bluuebunny/crossref_metadata_2025 huggingface dataset:
Relativistic derivation of laser-induced plasma profiles
Authors: Stroscio M. A. , Lee K. , Lindman E. L.
Published: March 2003

The relativistic corrections to the ponderomotive force for a general transverse plane wave of arbitrary polarization lead to an approximately twenty percent reduction in the single particle ponderomotive force for 10.6 μm CO2 light at 1016 W/cm2. The recent nonrelativistic derivation of laser-induced plasma profiles is extended to the relativistic regime by including the relativistic corrections to the ponderomotive force in the fluid equations. Specifically, analytic results are obtained which facilitate relating the number densities and flow velocities to the electric field strength at the sonic point; in addition, these relations allow the complete self-consistent steady state structure of the profile to be determined numerically. Several detailed comparisons of nonrelativistic and relativistic results are discussed.
Integral formulation for the two-dimensional spatial structure of drift and trapped-electron modes
Authors: Rewoldt G. , Tang W. M. , Frieman E. A.
Published: March 2003

Previous calculations of the linear growth rate and two-dimensional spatial structure of trapped-electron modes are made more general and more accurate in several ways. First, an integral equation formulation of the eigenmode problem allows arbitrary values of krρi (where kr is the radial wavenumber and ρi is the ion gyroradius) to be treated. Second, the ion response is generalized so that arbitrary ratios of the ion magnetic drift frequency to the mode frequency are allowed. Finally, the electron and ion collision operators have been improved to allow consideration of the plateau and Pfirsch–Schlüter regimes in addition to the usual banana regime. It is therefore possible to follow the transition in toroidal geometry from the trapped-electron mode to the collisionless and collisional drift modes. The method used involves expansion of the perturbed electrostatic potential in complete sets of radial and poloidal basis functions to convert the quasi-neutrality integral equation into a matrix equation.
Evolution of weak waves in inert binary mixtures
Authors: Rasmussen Maurice L.
Published: March 2003

The governing Burgers’ equation that describes the evolution of weak one-dimensional wave fronts in inert binary mixtures is derived.
Resonance cones in a bounded plasma for a finite source
Authors: Grabbe Crockett L.
Published: March 2003

The effect of a finite source on the warm plasma resonance cones in a bounded plasma is discussed. Graphs of the potential produced by a Gaussian gap source are presented for parameters which illustrate the individual resonance cones and their interference.
Interface statistics of a uniformly distorted heated turbulent wake
Authors: Kawall J. G. , Keffer J. F.
Published: March 2003

An experimental determination of statistical properties of the interface separating turbulent fluid and contiguous nonturbulent fluid in a slightly heated plane wake, subjected to a uniform and constant rate of strain, has been made by means of digital sampling and processing techniques. The results, which comprise intermittency factor and burst rate distributions, root-mean-square interface slopes and probability density functions of the durations of turbulent and nonturbulent fluid, indicate that, as in the case of the unstrained wake, the interface position may be regarded as a stationary Gaussian random variable.
Dynamical behavior of the fundamental triad-interaction system in three-dimensional homogeneous turbulence
Authors: Lee Jon
Published: March 2003

The fundamental triad-interaction system is the building block of the nonlinear interaction of the three-dimensional Navier–Stokes equations. It satisfies incompressibility, conserves energy and helicity, preserves measure under the time evolution, and involves an arbitrary parameter taking any value in [0,2π]. Under several values of this parameter, it is found that the fundamental triad-interaction system cannot be ergodic on the constant energy-helicity surface because of the extraneous constants of motion other than energy and helicity. This at once implies that isotropy is not possible for the spectral tensor, for isotropy calls for mixing which is a stronger requirement than ergodicity. Although the dynamics of a single triad-interaction system is not directly relevant to real homogeneous turbulence, a theoretical framework to investigate ergodicity and mixing and isotropy of the three-dimensional turbulence model by consistently including many fundamental triad-interaction systems is provided.
Long waves in inviscid compressible atmospheres: Isothermal atmosphere
Authors: Sachdev P. L. , Seshadri V. S.
Published: March 2003

Solitary waves and cnoidal waves have been found in an adiabatic compressible atmosphere which, under ambient conditions, has winds, and is isothermal. The theory is illustrated with an example for which the background wind is linearly increasing. It is found that the number of possible critical speeds of the flow depends crucially on whether the Richardson number is greater or less than one-fourth.
Dynamics of rotationally stabilized implosions of compressible cylindrical liquid shells
Authors: Book D. L. , Turchi P. J.
Published: March 2003

The dynamics of a rotating, cylindrical liquid shell (liner) adiabatically compressing a trapped medium (the payload) is investigated analytically and numerically. The state variables at minimum radius (turnaround) are computed as functions of pf, the peak payload pressure and u∞, the velocity the liner would attain if allowed to expand without restraint. For each choice of pf and u∞, the rotational speed is chosen to just stabilize the Rayleigh–Taylor modes at the liner-payload interface. The acceleration of the inner surface is largest immediately prior to turnaround, so that the initial rotational speed required for stabilization is close to that for an equivalent incompressible liner. Near turnaround the inner portion of the liner becomes significantly compressed, making the efficiency with which liner kinetic energy is transfered to the payload considerably less than that for an incompressible liner. The liner compression provided at turnaround alters the implosion dynamics and creates a pressure pulse propagating outward, analogous to a ’’water hammer’’. An additional result of compression is a slower rebound speed after turnaround, compared with the implosion speed.
Soluble model for the analysis of stability in an imploding compressible liner
Authors: Book D. L. , Bernstein Ira B.
Published: March 2003

