bluuebunny/crossref_metadata_2025 huggingface dataset:
Propagation of magnetohydrodynamic shocks in a thermally-conducting medium
Authors: Rosenau Philip , Frankenthal Shimshon
Published: March 2003

A theory of magnetohydrodynamic piston-driven disturbances in a thermally-conducting medium is presented, based on a phenomenological model which admits self-similar solutions. The motion consists of a thermal precursor followed by an isothermal shock. The magnetic field plays a fundamental role; even a very modest transverse magnetic field keeps the peak densities down, blocks the heat flow, and widens the perturbed domain. This, together with a decrease (increase) of post shock density (temperature) compares favorably with some measurements in the solar wind.
Density profile modification by light pressure in spherical geometry
Authors: Virmont J. , Pellat R. , Mora A.
Published: March 2003

The density profile modification which is generated by the radiation pressure of a powerful laser normally irradiating a spherical target is considered. Numerical simulation with a fluid code shows the formation of a nonmonotonic density profile, with an overdense bump detached in the underdense region. This shape is explained by a stationary model, and except for very small laser fields it, is shown to be the only one-dimensionally stable solution.
Energy deposition by fast protons in pellet fusion targets
Authors: Nardi E. , Peleg E. , Zinamon Z.
Published: March 2003

The energy loss of energetic protons in heavy metal targets is calculated at temperatures and densities of interest for pellet fusion. The contributions of bound and free electrons to the stopping power are considered. It is found that in the temperature range of interest the increase in the number of free electrons in the target plasma causes range shortening with increasing temperatures and specific volumes. In order to study this effect on the ablation process, a one-dimensional calculation of the hydrodynamic flow with energy deposition was carried out.
Nonlinear transport instability in a diffusive plasma
Authors: Sato Tetsuya
Published: March 2003

Fine structures of the unstable waves and the electron density profiles resulting from nonlinear spatial transport are studied numerically for a collisional flute mode instability. It is confirmed that the nonlinear transport produces regular pulse trains in both the electron density and wave amplitude profiles in the direction perpendicular to the electron drift (in the direction of the density gradient). Fourier spectral analysis of the nonlinear structure in that direction indicates two major spectral peaks. The main peak is the fundamental mode which leads to overall flattening of the density distribution in the entire unstable region. The second peak corresponds to the generated small-scale pulses resulting from a nonlinear instability associated with a strong wave-induced transport. In the steady state the pulses tend to merge and be smeared out to form a plateau in the density profile. These indicate the presence of two different, steady and pulsative, transports. Examination of the spatial structure finds that the pulse width is roughly the same size as the dominant wavelength of the primary wave which propagates in the direction of the drift. It is further found that the observed nonlinear mode can be explained by a nonlinear transport equation of the form nt+(n2)z+ky−2(n2)zzz=0, where ky is the wavelength of the dominant primary wave propagating in the direction of the drift and z denotes the coordinate perpendicular to the drift.
Nonadiabaticity in mirror machines
Authors: Cohen Ronald H. , Rowlands George , Foote James H.
Published: March 2003

An analytic technique for calculating magnetic-moment jumps Δμ of particles in magnetic traps, previously derived for particular two-dimensional vacuum fields, is generalized to nonvacuum fields of arbitrary complexity and applied to high-β mirror machines. The size of a jump depends on the behavior of the magnetic-field strength B (s) near the singularities of B in the complex s plane, where real s measures position along a field line. It is demonstrated that an intrinsic complication of mirror-machine magnetic configurations is the presence of multiple singularities of B, which become closely spaced for field lines near the axis. An expansion in r2 is used to determine Δμ in the closely spaced regime. The analytic theory is compared with results from a particle-orbit code for several axisymmetric nonvacuum fields, and is found to be in excellent agreement in both the well separated and closely spaced singularity regimes. Finite-β effects are examined using axisymmetric model fields derived from the long, thin equilibrium approximation, with parameters representative of present (2XIIB) and future (MFTF) mirror experiments. It is shown that increasing β appreciably lowers the maximum energy at which particles are confined. The effect is particularly significant if the plasma length is small compared with the vacuum field axial scale length and if the gyroradius is small compared with the plasma radius. The degradation is substantially reduced when the gyroradius at the energy limit is comparable to the plasma radius.
Wave absorption near the electron cyclotron frequency
Authors: Fidone I. , Granata G. , Ramponi G. , Meyer R. L.
Published: March 2003

Wave absorption for frequencies near the electron cyclotron frequency for the ordinary and extraordinary modes is investigated. The role of finite electron Larmor radius effects is discussed. A numerical analysis of the relevant dispersion relation in the weakly relativistic and nonrelativistic limit is presented. The density dependence (1/ne) of the damping of the extraordinary wave for not too small densities and the strong absorption of the ordinary wave for quasi-perpendicular propagation in a hot plasma (Te≳1 keV) are investigated numerically for several angles of incidence.
Experiment on nonadiabatic rf plugging in a cusped field
Authors: Hiroe S. , Sato T. , Watari T. , Hidekuma S. , Kumazawa R. , Adati K. , Shoji T. , Kawasaki S. , Miyahara A. , Akaishi K. , Kubota Y. , Watanabe N. , Miyake S.
Published: March 2003

