bluuebunny/crossref_metadata_2025 huggingface dataset:
Limitation of pressure of tokamak plasmas
Authors: Yoshikawa S.
Published: March 2003

With the previously obtained equilibrium solution for arbitrary plasma pressure distribution in toroidal geometry, it is shown that the plasma pressure is limited within the assumption of large aspect ratio expansion.
Numerical study of theta-pinch implosion including two-step ionization
Authors: Hui B. H. , Davidson R. C.
Published: March 2003

For parameters appropriate for high-density theta-pinch implosions it is shown that two-step ionization processes can lead to a large enhancement in the effective ionization rate and thereby play in important role in the implosion dynamics.
Rigid-rotor equilibria and wave propagation characteristics of magnetically confined nonneutral plasmas
Authors: Theiss A. J. , Mahaffey R. A. , Trivelpiece A. W.
Published: March 2003

The equilibrium and wave properties of cylindrical, magnetically confined, low-temperature, nonneutral plasma are investigated experimentally. These results are compared with a uniform radial density cold-fluid theory, rigid-rotor model that predicts equilibrium angular rotation frequencies of θ̇= (ωc/2) [1± (1−2ω2p0/ω2c)1/2]. The nonneutral plasma is created by injecting an electron beam through a nonadiabatic field step into a uniform magnetic field. Fast mode (+ sign) and slow mode (− sign) equilibria are investigated by measuring the average rotation frequency for various densities up to the limiting condition ω2p0=ω2c/2. Most of the essential features of these equilibria are verified. Azimuthally symmetric plasma waves are investigated for four equilibrium conditions. The measured phase characteristics of these waves agree with those predicted using a cold-fluid theory for a nonneutral plasma. These measurements confirm that plasma waves propagate in the absence of background neutralizing ions.
Comparison of amplifying modes and feedback oscillations in a beam-plasma experiment
Authors: Jones R. , Carr W. , Seidl M.
Published: March 2003

The beam-plasma instability in a strong magnetic field, (ωce≳ωpe), has been studied experimentally. Although the electron plasma waves have positive group velocity, oscillating instabilities are observed when reflections become important. The amplifying (convective) instability has waves which grow in space and saturate due to beam trapping. After saturation, the spectrum broadens and the beam spread increases due to nonlinear generation of sidebands. When reflective feedback is sufficiently strong, an oscillating instability appears. It has large amplitude near the electron gun, and also saturates by trapping for a weak beam. For stronger beams, several oscillating modes are present and quenching occurs, due to interactions between modes. The difference between amplifying and oscillating modes, quiescent broad spectrum versus quenching, is similar to the absolute instability observations, which occur for (ωce<ωpe, ω).
Saturation of the tearing mode
Authors: White Roscoe B. , Monticello D. A. , Rosenbluth Marshall N. , Waddell B. V.
Published: March 2003

A quasi-linear analytical model is used to describe the nonlinear growth and saturation of tearing modes with mode number m⩾2. The saturation of the magnetic island growth is the quasi-linear development of a single mode rather than a mode coupling process. The saturation amplitude, which is dependent on the form of the resistivity, is in good agreement with results obtained previously by numerically advancing the full set of nonlinear equations.
Flow through rotating porous annuli
Authors: Morel Josette , Lavan Zalman , Bernstein Barry
Published: March 2003

Similarity solutions to the incompressible axisymmetric Navier–Stokes equations have been obtained for the case of laminar flow in porous rotating annuli. The equations are reduced to a nonlinear ordinary differential system which is solved by a parametric differentiation method. The effect of radius ratio, radial Reynolds number, and the ratio of the radial flow rates at the two walls is investigated. For net injection the solutions are unique and tend to known asymptotic solutions. For net suction, regions of reversed flow are present and a multiplicity of solutions is encountered.
Collisions between Langmuir solitons
Authors: Pereira N. R.
Published: March 2003

Collisions between two equal Langmuir solitons with opposite velocities are studied numerically, as a function of soliton strength, velocity, and relative phase angle. The computations show that all three parameters are important in the outcome of a collision, for which qualitative estimates are given.
Dissipative Langmuir shock
Authors: Goldman Martin V. , Nicholson Dwight R.
Published: March 2003

