bluuebunny/crossref_metadata_2025 huggingface dataset:
Reply to ‘‘Comment on ‘Peeling of convection cells and the generation of sheared flow’ [Phys. Fluids B 4, 488 (1992)]’’
Authors: Drake J. F. , Finn J. M. , Guzdar P. N. , Shapiro V. , Shevchenko V. , Waelbroeck F. , Hassam A. B. , Liu C. S. , Sagdeev R.
Published: July 2002

The comments of Montgomery and Matthaeus on the authors’ paper1, have been answered. The results do not contradict those of Montgomery and Matthaeus but for simple case considered, transition to shear flow state and shape of initial vortices is explained. (AIP)
Three-dimensional toroidal magnetohydrodynamics equilibria with ‘‘canal’’ surface currents
Authors: Kaiser R. , Tasso H.
Published: July 2002

Three-dimensional magnetohydrodynamics equilibria with surface currents on a toroidal ‘‘canal’’ surface are constructed. Inside the surface the pressure is constant and the magnetic field vanishes. The vacuum magnetic field lines on the surface are closed in the poloidal section which corresponds to infinite rotational transform.
Quasi-three-dimensional electron holes in magnetized plasmas
Authors: Jovanović D. , Horton W.
Published: July 2002

Using the electron drift-kinetic equation and a hydrodynamic description for the ions new nonlinear vortex equations are derived taking into account the parallel trapping of the electrons in the positive potential regions. It is shown that the usual integration procedure for finding the coherent vortex structures for the E×B flows in the fluid description can be generalized to include the parallel acceleration eE∥∂f/∂v∥ producing the electron holes in the phase space. An example is considered in some detail.
Fast wave flow drive in a two-component plasma with low minority ion concentration
Authors: Gang F. Y.
Published: July 2002

Fast wave flow drive in a two-component plasma with low minority ion concentration is investigated. It is found that strongly sheared poloidal flow can be generated in a small region near the hybrid ion–ion resonance due the rapid spatial variation of the plasma velocity response to the fast wave electric field. The flow drive depends strongly on local plasma temperatures and is shown to be very effective in the edge region of a tokamak where the plasma temperature is low. The result is applied to a discussion of shear flow suppression of edge turbulence.
Numerical simulation of bootstrap current
Authors: Wu Yanlin , White R. B.
Published: July 2002

The neoclassical theory of bootstrap current in toroidal systems is calculated in magnetic flux coordinates and confirmed by numerical simulation. The effects of magnetic ripple, loop voltage, and magnetic and electrostatic perturbations on bootstrap current for the cases of zero and finite plasma pressure are studied. The numerical results are in reasonable agreement with analytical estimates.
Collective transport of alpha particles due to Alfvén wave instability
Authors: Breizman B. N. , Berk H. L. , Ye H.
Published: July 2002

Recently a new point of view has been developed for describing saturation of discrete modes excited by weak sources. The method applies to the evolution of energetic particles in the beam plasma instability as well as to the description of how alpha particles evolve when they destabilize Alfvén waves under reactor conditions. Over a wide range of parameters the system produces pulsations, where there are relatively brief bursts of wave energy separated by longer intervals of quiescence. There are two types of pulsations: benign and explosive. In the benign phase, valid when particle motion is not stochastic, the distribution function is close to that predicted by classical transport theory, and the instability saturates when the wave trapping frequency equals the expected linear growth rate. If the field amplitude in a burst reaches the level where orbit stochasticity occurs, the quasilinear diffusion causes rapid transfer of particle energy to wave energy and rapid flattening of the particle distribution function. The bursting phase is followed by a relatively long quiescent time interval, where the source provides the necessary free energy to regenerate the cycle. The critical issue is whether the instability develops to a high enough level to produce stochastic diffusion. In general, this question can be assessed by using mapping methods to obtain criteria of overlapping of orbit resonances. If overlap occurs, then the modes will saturate at a high level, which will result in significant anomalous transport effects. This picture is consistent with recent observations of energetic beam losses in tokamak experiments due to Alfvén mode excitation.
Production of superthermal electrons and ion cyclotron waves in a reversed-field-pinch plasma
Authors: Yoshida Z. , Hasegawa A. , Wakatani M.
Published: July 2002

Production of superthermal electrons through kinetic interactions with electromagnetic fluctuations is studied to account for observations of fast electrons and ion cyclotron waves in reversed field pinch plasmas. Low-frequency Alfvénic (torsional) modes can interact with electrons through the Landau resonance when the wavelength perpendicular to the magnetic field is as small as the ion gyroradius. Such kinetic Alfvén waves induce simultaneous diffusion (double diffusion) in the coordinate and velocity spaces, and produce a field aligned superthermal electron beam in the edge region. Microinstabilities are driven by the electron-beam and ion cyclotron waves are excited. Through these precesses the fluctuation energy in the low-frequency regime may be transported to the ion cyclotron frequency regime.
Physics of the magnetotail current sheet
Authors: Chen James
Published: July 2002