Under nonadiabatic conditions, rf plugging is accompanied by effective ion heating, which in turn causes increased particle losses from a cusp configuration. An empirical scaling relation for rf plugging of line cusp loss is obtained among the required rf electric field, the static magnetic field, and the plasma density, and is compared with the relation obtained by a linear theory.
Effect of magnetic perturbations on divertor scrape-off width
Authors: Boozer Allen H. , Rechester A. B.
Published: March 2003

A general method is developed for calculating the width, due to magnetic perturbations, of the scrape-off layer of a tokamak with a divertor. The method, which assumes the plasma particles are tied to the field lines, should provide a good estimate provided the predicted width is large compared to that given by particle diffusion or finite particle drift orbit effects. The general theory is applied to a simple analytic model of a divertor to indicate the expected magnitude of the scrape-off layer thickness.
Drag due to a striated boundary in slow Couette flow
Authors: Wang Chang-Yi
Published: March 2003

A highly viscous fluid separates a smooth plate moving in its own plane and a wavy plate. Due to the wavy striations, the mean flow is decreased and the mean drag is increased. The waviness makes the fluid appear to be anisotropic.
Nonlinear theory of drift waves in multispecies plasma
Authors: Gillet Claudine , Rogister André
Published: March 2003

The saturation level of drift waves in a multispecies plasma is estimated. The convection rate of each species across the plasma is calculated.
Experiments on second-sound shock waves in superfluid helium
Authors: Cummings John C. , Schmidt Dieter W. , Wagner Wolfgang J.
Published: March 2003

The waveform and velocity of second-sound waves in superfluid helium have been studied experimentally using superconducting, thin-film probes. The second-sound waves were generated with electrical pulses through a resistive film. Variations in pulse power, pulse duration, and bath temperature were examined. As predicted theoretically, the formation of a shock was observed at the leading or trailing edge of the waves depending on bath temperature. Breakdown of the theoretical model was observed for large pulse powers. Accurate data for the acoustic second-sound speed were derived from the measurements of shock-wave velocities and are compared with previous results.
Stability of heated laminar boundary layers in water with nonuniform surface temperature
Authors: Strazisar A. , Reshotko E.
Published: March 2003

As part of a continuing study of the stability of heated laminar boundary layers in water, an experiment has been performed for the case of nonuniform surface temperature where disturbances are introduced by a vibrating ribbon and the response measured using temperature compensated hot-film anemometry. Two types of nonuniform wall temperature distributions have been studied. These are: (a) power law distributions of the form ΔT= (Tw−T∞) =Axn, and (b) step changes in wall temperature. Measured mean velocity and temperature profiles agree with solutions of the mean boundary layer equations. Measured stability characteristics for power law temperature distributions indicate that, at a fixed Reynolds number and local ΔT, both the disturbance growth rate and the band of frequencies receiving amplification are reduced relative to the uniform wall temperature case when n<0 and increase relative to the uniform wall temperature case when n≳0. The maximum growth rate for ΔT =2.78°C (5°F) and n=−0.5 is negative indicating damped disturbances at all frequencies. Disturbance growth rates for step changes in wall temperature at first decrease and then increase relative to those for uniform wall temperature as the step change location is moved downstream.
Method of generalized coordinates and an application to Rayleigh–Taylor instability
Authors: Dienes John K.
Published: March 2003

The method of generalized coordinates is extended to the analysis of continuous bodies for which the degrees of freedom are independent velocity distributions in the spatial coordinates. The corresponding Lagrange equations contain generalized convective terms as well as the usual generalized forces and masses. Since the existence of a potential is not assumed, the equations of motion can be applied to media with arbitrary (possible dissipative) constitutive laws. Material deformation is characterized by the rate of strain, which is taken as the symmetric part of the velocity gradient, making the approach valid for arbitrarily large deformations. As an example, infinitesimal Rayleigh–Taylor instability is considered by analytic methods. Then, large amplitude Rayleigh–Taylor instability is represented with a single-degree-of-freedom analysis that shows the development (by numerical integration) of the known spike-and-bubble configuration of the unstable interface. The infinitesimal stability of a plastically deforming solid and the growth of the instability to large amplitudes are also considered.
Non-Newtonian flow along needles
Authors: Chen J. L. S. , Kubler E. A.
Published: March 2003

The analysis of incompressible laminar boundary-layer flow of power-law non-Newtonian fluids along thin needles is presented. Similarity velocity profiles and skin friction are obtained for pseudo-plastic, dilatant, as well as Newtonian fluids. Physical insights are gained by examining the effects of the flow behavior index and the needle size on the boundary layer flow.
Three-dimensional magnetohydrodynamic turbulence in cylindrical geometry
Authors: Montgomery David , Turner Leaf , Vahala George
Published: March 2003

