The behavior of resonant electrons depends on an inhomogeneity ratio R, which defines the external field gradient in relation to the wave amplitude. In the case ‖R‖<1, where electron trapping is possible, a hole (or an island) of particles is found to occur in phase plots of the distribution function. This causes the appearance of a transverse current coherent with the wave, which is most intense for ‖R‖≲0.6. The significance of these results to magnetospheric propagation of a quasi-monochromatic whistler pulse is discussed.
Absence of particle drift in magnetic fields of translational symmetry
Authors: Pellat R. , Schmidt G.
Published: March 2003

It is shown that a charged particle moving in a magnetic field described by the vector potential Ay=Bx+f (z) experiences no drift motion. This, of course, includes the case of parabolic field lines Ay=Bzx+αz2.
Hydromagnetic perturbations due to localized flows: An eddy theorem
Authors: Bird J. F.
Published: March 2003

The hydromagnetic far-field generated by localized regions of incompressible flow of electrically conducting media in uniform magnetic fields is derived explicitly in terms of the spin angular momentum of the flow. Some applications and a corollary result for bounded media are given.
Quasi-linear theory of the current-driven ion-acoustic turbulence in a weakly ionized plasma
Authors: Appert K. , Vaclavik J.
Published: March 2003

Saturation of the current-driven ion-acoustic instability in a weakly ionized plasma is investigated within the context of a quasi-linear model that includes the effects of collisions. The turbulent wave energy is calculated under the assumption that the waves are excited within the cone of a small angle. The results obtained compare favorably with the recent experimental observations of Ilić.
Collapse of very large amplitude ion waves
Authors: Forslund D. W. , Kindel J. M. , Lee K. , Godfrey B. B.
Published: March 2003

Recently extremely large supersonic amplitude ion waves have been observed in simulations of backscatter instabilities, electron beam interactions, and large amplitude Langmuir waves, which break in an unconventional symmetrical x-type manner. The conditions necessary for this type of breaking and simulations to support this theory are presented.
Current multiplication during relativistic electron-beam propagation in plasma
Authors: Chambers Frank W.
Published: March 2003

During the passage of a highly relativistic electron beam through a plasma, the net current can be greater than the beam current. This current increase can be caused by momentum transferred from the beam to the plasma via the two-stream instability. The current gain at saturation of the two-stream instability is computed, and the theoretical results agree well with a one-dimensional computer simulation of the phenomenon. An equation is derived for the total plasma current, including both the current driven by the two-stream instability and the current driven by the beam-induced electric field.
Effect of waveform and duration of impulse on the solution to the Basset−Langevin equation
Authors: Arminski Leslie , Weinbaum Sheldon
Published: March 2003

New analytic solutions to the continuum hydrodynamic equations for the transient response of a spherical particle at low Reynolds number to several simple excitation forces f(t) of varying duration and different waveforms are presented. The new solutions permit the exploration of the effect of the waveform and the duration of impulse on the relative magnitude of the inertia, quasi-steady Stokes’ drag and unsteady boundary layer (Basset) force components throughout the time history of the motion. It is shown that for an impulse of constant magnitude the net displacement of the particle is independent of both the duration and waveform of the excitation force. This simple result is used to explain why one obtains the correct Stokes−Einstein expression for the infinite time diffusion coefficient from a traditional Langevin analysis in which, historically, an incorrect quasi-steady linear Stokes resistance law has been used.
Stability of converging shock waves
Authors: Fong Kenneth , Ahlborn Boye
Published: March 2003

A computer program that determines the position of converging shocks and monitors the decay of radial perturbations of the shock fronts, described by their amplitude Δr and their center angle γ has been developed. With this program a region of stability for spherical and cylindrical shocks of different Mach numbers has been found, where perturbations will disappear before the wave has collapsed. The model was tested by comparison with an experiment and an analytically approximate model.
Turbulent interaction fronts in counterstreaming laser-produced plasma studies
Authors: Koopman David W. , Siebeneck H.-J. , Jellison G.
Published: March 2003

The formation of interaction fronts between an expanding barium laser-produced plasma and a partially photoionized deuterium background has been observed with holographic and schlieren diagnostics which employ resonant enhancement to achieve sensitivities of approximately 3×1013/cm3 for Baii ions. The front is found to be sharp, but turbulent, apparently due to Rayleigh–Taylor instabilities. The radius vs time behavior of the front is consistent with collisional coupling between the expanding plasma and the photoionized fraction of the background over the D2 pressure range 0–1000 mTorr. Data obtained with a microwave interferometer complement and support the conclusions based on optical diagnostics.
Measurement of the cross spectrum of random linear electrostatic waves in an isotropic Maxwellian plasma
Authors: Pottelettea) R.
Published: March 2003