The Earth's magnetotail plays an important role in the solar-wind–magnetosphere coupling. At the midplane of the magnetotail is a current sheet where the dominant magnetic field component reverses sign. The charged particle motion in and near the current sheet is collisionless and nonintegrable, exhibiting chaotic scattering. The current understanding of the dynamical properties of the charged particle motion is discussed. In particular, the relationships between particle dynamics and global attributes of the system are elucidated. Geometrical properties of the phase space determine important physical observables on both the micro- and macroscales.
Advances in gyrokinetic fluctuation theory: The gyrokinetic fluctuation–dissipation theorem and dielectric function*
Authors: Krommes John A.
Published: July 2002

Thermal-equilibrium fluctuation spectra of finite-β gyrokinetic (GK) plasmas are calculated by means of a GK fluctuation–dissipation theorem. Agreement is found with the earlier heuristic electrostatic calculations of Krommes et al. [Phys. Fluids 29, 2421 (1986)]. The formulas are interpreted in terms of the concept of a GK vacuum, whose large dielectric permittivity and magnetic permeability embody the shielding effects of the polarization drift and the parallel electric field. The finite-β quasimode action density 𝒩k is calculated. This is used to interpret the result of a formal resonance integration over the normal modes in terms of the equipartition law ωk𝒩k = T/2.
Temporally and spatially resolved optical emission and electron energy distribution function related to ionization waves
Authors: Ohe K. , Takeshima S. , Kimura T.
Published: July 2002

The variation of the electron energy distribution function (EEDF) to the radial direction is measured along the radially curved wave front of the ionization wave packets externally excited in a He positive column. The fluctuation of the high-energy tail caused by the wave is estimated from that of the radiation intensity.
Comment on ‘‘Quantum-molecular-dynamics simulations of liquid metals and highly degenerate plasmas’’ [Phys. Fluids B 4, 2044 (1992)]
Authors: Murphy R. D.
Published: July 2002

Comparisons of the accuracy of liquid sodium structure calculations are given. The accuracy required for calculations of thermodynamic properties and for meaningful validation of computational techniques is discussed.
Transport due to ion-temperature-gradient-driven magnetic drift modes
Authors: Heikkilä A. , Weiland J.
Published: July 2002

An advanced reactive fluid model is used to study the transport due to the toroidal ηi mode in the flat density limit. In this limit the density gradient scale length scales out from both the linear dispersion relation and the quasilinear transport coefficients. Simplified transport coefficients are derived for the flat density limit including also influence of electron trapping and are discussed in relation to the density modification experiments on the Tokamak Fusion Test Reactor (TFTR) [Proceedings of the 11th International Conference on Plasma Physics and Controlled Fusion Research (International Atomic Energy Agency, Vienna 1987), Vol. 1, p. 51]. The scaling properties with respect to various dimensionless parameters are discussed. In particular the scaling Xi ∼ ηi − ηith, which has also been derived by other authors for somewhat different situations, is found to be the relevant scaling in typical situations. A stabilizing and transport reducing effect of a high degree of electron trapping is pointed out.
Intense ion-beam-transport experiments using a z-discharge plasma channel
Authors: Neri J. M. , Ottinger P. F. , Rose D. V. , Goodrich P. J. , Hinshelwood D. D. , Mosher D. , Stephanakis S. J. , Young F. C.
Published: July 2002

A z-discharge plasma channel is used to confine and transport an intense proton beam. A pinch-reflex ion diode on the NRL Gamble II accelerator focuses a proton beam onto the entrance aperture of a 2.5 cm diam, 1.2 m long z-discharge transport system. The beam ions are charge and current neutralized in the discharge plasma, and execute betatronlike orbits in the magnetic field of the discharge. Ion beam diagnostics include shadowbox imaging and prompt-γ radiation measurements from LiF targets. Under appropriate conditions, 95% particle transport and 90% energy transport are observed, with the only energy loss attributed to classical stopping in the channel gas. The transverse phase-space distribution of the beam measured by the shadowbox is consistent with full charge and current neutralization of the transported beam.
Stability of drift-wave modons in the presence of temperature gradients
Authors: Jovanović D. , Horton W.
Published: July 2002

In the homogeneous Hasegawa–Mima equation, the dipole vortex or modon solution is well known to be robustly stable from both analytic and numerical studies. In the inhomogeneous plasma where ∇Te≠0 the corresponding vortex has an external structure extending into the high-temperature region. Lyapunov stability method is used to determine the stability properties of these extended vortex structures. The overall growth rate of deformation caused by the presence of temperature inhomogeneity is shown to be bounded by (R/LT)2, where R is the radius of the core of the vortex and LT is the scale length of the temperature gradient. The most important source of instability is identified as the excitation of monopolar and dipolar perturbations with short spatial scales ≲R, which are approximately independent of the presence of the density and temperature gradients.
Formation of the shear layer in toroidal edge plasma
Authors: McCarthy D. R. , Drake J. F. , Guzdar P. N. , Hassam A. B.
Published: July 2002

