bluuebunny/crossref_metadata_2025 huggingface dataset:
Grid turbulence in air and water
Authors: Frenkiel François N. , Klebanoff Philip S. , Huang Thomas T.
Published: March 2003

An experimental comparison of grid turbulence performed in a wind tunnel and in a water tunnel is described. The measurements were made in the initial stage of decay with mesh Reynolds numbers ranging from 12 800 to 81 000. Hot-wire and hot-film instrumentation combining analog and digital computing methods were used to measure higher-order correlations of the longitudinal component of turbulent velocity and higher-order moments of longitudinal turbulent velocity gradients. A comparison of the latter is obtained for an increase in Reynolds number without having to alter the flow geometry. Apart from the intrinsic interest of such measurements in water, the results show the non-Gaussian character of the turbulent fluctuation and compare the behavior of higher-order moments of turbulent velocity gradients to theoretical considerations for the small scale turbulent structure.
Recurrence of initial state of the Korteweg–de Vries equation
Authors: Abe Kanji , Abe Takashi
Published: March 2003

The Korteweg–de Vries equation is solved numerically by using the Fourier expansion method to clarify the recurrence of the initial state. A sufficiently accurate solution valid for large times as well as for small times is obtained. The solution does not show a clear recurrence.
New nonlocal analysis of collisionless drift wave in Vlasov plasma
Authors: Sanuki Heiji , Watanabe Tsuguhiro , Watanabe Masaaki
Published: March 2003

The WKB-type eigenmode analysis of an inhomogeneous Vlasov plasma is developed based on the exact integral equation. Thermal effects, namely, effects associated with the finite Larmor radius, Landau damping, cyclotron damping and so on are taken into account even if k2ρ2≳≳1 [k is of the order of ‖ψ′ (x)/ψ‖ ]. The ’’quantization condition,’’ which determines the eigenfrequency, is derived from the global localization condition of solutions. In the case of weak dissipation, this quantization condition reduces to a simple and more tractable form. Drift waves in a straight magnetic field with Gaussian density distributions are discussed numerically and analytically in detail. Results show that the growth rate of the fundamental mode (n=0) is the largest one.
Interface crossing frequency as a self-preserving flow variable in a turbulent plane jet
Authors: Oler J. W. , Goldschmidt Victor W.
Published: March 2003

The variation of the maximum interface crossing frequency with respect to downstream position is shown to be consistent with the principles of similarity for the plane jet.
Plasma heating by an intense relativistic electron beam: An experimental study
Authors: Greenspan M. A. , Ekdahl C. , Sethian J. D. , Wharton C. B.
Published: March 2003

A 3–20 kA, 300–350 kV, 60 nsec electron beam has been axially injected through various anode foils into a 1.6 m long, mirror confined, fully ionized hydrogen plasma, with an initial plasma density variable from 5×1011/cm3 to 2×1013/cm3. Beam propagation and total plasma heating were studied, and special studies were done of return current heating and direct ion heating by the beam. Total energy deposition efficiencies of 4%–30% were observed. Variations with parameters showed stronger heating with thinner anode foils and good agreement with theoretical predictions based on beam energy loss by trapping in the unstable waves generated by the two-stream instability. Return current heating was found to be only 10%–20% of the total heating for beam-to-plasma density ratios ⩽0.02. Anomalous plasma resistivity was observed in all cases; the use of a thinner anode foil strongly increased this resistivity during the beam, probably due to anomalous resistivity induced by the two-stream instability. Rapid ion heating was observed and inferred to be primarily by the return current interaction, by anomalous electron-ion energy transfer, and by radial electrostatic fields induced by the beam.
Simplified formulae for solitons in media with slowly varying inhomogeneity
Authors: Gianino Peter D. , Bendow Bernard
Published: March 2003

Simplified formulae are obtained for the motion of solitons in nonuniform media, and the results are illustrated for the case of a sinusoidally varying medium.
Viscous dominated interfacial electrohydrodynamic instability in polar geometry
Authors: Hoburg James F.
Published: March 2003

Interfacial electrohydrodynamic instability between fluid components with identical permittivity and viscosity but disparate conductivities for viscous dominated flows in polar geometry is described by an experiment and linear instability theory. Theoretical results are in agreement with a corresponding flat interface, distant boundary model for high mode numbers, and geometrically altered for mode numbers low enough for effects of boundary proximity and equilibrium interfacial curvature to be appreciable. Retardation and enhancement of growth rate are found in correspondence with radially decreasing and increasing conductivity, respectively. Experimental observations confirm a most rapidly growing mode for the latter and apparent lack of one for the former case, in agreement with the nature of the theoretical description.
Minimum energy state of a toroidal discharge
Authors: Reiman Allan
Published: March 2003

Previous analysis of the relaxation of a toroidal discharge used an incorrect expression for the energy of a force-free state. Although the primary conclusions remain essentially unchanged, the analysis using the correct expression is considerably different in some respects.
Asymptotic method for flow in unconfined aquifers
Authors: Shen M. C.
Published: March 2003

