bluuebunny/crossref_metadata_2025 huggingface dataset:
Lagrangian formulation of neoclassical transport theory
Authors: Bernstein Ira B. , Molvig K.
Published: March 2003

Neoclassical transport theory is developed in a Lagrangian formulation in contrast to the usual Eulerian development. The Lagrangian formulation is constructed from the three actions: magnetic moment, parallel invariant, and bounce-averaged poloidal flux. By averaging over the fast orbital time scales, an equation in the actions alone of the Fokker–Planck type is obtained. The coefficients give the rates of the elementary neoclassical scattering processes. This action space form of the kinetic equation contains in explicit form processes like banana diffusion and the kinematic Ware pinch. The associated fluxes can be computed by simple moments without having deviations from the local Maxwellian. All the trapped-particle contributions are of this explicit type. Another class of fluxes arise from perturbations to the Maxwellian and are termed implicit. The decomposition of the fluxes into explicit and implicit parts is a key feature of the Lagrangian formulation. These contributions correspond to distinct physical processes and have separate Onsager symmetry theorems (explicit and implicit) for their respective transport matrices. The theory does not depend on the details of the Fokker–Planck coefficients but only on some very general properties and is thus applicable—without modification of the formalism—to nonaxisymmetric and turbulent systems. This general formulation is the primary purpose of the work. To benchmark the theory, in the present paper, the tokamak transport coefficients (for the Lorentz gas) are computed and compared to the known Eulerian results, demonstrating the equivalence of the two formulations. The elementary processes responsible for the neoclassical pinch and bootstrap effects (somewhat obscured in the Eulerian picture) are identified and the physical basis for their Onsager symmetry relationship is clarified.
Fokker-Planck equation for a plasma in a magnetic field with electrostatic fluctuations
Authors: Matsuda Kyoko
Published: March 2003

An alternative procedure for the approach used by Ichimaru and Rosenbluth on transport problems of a plasma in a uniform magnetic field including the effects of fluctuating electric fields is proposed. The resultant kinetic equation reduces to the Rostoker equation in the case of a quiescent plasma and reduces to the quasilinear diffusion equation if the effects of the self-field of particles are ignored. The transverse particle diffusion coefficient obtained by our approach reduces to well-known classical results as special cases.
Determination of the longitudinal dispersion coefficient in flows subjected to high-frequency oscillations
Authors: Jaeger M. J. , Kurzweg U. H.
Published: March 2003

Experimental measurements of the longitudinal dispersion coefficient in oscillatory pipe flow of binary gas mixtures at high oscillation frequencies are presented. The magnitude of the dispersion coefficient is shown to be directly proportional to the product of the square of the oscillation amplitude and the first power of frequency.
Nonlinear excitation of magnetostatic fluctuations by kinetic drift-Alfvén waves
Authors: Kaw P. K. , Chen Liu
Published: March 2003

For typical tokamak parameters, it is shown that superthermal magnetostatic convective-cell fluctuations can be nonlinearly excited by a moderate level of kinetic drift-Alfvén turbulence (e.g., δn/n0∼1%). Effects on the plasma cross-field transport and the nonlinear evolution of drift-Alfvén turbulence are also briefly discussed.
Emission, absorption, and tunneling of whistler waves in an inhomogeneous magnetic field
Authors: Ellis R. F. , Tsakiris G. D. , Boyd D. A.
Published: March 2003

Measurements of electron cyclotron emission parallel to a magnetic field in the regime where finite density effects are important and measurements of electron cyclotron wave tunneling parallel to a magnetic field are reported. The experiments were conducted in a low-temperature (Te ∼2 eV) moderate-density (ne =3×109–3×1012 cm−3) gas discharge plasma in a magnetic mirror geometry. Experimental results are compared with two models, both of which employ Kirchoff’s law to relate emission and absorption. In one model, absorption from hot-plasma theory is calculated and in the other a cold-plasma Budden tunneling type analysis is employed. Both models are in reasonable agreement, with the data generally bracketing the experimental results, and the experiment could not resolve which model is superior. The utility of whistler mode cyclotron emission as an electron temperature diagnostic measurement on mirror machines is confirmed.
Radio-frequency wave enhanced runaway production rate
Authors: Chan V. S. , McClain F. W.
Published: March 2003

Enhancement of runaway electron production (over that of an Ohmic discharge) can be achieved by the addition of radio-frequency waves. This effect is studied analytically and numerically using a two-dimensional Fokker–Planck quasilinear equation.
Dependence of fast magnetic reconnection on electrical resistivity in an isolated current-sheet system
Authors: Ugai Masayuki
Published: March 2003

Computer simulation shows that, initiated by a resistive disturbance, the rarefaction of the current-sheet plasma and the subsequent remarkable thinning of the current-sheet region occur; once the fast reconnection builds up, the plasma density is extremely rarefied near the neutral point. The development of fast reconnection provides a situation favorable to the occurrence of a current-driven instability. The energy conversion rate associated with the fast reconnection is found to have a weak dependence on the magnetic Reynolds number Rm0 and tends to scale as (log10 Rm0)−1 for large Rm0. These results come from the fact that for larger Rm0 the diffusion region that is spontaneously established has a smaller width and hence a larger current density to compensate for the smaller magnitude of electrical resistivity. Effective energy conversion can be realized even in the presence of rigid walls.
Theory and simulation of one-dimensional Raman backward and forward scattering
Authors: Estabrook Kent , Kruer W. L.
Published: March 2003

