bluuebunny/crossref_metadata_2025 huggingface dataset:
The initial value problem of a rising bubble in a two-dimensional vertical channel
Authors: Yang Yumin
Published: July 2002

The initial value problem of the rising of a long bubble in a two-dimensional vertical channel of inviscid fluid is studied. It is demonstrated numerically that the bubble nose converges to the steady-state solution for a given surface tension independently of initial conditions. The steady state depends on the surface tension, and is characterized by a particular shape and a constant rising speed. It is also shown that a singularity of curvature develops at a finite time when the surface tension is nonzero.
Onset of salt finger convection in a gravity gradient
Authors: Chen C. F. , Chen Falin
Published: July 2002

It is shown that the steady onset of salt finger convection in a double-diffusive layer is exactly analogous to the small-gap Taylor–Couette problem. The results presented by Chandrasekhar [Hydrodynamics and Hydromagnetic Stability (Clarendon, Oxford, 1961)] for the Taylor–Couette problem are extended to cover a wider range of application in the present case.
Development of the Stokes flow field associated with a line vortex perpendicular to a plane wall
Authors: Sozou C. , Pickering W. M.
Published: July 2002

A viscous incompressible fluid occupying the space θ≤π/2 and bounded by the wall θ=π/2 of a spherical polar coordinate system (r,θ,φ), is stirred by a line vortex along the line θ=0 which is switched on at time t=0. The line vortex is perpendicular to the wall. The development of the flow configuration is considered for the case where the poloidal flow is weak and does not affect the structure of the inducing azimuthal flow. The problem is formulated in terms of the similarity variable r/2(νt)1/2 and the polar angle θ, where ν is the kinematic viscosity of the fluid. An analytical solution is constructed for the azimuthal flow. At any given station r the steady azimuthal velocity field is, practically, reached within time r2/ν. The equations governing the poloidal flow are coupled partial differential equations of mixed elliptic–parabolic type which are transformed to equations that are elliptic throughout the solution domain. These equations are solved numerically using the methods of successive overrelaxation and fast Fourier transform. The results show that the poloidal flow in a meridional plane at time t forms closed loops about the point r≊1.58(νt)1/2, θ=π/4, where the velocity has only an azimuthal component. The case of a diffusing configuration from the steady state, due to switching off at t=0 of the agent generating the flow, is also considered. For this case the poloidal field consists of open streamlines and at t=2r2/ν its intensity is a very small fraction of that associated with the steady state.
Kinetic relaxation of a non-Maxwellian monatomic gas in a state of gross rest
Authors: Baganoff D.
Published: July 2002

The kinetic relaxation of a monatomic gas in a state of gross rest is studied by use of Maxwell’s second-order moment equation. The molecular models considered range from the hard sphere to the Maxwell molecule. The development is exact for an ellipsoidal distribution and becomes a good approximation for more general distributions. The results show that the relaxation of second-order moments is nearly exponential for power-law molecules and that the characteristic time μ/p appears as the principal controlling parameter while the power-law constant plays a secondary role. Comparisons between results of numerical simulations using Bird’s direct simulation Monte Carlo method and theory show excellent agreement for both hard-sphere and Maxwell molecules.
Derivation of a model Reynolds-stress transport equation using the renormalization of the eddy-viscosity-type representation
Authors: Yoshizawa Akira
Published: July 2002

Terms in an asymptotic expansion for the Reynolds stress with the eddy-viscosity approximation as the leading part are summed up partially but infinitely. This renormalization procedure leads to a model Reynolds-stress transport equation. The equation is shown to retain the important structures of the counterparts in the conventional second-order modeling that are widely used for the study of engineering turbulence. The present method clarifies the mathematical properties of each term in the conventional models, specifically, the prominent difference between the roles of the slow and rapid terms in the pressure–strain correlation function.
The absence of inactive regions in turbulent flow: Evidence from light scattering experiments
Authors: Pak H. K. , Goldburg W. I.
Published: July 2002

Many have proposed that the turbulent velocity field consists of both ‘‘active’’ and ‘‘inactive’’ regions. In the language of fractals, this implies that the dimension D of the support of the inertial-range velocity difference V(R) is less than 3 when R is in the inertial range. However, light scattering measurements of the homodyne photon correlation function obtained from grid-generated flow, give no evidence that inactive regions of the flow exist.
Stability of a falling liquid film in the presence of interfacial viscous stress
Authors: Oron Alexander , Edwards David A.
Published: July 2002

The role of interfacial viscosities in a two-dimensional vertically falling liquid film is examined. A nonlinear evolution equation for the free interface displacement from planar shape is found to possess classical form (i.e., combining the Korteweg–de Vries and Kuramoto–Sivashinsky equations), with interfacial viscosities supporting the existence of a dispersive term whose physical role has formerly been shown in the literature to effect an ordering of interfacial disturbances in the form of solitonlike patterns.
Control of the spanwise structure of a bluff-body wake by changes in boundary-layer thickness at separation
Authors: Konak S. , Rockwell D.
Published: July 2002

