bluuebunny/crossref_metadata_2025 huggingface dataset:
Long time plasma equilibrium
Authors: Hu Pung Nien
Published: March 2003

Plasma equilibrium with dissipation is governed by more equations than the one used for stability problems in ideal magnetohydrodynamics. Consequently, as transport processes became more important in fusion experiments, it is necessary to determine whether an equilibrium will eventually be reached after a long time at the end of the transport processes. A study is made of a cylindrical plasma with an ohmic heating current as an approximation to a large aspect-ratio tokamak. For comparison, both single-fluid theory and two-fluid theory are used. It is found that no equilibrium exists in the single-fluid theory with a plasma temperature dropping to zero at a finite radius, while such an equilibrium does exist in two-fluid theory provided that the electron temperature is higher than twice the ion temperature. Both the low-pressure and high-pressure cases are studied in the tokamak parameter range. Analytical results for the plasma behavior near its edge are also obtained.
A linear analysis of energy budgets in stratified viscous free shear layers
Authors: Miller James R.
Published: March 2003

The presence of shear instability can lead to the generation of turbulence in a stably stratified fluid. Using linear hydrodynamic stability theory, a turbulent kinetic energy budget is computed for an unbounded viscous shear layer for which the hyperbolic tangent shear layer is used to define the mean flow. For neutrally stable flows, the turbulent production due to the action of the Reynolds stress on the mean shear flow is balanced by viscous dissipation and the conversion to potential energy through the buoyancy term. The calculations show that maximum production of turbulent energy occurs at the center of the shear layer and that some of this energy is then transported to the edges of the shear layer where viscous dissipation occurs and some of the energy is converted to potential energy near the center of the flow. As the horizontal wavenumber decreases, the viscous dissipation becomes more important than the buoyancy term in removing energy from the flow. As the Reynolds number increases, the production term is concentrated over a narrower region at the center of the shear layer. Streamlines for neutral and stable conditions are presented to show the flow patterns of the disturbances in the x–z plane. Some possible atmospheric and oceanic applications are suggested in the last section.
Absolute instability of stimulated Brillouin scattering in drifting plasmas
Authors: Johnston T. W. , Mitchel G. R. , Grek B.
Published: March 2003

Absolute instability analysis of the coupled modes for stimulated Brillouin scattering for plasmas drifting at velocities rather greater than Mach 0.5 shows that oblique forward scatter is favored rather than backscatter, which is generally stable. For typical laser-target interaction parameters, a threshold (Iλ2) near 2×1015 W cm−2 μm2 seems reasonable. Light is not lost by re-emission but only diverted to more oblique incident angles and red-shifted. In laser-produced plasmas, reflection near critical density is needed to see the effect. For any condition (including supersonic plasma) absolute instability can only produce red-shifted light.
Electrostatic two-stream instability for a scattered relativistic electron beam and collisional plasma
Authors: Newberger Barry S. , Thode Lester E.
Published: March 2003

The Vlasov stability theory of the two-stream instability of a scattered relativistic electron beam in a collisional plasma is presented. New analytic results demonstrating the effect of a small but finite scatter (temperature) on the cold beam dispersion relation are given. These provide a basis for a discussion of the continuous transition, with increasing scatter, from the hydrodynamic to kinetic regime of instability. Numerical solutions of the dispersion relation are presented to illustrate some general features observed as well as trends in scaling with the beam parameters.
Comments on ‘‘Propagation of discontinuities along bi-characteristics in magnetohydrodynamics’’
Authors: Schmitt H.
Published: March 2003

Comments on the propagation of acceleration waves of arbitrary shape, which propagate into a gas at rest and is a constant state permeated by a magnetic field, is made. (AIP)
Motion of a contact line
Authors: Pismen L. M. , Nir A.
Published: March 2003

A multiscale expansion approach is applied to the solution of the free-boundary Stokes’ problem describing flow in the vicinity of a moving contact line. A solution free of singularities is obtained for the case of a liquid advancing into an inviscid medium. The force singularity reported in earlier studies is relaxed as the dynamic contact angle approaches π in the immediate vicinity of the moving contact line. This solution formally breaks down at a nonvanishing viscosity ratio of the receding and advancing fluids, but it still holds approximately for the case of a volatile liquid advancing into gas when Stefan flow in the gas phase is taken into account.
Highly supersonic ion pulses in a collisionless magnetized plasma
Authors: Schrittwieser R. , Rasmussen J. Juul
Published: March 2003

The initial transient response of a collisionless plasma to a high positive voltage step is investigated. Four different pulses are observed. An electron plasma wave pulse is followed by an ion burst. The latter is overtaken and absorbed by a highly supersonic ion pulse. Thereafter, an ion rarefaction pulse with roughly the ion acoustic velocity propagates into the other direction. The supersonic pulse is tentatively explained as the result of a transient Buneman instability. Together with the rarefaction pulse, it forms the first cycle of an instability which is customarily considered a current- driven ion acoustic one, but is, in fact, a potential relaxation instability.
Curvature-induced interchange mode in an axisymmetric plasma
Authors: Wickham Michael , Vandegrift Guy
Published: March 2003