Computer simulations and theory are used to illustrate the linear and nonlinear behavior or Raman backward and forward scattering in laser-irradiated plasmas. The heated-electron distributions, nonlinear Landau damping, bandwidth of the scattered light, and other results of nonlinear simulations in homogeneous and nonhomogeneous plasmas are described. The characteristics of Raman scattering in a plasma with a quite high background temperature (64 keV) are examined, which are relevant to CO2-heated plasmas. Finally the effects of self-generated magnetic fields are pointed out, which can reduce Raman scattering by inhibiting the transport of hot electrons, and the reduction of Raman scattering by use of laser light with a large bandwidth is described.
Ion trajectories in a space-charge wave on a relativistic electron beam
Authors: Russell D. A. , Ott Edward
Published: March 2003

Motivated by the possibility of collective acceleration of ions trapped in an accelerating space-charge wave on a strongly magnetized electron beam, the ion trajectories in such a configuration are studied. The motions perpendicular and parallel to the beam direction are coupled by a nonlinear term in the ion Hamiltonian that is proportional to the wave amplitude. Because of this coupling, the motion deviates markedly from that of a linear harmonic oscillator in certain resonant regions of phase space. A sequence of canonical transformations is used to study the motion in these regions. It is shown that wave amplitudes that are too small to trap beam electrons are too small to cause these reasonances to overlap. In the absence of such overlap, the motion is not discernibly ergodic in any three-dimensional subspace of the energy hypersurface bcause there exists a third constant of the motion in addition to the total energy and angular momentum. These conclusions are verified using surface-of-section techniques to study numerically integrated ion trajectories. It is observed that the third constant of the motion constrains on ion initially trapped in a potential well of the wave to remain trapped in the well. Therefore, within the bounds of the physical model presented here, ergodic behavior poses no threat to attempts at collective ion acceleration in space-charge waves on a electron beam.
Small-signal theory of a large-orbit electron-cyclotron harmonic maser
Authors: McDermott D. B. , Luhmann N. C. , Kupiszewski A. , Jory H. R.
Published: March 2003

The small-signal theory of a harmonic gyrotron is presented for the case of axis-encircling electron orbits. The beam current required for oscillation is found to be highly dependent on the electron energy. Gyrotron cavities operating on this principle at very high harmonic numbers (n≂10) and high frequency in weak magnetic fields are well matched to low-current, moderate-energy, rf-accelerated electron beams (≂50 mA, ≂250 keV), resulting in compact submillimeter wave systems.
Beam–plasma interactions in a positive ion–negative ion plasma
Authors: Intrator Tom , Hershkowitz Noah , Stern Raul
Published: March 2003

An electron-free plasma consisting of negative ions (SF6−) and positive ions (Ar+), and negligible neutral-ion collision frequencies has been created in the laboratory. This plasma has a mass ratio of approximately 3.5-similar to many computer particle-in-cell simulated systems. A fluid description of this positive and negative ion confinement (PANIC) plasma is given and compared to experimental measurements of a beam–plasma instability for both beam species and a wide range of beam energies. The fluid dispersion relation and most growing modes are predicted to be insensitive to many parameters of the PANIC beam–plasma system, and found to the consistent with the data.
Electron distribution functions in a current sheet
Authors: Stenzel R. L. , Gekelman W. , Wild N.
Published: March 2003

Using a novel directional velocity analyzer the electron distribution function  f(v,r,t) is measured in a magnetic-field-line reconnection experiment. Runaway electrons are observed inside the current sheet, a result important for transport processes and instabilities.
d-3 He reaction measurements during fast wave minority heating in the PLT tokamak experiment
Authors: Chrien R. E. , Strachan J. D.
Published: March 2003

Time- and energy-resolved d-3He fusion reactions have been measured to infer the energy of the d+ or He++ minority ions heated near their cyclotron frequency by the magnetosonic fast wave. The average energy of the reacting 3He ions during 3He minority heating is in the range of 100–400 keV, as deduced from the magnitude of the reaction rate, its decay time, and the energy spread of the proton reaction products. The observed reaction rate and its scaling with wave power and electron density and temperature are in qualitative agreement with a radial reaction rate model using the minority distribution predicted from quasilinear velocity space diffusion. Oscillations in the reaction rate are observed concurrent with sawtooth and m=2 magnetohydrodynamic activity in the plasma.
Energy confinement studies in the tandem mirror experiment (TMX): Power balance
Authors: Grubb D. P. , Allen S. L. , Casper T. A. , Clauser J. F. , Coensgen F. H. , Correll D. L. , Cummins W. C. , Davis J. C. , Dietrich D. , Drake R. P. , Foote J. H. , Fortner R. J. , Futch A. H. , Goodman R. K. , Gryczkowski G. E. , Hooper E. B. , Hornady R. S. , Hunt A. L. , Karmendy C. V. , Nash T. , Nexsen W. E. , Pickles W. L. , Porter G. D. , Poulsen P. , Simonen T. C. , Slaughter D. R. , Hallock G. A. , Strand O. T.
Published: March 2003