Intense Langmuir waves in a uniform, one-dimensional plasma are described by a nonlinear Schrödinger equation. When the effect of linear damping is included, steady-state shock wave solutions are found. Infinitely extended shock waves are produced by Landau damping; these shocks are moving with respect to the laboratory frame. Semi-infinitely extended shock waves are produced by either collisional or Landau damping; these shocks are stationary in the laboratory frame, and have an energy flux through the boundary.
Kinetic description of negative-mass instability in an intense relativistic nonneutral E layer
Authors: Uhm Hwan-sup , Davidson R. C.
Published: March 2003

The negative-mass stability properties of a relativistic nonneutral E layer are investigated within the framework of the Vlasov–Maxwell equations. It is assumed that the E layer is thin with radial thickness (2a) much smaller than the mean radius (R0), and that ν/γ0≪1, where ν is Budker’s parameter and γ0mc2 is the electron energy. The equilibrium electron charge is partially neutralized by a positive ion background with density n0i(r) =fn0e(r), where f=const=fractional charge neutralization. Moreover, no a priori restriction is made to low beam density (ω2p≪ω2c is not assumed), and the stability analysis is carried out for perturbations about the electron equilibrium f0e= (N0/2Δ) δ (U−γ̂mc2) ⊕[Δ2−(Pϑ−P0)2], where N0, Δ, γ̂, and P0 are constants, U is an effective energy variable, and Pϑ is the canonical angular momentum. The negative-mass growth rate is calculated including the effects of (a) equilibrium self-fields, (b) transverse magnetic perturbations (δB≠0), (c) the presence of inner and outer cylindrical conductors, and (d) a spread in canonical angular momentum (2Δ). All of these effects are shown to have an important influence on stability behavior.
Effect of broadband noise on plasma instabilities
Authors: Benford Gregory , Correll D. L.
Published: March 2003

For current-driven ion cyclotron waves, it is demonstrated that broadband noise can affect ion orbits. An ansatz is framed that this effect can be represented by a diffusive broadening of the wave-particle resonance. This assumption gives a linear scaling of the onset electron drift velocity with average noise potential φ. Experiments show that mode linewidths increase, but the total absorbed power remains constant. The observed scalings agree with a resonantly broadened picture.
Nonlinear classical theory of induced Compton scattering by relativistic charges
Authors: Johnston Shayne , Kulsrud Russell M.
Published: March 2003

Attention is focused on the resonant interaction between a single charged particle, treated relativistically, and two coherent electromagnetic waves. This model interaction is chosen to elucidate aspects of the nonlinear theory of induced scattering. A well-defined problem of finite duration is studied, namely, the induced scattering of plane radiation pulses of arbitrary shape. The factors which affect the net wave conversion from one pulse to the other by a nearly resonant particle are investigated analytically.
Near field diffraction pattern of ion acoustic waves
Authors: Christensen Thomas , Hershkowitz Noah
Published: March 2003

Grid-excited linear ion-acoustic waves are found to exhibit amplitude modulations which resemble nonlinear particle trapping or the beating of two modes. The modulation is shown to be the antenna pattern of the exciting grid. Double-plasma waves display the same behavior although the modulations are weaker. A model that explains this difference in terms of the excitation mechanisms is suggested.
Amplification of helical disturbances in a round jet
Authors: Lopez J. L. , Kurzweg U. H.
Published: March 2003

The inviscid stability of an unbounded round jet against infinitesimal disturbances of arbitrary asymmetry is examined. Under certain conditions nonaxisymmetric modes of small angular wavenumber are shown to be more unstable than their axisymmetric counterpart.
Nonlinear cylindrical ion-acoustic waves in a warm collisional plasma
Authors: Tagare S. G. , Shukla P. K.
Published: March 2003

The propagation of a nonlinear cylindrical ion-acoustic wave in a collisional plasma is shown to be governed by the modified Korteweg–de Vries–Burgers equation. The stationary shock solution valid at early times is presented.
Theory of thermodynamic coupling in surface reacting boundary layers
Authors: Tambour Y. , Gal-Or B.
Published: March 2003