A theoretical and experimental description of the curvature-induced electrostatic interchange mode in a simple mirror confined low-β plasma is given. The frequency, growth rate , and nonflute-like effects have been measured and compared with theory. Effects due to radial electric field, finite ion Larmor radius, line-tying, wall radius, and parallel electron response are discussed.
Formation and dynamics of a rotating proton ring in a magnetic mirror
Authors: Dreike P. L. , Greenly John B. , Hammer D. A. , Sudan R. N.
Published: March 2003

Experimental results are presented on the formation and dynamics of a rotating energetic proton ring in a magnetic mirror field. An annular 430 keV proton beam from a magnetically insulated diode is injected through a cusp-like magnetic field to form a rotating proton beam in a 2 m long solenoidal magnetic field. With 15–400 mT of neutral gas in the 40 cm diam experimental chamber up to 83% of the 350 J total beam energy is in rotation, the axial velocity dispersion is small, and the beam is sharply defined radially with inner and outer radii of 7 and 13 cm, respectively. The beam is 90%–100% axially current neutralized by currents induced in the beam-generated plasma. Azimuthal plasma currents are observed in air, but not in hydrogen. In hydrogen a ring containing 5×1015 protons is formed with sufficiently small axial velocity dispersion so that the protons are confined axially by their own 3% diamagnetic well as they propagate about 1.3 m in an 8 kG solenoidal field. In air, up to 15% of the beam axial energy is inductively coupled to the induced plasma currents, and ≳50% reflections are achieved from a 1.23 mirror ratio magnetic mirror located 2 m from the ion injector. About 1% inductive energy coupling to a wall resistor array was observed in both air and hydrogen. A peak ring diamagnetism of 875 G was observed 50 cm from the injector at a point where the applied field was 11 kG (near the peak of an upstream mirror); this ring contained about 1×1016 protons.
The Tormac V experiment
Authors: Brown I. G. , Feinberg B. , Kunkel W. B. , Levine M. A. , Niland R. A. , Shaw R. S. , Vaucher B. G.
Published: March 2003

Tormac (Toroidal Magnetic Cusp) is a plasma confinement concept combining the favorable magnetohydrodynamic stability properties of a cusp geometry with the good particle confinement inherent to closed field geometry. A conceptual Tormac plasma has two regions; an interior region in which a toroidal bias or stuffing field is embedded, and an exterior or surface region confined by mirror trapping along open field lines. The combination of these two regions is expected to lead to a configuration having confinement substantially superior to that of a mirror, and to allow the plasma to be stable to high β. The Tormac V experiment is an attempt to establish such a configuration and to investigate the characteristic behavior of the Tormac plasma. The Tormac concept, the Tormac V experimental setup, and the results are described.
Convective flow with subcritical instability
Authors: Neu John C.
Published: March 2003

An asymptotic analysis of subcritical instability in double diffusive convection is presented. Using a modified perturbation method, a Landau equation that determines how the amplitude of the convection evolves in time is derived. From the Landau equation, it is found that in certain cases, stable finite amplitude convection can exist even when the rest state with no flow is locally stable. The perturbation analysis complements and unifies previous work which is primarily qualitative or numerical in character.
Banana drift transport in tokamaks with ripple
Authors: Linsker R. , Boozer A. H.
Published: March 2003

Ripple transport in tokamaks is discussed for the ’’banana drift’’ collisionality regime, which lies below the ripple plateau regime treated earlier. The physical mechanisms that dominate banana drift transport are found to differ from those considered in previous work on this regime, and consequently the resulting transport coefficients can differ by several orders of magnitude.
Analytic models for design of laser-generated shock-wave experiments
Authors: Trainor R. J. , Lee Y. T.
Published: March 2003

Analytic models are derived for two important processes in laser-generated shock-wave phenomena: preheat energy deposition by suprathermal electrons and hydrodynamic shock attenuation. Predictions of the models are compared with available experimental data and other theoretical treatments, including extensive hydrodynamic code calculations, and in all cases good agreement is found. Combination of the models permits calculation of the maximum shock pressure attainable under any given set of direct irradiation conditions. Analytic expressions for optimum laser pulse length, target thickness, and laser intensity as functions of laser energy are also derived.
Stability of charged beam propagation through a relativistic hollow electron beam
Authors: Uhm Han S.
Published: March 2003

Stability properties of a charged beam propagation through a relativistic hollow electron beam are investigated, in connection with present experimental applications in the collective particle accelerator. The stability analysis is carried out for long axial wavelength and low-frequency perturbations. A closed algebraic dispersion relation for coupled transverse oscillations is obtained for the solid and hollow beams with sharp-boundary density profiles. One of the most important features in the analysis is that the typical growth rate of the transverse oscillation is of the order of the hollow beam diocotron frequency ωD, thereby severely limiting the solid beam propagation through a relativistic hollow electron beam. Particularly, for a solid beam with a small radius, the fundamental mode perturbation (i.e., the dipole oscillation) is the most unstable mode.
Comment on ‘‘Exact symmetry of the second-order nonlinear conductivity for a relativistic turbulent plasma’’
Authors: Brandt Howard E.
Published: March 2003