An asymptotic theory is developed for the solution of linear equations governing unsteady flow in unconfined aquifers. The method used here is based upon the so-called ray method, involving a phase function and an amplitude function. The phase function satisfies a dispersion relation, the solution of which yields a family of time-space curves called rays. The amplitude function satisfies a transport equation and is determined by integration along a ray. An example concerning flow from a well over a nonuniform bottom is considered to illustrate the method.
An experimental test of the electromagnetic ion cyclotron instability within the earth’s magnetosphere
Authors: Mauk B. H. , McPherron R. L.
Published: March 2003

The ATS−6 geostationary satellite has observed many examples of propagating, electromagnetic Alfv́en/ion cyclotron waves in both plasma particle and magnetic field data. These waves have been viewed predominantly near the afternoon and dusk regions of the earth’s magnetosphere with normalized frequencies (ω/ΩH+) ranging between 0.05 and 0.5. Viewed from an average geomagnetic latitude of +10°, the waves have only been observed to propagate northward, suggesting that they are generated within the equatorial or minimum ‖B‖ regions. Two wave events have been chosen for detailed analysis. Both events appeared coincidentally with the encounter of cool plasma populations (5 eV) which joined the hot populations already present (10–40 keV). These coincidences suggest the popular, yet largely untested, electromagnetic ion cyclotron instability as the wave generation mechanism. As a test of this hypothesis, ion cyclotron amplification profiles are obtained by evaluating the linear growth rate integrals under the measured, anisotropic hot ion distributions. The measured frequencies for both of the chosen events are in good agreement with the quite restricted values which correspond to the peaks of the amplification profiles. As a result of magnetic field inhomogeneities, the interactions remain within the linear regime.
Investigation of natural transition in the inlet region of a two-dimensional duct flow
Authors: Rajagopalan S. , Antonia R. A.
Published: March 2003

Natural transition from laminar to turbulent flow in the inlet region of a two-dimensional duct has been investigated with the use of a surface hot film, measuring the wall shear stress fluctuation τ′w, and a single hot wire, measuring the velocity fluctuation u′. With a free-stream turbulence level of 0.05% at the duct inlet, the transition Reynolds number Ra, based on average velocity Ua and duct width 2d, is 11 600. The transition process appears to arise from an instability which leads to the formation of turbulent regions which have features similar to those of turbulent spots in a laminar boundary layer with zero pressure gradient. The intermittency factory γ associated with the turbulent regions is a maximum at the wall and decreases to a minimum on the center line. The space-time correlation between τ′w and u′ is consistent with the existence of an organized structure during transition. Ensemble averaged shapes of τ′w and u′ are determined for both laminar and turbulent parts of the flow. The wall shear stress increases with distance from the leading edge of the turbulent region and is a maximum near the trailing edge. At distances from the wall greater than 0.3d, the flow within the turbulent region first declerates before accelerating toward the trailing edge. The average shape of the turbulent region is, within the uncertainty of the data, symmetrical about the center line of the duct.
Fluctuations and transport in an inhomogeneous plasma
Authors: Nevins William M. , Chen Liu
Published: March 2003

A formalism is developed to calculate the equilibrium fluctuation level in an inhomogeneous plasma. This formalism is applied to the collisionless drift wave in a sheared magnetic field. The fluctuation level is found to be anomalously large due to both the presence of weakly damped normal modes and convective amplification. As the magnetic shear is reduced, the steady-state fluctuation spectrum is found to increase both in coherence and in amplitude. The transport associated with this mode is evaluated. The diffusion coefficient is found to scale as D∝B2/nT1/2.
Study of turbulent heating effects in the high beta tokamak Torus II
Authors: Georgiou G. E. , Marshall T. C. , Weber P. G.
Published: March 2003

Torus II is a rectangular cross section, high beta tokamak which has a glass vacuum vessel (aspect ratio of 3.5) filled with 12 mTorr helium. The plasma is heated by turbulent poloidal skin currents, induced by a fast (τr=1.7 μsec) reversal of the toroidal field which converts a toroidal Z pinch plasma into a tokamak plasma. By using the broadening of He II 4686 Å and impurity lines, it is found that strong turbulence (Ẽ⩽30 kV/cm microscopic fields at frequency ⩽ωpi≈3×1010 rad/sec) is induced during the heating phase. The turbulent Ẽ fields maximize in the region of maximum induced poloidal skin current (α∂Bφ/∂r). The resulting high beta tokamak plasma, with <β≳v≈10% and ne≈1015 cm−3, has an initially peaked radial temperature profile with Ti≈180 eV at the plasma center. A few microseconds later, the He II-determined ion temperature becomes nearly spatially flat at Ti≈75 eV, and then decreases slowly in time. Impurity ion lines indicated a temperature approximately 100 eV greater than He II. All line profiles indicated a poloidal circulation with Er×Bφ characteristics and Er≈100 V/cm radially inward. The spectroscopy was done in the visible region using a six channel polychrometer having a 0.2 Å resolution, which is capable of radial scans of the plasma. The details of turbulent heating derived from the analysis of ion line profiles are presented.
Excitation of the plasma and lower oblique resonances in a Maxwellian magnetoplasma of weak density
Authors: Thiel J. , Decreau P. M. E.
Published: March 2003