The power balance in the Tandem Mirror Experiment (TMX) is studied for several days of operation. Between them, these days typified the operating range of TMX. Examining the power balance on axis, it is found that 60% to 100% of the power is carried to the end walls by escaping central-cell ions. Globally, these calculations account for 70% to 100% of the input power on each of the days studied. Based upon the power balance, the energy confinement times of the particle species are calculated. The end-cell ion energy confinement time is similar to that achieved in the 2XIIB single-cell magnetic mirror experiment, whereas the electron energy confinement in TMX was 10 to 100 times better. The central-cell ion energy confinement in the central flux tube was determined by axial particle loss. At the central-cell plasma-edge radial particle transport and charge exchange with the fueling gas are important processes.
Parametric instabilities near the critical density in steepened density profiles
Authors: Estabrook Kent , Kruer W. L.
Published: March 2003

Computer simulations of laser light absorption and hot-electron generation by the ion-acoustic decay and oscillating two-stream instabilities in nonlinearly steepened density profiles are presented. The steepened density scale length is estimated and used to estimate a condition for instability generation.
Intense electromagnetic solitary pulses in plasmas
Authors: Shukla P. K.
Published: March 2003

The quasistatic slow plasma response to an intense electromagnetic wave is shown to result in a solitary wave structure of an arbitrary amplitude.
Finite-width currents, magnetic shear, and the current-driven ion-cyclotron instability
Authors: Bakshi P. , Ganguli G. , Palmadesso P.
Published: March 2003

Earlier results showing that nonlocal effects due to even a small magnetic shear produce a significant reduction of the growth rate of the ion-cyclotron instability driven by a uniform current are now generalized to finite-width currents. Externally prescribed as well as self-consistent shears are considered. If the current width Lc exceeds the shear length Ls, the previous results are recovered. Shear becomes less effective with reduction of Lc, and for typical parameters, the growth rate attains its (shearless) local value for Lc/ Ls ≲10−2. Nonlocal effects of the finite current width itself come into play if Lc is further reduced to a few ion Larmor radii and can quench the instability.
Kinetic and fluid ballooning stability in anisotropic ion tokamaks
Authors: Cooper W. Anthony
Published: March 2003

The derivation of a kinetic ballooning mode equation for multiple anisotropic fluid ion plasmas and Maxwellian adiabatic electrons is presented. Considering the magnetohydrodynamic (MHD) limit, a fluid ballooning mode equation similar to that derived from the Kruskal–Oberman energy principle is obtained, except that the energetic ions do not contribute to the instability driving mechanism because they drift across the destabilizing curvature region at a rate that is faster than the oscillation of the mode. A numerical example shows that the Kruskal–Oberman critical beta βc ≂2.65% can be increased to βc ≂4.1% when the ratio of peak energetic ion beta to peak total beta βh0/β0 =0.3. Finite Larmor radius (FLR) corrections are also evaluated.
Quasilinear theory of suprathermal ions in mirror machines in the presence of radio-frequency fluctuations
Authors: Hafizi B. , Aamodt R. E.
Published: March 2003

A theory of fast-ion generation in the 2XIIB mirror experiment due to a single resonant electrostatic ion-cyclotron mode is presented. Assuming weak radial gradients of the magnetic induction, which appear to be consistent with experimental data, it is shown that ions with small parallel excursions can be accelerated into the 40 keV region. Allowance for a periodic temporal variation of the amplitude of the mode results in stochastic motion of those ions whose range of parallel excursions form a limited but significant fraction of the plasma length. The diffusion coefficients of this class of ions are computed in the quasilinear approximation. The corresponding diffusion times are in reasonable accord with those from the experiment.
Nonlinear saturation of nonresonant internal instabilities in a straight spheromak
Authors: Park W. , Jardin S. C.
Published: March 2003

An initial value numerical solution of the time-dependent nonlinear ideal magnetohydrodynamic equations demonstrates that spheromak equilibria which are linearly unstable to nonresonant helical internal perturbations saturate at low amplitude without developing singularities. These instabilities thus represent the transition from an axisymmetric to a nonaxisymmetric equilibrium state, caused by a peaking of the current density.
A bifurcation problem in field-reversed configurations
Authors: Clemente R. A.
Published: March 2003

The equilibrium of a class of field-reversed configurations in an external magnetic field is studied analytically. Bifurcation points in parameter space appear when the elongation of the separatrix is equal to 1.61 or to 0.23. In general, for fixed parameters, two equilibria are possible, one of which is almost spherical while the other is highly prolate or, alternatively, highly oblate. The nearly spherical equilibrium corresponds to a lower energy condition.
Creation of high-energy electron tails by means of the modified two-stream instability
Authors: Tanaka Motohiko , Papadopoulos K.
Published: March 2003

Particle simulations of the modified two-stream instability demonstrate strong electron acceleration rather than bulk heating when the relative drift speed vd is below a critical speed Vc. A very interesting nonlinear autoresonance acceleration process is observed which accelerates the electrons much above the phase speed of the linearly unstable modes. Simple criteria are presented that predict the value of Vc and the number density of the accelerated electrons.
Spatially periodic suspensions of convex particles in linear shear flows. III. Dilute arrays of spheres suspended in Newtonian fluids
Authors: Zuzovsky M. , Adler P. M. , Brenner H.
Published: March 2003