Another known exact symmetry of the second-order nonlinear conductivity for a relativistic turbulent plasma is presented.
The inviscid stability of Long’s vortex
Authors: Foster M. R. , Duck P. W.
Published: March 2003

The inviscid stability of Long’s vortex, which is believed to model tornado-like flows, is investigated using a finite-difference method. Flows of this type are found to be generally unstable to small, short-wave, helical disturbances, while no instabilities to axisymmetric modes have been found using this method. This instability provides a possible mechanism for the development of ’’suction vortices’’ in tornadoes.
The lifetime of nonlinear whistlers
Authors: Laedke E. W. , Shukla P. K. , Spatschek K. H. , Yu M. Y.
Published: March 2003

The newly found time-derivative-dependent ponderomotive force and velocity modulation contributions in nonlinear whistler wave propagation are incorporated into the multidimensional stability analysis. It is shown by the Liapunov method that stable one-dimensional whistler solitons exist. As a further result, it is demonstrated that the growth rate of the transverse bending instability, which is driven by the time-derivative-dependent ponderomotive force, is insignificant. This implies the observability of whistler solitons.
Flux loss during the equilibrium phase of field-reversed configurations
Authors: Tuszewski M. , Armstrong W. T. , Bartsch R. R. , Chrien R. E. , Cochrane J. C. , Kewish R. W. , Klingner P. , Linford R. K. , McKenna K. F. , Rej D. J. , Sherwood E. G. , Siemon R. E.
Published: March 2003

Field-reversed configurations are consistently formed at low filling pressures in the FRX-C device, with decay time of the trapped flux after formation much larger than the stable period. This contrasts with previous experimental observations.
Reduction in hot electron transport on dielectric targets at high laser irradiance
Authors: Decoste R. , Kieffer J.-C. , Piché M. , Pépin H. , Lavigne P.
Published: March 2003

Conducting properties of the target material are shown to affect both the penetration depth and lateral extent of hot electron transport in experiments with nsec-CO2-laser pulses incident on various planar layered targets. At an irradiance around 5×1013 W/cm2 on metal targets most hard x-rays are emitted outside the focal spot. The hard x-ray emission area is reduced by a factor of ten when the conducting target material is replaced by a dielectric of similar Z. The inward transport is likewise reduced. Strong electric fields produced by a local negative charge accumulation in a dielectric may explain the transport reductions.
Boundary effects on the dynamics of channels generated by laser-initiated discharges
Authors: Horton L. D. , Gilgenbach R. M.
Published: March 2003

The dynamics of unbounded and bounded reduced density channels have been characterized by means of ruby laser schlieren photography. These channels are produced by CO2 laser-initiated discharges in clean atmospheric pressure air. Bounded channels exhibit a significant compression in width and earlier onset of fine scale turbulence. These results could impact proposed designs for inertial fusion reactors relying upon reduced density channels for particle transport through gas blankets.
A shear instability induced by a composite internal wave
Authors: Müller Michael R. , Karlsson S. K. F.
Published: March 2003

Experiments have been performed in a thermally stratified two-layer shear flow with a nonzero mean velocity to observe the effects of artifically introduced low frequency internal waves on higher frequency, Kelvin–Helmholtz waves growing spatially on the density interface. Phillips’ model for wave-induced shear across an interface is extended to the two first-mode wave trains which can propagate in such a flow. It is shown that the Richardson number becomes a function of the phase of the internal composite waves and that its minimum value is either at the front or at the back face of the waveform depending on the sign of the background vorticity. Measurements are presented of the phase-averaged temperature and velocity fields of generated internal waves and show the waves breaking down on the face where the Richardson number was found to be at a minimum. The breakdown is characterized by the rapid growth of high frequency waves which appear to be phase locked on the parent internal gravity wave. Possible instances where this type of breakdown could occur in nature are discussed.
Experimental study of an ‘‘incipient spot’’ in a transitional boundary layer
Authors: Amini J. , Lespinard G.
Published: March 2003

A turbulent spot was created artificially in a transitional boundary layer by means of a point disturbance which was made as reproducible as possible. Single-probe hot-wire measurements of the streamwise velocity component were used to study the structure of the disturbance prior to its breakdown into a spot. The ’’incipient spot’’ in this experiment is found to be highly evolutionary, its length increasing by almost 100% during transit past a fixed location. The contour of the incipient spot, when projected on a plane parallel to the wall, is arrowheaded in shape with an apex which is considerably sharper than that of a turbulent spot. In the plane of symmetry, rapid fluctuations are observed far from the wall; closer to the wall, a velocity excess occurs and regions of streamwise momentum defect and excess develop alternately in the spanwise direction. Time history at a fixed streamwise location shows that the central excess region is crossed by a ’’defect bridge’’ connecting the downstream ends of the adjacent defect regions. The incipient spots in this experiment propagate considerably faster than the three-dimensional wave packets, which have been investigated by others who applied the same, yet much weaker, disturbance source.
Period between bursting in turbulent boundary layers
Authors: Bandyopadhyay Promode R.
Published: March 2003