Thermodynamic coupling effects become important in such applications as injection of low molecular gases into boundary-layer flows, ablative thermal protection processes, chemically reacting flows, and membrane transport processes which involve large gradients of temperature or concentrations. Thermodynamic couplings due to thermal diffusion, diffusion-thermo and ob aliam diffusion effects in multicomponent compressible laminar boundary layers with nonequilibrium surface chemical reactions are analyzed and compared with other available analyses for simpler specific cases. A generalized mathematical description of the boundary conditions associated with surface reactions and thermodynamic coupling contributions to the various fluxes is also presented. The boundary conditions are transformed into total enthalpy-concentration fields, and a new generalized Damkohler number for surface reactions is defined. The applicability of the present theory is demonstrated by new solutions to surface catalytic reactions with coupled heat and mass transfer at the stagnation region with and without blowing or suction. These results are then compared with Chung’s uncoupled solutions.
Kinetic theory analysis of rarefied gas flow through finite length slots
Authors: Raghuraman P. , Willis D. R.
Published: March 2003

A kinetic theory analysis is made of the flow of a rarefied monatomic gas through a two-dimensional slot connecting two reservoirs. Numerical solutions are obtained by the moment and discrete ordinate methods. The former method portrays the transition regime characteristics well, but has limitations in the free molecule regime. The latter method gives accurate results in the free molecule and slip regime and bolsters confidence in the accuracy of the transition regime results. The numerical solution for the mass flux through the slot agrees well with an approximate analytic solution of the moment equations for length-to-width ratios from 6 to 0.5, pressure ratios from 0.8 to 0.1, and Knudsen numbers from 5 to 0.5.
Electrohydrodynamic mixing and instability induced by co-linear fields and conductivity gradients
Authors: Hoburg J. F. , Melcher J. R.
Published: March 2003

Scaling laws for field induced mixing of a semi-insulating liquid of uniform viscosity η and permittivity ε, but of inhomogeneous conductivity, are deduced for motions with characteristic times long compared with viscous-diffusion and charge relaxation times. In an electric field, E, time is shown to scale with electric-viscous time τev=η/εE2. An experiment involving mixing of a highly conducting thin layer into a lesser conducting bulk region uses temporal current evolution to confirm scaling. A simple mixing model is shown to correlate with experimental results. Linear instability mechanisms underlying the mixing process are described by a bulk-coupled model, with viscous diffusion effects included. Eigenfrequencies are determined as they depend on conductivity variation and ratio of viscous diffusion to electric-viscous time. Static instabilities and overstabilities are predicted. Corresponding eigenfunctions and streamlines lend insights into the onset of instability leading to a turbulent mixing state.
Observed instabilities in the trapped ion regime in the levitated octupole
Authors: Drake J. R.
Published: March 2003

Two unstable modes were observed in the average minimum-B region of the levitated octupole operating with a weak toroidal field (safety factor of approximately 0.25) and collisionless ions. One mode propagated in the electron diamagnetic drift direction and the other mode propagated in the ion diamagnetic drift direction. The frequencies of the modes were much greater than the ion detrapping collision frequency and slightly less than the trapped ion bounce frequency. The electron collisionality was intermediate between the collisionless trapped ion mode and the dissipative trapped ion mode regimes. Density fluctuation levels from 5% to 50% and enhanced transport approaching Bohm diffusion were the manifest effects of the instabilities. When the ion collisionality was increased by cooling the ion temperature, the unstable fluctuations were not seen.
Computer simulation of radio frequency confinement of a plasma near critical density
Authors: Gitomer S. J. , Shohet J. L.
Published: March 2003

The time evolution of an initially uniform slightly underdense (ωe≲ω) plasma in a resonant cavity has been studied using two-dimensional electromagnetic simulations. The ponderomotive force compresses plasma into the nodes of the applied radio frequency field. The plasma buildup at the nodes terminates either when the plasma pressure increases to equal the field pressure or when phase space breaking occurs. Explanations of the density buildup and tail formation of the particle distribution functions are provided.
Analytical evaluation of the interface displacement for the free shear layer problem
Authors: Pérez-de-Tejada Héctor
Published: March 2003

The transverse displacement of free shear layers as inferred from von Kárman’s condition is estimated analytically uisng conventional bondary layer theory. The displacement of the dividing streamline can be expressed in terms of the maximum viscous stress present within the mixing region.
Oscillating beam-plasma instabilities excited by single and counterstreaming beams
Authors: Jones R.
Published: March 2003

Oscillating beam-plasma instabilities are created by applying feedback to amplifying (convective) modes. A simple theory of such instabilities is presented and compared with experiments employing one and two (counterstreaming) beams.
Interfacial electrohydrodynamic instability in normal electric field
Authors: Kath Gary S. , Hoburg J. F.
Published: March 2003