An experimental study is presented of the cross-power spectrum of the random high-frequency signals received by two small dipole antennas immersed in a stable, isotropic and collisionless plasma. These signals are due to the high-frequency microfield, i.e., to the random linear electrostatic wave field excited by the thermal motion of the electrons. For a Maxwellian plasma, the cross spectrum exhibits a main resonance peak slightly above the plasma frequency, and from this spectrum the electron density and temperature can be determined. The experiment has been performed in a laboratory plasma near thermal equilibrium. The results are in agreement with the theory, and show that the cross spectrum is very sensitive to any departure of the plasma from thermal equilibrium.
Boundary layer transition
Authors: Blackwelder R. F.
Published: March 2003

It is suggested that boundary layer transition on a flat plate may be considered as a cascade of at least three distinct instabilities. The oscillation frequency of the velocity ’’spike’’ is predicted by the growth of a localized free shear layer that is a result of the earlier instabilities.
Variational approach to strongly nonlinear Schrödinger equations
Authors: Anderson D. , Bonnedal M. , Lisak M.
Published: March 2003

By means of a variational approach using trial functions, approximate analytical solutions are found for strongly nonlinear one-dimensional Schrödinger equations, in good agreement with numerical results.
Effect of ionic temperature on the modulational instability of ion acoustic waves in a collisionless plasma
Authors: Durrani I. R. , Murtaza G. , Rahman H. U. , Azhar I. A.
Published: March 2003

Using the Krylov–Bogoliubov–Mitropolski method, the modulational instability of ion-acoustic waves in a collisionless plasma consisting of isothermal electrons and adiabatic ions is studied. It is found that with the inclusion of ion temperature the modulational instability sets in much earlier.
Observations of the nonlinear phase of a noncircular cross section toroidal kink instability
Authors: Allen A. W. , Goldenbaum G. C.
Published: March 2003

A low pressure region is observed to propagate from the boundary to the interior in the nonlinear phase of a toroidal kink instability.
Magnetic gradient effects on the universal drift instability
Authors: Winske D. , Gary S. Peter
Published: March 2003

The linear Vlasov theory of the universal instability driven by a density gradient in a unidirectional magnetic field is considered in the slab model with the local approximation. The electrostatic approximation is used, but the full resonant effects of a magnetic field gradient drift are included for the ions. Both electron and ion ∇B effects reduce the growth rate, but the latter is more important. It is shown that the nonresonant ion ∇B approximation fails at relatively low β and that the conventional resonant ion approximation becomes invalid as β increases.
Influence of ion-ion collisions and kinetic effects on minidisruptions of confined plasmas
Authors: Ara G. , Basu B. , Coppi B.
Published: March 2003

Resistive m=1 modes associated with minidisruptions of current carrying plasmas are shown to be strongly influenced simultaneously by the effects of finite ion gyroradius, finite drift wave frequency, and ion-ion collisions in the plasma regimes of interest. The modes acquire finite frequency of oscillation and, for low β, the reduction in their growth rates is due mainly to the drift wave frequency, the effect of ion-ion collisions being slight (less than 10% effect); but, even for low β, ion-ion collisions significantly alter the radial structure of the modes. As a result, the reconnecting mode, which tends to lose its radial localization above a threshold temperature, remains well-localized when ion-ion collisions are included.
Some properties of the large structure in a fully developed turbulent duct flow
Authors: Rajagopalan S. , Antonia R. A.
Published: March 2003

Some characteristic features of the large scale in a fully developed, two-dimensional, turbulent duct flow have been investigated with the use of a wall shear stress probe and a single hot wire, traversed across the duct. From space-time correlation measurements of wall shear stress and velocity fluctuations, the large scale structure is observed to be inclined at an angle of about 13° for y/d ≳ 0.15, where d is the duct half-width. The convection speed Uc of wall shear stress fluctuations is equal to 0.62 U0 for Rd ≳ 3.5×104, where U0 is the center-line velocity and Rd is the Reynolds number based on center-line velocity and duct half-width. The convection speed of velocity fluctuations is approximately constant over a wide range of Reynolds numbers. The integral length scale of wall shear stress fluctuations is nearly 0.38d. Joint probability density functions of velocity and wall shear stress fluctuations are presented and discussed.
Structure of the temperature field in the turbulent wake behind an asymmetrically heated plate
Authors: Morela) R. , Rey C. , Awad M. , Mathieu J. , Schon J. P.
Published: March 2003

The turbulent properties of a thermal wake are investigated in the particular case where the initial conditions producing the kinematic wake and the temperature field are different from one another. In such a case it is observed that the correlation coefficient Rvϑ is not zero at the point where the mean temperature gradient is zero. Accordingly, there is a region where the ’’production terms’’ of the temperature variance are negative. Comparisons are made between kinematic and thermal structures determined from a spectral analysis. The thermal field is found to have some degree of independence from the kinematic field. The large and small structures of each field are different, but they can be related by translating the axis uv̄=0 of the thermal wake until it coincides with the axis vθ̄=0 of the kinematic wake.
Thermoelectric magnetohydrodynamics in closed containers
Authors: Shercliff J. A.
Published: March 2003