In a Maxwellian magnetoplasma, where the plasma frequency is lower than the electron gyrofrequency, the plasma resonance may be excited at short distances and the lower oblique resonance at large distances from the source.
Rippling of the critical surface by four-wave processes in a laser-irradiated plasma
Authors: Woo Wee , DeGroot J. S. , Barnes C.
Published: March 2003

Rippling of the critical surface is investigated by a four-wave process in which two electromagnetic waves are scattered by an ion perturbation for very high intensities in a laser-irradiated plasma. The mechanism is the parametric oscillating two-stream instability for the electromagnetic waves. The instability grows in the direction of the laser magnetic field; however, it hardly grows in the direction of the laser electric field. The thresholds and growth rates are obtained by a phase-integral method, and there are optimized wavenumbers and pump fields for the growth. Results of two-dimensional fluid and three-dimensional particle calculations agree with the theoretical predictions. The theory also seems to be consistent with the observations in laser experiments.
Study of plasma density fluctuations by the correlation of crossed CO2 laser beams
Authors: Surko C. M. , Slusher R. E.
Published: March 2003

A technique is described which uses correlation of the forward scattering from two intersecting laser beams to measure the spatial distribution ñ(r) of density fluctuations in a plasma directly. Model calculations are presented for the case of low frequency density fluctuations in a tokamak plasma, and experimental results are described for fluctuations in the Alcator A tokamak. Other potential uses of the crossed-beam correlation technique are discussed such as measurement of the nonequal time correlation function which can yield information about the propagation velocity of the density fluctuations.
Phenomenological model of shock initiation in heterogeneous explosives
Authors: Lee E. L. , Tarver C. M.
Published: March 2003

An ignition and growth concept is used, within the framework of a one-dimensional Lagrangian hydrodynamic code, to model the shock initiation of heterogeneous solid explosives. The leading shock wave of an initiating pulse is assumed to ignite a small fraction of the explosive at localized heated regions. These ignited regions then grow as material is consumed at their boundaries. The growth rate for a particular material is assumed to have the characteristic pressure dependence of high-pressure laminar burning experiments. Results of the model calculations are in good quantitative agreement with recent manganin pressure gage and particle velocity gage measurements of the buildup of the initiating shock front to detonation for both sustained and short duration pulses in four solid explosives: PBX−9404, TATB, cast TNT, and PETN. The predicted run distances to detonation as functions of shock pressure at various initial densities and the predicted reaction zone lengths of the fully developed detonation waves also correlate well with experimental data for these four solid explosives.
Steady-state treatment of relativistic electron beam erosion
Authors: Sharp William M. , Lampe M.
Published: March 2003

The head of a relativistic electron beam propagating into un-ionized or weakly ionized gas is not self-pinched and expands freely, causing the beam to take on a ’’trumpet’’ shape. The region where the beam pinches, referred to as the ’’pinch point’’, moves steadily back into the beam because of the reduced ionization rate at the expanding beam head and energy loss to the induced electric field. This beam head ’’erosion’’ is modeled by assuming that the axial beam profile is stationary in a reference frame moving with the pinch point. This assumption allows the beam equations to be written in time-independent form, and radial averaging then yields a set of one-dimensional ordinary differential equations for the beam radius and energy, the mean pinch force, and the background conductivity. Solution of these equations with appropriate boundary conditions gives both the erosion rate and the beam axial structure. The results of extensive numerical calculations are presented, along with analytic estimates of the erosion rate, degree of current neutralization, and axial scale lengths.
Classical diffusion in the presence of an X point
Authors: Auerbach S. P. , Boozer Allen H.
Published: March 2003

Classical plasma diffusion is studied in a two-dimensional system with an X point, the third dimension (the Z axis) being a symmetry direction. Several exact results are presented which give a good qualitative understanding of the diffusive flow in such a system. A soluble model which illustrates these results is also presented. For a scalar resistivity, the results may be summarized as follows: (a) The pressure gradient dP/dΨ (Ψ is the poloidal flux) does not vanish on the separatrix; i.e., the diffusion coefficient D(Ψ) is finite there. (b) Neglecting viscous or inertial effects, the poloidal flow follows lines of constant Hamada angle (defined in the text). This has the consequence that (i) all flow across the separatrix is channeled through the X point, and (ii) the flow velocity along the separatrix is formally infinite. Including viscous or inertial effects would, of course, remove this singularity while modifying the flow only in a small boundary layer region near the separatrix. For a tensor resistivity these conclusions are modified. In particular, a fraction η∥/η⊥ of the particle flow crosses the separatrix through the X point, where η∥ and η⊥ are, respectively, the parallel and perpendicular resistivities.
Simulation of cyclotron wave growth in a helical slow wave structure
Authors: Faehl R. J. , Newberger B. S. , Godfrey B. B.
Published: March 2003

Growth of large amplitude coherent cyclotron waves on unneutralized relativistic electron beams has been studied analytically and numerically. The mechanism for growth is the unstable coupling of helical waveguide modes with relativistic electron beam cyclotron waves. Approximate analytic growth rates are found to be in good agreement with the exact numerical solution of the linearized plasma equations on a self-consistent cylindrical beam equilibrium. Particle simulations performed in cylindrical geometry quantitatively confirm the theory. The calculations were conducted in both an infinite medium and realistically terminated configuration. In the latter, matched impedances on the helix were required to reduce transients and unwanted reflections to tolerable levels. Saturation in both cases is due either to convection or, in sufficiently long waveguides, growth of the wave until it physically intersected the helix.
A model of anomalous absorption, backscatter, and flux limitation in laser-produced plasmas
Authors: Colombant D. G. , Manheimer Wallace M.
Published: March 2003