Surface-coupled electrohydrodynamic instability at the interface between miscible fluid components with identical permittivity, mass density, and viscosity but disparate conductivities, as stressed by an equilibrium normal electric field, is described in the instantaneous relaxation limit. Long wave, inertia-dominated and short wave, viscous-dominated regimes of the dispersion relation are identified. Experimental studies, using freon 113 as a base liquid, compare observed interfacial displacements as functions of time with growth rates predicted by the model. Correlation varies from almost perfect to experimental growth only 0.1 as fast as predicted by theory, with all observed motions in the inertia-dominated regime. Instability dynamics at the scale of interfacial conductivity distribution are documented by allowing diffusion before electric field application.
Stationary convective-like modes in a plasma slab with magnetic shear
Authors: Dagazian R. Y. , Paris R. B.
Published: March 2003

The combined effects of resistivity and viscosity on a magnetohydrodynamically unstable plasma slab are shown to be responsible for the existence of a stationary (marginal) mode. This mode gives rise to plasma convection in a shear-free situation when nonlinear effects are taken into account. In the case of a sheared magnetic field, it still extends over the entire width of the slab and is driven by what would be an interchange localized about the resonant (k⋅B(0)=0) surface in the absence of dissipation. The critical value of the plasma analog of the Rayleigh number in hydrodynamics is calculated as a function of shear, mode wavenumber, and dissipation (represented by the square of the Hartmann number).
Long wavelength m=1 magnetohydrodynamics of a theta pinch
Authors: Miller G.
Published: March 2003

The treatment of the magnetohydrodynamic problem of a sharp-boundary theta pinch plasma column in the presence of perturbing magnetic fields is extended to include long wavelength m=1 motion. The long wavelength m=1 instability, which is a serious problem for fusion devices based on the theta pinch, is explained in a simple way. Plasma equations of motion which are suitable for modeling of complicated experimental situations are given. The high-beta stellarator is discussed.
Analytic description of steady separation from curved surfaces
Authors: O’Brien Vivian
Published: March 2003

Effects of wall curvature on steady separation phenomena are examined by exact analysis for Stokes flow between eccentric cylinders. Curvature alone, convex or concave, determines nothing in the stagnation regions for all features depend upon the total flow field, including the angle of departure of the separation streamline. However, the angular relationships among the curves streamfunction Ψ=0, vorticity ζ=0, and along-wall velocity component vβ=0 at the stagnation point are universal. They are valid for all Reynolds number, internal or external laminar flow.
Kinetic theory of turbulent flows. II
Authors: Lewis M. B.
Published: March 2003

Recent developments on deriving generalized hydrodynamic equations from the Liouville equation for turbulent flows are examined for their limitations and are extended to stronger turbulence.
Quasi-linear transport model for mirror machines
Authors: Berk H. L. , Stewart J. J.
Published: March 2003

A quasi-linear model to describe the evolution of a mirror plasma is presented. It is shown that, as in the 2XIIB mirror experiment, a plasma stream sufficiently reduces rf turbulence so that a high density steady state mirror plasma can be sustained by a neutral beam. The scaling law for this plasma configuration is derived. The energy lifetime is found to be the Spitzer electron-ion drag time even when electron thermal conduction to the external plasma can be neglected.
Steady plasma flow with a shock in a mirror
Authors: Weitzner Harold
Published: March 2003

Based on scaled version of the equations of ideal magnetohydrodynamics it is shown how to construct a steady flow with a shock in a mirror. The upstream state is supersonic, but essentially arbitrary. The shock must be Mach number one on axis although the Mach number may rise rapidly off axis. The shock is extremely effective in converting the directed streaming energy of flow into randomized thermal energy. Such flow patterns may be of interest in very long theta pinches where quasi-steady flow may obtain or in plasma gun devices where the gun injects a plasma along a magnetic field.
Cylinder drag at low Reynolds number
Authors: Huner Burke , Hussey R. G.
Published: March 2003

Drag measurements were made on circular cylinders in the range of Reynolds number Re (based on diameter) 0.23 to 2.6. Empirical corrections were used to account for the effects of finite boundaries and finite lengths. The boundary correction was small (<0.1%), but the length correction ranged up to 6.6%. The experimental results agree well with the theory of Kaplun for Re<0.5 and with the numerical results of Takami and Keller at Re=1 and 2.
Axially symmetric boundary layers on a finite disk
Authors: Bloor M. I. G. , Ingham D. B.
Published: March 2003