A soluble model of the development of the linear pertubations about a time-varying state of a compressible medium is presented. A Lagrangian description is employed to rederive the equations for the self-similar motion of an ideal fluid and to obtain the linearized equations of motion for pertubations about a general time-varying basic state. The resulting formalism is applied in cylindrical geometry to calculate the growth of flute-like modes associated with a similarity solution modeling the implosion and expansion of a fluid liner. A complete solution is obtained for the perturbed motion. The only modes for which the perturbation amplitudes grow faster than the unperturbed liner radius during both implosion and expansion are divergence- and curl-free. Numerical and analytical results are obtained for these and shown to reduce, in the short-wavelength limit, to the Rayleigh–Taylor instability found previously for incompressible time-independent basic states. In addition, a new kind of instability is found: a class of overstable internal modes (sound waves), which are ’’pumped up’’ in amplitude during implosion, but decay during the expansion phase.
Evolution of the explosive instability in a simulated beam plasma
Authors: Jones Michael E. , Fukai J.
Published: March 2003

The evolution of the explosive instability in a beam-plasma system has been studied using two different computer models; a particle-in-cell simulation as well as a fluid model. The initial development of the instability agrees well with the solution of the usual mode coupling equations. The results indicate that the instability in this system saturates because of trapping of electrons by more than one wave leading to a nonlinear frequency shift and a damping of the initially undamped waves.
Variational approach to nonlinear self-focusing of Gaussian laser beams
Authors: Anderson D. , Bonnedal M.
Published: March 2003

The problem of nonlinear self-focusing of Gaussian laser beams is reformulated in terms of a variational principle. By means of approximating Gaussian functions, expressions are obtained for the equilibrium radii and nonlinear frequency shifts of stationary self-trapped laser beams. The nonsteady propagation is given an illuminating form in terms of a potential function description. The analysis confirms the recent results obtained by moment theory as opposed to those based on paraxial ray approximations.
Potential-confined cold plasma stabilization of loss-cone modes in mirror machines
Authors: Baldwin David E. , Jong Raynard A.
Published: March 2003

The analysis of cold plasma stabilization of the drift-cyclotron-loss-cone mode in mirror machines is extended to conditions in which the cold plasma is confined by a weak local minimum in the ambipolar potential. These conditions allow stabilization with less electron energy drain than simple axial flow of cold plasma. Scaling laws are derived for the required cold plasma flux, the resulting fluctuation induced ion diffusion, the steady state electron temperature, and the trapped-ion lifetime.
Electrostatic self-plugging of a picket fence cusped magnetic field
Authors: Hershkowitz Noah , Smith John R. , Kozima Hideo
Published: March 2003

Emissive Langmuir probes are used to map the plasma potential in the neighborhood of a picket fence cusped magnetic field. Positive potential ’’islands’’ are found in front of the picket fence conductors showing ion confinement by electrostatic self-plugging of the cusp leaks. This mechanism results in channels whose widths are the order of the hybrid cusp leak widths recently reported.
Influence of equilibrium flows on tearing modes
Authors: Pollard R. K. , Taylor J. B.
Published: March 2003

Early investigations of resistive instability assumed that the plasma was at rest. However, recent work showed that the influence of the natural diffusion velocity (v∼η/a) on resistive tearing modes was important even in the limit η→0. Here, the effect of a more general velocity, of the same order as the natural resistive diffusion velocity, but otherwise arbitary, is investigated. It is found that as η→0 the effect on the stability threshold is finite and independent of the velocity except for its sign. Hence, the threshold is discontinuous at v=0. There is an additional effect of velocity on modes of finite growth rate which may be stabilizing or destabilizing according to the sign and magnitude of the velocity. The present calculations of these effects agree well with numerical simulations of tearing modes.
Kinetic theory for fluctuations and noise in computer simulation of plasma
Authors: Langdon A. Bruce
Published: March 2003

An accurate theory of fluctuations and noise in computer simulation of plasma is developed. The analytic method describes the space and time discretization exactly and the results reduce simply and correctly to the standard results of plasma kinetic theory in the limit of small space and time step. If the particles are imagined to be a Monte-Carlo sampling of the phase space, then the fluctuations in this sampling, as modified by collective effects, are a concern of this paper. This theory is of interest in theoretical and empirical studies to understand the character of representation by simulation methods of plasma processes such as transport.
Verification of a simple collision operator for one-dimensional plasma by simulation experiments
Authors: Virtamo Jorma , Tuomisto Harri
Published: March 2003