Liquid metal in a closed container made of dissimilar metal under a magnetic field is, in general, set into motion by thermoelectric effects if the interfacial temperature is nonuniform, a situation likely to occur in fusion reactor blankets owing to the high thermoelectric power of lithium. The paper sets out the general problem for the case where the field is uniform and so strong that inertial and viscous effects are negligible and where the container wall thickness is small and uniform. Extended cylindrical portions of interface, parallel to the magnetic field, are excluded. Particular attention is paid to containers which are axisymmetric about the field direction and several solutions are found for the case of a spherical container. Many of these imply drastic changes in the total heat transport as compared with pure conduction in the static liquid.
On the theory of astron equilibria
Authors: Lovelace R. V. , Larrabee D. A. , Fleischmann H. H.
Published: March 2003

The theory of astron ion-ring equilibria is considered from a new point of view. In contrast with previous equilibria, the new equilibria have a distribution of canonical momentum which is invariant to axisymmetric changes in the external magnetic field. As a function of the single particle constants of the motion, the energy ℋ, and the canonical momentum 𝒫ϑ, the distribution function, f (ℋ,𝒫ϑ) is written as f=g (𝒫ϑ) ℱ (ℋ,𝒫ϑ)[𝒜 (ℋ,𝒫ϑ)]−1. Here, g (𝒫ϑ) is the invariant distribution function for canonical momentum; 𝒜 (ℋ,𝒫ϑ) is the area of the poloidal (r,z) plane accessible to a ring particle with constants ℋ and 𝒫ϑ; and ℱ (ℋ,𝒫ϑ) is a nonnegative function having the normalization ℱ dℋ ℱ=const. The possibility of a third constant of the single particle motion is not included. In contrast with some previous equilibria, f (ℋ,𝒫ϑ) is nonzero only in the regions of the 𝒫ϑ,ℋ plane in which there are trapped particle orbits. With this representation of f, it becomes possible to study the adiabatic compression of ion-ring Vlasov equilibria.
Precession and kink motion of long astron layers
Authors: Lovelace R. V.
Published: March 2003

A study is made of the stability of the low-frequency precession and kink modes of a long astron particle layer embedded in a dense low-temperature plasma. The precessional motion corresponds to a toroidal mode number n= 1 and the kink motion to n≳ 2. Two types of precession of nonrelativistic ion layers are analyzed in detail. For frequencies ω such that α2Ω2≪‖ω‖2≪Ω2, there is a precession mode with the real part of the frequency ωr≈−(ηe/2) Ω. Here, Ω is the average circulation frequency for the layer ions; α≡ vA/v̄ϑ≪ 1 with vA the plasma Alfvén wave speed, and v̄ϑ the average azimuthal velocity of the layer ions; and ηe is the effective external magnetic field index. This mode shows the well known negative energy type of instability due to dissipation for ηe< 0, which corresponds to a mirror field. For frequencies ‖ω‖2≪α2Ω2, there is a magnetohydrodynamic precession mode with a frequency ω≈± (ηe/ζ)1/2αΩ, where ζ is the loading factor, which is a measure of the layer strength. This mode has a magnetohydrodynamic type of instability for ηe< 0. For the kink modes, a necessary and sufficient condition for stability is shown to be ηs< 3, where ηs is the self-magnetic field index.
Rigid-drift magnetohydrodynamic equilibria for cylindrical screw pinches
Authors: Turner Leaf
Published: March 2003

The equations of magnetohydrodynamic equilibrium are solved using the rigid-drift assumption for a screw pinch with an arbitrarily pitched current. Instead of the customary isothermal assumption, the pressure is assumed to be proportional to the square of the number density (which implies a temperature that is proportional to the number density). Analytical formulae are presented for the profiles of the equilibrium magnetic field components, Bϑ(r) and Bz(r), and for the equilibrium pressure profile, p (r). The relative shapes of these profiles (which can exhibit hollow pressure and/or reversed Bz behavior) are determined by specification of only two parameters: the value of the local plasma beta at r=0 and a quantity related to the pitch of the current. A set of profiles that resemble those experimentally observed in reversed-field pinches is presented.
General quasi-linear theory of parametric instabilities
Authors: Sperling J. L.
Published: March 2003

The general form of the quasi-linear equation is derived for plasmas in which there is a finite amplitude pump wave. Electrostatic turbulence is considered and the pump wave is treated in the dipole approximation. Appropriate number, momentum, and energy moment constraints are shown to be computable from the diffusion equation. The derivation of an H theorem indicates that the quasi-linear diffusion of parametric instabilities always tends to an accessible asymptotic steady state.
Trapped electron instability in a linear multi-mirror experiment
Authors: Grubba) D. P. , Emmert G. A.
Published: March 2003