A numerical calculation of the steady flow in a laminar boundary layer on a fixed circular disk of finite size induced by some external axially symmetric motion is presented. The flow external to the boundary layer consists of a potential vortex which is coincident with the axis of the disk and an inward radial motion proportional to a power of the distance from the axis, r−m. Integration of the boundary layer equations is carried out starting at the edge of the disk and proceeding inward until a terminal solution is obtained. A numerical technique is employed which allows a solution to be obtained very near the center despite the extreme thickness of the boundary layer. A surprising result is the apparent lack of dependence of the terminal solution on either the conditions at the edge of the disk or the value of m for m<1. The limiting case when the spin vanishes is also calculated and the results support the view of Brown and Stewartson that algebraic decay can exist at a singular point in the boundary layer.
Turbulent buoyant plumes
Authors: Yih Chia-Shun
Published: March 2003

The velocity and temperature distributions in turbulent buoyant induced by a line source or point source of heat are calculated by assuming the eddy viscosity and eddy diffusivity to be constant in any cross section of the plume. Two solutions in closed forms are obtained for the two-dimensional plume, corresponding to turbulent Prandtl number σ equal to 2/3 and 2. Two such solutions are also obtained for the round plume, corresponding to σ equal to 1.1 and 2. The solution for σ=2/3 is compared with previous measurements for two-dimensional plumes, and the solution for σ=1.1 is compared with previous measurements for the axisymmetric plume. The analytical and experimental results agree well in the two-dimensional case, and satisfactorily in the axisymmetric case.
Two-dimensional boundary-value problem for ion-ion diffusion
Authors: Tuszewski M. , Lichtenberg A. J.
Published: March 2003

Like-particle diffusion is usually negligible compared with unlike-particle diffusion because it is two orders higher in spatial derivatives. When the ratio of the ion gyroradius to the plasma transverse dimension is of the order of the fourth root of the mass ratio, previous one-dimensional analysis indicated that like-particle diffusion is significant. A two-dimensional boundary-value problem for ion-ion diffusion is investigated. Numerical solutions are found with models for which the nonlinear partial differential equation reduces to an ordinary fourth-order differential equation. These solutions indicate that the ion-ion losses are higher by a factor of six for a slab geometry, and by a factor of four for circular geometry, than estimated from dimensional analysis. The solutions are applied to a multiple mirror experiment stabilized with a quadrupole magnetic field which generates highly elliptical flux surfaces. It is found that the ion-ion losses dominate the electron-ion losses and that these classical radial losses contribute to a significant decrease of plasma lifetime, in qualitiative agreement with the experimental results.
Swelling effects of electromagnetic waves near the critical density
Authors: Faehl R. J. , Roderick N. F.
Published: March 2003

Numerical techniques have been used to study the intensity pattern of a high-frequency electromagnetic wave near the critical density for conditions typical of laser fusion plasmas. The investigation considered nonlinear density profiles, collisional absorption, and finite bandwidth effects. Using the results of these calculations as a guide, elementary analytic models were developed to describe the behavior of the intensity pattern. Results of the numerical and analytic methods indicate the following: (i) For a nonlinear but monotonic density profile, the swelling factor can be related to the Airy function pattern by a simple scale factor; (ii) for collisional absorption below 50%, a linear relation holds between the intensity and the absorption; (iii) for laser bandwidth Δω/ω0<15%, the intensity is reduced in a manner similar to that associated with collisional absorption. Within the ranges given, accuracy of the analytic models is within 10% of the numerical results. These semiquantitative models provide simple, useful tools for estimating the intensity patterns near the critical density.
Dynamics of high β tokamaks
Authors: Strauss H. R.
Published: March 2003

The reduced nonlinear low β tokamak magnetohydrodynamic equations are extended to the case of high β. A large aspect ratio ordering is used. The dynamics can be described using only three variables: the stream functions for the poloidal magnetic field and velocity, and the pressure. The equations are solved numerically to find two-dimensional equilibria. These equilibria can be unstable to ballooning modes, which tend to grow to large amplitude in nonlinear, three-dimensional computations.
Flux surface shape and current profile optimization in tokamaks
Authors: Dobrott D. R. , Miller R. L.
Published: March 2003