The suitability of a simplified Fokker–Planck collision operator for a one-dimensional electron plasma is verified by simulation experiments. Differences in previous determinations of relaxation time are clarified. The homogeneous collision operator is applied as a model to the nonlinear heat conduction problem, which is solved by making use of an eigenfunction expansion.
One-dimensional boson soliton collisions
Authors: Montes Carlos , Peyraud Jean , Hénon Michel
Published: March 2003

One-dimensional photon solitons and plasmon solitons due to nonlinear scattering of bosons by plasma particles are governed by the same type of nonlinear integrodifferential kinetic equation. A numerical study shows that paired collisions between boson solitons can take place at a finite range the same as for particles having a potential. The existence of two exact invariants of motion forces the two outgoing solitons to be equivalent to the incoming ones after exchanging their identities. Multiple soliton collisions violate this.
Development of local turbulent drag reduction due to nonuniform polymer concentration
Authors: McComb W. D. , Rabie L. H.
Published: March 2003

Turbulent drag reduction produced by injection of polymer at the centerline of a pipe flow was found to increase with streamwise distance from the injection point. This was due to radial dispersion of the injected polymer. A tentative relationship between the two is proposed.
Algebraic internal wave solitons and the integrable Calogero–Moser–Sutherland N-body problem
Authors: Chen H. H. , Lee Y. C. , Pereira N. R.
Published: March 2003

The Benjamin–Ono equation that describes nonlinear internal waves in a stratified fluid is solved by a pole expansion method. The dynamics of poles which characterize solitons is shown to be identical to the well-known integrable N-body problem of Calogero, Moser, and Sutherland.
Radiated electron Bernstein waves
Authors: Ohnuma T. , Ogiwara Y. , Ohmori S. , Adachi S. , Hirayama K.
Published: March 2003

The phase, group, and ray velocity surfaces of electron Bernstein waves are obtained theoretically.
Space charge neutralization regions for mixed positive and negative ion beams
Authors: Dolique J. M.
Published: March 2003

As in the previous studied case of space charge neutralization of positive ion beam by electron injection, there are necessary conditions on mean and thermal speeds at the mixing position, for the downstream mixed positive and negative ion beam to be stable and space charge neutral.
Measurements of dispersion relation of waves in a turbulently heated plasma using microwave scattering
Authors: Mase A. , Tsukishima T. , Iguchi H. , Ito Y. , Kawabe T.
Published: March 2003

The time-resolved dispersion relation of the waves excited in a turbulently heated plasma is studied using the microwave scattering method. The phase velocity of the wave is observed to increase with time, presumably indicating the increase in the electron temperature.
Isothermal expansion of a two-phase fluid in a magnetohydrodynamic generator duct
Authors: Kurzweg U. H. , Elkins R. E. , Trovillion T. A. , Lindgren E. Rune
Published: March 2003

A model for one-dimensional, zero-slip, two-phase flow through a Faraday magnetohydrodynamic generator is developed and used to determine the variation in duct cross section as a function of entrance conditions and load factor for uniform power output and velocity along the duct.
Comments on ’’Large structure in a turbulent boundary layer’’
Authors: Falco R. E.
Published: March 2003

A comparison made by Brown and Thomas of the angle formed by the locus of certain spatial separations with the angle of the backs of large eddies in one of the author’s smoke photographs is shown to be invalid.
Comments on ’’Wave fronts of nonlinear waves in a vibrationally relaxing gas’’
Authors: Parker D. F.
Published: March 2003

By a slight modification of Ishii’s procedure, it is shown that his recently derived results for weak shock propagation apply only when conditions behind the shock are nearly uniform.
Reply to the comments of D. F. Parker
Authors: Ishii R.
Published: March 2003

In response to comments by Parker, it is claimed by Ishii that Parker’s comments and corrections are based upon a misinterpretation and misunderstanding of Ishii’s procedure.
Linear stability analysis for the ablation flow near a cylindrical pellet in a plasma
Authors: Parks Paul B.
Published: March 2003

The stability of a one-dimensional cylindrically symmetric quasi-steady ablation flow near a solid hydrogen pellet is investigated. The gas-dynamic conservation equations describing the flow are linearized in order to look for growing perturbations of the helical type. The problem is treated both analytically and numerically and comparisons are made between both approaches. The analysis reveals that the ablation process itself has no significant instabilities.
Plasma diffusion due to magnetic field fluctuations
Authors: Okuda H. , Lee W. W. , Lin A. T.
Published: March 2003

Plasma diffusion due to magnetic field fluctuations has been studied in two dimensions for a plasma near thermal equilibrium and when the fluctuations are suprathermal. It is found that near thermal equilibrium, electron diffusion varies as B−2 when the collisionless skin depth is greater than the thermal electron gyroradius and is generally smaller than the diffusion due to collisions or electrostatic fluctuations for a low-β plasma. When the suprathermal magnetic fluctuation exists because of macroscopic plasma currents, electron diffusion is enhanced due to the coalescence of current filaments and magnetic islands. Magnetic field energy is found to condense to the longest wavelength available in the system and stays there longer than the electron diffusion time scale.
Plasma laser pulse amplifier using induced Raman or Brillouin processes
Authors: Milroy R. D. , Capjack C. E. , James C. R.
Published: March 2003