Ideal magnetohydrodynamic turbulence is treated using more realistic boundary conditions than rectangular periodic boundary conditions. The dynamical equations of incompressible magnetohydrodynamics and the associated fields are expanded in a set of vector eigenfunctions of the curl. The individual eigenfunctions represent force-free fields, but superpositions of them do not. Three integral invariants have simple quadratic expressions in the expansion coefficients: the total energy, the magnetic helicity, and the cross helicity. The invariants remain temporally constant in the face of a truncation at a large but finite number of coefficients. Boundary conditions imposed are those for a rigid, perfectly-conducting cylindrical boundary, with an arbitrary periodicity length parallel to the axis. Canonical distributions are constructed from the invariants. Mean-square turbulent velocity fields 〈v2〉 have finite values for virtually all initial conditions, including quiescient ones. The stability problem can be reformulated as a search for values of the integral invariants which will minimize 〈v2〉. This leads to a principle of extremal helicity, which requires a magnetic configuration which will minimize 〈v2〉 for a given total energy. The development of helical macroscopic structures in the cylinder as a function of increasing ratio of axial current to axial magnetic flux is predicted.
Synchrotron-like radiation from intense laser beams in dense plasmas
Authors: Waltz R. E. , Manley O. P.
Published: March 2003

It is shown that when an intense, focused laser beam interacts with a dense plasma, relativistic effects may lead to observable synchrotron-like x-ray emission. For currently achievable Nd:glass laser intensities, the detectability of 10 keV x rays is expected to be enhanced by anisotropy of the source and by strong polarization.
Depolarization in laser probing of inhomogeneous magnetized plasmas
Authors: Lehmberg R. H. , Stamper J. A.
Published: March 2003

Density gradients and magnetic fields transverse to the propagation direction can produce polarization dependent phase shifts in a laser probing beam used for Faraday rotation studies of longitudinal magnetic fields in plasmas. The resulting depolarization should be considered when probing with fast optics near the critical density.
Stability of interchange modes in a hot electron plasma
Authors: Dominguez R. R. , Berk H. L.
Published: March 2003

A self-consistent electromagnetic theory is presented, for arbitrary β, of the flute-interchange mode of a hot-electron plasma where the hot-electron guiding-center drift frequency may be comparable to or larger than the ion-cyclotron frequency. In the presence of bad curvature, an interchange instability exists at small and large precessional frequency, and this instability is stabilized by cold electrons. Electromagnetic theory introduces finite-β corrections that only modify the results of a simple electrostatic theory that includes only the external drifts.
Enhancement of drift waves by localized lower hybrid waves
Authors: Wong K. L. , Bellan P. M.
Published: March 2003

The enhancement of low frequency oscillations by lower hybrid waves at electric fields lower than the thresholds of other parametric decay processes is presented. The frequencies and wavelengths of these oscillations agree with the collisional drift wave dispersion relation. The enhancement is localized deep inside the plasma density gradient. The excited drift waves change the density profile and the lower hybrid wave trajectory.
Mode mixing of large scale fluctuations in JFT-2 tokamak
Authors: Odajima K. , Wakatani M. , Maeno M. , Fujisawa N.
Published: March 2003

Low frequency fluctuations in the JFT-2 tokamak are investigated. The fluctuations propagate in the direction of the electron diamagnetic drift velocity and have a toroidal mode number n=1. Density fluctuations reveal that the m=2 mode is dominant; on the other hand, magnetic field fluctuations show a poloidal mode number m=3. The apparent discrepancy is explained by a sum of m=2, m=3, and/or m=4 modes. Theoretical analysis based on the magnetohydrodynamic theory of kink and tearing modes agrees well with experimental observations.
Temperature-jump problem with arbitrary accommodation
Authors: Loyalka S. K. , Siewert C. E. , Thomas J. R.
Published: March 2003

A concise and accurate result for the temperature-jump coefficient based on the linearized BGK model and arbitrary accommodation is reported. The jump coefficient is expressed as a power series in (1-α), and values of the expansion coefficients are given.
Effect of Hall currents on the hydromagnetic flow in an annular channel with a radial magnetic field
Authors: Sastry V. U. K. , Bhadram C. V. V.
Published: March 2003

The influence of Hall currents on hydromagnetic Poiseuille flow in an annular channel is discussed using the Runge–Kutta–Merson method. The axial flow is found to be enhanced by Hall currents and the particles swirl around the inner cylinder.
Ramsauer–Townsend effect and the electrical conductivity of a partially ionized gas
Authors: Chen Robert L. W. , Hobbs Edward R.
Published: March 2003

Calculations of the electrical conductivity of a partially ionized gas with assumed model functions representing electron-neutral particle collision cross sections have been extended to new models characterizing the Ramsauer minima. Consistent patterns are noted in the present and earlier results.
A re-analysis of exponential rigid-rotor astron equilibria
Authors: Lovelace R. V. , Larrabee D. A. , Fleischmann H. H.
Published: March 2003

Previous studies of exponential rigid-rotor astron equilibria include particles which are not trapped in the self-field of the configuration. The modification of these studies required to exclude untrapped particles is derived.
Radial ion energy measurements in a fast theta pinch
Authors: Chiang T. T. , DeSilva A. W.
Published: March 2003

An electrostatic retarding field energy analyzer is used to study the ion heating and thermalization of the radial ion energy in the Maryland fast theta pinch. From the time of arrival and the angle dependence of the ion peaks, those ions reflected from the piston front with twice the piston velocity and those ions carried along with the piston can be distinguished. The space- and time-resolved data are further supported by neutron measurements and hybrid code results. A number of micro-instabilities are proposed to explain the ion heating and thermalization.
Computer simulation studies of strong proton rings
Authors: Marsh S. J. , Drobot A. T. , Golden J. , Kapetanakos C. A.
Published: March 2003