Flow separation from a blunt trailing-edge gives rise to inclined vortex formation in a manner similar to the well-known structure from a circular cylinder. By extracting a portion of the boundary layer on one side of the trailing edge, it is possible to generate large-scale vortex formation having a high degree of spanwise uniformity. This two-dimensional, large-scale vortex formation is accompanied by a substantial decrease in the near-wake fluctuation level.
Dynamics of laminar magnetic vortex rings
Authors: Roesgen T. , Gharib M.
Published: July 2002

Preliminary results are reported for an experiment studying the dynamics of laminar magnetic vortex rings. These are formed through injection of a magnetic fluid (ferrofluid) into a nonmagnetic carrier liquid. An external magnetic field is used to strain the magnetic cores of the propagating rings without an additional external flow and away from solid boundaries. Varying field-dependent growth rates and the development of field-induced instabilities can be observed. Results are presented from an automated analysis of digitally recorded video sequences, resulting in time records of the evolving ring radii.
Magnetic condensation instability in nonuniform unmagnetized plasmas
Authors: Shukla P. K.
Published: July 2002

It is shown that an impurity radiation cooling can give rise to a novel magnetic condensation thermal instability in nonuniform unmagnetized electron plasmas. The resulting enhanced magnetic fluctuations can be responsible for the magnetic turbulence in unmagnetized plasmas.
The implosion of a two-layer spherical shell target
Authors: Piriz A. R.
Published: July 2002

An analytical model is developed to describe the parameters of the fuel and the pusher at peak compression when a two-layer spherical shell target is imploded by a single pressure pulse. The entropy generated by shock waves during the implosion is calculated and an approximate description of the process of central hot spot formation is given. The stagnation stage of a compressible shell is described and scaling laws for the final stage are found. Comparisons with available simulation data are presented and the effect of the thermal conduction in the formation of the central spark is discussed.
Gyrokinetic theory of the screw pinch
Authors: Stéfant Robert J.
Published: July 2002

The gyrokinetic differential equation for waves propagating in a hot collisionless current-carrying plasma is derived in cylindrical geometry. It is shown that the averaging of the wave electric field over the ion Larmor circle leads to a transcendental differential equation (d.e.) of infinite order in the radial derivative. This reduces to a d.e. of sixth order when the scale length of the plasma inhomogeneity Ln is greater than the ion gyroradius ρi by a factor (M/m)1/2, where M and m are, respectively, the ion and electron mass. This sixth-order d.e. describes the properties of the two (compressional and torsional) Alfvén modes and the ion acoustic mode. When Ln <(M/m)1/2ρi, the plasma can only support modes of the magnetokinetic (short wavelength) type. In the absence of a finite Larmor radius (FLR) effect, shear, and equilibrium current, we find that the correct equation to start with is the Hain and Lust [Z. Naturforsch. A 13, 936 (1958)] d.e. of second order that is singular at the Alfvén resonance layer (ARL). The ARL behaves in that case like a Budden absorption layer that traps the global Alfvén eigenmodes (GAEM) inside the plasma cavity where they are damped by transit time magnetic pumping (TTMP). The logarithmic singularity does not disappear with the introduction of the FLR effect in the Hain and Lust d.e., but only with the TTMP damping term. There is no mode conversion between the fast magnetosonic mode and the shear or magnetokinetic mode at the ARL or anywhere in the plasma. In the presence of shear and equilibrium current, the correct equation to use is a d.e. of fourth (or greater) order whose solutions descibe the shear Alfvén mode in the long wavelength limit or the magnetokinetic mode at shorter wavelengths. In the true magnetohydrodynamic (MHD) limit, both modes become degenerate.

It is shown that the slow Alfvén eigenmodes are (almost) completely decoupled from the fast magnetosonic wave and therefore the growth rates show no dependence on the poloidal number m. The quicker the current density drops from the cylinder axis, the more unstable the modes are. This fourth-order d.e. is singular at the hybrid resonances, not at the ARL. It is therefore found that no normal mode solution can exist for linear shear Alfvén perturbations in the full FLR limit.
Electron behavior during electron cyclotron resonance heating in a stellarator
Authors: Trost P.K. , Shohet J. L.
Published: July 2002

Experimental and theoretical studies of the electron energy distribution during electron cyclotron resonant heating of a target plasma in the Interchangeable Module Stellarator (IMS) [IEEE Trans. Plasma Sci. PS-9, 212 (1981)] have been made. The experimental results show an electron energy distribution with a bulk Maxwellian component (f0) with a temperature of 10–25 eV, and a warm component (f1) with an average energy of 140–160 eV. The electron energy distribution is obtained numerically with a particle-following Monte Carlo simulation. To model the electron cyclotron heating interactions with the electrons, an rf collision model based on stochastic electron–wave interactions is used. Results from this simulation are compared to experimental results. The experimental measurements and the calculated distributions agree well, to within experimental error.
Effect of current profile shape on second region access in high-beta tokamak plasmas
Authors: Phillips M. W. , Hughes M. H. , Todd A. M. M. , Okabayashi M. , Kaye S. M. , LeBlanc B.
Published: July 2002