A device which uses an induced Raman or Brillouin scattering process to amplify laser pulses is described. A technique is presented to analyze the amplification of ultrashort laser pulses with effects such as pump depletion included. The results of the examples considered indicate that such a device can be realized with current technology.
Large mode-number tearing and twisting modes
Authors: Hazeltine R. D. , Strauss H. R. , Mahajan Swadesh M. , Ross David W.
Published: March 2003

The radial width, w, of the boundary layer associated with tearing and twisting modes is always much smaller than equilibrium length scales. However, for the large mode number perturbations which seem particularly relevant to anomalous tokamak radial transport, the poloidal wavelength, k⊥−1, can become short enough to cast doubt on previous analyses, which neglect finite −k⊥w terms. The effect of such terms on prominent electromagnetic eigenmodes is studied here, both analytically and numerically. The two methods agree qualitatively, and show that the growth rates of Δ’-driven tearing modes are reduced by finite k⊥w, while certain other tearing and twisting mode growth rates are enhanced.
Alfvén-ion-cyclotron instability for axially bounded plasma
Authors: Rognlien T. D. , Watson D. C.
Published: March 2003

The Alfvén-ion-cyclotron instability is studied for a model where the ions are confined axially by a quadratic electrostatic well. Comparison between the homogeneous plasma dispersion relation, an effective dispersion relation including the effect of axially bouncing ions, and the complete eigenvalue solution shows that the first two approximate solutions are quite accurate for plasma lengths on the order of the ion gyroradius. The eigenmode with odd electric field symmetry is found to be the most unstable. Comparison is made with a previously reported particle simulation which imposes linear polarization for the electric field. It is found that the linear polarization constraint can give the unphysical result of instability at vanishingly small plasma β⊥ for certain parameters.
Simulation of the mirror drift cone instability
Authors: Winske D.
Published: March 2003

Results of particle simulation of the mirror drift cone instability, a high frequency (∼lower hybrid) flute mode with loss-cone ions, are presented and compared with theory. Possible saturation mechanisms are discussed, and measurements of the diffusion of ions into the loss cone are presented and compared with quasi-linear theory.
Bernoulli forces on an elliptical cylinder by a nonuniform flow
Authors: Parker E. N. , Tsinganos K. C.
Published: March 2003

A simple expression for the aeroydynamic lift on an elliptical cylinder in a nonuniform, inviscid, free stream is derived. The derivation is exact for a flow with uniform vorticity and directed perpendicular to the axis of the cylinder. The derivation is approximate for a general large scale flow, for which the force is calculated to first order in the derivatives of the initial free-stream velocity Ui(x,y,z).
Decay of homogeneous turbulence from a given state at higher Reynolds number
Authors: Deissler R. G.
Published: March 2003

The hierarchy of turbulence equations is closed by several methods, but good results for higher Reynolds numbers are obtained only for a closure by specification of initial conditions. Four terms of an exponential series, which is an iterative solution of the Navier–Stokes equation, are used in the closure. A complete solution, in the sense that the evolution of all of the initially specified spectra can be calculated, is obtained. This cannot be done by using a Taylor series, regardless of how many terms are retained. The results indicate that purely viscous decay becomes negligible compared with inertial decay as Reynolds number becomes large.
Preferential entrainment in a two-dimensional turbulent jet in a moving stream
Authors: Anderson Paul , LaRue John C. , Libby Paul A.
Published: March 2003

Measurements in a two-dimensional helium jet discharging into a moving airstream establish that entrainment at the upstream edges of turbulent structures is dominant with the consequence that the velocity and helium concentration are lower at these edges. These results are consistent with earlier data showing preferential entrainment at the downstream edges of turbulent structures in both boundary layers and wakes, since in all cases entrainment at leeward edges predominates.
Internal wave motion in a periodic stratification
Authors: Malvestuto Vincenzo
Published: March 2003

The problem of local internal waves is studied within an infinite medium with a mean density profile described by a periodic Brunt–Väisälä frequency N (z). This appears to be the analog of the quantum-mechanical problem for a particle in a unidimensional lattice potential. Explicit calculations and detailed analysis are carried out for a delta shaped N2(z) profile, paralleling the so-called Dirac-comb model for the quantum crystal. The analysis of this rather special case was motivated by recent oceanographical observations in the Mediterranean showing a sort of periodic behavior in the fine structure of density profiles. The selection of Brillouin zones for the wavenumbers of internal waves and the existence of frequency gaps appear to be the most interesting issues of the study of the dispersion relation. Corrections for a finite depth of the ocean and for a finite extent of the density gradients are also suggested.
Numerical computation of steep gravity waves in shallow water
Authors: Vanden-Broeck J.-M. , Schwartz L. W.
Published: March 2003

An efficient numerical scheme to compute steep gravity waves in water of shallow uniform depth is described. The problem is formulated as a system of integrodifferential equations for the free surface. A numerical procedure based on Newton’s iterations is devised to solve these equations. Solutions of high accuracy for depth as small as 1/120 of a wavelength are presented. Numerical confirmation is obtained for the existence of maxima of the potential and kinetic energies of the waves as functions of the steepness.
Some physical aspects of the nonequilibrium, supersonic, corner expansion flow of ionized gases
Authors: Igra O. , Barcessat M.
Published: March 2003