The equilibrium and stability of axisymmetric toroidal edge plasma in the presence of an anomalous ballooninglike transport is studied. The equilibrium density evolves so that the transport rate, D⊥/Ln2 equals the sound transit time, cs/πqR. As a result, confinement is coupled to the local sound velocity such that a reduced sound velocity (larger ion mass) leads to improved confinement. A result of the large asymmetric transport is the generation of nearly sonic parallel flows which allow the system to be unstable to the Stringer spin-up instability. For weak magnetic pumping, a large poloidal rotation of order the poloidal sound speed (acs/qR) is driven, forming a localized shear layer. The direction of rotation corresponds to a negative radial electric field in the closed flux region. For strong magnetic pumping the rotation is equal in magnitude and opposite in direction to the ion diamagnetic drift, the neoclassical result. Particle sources localized in poloidal angle can strongly impact the rotation. A source placed between the bottom and the outside of the torus enhances the rotation while the same source placed between the top and the inside retards the rotation. However, a large enough source at the latter location will drive the rotation in the other direction, reversing the sign of the electric field. The implications of the results for understanding Ohmic, L-mode, and H-mode discharges are discussed.
Kinetic approach to a pressure-gradient-driven tokamak resistive instability in the banana regime
Authors: Shaing K. C. , Callen J. D.
Published: July 2002

A new resistive, low-frequency (ω≪ωba ∼νa, where ω is the frequency of the mode and ωba and νa are the bounce frequency and collision frequency for species a) instability is found in a tokamak geometry. The mode is driven unstable by the parallel viscous (bootstrap) current induced by the radial pressure gradient. It has a growth rate γ∼(ω2*eνi)1/3 for νi≫ω*e, where ω*e is the electron diamagnetic drift frequency and νi is the ion–ion collision frequency. The frequency dependence of the parallel viscosity is also derived and utilized to show that drift wave branches of these modes are stable, but that this new mode remains unstable when the diamagnetic drift effects are included.
Investigation of finite beta modified drift wave in a tokamak plasma
Authors: Fredrickson E. D. , Bellan P. M.
Published: July 2002

The saturated state of a low-frequency, coherent, m=2, global mode has been studied in the Encore tokamak using probe techniques. The mode is found to have large fluctuations in density, electron temperature, space potential, and magnetic field. The experimental measurements were compared with the predictions of a computer code, based on a linear, two-fluid theory of the coupling of drift and shear-Alfvén modes. This comparison led to the identification of the mode as a finite beta modified drift wave.
Free-stream turbulence near a wall
Authors: Uberoi Mahinder S. , Detman Thomas R.
Published: July 2002

Turbulence is idealized as discrete vortex filaments. Velocities associated with vortex filaments and their images in the wall show that turbulent velocities normal to the wall decrease monotonically to zero and those parallel to the wall increase at the wall, in agreement with more elaborate theories of others. A bulge along the entire inside periphery of a wind tunnel is used to produce free-stream turbulence of a scale much larger than thickness of boundary layer at the wall. Our experiments and theory agree with other experiments where a moving wall was used to eliminate the wall boundary layer.
Observation of plasma waves from absolute stimulated Raman scattering
Authors: Villeneuve D. M. , Walsh C. J. , Baldis H. A.
Published: July 2002

Time-, frequency-, and wavenumber-resolved Thomson scattering techniques have been used to identify electron plasma waves driven at the quarter-critical surface by a CO2 laser in a preformed plasma. The clear signature of absolute stimulated Raman scattering was observed, namely ωp≊ω0/2 and kp≊k0. In addition, some plasma waves with larger wavenumber were seen, perhaps corresponding to coupling with ion waves produced by stimulated Brillouin scattering. The level of ω0/2 scattered light, calculated from the observed level of plasma waves, should have been several orders of magnitude above the detection threshold, yet no such emission was seen.
Analytic approach to the problem of nonlinear thermal conduction in laser-produced plasmas
Authors: Kaddour-Djebbar Habib , Moses Gregory A.
Published: July 2002

A nonlinear hyperbolic heat equation, established from Grad’s ‘‘13-moments’’ method [Commun. Pure Appl. Math. 2, 331 (1949)] is presented as an alternative to the classical heat diffusion equation for the treatment of thermal conduction in laser-produced plasmas. In the limiting case of a free streaming plasma, it is shown that this equation naturally generates the classical flux limiter, therefore absolving the recourse to empirical adjustments. The ensuing heat equation is a nonlinear wave equation with a front velocity determined by the thermal speed of electrons. When the collision term provides the dominant effect, the resulting equation is a nonlinear diffusion equation. Exact analytic solutions to these equations are obtained for an identical set of conditions and used to compare the speeds of thermal propagation and delimit the domain of applicability of the diffusion equation.
Amplitudes and wavelengths of wavy Taylor vortices
Authors: Bust G. S. , Dornblaser B. C. , Koschmieder E. L.
Published: July 2002

The wave height and wavelength of wavy Taylor vortices have been measured in a fluid column of aspect ratio 31 and radius ratio 0.88. The fluid was either water or 10 cS silicone oil. The wave height as well as the wavelength were found to increase with Reynolds number until 1.8Rc for a state with 15 pairs of vortices and four azimuthal waves. Subsequent changes in the wave height and azimuthal wavenumber seem to be primarily caused by changes in the number of vortices which are caused by the increase of the wavelength.
Flow of a rarefied gas past a circular cylinder
Authors: Yamamoto Kyoji , Sera Kazuyuki
Published: July 2002