Expressions are derived for the rheological coefficients appropriate to the simple shearing, pure straining, and pure vortex motions of dilute cubic arrays of spherical particles suspended in Newtonian liquids, including simple, body-centered, and face-centered systems. Comparable asymptotic coefficients are also given for concentrated suspensions of almost touching spheres in simple cubic array in the lubrication-theory limit.
Interfacial progressive gravity waves in a two-layer shear flow
Authors: Pullin D. I. , Grimshaw R.
Published: March 2003

Nonlinear interfacial gravity waves in a two-layer Boussinesq fluid are studied. In a previous paper, nonlinear waves on a vortex sheet separating two layers, each of constant density and velocity were considered. In the present paper the basic flow model consists of a constant vorticity upper layer bounded by a rigid surface and an irrotational lower layer of infinite depth with continuity of the unperturbed velocity at the density interface. Numerical solutions obtained from an exact formulation in terms of a complex-valued integral equation for the shape and local vortex-sheet strength of the wave profile are compared with results from a second-order Stokes expansion. It is found that the wave of maximum amplitude displays different geometrical features depending on the unperturbed flow parameters. These include waves containing an S-shaped section, waves with cusped crests and surface-constrained waves with long flat crests. Wave integral properties calculated, including the flux of momentum and energy in the wave propagation direction, showed monotonic variation with increasing wave amplitude.
Unsteady aspects of a low mach number jet
Authors: Laufer John , Zhang Jia Xiang
Published: March 2003

Experiments on the flow development along the first diameter of a low Mach number jet are described. It is shown that the flow is governed by a local shear layer instability coupled with a feedback mechanism that determines the positions of the nonlinear amplitude saturation of the unstable modes. The spreading is a stepwise phenomenon associated with the saturation locations. In general these locations move randomly in time and space, resulting on the average in a linear spreading rate.
Interchange stability of an axisymmetric, average minimum-B magnetic mirror
Authors: Ferron John R. , Wong Alfred Y. , Dimonte Guy , Leikind Bernard J.
Published: March 2003

An axisymmetric magnetic mirror with large diameter and easily variable mirror ratio is described. The magnetic field configuration is a simple mirror with an average minimum-B field region on the outer surface. Experimental results are given which demonstrate that the surface field region ensures interchange stability. Stability can be maintained with both positive and negative radial plasma pressure gradients provided that the product of the pressure gradient and specific flux volume gradient is positive.
Fast reconnection of magnetic fields in a plasma
Authors: Hu Pung Nien
Published: March 2003

The reconnection process of magnetic fields in a plasma is analytically studied by perturbing the boundary conditions on a slab of incompressible plasma with a resonant surface inside. It is found, for small resistivity, that the reconnection takes place on an Alfvén time scale and continues into a slow time scale t1=η1/3t. Both time scales are faster than the usual tearing time scale. Furthermore, the plasma evolves globally from its initial equilibrium on the slow time scale and settles down to a different final equilibrium.
‘‘Stabilization’’ of the lower-hybrid-drift instability in finite-β plasmas
Authors: Drake J. F. , Huba J. D. , Gladd N. T.
Published: March 2003

The stability properties of the lower-hybrid-drift instability are reexamined for finite-β plasmas. In contrast to previous results, it is found that finite-β does not stabilize the instability in the sense that the growth rate becomes negative. Rather, as β increases, the fastest growing mode shifts to longer wavelengths and makes a transition to an ion-cyclotron mode when the growth rate falls below the ion-cyclotron frequency.
Space potential profiles in ELMO Bumpy Torus (EBT) experiment
Authors: Bieniosek Frank M. , Connor Kenneth A.
Published: March 2003

Spatially resolved measurements of the electric space potential in the ELMO Bumpy Torus (EBT) have been made by a heavy ion beam probe. The EBT-I device is characterized by positive potentials in the surface plasma the order of 100 V and by a nearly symmetric potential well in the core plasma of up to 300 V with respect to the surface potential. The EBT-S device has a similar potential structure with well depth and peak potential similar to or greater than that of EBT-I. Peak potential and well depth increase as the edge gas pressure is lowered and as the microwave power is increased. The potential structure is strongly linked to the specific heating geometry. The ambipolar electric field is large enough generally to dominate the core electron neoclassical diffusion. The potential profile is approximately parabolic in the core, which is shown to be a natural consequence of the spatially uniform plasma source function.
An electron cyclotron maser instability for astrophysical plasmas
Authors: Freund H. P. , Wong H. K. , Wu C. S. , Xu M. J.
Published: March 2003

The electron cyclotron maser instability is analyzed for a plasma which consists of a suprathermal electron component characterized by velocity-space anisotropies in directions both parallel and perpendicular to the ambient magnetic field, as well as a high-density thermal plasma in which ωe∼Ωe (where ωe and Ωe are the electron plasma and cyclotron frequencies). The complete relativistic resonance condition is used and shown to result in a ‘‘resonance ellipse’’ in momentum space. The instability is considered for both cold and warm suprathermal electron distributions, and for frequencies ω∼Ωe in the ordinary mode and ω∼2Ωe in the fast extraordinary mode. It is shown that the growth rates are comparable for these harmonics over a wide range of parameters which, since they are escape modes of the plasma, can lead to comparable radiation intensities.
The excitation of microwaves by a relativistic electron beam in a dielectric-lined waveguide
Authors: Shoucri Magdi
Published: March 2003