Fluid simulations of laser light absorption and backscatter for planar targets are presented for various laser irradiances, wavelengths, target materials, laser pulse lengths, and simulated prepulse conditions. Physical processes included in the model are inverse bremsstrahlung, resonant absorption, absorption by ion-acoustic fluctuations, and Brillouin backscatter. For the anomalous processes, self-consistent transport coefficients are derived and used throughout the time-dependent, one-dimensional code. Flux limitation is thus taken into account as a result of the physical processes included. Interplay between the various absorption mechanisms and backscatter are uncovered in this study. Comparisons with experiments are presented and suggestions for further experiments are made.
Two-dimensional electrostatic turbulence with variable density and pressure
Authors: Montgomery David , Turner Leaf
Published: March 2003

Large-scale turbulence transverse to a uniform dc magnetic field is considered from the point of view of a two-fluid model of an electrostatic plasma of variable density. An approximation motivated by ’’geostrophic’’ techniques of dynamic meteorology is introduced. It is argued that the inverse cascade phenomenon should persist in the presence of variable pressure and density.
Thermal equilibrium properties of an intense ion beam with rotational and axial motion
Authors: Chen James , Davidson Ronald C.
Published: March 2003

The Vlasov equilibrium properties of a rotating, nonrelativistic, cylindrically symmetric ion beam propagating parallel to a uniform applied magnetic field B0êz are investigated. Equilibrium properties are calculated for the choice of ion beam distribution function corresponding to thermal equilibrium, i.e., fb0(H,Pϑ, Pz) = (const)exp[−(H+ωbPϑ−Vz Pz)/T], where H is the energy, Pϑ is the canonical angular momentum, Pz is the axial canonical momentum, Vz= const is the mean axial velocity, and −ωb=const is the angular velocity of mean rotation. The investigations include: (a) exact analytical solutions in special limiting cases, (b) properties of the general solutions, (c) necessary and sufficient conditions for radially confined equilibria, and (d) numerical solutions in regimes where solutions are not accessible analytically.
On the realizability of magnetohydroelectric interaction
Authors: De Bibhas R.
Published: March 2003

A variant of the initially proposed magnetohydroelectric theory that may bring the theory within the realm of experimental verifiability and practical applicability is suggested.
Nonlinear theory of type II irregularities in the equatorial electrojet
Authors: Barone S. R.
Published: March 2003

The two fluid equations of motion describing type II irregularities in the equatorial electrojet are reformulated in terms of a scalar and vector potential for the fluid momentum densities. Elimination of the vector potential yields a single equation, first order in time, for the time evolution of the ionization density. Following Sudan and Keskinen, this equation is solved in the direct interaction approximation for the nonlinear spectral width of the two-dimensional, steady-state turbulence. Numerical results are given for the power law wavenumber spectrum which results from theoretical considerations, computer simulations, and observations of type II irregularities. These results extend the work of Sudan and Keskinen to smaller wavenumbers and higher levels of turbulence.
Numerical solution of the drift kinetic equation
Authors: Santarius John F. , Hinton F. L.
Published: March 2003

The nonadiabatic part of the electron distribution function in toroidal geometry is investigated through numerical solution of a drift kinetic equation. A Lorentz collision operator is used for both trapped and untrapped electrons. No special conditions are invoked at the trapped-untrapped electron boundary. Poloidal and pitch angle dependence of the electron guiding center drifts are included without bounce averaging. Radially local growth rates are found for the trapped electron mode with ion inertia and Landau damping retained. Comparison is made with simplified descriptions of collisions and drifts, and the dependence of growth rate and distribution function on collision frequency is examined.
Observations of the three-dimensional nature of unstable flow past a cavity
Authors: Rockwell D. , Knisely C.
Published: March 2003

The spanwise structure of the free-shear layer along the mouth of a cavity was visualized using the hydrogen bubble technique. Examination of the distortion of spanwise sheets of timelines reveals some of the features of interaction of secondary (longitudinal) and primary vorticity. The spanwise wavelength of the longitudinal vorticity ranged from a wavelength approximately the same as that between primary vortices to a wavelength about half as large. Patterns corresponding to large wavelengths were discernible well upstream, suggesting that they are associated with relatively weak three-dimensional effects. On the other hand, the shorter wavelength patterns became pronounced farther downstream in the region where the primary vortices were very mature. The large scale recirculation vortex between the free-shear layer and the walls of the cavity is felt to influence, to some degree, this three dimensionality.
Nonlinear interaction of two waves in boundary-layer flows
Authors: Nayfeh Ali H. , Bozatli Ali N.
Published: March 2003