Available measurements in turbulent boundary layers having zero, favorable, or adverse pressure gradients have been used here to show that a universal value of the nondimensional period between bursting does not exist.
The probability density function of a passive scalar in turbulent shear flows
Authors: Kollmann W. , Janicka J.
Published: March 2003

The transport equation for the probability density function of a scalar in turbulent shear flow is analyzed and the closure based on the gradient flux model for the turbulent flux and an integral model for the scalar dissipation term is put forward. The probability density function equation is complemented by a two-equation turbulence model. Application to several shear flows proves the capability of the closure model to determine the probability density function of passive scalars.
Focusing of waves in turbulent inhomogeneous media
Authors: Kulkarny V. A. , White B. S.
Published: March 2003

Growth of large fluctuations in the amplitude of high-frequency waves or shocks propagating through turbulent, inhomogeneous media is investigated stochastically with geometrical acoustics. Previous efforts use linearization which is not uniformly valid at large distances and large variations in the ray tube area. The present analysis retains the nonlinear terms crucially important to focusing and growth of singular fluctuations in the amplitude. It is shown, in two dimensions, that the fluctuations of the ray-tube area grow exponentially and caustics occur on every ray, repeatedly, on a distance scale of a σ−2/3, where the fluctuations in ray directions are still small, O(σ2/3). Here, σ≪1 is the standard deviation and a is the correlation length of the wave velocity distribution in the medium. Probability densities for the occurrence of caustics are given. Also, the moments of the ray-tube area distribution and amplitude related statistics are developed for distances well into the region of caustic formation. Finally, a method is presented for relating the theoretical predictions to measurements on an image plane.
Experiments on the influence of magnetic fields on the viscosity of water and a water-NaCl solution
Authors: Viswat E. , Hermans L. J. F. , Beenakker J. J. M.
Published: March 2003

The influence of external magnetic fields on the viscosity of water at 295 K was investigated in a differential experiment. With fields up to 2.3 T either parallel to or perpendicular to the flow, an upper limit to relative changes was established as 3×10−5. This result is contradictory to earlier results by other authors, who reported relative viscosity increases up to 3×10−3 at comparable field strengths.
Turbulent relaxation of compressible plasmas
Authors: Hameiri Eliezer , Hammer James H.
Published: March 2003

Relaxation of plasmas via turbulence is treated by the use of a maximum entropy principle. The relaxed states are always stable to ideal modes. Taylor’s theory of field reversal is extended to finite pressure plasmas and given a rigorous support by using symmetries in the equations to determine preferred conservation laws. Relaxed states of field-reversed ϑ pinches are predicted, some with self-reversal of the magnetic field.
Transport theory of tokamak plasmas with large toroidal rotation
Authors: Wong Seung Kai , Burrell Keith H.
Published: March 2003

The neoclassical transport theory for tokamak plasmas in the plateau to Pfirsch–Schlüter regimes is extended to cases in which the parallel flow can become comparable to the ion thermal velocity. Important changes are found in the qualitative structure and the quantitative predictions of the theory. Solutions for both pure and impure plasmas in the plateau regime are obtained.
Nonadiabatic particle response in toroidal geometry
Authors: Schep T. J. , Braams B. J. , Pegoraro F.
Published: March 2003

The nonadiabatic part of the particle response to low-frequency electromagnetic modes with long parallel wavelengths is discussed. Analytic approximations to the kernels of the integrals that relate the amplitudes of the perturbed potentials to the nonadiabatic part of the perturbed density in an axisymmetric toroidal configuration are presented and the results are compared with numerical calculations. It is shown that both in the plane slab and in toroidal geometry the kernel contains a logarithmic singularity. This singularity is associated with particles with vanishing parallel velocity so that, in toroidal geometry, it is related to the behavior of trapped particles near their turning points. In contrast to the plane slab, in toroidal geometry this logarithmic singularity is mainly real and associated with nonresonant particles. Apart from this logarithmic term, the kernel contains a complex regular part arising from resonant as well as from nonresonant particles.
Plasma sweeper to control lower-hybrid wave coupling
Authors: Motley R. W. , Glanz J.
Published: March 2003

Experimental tests of an Ẽ×B̃ plasma sweeper, designed to control the plasma density near the mouth of a phased waveguide array, are described.
Internal heat deposition in laser highly accelerated targets
Authors: Ripin B. H. , McLean E. A. , Stamper J. A.
Published: March 2003

A novel method is described from which estimates of the internal pressure or temperature of highly accelerated material can be made. The technique utilizes the relationship of the initial free expansion properties of a fluid boundary to internal pressure. The technique is applied to Nd-laser ablatively accelerated targets; the results compare well with target rear surface temperature measurements using time-resolved optical pyrometry.
The touching pair of equal and opposite uniform vortices
Authors: Saffman P. G. , Tanveer S.
Published: March 2003

The shape and speed of a pair of touching finite area vortices are calculated and an error in previous work corrected.
Subharmonic generation by resonant three-wave interaction of deep-water capillary waves
Authors: Banerjee P. P. , Korpel A.
Published: March 2003

Subharmonic generation has been observed during the propagation of deep-water capillary waves. The observations are shown to be in agreement with the theory of degenerate resonant noncollinear three-wave interaction in a nonlinear, dispersive medium.
The velocity field induced by a helical vortex filament
Authors: Hardin Jay C.
Published: March 2003