The flow fields of supersonic, nonequilibrium corner expansion flows of ionized gases have been solved numerically, for three different gases, using the method of characteristics. Special attention has been given to the effect that the gas mass and its ionization potential have upon the solution obtained. It was found that the ratio between the atomic mass of the element considered and its ionization potential ma/ϑI, plays an important role in establishing thermal equilibrium. Gases having a small value of ma/ϑI will approach thermal equilibrium at a faster rate than those having a larger value of ma/ϑI. On the other hand, the approach to chemical equilibrium is controlled by the recombination rate which is strongly temperature dependent. Therefore, fast reduction in temperature, in the expansion field, promotes a rapid approach to chemical equilibrium. The effect of the electron-atom collision cross section σea, on the numerical results obtained, is also studied. It is shown that accurate knowledge of σea is required to evaluate the plasma electronic properties (Te and α), but even a rough estimate of σea is sufficient for the evaluation of the gross properties of the plasma (p, ρ, and T).
Structure of relativistic shock waves in simple gases
Authors: Chapline G. F. , Weaver T. A.
Published: March 2003

Numerical solutions of the exact relativistic nonlinear Boltzmann equation have been obtained which describe the structure of relativistic shock transitions in dilute one-component simple gases. When the speed of the shock wave is near the speed of light, the calculated velocity profiles, as viewed in the rest frame of the shock wave, are similar to the velocity profiles of weak nonrelativistic shock waves. Starting from this observation an analytic theory for the velocity profile is derived which is accurate for all relativistic energies and may be used to study relativistic shock waves in nonideal fluids where the Boltzmann equation is not valid.
Particle dynamics in low frequency electromagnetic waves in inhomogeneous plasma
Authors: Hasegawa Akira
Published: March 2003

Phase space dynamics of plasma particles in low frequency (ω≪ωci) electromagnetic waves in a low beta inhomogeneous plasma is obtained including the effects of finite ion gyroradius, bounce resonance, and gradient B and diamagnetic drifts. Application of the results to particle flux observations in the magnetosphere is discussed.
Semi-stellarator field stabilization of tokamak plasma
Authors: Ikezi H. , Schwarzenegger K. F. , Ludescher C.
Published: March 2003

The effects of the stellarator field on the positional stability of tokamak plasmas has been studied experimentally. The semi-stellarator field can be substituted for the vertical field and significantly improves the stability of a tokamak plasma.
Analytic eigenvalue equations for collisionless drift waves in tokamaks
Authors: Catto Peter J. , Tsang K. T.
Published: March 2003

Recently, collisionless drift waves in sheared magnetic fields were shown to be stable. The validity of the analytic model employed in one of these investigations is examined in detail.
Motion of fluid with constant vorticity in a singly-connected region
Authors: Su C. H.
Published: March 2003

An equation for invariant curves in the motion of a vortex blotch is derived. Kirchhoff’s elliptical vortex is shown to satisfy the equation. It is also found that small but finite harmonic derivations from a circular vortex are themselves steady motions.
Stress tensor of dilute polymer solutions
Authors: Lhuillier D.
Published: March 2003

The Kramers–Giesekus stress tensor is shown to be incompatible with an Oldroyd time derivative in the evolution equation of polymer deformation.
Comparison of local and nonlocal theories of the collisional drift instability
Authors: Ellis R. F. , Marden-Marshall E.
Published: March 2003

Two nonlocal cylindrical models of the collisional drift instability of a weakly ionized plasma are solved numerically and compared with the local slab model. It is shown that the local slab is inadequate in describing how mode stability varies with azimuthal mode number.
Nonlocal hybrid-kinetic stability analysis of the mirror-drift-cone instability
Authors: Davidson R. C. , Uhm Han S. , Aamodt R. E.
Published: March 2003

A hybrid-kinetic model (Vlasov ions and cold-fluid electrons) is used to develop a fully nonlocal theory of the mirror-drift-cone instability. The stability analysis assumes electrostatic flute perturbations about a cylindrical ion equilibrium f0i(H⊥−ωiPϑ, vz), where ωi=const is the angular velocity of mean rotation. The radial eigenvalue equation for the potential amplitude φ (r) is solved exactly for the particular choice of f0i corresponding to a sharp-boundary (rectangular) density profile. The resulting dispersion relation for the complex eigenfrequency ω is investigated numerically for a broad range of system parameters including the important influence of large ion orbits and ion thermal effects. It is found that the instability growth rate is typically more severe for fast rotational equilibria (ωi=ω̂+i) with axis encircling orbits than for slow rotational equilibria (ωi=ω̂−i). Stability behavior is investigated for the entire range of r̂Li/Rp allowed by the equiibrium model (0<2r̂Li/Rp<1).
Aspects of a renormalized weak plasma turbulence theory
Authors: Krommes John A. , Kleva Robert G.
Published: March 2003