The dissipative trapped electron instability is observed in the linear multi-mirror experiment. This instability is observed in two forms, one driven by the electron temperature gradient, and one driven by finite Larmor radius effects. The experimental results are in reasonable agreement with the theoretical predictions of the linear dispersion relation.
Observations of the instabilities of a round jet and the effect of cocurrent flow
Authors: Freeman R. W. , Tavlarides L. L.
Published: March 2003

Experimental observations of a fully developed round jet entering a second, less dense, immiscible liquid reveal that cocurrent flow of the outer fluid can eliminate instabilities. Both helical and axisymmetric disturbances were observed.
Excess pressure drop of polymer solutions in laminar capillary tube flows
Authors: Ouibrahim A.
Published: March 2003

Beyond a critical shear rate, laminar flows of polymer solutions display an excess pressure drop, ΔPe, localized at the capillary tube entrance and linearly shear dependent. The measured pressure drop represents the viscous contribution and the elastic effects ΔPe. The relative apparent viscosity is therefore determined.
Velocity slip and temperature difference of gas mixtures in quasi-one-dimensional nozzle flows
Authors: Nanbu K.
Published: March 2003

The velocity slip and temperature difference are examined using two-temperature thirteen moment equations. It is shown that the velocity slip becomes maximum just beyond the throat and the temperature difference is appreciable in the supersonic flow regions.
Gravitational instability in the presence of suspended particles and rotation
Authors: Raghavachara) M. R.
Published: March 2003

The effect of uniform rotation on the gravitational instability of an infinitely extending homogeneous self-gravitating medium in the presence of suspended particles has been studied and it has been shown that Jeans’ criterion remains unaffected.
Equilibria of diffuse high beta stellarators
Authors: Freidberg J. P. , Dagazian R. Y. , Barnes D. C.
Published: March 2003

The ideal magnetohydrodynamic equilibrium of a diffuse high-β stellarator is investigated by an asymptotic expansion in the inverse aspect ratio. The basic new feature of the calculation is that the lowest order flux surfaces are assumed noncircular and nonconcentric. Equilibria are found for a wide range of experimentally interesting parameters. Finally, the connection of the high-β expansion with the low-β stellarator expansion is discussed in detail.
Effects of Congo Red on the drag reduction properties of polyethylene oxide
Authors: Inge Claes , Johansson Arne V. , Lindgren E. Rune
Published: March 2003

Addition of minute amounts of Congo Red (a benzidine derivative) to polymer additives of polyethylene oxide greatly affect the turbulent drag reduction characteristics of the polymer. A dipole type cross coupling mechanism is suggested which could possibly explain the flow behavior of these dilute additive solutions in drag reduction.
Sound-wave propagation in a rarefied gas
Authors: Loyalka S. K. , Cheng T. C.
Published: March 2003

The problem of sound wave propagation in a rarefied gas is studied by the use of the linearized BGK model and diffuse reflection boundary conditions. The relevant integrodifferental equation and boundary conditions for the half-space are converted to a system of linear integral equations, which is then solved by a straightforward numerical differencing technique. The present results are in better agreement with the experimental results of Meyer and Sessler and Greenspan than the BGK model results of Sirovich and Thurber and Buckner and Ferziger who, respectively, use analytical continuation and an approximate boundary condition.
Probe measurements on a shock precursor
Authors: Barach John Paul
Published: March 2003

A shock front of speed Vs from 0.6 to 5×106 cm/sec is launched by a capacitor discharge in one end of a 10 cm i.d. Pyrex pipe 150 cm long. Initial gas pressures range from 0.05 to 1.35 Torr of argon and observations with internal probes are carried out at positions down the tube, z of 73 to 117 cm. A steady magnetic field is applied and the shock, detected by pressure traces, compresses the field by 1.7: 1. Ahead of this shock a precursor is found which produces a magnetic field change which is abrupt (risetime=0.7 μsec) and substantial (approximately 50% of the imposed field). The size of this diamagnetic field change increases with Vs in agreement with a simple diamagnetic model which includes substantial radial flow. The location of precursor field change moves upstream toward the shock with reduced Vs and the strength of the field change is reduced at radii nearer the tube walls. Measurements of excitation temperature yield values of kTe=2.0 eV for the shock and 2.5 eV for the precursor region.
Two-dimensional Hartmann flows of fluids with cross-stream dependent electrical conductivity
Authors: Trovillion T. A. , Kurzweg U. H. , Elkins R. E. , Lindgren E. Rune
Published: March 2003