Results are reported from a numerical simulation study on the propagation of a rotating proton pulse and the formation and trapping of the resulting strong proton ring. It is observed that the self-magnetic field has a very pronounced effect on the dynamics of such systems. In addition, it is observed that rings trapped in a magnetic mirror field are r, z stable for the entire confinement time tested of 550 nsec and suffer neither axial nor radial particle losses.
Lognormality of gradients of advected scalars
Authors: Hill R. J. , Bowhill S. A.
Published: March 2003

The gradient of an advected scalar in turbulent flow is treated in a coordinate system moving with a fluid particle. This Lagrangian coordinate system is chosen to be rotating such that the gradient vector lies along the 1-axis at all times; the final results are independent of this particular coordinate system. In the absence of diffusion, the magnitude of the gradient at the position of the fluid particle is shown to be a lognormal random process. The action of diffusion is to reduce the probability density for the largest values of the gradient.
Analytical approximations in the theory of turbulent diffusion
Authors: Weinstock J.
Published: March 2003

It is pointed out that numerical and simulational calculations of the Lagrangian decay time τL are easily explained by straightforward analytical approximations. This result demonstrates the usefulness of these approximations for problems of turbulent transport. A calculation is then made of the turbulent diffusion coefficient D in terms of an arbitrary energy spectrum, for homogeneous isotropic turbulence. This relation is compared with previous results.
Resonant damping of ion acoustic waves in a corrugated plasma
Authors: Schott L.
Published: March 2003

Using the two-fluid model it is shown that ion acoustic waves are damped in a plasma whose density is stationary in time but modulated periodically in space. The damping is strongest for modes with wavenumbers one half of the wavenumber of the density modulation. The maximum damping constant measured in ion wavenumbers is equal to one half of the relative amplitude of the density modulation.
Runaway electrons in collective electric fields
Authors: Hui B. H. , Winsor N.
Published: March 2003

The interactions of runaway electrons with the anomalous-Doppler-shifted mode and a bump-on-tail mode are studied numerically using the Fokker–Planck equation with a self-consistent quasi-linear diffusion operator. It is shown that a velocity threshold exists, below which electrons are not pitch-angle scattered by the self-consistent electric fields. The observed long-time behavior of synchrotron radiation data implies that this velocity threshold must shift to higher velocity as an experiment progresses.
Anomalous heating by ion sound turbulence
Authors: Dum C. T.
Published: March 2003

The kinetic equation for electrons including Coulomb collisions and scattering by ion sound and related spectra is reduced to a system of equations for the energy distribution and the anisotropic part. The energy distribution is obtained for the cases where Coulomb collisions, runaway or turbulent heating dominates. Resistivity, heating rate, and the dispersion relation are significantly modified for the self-consistent non-Maxwellian distribution. Applications to turbulent heating by ion sound are made.
Anomalous electron transport equations for ion sound and related turbulent spectra
Authors: Dum C. T.
Published: March 2003

A complete set of anomalous electron transport equations is derived for ion sound and related spectra. Turbulence causes a drastic modification of magnitude and structure of the transport effects. The self-consistent distribution function is also used to determine wave growth. The important role of the new contributions to wave growth, resistivity, and heat conduction in experiments as well as their description by codes are discussed.
Ion acoustic turbulence in a large-volume plasma
Authors: Kawai Y. , Hollenstein Ch. , Guyot M.
Published: March 2003

Ion acoustic turbulence excited by the current-driven ion acoustic instability in a large-volume plasma is studied experimentally. As the electron drift velocity increases, the fluctuation level of the waves increases and at the same time the peak of the turbulence spectrum shifts to a lower frequency. The resulting power spectrum agrees with that predicted by Horton. The effective collision frequency ν of the plasma is measured as a function of the electron drift velocity vd in the presence of the ion acoustic turbulence. For an electron drift velocity below 0.05 ve the effective collision frequency ν/ωpe varies such that vd/ve remains approximately constant and for the drift velocity above 0.09 ve the effective collision frequency is observed to be proportional to vd/ve. It is found that these results can be explained by using the theoretical model of Horton, in which the induced ion-wave scattering dominates the turbulence spectrum and the turbulent collision frequency limits the spectrum at small kλD.
Influence of magnetic shear on the lower-hybrid-drift instability in toroidal reversed-field pinches
Authors: Davidson R. C. , Gladd N. T. , Goren Y.
Published: March 2003

The influence of magnetic shear on the lower-hybrid-drift instability is investigated, including application to microstability properties of post-implosion reversed-field-pinch profiles. Two complementary analyses are performed. One analysis includes the influence of magnetic shear and finite ion beta in a fully electromagnetic model that assumes Te/Ti≪1, but otherwise incorporates the effects of transverse magnetic perturbations (δB≠0). The other analysis includes the influence of magnetic shear and finite Te/Ti in an electrostatic model that neglects finite plasma beta effects. In both cases, it is found that sufficiently strong magnetic shear can completely stabilize the lower-hybrid-drift instability. The theoretical model is used to investigate the microstability properties of post-implosion reversed-field-pinch profiles. It is shown that the lower-hybrid-drift instability persists in regions of moderate magnetic shear only if the local density gradient is sufficiently large. Moreover, for the diffuse profiles anticipated in the Los Alamos ZT-40 experiment, the lower-hybrid-drift instability is completely stabilized.
Variational theory of drift and tearing eigenmodes in slab geometry
Authors: Hazeltine R. D. , Ross David W.
Published: March 2003