First-order nonlinear interactions of Tollmien–Schlichting waves of different frequencies and initial amplitudes in boundary-layer flows are analyzed using the method of multiple scales. Numerical results for flow past a flat plate show that the spatial detuning wipes out resonant interactions unless the initial amplitudes are very large. Thus, a wave having a moderate amplitude has little influence on its subharmonic although it has a strong influence on its second harmonic. Moreover, two waves having moderate amplitudes have a strong influence on their difference frequency. The results show that the difference frequency can be very unstable when generated by the nonlinear interaction, even though it may be stable when introduced by itself in the boundary layer.
Rayleigh–Taylor instability in the presence of an oscillating magnetic field permeating both heavier and lighter fluids
Authors: Chakraborty B. B.
Published: March 2003

Rayleigh–Taylor instability of a heavy fluid, supported by a lighter one, in the presence of a uniform, horizontal, and oscillating magnetic field permeating both the fluids is studied. The fluids are taken as inviscid, uniform, incompressible, and infinitely conducting. The amplitude of the oscillating part of the field is taken to be small compared with its steady part. The conditions under which the model calculations are valid are obtained first. The dispersion relation is obtained in the form of a third-order differential equation, with time as the independent variable and with periodic coefficients, for the vertical displacement of the surface of separation of the two fluids from its equilibrium position. The oscillatory magnetic field of frequency ω and steady part H0 has a stabilizing influence on a mode of disturbance which is unstable in a steady field of strength H0. The oscillatory field has either no stabilizing influence or a destabilizing influence in some special cases. However, for reliable results in these cases, a more realistic model of Rayleigh–Taylor instability should be considered taking the finite conductivity of the fluid into account.
Propagation of discontinuities along bi-characteristics in magnetohydrodynamics
Authors: Singh R. S. , Sharma V. D.
Published: March 2003

An explicit criterion for the growth and decay of weak discontinuities of arbitrary shape along bi-characteristics is given. The effects of a magnetic field and the upstream flow Mach number on the growth and decay properties of plane and cylindrical waves are discussed.
Spherical thermal waves in laser plasmas
Authors: Montañes J. L. , Sanmartín J. R.
Published: March 2003

The thermal wave produced in a uniform plasma, when energy is absorbed on a spherical surface such that convection is negligible, is analyzed using an integral method, which is very accurate. The curvature speeds up (slightly slows down) the inner (outer) wave front and does not affect the temperature maximum.
Distribution function of an inhomogeneous plasma in the presence of an oscillating magnetic field
Authors: Nag Tarasankar , Dasgupta Brahmananda
Published: March 2003

The distribution function f of a plasma in a magnetic field consisting of a steady plus an oscillating part has been determined by solving Vlasov’s equation and assuming that the frequency of oscillation is much less than the cyclotron frequency.
Reply to comments by L. L. Lengyel
Authors: Parks P. B. , Turnbull R. J.
Published: March 2003

In reply to comments by Lengyel, it is asserted that boundary conditions used in the pellet ablation model are quite satisfactory but that a more realistic equation of state than the ideal gas law should have been used.
Reply to the comments of M. Bornatici and F. Engelmann
Authors: Antonsen Thomas M. , Manheimer Wallace M.
Published: March 2003

In reply to Bornatici and Engleman, the authors justify their neglect of relativistic broadening of cyclotron resonances on the basis of the small range within which relativistic effects are important. (AIP)
Nonlinear excitation of convective cells by interchange modes and spectrum cascade processes
Authors: Pavlenko V. P. , Weiland J.
Published: March 2003

Convective cell formation due to interchange modes has been studied. The spectral cascade processes between such waves have been considered in the limit k∥=0 where the influence of gravity is particularly strong. Possibilities for up conversion are found.
Perturbation analysis of single Langmuir solitons
Authors: Bondeson Anders
Published: March 2003

An investigation is made of the effects of perturbations on single solitary wave solutions to the Zakharov equations. The main results are expressions, to first order in the perturbation, for the time evolution of the soliton parameters. It is shown that an adiabatically perturbed solitary Langmuir wave generally emits free ion-sound waves in the form of shelves at zero frequency and wavenumber. The evolution equations for the solition parameters include frequency and velocity shifts induced by the radiated ion sound.
Two-dimensional analysis of the stability of particulate sedimentation
Authors: Hill C. D.
Published: March 2003

The solution of the equations for a two-phase flow which models steady sedimentation is shown to be stable to small perturbations when diffusivity terms are included. The two-dimensional forms of the equations are employed, and it has been assumed that the drag coefficient is constant.
Hot- and cold-wire sensitivity corrections for moments of the fine scale turbulence in heated flows
Authors: Park Joel T. , Van Atta Charles W.
Published: March 2003

A method is presented for the correction of measured higher-order moments of hot-wire velocity and cold-wire temperature signals for the respective parasitic sensitivities to temperature and velocity fluctuations. The method is applied to third-order moments of time derivatives and higher-order structure functions, 〈 (Δu)p(Δϑ)q) 〉, measured in a marine boundary layer, where u is the velocity, ϑ is the temperature, and Δu=u (x+r)−u (x). Corrections are less than 5% for 〈 (dϑ/dt)3〉, 7% for 〈 (dϑ/dt)2 (du/dt) 〉, over 200% for 〈 (dϑ/dt)(du/dt)2〉, and less than 0.1% for 〈 (du/dt)3〉. The dominant correction to the third-order temperature moments arises from the velocity sensitivity of the cold wire whereas the dominant correction for the cross statistics was the temperature sensitivity of the hot wire.
Axis encircling ion gyroinstability
Authors: Catto Peter J. , Aamodt R. E. , Rosenbluth M. N. , Byers J. A. , Pearlstein L. D.
Published: March 2003