The effect of current density distribution in tokamak plasmas is examined on the access to the second stability regime of high-n ballooning modes. The main factor in determining access to the second stability regime is to lower shear sufficiently on each flux surface. This is achieved by broadening the current profile. A general method of finding equilibria with access to the second region of stability is presented. The value of on-axis safety factor q0 is found not to be a good measure of the type of profile required for second region access.
A kinetic theory for the electron cyclotron maser interaction in a lossy cylindrical waveguide: Mode coupling among all supported waveguide modes
Authors: Schill Robert A.
Published: July 2002

A general dispersion relation is derived assuming all supported empty waveguide modes are included in the electron cyclotron maser interaction within a good conducting cylindrical waveguide. Four energy transfer mechanisms exist of which three are directly related to the beam–wave interaction. The beam modes are shown to be coupled as a consequence of azimuthal asymmetry in the fields. New contributions to the instability terms result. Assuming single mode operation, new contributions to both the instability and the stability terms are obtained. Growth rates are examined. It is explicitly shown that all instability, stability, and coupling contributions due to a particular transverse magnetic mode vanish if a beam dispersion curve just grazes the empty waveguide dispersion curve of that mode. By adjusting the radius of a radially thin beam, the dominant azimuthally symmetric mode of operation can be adjusted.
A possible plasma wave chaos
Authors: Nambu Mitsuhiro , Kawabe Tetsuji
Published: July 2002

A model equation for the ionization wave (Duffing’s equation) is studied. The system shows chaotic behavior via an intermittent route to chaos. It is left for experimentalists to devise experiments to test the theoretical predictions.
Gyroinvariant high-order orbit theory for unidirectional magnetostatic fields: New approach
Authors: Martin Pablo , Haines Malcolm
Published: July 2002

Gyroinvariant drift velocities and first adiabatic invariants have been determined in a unidirectional magnetic field B=B(x,y)b̂, to fourth and third order of accuracy, respectively. The new method described here uses nonanalytical complex functions and successive integration by parts, combined with a suitable average over a quasiperiodic function. A suitable definition of the guiding center to any order is discussed and its position determined to fourth order of accuracy. A non-Hamiltonian method is described to find the first adiabatic invariant.
Transport barrier in ion temperature gradient driven turbulence
Authors: Guzdar P. N. , Drake J. F. , Dimits A. M. , Hassam A. B.
Published: July 2002

Fluid simulations of long ηi modes are presented that demonstrate that the density profile plays a much more profound role in controlling global energy confinement than would be expected from simple marginal stability considerations. Specifically, local steepening of the density gradient produces an effective transport barrier that allows ion global confinement to improve dramatically. The threshold value ηi =d ln(Ti)/d ln(n) required for instability ηic plays a fundamental role in the formation of the transport barrier—no transport barrier forms for ηic<1. The implication of these results for understanding ion energy confinement in tokamaks is discussed.
Nonlinear theory of trapped-electron temperature-gradient-driven turbulence in flat density H-mode plasmas
Authors: Hahm T. S.
Published: July 2002

Ion-temperature-gradient turbulence-based transport models have difficulties reconciling the recent DIII-D H-mode results [Proceedings of 17th European Conference on Controlled Fusion and Plasma Heating (EPS, Geneva, 1990), Vol. 1, p. 271], where the density profile is flat, but χe>χi in the core region. In this work, a nonlinear theory is developed for recently discovered ion-temperature-gradient trapped-electron modes propagating in the electron diamagnetic direction. This instability is predicted to be linearly unstable for LTi/R≲kθρs≲ (LTi/R)1/4. They are also found to be strongly dispersive even at these long wavelengths, thereby suggesting the importance of the wave–particle–wave interactions in the nonlinear saturation phase. The fluctuation spectrum and anomalous fluxes are calculated. In accordance with the trends observed in DIII-D, the predicted electron thermal diffusivity can be larger than the ion thermal diffusivity.
Two-dimensional kinetic field-reversed equilibria
Authors: Webster R. B. , Schwarzmeier J. L. , Lewis H. R. , Choi C. K. , Terry W. K.
Published: July 2002

A two-dimensional kinetic description of field-reversed equilibria has been developed. Three equilibrium models are presented: a kinetic model, a rigidly rotating model, and a magnetohydrodynamics (MHD) model. The kinetic model of equilibrium provides spatial distributions of the macroscopic moments, including velocity shear, that are in good agreement with experimental observations. The rigidly rotating and MHD models allow more general pressure profiles than previous studies. These models, which allow the computation of a wide range of equilibria, suggest that for parameters typical of the current experiments kinetic modifications of the equilibrium are small; however, they may be important if the field-reversed configuration is interacting strongly with a magnetic mirror. Also, the ability to compute kinetic equilibria makes possible a self-consistent examination of the stability of field-reversed configurations, which is believed to be strongly influenced by kinetic effects.
The nonlinear evolution of a free electron laser with electromagnetic wigglers
Authors: Seo Yoonho
Published: July 2002