A variational formulation of the radial eigenmode equations describing kink-tearing modes, drift-tearing modes, and drift modes, in slab geometry, is derived. The formalism is shown to provide accurate dispersion relations for a wide range of problems, with fewer approxmimations and less analytical effort than conventional methods require. Furthermore, derivation from a unified framework illuminates the relationships between different instabilities. The variational method is particularly well suited to the approximate solution of physically realistic problems, heretofore considered tractable only by numerical methods.
Measurement of vibrational population distributions in a supersonic expansion of carbon monoxide
Authors: Bender D. J. , Mitchner M. , Kruger C. H.
Published: March 2003

The results of an investigation of the vibrational kinetics of carbon monoxide in a supersonic expansion are presented. In the experiments, arc-heated argon was seeded with CO (5–20%) and expanded to Mach numbers of 4.0 to 4.2. The vibrational state of the gas was determined by obtaining individual vibrational populations from the CO overtone emission spectra. The vibrational distribution at the nozzle exit was observed to be non-Boltzmann, in good quantitative agreement with the anharmonic model of vibrational relaxation.
Accuracy of structure functions of temperature in turbulent shear flows
Authors: Antonia R. A. , Van Atta C. W.
Published: March 2003

An estimate is made of the accuracy in computing second-, third-, and fourth-order time structure functions of temperature fluctuations on the axis of a slightly heated turbulent round jet. The estimate is based on a knowledge of higher-order moments of the structure functions and of their integral time scales. For the particular data chosen, the root mean square error in computing second-and fourth-order moments is found to be small and effectively constant over a wide range of the temporal (or spatial) separation, which spans the inertial subrange. Comparison is made with some convergence trends observed in atmospheric boundary layer measurements.
Effects of the initial condition on the axisymmetric free shear layer: Effects of the initial momentum thickness
Authors: Hussain A. K. M. F. , Zedan M. F.
Published: March 2003

Spurred by large discrepancies among previous data on the free shear layer, effects of the initial condition on the characteristic measures of an axisymmetric air free shear layer were investigated experimentally. The initial, boundary layer state (i.e., laminar or turbulent), momentum thickness Reynolds number Rϑe, and fluctuation intensity u″pe/Ue have been taken as three characteristic identifiers of the initial condition. The discrepancies among published data are reviewed, and data showing the effects of variations in Rϑe (at constant u″pe/Ue) for both initially laminar and tripped (turbulent) boundary layers are reported. It is found that the spread rate, similarity parameter, and peak turbulent intensity in the self-preserving region are essentially independent of Rϑe, but dependent on whether the initial boundary layer is laminar or tripped (turbulent). Initially, tripped shear layers manifest two stages of linear growth. The virtual origin as well as the distance required for attainment of self-preservation depend noticeably and systematically on Rϑe. The mean velocity and turbulence intensity profiles appear to reach self-similarity together when the initial boundary layer is laminar, but not when the initial boundary layer is turbulent.
Turbulent flow over a periodic rough surface
Authors: Mulhearn P. J.
Published: March 2003

In a deep, turbulent flow with negligible advection, flowing over a surface roughened by regularly spaced, two-dimensional roughness elements, measured Reynolds shear stress decreased as the surface was approached. The depth of the region of shear-stress deficit was of the order of ten element spacings. Streamwise variations in mean velocities were unable to account for the magnitude of the shear-stress deficit, and the log-law estimate of surface shear disagreed with that measured directly by a drag balance. The data are presented as further information on a puzzling phenomenon.
Classical diffusion in large-aspect toroidal plasmas
Authors: Pao Young-ping
Published: March 2003

Time-dependent classical diffusion in large-aspect toroidal plasmas with a circular section is studied for both low-β and high-β cases. In the low-β case, both the fast and slow phases are examined and the difference between the slow phase and the quasi-stationary theory is discussed.
Nonlinear heat and particle transport due to collisional drift waves
Authors: Nishi-Kawa K. I. , Hatori T. , Terashima Y.
Published: March 2003

A nonlinear analysis of collisional drift instability is developed in a slab model based on the two fluid equations, where inhomogeneities in electron and ion temperatures and unperturbed current are included in addition to ion inertia, finite ion gyroradius, and viscosity. A systematic expansion is introduced by taking ε=‖κ‖l as a smallness parameter, where κ is the degree of density gradient and l is the linear scale of the slab along the density gradient. The nonlinear development of the drift wave near marginal stability is studied on the basis of the model equations. A new feature, hard excitation, has been found, which is due to the effects of the nonlinear frequency shift and the electron temperature gradient. The saturation amplitude is calculated, and the expressions for wave-associated particle and heat fluxes are obtained. A comparison of the expressions with the experimental results of a stellerator device is also made.
Finite Larmor radius equations in an arbitrary near-theta pinch geometry
Authors: Pearlstein L. D. , Freidberg J. P.
Published: March 2003