The equations for two-dimensional Hartmann flow through ducts of rectangular cross section are solved numerically by the Peaceman–Rachford alternating direction implicit method for boundary conditions appropriate to those encountered in a Faraday magnetohydrodynamic generator. Cross-stream variation in fluid electrical condictivity as well as variable conductivity of the electrode walls are considered and quantities such as velocity distribution, current streamline distribution, volume flow rate, and conversion efficiency are obtained for a range of Hartmann numbers up to M=100. Results show that decreasing the electrical conductivity in a continuous manner from a high value near the walls to a minimum along the duct axis leads to a high velocity region near the duct axis, a result differing from the essential slug flow character found for Hartmann flows of constant conductivity fluids at high M. The known one-dimensional Hartmann flow solutions are found to give excellent agreement with the two-dimensional results for constant conductivity fluids whenever the product of the duct aspect ratio and the square root of the Hartmann number is greater than about ten.
Three-dimensional flow with neutral points
Authors: Rosenau Philip
Published: March 2003

Some special three-dimensional problems of incompressible flow in the presence of magnetic neutral points are considered. For that purpose, the group invariant properties of the incompressible magnetohydrodynamic equations are studied and isomorphic mappings, together with a family of similarity solutions, are constructed. Two cases which are analyzed explicitly, show the variety of three-dimensional topologies which may vary very significantly from the planar case. Particularly, three-dimensional topology without resistivity may be similar to planar topology with finite resistivity, and the number of neutral points is determined by the boundary conditions.
Self-similar power-driven expansion into vacuum
Authors: Farnsworth Archie V. , Widner Melvin M. , Clauser Milton J. , McDaniel Patrick J. , Lonngren Karl E.
Published: March 2003

Planar, power-driven expansion into a vacuum is found to be self-similar for a power-law driving source for the two ideal cases of a thick slab and a thin foil. For the thick slab expansion, an asymptotic solution for the far-blowoff region is obtained and a numerical solution is present for the rest of the expansion wave. For the thin foil expansion, an analytical solution is obtained. In both cases, the solutions exhibit an unbounded flow field with velocities tending to infinity as a consequence of the continuum assumption, a finite temperature limit for the far-blowoff material, and density profiles that decrease as a Gaussian in the far expanded material.
Damped double solitons in the nonlinear Schrödinger equation
Authors: Pereira N. R. , Chu Flora Y. F.
Published: March 2003

The nonlinear Schrödinger equation modified by a damping term is investigated numerically for initial conditions other than single solitons. With damping, colliding solitons still pass through each other, but the breather can change qualitatively into two continuously interacting but separated solitons. These results are consistent with a slow change in the inverse scattering eigenvalues due to the damping.
Interpretation of the ponderomotive potential for a magnetized particle in a low-frequency wave
Authors: Carya) J. R. , Hammer James H.
Published: March 2003

One term in the expression for the ponderomotive potential of a low-frequency magnetoplasma wave has a simple interpretation: It is the parallel-electric-field potential produced directly by the wave.
Secondary instability in boundary-layer flows
Authors: Nayfeh Ali H. , Bozatli Ali N.
Published: March 2003

The stability of a secondary Tollmien–Schlichting wave, whose wavenumber and frequency are nearly one half those of a fundamental Tollmien–Schlichting instability wave, is analyzed using the method of multiple scales. Under these conditions, the fundamental wave acts as a parametric exciter for the secondary wave. The results show that the amplitude of the fundamental wave must exceed a critical value to trigger this parametric instability. This value is proportional to a detuning parameter which is the real part of k − 2K, where k and K are the wavenumbers of the fundamental and its subharmonic, respectively. For Blasius flow, the critical amplitude is approximately 29% of the mean flow, and hence many other secondary instabilities take place before this parametric instability becomes significant. For other flows where the detuning parameter is small, such as free-shear layer flows, the critical amplitude can be small, thus the parametric instability might play a greater role.
Induced emission of extraordinary mode radiation in tokamaks
Authors: Freund H. P. , Lee L. C.
Published: March 2003

The implications of the formation of a positive slope in the runaway electron tail in tokamak plasmas are investigated in regard to the radiation in the vicinity of the electron plasma frequency. In particular, it is shown that the amplification of extraordinary mode waves may result.
Normal mode analysis with absorption effects of a laser beam in a plasma waveguide
Authors: McMullin J. N. , Capjack C. E. , James C. R.
Published: March 2003

Normal mode theory is used to derive a general expression for the field of a laser beam in a plasma waveguide while accounting for absorption. The plasma density profile in the waveguide includes the effects of nonparabolic radial terms and of axial dependence. For a slowly varying, nearly parabolic waveguide, the beam is shown to be aberrated due to the phase shift of the coefficients of the normal mode expansion. An expression for the energy density of a beam with a finite spectrum is found.
A theory of electron energy confinement in tokamaks
Authors: Manheimer Wallace M. , Antonsen Thomas M.
Published: March 2003