The nonlinear evolution of a free electron laser (FEL) with an electromagnetic wiggler in the high gain regime is investigated. Two opposite configurations for the wiggler field propagation direction are considered: the wiggler field propagating counter to the electron beam, which is subject to a depletion in the nonlinear stage, and the one propagating parallel to the electron beam, which is subject to an amplification. Especially for the latter case, the possibility of an explosive instability has been fully investigated. A self-consistent set of equations is derived and solved numerically. In the Compton regime the radiation field saturates at a peak amplitude a2=0.6(ωpb/ω1)4/3a1/3w, where a(aw) is the usual normalized vector potential of the radiation (wiggler) field and ωpb(ω1) is the beam plasma (radiation) frequency in the ponderomotive wave frame. In the Raman regime the FEL instability saturates either by particle trapping or by detuning from the resonance due to the nonlinear frequency of the beam mode, depending on the initial wiggler strength. For the copropagating wiggler field system the explosive behavior can be seen only in an impractically small wiggler strength region. In a parameter regime of practical interest the behavior of the radiation field around the saturation is not affected much by the pump depletion or amplification.
Reply to the comments of Wang
Authors: Zhang Shi-Chang
Published: July 2002

In this reply, it is shown that Wang’s criticism of the gyrokinetics presented in Phys. Fluids B 1, 2502 (1989) is, both mathematically and physically, not justified.
Symmetries and global transport equations
Authors: Coppi B. , Pegoraro F.
Published: July 2002

The anomalous transport of the electron thermal energy and that of the longitudinal current density are related to each other and described by a diffusion matrix equation. The symmetry properties of the matrix diffusion coefficients are identified and used to prescribe realistic conditions on the radial profiles of the electron temperature T and of the current density J∥.
Computer simulation of a high-power dielectric Čerenkov maser amplifier
Authors: Weatherall James C. , Main William
Published: July 2002

A computer simulation is used to study the growth and saturation of the electromagnetic wave in a dielectric Čerenkov amplifier. The calculation is done in a reference frame moving with the wave, which reduces the field solution to an inversion of Poisson’s equation in two dimensions; it includes self-consistently the evolution of space charge in the electron beam. The simulations are used to study a high-power X-band amplifier in high-current and low-current operating regimes. Comparison is made with experiment. The simulations identify operating parameters, frequency bandwidths, saturation lengths, saturation powers, and electromagnetic stresses on the dielectric.
Excitation characteristics of sideband wave in a radio frequency stabilized simple mirror plasma
Authors: Takeno H. , Yasaka Y. , Itatani R.
Published: July 2002

A nonlinearly excited sideband wave due to a magnetohydrodynamic interchange mode is observed in a radio frequency (rf)-produced simple mirror plasma, and its excitation is discussed. The measured amplitude of the sideband wave field is compared with the theoretical value showing the agreement in order of magnitude, but the radial distribution is different. As the rf current of the production source is changed, the sideband excitation level varies and this variation is explained by the density fluctuation and the difference of the dispersion relations between pump and sideband waves. Using the difference of the dispersion relations, it would be possible to suppress the sideband excitation and to reduce its destabilizing contribution.
The diocotron instability of a general relativistic electron beam
Authors: Chen H. C.
Published: July 2002

The diocotron instability of a general relativistic electron beam is studied using a macroscopic, cold fluid model. In contrast with the previous treatments where the theoretical analyses are carried out for an annular electron beam in a guided magnetic field, such that plasma frequency ≪ cyclotron frequency, the restriction on the magnitude of the beam density and guiding magnetic field is removed in deriving and solving the general eigenvalue equation. In the limit of long axial wavelengths, a dispersion relation is extracted for the special case of a sharp boundary density profile. The stability properties are investigated for a broad range of beam parameters. The results show that the kink mode can be unstable as the plasma frequency approaches the cyclotron frequency.
A unified theory of gyrotron and peniotron interactions
Authors: Lashmore-Davies C. N.
Published: July 2002

The thin beam model of an axis-encircling relativistic electron beam in a uniform, constant, external magnetic field in a cylindrical waveguide is used to develop a unified theory of the various interactions of such a beam with the electromagnetic field. The model includes the gyrotron interaction (longitudinal displacement of the beam) and the peniotron interaction (transverse displacement of the beam). Space-charge effects are included. The resulting self-fields influence the boundary conditions of the perturbed electromagnetic field across the electron beam. For a beam with only azimuthal equilibrium flow and for propagation perpendicular to the equilibrium external magnetic field the well-known gyrotron instabilities are recovered. In addition, it is shown that the transverse beam modes (slow peniotron) are unstable for resonant interaction with the transverse electric (TE) waveguide mode. A general dispersion relation for propagation at any angle is derived for a beam with arbitrary energy and arbitrary pitch angle. This dispersion relation includes gyrotron, cyclotron autoresonance maser (CARM), peniotron, and harmonic autoresonant peniotron (HARP) interactions and the coupling between TE and transverse magnetic (TM) waveguide modes. For weak space charge, analytic expressions for the growth rates of the Doppler-shifted cyclotron resonance interaction of TE and TM modes with the gyrotron and slow peniotron modes are obtained.
The operation of stochastic heating mechanisms in an electromagnetic standing wave configuration
Authors: Gell Y. , Nakach R.
Published: July 2002