A renormalized Vlasov turbulence theory, derived by neglecting a mode coupling term in the direct interaction approximation, is discussed. The theory reduces correctly to weak turbulence theory; it predicts both diffusion and polarization effects of the turbulent medium on test particles, as well as the inverse effects of the test particles on the medium. A heuristic, physical algorithm is presented for constructing the equations. The theory of the renormalized dielectric function is reviewed.
Oscillations of a bounded plasma in the lower-hybrid range
Authors: Gore R. A. , Lashinsky H.
Published: March 2003

Q-machine experiments are described in which discrete resonant modes characteristic of the finite length and radius of a plasma column in which (ωpe/ωce)2<<1 are excited by an inductive coupler in the lower-hybrid range of frequencies. The experimental results are in agreement with an analysis in which ion effects and electron thermal effects are taken into account. Inductive coupling is found to give high-efficiency excitation of single modes without resonance cones. The dependence of mode properties on plasma parameters and geometric parameters is examined in the linear regime and the relation of these experiments to plasma heating and to the suppression of drift instabilities by lower-hybrid fields is discussed.
Conditional eddies in isotropic turbulence
Authors: Adrian Ronald J.
Published: March 2003

Isotropic turbulence is examined for the existence of conditional flow structures by computing estimates of the velocity u(x+r, t) given that the velocity at (x, t) assumes some specified value, u(x, t). In general, the best mean-square estimate of u(x+r, t) is the conditional average 〈u(x+r, t) ‖ u(x, t) 〉. This quantity is approximated in terms of second- and third-order two-point spatial correlations using nonlinear estimation techniques. The estimate predicts conditional eddies that are vortex rings axisymmetric about the direction of u(x, t). Averaging these estimates over all values of u(x, t) yields two-point moments that are correct through third order.
Magnetohydrodynamic pipe flow in nonuniform, axisymmetric fields
Authors: McMichael J. M. , Deutsch S.
Published: March 2003

The perturbation of Poiseuille pipe flow by nonuniform, axisymmetric magnetic fields with weak axial gradients is treated theoretically for small magnetic Reynolds numbers and finite Hartmann and Reynolds numbers. Numerical examples for pipe flow through a finite length magnet solenoid are given. The results indicate that separated flow may develop in the fringing magnetic fields accompanied by appreciable local static pressure gradients and high local current densities.
Recurrent motions in certain continuum dynamical systems
Authors: Thyagaraja A.
Published: March 2003

Recent observations of Yuen and Ferguson on the dynamical structure of nonlinearly saturated, spatially periodic solutions of the nonlinear Schrödinger equation are given a simple analytical explanation. It is shown that many nonlinear systems can be described as effectively possessing a finite number of degrees of freedom even though the evolution equations formally relate to a continuum. Powerful theorems in general dynamics then lead to the existence of generally recurrent motions which need not, however, be quasi-periodic or even almost periodic. An explicit example is given to show that a system need not be conservative in order to exhibit recurrence. Explicit estimates of the effective number of degrees of freedom are given for the important nonlinear Schrödinger equation and the Korteweg–de Vries equation.
Pseudo-classical transport in a sheared magnetic field: Theory and simulation
Authors: Nevins William McCay , Harte Judith , Gell Yakov
Published: March 2003

The cross-field transport due to the trapping of electrons in a finite amplitude wave (pseudo-classical transport) is investigated. Both finite wave frequencies and magnetic shear are included. The single particle orbit equations are solved to obtain the trapping criterion as well as the trapped particle orbit width and bounce frequency. Using a random walk model, the scaling of the pseudo-classical transport coefficients with the parameters of the plasma and wave are deduced. This scaling is employed to extend a previous calculation of the transport coefficients to include magnetic shear which is found to reduce these transport coefficients. Computer simulations of this transport process are presented. The measured transport rates are in very good agreement with the previous kinetic calculation in the absence of magnetic shear and with this extension of pseudo-classical transport theory which includes magnetic shear.
Bremsstrahlung in a magnetized plasma
Authors: Jones Roger D. , Pytte A.
Published: March 2003

Using Kirchoff’s law, the bremsstrahlung emission coefficient, in the dipole approximation, is calculated for a magnetized plasma. Effects due to dynamic screening, large momentum transfer between particles, and overlapping of particle wavefunctions during close collisions are taken into account.
Comments on ’’Probe theory for arbitrary shape in a large Debye length, stationary plasma’’
Authors: Shimizu T. , Dote T.
Published: March 2003

A method for locating the space potential in a large Debye-length plasma is criticized, on the basis of a computer calculation, as being possibly physically unrealistic.
Reply to comments by T. Shimizu and T. Dote
Authors: Chang Jen-Shih , Laframboise J. G.
Published: March 2003

In response to a criticism of a method for determining the space potential in a plasma, it is claimed that the criticism is invalid because clearly stated limitations of the method were ignored and also because of the critic’s use of an unsuitable logarithmic horizontal scale in their argument.
Theory of strongly turbulent two-dimensional convection of low-pressure plasma
Authors: Sudan R. N. , Keskinen Michael J.
Published: March 2003