An exact analytical solution for the velocity field, both interior and exterior, induced by an infinite right-handed helical vortex filament is derived. Due to the way the variables combine in this solution, the paper also shows that it is possible to derive a stream function for this nonaxisymmetric flow. Sample calculations of these expressions are included.
Similarity solutions and experiment for turbulent wakes
Authors: Hariri A. , Libby Paul A. , LaRue John C.
Published: March 2003

Available data for the turbulent wake of unheated and heated cylinders are compared to far-wake solutions obtained from the relevant equations prior to application of any closure assumption. It is found that such comparisons require a new determination of the virtual origin significantly different from traditional values and at the same time provide a sensitive criterion to decide if the stations at which data are collected are sufficiently far downstream for far-wake solutions to apply.
The nonlinear filamentation of lower-hybrid waves by ion-ion hybrid perturbations
Authors: Tagare S. G. , Rolland P.
Published: March 2003

The problem of the nonlinear filamentation of lower-hybrid waves in a two-ion species magnetized plasma has been investigated. The dominant nonlinear effect comes from the existence of two ion species if the concentration of second ion species is larger than (me/mi)s−1 (with 1<s<3/2). The nonlinear Schrödinger equation and the modified nonlinear Schrödinger equation describing the nonlinear self-distortion of the propagation cones of lower-hybrid waves due to the interaction with low-frequency ion-ion hybrid perturbations are derived for the case of fast phase variation. In the case of slow phase variation the nonlinear self-distortion of the propagation cones of lower-hybrid waves is described by the modified Korteweg–deVries equation when the ion-ion wave is at the Buschbaum frequency. The nonlinear equation which governs the asymptotic state of filamentation admits an exact solution, describing solitons, envelope solitons, or cusped envelope solitons for the electric field. These solitons represent the nonlinear stage of the evolution of the purely growing mode which appears in the parametric analysis.
The stability of flute modes in the ELMO Bumpy Torus
Authors: El-Nadi Adel
Published: March 2003

A radial normal mode analysis is carried out to study the stability of fluidlike flute modes in a simplified model of the ELMO Bumpy Torus. The corresponding stability conditions are obtained.
Electron radial transport in tandem mirrors in the low collision frequency limit
Authors: Myra J. R. , Catto Peter J. , Hazeltine R. D.
Published: March 2003

A variational principle formulation is used to calculate the electron radial transport coefficients in a nonaxisymmetric tandem mirror, in the low collisionality regime. Explicit analytical estimates are given for two important classes of electrons. The implications of symmetry, end currents, and ambipolarity are discussed in detail in order to demonstrate their potentially important effect on the radial particle loss rates.
Stability of helically symmetric straight equilibria
Authors: Mond M. , Weitzner H.
Published: March 2003

The stability of straight helically-symmetric low-β systems is studied. Two families of equilibria are investigated which differ from each other by the ordering of the physical variables in β. The energy principle as well as eigenmode analysis are used in order to check the stability properties of the equilibria. It is found that low shear systems are stable to interchangelike modes. It is shown that interchange stability is necessary and sufficient for stability. Thus, low shear, zero net current configurations are found which are stable. Systems with arbitrary shear are found to be stable but also to have neutrally stable modes which are localized around rational flux surfaces.
Behavior of charged particles confined in a magnetic mirror
Authors: Bora D. , John P. I. , Saxena Y. C. , Varma R. K.
Published: March 2003

Experimental investigations of the nonadiabatic leakage of charged particles from a magnetic mirror have been conducted. The observations reveal the existence of multiple lifetimes for particles with similar energy and pitch angle. The variations of the time scales as a function of the particle density and radial position are investigated.
Exhaust rate measurements in a divertor with large mirror ratio
Authors: Strait E. J.
Published: March 2003

The parallel ion fluid velocity in the scrape-off layer of a poloidal divertor is observed to vary inversely with the mirror ratio in the divertor’s throat for ratios ranging from 1 to 5, in good agreement with models developed for bundle divertors. The density variation on a diverted field line also agrees qualitatively with the models, but the observed electric field does not.
A two-grating method for combined beam splitting and frequency shifting in a two-component laser-Doppler velocimeter
Authors: Glezer Ari , Coles Donald
Published: March 2003

The use of a rotating radial phase grating to carry out beam splitting and frequency shifting in a laser-Doppler velocimeter is briefly reviewed. This technique is not new. However, the present design adds a substantial new element by using two overlapping radial gratings to produce a two-channel system in which channel separation can be accomplished by electronic filtering of the signal from a single detector.
Conical vortices: A class of exact solutions of the Navier–Stokes equations
Authors: Yih C.-S. , Wu F. , Garg A. K. , Leibovich S.
Published: March 2003