A set of fluid-like equations is derived which describes the stability of a diffuse, high β, arbitrary, near-ϑ pinch configuration. The equations simultaneously include geometric effects which drive ideal magnetohydrodynamic instabilities and kinetic effects which give rise to finite Larmor radius stabilization. A simple heuristic procedure is given for determining these equations in addition to a full derivation starting from basic principles.
Reversed-field configuration generated by a rotating relativistic electron beam
Authors: Sethian J. D. , Hammer D. A. , Gerber K. A. , Spector D. N. , Robson A. E. , Goldenbaum G. C.
Published: March 2003

A reversed-field plasma confinement geometry has been produced by plasma currents induced by a rotating relativistic electron beam injected into 85 mTorr neutral hydrogen. The resulting belt-pinch-like configuration has a rectangular cross section, with length-to-width ratio of 20, and midplane β=0.5. An equilibrium model, fitted to measurements of the excluded flux and induced axial (ΔBz) and azimuthal (Bϑ) magnetic fields, is in agreement with the annular plasma observed with radial Thomson scattering scans, CO2 interferometry, and end-on streak photographs. After beam passage, ΔBz remains constant for 5 μsec until Bϑ becomes small, at which time the plasma collapses radially. The observed decay times of 4 μsec and concurrent increase in Te (from 5 to 10 eV) are consistent with classical dissipation of the induced currents.
Digital bispectral analysis of self-excited fluctuation spectra
Authors: Kim Y. C. , Powers E. J.
Published: March 2003

Digitally implemented bispectral analysis is used to distinguish between spontaneously excited modes and coupled modes in a self-excited fluctuation spectrum by measuring the degree of phase coherence between the interacting waves.
Finite amplitude solitary Alfvén waves
Authors: Yu M. Y. , Shukla P. K.
Published: March 2003

Exact solitary Alfvén waves are considered taking into account small, but finite β effects. The solitary waves consist of density humps whose amplitude has an upper limit.
Self-consistent potential for a relativistic magnetized electron beam through a metallic boundary
Authors: Tajima T. , Mako F.
Published: March 2003

A self-consistent, steady-state potential for a relativistic electron beam entering a grounded metallic box in an infinite magnetic field is obtained. Application to collective ion acceleration is discussed.
Experiment on resonant wave-particle interaction at the ion gyroharmonic frequencies
Authors: Schmitt J. P. M.
Published: March 2003

Fast ions are generated when a plasma is irradiated by an electromagnetic wave at an ion cyclotron harmonic frequency. Separate resonances are observed for the potassium isotopes up to the 13th harmonic. At high power levels, resonant interaction is also observed at the half-integer harmonics.
Measurements of hose instability of a relativistic electron beam
Authors: Lauer E. J. , Briggs R. J. , Fessenden T. J. , Hester R. E. , Lee Edward P.
Published: March 2003

The observed disruption of a self-focused, relativistic electron beam propagating through a gas is shown to result from the growth of m=1 (’’kink’’ or ’’hose’’) perturbations. Measurements of the frequency dependence of the spatial amplification rate are presented. An upper cutoff to the frequency range for hose amplification is observed, in agreement with a theoretical model that includes the damping effects of a spread in the particle betatron frequency.
Computer simulation of the sideband instability
Authors: Shoucri Magdi M.
Published: March 2003

The physical origins of the growth of sidebands of a large amplitude plasma wave are studied numerically. It is shown that in the first phase of the nonlinear evolution of a large amplitude plasma wave the spatially averaged distribution function shows the formation of a stable bump and, for the case presented, the phase velocity of the lower sideband falls on the side of the bump having a positive slope. In the second phase of the evolution of the system, the sidebands saturate and the bumpy region of the spatially averaged distribution function takes a shape close to a flat plateau.
Quasi-linear stabilization of lower-hybrid-drift instability
Authors: Davidson R. C.
Published: March 2003

The quasi-linear evolution of the lower-hybrid-drift instability is investigated for cross-field current velocities less than the ion thermal velocity (Vd<vi). It is shown that current relaxation (Vd→0) and plateau formation (∂Fi/∂vy→0) in the ion velocity distribution are generally competing processes for stabilization. A detailed analysis of the energetics of the system is utilized to estimate the saturation level ℰs=ℱdkyℰky (t→∞) of the turbulent field fuctuations.
Astron stability against poloidal perturbations
Authors: Lovelace R. V.
Published: March 2003

An energy principle and stability requirements are derived for low-frequency poloidal perturbations of an astron ion ring embedded in a dense, low-temperature plasma. The particle ring equilibrium has a general distribution function f (H, Pϑ), with H the Hamiltonian and Pϑ the canonical momentum in the toroidal direction. The axisymmetric perturbations are treated rigorously using the Vlasov equation for the ring and the equations of ideal magnetohydrodynamics for the plasma. An explicit integration of the Vlasov equation is obtained for conditions where the particle motion is ergodic in the poloidal plane. For finite axial-length rings, a new term in the perturbation energy is found to arise from the betatron effect of the toroidal electric field perturbation. This has an explicitly stabilizing effect if (∂/∂H) f⩽0. The stabilizing effect of this term is required for, but does not guarantee, the existence of stable equilibria with conducting walls removed to large distances.
Effect of sources upon collisional transport in tokamaks
Authors: Stacey W. M.
Published: March 2003