A one-dimensional thermal transport code has been employed to study electron energy confinement in tokamaks. At each time step of the computations, each point in the profile is examined to determine whether it is linearly stable to either the dissipative trapped electron mode or the internal kink and tearing modes. If the point is determined to be unstable, an anomalously large electron thermal conductivity is turned on in the vicinity of that point. The electron temperature profile is found to relax to a marginally stable state. Our code predicts the scaling of confinement time with density in Alcator, and the scaling of temperature half-width with q (a) in Tokamak Fontenay aux Roses.
Spectral properties of stimulated Raman radiation from an intense relativistic electron beam
Authors: Gilgenbach R. M. , Marshall T. C. , Schlesinger S. P.
Published: March 2003

Spectra have been obtained in the range of wavelengths from 1–3 mm for the stimulated Raman scattering from an intense relativistic electron beam which propagates in a rippled magnetostatic field (’’zero frequency pump’’). The Raman scattering from the plasma space charge wave and the cyclotron wave idler modes has been observed and the frequency dependence upon beam energy, rippled period, and guiding magnetic field is found to be in accord with theory. Results suggest that the spectral linewidth for the scattered radiation is influenced by beam energy spread and the amplitude of the rippled field pump.
Cyclotron harmonic damping in stimulated Raman scattering from an intense relativistic electron beam
Authors: Gilgenbach R. M. , Marshall T. C. , Schlesinger S. P.
Published: March 2003

In stimulated Raman scattering from an intense relativistic electron beam, strong damping of the pump and scattered waves at cyclotron harmonics was observed. This damping accounts for minima in the growth rate at particular values of magnetic field.
Comments on ’’Magnetohydrodynamic equilibrium of plasma confined in a spherical microwave cavity’’
Authors: Hatch Albert J.
Published: March 2003

These comments summarize the modal dependence of stability of confined overdense and underdense plasma cores in spherical cavities, correct mistakes in pressure distributions and in modal frequencies of plasma-loaded spherical cavities, and point out an inherent degeneracy limitation of perfectly spherical cavities.
Reply to comments by Albert J. Hatch
Authors: Woods C. H.
Published: March 2003

Shape changing effects of spatial variations of electromagnetic fields in the vicinity of small plasma spheres can be avoided by modal combinations giving uniform pressure over the plasma sphere. Practically, it is necessary to design configurations for which the actual modes are sufficiently good approximations to spherical cavity modes. Misprints in Table II and in Eq. (24) are corrected.
Investigation of the free electron laser with a guide magnetic field
Authors: Kwan T. , Dawson J. M.
Published: March 2003

The free electron laser with a static guide magnetic field has been investigated theoretically and by computer simulation using a fully relativistic electromagnetic particle code which has one spatial and three velocity dimensions. By passing a relativistic electron beam through a helical magnetic field, high frequency electromagnetic radiation is generated by its coupling to the negative energy electrostatic beam modes through the helical magnetic field. In the regime of strong guide field where Ωce/γ≫k0v0z, the dispersion relation is obtained by using a fluid model for the electron beam and the growth rates are solved for numerically. Reasonable agreement between the theory and the simulations has been obtained. It was found that the growth rate increases linearly with magnetic ripple strength but decreases with the strength of the guide field. In addition, the growth rates also increase slightly with the beam energy. For a reasonably strong guide field (e.g., Ωce=6.0ωpe), the growth rate can be on the order of 0.1ωpe and the efficiency of radiation production has been found to be as high as 16%. However, the efficiency decreases with the strength of the guide field. A theory for the saturation level is developed which relates the efficiency to the continued growth of the electromagnetic wave after the onset of trapping by the electrostatic field. It is found that the growth continues for about one bounce time and the observed saturation levels are reasonably well explained.
Buoyancy effects in a wind tunnel simulation of the atmospheric boundary layer
Authors: Rey C. , Schon J. P. , Mathieu J.
Published: March 2003

The effect of buoyancy on the characteristics of boundary layers developing on smooth and rough plates has been investigated experimentally. The results are compared with atmospheric surface layer data. A study is made of the limitations of the Monin–Obukhov similarity theory as applied to wind tunnel flows. These limitations are mostly due to Reynolds number effects while in the atmosphere the limitations are probably due to unsteady motions and upstream inhomogeneities. The combined effects on the turbulence spectra of an unstable temperature stratification and variations in the Reynolds number are discussed. It is shown that buoyancy acts mainly on the temperature and on the vertical velocity spectra. This role is specially important for the large turbulent structures. The longitudinal velocity spectrum is not affected very much by buoyancy.
Temperature, concentration, and velocity in jets, flames, and shock tubes
Authors: Lederman S. , Celentano A. , Glaser J.
Published: March 2003

Temperature, concentration of species, and velocity in jets, flames, and shock tubes are obtained by means of modern diagnostic techniques utilizing lasers. It is shown that neutral as well as ionized species concentration and temperature are measurable utilizing those techniques. The nonintrusive character of the optical probes permits its application to chemically reacting flow fields. Furthermore, the instantaneous and simultaneous character of the experimental data obtained permit the derivation of correlation and cross-correlation parameters in addition to the turbulent intensity.
Stimulated scattering of light by ion modes in a homogeneous plasma: Space-time evolution
Authors: Cohen Bruce I. , Max Claire Ellen
Published: March 2003