The ’’direct interaction approximation’’ of Kraichnan as modified by Kadomtsev is employed to develop a strong two-dimensional turbulence theory which predicts both nonlinear frequency broadening and a power law for the spectrum of a convecting plasma. These results are compared both with experimental observations and numerical simulations.
Cavitation of a bubble in an inviscid compressible liquid, with comparisons to a viscous incompressible liquid
Authors: Lastman G. J. , Wentzell R. A.
Published: March 2003

A model of a bubble, consisting of an adiabatic gas surrounded by an inviscid compressible liquid with surface tension at the liquid-gas interface, is studied in order to explain experimental results not explained (or not adequately explained) by the viscous incompressible liquid model. The inviscid compressible liquid model is used to predict various characteristics of cavitating and noncavitating bubbles. In particular, compressibility accounts for the rapid damping of bubble oscillations after the cavitation phase; an upper bound is determined for the pressure produced by cavitation; the sharp pressure spike at the initiation of cavitation is predicted; the threshold bubble radius for the onset of cavitation is estimated; and the range of bubble radii is estimated, for which the tension pulse is reproduced for certain noncavitating conditions. In many instances comparisons are made between the viscous incompressible liquid model and the inviscid compressible liquid model.
Surface tension restoring forces on gravity waves in narrow channels
Authors: Heckerman David , Garrett Steven , Williams Gary A. , Weidman Patrick
Published: March 2003

Surface tension restoring forces are investigated for low amplitude gravity waves propagating in narrow channels. Liquids which do not wet the container walls experience a nonuniform displacement of the meniscus as the wave passes. The variation of surface curvature leads to a surface tension force which increases the velocity of the gravity wave. The effect is substantial in experiments with water in Plexiglass channels. The dependence on channel width and contact angle has been investigated, and agreement is found with a simple theoretical model. Addition of a wetting agent to the water eliminates the effect, decreasing the velocity to within 1% of the classical dispersion relation.
Shape stability for a plasma contained within a standing electromagnetic field
Authors: Ensley Donald L.
Published: March 2003

For an over-dense plasma located within a resonant cavity and surrounded by standing electromagnetic radiation, it is shown that shape stability depends only on the ratio of the mean plasma radius (ra) to the wavelength of the surrounding radiation. For an initial cavity mode wavenumber k10, stability occurs for k10 ra≲π. Becausetheplasma-surfaceoscillation frequency νλ is shown to scale linearly with λ (the order of the surface wave), νλ remains small compared with the electromagnetic field frequency for stable plasmas. These results are of significance in designing inertial fusion experiments in which intense electromagnetic fields are used for heating and compressing a dense plasma.
Wave-particle interaction in the late beam-plasma instability
Authors: Freese K. B. , Walsh J. E. , Lohr John
Published: March 2003

Experiments are reported on the beam-plasma instability at times after saturation when the electron distribution function exhibits a high energy tail. The results show that high energy electrons are produced by a velocity resonant wave-particle interaction. The experiments were formed on quite different devices at Dartmouth College and The University of Texas; however, the results from the two laboratories are consistent.
Linear and nonlinear theory of ballooning trapped electron mode
Authors: Rogister André , Hasselberg Günter
Published: March 2003

The linear and nonlinear theories of the trapped electron mode are developed in the limit where the modes overlap many rational surfaces. In cases where shear stabilization is annihilated by toroidal coupling, it is found that the radial width of the mode increases with increasing level of turbulence until ion Landau damping balances the destabilizing effect of trapped electrons. Knowledge of the turbulence level enables the evaluation of the anomalous particle and energy transport. The diffusion coefficient scales with temperature, magnetic field, and density as the superbanana diffusion coefficient due to field asymmetries. Radial localization of the destabilizing trapped electron term caused by the difference between the pitch of the magnetic field and that of the mode results in a reduction of the linear growth rate of order Δ/Xt, where Δ is the spacing between rational surfaces and Xt is the radial wavelength.
Observations of a highly collisional toroidal plasma equilibrium
Authors: Allen A. W. , Antoniades J. A. , Goldenbaum G. C.
Published: March 2003

The time evolution of temperature and density profiles in a finite beta, noncircular cross section (b/a=2) toroidal plasma (R0/a=2) has been measured. Measurements show ion temperatures decreasing as the density is increasing along the major radius at the z=0 midplane. For these conditions, the electron temperature remains approximately uniform over the cross section. A recent theoretical model for highly collisional circular cross section plasma predicts qualitatively similar temperature and density profiles which are different from those for the less collisional Pfirsch–Schlüter regime.
High beta stellarator stability theory
Authors: Schmidt Michael J.
Published: March 2003

An analytic study of the stability of a straight diffuse high beta stellarator with arbitrary wall corrugation is presented. It is found that a solvability condition for the equilibrium of such a plasma is intimately related to a sufficient condition for stability. The results of the calculation suggest that if the equilibrium model is valid, then all high beta stellarators are unstable.
Diffusion coefficients of low frequency electromagnetic turbulent plasma
Authors: Yamagishi T.
Published: March 2003