Axisymmetric tokamak equilibria of noncircular cross section are analyzed numerically to study the effects of flux surface shape and current profile on ideal and resistive interchange stability. Various current profiles are examined for circles, ellipses, dees, and doublets. A numerical code separately analyzes stability in the neighborhood of the magnetic axis and in the remainder of the plasma using the criteria of Mercier and Glasser, Greene, and Johnson. Results are interpreted in terms of flux surface averaged quantities such as magnetic well, shear, and the spatial variation in the magnetic field energy density over the cross section. The maximum stable β is found to vary significantly with shape and current profile. For current profiles varying linearly with poloidal flux, the highest β’s found were for doublets. Finally, an algorithm is presented which optimizes the current profile for circles and dees by making the plasma everywhere marginally stable.
Four pole approximation to the Maxwellian distribution
Authors: Ward Michael A. V.
Published: March 2003

An approximation to the Maxwellian is developed which is analytic in the complex velocity plane and is characterized by four symmetric simple poles.
Rate of energy loss by a charge moving in a turbulent plasma
Authors: Swami K. C. , Sharma S. R.
Published: March 2003

The rate of energy loss by a charged particle moving in a turbulent plasma is considered using wave theory formalism, and the loss rate is calculated for the case of weak electrostatic turbulence.
Fourth order envelope equation for nonlinear dispersive gravity waves
Authors: Roskes G. J.
Published: March 2003

A fourth order envelope equation is derived to describe the propagation of self-modulating gravity wave packets on deep water.
Stability of a finite amplitude ion acoustic wave in plasmas
Authors: Shukla P. K.
Published: March 2003

The modulational instability of a finite amplitude ion-acoustic wave in the presence of trapped ions is considered. The wave is found to be stable.
Wave analysis of the tokamak drift mode
Authors: Cheung Lung
Published: March 2003

Certain wave properties of large aspect ratio tokamak current-drift mode from the drift-kinetic equation by means of the expansion are studied. Using this small-inverse aspect ratio expansion, the wavefunction and the wave frequency-shift corrected to higher order have been systematically evaluated.
Radial and axial compression of a hollow electron beam using an asymmetric magnetic cusp
Authors: Destler W. W. , Rhee M. J.
Published: March 2003

The injection of hollow, relativistic electron beams through a narrow asymmetric magnetic cusp field has been investigated analytically. Preliminary experimental results are in good agreement with the analytical theory.
Free convection in the presence of both vertical and horizontal temperature gradients
Authors: Sweet D. , Jakeman E. , Hurle D. T. J.
Published: March 2003

The occurrence of oscillatory solutions to the Bénard problem in the presence of horizontal temperature gradients is investigated as a function of Prandtl number and of the ratio of the applied vertical and horizontal gradients using a linear, mean field approximation. It is shown that in low Prandtl number fluids, even small horizontal gradients readily generate oscillatory modes.
Effect of polymer viscoelasticity on the initial growth of a vapor bubble from gas nuclei
Authors: Ting Robert Y.
Published: March 2003

The effect of polymer viscoelasticity on the initial growth of a vapor bubble from a gas nucleus is studied by analyzing such a growth in a three-constant Oldroyd fluid. At zero polymer concentration, the result reduces to the case of a Newtonian solvent and agrees with the Plesset–Zwick theory. Numerical results show that polymer viscoelasticity retards the bubble growth, but the retardation effect is rather small.
Freely interacting transonic boundary layers
Authors: Bodonyi R. J. , Kluwick Alfred
Published: March 2003

Transonic free interactions for compressive and expansive boundary-layer flows are studied numerically and analytically. The results are qualitatively the same as those in supersonic interacting flows. However, it is found that the upstream decay is either algebraic or exponential, depending on whether the transonic interaction parameter is zero or not. The asymptoptic structure of the singularity in expansive free interactions is derived and comparison with the numerical computations shows good agreement.
Monte Carlo evaluation of the transport properties of polyatomic gases
Authors: Chatwani Ashok U. , Ferron John R.
Published: March 2003

Transport properties for a square well potential model containing a sphero-cylindrical core are calculated by Monte Carlo sampling of the classical trajectories.
Stable approximate equations for ion-acoustic waves
Authors: Broer L. J. F. , Sluijter F. W.
Published: March 2003

Following a method developed in the theory of long water waves, stable approximate equations for ion-acoustic waves are derived from approximate Hamiltonians. Results are given for three cases, viz., low amplitude, long wavelength, and the Boussinesq approximation for fairly long, fairly low waves.
Novel computer simulation of electron swarm motion
Authors: Friedland L.
Published: March 2003