Expressions for radial particle and heat fluxes are derived from a fluid formulation in which particle and heat sources are included. The derivation is carried out for a two-species collisional plasma in which the transport is dominated by ion-impurity collisions. The momentum transfer due to the introduction of the source and the alteration of poloidal particle and heat flows due to poloidal asymmetries in the sources are found to contribute to the particle and heat fluxes and thus to provide a potential mechanism for impurity control.
Calculations of the effects of incomplete preionization in high voltage theta pinches
Authors: Sgro A. G.
Published: March 2003

The hybrid model presented previously has been extended to include the effects of incomplete pre-ionization by the addition of a multistep ionization process. The difference between a fully pre-ionized and a weakly pre-ionized implosion is illustrated, and the predictions of the model are compared with data from high voltage ϑ-pinch experiments by illustrating the degree to which the computed density and magnetic field profiles agree with experiment. Due to incomplete pre-ionization, all the plasma at a point is not accelerated simultaneously by the sheath, so that the radial density profiles are broader and the peak densities are lower than in the corresponding fully pre-ionized implosion. A differential rotation of the imploding plasma column is shown to affect the implosion dynamics and radial density distribution. It is demonstrated that the withdrawal of flux from the tube during a staged theta pinch experiment may result in plasma hitting the wall and traumatizing it.
Evolution of multiple electron beams in a toroidal anomalous resistivity experiment
Authors: Richardson R. , Gentle K. W. , Leifeste G. T.
Published: March 2003

Hydrogen plasmas (n∼2×1010 cm−3) in a toroidal magnetic field are subjected to parallel dc electric fields much greater than the runaway value. Detailed measurements of the electron velocity distributions reveal the simultaneous presence of multiple electron beams. The beams are presumably generated by intense localizations of the applied voltage.
Plasma heating by Alfvén wave excitation in the Proto-Cleo stellarator
Authors: Golovato S. N. , Shohet J. L.
Published: March 2003

Alfvén wave heating experiments have been done in the Proto-Cleo l=3, seven field period stellarator. The Alfvén waves were excited by a helical wave launcher which surrounds the entire torus. Doubling of both the electron and ion temperatures was observed with electrons and ions heated independently by the wave. The effectiveness of the heating changes, as predicted by theory, when experimental parameters were varied. Evidence of the existence of Alfvén wave resonant surfaces in the plasma were also observed. Some enhanced plasma loss occurred when Alfvén wave heating was applied to the plasma. Several possible mechanisms for this enhanced loss were studied but no clear explanation was found.
Proper use of quantum mechanics in plasma turbulence
Authors: Elsässer Klaus
Published: March 2003

The classical limit of the quantum mechanical Vlasov equation is a canonical Vlasov equation which is generally different from the usual one. Therefore, one has to discriminate between the velocity operator v0= (p−esA0/c)/ms appearing in the vertex for transverse interactions and the true velocity operator v= (p−esA/c)/ms. It is shown that erroneous results for the dielectric tensor as obtained by Harris are explained by this fact.
A space-time approach to the Vlasov–Poisson equations
Authors: Manley O. P.
Published: March 2003

A nonlinear Klein–Gordon equation equivalent to the Vlasov–Poisson equations is derived. It places in evidence the explicit nature of the nonlinearities inherent in the simplest nontrivial plasma model, viz., the one-dimensional electron gas.
Diffusion of action in some nonlinear wave fields
Authors: West Bruce J.
Published: March 2003

The transfer of action among the modes in certain nonlinear random wave fields is described by a cubic Boltzmann equation. For two space scales, this equation reduces to a diffusion equation for action in k space.
Boundary-value problems in stratified shear flows with a nonlinear critical layer
Authors: Margolis Stephen B. , Su C. H.
Published: March 2003

Approximate solutions of nonlinear boundary-value problems arising in inviscid stratified shear fluid flows over relatively small obstacles are considered. The presence of a critical layer in the flow field leads to a failure of the linear theory, necessitating the derivation of a nonlinear critical layer equation. The solution of this second-order differential equation for the horizontal velocity is found to be discontinuous along the streamline which passes through the upstream critical point. In the analysis, three constants of motion along a streamline are used to study flows involving slip and split streamlines emanating from this point. The matching of the critical layer (inner) and the linearized outer solutions is discussed and some examples of steady flows over an obstacle and waves propagating with constant speed are given.
Origin of oscillatory convection in a porous medium heated from below
Authors: Horne R. N. , O’Sullivan M. J.
Published: March 2003

In order to investigate the significance of cyclic interaction in the evolution of fluctuating convective flow in a rectangular cell of porous material, the behavior of confined and unconfined flows are compared. In the latter case the constant pressure boundary condition at the top surface does not force the fluid to recirculate around the cell. However, regular oscillatory flow similar to that which occurs in an enclosed cell is still observed. This indicates that the oscillatory flow arises from the instability of the thermal boundary layer on the heated bottom surface. In both cases the frequency of the oscillatory flow is proportional to the Rayleigh number to the power of 3/2.
Wave fronts of nonlinear waves in a vibrationally relaxing gas
Authors: Ishii Ryuji
Published: March 2003