Diffusion coefficients for low frequency electromagnetic turbulent plasmas have been derived by the statistical method of Weinstock.
Resistive ion-ion-hybrid instability in current-carrying plasmas
Authors: Lee Kai Fong , Chu Louis W. M.
Published: March 2003

Obliquely propagating ion-ion-hybrid waves are found to be unstable in a collisional, fully ionized plasma with two ion species and carrying a field-aligned current.
Inductive effects in flux conserving tokamaks
Authors: Bateman Glenn
Published: March 2003

The evolution of flux conserving sequences of equilibria in circular cylindrical geometry is considered as the plasma is heated or compressed. It is shown that force-free currents are induced when the low pressure region at the edge of the plasma is compressed against a flux conserving wall. A force-free surface current is induced if there is a vacuum region between the expanding plasma and the wall. These edge currents run opposite to the direction of the current in the main body of the plasma. The force-free currents can be avoided or reversed at the edge of a plasma with diffuse resistivity profile by programming the total longitudinal current as the plasma is heated or compressed.
Interaction between two force-free plasma vortices
Authors: Davidson J. , Wells D. R.
Published: March 2003

Calculations show that the magnetic J×B and Magnus ρ (ξ×v) interactions between two force-free plasma vortices exhibit a long range dipole-dipole attraction, caused by their toroidal currents along with a strong short range repulsion due to their poloidal currents. This corresponds to their behavior.
Possible inverse cascade behavior for drift-wave turbulence
Authors: Fyfe David , Montgomery David
Published: March 2003

The turbulent behavior of a two-dimensional dynamics of electrostatic drift-wave turbulence, proposed by Hasegawa and Mima, is explored analytically and numerically. A dual-cascade hypothesis leads to modal potential spectra which vary as k−14/3 at lower k and k−6 at higher k.
Suppression of an instability by the introduction of external turbulence
Authors: Hershcovitch Ady , Politzer Peter A.
Published: March 2003

The problem of suppression of a plasma instability by the introduction of an externally controlled spectrum of turbulent electric fields is considered. The theory of strong turbulence is extended to include external fields, and is applied to the half-cyclotron frequency instability occurring in counterstreaming, magnetically confined electron beams. Experimental results from such an electron beam system are presented which confirm that the suppression of the instability is due to resonance broadening.
Discontinuity formation due to gravity wave propagation in a shear layer
Authors: Teitelbaum H. , Sidi C.
Published: March 2003

The propagation of internal gravity waves in shear is investigated theoretically. The known solution of the problem is modified by a technique based on characteristic surfaces. It consists of taking as a new independent variable a family of characteristics. The new solution shows that a tangential discontinuity appears below the critical level. The horizontal velocity and the density pertubation remain bounded up to the discontinuity.
Asymptotic solutions of the energy equation for viscous supersonic flow past corners
Authors: Rizzetta D. P.
Published: March 2003

When a compressible laminar boundary layer encounters a corner, a viscous-inviscid interaction occurs. The correct mathematical structure for such interactions at large Reynolds numbers is provided by the asymptotic triple-deck theory. Within this framework, solutions of the energy equation for supersonic flow past compression and expansion corners are considered. The limiting structure for far upstream and downstream temperature profiles is examined and a linearized solution for wall heat transfer is derived for very small corner angles. For corners of larger angles, numerical solutions of the energy equation are presented, including cases with separation.
Observation of the effect of shear on vortex diffusion in a collisional plasma
Authors: Navratil G. A. , Post R. S. , Ehrhardt A. Butcher
Published: March 2003

The addition of a weak toroidal magnetic field to a poloidal octupole field confining a collisional helium plasma, ne∼5×1011 cm−3, Ti∼Te∼0.2 eV, was observed to damp the nonthermal vortex spectrum and associated anomalous diffusion previously observed with a purely poloidal field. As a result, the plasma was observed to diffuse across field lines solely by classical diffusion when Bt/Bp≳0.1.
Kinetic theory of neutral hydrogen atoms penetrating a hydrogen plasma half-space: Analytic solution
Authors: Burrell Keith H. , Chu Cheng
Published: March 2003

Transport of neutral hydrogen atoms in uniform temperature hydrogen plasma half-spaces is considered. Using arbitrary ion distribution functions, analytic neutral solutions are found depending on one spatial and three velocity variables. These are evaluated for a Maxwellian distribution.
Transport to thermal equilibrium of a pure electron plasma
Authors: O’Neil T. M. , Driscoll C. F.
Published: March 2003

The transport of a pure electron plasma column across an axial magnetic field is considered, the transport being due to binary electron–electron collisions. The Boltzmann equation is expanded in inverse powers of the magnetic field, with the radial electric field and density gradient ordered self-consistently. The first nonvanishing terms in the particle flux involve the third derivative of the density and the second derivative of the electric field. An H theorem is used to show that this flux drives the plasma to a confined thermal equilibrium density profile. The electrons can come to thermal equilibrium with each other and still be confined magnetically, since the total canonical angular momentum is conserved. The final equilibrium can be predicted from the initial total number of particles, angular momentum, and energy. The approach to equilibrium is shown in a numerical example.