The flow of a rarefied gas past a circular cylinder at low Mach numbers is studied on the basis of the linearized Bhatnager–Gross–Krook model equation. The flow field is divided into two regions: the kinetic region adjacent to the cylinder and the near continuum region outside it. The Oseen–Stokes equation is treated in the near continuum region. In the kinetic region, the simultaneous integral equations for the flow velocity, density, and temperature are derived from the model equation. These equations are solved numerically by matching with the Oseen–Stokes solution. The distributions of the flow velocity are obtained for a wide range of the Knudsen numbers. The drag on the cylinder is also calculated and is favorably compared with the previous formulas valid for small and large Knudsen numbers.
Numerical study of the initial condition dependence of Burgers’ turbulence
Authors: Mizushima Jiro , Saito Yoshio
Published: July 2002

The initial condition dependence of the statistical properties of Burgers’ turbulence is investigated by numerical simulations. As a result, the energy spectrum of the form ka in the lowest wavenumber range is shown not to change in time as long as the value of a is in the range [0,2]. It is also shown that the appearance of the k−2 spectrum and the time dependence of Taylor’s microscale are the universal properties of Burgers’ turbulence, and are independent of the initial conditions. On the other hand, the energy decay law and the time development of the skewness of the velocity derivative are dependent on the initial conditions. Especially, the energy decay law is shown to take the form, ℰ(t)∝t−p, where p has a value in the range [0.63–1.14] depending on the large-scale structure of the turbulence.
Boundary temperature effect in a highly rarefied gas
Authors: Sone Yoshio
Published: July 2002

A method of solution describing the steady behavior of a free molecular gas around a group of bodies at rest and with various temperature distributions is presented. For any closed system and a class of unbounded systems, the velocity distribution function is expressed by a series consisting of the boundary data (temperature and accommodation coefficient) on the past path of the specularly reflecting molecules.
Radial eigenmodes of the discrete Alfvén spectrum
Authors: Tsui K. H.
Published: July 2002

The eigenfrequencies and eigenmodes of the discrete Alfvén spectrum for a straight tokamak plasma with constant current density profile are solved analytically. The results offer a clear physical insight into the eigenfrequency scaling and mode asymmetry mentioned in earlier works using numerical calculations and a variational technique for a real plasma profile. It is also shown that the ion-cyclotron frequency broadens the spacing of the eigenfrequencies of the ideal magnetohydrodynamic spectrum.
Electron heating by waves in the ion-cyclotron frequency range
Authors: Fruchtman Amnon
Published: July 2002

The interaction between waves in the ion-cyclotron frequency range and a hot-electron ring is studied. The configuration is approximated by a slab geometry in which the hot-electron ring is a few Larmor radii thick, the confining magnetic field is uniform, and the hot-electron distribution function is anisotropic. The wave vector of the incident wave is nearly perpendicular to the magnetic field with a small parallel component, so that both parallel streaming and finite Larmor radius effects are present. It is shown that a significant part of the energy flux may be absorbed by the electrons in a single pass of the wave through the ring. This process may be responsible for the electron ring heating observed in the Elmo Bumpy Torus-S [Nucl. Fusion 23, 49 (1983)] recently. Numerical results of energy absorption and wave transmission are presented for a wide range of parameters. For two special cases, the Born approximation and finite Larmor radius expansions enable us to simplify the analysis. The energy absorption calculated under the approximations is compared with the more exact treatment.
Finger breakup in Hele–Shaw cells
Authors: DeGregoria A. J. , Schwartz L. W.
Published: July 2002

It is shown that a boundary integral simulation of fingering in Hele–Shaw cells generates patterns of finger breakup similar to those observed experimentally at low values of reciprocal capillary number τ. It is also shown that, when random noise is introduced in the interface position at a value of τ for which a stable finger would otherwise occur, similar patterns of finger breakup are generated. This supports the hypothesis that the observed behavior is caused by a nonlinear instability driven by experimental or numerical noise at very low values of τ.
A simultaneous concentration of a vortex and a magnetic field in magnetohydrodynamic flows
Authors: Kambe T.
Published: July 2002

A three-dimensional magnetodydrodynamic flow with a combined effect of convection and diffusion is reduced to a two-dimensional problem by a variable transformation. The original field is composed of a unidirectional vorticity and an aligned magnetic field superimposed on an axisymmetric straining flow in an incompressible, viscous, electrically conducting fluid. By restricting consideration to the axisymmetric vorticity and magnetic fields, an exact solution is presented, which shows time evolution from general initial profiles. In a particular case of constant straining, the solution simultaneously approaches the state of a concentrated cylindrical vortex and a magnetic tube of Gaussian profile sharing a common symmetry axis.
Comments on ‘‘Turbulent effects on the chemical reaction for a jet in a nonturbulent stream and for a plume in a grid-generated turbulence’’ [Phys. Fluids 2
7, 77 (1984)]
Authors: Bilger R. W. , Mudford N. R. , Atkinson J. D.
Published: July 2002