A two-parameter family of exact axially symmetric solutions of the Navier–Stokes equations for vortices contained within conical boundaries is found. The solutions depend upon the same similarity variable, equivalent to the polar angle φ measured from the symmetry axis, as flows previously discussed by Long and by Serrin, but are distinct from the cases they treated. The conical bounding stream surfaces of the present solution can be located at any angle φ=φ0, where 0<φ0<π. The flows in all of these cases, when solutions exist, are finite everywhere except at the cone vertex which is a source of axial momentum, but not of volume. Solutions are of three types, flow may be (a) towards the vertex on the axis and away from the vertex at the conical boundary, (b) towards the vertex both on the axis and at the cone, or (c) away from the vertex on the axis and towards it at the bounding cone. In the first and second case, strong shear layers form on the cone walls for high Reynolds numbers. In case (c), a region of strong axial shear and strong axial vorticity forms near the axis, even for low Reynolds numbers. The qualitative nature of the possible solutions is deduced, using methods of argument due to Serrin, and examples of flows are numerically computed for cone half-angles of π/4, π/2 (flows above the plane z=0), and 3π/4. Regions of the parameter space where solutions are proven not to exist are given for the cone half-angles given above, as well as regions where solutions are proven to exist.
Instability and confined chaos in a nonlinear dispersive wave system
Authors: Caponi Enrique A. , Saffman Philip G. , Yuen Henry C.
Published: March 2003

Calculations of a discrete nonlinear dispersive wave system show that as the degree of nonlinearity increases, the system experiences in turn, periodic, recurring, chaotic, transitional, and periodic motions. A relationship between the instability of the initial configuration and the long-time behavior is identified. The calculations further suggest that the corresponding continuous system will exhibit chaotic motions and energy-sharing among a narrow band of unstable modes, a phenomenon which we call ‘‘confined chaos.’’
A modulated point-vortex model for geostrophic, β-plane dynamics
Authors: Zabusky Norman J. , McWilliams James C.
Published: March 2003

A new modulated point-vortex model is presented for the equivalent barotropic equations of potential vorticity: qt−ψyqx +ψxqy=0, (q=κ+βy, κ=∇2ψ−γψ). The discrete model conserves ∑m(qm0 −β*ym)2 in analogy with the conserved ∫ ∫κ2 dx dy. An analytical study is made for the general two point-vortex system. For equal vortices, the solution has a monotonic drift ∝(−β). A comparison is made of numerical solutions of the point-vortex model and corresponding solutions of a finite-difference model on a periodic domain. For an initially monopolar distribution of ∇2ψ−γ2ψ, an x drift in the direction of sign (−β) and a y drift in the direction of the sign of the extremum of κ is obtained in both cases that are in agreement at short times. The y drift is associated with the development of a spreading Rossby wave wake, as a consequence of the conservation law. For a ‘‘tilted’’ dipolar region of vorticity we observe near-periodic oscillations. The modulated point-vortex model is also applicable to drift waves in a plasma.
Filamentary instability of a relativistic electron beam in an anisotropic plasma
Authors: Shukla P. K. , Yu M. Y. , Lakhina G. S.
Published: March 2003

The collisional beam-Weibel instability is explained in terms of unstable magnetostatic modes. Previous investigations are extended to include anisotropic distributions. The nonlinear evolution of beam filamentation is interpreted in terms of a theory of magnetostatic mode turbulence.
Experimental investigation of the linear and nonlinear properties of an impurity-driven drift wave
Authors: Allen G. R. , Yamada M. , Rewoldt G. , Tang W. M.
Published: March 2003

An impurity-driven drift wave is observed to be destabilized by the reversed density gradient of a singly ionized heavy-impurity-ion population in a Q-machine plasma. The evolution of the instability is investigated as it progresses from the initial linear exponential growth phase, into a nonlinear saturated state, whereupon strong radially outward anomalous diffusion is observed. The relationship between the anomalous diffusion coefficient and the wave amplitude is in agreement with estimates obtained from the nonlinear drift-wave turbulence theory of Dupree.
Propagation of an intense charge-neutralized ion beam transverse to a magnetic field
Authors: Ishizuka Hiroshi , Robertson Scott
Published: March 2003

It is shown experimentally that an intense, pulsed, charge-neutralized proton beam (140 kV, 10 A/cm2, 800 nsec) will pass through a region of transverse magnetic field of up to 2 kG without being significantly deflected. Electric probe measurements show that within the magnetic field a polarization electric field E is set up such that E+v×B=0, where v is the beam velocity and B is the applied magnetic field. Data for propagation are consistent with the polarization drift model of Schmidt which applies to plasmas having a dielectric constant ε≫1; however, propagation was not observed unless ε≳400.
Measurement of ion-acoustic wave velocity in a pulsed plasma
Authors: Abt Norman E. , Guethlein Gary , Stearns J. Warren
Published: March 2003

A novel method for measuring the velocity of ion-acoustic waves is presented. The difference frequency between transmitted and received signals is observed as the transmitted frequency is swept linearly in time. This difference frequency is constant and proportional to the wave velocity. Temperatures inferred from the velocity agree with Langmuir probe measurement made on a hydrogen plasma.
Temperature limit in ECH hot electron plasmas
Authors: Uckan N. A.
Published: March 2003