The dispersive properties of a relativistic electron beam in a dielectric-loaded waveguide are investigated. The linearized fluid and Maxwell’s equations are used to derive the dispersion relation and to study the eigenmodes for the system. The Čerenkov microwave radiation mechanism is investigated.
Instability of the boundary layer between a streaming plasma and a vacuum magnetic field
Authors: Peter William , Ron Amiram , Rostoker Norman
Published: March 2003

Analysis is carried out for the long-wavelength stability of the boundary layer formed when a plasma or neutralized ion beam is incident upon, and reflected by, an applied magnetic field. This equilibrium is similar to the Ferraro–Rosenbluth sheath which forms the basis for many models in magnetic fusion and magnetospheric physics. For wavelengths much greater than the sheath thickness ah, the equilibrium is unstable with growth rate (in the regime kah≪m/M ) proportional to (kg)1/2≡(kahΩiΩe) 1/2. The nonlinear evolution of the instability describes plasma propagation across the magnetic field. This instability is similar to the classical flute instability except that polarization along the boundary is due to electron, and not ion, motion.
On the density oscillations of a warm particle bunch
Authors: Channell Paul J. , Sessler Andrew M. , Wurtele Jonathan S.
Published: March 2003

The density oscillations of warm particle bunches is investigated theoretically. Two different mathematical approaches are employed to derive the basic equation describing density oscillations; one is a fluid approach and the second is a more general Green’s function formulation. The motion is analyzed in first-order perturbation theory where it is shown, under the assumption of no degeneracy, that there are only stable oscillations. Second-order perturbation theory gives damping of the motion. The perturbation theory is examined, and a criterion is exhibited for its proper use. Thus, when the resistivity is small enough (but nonzero) the motion is stable, but when the resistivity is large the motion is essentially unstable with a growth rate which is that of an unbunched beam. The criterion is approximately evaluated using a model for a bunched beam.
Laser irradiation of disk targets at 0.53 μm wavelength
Authors: Mead W. C. , Campbell E. M. , Estabrook Kent , Turner R. E. , Kruer W. L. , Lee P. H. Y. , Pruett B. , Rupert V. C. , Tirsell K. G. , Stradling G. L. , Ze F. , Max C. E. , Rosen M. D. , Lasinski Barbara F.
Published: March 2003

Results and analyses are presented for laser irradiation of Be-, CH-, Ti-, and Au-disk targets with 0.53 μm light in 3–200 J, 600–700 psec pulses, at nominal incident intensities from 3×1013 to 5×1015 W/cm2. The measured absorptions are higher than observed in similar 1.06 μm irradiations, and are largely consistent with modeling which shows the importance of inverse-bremsstrahlung and Brillouin scattering. Observed red-shifted back-reflected light shows that Brillouin scattering occurs at low to moderate levels. Backscattering fractions up to 30% were observed in the f/2 focusing lens. The measured fluxes of multi-keV x rays indicate hot-electron fractions of 1% or less, with temperatures of 6 to 20 keV which are consistent with resonance absorption or perhaps 2ωpe. Measurements show 30%–50% efficient conversion of absorbed light into sub-keV x rays, with time-, angular-, and spatial-emission distributions which are generally consistent with non-local-thermodynamic-equilibrium modeling using inhibited thermal electron transport.
Enhancement of neoclassical transport coefficients by a poloidal electric field in tokamaks
Authors: Chang C. S.
Published: March 2003

The effect of an equilibrium poloidal electric field on the neoclassical transport coefficients is studied in the banana regime, and a significant enhancement (a factor of 2 or more) is obtained for the physically interesting case where the magnitude of the electrostatic potential inhomogeneity is of the same order as the magnetic field inhomogeneity in a tokamak.
Particle exchange in the plug of a thermal barrier tandem mirror
Authors: Catto P. J. , Carrera Rodolfo
Published: March 2003

The collisional fluxes of trapped electrons escaping from the plug, and the center cell electrons passing over the thermal barrier and becoming trapped, are evaluated for a simple thermal barrier model appropriate to present tandem mirror experiments.
Charged particle motion near a linear magnetic null
Authors: Kim Jin-Soo , Cary John R.
Published: March 2003

Charged particle motion near the null of a two-dimensional magnetic field is studied. Specifically, the magnetic field is given by the vector potential A=ẑψ0[(y/a)2+(εx/a)2], in which ψ0,a, and ε are constants with ε parameterizing the ellipticity of the flux surfaces. Conservation of canonical z momentum pz reduces the number of nontrivial degrees of freedom to two. Scaling reduces the number of parameters in the system to two, ε and σ (the sign of pz ). Analytical and numerical methods are used to study the nature of orbits. The results are expressed conveniently in terms of ε and Q≡(2mE)1/2/pz. When ε is unity, the additional symmetry implies integrability. When ε is less than unity (the case ε>1 is trivially related) three regimes are found: (1) For ‖Q‖≫1 particle orbits are regular, (2) for ε3/2≲‖Q‖≲1 most particle orbits are stochastic, and (3) for ‖Q‖≪ε3/2 particle orbits are regular, with the third invariant being the magnetic moment.
Ion-acoustic solitary waves in a magnetized plasma with arbitrary electron equation of state
Authors: Witt E. , Lotko W.
Published: March 2003