The interesting paper of Komori and Ueda1 raises questions of both a theoretical and experimental nature.
Reply to comments of Bekefi and Fajans
Authors: Gold S. H. , Black W. M. , Freund H. P. , Granatstein V. L. , Jackson R. H. , Efthimion P. C. , Kinkead A. K.
Published: July 2002

Both the free-electron laser (FEL) and cyclotron-maser (CM) instabilities can play a role in wave generation laser experiments employing both an axial guide magnetic field and a transverse wiggler magnetic field. The experimental distinction between these two mechanisms can only be made by comparing measured radiation characteristics with the predictions of either model. For a recent intense beam experiment [Phys. Fluids 26, 2683 (1983)], most of the data are in good agreement with the FEL mechanism, as previously concluded, rather than with the CM instability, and the data taken far from gyroresonance are of unambiguous FEL origin.
Dynamics of space-charge waves in the laser beat wave accelerator
Authors: Tang C. M. , Sprangle P. , Sudan R. N.
Published: July 2002

The excitation of plasma waves by two laser beams, whose frequency difference is approximately the plasma frequency, is analyzed. Our nonlinear analysis is fully relativistic in the axial and transverse directions and includes mismatching of the laser beat frequency to the plasma frequency, time dependent laser amplitudes, and an applied transverse magnetic field (surfatron configuration). Our analytical results for the large amplitude plasma waves include an axial constant of motion, accelerating electric field, and its phase velocity. The analytical results in the weak laser power limit are in good agreement with numerical results obtained from the complete equations. The imposed transverse magnetic field is found to increase the effective plasma frequency, but has little effect on the plasma dynamics.
Nonlinear resistive g mode and electron heat conductivity in torsatron/heliotron plasmas
Authors: Shaing K. C. , Carreras B. A.
Published: July 2002

An electron heat conduction coefficient χe induced by the nonlinear saturation of the resistive g mode in a stellarator is calculated. It agrees reasonably well with the anomalous χe values inferred from Heliotron-E [Nucl. Fusion 24, 305 (1984)] discharges.
Nonlinear lengthening of a triangular acoustic pulse
Authors: Temkin S. , Maxham D.
Published: July 2002

A theoretical and experimental study is reported of the lengthening and attenuation of triangular acoustic pulses of finite amplitude. The pulses studied in the laboratory are the leading portions of individual N waves, which are produced in a conical-driver shock tube. The facility has been used to produce N waves with nondimensional pressure jumps across the leading front in the range 0.02–0.17. The length of the leading portion of the wave was measured in terms of its transit time at two different locations. Pulse lengthenings were measured in the weak shock wave range and were found to be in agreement with the well-known theoretical predictions. On the other hand, our measurements of the pulse’s amplitude decay did not compare favorably with the same theory, mainly because of uncertainties associated with the flow field immediately behind the shock front. A new derivation of the theoretical predictions is also presented for lengthening and decay of a triangular pulse that is based on simple physical arguments.
Linear studies of resistive interchange modes in a cylindrical reversed field pinch
Authors: Mirin A. A. , O’Neill N. J. , Killeen J. , Bonugli R. J. , Ellis M. J.
Published: July 2002

Resistive interchange modes in a cylindrical reversed field pinch are studied using a one-dimensional, linear, compressible initial value code. Separate equations for the electron and ion temperature perturbations are solved. Hall terms and the thermal force vector are included in Ohm’s law. Anisotropic thermal conductivity and viscosity are included in the code model. Calculations are carried out for various values of poloidal and toroidal mode number, Lundquist number, Suydam parameter, Hall parameter, thermal conductivity, viscosity, etc., with respect to uniform density equilibria known to be stable to tearing modes. It is shown that in the cold ion limit sufficiently large Hall terms cause all modes that are tested to become stable. However for Ti=Te and ignoring the effects of viscosity and thermal conductivity, there is a critical value of the ratio of Alfvén to ion cyclotron frequency above which the ‘‘even’’ mode not only dominates the ‘‘odd’’ mode but is likely to have a growth rate significantly larger than that of the odd mode in the absence of Hall terms. Inclusion of a classical tensor thermal conductivity, while having little effect on the odd mode in the absence of Hall terms, does stabilize the even mode for sufficiently large Hall parameter. Inclusion of a classical tensor viscosity reduces the growth rate of (but does not necessarily stabilize) the odd mode. Inclusion of Hall and thermal force terms, tensor thermal conductivity and tensor viscosity causes all modes that are tested to stabilize. Results are compared to other contemporary studies.
Magnetized Fokker–Planck equation with quasilinear diffusion for nonaxially symmetric velocity distribution functions
Authors: Hassan Mohamed H. A.
Published: July 2002

The kinetic equation governing the evolution of a nonaxially symmetric velocity distribution function of plasma particles in a uniform magnetic field, including the effects of collisions as well as quasilinear diffusion, is presented and analyzed. It is shown that, if the test particles’ orbits are straight lines, the kinetic equation reduces to a standard Fokker–Planck form with friction, collisional diffusion, and quasilinear diffusion coefficients all expressible in terms of scalar potentials. These potentials are simple generalizations of Rosenbluth potentials and can easily be used in numerical solutions of the Fokker–Planck equation.
The effect of ensemble averaging on transverse vorticity measurements in forced shear flows
Authors: Disimile Peter J.
Published: July 2002