During the past two decades the production of high-beta, hot electron plasmas with electron cyclotron heating (ECH) has been demonstrated in open and closed geometries. Compilation of data from these experiments shows that in all cases the limiting hot electron temperature is determined by the scaling law ρ/L=const (∼5–6×10−2), where ρ is the hot electron gyroradius (relativistic) and L is the magnetic-field scale length. Results cover a wide variety of conditions in these experiments with a factor of 2 change in device dimensions and more than an order-of-magnitude change in magnetic fields (∼1–10 kG), ECH frequencies (∼2.4–55 GHz), and hot electron temperatures (∼10–1300 keV). The observed scaling law suggests that nonadiabatic effects play an important role in determining the limiting hot electron temperature. It is shown, however, that although in all previous experiments the limiting temperature is determined by the ρ/L criterion future experiments may not reach this limit.
Decay of a plasma created between negatively biased walls
Authors: Chen Francis F.
Published: March 2003

When a slab plasma is created between negatively biased walls with a vacuum gap between the plasma and the wall, the rate of decay of the density is governed by the space-charge limit to the ion current. This limit is modified by the ion velocity gained in a presheath. It is shown that the sheath criterion implies eventual stagnation of an initially fast-moving sheath, followed by a slower motion on a different time scale.
Detonation driven induction generators with parallel and antiparallel external and induced magnetic fields
Authors: Wilhelm H. E.
Published: March 2003

Based on Maxwell’s equations, the electric current and voltage pulses induced in explosion driven induction generators (Rm =μ0σvL≫1) with plane electrodes and homogeneous external magnetic field B0 are calculated analytically for two plasma shock flows, (i) the jet flow with shock speed v(t)=v0, t≥0, and (ii) the plane detonation flow with shock speed v(t)=(2/3)(E0/ρ0)1/3t−1/3, t≥0. The external load circuit with resistance R0 and inductance L0 is connected either (I) to the downstream ends or (II) to the flow entrance ends of the electrodes so that the magnetic self-field B̃(t) of the generated current I(t) is (I) parallel and (II) antiparallel to the transverse external field B0. In both generator models I and II, the jet flow produces large current and voltage pulses, whereas the detonation flow generates considerably smaller and shorter current and voltage pulses. In all cases, the magnetic self-field B̃(t) of the generated current I(t) is of the order-of-magnitude of B0, but the generator with electrode wiring I (positive superposition of B̃ and B0) produces considerably more power and energy than the generator with electrode wiring II (negative superposition of B̃ and B0).
Comparison of plasma focus calculations
Authors: Eltgroth Peter G.
Published: March 2003

A simple model for the current history of plasma focus experiments is presented. The presence of a leak current which does not pass through the plasma sheath is allowed. Results are found to compare quite well with those of much more sophisticated two-dimensional magnetohydrodynamic calculations. For the Frascati experiment, which has detailed current measurements, computed results do not agree with experimentally derived values. A reasonable match for the total current in the Frascati experiment can be found by lowering the leak current. Both total and leak current can be matched if a mass loss from the run-down region is allowed.
Stability theory of drift-type flute modes in finite-β plasmas
Authors: Migliuolo Stefano
Published: March 2003

The linear theory of flute modes in a finite-β, inhomogeneous, magnetized plasma is developed. The collisionless Vlasov equation is used in a slab geometry, including the effects of a constant gravity field. The magnetic drift mode and the g×B mode are examined, and their stability properties are described. These two ‘‘modes’’ are shown to be different limits of the general finite-β interchange mode. The wave-particle resonances, between the flute modes and the particles that ∇B drift perpendicular to the unperturbed magnetic field, are included in a self-consistent manner.
Energy and momentum deposition in plasmas due to the lower hybrid wave by a finite source
Authors: Nakajima Noriyoshi , Abe Hirotada , Itatani Ryohei
Published: March 2003

Heating and current generation due to the lower hybrid wave are studied using particle simulation. In contrast with previous work, where only a single mode is treated, the main interest of this work is focused on the physical problems of a propagation cone consisting of many Fourier-expanded modes. It is found that the trajectory of the propagation cone is well described up to the lower hybrid resonance layer using both the cold plasma approximation and the WKB method. An ion cross-field drift due to the ponderomotive force is observed. A main discovery of this work is that the modes in the upper portion of the spectrum of the antenna play a key role in the creation of the ion high-energy tail. This process cannot be explained by the linear theory and is called the cascade process judging from the time variation of the damping of each mode. The particle model is significantly improved using the elongated grid and the quadratic spatial interpolation. Applications of this model to simulations of other problems are expected to be fruitful in research on plasma physics and nuclear fusion.
Theory of phase-space density holes
Authors: Dupree Thomas H.
Published: March 2003

A Bernstein–Green–Kruskal mode consisting of a depression or ’’hole’’ in the phase-space density is shown to be a state of maximum entropy subject to constant mass, momentum, and energy. The parameter space of such holes is studied. The maximum entropy property is used to develop a simplified approximate analytic method as well as to infer the results of hole collisions including coalescing and decay. The maximum entropy property suggests that random, turbulent fluctuations tend to form into such self-trapped structures and this nonperturbative concept is related to the physics of ’’clumps’’ which occur in a renormalized perturbative theory of turbulence.
Verification of the classical theory of helical transport in stellarators
Authors: Mynick H. E.
Published: March 2003