The oblique propagation of fully nonlinear, slow ion-acoustic solitary waves in a collisionless, low-beta, magnetized plasma is examined. The analysis includes the effects of a finite ion pressure, electron trapping, and multicomponent particle populations. The existence of both compressive and rarefactive modes propagating obliquely to the magnetic field in a plasma with two distinct Boltzmann electron populations and cold ions is demonstrated. It is shown that paired electrostatic shocks observed over the Earth’s auroral zone may be closely related to the rarefactive modes. As a measure of the collisionless dissipation encountered by the solitary waves, the linear response of the plasma to slow ion-acoustic waves is also examined.
Runaway electron instability in the high-density (ωp
e/Ωe>0.5), low-electric-field (E/ED<0.05) regime
Authors: Gandy R. F. , Hitchcock D. A. , Mahajan S. M. , Bengtson Roger D.
Published: March 2003

The characteristics of the runaway instability are studied for the high-density (ωpe/Ωe>0.5) and low-electric-field (E/ED<0.05) cases. For this experimentally relevant case, the wave oscillation frequency as well as the growth rate are calculated for a variety of plasma parameters.
Fingers in a Hele–Shaw Cell with surface tension
Authors: Vanden-Broeck Jean-Marc
Published: March 2003

McLean and Saffman’s model for the fingering in a Hele–Shaw cell is solved numerically. The results suggests that a countably infinite number of solutions exist for nonzero surface tension. This set of solutions contains the solution previously obtained by McLean and Saffman.
Wave formation and growth during sedimentation in narrow tilted channels
Authors: Davis Robert H. , Herbolzheimer Eric , Acrivos Andreas
Published: March 2003

A linear-stability analysis is performed to investigate in detail the conditions for wave formation and growth during sedimentation in long, narrow channels that are inclined from the vertical. The maximum amplification rates of such waves are predicted by solving the equations governing the instabilities both asymptotically for long-wavelength disturbances and also numerically for disturbances with moderate wavelengths. The general trends set forth by the linear theory are found to be consistent with experimental observations. In particular, it is shown that very tall and narrow vessels not only give the largest enhancement in the settling rate but also significantly increase the stability of inclined settling systems.
Computation of turbulent flow over a moving wavy boundary
Authors: McLean John W.
Published: March 2003

Numerical solutions via Newton’s method of the Reynolds-averaged Navier–Stokes equations for steady flow over a two-dimensional wavy surface indicates that by using a simple algebraic eddy-viscosity model, the distribution of wall pressure and shear stresses and the corresponding drag coefficients can be predicted. Computations are compared with experimental results over rigid wavy surfaces and moving flexible boundaries. For small-amplitude wavy surfaces, computed values of the wall stresses agree well with the experimental measurements. For larger-amplitude waves, regions of reverse flow in the trough of the wave are predicted.
Speckle velocimetry study of vortex pairing in a low-Re unexcited jet
Authors: Meynart Roland
Published: March 2003

Application of speckle velocimetry in a round jet (Re=2300) provides instantaneous 2-D velocity fields and vorticity maps of the interaction between unstable vortices. Detailed descriptions of the pairing process and of the large-scale structures observed near the end of the potential core are obtained without excitation of the jet and without the smearing effects of the conditional sampling method.
Kinematics of velocity and vorticity correlations in turbulent flow
Authors: Bernard Peter S.
Published: March 2003

The kinematic problem of calculating second-order velocity moments from given values of the vorticity covariance is examined. Integral representation formulas for second-order velocity moments in terms of the two-point vorticity correlation tensor are derived. The special relationships existing between velocity moments in isotropic turbulence are expressed in terms of the integral formulas yielding several kinematic constraints on the two-point vorticity correlation tensor in isotropic turbulence. Numerical evaluation of these constraints suggests that a Gaussian curve may be the only form of the longitudinal velocity correlation coefficient which is consistent with the requirement of isotropy. It is shown that if this is the case, then a family of exact solutions to the decay of isotropic turbulence may be obtained which contains Batchelor’s final period solution as a special case. In addition, the computed results suggest a method of approximating the integral representation formulas in general turbulent shear flows.
A nonlinear kinetic energy principle for two-dimensional collision-free plasmas
Authors: Schindler K. , Goldstein H.
Published: March 2003

In this paper a nonlinear kinetic energy principle is derived for two-dimensional collision-free plasmas and its properties are discussed. The present approach provides a simplified derivation of the small-amplitude limit derived earlier by a different technique.
The characteristics of salt fingers in a variety of fluid systems, including stellar interiors, liquid metals, oceans, and magmas
Authors: Schmitt Raymond W.
Published: March 2003

The growth rates, flux ratios, wavenumbers, and bandwidths of salt fingers are computed for Prandtl numbers from 10−7 to 104 and diffusivity ratios from 1 to 108, using the exact similarity solutions of Schmitt [Deep-Sea Res. 26A, 23 (1979)]. This model successfully explains the variation in flux ratio in the heat/salt and salt/sugar systems and produces salt-finger spectra in agreement with ocean observations. The calculations presented here should be useful in the study of double diffusion in astrophysics, chemistry, geology, metallurgy, meteorology, and oceanography, and may be applicable to problems in the growth of semiconductor crystals.
Some new gravity waves in water of finite depth
Authors: Vanden-Broeck Jean-Marc
Published: March 2003