Propagation of nonlinear waves in a vibrationally relaxing gas is considered. The nonlinear behavior of wave fronts, the characteristic front and the shock front, are investigated in detail. The flows are thought of as being produced in a semi-infinite cylindrical pipe terminated by a piston, when the piston begins to move with a small velocity compared with the frozen speed of sound. The gas is initially at rest, but some nonuniformities are introduced into the initial state of the gas along the axis of the cylinder.
Neoclassical current in a toroidally-confined multispecies plasma
Authors: Hirshman Steven P.
Published: March 2003

The parallel currents in a toroidally-confined plasma is shown to consist of the current in response to the parallel electric field, the Pfirsch–Schlüter current which is required by charge neutrality, and the bootstrap current which flows to maintain a balance between the viscous and friction forces along the magnetic field. The steady state momentum equation is used to obtain an Ohm’s law relating the neoclassical current to the cross-field fluxes of particles and heat in a multiple ion species plasma. It is found that the presence of impurities does not alter the magnitude of the bootstrap current. Thus, the neoclassical beta limit established by the bootstrap current is insensitive to the impurity content of the plasma. The magnitudes of the bootstrap current and conjugate Ware fluxes are calculated in the transition from the long mean-free-path to collisional regime.
Scattering of drift waves by parametric interaction
Authors: Satya Y. , Schmidt G.
Published: March 2003

It is shown that the interaction of collisionless drift waves propagating in different directions can effectively exchange energy via interaction of a quasi-mode. The process is nonlinear electron Landau damping, and may explain the near isotropic distribution of drift waves in tokamak experiments.
Spectral formulation of the dissipative trapped-electron instability
Authors: Denavit J. , Rathmann C. E.
Published: March 2003

An analysis and computer simulations of dissipative trapped electron modes in toroidal plasmas based on the electron drift-kinetic equation Fourier transformed with respect to the poloidal and toroidal angles are presented.
Interchange instabilities in a compressible plasma
Authors: Pritchett P. L. , Wu C. C. , Dawson J. M.
Published: March 2003

The interchange instability induced by gravity in a compressible plasma is investigated by numerical methods based on the equations of ideal magnetohydrodynamics. Eulerian computer codes have been developed to integrate in time both the linear and nonlinear forms of these equations. In the linear case the results are compared with a generalization of a normal mode analysis performed by Newcomb. Predictions regarding the growth rate and spatial distribution of these modes and their stabilization by sheared magnetic fields are confirmed in the computer runs. In the nonlinear case inclusion of diffusion and damping terms in the numerical code permits the unstable mode to be followed to a final stable state. The numerical results indicate that for a sheared magnetic field there is a displaced equilibrium state involving a strongly distorted plasma distribution.
Current-driven instabilities and resultant anomalous effects in isothermal, inhomogeneous plasmas
Authors: Yamada M. , Hendel H. W.
Published: March 2003

The evolution and effects of current-driven instabilities in isothermal, inhomogeneous plasmas are investigated in both theory and experiment. Sucessive destabilizations of four different instabilities, low-frequency drift wave, ion-cyclotron drift wave, high-frequency (continuous-spectrum ion-cyclotron) drift wave, and high-frequency electron wave, are observed in Q-device plasmas with increased current, and explained by a theory based on fluid and kinetic equations. Anomalous effects resulting from wave-particle interactions, i.e., enhanced resistivity, ion heating, and electron viscosity, are compared with predictions based on quasi-linear calculations. Analogous to ion sound causing important anomalies in the transport coefficients for plasmas with Te/Ti≫1, high-frequency, continuous-spectrum drift waves determine anomalous plasma behavior in inhomogeneous plasmas with Te/Ti≃1.
Force balance and density criteria for double sheaths in plasma
Authors: Bergeron Kenneth D. , Wright Thomas P.
Published: March 2003

Two aspects of double sheaths (nonneutral regions) in plasmas are studied via analytic models. First, the motion of the structure through the plasma is analyzed by considering the force balance among the various species. A general proof is presented which shows the net acceleration of the sheath is zero in the absence of dissipative processes. A specific example is given which shows that a pressure difference between the two sides of the sheath results in the enhancement of the beam current into the low pressure side rather than acceleration of the sheath. The effect of beam-plasma interactions is also discussed. The second part of the analysis is the derivation of separate (though nearly identical) density criteria for sheath nucleation and sheath maintenance in equilibrium. These are compared with experimental results of Lutsenko, Sereda, and Kontsevoi and reasonable agreement is obtained.
Stochastic ion heating by a lower hybrid wave
Authors: Karney C. F. F.
Published: March 2003

The motion of an ion in a lower hybrid wave in a tokamak type plasma is studied. For ions with ν⊥≳ω/k⊥ the motion is stochastic for fields satisfying E/B0≳ (1/4)(Ωi/ω)1/3(ω/k⊥). Provided that the perpendicular phase velocity, ω/k⊥, can be slowed down to a few times the ion thermal speed, this stochastic ion motion may be an important mechanism by which injected rf power near the lower hybrid frequency can directly heat the ions.