Quasi-instantaneous and ensemble averaged transverse vorticity time series were obtained in a weakly excited, single-stream mixing layer using a four-wire array. These data indicate that absolute values of instantaneous vorticity can be approximately an order of magnitude greater than the ensemble (or phase) averaged vorticity.
Resistive tearing modes in the presence of equilibrium flows
Authors: Bondeson A. , Persson M.
Published: July 2002

A combined numerical and analytical study is presented of the linear stability problem for resistive tearing modes in the presence of perpendicular and parallel equilibrium flows. Detailed information is given about growth rates and the shape of the marginal stability curve. In the case of purely perpendicular flows, a region in parameter space is found where the growth rate is complex, and the region of instability is larger than previously recognized. An exact analytic solution is found for parallel flows when the plasma response is dominated by viscous forces.
Alfvén resonance absorption and its role in radio-frequency stabilization
Authors: Byers J. A.
Published: July 2002

The occurrence of Alfvén resonance absorption, a linear wave process, in a thin layer within the density gradient of a magnetized plasma for ω<ωci and its absence for ω>ωci can produce significant changes in the wave spatial structure for small changes in wave frequency about ωci. This process, as modified by global mode resonances, is suggested to be a major contributing factor in the explanation of the sudden appearance in Phaedrus [Phys. Rev. Lett. 51, 1955 (1983)] of radio-frequency (rf ) stabilization of interchange modes, when changing ω from just below ωci to just above ωci.
Bifurcation of solutions of a field-reversed cylindrical model
Authors: Lara Luis , Fontán Constantino Ferro , Gratton Fausto T.
Published: July 2002

It is shown that the self-consistent solutions of Vlasov steady states for the double delta distribution model of cylindrical field-reversed configurations, generated by large ion orbits, have bifurcations within a definite interval of values for the total number of ions. The conjugate states have the same number of particles and the same radius of confinement but different azimuthal canonical momentum, orbit patterns, and magnetic fields. It is also shown that the states with a lower canonical momentum have a smaller energy content.
Flow over bodies with suction through porous strips
Authors: Nayfeh A. H. , Reed H. L. , Ragab S. A.
Published: July 2002

This article addresses the steady, incompressible flow past a two-dimensional or an axisymmetric body with suction through porous strips. Closed-form solutions for each flow quantity are developed in the context of linearized triple-deck theory using Fourier transforms. To demonstrate the validity of these closed-form solutions, we compare the wall shear stress and pressure coefficients and the streamwise velocity profiles from the linearized theory are compared with those obtained by the numerical integration of both interacting and conventional boundary-layer equations. The agreement between the linearized triple-deck and interacting boundary-layer equations for the suction configurations proposed for laminar flow control is good; however, the conventional boundary layers, which fail to account for upstream influence, are shown to be in poor agreement with both interacting boundary layers and the linearized triple deck. Combining these linearized closed-form solutions with a perturbation scheme has enabled development of a simple linear optimization scheme to determine the number, spacing, and mass flow rate through the strips on two-dimensional and axisymmetric bodies.
Dispersion of discrete particles by continuous turbulent motions: New results and discussions
Authors: Desjonqueres P. , Gouesbet G. , Berlemont A. , Picart A.
Published: July 2002

A number of results for the Tchen theory of dispersion of discrete particles by continuous turbulent motion are recalled. A Frenkiel family of Lagrangian correlation functions is used and the main results are rewritten in nondimensional form. The theory is completed by a new relation expressing the mean square of the relative particle velocity. The validity of the Stokes contribution to the Tchen equation of motion is examined. Numerical results are given and discussed.
Experimental study of equilibrium in a bumpy torus
Authors: Hiroe S. , Cobble J. A. , Colchin R. J. , Chen G. L. , Connor K. A. , Goyer J. R. , Solensten L.
Published: July 2002

Plasma equilibrium in the ELMO Bumpy Torus (EBT) [in Plasma Physics and Controlled Nuclear Fusion Research (IAEA, Tokyo, 1974), Vol. 2, p. 141; Plasma Phys. 25, 597 (1983)] was studied experimentally by measurements of the electrostatic potential structure. Before an electron tail population is formed, the electric field is found, roughly speaking, to be in the vertical direction. The appearance of a high-energy electron tail signals the formation of a negative potential well, and the potential contours start to nest. The potential contours are shifted inward with respect to the center of the conducting wall. The electric field between the plasma and the conducting wall forces the plasma inward, balancing the outward expansion force. This force balance provides a horizontal electric field that cancels the concentric radial electric field locally at the separatrix of the potential contour and leads to convective energy loss.
Collective CO2 laser scattering on moving discharge structures in the submillimeter range in a magnetohydrodynamic generator
Authors: de Haas J. C. M. , Schenkelaars H. J. W. , van de Mortel P. J. , Schram D. C. , Veefkind A.
Published: July 2002