An idealized plasma model in which all the ion guiding centers lie along the magnetic axis of a cylindrically symmetric plasma is investigated. The radial eigenvalue equation is derived and solved for this strongly unstable limit. Many of the physical features predicted by simple analytic limits of the WKB phase integral condition are verified by a comparison with the results of a particle simulation.
Magnetohydrodynamical interchange instability in low-β plasmas in sheared systems
Authors: Yoshikawa Shoichi , White R. B.
Published: March 2003

The stability criterion of a magnetized plasma with respect to interchange in a sheared configuration was reexamined. By retaining the finite growth rate, the singularity at the magnetic surface, where the perturbation is constant along the magnetic line, is removed. The resultant wave equation yields the result that the Suydam condition is both a necessary and a sufficient condition for stability at least for the plasma pressure less than (1−Δ) βc. Here, βc is the maximum β for the original Suydam criterion and Δ is a small positive number (less than 0.03), which presumably can be made arbitrarily small by improving the numerical approximation.
Electric sheath and presheath in a collisionless, finite ion temperature plasma
Authors: Emmert G. A. , Wieland R. M. , Mense A. T. , Davidson J. N.
Published: March 2003

The plasma-sheath equation for a collisionless plasma with arbitrary ion temperature in plane geometry is formulated. Outside the sheath, this equation is approximated by the plasma equation, for which an analytic solution for the electrostatic potential is obtained. In addition, the ion distribution function, the wall potential, and the ion energy and particle flux into the sheath are explicitly calculated. The plasma-sheath equation is also solved numerically with no approximation of the Debye length. The numerical results compare well with the analytical results when the Debye length is small.
Nonlinear mode coupling and saturation of decay instability in ion beam-plasma system
Authors: Honzawa T. , Hollenstein Ch. , Vaclavik J. , Kawai Y.
Published: March 2003

Properties of nonlinear mode coupling for the decay instability of the fast ion beams are experimentally clarified. Experimental results are qualitatively explained by parametric instability theory. Further, the nonlinear damping of the instability, due to the excitation of a new subharmonic wave by mixing with the pump, is observed to seriously affect its saturation.
Dimensionality and dissipation in Langmuir collapse
Authors: Goldman Martin V. , Rypdal K. , Hafizi B.
Published: March 2003

The nonlinear Schrödinger equation provides a model for Langmuir evolution at low energy density and wavenumber. This equation is studied using virial theorem techniques. Stationary solitons and pulsating solitons (related to ’’breathers’’) are found in one dimension, as well as collapsing packets in two or more dimensions. Initial wave-packet collapse thresholds and times are found, with and without constant collisional damping. In three dimensions, a narrow collapsing core is observed to break away from an initial Gaussian packet and become asymptotically self-similar with time.
Local sufficient condition for magnetohydrodynamic stability of closed line systems
Authors: Hameiri Eliezer
Published: March 2003

A sixth-order system of ordinary differntial equations along field lines is shown to have lower energy than the full magnetohydrodynamic system and thus offers a sufficient condition for stability. The two energies agree for all modes localized on field lines so that our criterion appears to be not overly restrictive. It is indeed the most optimistic sufficient condition in the literature. The criterion can be reduced to an eigenvalue problem of a single second-order integro-differential equation.
An unstable solution of hydromagnetic equations in a plasma cylinder and pulsar magnetic fields
Authors: Ray Alak
Published: March 2003

An equilibrium solution of hydromagnetic equations in an infinitely long plasma cylinder with rigid circular boundaries is constructed. The interior nonaxisymmetric solution joins continuously to a dipole-like field in the vacuum. A variational principle to test the linear stability of the solution, similar to that of Bernstein and others, is formulated. This variational principle admits arbitrary trial functions, and the boundary conditions as well as the eigenvalue and vacuum field equations are obtained on minimization. Using this variational principle, the solution is found to be unstable to perturbations which reconnect magnetic field lines on the surface through the vacuum. The evolution of pulsar magnetic fields is discussed in relation to this unstable solution.
Guiding center drift equations
Authors: Boozer Allen H.
Published: March 2003

The equations for particle drift orbits are given in a new magnetic coordinate system. This form of the equations separates the fast motion along the magnetic field lines from the slow motion across the lines. In addition, less information is required about the magnetic field structure than in alternative forms of the drift equations.
Collective drag experienced by an electron beam in the pure runaway regime
Authors: Morales G. J.
Published: March 2003

A calculation is presented of the drag experienced by a continuously accelerated cold electron beam due to the swept excitation of the finite bandwidth two-stream instability.
Method of evaluating the effects of particle scattering by fluctuations
Authors: Hershcovitch Ady
Published: March 2003

A simple and heuristic procedure for computing an effective scattering frequency of particles by low frequency waves is outlined. Application to an experiment and a computer simulation yield good agreement.
Explorations of the apparent Weissenberg effect in water
Authors: Shlien D. J. , Bobrovsky B. Z. , Brosh A.
Published: March 2003