Stimulated Brillouin scattering, filamentation, and induced Thomson scattering are studied for a coherent electromagnetic plane wave propagating in a uniform plasma. A generalized Green’s function is found that describes the impulse response for stimulated scattering by electron and ion modes. Explicit asymptotic Green’s functions are calculated for those parametric instabilities involving ion modes or quasi-modes. Special attention is given to whether the instabilities are convective or absolute. For a traveling wave pump in a uniform plasma, Brillouin and induced Thomson backscatter can be absolute, but sidescatter is convective; filamentation of traveling waves is always convective. Spatial growth rates are calculated for convectively unstable modes. Finally, the competition of filamentation and stimulated Brillouin scattering is considered for parameters typical of real laser-fusion experiments.
Energy properties of ion acoustic waves in stable and unstable plasmas
Authors: Jensen V. O. , Lynov J. P.
Published: March 2003

Energy exchange between potential energy and ion kinetic energy in an ion acoustic wave is considered. In order to investigate the linear Landau damping or growth, the energy is calculated by use of first-order quantities only so that nonlinear effects are not involved. It is found that for ion acoustic waves that are growing or damped in space the time average of the sum of the potential and the kinetic energy density is independent of position. Energy absorption spectra in particle velocity space are calculated; they are relatively broad and complicated functions. This shows that plasma ions of all velocities exchange energy with the wave.
Warm plasma effects on drift cyclotron loss cone mode
Authors: Ng P. H. , Gladd N. T. , Liu C. S.
Published: March 2003

Although plasma density gradients in mirror machines are larger than the theoretical threshold for the drift cyclotron loss cone instability, turbulence is experimentally observed only at low harmonics of the ion cyclotron frequency. The evolution of the drift cyclotron loss cone instability as the loss cone velocity distribution is progressively filled with a warm Maxwellian component is studied. The addition of the warm plasma results in both a lowering of the growth rate and a distortion and narrowing of the frequency spectrum. Under conditions typical of an almost filled loss cone, the numerical result shows that the growth rate is largest for the lower ion cyclotron harmonics and is quite consistent with experimental observations.
Betatron resonance instabilities in axisymmetric field-reversed systems
Authors: Finn John M. , Sudan R. N.
Published: March 2003

The effect of betatron resonances of the axis encircling, or ring, particles on the low frequency hydromagnetic stability of field reversed configurations is studied. It is found that modes with phase velocity parallel to the ring current are destabilized, and those with phase velocity opposite to the current are damped. For fully field reversed systems with moderate to large aspect ratio, the modes can grow on a hydromagnetic time scale. For rings with a smaller degree of field reversal, or with aspect ratio near unity, the growth rate is exponentially smaller.
Theory of parametric resonance in a current carrying magnetized plasma
Authors: Aliev Yu. M. , Stefan V.
Published: March 2003

The theory of parametric resonance is applied to a current-carrying magnetized plasma. The influence of a static drift between electrons and ions on the evolution of parametric instabilities is considered for both the low- and high-frequency domains, with the ion dynamics being neglected in the high-frequency susceptibility. It is shown that static drift can stabilize or facilitate parametric growth of turbulent noise.
Stability theory of a relativistic electron beam-plasma system with finite geometries
Authors: Tajima T.
Published: March 2003

An extensive study of the stability of a relativistic electron beam-plasma system in finite (cylindrical) geometries is performed. The analysis is based on the collisionless fluid theory; it accomodates both the finiteness and relativistic effects by employing the full set of Maxwell’s equation. Finite boundaries of the beam and plasma are found to have a stabilizing effect on the two stream instability under a static magnetic field. The instability tends to have a smaller growth rate when the plasma radius becomes smaller and the magnetic field becomes stronger. In the extreme case of an infinite magnetic field, the marginal beam density for stability is a sharply increasing function of the relativistic factor γ0 and the inverse of the plasma radius, and a mildly decreasing function of the plasma electron density. Surface modes of the filamentation instability in cylindrical geometry for a thin hollow beam are also examined. Possible applications of the present theory to the long solenoid reactor configuration and the runaway electron problem in a low densith regime of a tokamak are discussed.
Externally driven magnetic reconnection and a powerful magnetic energy converter
Authors: Sato Tetsuya , Hayashi Takaya
Published: March 2003

Numerical simulation of two-dimensional compressible magnetic reconnection is carried out for more than a dozen cases with different anomalous resistivities and boundary conditions. After a quiescent stage of magnetic energy buildup, anomalous resistivity leads to an abrupt conversion of the stored magnetic energy into the plasma bulk motion and heat. Consequently, plasma jets as high as the local Alfvén speed are generated downstream of the magnetic separatrix. Slow shocks formed just downstream of the separatrix and fast mode expansion in the upstream region play a leading role in the formation of strong plasma jets. Anomalous resistivity is the primary cause of the abrupt onset of reconnection. Once reconnection preceeds, however, its ultimate fate no longer seems to be dependent on the resistivity, but is largely controlled by the boundary conditions.
A higher-order nonlinear interaction among spectral components
Authors: Motohashi Tatsuo
Published: March 2003