Collective scattering of CO2 laser light on electrons is used to determine the radial scale length of the discharge structures occurring in a closed cycle magnetohydrodynamic generator. Hetero- dyne detection of scattered radiation is used to obtain a spatial resolution in the submillimeter range and to increase the signal to noise ratio. A discharge model is formulated to interpret the measured signals. The scale length of the electron density fluctuations is found to be (2.5±0.5) ×10−4 m.
Drift vortices in a rotating magnetoplasma
Authors: Shukla P. K. , Yu M. Y.
Published: July 2002

It is shown that solitary drift vortices can exist near the outer edge of a rotating magnetoplasma. The plasma rotation modifies the existence region of the usual drift vortices.
Comments on ‘‘A generalized BKW solution of the nonlinear Boltzmann equation with removal’’ [Phys. Fluids 2
7, 2599 (1984)]
Authors: Santos A. , Brey J. J.
Published: July 2002

It is shown that there is a direct relationship between the solutions of the Boltzmann equation for a homogeneous system of Maxwell molecules with and without particle removal.
Self-consistent structure of an ionization wave produced by microwave breakdown in atmospheric air
Authors: Anderson D. , Lisak M. , Lewin T.
Published: July 2002

A self-consistent analysis is given for the development of an air discharge produced by microwaves with powers above the breakdown threshold. The structure of the ionization wave is derived for planar geometry and for arbitrary initial conditions. The theoretical predictions are in excellent agreement with previous results obtained by numerical simulations.
Quasilinear theory of uniformly magnetized inhomogeneous plasmas: Electromagnetic fluctuations
Authors: Yasseen F. , Vaclavik J.
Published: July 2002

The equations of quasilinear theory are derived for a uniformly magnetized inhomogeneous plasma interacting with electromagnetic field fluctuations. The derivation avoids the use of the random phase approximation, and requires no assumption on the ratio of the Larmor radius to the fluctuation wavelength. These equations are used to obtain the transport equations for each plasma component. The latter satisfy the necessary conservation properties, and yield explicit expressions for various fluxes.
Navier–Stokes boundary conditions of a gas mixture
Authors: Lohöfer G.
Published: July 2002

The Navier–Stokes velocity and density boundary conditions of a multicomponent gas mixture in front of a wall are considered. The following gas–wall interactions are taken into account: partially inelastic interactions between the gas molecules and the wall (accommodation), conversion among the different molecule species (ionization, etc.), and gas flow through the wall. Since the influence of the kinetic boundary layer on the gas continuum is negligible, the moments in the boundary conditions for the Navier–Stokes equations are calculated with the first-order Chapman–Enskog solution (Maxwell’s method).
Dynamics of nonlinear drift waves in an inhomogeneous magnetic field
Authors: Shukla P. K.
Published: July 2002

Accounting for an inhomogeneous magnetic field and finite Larmor radius effects, a set of nonlinear mode coupling equations is derived for finite amplitude drift waves in plasmas. It is shown that the present nonlinear equations admit localized dipole vortices. Conditions for the existence of these vortices are given.
Parametric decay during lower hybrid heating on a tokamak
Authors: Lohr John , Ohkawa Tihiro
Published: July 2002

Injection of radio-frequency power at twice the lower hybrid frequency results in parametric decay of the pump wave into electrostatic ion-cyclotron modes. The location of the conversion point is inferred from the data.
Compatibility of Alfvén ion-cyclotron and magnetohydrodynamic stability criteria for an axisymmetric magnetic mirror
Authors: Smith Gary R. , Berk H. L. , LoDestro L. L.
Published: July 2002

The stability of an axisymmetric magnetic-mirror cell surrounded by a conducting wall is studied using the sharp-boundary model. Depending on the ion pressure model p(B), magnetohydrodynamic (MHD) stability can be achieved in certain ranges at either high or low β. Suppression of the Alfvén ion-cyclotron microinstability requires the mirror cell to be short (length≲20 ion Larmor radii). Adiabaticity of ion orbits is then found to be a constraint that is difficult to satisfy. Within the approximations used in this paper, satisfaction of all constraints is achieved in only a small region of parameter space.
The ablation of planar targets driven by suprathermal electrons
Authors: Gratton R. , Piriz A. R.
Published: July 2002

When an intense laser pulse of large wavelength impinges on a solid, the absorption region is pushed back by the evaporated plasma to a distance zcr from the surface, which may be of the order of or even larger than the beam radius rs. Therefore (in addition to the absorption processes, not treated here), the energy transport through the outflowing plasma plays a key role in the interaction. The correct way to interpret the experimental results seems to be to assign the transport mainly to the almost freely streaming suprathermal electrons coming from the absorption region. This is confirmed by a simple steady-state model which accounts for the two-dimensional effects arising when zcr≥rs. In spite of the over-simplifications needed to handle the problem analytically, the model provides scaling laws in fair agreement with the published experimental data.
Electrostatic electron surface modes on a plasma–vacuum interface of finite width
Authors: Jones Roger D.
Published: July 2002

The electron surface mode dispersion relation, including Landau damping, is obtained for a vacuum–plasma interface. Unlike previous work, the interface is permitted to have a finite width and no wall boundary conditions are assumed. When the density gradient scale length Ln is large compared with a Debye length k−1D and small compared with a surface mode wavelength 2πk−1, then the mode frequency is ω=(ωp/21/2) (1+kLn/6), and the Landau damping rate is γ =−[6/(2π)1/2]ωp/(kDLn). These expressions are much different than the comparable expressions for a wall-confined plasma.
On the shore singularity of water–wave theory. II. Small waves do not break on gentle beaches
Authors: Meyer R. E.
Published: July 2002