The possibility of the operation of stochastic heating mechanisms of charged particles in a configuration consisting of a left-handed circularly polarized standing electromagnetic wave and a uniform magnetic field, has been studied numerically and theoretically. It is found that such a configuration induces stochasticity, the threshold of which is dependent on two independent parameters, determined by the frequency and the amplitude of the wave and the strength of the magnetic field. From the theoretical analysis, it emerges that the origin of onset of large-scale stochasticity is the destabilization of fixed points associated with an equation describing the motion of the particles in an electrostatic-type potential having standing wave characteristics. The comparison of the theoretical predictions with the numerical results is found to be quite satisfactory. Possible applications to realistic plasmas have been discussed.
Instability of electrostatic waves in nonuniform weakly ionized magnetized plasmas
Authors: Shukla P. K. , Dwivedi C. B. , Das A. C. , Bharuthram R.
Published: July 2002

Novel electrostatic instabilities are shown to exist in a weakly ionized magnetoplasma having equilibrium density and electron temperature gradients. The growth rate of the instabilities critically depends on collisions between charged particles and neutral atoms. It is suggested that the present instabilities could be potential candidates for generating enhanced fluctuations during strong auroral activities in the E region of Earth’s ionosphere, in cometary plasmas, as well as in controlled laboratory experiments.
Filamentation, current profiles, and transport in a tokamak
Authors: Taylor J. B.
Published: July 2002

A tokamak with slightly imperfect magnetic surfaces should have a microscopically filamented current structure. If so, its equilibrium has an analog in the dynamics of interacting charged rods. Then there will be a natural current profile, analogous to thermal equilibrium of the rods (and the natural profile can be calculated by conventional statistical mechanics). This would account for the phenomenon of profile consistency or resilience in tokamaks. In addition to the natural profiles, this filamentary model also predicts an anomalous inward flux of both heat and particles in a tokamak, as well as an anomalous diffusion. These ‘‘inward-pinch’’ components are related to the current gradient.
Effect of particle losses on the equilibrium profiles of a non-neutral plasma
Authors: Holland D. L. , Morales G. J. , Fried B. D.
Published: July 2002

A technique is presented for constructing a self-consistent Vlasov equilibrium for a bounded single species plasma confined by a strong magnetic field. The equilibrium incorporates particle losses to the surrounding wall due to large gyroradii, a feature not previously considered. Specific examples of the density and potential profiles including particle losses are given.
A class of coherent vortex structures in rotating non-neutral plasma
Authors: Lund Steven M. , Davidson Ronald C.
Published: July 2002

A class of nonaxisymmetric (∂/∂θ≠0) rotating equilibria is investigated theoretically for strongly magnetized, low-density (ωpe2/ωce2≪1) pure electron plasma confined radially by a uniform axial magnetic field B0ez between concentric, perfectly conducting, cylindrical walls located at radii r=rw and r=rI≤rw. The analysis is based on a nonrelativistic, guiding-center model in the cold-fluid limit that treats the electrons as a massless fluid (me→0) with E×B flow velocity Ve=−(c/B0)∇φ×ez. Assuming two-dimensional spatial variations (∂/∂z=0), the continuity-Poisson equations are analyzed for rotating coherent structures that are stationary (time independent) in a frame of reference rotating with angular velocity ωr=const about the cylinder axis (r=0). The equilibrium Poisson equation ∇2ψ=−4πe2ne(ψ)+2ωreB0/c is solved exactly for the particular case where the electron density ne(ψ) is a linear function of the streamfunction ψ=−eφ+ωr(eB0/2c)r2, and the plasma fills the region between the conducting walls, with ne=0 at r=rI and r=rw. It is found that this class of rotating equilibria can exhibit large-amplitude, nonaxisymmetric, vortex structures characterized by strong azimuthal density bunching and circulating electron flow within the density bunches. Nonlinear stability properties are investigated using the Lyapunov method, and the vortex equilibria with azimuthal mode number l=1 are shown to be stable.
Ion-temperature-gradient-driven modes in neoclassical regime
Authors: Yagi M. , Wang J. P. , Kim Y. B. , Azumi M.
Published: July 2002

A reduced set of neoclassical fluid equations, consisting of the parallel ion flow velocity v∥, the generalized potential F, the ion pressure p, and the parallel ion heat flow q∥, is derived. The resultant equations are the extension of reduced fluid equations derived from Braginskii equations with the high collisionality to the equations relevant to a fusion plasma with low to intermediate collisionality. The linear ηi mode dynamics is reinvestigated by using the resultant model equations. The effects of the perpendicular compressibility in the ion pressure response, the parallel heat flow, and the neoclassical viscosity are analyzed both analytically and numerically. It is stressed that the closure condition of neoclassical viscosity changes the sign of energy dissipation and seriously affects the stability of ηi modes.
Linear analysis of backward wave oscillations in azimuthally varying transverse electric (TE) modes
Authors: Ganguly A. K. , Park G. S. , Armstrong C. M.
Published: July 2002

A linear analysis for a gyrotron backward wave oscillator operating at a general transverse electric (TEln) mode of a cylindrical waveguide (slotted or uniform cross section) has been developed using a Maxwell–Vlasov equation under the tenuous beam approximation. The equation is solved by Laplace transformation to allow easy insertion of the boundary values. The start-oscillations conditions are determined from an interference of the waveguide and beam modes with appropriate amplitudes and phases. The theory is used to determine the design parameters for stable operation of a second cyclotron harmonic gyropeniotron amplifier at 35 GHz in the π mode of a six vane magnetron-type circuit with a 70 kV, 3 A beam.
Half-coalescence ideal magnetohydrodynamic instability of the q=1 magnetic island in tokamaks
Authors: Lee J. K. , Chu M. S. , Liu C. S. , Drake J. F.
Published: July 2002