The results of Chen and Saffman, showing that periodic gravity waves in water of infinite depth are not unique, are generalized for waves in water of finite depth. Some new types of waves are discovered and discussed.
Self-refraction of nonlinear capillary-gravity waves
Authors: Banerjee P. P. , Korpel A. , Lonngren K. E.
Published: March 2003

Self-refraction effects have been observed during the propagation of deep-water capillary-gravity waves. The observations are shown to be in qualitative agreement with the theory of self-focusing and defocusing in a cubically nonlinear medium in the presence of diffraction.
Experimental and numerical investigation of a turbulent boundary layer subjected to a sudden transverse strain
Authors: Cousteix J. , Aupoix B. , Arzoumanian E. , Fulachier L.
Published: March 2003

A fully developed two-dimensional boundary layer on a cylinder is subjected to a sudden transverse strain by rotating the downstream part of the cylinder with a peripheral wall velocity approximately equal to the external velocity. This distorted boundary layer has a ‘‘complex-flow’’ structure. The present paper deals with both experimental and numerical investigations of this complex flow. The experiments have been carried out in the near-wall region (buffer layer and viscous sublayer). Calculations have been made with a model of the k-ε type which takes into account the anisotropy of turbulent viscosity. Although the general agreement between experiment and calculations is good, some discrepancy, especially with respect to the behavior of the mean flow, is observed in the near-wall region and experiments do not support the linear evolution of the hodograph as predicted by calculations. The results suggest that the collaterality of the flow is first obtained in a very thin wall layer and extends progressively into the outer boundary layer.
Has a small-scale structure in turbulence been experimentally verified?
Authors: Johnson Frank D. , Eckelmann Helmut
Published: March 2003

Various investigators have found considerable experimental evidence for small-scale flow structures in wall-bounded turbulent flow within the last 15 years. Experiments by Willmarth and Bogar in 1977 [Phys. Fluids 20, S9 (October, Part II, 1977)] provided the high point to date in efforts to measure small-scale phenomena associated with turbulence; the unexpected results of these investigations were ascribed to extremely small flow structures of a scale which previously had remained undetected. Since publication of the work of Willmarth and Bogar, neither verifications nor contradictory results have been published by other investigators. The present experimental studies seem to contradict the thesis of Willmarth and Bogar, making small-scale phenomena responsible for the unusual results of their experiments.
Molecular velocity distribution functions in an argon normal shock wave at Mach number 7
Authors: Holtz T. , Muntz E. P.
Published: March 2003

The streamwise and normal moments of molecular velocity distribution functions throughout an argon normal shock wave have been measured in a Mach number 7.18 wind tunnel flow, and the experimental data have been compared with several analytical and numerical solutions. In the experiments, the molecular population distributions parallel and perpendicular to the direction of flow were derived using a Fabry–Perot etalon to resolve the Doppler shifts in electron-beam-stimulated fluorescence of the gas atoms. Predictions from Monte Carlo techniques give close agreement with the details of the experimental nonequilibrium distribution function contours. Bimodal Maxwellian and ellipsoidal functional forms show only general agreement with overall profile breadth.
Observation of self-binding turbulent fluctuations in simulation plasma and their relevance to plasma kinetic theories
Authors: Berman R. H. , Tetreault D. J. , Dupree T. H.
Published: March 2003

Non-wave-like fluctuations of the phase-space density are observed in simulations of turbulent plasma. During decay from an initial state, the mean square fluctuation level decays at a much slower rate than that of an individual fluctuation. The distribution function of the fluctuation amplitudes becomes non-Gaussian (skewed) in favor of negative fluctuations. An enhancement in the aggregate fluctuation lifetime is also observed when the turbulence is driven by an external source. A model based on a collection of self-binding negative fluctuations, called phase-space density holes, can explain the observations. Collisions between holes produce hole fragments and lead to fluctuation decay. However, the hole fragments are self-binding and tend to recombine into new holes. The implications of these results for kinetic theories of plasma turbulence are discussed. In particular, it is shown that the theory of clumps, when suitably modified to include fluctuation self-binding, can explain many features of the nonlinear instability recently observed in computer simulations.
Growth of phase-space density holes
Authors: Dupree T. H.
Published: March 2003

Phase-space density holes are shown to grow in a plasma for any nonzero electron–ion drift velocity. As a hole grows, its depth, velocity width, and electrostatic potential increase. For a hole with velocity u, the growth rate is of order −v2e f′0e (u)v2i  f0i(u) times the bounce frequency of a particle trapped in the hole. The theoretical predictions agree reasonably well with a recent computer simulation. The results call into question the role of linear stability theory. Energy and momentum conservation are analyzed in detail, and the relationship to the clump instability is discussed.
Localization of circularly polarized intense electromagnetic waves in relativistic plasmas
Authors: Rao N. Nagesha , Varma Ram K. , Shukla P. K. , Yu M. Y.
Published: March 2003

Localization of a circularly polarized, high-intensity electromagnetic field in a relativistic, unmagnetized plasma is considered. A new class of double-hump electromagnetic soliton solutions having nonzero high-frequency field intensity at the center is found for subsonic as well as supersonic velocities. For subsonic velocities, these solitons are found to be accompanied by density dips whereas supersonic solitons are associated with density humps. Parameter regions for the existence of different types of electromagnetic solitons are obtained explicitly. A few limiting cases of the general solutions obtained in the present theory are also discussed.
Stabilization of the lower-hybrid drift instability by resonant electrons
Authors: Chen Yu-Jiuan , Nevins W. M. , Birdsall C. K.
Published: March 2003