The apparent discrepancies of the classical theory of helical transport in stellarators, versus two recent numerical studies of stellarator transport, are investigated. Numerical results are presented, verifying the classical theory, when the model for the magnetic field has the simple form assumed by the classical theory. When the helical contribution to the total transport is isolated numerically, and the different energy dependence of the particle distribution is accounted for, the results of one of the numerical studies is brought into substantial agreement with theory. It is argued that the anomalously favorable low collisionality results of the second numerical study are due partially to numerical procedure, and partly to a more complicated spatial dependence of the magnetic field.
Long wavelength collisional tearing modes in a stochastic magnetic field
Authors: Kleva Robert G.
Published: March 2003

Renormalized statistical equations which characterize a long wavelength resistive tearing mode when the magnetic field is stochastic are derived. The theory predicts a broadening of the current layer of the mode due to enhanced perpendicular electron motion. This increase in the current layer width is significant for fluctuation levels 〈(δB/B)2〉 as small as 10−8, where 〈(δB/B)2〉 is the ratio of the energy in the magnetic fluctuations to the equilibrium magnetic energy. As a consequence of this broadening, the transition from exponential to algebraic growth is not attained until the magnetic energy density of the mode exceeds the total magnetic energy density of all the other fluctuations.
Renormalization of plasma turbulence in toroidal geometry
Authors: Hazeltine R. D.
Published: March 2003

Action-angle variables are used to renormalize the nonlinear drift-kinetic equation in an asymmetric torus. Special cases of the result are shown to agree with previous nonlinear theories.
Alfvén wave cyclotron resonance heating
Authors: White R. B. , Yoshikawa Shoichi , Oberman C.
Published: March 2003

The resonance absorption of fast Alfvén waves at the proton cyclotron resonance of a predominately deuterium plasma is investigated. An approximate dispersion relation is derived, valid in the vicinity of the resonance, which permits an exact calculation of transmission and reflection coefficients. For reasonable plasma parameters significant linear resonance absorption is found.
Scattering and collpase of Langmuir waves driven by a weak electron beam
Authors: Hafizi B. , Weatherall J. C. , Goldman Martin V. , Nicholson Dwight R.
Published: March 2003

The evolution of Langmuir waves predicted by the beam-driven Zakharov equations is studied numerically with high resolution in one and two dimensions, for parameters appropriate to type III solar radio bursts at 0.5 a.u. It is found that collapse is preceded by momentum transfer to ion-acoustic quasimodes even in the absence of a weak solar magnetic field. The early evolution is similar in one and two dimensions. A zero momentum condensate forms in both cases, but its subsequent behavior differs in one dimension and two dimensions. The corresponding real-space wave packets collapse rapidly in two dimensions, but evolve as slowly growing solitons in one dimension. Detailed comparisons are made with other (one-dimensional) models of ’’strong’’ Langmuir turbulence associated with type III bursts.
Marginal stability of impulsively initiated Couette flow and spin-decay
Authors: Neitzel G. P.
Published: March 2003

A viscous, incompressible fluid is contained within an infinitely long circular cylinder or between a pair of infinitely long concentric cylinders. In both cases, the entire system is in a state of rigid-body rotation. At time t = 0 the outer flow boundary is impulsively brought to rest, giving rise to a potentially unstable, unsteady swirl flow. The stability of these flows is examined by employing energy theory with a marginal stability criterion to obtain lower bounds on the onset times for instability. In some cases, the asymptotic steady-state flow will be stable, with any instability merely a transient, while in other cases, stability of the asymptotic state is not guaranteed.
Single and multiple waves induced by power absorption
Authors: Armstrong Bruce , Ahlborn Boye , Liese Wolfgang
Published: March 2003

Sub- and supersonic wave fronts produced by heat input have been generated in a shock tube driven by a step current pulse of variable magnitude (4–50 kA, duration up to 160 μsec). At high current and low fill gas densities, the supersonic mode appears and no substantial compression is possible. The limiting current Ic to reach this supersonic mode is determined as a function of the fill gas pressure. Front velocities, pressures, and electron densities are measured, and the heating characteristic (maximum enthalpy as function of the net absorbed energy flux) is derived. Scaling laws are obtained for the fluid parameters as a function of fill gas density and current. The measurements are interpreted in terms of one-dimensional wave model calculations. Studies with two stepped power pulse reveal that multiple shocks with a region of substantially increased density can be obtained only if the total current It remains below the critical value Ic. For It≳Ic, a supersonic heat wave is created after the transient phase, and multiple shocks with increased density can no longer be achieved.
Stochasticity and the random phase approximation for three electron drift waves
Authors: Terry Paul , Horton Wendell
Published: March 2003

The interaction of three nonlinearly coupled drift waves is investigated for the occurrence of stochastization of the phases and the applicability of the random phase approximation. The drift wave nonlinearities include the E×B and polarization drift couplings for waves that are linearly unstable for appropriate values of the perpendicular wavenumber. The conservation properties and sample numerical solutions for the exact three wave interaction are given along with the conservation properties and solutions of the corresponding random phase approximation equations.