The puzzling phenomenon in which water is observed to suddenly climb partially up a vertical rotating shaft whose tip was initially just in contact with the free surface is explored. This phenomenon occurs when the rotational rate is increased above a certain threshold. In an attempt to make some progress on understanding the phenomenon, it is explored by detailed observations and by varying parameters of the problem. Observations are presented with the aid of photographs of the surface waves and of tracer particle path elements. The effect of varying the shaft diameter, immersion of depth of the shaft tip into the water, and the effect of varying some fluid properties are investigated. In addition, extraneous effects such as irregularities in the driving mechanism and shaft, external disturbances of the fluid, and vessel size are eliminated as possible causes of the phenomenon. Despite these explorations of characteristics of the phenomenon, we have not found a satisfactory explanation of it. Another interesting instability was also observed. The water near the fluid surface in the undisturbed state flows radially outward in a regulary laminar fashion. However, small disturbances of the fluid can cause shedding of vortices whose axes are in the tangential direction and which are swept outward.
Oblique collision of ion-acoustic solitons
Authors: Ze Frederic , Hershkowitz Noah , Lonngren Karl E.
Published: March 2003

Identical spherical outgoing ion-acoustic solitons are launched from two separated spheres. The solitons collide in the plane midway between the spheres. The collision is inelastic in that a soliton-like object is created during the collision. Many of the characteristics of the interaction of the solitons are found to be similar to those of solutions to the Kadomtsev–Petviashvili equation. Similar observations were obtained for cylindrical outgoing ion-acoustic solitons and were contrasted with cylindrical pseudo-wave interactions.
Two-dimensional analysis of trapped-ion eigenmodes
Authors: Marchand R. , Tang W. M. , Rewoldt G.
Published: March 2003

The first fully two-dimensional eigenmode analysis of the trapped-ion instability in an axisymmetric toroidal geometry is presented. The poloidal structure is taken into account by Fourier-expanding the perturbed electrostatic potential, φ, in ϑ. Assuming that the perturbation varies mildly over a typical ion-banana-width, ρbi, each poloidal harmonic is expressed as a truncated Taylor series in the minor radius to account for the radial structure. The resulting set of coupled ordinary second-order differential equations is solved numerically by the method of finite elements. The formalism is also applicable to the radially local and one-dimensional radial approximations. Results obtained in these limits are presented and found to be in reasonable agreement with previous calculations. In low shear plasmas, the full two-dimensional calculation is in qualitative agreement with the one-dimensional radial approximation. However, for higher shear the two-dimensional calculation yields a somewhat different picture for the radial structure of the instability. The analysis presented is limited to long radial wavelength and electrostatic perturbations.
Kinetic equations for low frequency instabilities in inhomogeneous plasmas
Authors: Antonsen Thomas M. , Lane Barton
Published: March 2003

Kinetic equations for low frequency, short perpendicular wavelength, electromagnetic perturbations in an inhomogeneous, magnetically confined plasma are developed. The analysis makes use of the recently developed high toroidal mode number expansion to reduce the lowest-order system of equations to a set of ordinary (along the field line) integro-differential equations. Included in these equations are the effects of finite Larmor radius, magnetic shear, trapped particles, and nonuniform magnetic curvature drifts. Perturbed fields are represented by a scalar potential and two components of the vector potential. Thus, the effects of the compressional component of the perturbed magnetic field are retained and the equations are valid for arbitrary values of the plasma pressure. The extension of the high toroidal mode number expansion to nonaxisymmetric configurations is discussed.
Beam-induced currents in toroidal plasmas of arbitrary aspect ratio
Authors: Start D. F. H. , Cordey J. G.
Published: March 2003

The effect of trapped electrons on plasma currents driven by fast ion beams is calculated for tokamaks of arbitrary aspect ratio. The theory uses a model operator to simulate electron-electron collisions and applies to the banana regime of small collision frequency.
Transient thermocapillary flow in thin liquid layers
Authors: Pimputkar Sudheer M. , Ostrach Simon
Published: March 2003

A spatially varying temperature distribution imposed on the free surface of a liquid leads to an effective tractive force on the surface because of the dependence of surface tension on temperture. A solution for transient flow in infinite thin layers is presented. The layer is thin enough so that inertial forces are negligible. The equations of motion are nondimensionalized by an explicit scaling procedure. Small-time and large-time solutions are obtained with variation of surface height as part of the solution.
Surface heating, density rippling, and propagation cones in high-power lower-hybrid heating
Authors: Matsuda Kyoko , Matsuda Y. , Guest G. E.
Published: March 2003

A two-and-one-half dimensional electrostatic particle simulation code has been applied to study power penetration of the lower-hybrid plasma heating. Strong surface electron heating (stochastic) is observed. Density ripples due to ponderomotive forces along a constant magnetic field appear, not near the plasma surface, but slightly deeper inside the plasma. As an effect of surface heating, the lower-hybrid propagation cones are bent more toward the magnetic field lines, impairing penetration of the lower-hybrid waves.
Staged laser heating of a magnetically confined plasma
Authors: Quimby David C. , Steinhauer Loren C.
Published: March 2003