The lower-hybrid drift instability is studied with a two-dimensional electrostatic simulation code. Simulations show good agreement of the measured local growth rates and frequencies with the results of local theory during the early stage of wave growth. At later times nonlocal effects become important, and a coherent mode structure develops. This normal mode is observed to propagate up the density gradient. At zero plasma beta and zero electron temperature, it is found that the lower-hybrid drift instability is stabilized by the local current relaxation due to both ion quasilinear diffusion and electron E×B trapping which causes electron heating to occur.
Measurement of sloshing-ion spatial profiles in end cell of tandem mirror experiment-upgrade (TMX-U)
Authors: Orzechowski T. J. , Allen S. L. , Foote J. H. , Goodman R. K. , Molvik A. W. , Simonen T. C.
Published: March 2003

Neutral-beam injection is used to establish an energetic sloshing-ion distribution in the end cells of the Tandem Mirror Experiment-Upgrade (TMX-U). The angular and radial distributions of these ions are measured with arrays of secondary-emission detectors. Unfolding the angular distribution gives the axial extent of the sloshing ions. Sloshing-ion density measurements from the charge-exchange flux indicate a high-density (nis≂3 to 6×1012 cm−3) but narrow (FWHM ∼16 cm) sloshing-ion plasma.
Brillouin scattering of multiline laser light in a flowing plasma corona
Authors: Short R. W. , Williams E. A.
Published: March 2003

Multiline lasers have been suggested as a means of reducing stimulated Brillouin scattering (SBS) from laser fusion target plasmas. It is shown that because of interaction between incident and reflected laser lines, Brillouin scattering may still occur even if each line individually is below SBS threshold. The resultant scattering tends to be beneficial, however, as it is primarily the outgoing light which is scattered back into the plasma by the interaction.
Viscoelastic fluid flow exhibiting hysteritic phase changes
Authors: Hunter J. K. , Slemrod M.
Published: March 2003

In the present paper a mathematical theory is given for a viscoelastic fluid exhibiting a hysteresis loop in the shear stress versus shear rate plane. The main rheological idea is to introduce a constitutive equation of rate type whose steady shear stress versus shear rate locus is nonmonotone. The main mathematical idea is to use a local shock structure theory to pick out the admissible solutions in loading and unloading of the applied driving force.
Continuous coating with gravity and jet stripping
Authors: Tuck E. O.
Published: March 2003

A thin layer of viscous fluid is transported by a vertical plane surface moving steadily upward under gravity. Some fluid drains downward, a tendency that can be augmented by blowing an air jet upon the layer from the side. An analysis is provided of the possible steady-flow solutions, leading to a relationship between the ultimate layer thickness and the strength of the jet. In order to test stability, a study is made of corresponding unsteady flows, the conclusion being that the stripped flow is stable to perturbations of long wavelength.
Stability of rotating liquid drops I. Uncharged drops
Authors: Luyten P. , Callebaut D. K.
Published: March 2003

The oscillations and the instability of a uniformly rotating liquid drop endowed with surface tension are investigated. The linearized equations of motion are solved using ‘‘modified’’ spheroidal coordinates. A general energy integral technique which is more adequate than the virial method is developed to yield the dispersion relations. The equilibrium figure is first approximated by a spheroid. The dynamical and secular instabilities are calculated in general. In the latter case bifurcation occurs towards nonrotationally symmetric equilibria. Then the exact equilibrium figure is studied by the same energy integral technique. The results are compared with those of the spheroidal approximation and with the numerical calculations of Brown and Scriven.
Axial coherence functions of circular turbulent jets based on an inviscid calculation of damped modes
Authors: Plaschko Peter
Published: March 2003

It is often assumed that damped instability modes may exist even in the absence of viscosity, if during the downstream evolution of the waves, velocity gradients become too small to support amplified disturbances. A modified inviscid calculation of damped modes is done, and the corresponding eigenvalues are compared with those given by the Orr–Sommerfeld theory. It is shown that the use of inviscid results in a slow-flow divergence stability theory and in a linear turbulence model yields theoretical predictions for amplitudes, phases, and coherence functions that are in reasonable agreement with experimental trends.
Stabilization of the tearing mode in high-temperature plasma
Authors: Drake J. F. , Antonsen T. M. , Hassam A. B. , Gladd N. T.
Published: March 2003

An analytical and numerical study of the stability of tearing modes is carried out using the Braginskii fluid equations. An electron temperature gradient coupled with finite (nonzero) parallel thermal conductivity causes large parallel currents to flow in the vicinity of the singular layer (where k⋅B=0). The pressure-driven currents are stabilizing and in the limit βL2s/L2n>1, where β is the ratio of the thermal to magnetic pressure and Ls and Ln are the magnetic shear and density scale lengths, the linear tearing mode no longer exists. In this high-β limit, the magnetic perturbation of the tearing mode is completely shielded from the singular layer so that no reconnection of the magnetic field can take place. The relationship between the tearing mode and previously investigated temperature-gradient-driven modes and the implications of the results for resistive modes in present and future tokamak discharges is discussed.