The ideal magnetohydrodynamic instability of a symmetric q=1 magnetic island is studied by using an initial value method for a pressureless cylindrical tokamak plasma. It is shown that the island is unstable to a half-coalescence motion which destroys the up–down symmetry of the magnetic configuration. The mode characteristics are qualitatively similar to those predicted by Bussac et al. [Phys. Lett. 105A, 51 (1984)].
Bounce averaged Fokker–Planck theory of non-Maxwellian tail particles
Authors: Chiu S. C.
Published: July 2002

To take into account highly non-Maxwellian tail distributions expected in fusion and/or auxiliary heated plasmas, a self-consistent scheme of separating the non-Maxwellian tail particles from the Maxwellian bulk in the quasilinear Fokker–Planck equation is proposed. The resulting equation for tail particles is the same as that for a minority species, but with a different boundary condition at low energies. Transport fluxes of energetic particles can then be calculated as a minority species that can be easily added onto existing transport theory for the bulk species. Expressions for neoclassical fluxes of tail particles in the banana regime are obtained in terms of the solution of a steady-state minority tail distribution which takes the place of the Maxwell distribution of a bulk species. The existence of a solution is demonstrated, and simple model analytic solutions are given.
Bounce-resonant transport of the plasma ions in a bumpy torus
Authors: Chang C. S.
Published: July 2002

Plateau-type ion diffusion caused by the resonance between the periodic motion of the ions parallel to the magnetic field and the poloidal E×B is calculated in a bumpy torus. It is found that the loss of ion particles through this bounce resonance can be very significant when the resonance condition (Ω≊kvth) is met.
Simplified action principle formulation of the magnetohydrodynamic equations
Authors: Nassar Antônio B. , Putterman Seth J.
Published: July 2002

A simple, direct, alternative derivation of the magnetohydrodynamic force law from an action principle is presented.
Low-frequency plasma-waveguide cutoff
Authors: Eways Saad E. , Oakes M. E.
Published: July 2002

A new low-frequency cutoff for the m=−1 fast wave in a cold cylindrical plasma in the ion-cyclotron frequency range is reported for the completely-filled plasma waveguide. The presence of a vacuum gap between the plasma and the conducting wall enables the wave to propagate to arbitrarily small frequencies. For ω∼ωci, this mode is a surface wave and undergoes a resonance at the ion-cyclotron frequency.
Formation and damping of relativistic strong shocks in a Synge gas
Authors: Lanza A. , Miller J. C. , Motta S.
Published: July 2002

Results are presented from a detailed study of the formation of strong relativistic shocks from simple waves in a fluid obeying the Synge equation of state for a relativistic particle gas. Subsequent damping is also followed, and the results are compared with those obtained previously for a model radiation-dominated gas. In this paper, planar flow is considered and self-gravity of the waves is neglected.
The growth of a shear-free mixed layer in a linearly stratified fluid
Authors: Fernando Harindra J. S. , Long Robert R.
Published: July 2002

An experimental study is described that deals with the nature of the entrainment zone of a linearly stratified fluid when the turbulence in the mixed layer is generated by an oscillating grid. Measurements include the interfacial-layer thickness, frequency, and amplitude of the interfacial waves and the buoyancy flux at the entrainment interface. These measurements were compared with a theory proposed by Long [J. Fluid Mech. 84, 43 (1978)], part of which (the mixed-layer deepening law) has already been verified by Folse et al. [Phys. Fluids 24, 396 (1981)]. After a certain depth of the mixed layer, the entrainment rate shows an abrupt increase, and this may possibly be caused by wall effects as shown in our previous investigations.
Shock implosion of a small homogeneous pellet
Authors: Fujimoto Yasuichi , Mishkin Eli A. , Alejaldre Carlos
Published: July 2002

A small spherical, or cylindrical, pellet is imploded by an intensive, evenly distributed, short energy pulse. At the surface of the pellet the matter ionizes, its temperature and pressure rapidly rise, and the ablated plasma, by reaction, implodes the inner nucleus of the pellet. The involved structure of the energy absorbing zone is idealized and a sharp deflagration front is considered. With an almost square energy pulse, slightly dropping with time, the solution of the mass, momentum, and energy conservation equations of the compressed matter, is self-similar. The differential equation of the nondimensional position of the deflagration front, its integral, and the magnitude and shape of the outside energy pulse are derived. The process of ablation is shown to depend solely on the nondimensional velocity of the gas just ahead of the deflagration front, minus the speed of sound, or the ratio of the gas densities across the deflagration front.
Nonlinear saturation of stimulated Raman scattering in a collisional homogeneous plasma
Authors: McKinstrie C. J. , Simon A.
Published: July 2002