Staged laser heating uses simultaneous laser irradiation and magnetic compression to heat a plasma. An analytic model and one-dimensional magnetohydrodynamic computations are presented in order to characterize plasma conditions achievable by this method. In particular, results relevant to a recent experiment and results relevant to a fusion reactor plasma are described.
Dielectric response in guiding center plasma
Authors: Krommes John A. , Similon Philippe
Published: March 2003

The dielectric function for a guiding center plasma is derived from the direct-interaction approximation. For the special case of thermal equilibrium, the result agrees with, although it is more detailed than, an earlier calculation of Taylor. An explicit formula for the collision operator Σ′ is given. The calculation illustrates several important features of renormalized turbulence theory: (i) cancellation between the so-called diffusion and polarization parts of Σ′ and (ii) the role of the renormalization in providing the proper description of adiabatic response.
Utilization of the moment generating function in the kinetic solution of plane-shock structures
Authors: Narusawa Uichiro
Published: March 2003

The moment generating function has been utilized (1) to reformulate the BGK-model equation for a diatomic gas, and (2) to obtain the BGK–Mott-Smith solution of the plane-shock structure of a monatomic gas, thus suggesting the possibility of its use for more complex kinetic problems.
A model for laser driven ablative implosions
Authors: Max Claire E. , McKee C. F. , Mead W. C.
Published: March 2003

A theoretical model is presented describing the spatial structure and scaling laws of laser driven ablative implosions. The effect of inhibited electron thermal transport is explicitly included. The theory is in excellent agreement with results from a computer hydrodynamics code, under conditions when heat flow is flux-limited at the critical surface and suprathermal electrons do not form a dominant energy transport mechanism.
Stochastic ion heating by an electrostatic wave in a sheared magnetic field
Authors: Gell Y. , Nakach R.
Published: March 2003

Effects of the shear of the magnetic field on the stochastic acceleration of ions due to an electrostatic wave with a frequency in the lower-hybrid range are considered. An appropriate Hamiltonian formalism is used to analyze the equations of motion numerically and theoretically. The surface of section method is used to visualize the solutions and to compare these with the theoretical predictions. From this analysis it appears that there exists an upper adiabatic barrier for the stochastic region which seems to be responsible for the formation of a hot tail in the ion velocity distribution. In addition to lowering the threshold for the onset of stochasticity, the effect of shear is to shift the tail structure to lower values of the velocities. Consequently, these results might help to improve the efficiency of heating by external radiation in the lower-hybrid frequency range.
Parametric decay into ion cyclotron waves and drift waves in multi-ion species plasma
Authors: Ono M. , Porkolab M. , Chang R. P. H.
Published: March 2003

Parametric decay processes near the ion cyclotron frequency are investigated experimentally and theoretically in multi-ion species plasmas. The relevant theoretical dispersion relation of the parametric coupling is derived, including the ion drift motion. Experimental data obtained in the Princeton L-4 device verify these theoretical predictions in some detail. In a helium-neon plasma, the relative ion drift motion excites electrostatic ion cyclotron waves (the kinetic ion-ion hybrid mode) when ω0≳ΩHe +ΩNe. In a region of large density gradient, the ion drift motion also excites low-frequency drift waves when ω0≳ΩHe+ω*. The experimental data are found to agree well with the theory. The relevance of these processes to ion cyclotron heating of fusion plasmas is discussed.
Quasi-linear effects of linearly unstable compressional Alfvén waves
Authors: Migliuolo S. , Patel V. L.
Published: March 2003

The nonlinear interaction between Alfvén waves and magnetospheric plasma particles is examined, for the situation in which compressional and transverse modes are strongly coupled. Attention is given to the quasi-linear energy changes of the particles, due to the interaction with linearly unstable waves. Saturation of the unstable oscillations is achieved via a reduction of the perpendicular component of the particle temperature and an increase in the parallel component. The decrease in T⊥ leads to a reduction of the diamagnetic current, thereby lowering the compressional component of the oscillating magnetic field. The decrease in T⊥, when coupled to the increase in T∥, also results in a reduction in the temperature anisotropy of the plasma. The latter effect yields substantially reduced (linear) growth rates.
Derivation of the amplitude equation at the Rayleigh–Bènard instability
Authors: Cross M. C.
Published: March 2003

The full amplitude equation (as introduced by Newell and Whitehead and Segel) is derived directly from the hydrodynamic equations for both ’’free’’ and ’’rigid’’ upper and lower boundaries. The coefficients involved, including the interaction parameter of nonparallel rolls, are explicitly calculated for both boundary conditions and all Prandtl numbers.
Propagation of very slow lower hybrid waves in the Octopole Tokamak
Authors: La Haye Robert J. , Armentrout Charles J. , Petersen Peter I. , Stambaugh Ronald D.
Published: March 2003

A multi-element slow wave structure has been used to couple radio-frequency (rf) power to very slow lower hybrid waves in the Octopole-Tokamak plasma. Probing of the distribution of wave power in the plasma revealed strong amplitude modulation and scattering of the wave; however, direct evidence for the propagation of slow waves was obtained by measuring the toroidal wave speed.