A higher-order nonlinear interaction was measured in the wake behind a thin flat plate. In the experiment, a sound with two frequencies was used to specify the frequencies of interacting components. A new spectrum with many spectral components was found.
Nonlinear equation of evolution for electron plasma waves including collisions
Authors: Kunhardt E. E.
Published: March 2003

A nonlinear equation of evolution for electron plasma waves is derived. The effects of collisions are included in this model.
Stability properties of a field-reversed ion layer in a background plasma
Authors: Uhm Han S. , Davidson R. C.
Published: March 2003

Stability properties of an intense proton layer (P layer) immersed in a background plasma are investigated within the framework of a hybrid model in which the layer ions are described by the Vlasov equation, and the background plasma electrons and ions are described as macroscopic, cold fluids. Moreover, the stability analysis is carried out for frequencies near multiples of the mean rotational frequency of the layer. It is assumed that the layer is thin, with radial thickness (2a) much smaller than the mean radius (R0). Electromagnetic stability properties are calculated for flute perturbations (∂/∂z=0) about a P layer with rectangular density profile, described by the rigid-rotor equilibrium distribution function f0b= (minb/2π) δ (U−T̂) G (vz), where nb and T̂ are constants, mi is the mass of the layer ions, G (vz) is the parallel velocity distribution, and U is an effective perpendicular energy variable. Stability properties are investigated including the effects of (a) the equilibrium magnetic field depression produced by the P layer, (b) transverse magnetic perturbations (δB≠0), (c) small (but finite) transverse temperature of the layer ions, and (d) the dielectric properties of the background plasma. All of these effects are shown to have an important influence on stability behavior. For example, for a dense background plasma, the system can be easily stabilized by a sufficiently large transverse temperature of the layer ions.
Structural features of the plane turbulent jet
Authors: Moum J. N. , Kawall J. G. , Keffer J. F.
Published: March 2003

An experimental investigation of a two-dimensional turbulent jet in a quiescent environment has been carried out to determine the structural characteristics of the outer, intermittent turbulent motion. An overall picture of this motion was deduced from the results which indicate that, on the average, the turbulent bulges are of the same order of magnitude in the three coordinate directions and are tilted backward at an angle of approximately 26° with respect to the lateral axis but have no spanwise yaw. Furthermore, it was found that there is no periodicity associated with the motion and that no correlation exists between bulges on opposite sides of the jet center line.
Mutual slip-through of a pair of vortex rings
Authors: Yamada Hideo , Matsui Tatsuya
Published: March 2003

Mutual slip-through of two identical vortex rings, traveling along a common axis in the same direction, was experimentally achieved in air at various Reynolds numbers between 800 and 2000 and observed by using the smoke wire technique and cigarette smoke. The motions of a pair of vortices agree very well with an approximate potential theory based on the Biot–Savart law.
Stability of the equations for particulate sedimentation
Authors: Hill C. D. , Bedford A.
Published: March 2003

The solution of the equations for two-phase flow which models the steady sedimentation of a uniform distribution of particles in a liquid has been shown to be unstable to small perturbations. It is shown that when a diffusivity term (a force on the particles which is linear in the gradient of the particle concentration) with sufficiently large coefficient is included, the solution is stable and, furthermore, the equations are hyperbolic.
Destruction of cyclotron resonances in weakly collisional, inhomogeneous plasmas
Authors: Huba J. D. , Ossakow S. L.
Published: March 2003

It is shown, both analytically and numerically, that cyclotron resonances can be destroyed in dense (ωp≳Ω, where ωp is the plasma frequency and Ω is the cyclotron frequency), weakly collisional, inhomogeneous plasmas when (ν/Ω) k2r2L≳1, where ν is the collision frequency and rL is the mean Larmor radius. The theory is based upon a model Fokker–Planck equation. It is found that the particles make a transition from magnetized to unmagnetized behavior. This is an important result since it indicates that the ion-and electron-cyclotron-drift instabilities transform into their unmagnetized counterparts, the lower-hybrid-drift instability and the ion-acoustic instability, respectively. The ion-cyclotron-drift (or drift-cyclotron instability) is examined in detail and is found to become the lower-hybrid-drift instability in the region of maximum growth when (me/mi)1/2ω/Ωi≳νii/ Ωi ≳me/mi for Te≈Ti plasmas. The first inequality is required to overcome electron viscuous damping, while the second allows the ions to become ’’unmagnetized.’’ Applications to the equatorial F region of the ionosphere and the tandem mirror experiment (TMX) are discussed.