Using multiple timescale analysis, the nonlinear saturation of the stimulated Raman scattering instability is examined in a collisional homogeneous plasma. This purely temporal problem, with a ubiquitous driver and arbitrary damping for each wave, is solved for incident pump amplitudes exceeding threshold by the factor m (where m can be much larger than unity). New expressions are obtained for the saturated amplitude of each wave, and it is demonstrated that the nonlinear frequency shift vanishes. The reflection coefficient is (Ω2/Ω1)3[(m−1)/m2], where Ω1 and Ω2 are the frequencies of the incident and scattered electromagnetic waves. This is to be compared with a previous calculation with only one wave damped in which the reflection coefficient is Ω2/Ω1. A result which includes the effect of mismatch is also given. In addition, it is shown that the complete time dependence can be obtained in the threshold regime (m−1≪1).
Kinetic stability properties of an intense relativistic electron ring in a high-current betatron accelerator
Authors: Uhm Han S. , Davidson Ronald C. , Petillo John J.
Published: July 2002

The kinetic stability properties of an intense relativistic electron ring located at the midplane of an externally applied betatron field are investigated within the framework of the linearized Vlasov–Maxwell equations, including the important influence of electromagnetic effects and surface-wave perturbations. Stability properties are calculated for eigenfrequency ω near harmonics of the relativistic cyclotron frequency ωcz in the applied betatron field. Making use of the large-aspect-ratio assumption (R0≫ac), a closed algebraic dispersion relation is obtained for the longitudinal instability, assuming that the electron ring is located inside a perfectly conducting toroidal shell. Several points are noteworthy in this analysis. First, transverse electromagnetic effects can provide complete stabilization provided the ring current is sufficiently large. Second, for the case where there are no ions (f=0) and the betatron focusing force exceeds the self-field defocusing force (2ω2β =ω2cz −ω2Pb/γ2b >0), it is found that stabilization occurs at sufficiently low transverse temperature of the beam electrons. Third, for the case where ω2β <0 and the transverse temperature of the beam electrons is sufficiently low, it is found that surface perturbations on the electron beam drive a radial kink instability.
Fast ion predictions from a simple hot-electron model
Authors: Mitrovich Dushan
Published: July 2002

A simple diffusion model of hot electrons is described that calculates both the heating of the target by the hot electrons and their pressure effect on plasma blowoff. Over a large portion of the target volume the model simplifies even further to one in which the hot electrons can be treated as a second electron component in equilibrium with the electric field. The pressure from this component changes the hydrodynamic behavior of the corona by producing an increased velocity ion blowoff. The simplified model was implemented in a hydrodynamic simulation code, giving predictions of ion blowoff that agree quantitatively with experimental data.
Additive noise and the radial electric field in systems with convective and diffusive losses
Authors: Hastings D. E. , Auerbach S. P.
Published: July 2002

The charge balance equation in systems with convective and diffusive losses is a nonlinear differential equation that is known to possess multiple solutions. A functional of the potential, which can be identified as akin to a generalized entropy production rate, is defined. It is shown that the addition of a small amount of noise in the system will pick the solution that globally minimizes this functional.
Standing envelope solitons in plasmas
Authors: Mofiz U. A. , Angelis U. de , Shukla P. K. , Rao N. N.
Published: July 2002

The quasistationary slow plasma response to the Langmuir and electromagnetic waves is investigated. Conditions for the wave localization are obtained analytically, and new kinds of soliton profiles are found.
Numerical study on charged particle accelerations in the plasma focus
Authors: Kondoh Yoshiomi , Mamada Minoru
Published: July 2002

Collective features of accelerated ions in the plasma focus are investigated theoretically by using a computer simulation. It is shown that an effective heating of ions by the acceleration of ions occurs without collisions in the collapse phase. A hybrid plasma diode model is used for the particle accelerations after disruption of the focused plasma by the m=0 mode instability. It is shown that ions are efficiently accelerated in the disrupted region toward the downstream direction with respect to the discharge current, and that the energy of the accelerated ions is spread rather widely over the scale of 100 keV, as was observed in experiments.
Particle migration in rotating liquids
Authors: Annamalai P. , Cole R.
Published: July 2002

An analytical solution predicting the behavior of particles in the presence of both gravitational and rotational fields is obtained at the limit of quasisteady creeping flow. The experiments performed in the present work using fluid particles, as well as the experiments already reported on solid particles, agree satisfactorily with the theory.
Ion acceleration via wave–particle interaction in a pulsed beam–plasma system
Authors: Honzawa Tadao , Kuroda Masataka
Published: July 2002

Ion acceleration via wave–particle interaction is experimentally studied in a pulsed ion-beam–plasma system including nonlinear waves of two different modes. Wave fronts of the two modes are observed to accelerate separately a portion of the upstream plasma ions. To interpret the observed maximum energy of the accelerated ions, it is found that the Boltzmann relation for electrons is not valid for large amplitude waves (δN/N≳0.3) and it should be replaced by the equation given by Forslund and Shonk [Phys. Rev. Lett. 25, 1699 (1970)].
Renormalized reduced magnetohydrodynamics
Authors: Kleva Robert G.
Published: July 2002