The model of gravitational surface waves on beaches of small slope formulated in Part I [Phys. Fluids 29, ▪▪▪ (1986)] and its mathematical theory [R. E. Meyer, Adv. Appl. Math. (in press)] are used to show how an incident-wave amplitude can be defined so that a bound on it guarantees solutions which respect the assumptions of the model everywhere and forever. The structure of those solutions ‘‘far’’ from shore is then compared with that predicted ‘‘near’’ shore by the classical, linear theory [Commun. Pure Appl. Math. 1 (1948)] to remove the indeterminacies of both theories and to develop a unified theory which describes the whole shoaling process for unbroken waves of arbitrary time-dependence on inviscid water. These results indicate that the beach theory [Waves on Beaches (Academic, New York, 1972), p. 357 and Phys. Fluids 29, ▪▪▪ (1986)] captures and elucidates the basic singularity structure underlying the shore behavior of gravitational surface waves.
The poloidal potential in the low-collisionality regime in a nonaxisymmetric torus
Authors: Hastings D. E. , Tolliver J. S.
Published: July 2002

The poloidal potential is calculated numerically in the low-collisionality regime for nonaxisymmetric tori such as stellarators and bumpy tori. It is found that even fairly deep into the superbanana regime, the poloidal potential retains the simple azimuthal dependence of the plateau regime.
The contribution of cyclotron heating induced spatial modulation of electron magnetization to tokamak current drive
Authors: Hayes M. A. , Brown M. R.
Published: July 2002

Application to a tokamak of electron-cyclotron resonant heating (ECRH) injected at a given poloidal angle will result in a small but important variation of average electron magnetic moment with poloidal angle. This, coupled with the dependence of magnetic field strength on poloidal angle, will result in the transmission of a net toroidal force to the electrons, the direction and magnitude of which depend on the poloidal angle at which the ECRH is injected and the direction of velocity of the electrons by which it is absorbed. The geometries for which this mechanism adds to the Fisch–Boozer mechanism [Phys. Rev. Lett. 45, 720 (1980)] are described, as are those for which this mechanism is in opposition. Taking this mechanism into account, it is demonstrated that electrons at large minor radii can be driven with significantly greater efficiency if resonance is on the inboard side of the tokamak than if it is on the outboard side, and the ratio of the two efficiencies is calculated for the case of Coulomb collisionality in the limit of large Larmor radius. The case of turbulence-dominated collisionality is considered, and a general prediction of the ratio of the efficiency of this drive mechanism to that of the Fisch–Boozer mechanism is presented, in which the ratio of the efficiencies is given in terms of the dependence of the slowing-down time on velocity. The mechanism described herein provides a significant correction to predictions of current drive efficiency for infinite Larmor radius Coulomb collisionality, and is likely to provide a more significant correction yet for more realistic models of collisionality.
Measurements of the hot-electron density during thermal-barrier operation in a tandem mirror experiment
Authors: James R. A. , Ellis R. F. , Lasnier C. J. , Grubb D. P. , Casper T. A.
Published: July 2002

Thermal-barrier operation of a tandem mirror requires the generation of a dense population of energetic, mirror-trapped electrons. This has been confirmed by experimental results from the initial thermal-barrier experiments in the Tandem Mirror Experiment-Upgrade [Phys. Rev. Lett. 53, 783 (1984)]. For discharges with similar operating conditions, a dramatic enhancement of the axial confinement time was observed only when the mirror-confined hot-electron density was a large fraction of the total electron density at the position of the thermal barrier. These results are in excellent agreement with theoretical predictions.
Stimulated Raman scattering in a lossy magnetized relativistic electron beam
Authors: Schill Robert A. , Seshadri S. R.
Published: July 2002

A general, systematic theoretical study is given for stimulated Raman scattering from a relativistic electron beam with the inclusion of collision and mismatch losses. Shown to be internally consistent, a set of coupled amplitude transport equations is derived for the three-wave interaction among the transverse electromagnetic pump wave, the longitudinal slow space-charge wave, and the transverse (either electromagnetic or electrokinetic) signal wave. The wave instability, amplitude thresholds, and growth rates are examined in the parametric case. In the laboratory frame, the nature of the instability is shown to be strictly convective. The velocity of the convective instability is determined. The nonlinear problem is treated analytically and numerically. Comparisons are made for various magnetostatic field strengths. Important for free-electron laser design, exact analytical expressions for the spatial and temporal periods of the signal wave are determined in the no-loss case. Three-wave coupling where the idler wave is a transverse electrokinetic wave is analyzed. No such coupling is shown to exist.
Effect of a fluid flow outside a nearly spherical, expanding gas bubble on the growth of its radius
Authors: Chakraborty B. B.
Published: July 2002

A nearly spherical gas bubble expands adiabatically in an inviscid and incompressible fluid flowing past it. Rayleigh’s formula for the growth of the radius of the bubble is modified in the presence of the flow of the fluid.