A renormalized reduced magnetohydrodynamics turbulence theory based upon the direct-interaction approximation is presented. Importantly, the statistical equations derived conserve energy. The equations also properly contain the effects of magnetic shear. For stationary and homogeneous turbulence in a uniform mean magnetic field, the direct-interaction approximation naturally separates into two parts: a coherent part that can be interpreted in terms of a frequency- and wavenumber-dependent turbulent resistivity and viscosity, and an incoherent nonlinear mode coupling source term. In a two-dimensional isotropic spectrum that is narrow in wavelength (the spread in wavenumber of the energy containing modes is small compared to the mean wavenumber), the plasma response at nearby wavelengths is characterized by a turbulent resistivity that depends only on the kinetic energy of the fluctuations, while the turbulent viscosity is negligible in comparison. At much shorter wavelengths the turbulent resistivity and viscosity are identical and both depend on the total energy in the fluctuations including the magnetic energy.
High-power microwave plasma pulse compression
Authors: Manheimer Wallace M. , Ripin Barrett H.
Published: July 2002

It is shown that a plasma-loaded waveguide is sufficiently dispersive that very high-power microwave pulse compression is possible. The input microwave pulse can be either chirped or fixed frequency, if the waveguide plasma parameters are steady or variable in time, respectively. The initial calculations presented here are for a one-dimensional plasma.
Energy decay of three-dimensional isotropic turbulence
Authors: Hosokawa Iwao , Yamamoto Kiyoshi
Published: July 2002

The trend of energy decay of three-dimensional isotropic turbulence with a particular initial condition for various Reynolds numbers is investigated by comparing the data obtained using different methods. The question is then raised whether the curves of energy decay for different Reynolds numbers can cross each other.
Reply to comments of Catto and Myra
Authors: Shaing K. C.
Published: July 2002

If τa≪τD, where τa(τD) is the relaxation time for the radial electric field (plasma density and temperature), a unique, stable value of the radial electric field is determined on the time scale τa≪τ≪τD.
Analogy between hyperscale transport and cellular automaton fluid dynamics
Authors: Yakhot Victor , Bayly Bruce J. , Orszag Steven A.
Published: July 2002

It is argued that the dynamics of a very large scale (hyperscale) flow superposed on the stationary small-scale flow maintained by a force f(x) is analogous to the cellular automaton hydrodynamics on a lattice having the same spatial symmetry as the force f.
A finite-Larmor-radius dispersion functional for the Vlasov-fluid model
Authors: Lewis H. Ralph
Published: July 2002

A dispersion functional for the Vlasov-fluid model is derived as a finite-Larmor-radius (FLR) expansion in which the eigenfrequency is not assumed to be small compared to the ion gyrofrequency and secularities in the gyrophase angle never occur. The expansion is carried out in the local E0×B0 drift frame. Use of the dispersion functional for calculating the small-signal response of a plasma is compared to using an approximate dispersion differential equation. The linearized Vlasov-fluid model is examined with particular reference to the questions of treating the initial-value problem correctly and specifying a generally valid gauge condition. Calculational details for applying the dispersion functional to a general linear screw pinch are presented.
Diffusion and coagulation of magnetic dipole particles in inhomogeneous magnetic fields
Authors: Wilhelm H. E.
Published: July 2002

A theory of the diffusion of macroscopic, magnetic particles (suspended in gaseous or liquid media) in density and magnetic field gradients is developed from first principles (Fokker–Planck equation). The influence of the random, fluctuating magnetic fields, produced collectively by the magnetic dipole particles in their thermal motions on the diffusing particle, is taken into account in a self-consistent way. It is shown that the anisotropy in the particle diffusion, caused by the coupling of translational and rotational degrees of freedom (Magnus effect), is small in most physical situations. As an application, the steady-state boundary-value problem for the diffusion of magnetic grains in the inhomogeneous magnetic field of an adsorbing sink dipole and an external, homogeneous magnetic field is solved by means of a stream and Green’s functions approach. The coagulation coefficient for magnetic dipole particles in the presence of an external magnetic field is derived. The results are discussed with regard to the coagulation of magnetic grains and the formation of magnetic chains.
Finite Larmor radius stabilization of an ideal interchange mode in a high-shear helical system
Authors: Wakatani M. , Sugama H. , Hasegawa A.
Published: July 2002

Finite Larmor radius (FLR) magnetohydrodynamic equations for stellarators are solved numerically to study the linear mode structure of the drift interchange mode. FLR stabilization correlates with the reduction of the phase difference between the pressure perturbation (or the magnetic perturbation) and the potential perturbation. In a cylindrical plasma model with a fixed boundary, the FLR effect, however, is found to destabilize the interchange mode in the large diamagnetic drift velocity regime.
Competition of electron-cyclotron maser and free-electron laser modes with combined solenoidal and longitudinal wiggler fields
Authors: Lin A. T. , Lin Chih-Chien
Published: July 2002

A relativistic electron beam with a finite transverse dc momentum (β⊥=1/γ0) passing through a region of combined uniform solenoidal and longitudinal wiggler magnetic fields is observed to convert 25% of its kinetic energy into coherent radiation at frequency ω=γ20(kwV0+Ωc/γ0) if the phase velocity of the generated wave is slightly above the speed of light. In this situation, the bunchings of the slow electron-cyclotron mode and free-electron laser modes with combined solenoidal and longitudinal wiggler fields (lowbitron) are observed to compensate each other, which gives rise to a finite threshold for lowbitron operation. In order to attain high efficiency, the wiggler strength of a lowbitron must substantially exceed the threshold.