A novel computer simulation technique for the study of properties of electron swarms in gases is presented. As an example, the method is applied to nitrogen at E/N values of 10−16–10−15 V cm2. A strong directional anisotropy in the electron velocity distribution function is observed. The anisotropy is especially strong at electron energies for which the inelastic collision cross section is large relative to the total collision cross section. The first asymmetric term in the expansion of the distribution function in spherical harmonics can be as high as 70% of the value of the symmetric part of the distribution. A comparison with the computer simulation shows, however, that in spite of such strong anisotropy in nitrogen at these values of E/N, the solution of the Boltzmann equation based on the first two terms of the spherical harmonic expansion, gives correct values of electron drift velocity, average electron energy, and average vibrational excitation frequency.
Plasma oscillations and Landau damping
Authors: Crownfield F. R.
Published: March 2003

The Fourier–Hermite expansion is used to follow the time development of a non-analytic initial perturbation of the linearized Vlasov–Poisson system. The calculations differ from some previous applications of the Fourier–Hermite expansion in that they relax certain symmetry conditions on the distribution functions and in that many coefficients are required to describe the initial conditions. The results confirm Weitzner’s prediction of the asymptotic t−3 time dependence for this problem, and exhibit the way in which this behavior develops. An appendix outlines the way in which the initial conditions are expanded in Hermite functions.
Observation of nonlinear Landau damping of a broad-band spectrum of electron plasma waves
Authors: Gervais F. , Olivain J. , Quemeneur A. , Matthieussent G.
Published: March 2003

Considering the interaction of a spectrum of electron plasma waves with a plasma, in the framework of weak turbulence analysis, a formulation of the nonlinear Landau mechanism is developed, which takes into account finite radial geometrical effects. The formulation of the spectrum evolution and of the deformation of the distribution is given. Experimental results concerning the spectrum and the distribution are compared with this analysis. In particular, the observation of the beat disturbance identifies the mechanism. Moreover, an experimental limit of validity of the weak turbulence analysis is given.
Nonlinear distortion of propagation cones of lower hybrid wave in an inhomogeneous plasma
Authors: Sanuki H. , Ogino T.
Published: March 2003

Nonlinear propagation of externally driven waves in the lower hybrid frequency range in an inhomogeneous plasma are investigated. The results of finite temperature, inhomogeneity of the plasma, and density depression due to the ponderomotive force are emphasized since these effects are responsible for the propagation characteristics of the waves. The results show that the waves are localized in a spatial wave packet that propagates into the plasma center along the conical trajectory which makes a small angle with respect to the confining magnetic field.
Three-wave parametric-decay instability with arbitrary dissipation in homogeneous plasmas
Authors: Fuchs Valdimir
Published: March 2003

The theory of the nonlinear decay of a steady incident pump wave into two oppositely propagating modes in a bounded homogeneous region is extended to include arbitrary dissipation on each wave. A new representation of the coupled mode equations shows that, in addition to the usual coupling nonlinearity, two transverse-wave-damping-induced nonlinearities appear, leading to enhanced saturation. A threshold analysis yields general absolute and convective instability criteria extending earlier results of Kroll, and of Porkolab and Chang. The steady-state boundary value problem is solved to obtain the eigenvalue of the stimulated backscattering problem, the anomalous reflectivity, or the convective amplification of a noise source. Good agreement is found between the results of analytical and numerical integrations.
Radiation coupling of Bernstein modes in a ring plasma
Authors: Hoffman J. M. , Aamodt R. E.
Published: March 2003

Motivated by the observation of anomalously intense radiation at frequencies sharply peaked about the electron cyclotron harmonics, the behavior of high frequency flute modes in a weakly inhomogeneous magnetoplasma is investigated. The longitudinal approximation is eschewed and the coupling of Bernstein modes with electromagnetic modes is analyzed. A graphical method is described for visualizing the salient features of mode behavior in this inhomogeneous plasma, and a highly resonant coupling instability is proposed as the energy generating mechanism for the radiation.
Neutral beam driven convective loss cone instability in toroidal geometry
Authors: Hitchcock D. A. , Brecht S. H. , Horton Wendell
Published: March 2003

When a neutral beam is injected into a tokamak obliquely to the magnetic field, a region where ∂Fb/∂v2⊥≳0 may develop which can drive the convective loss cone instability. From a slab model with magnetic shear, low thresholds (nb/ne∼10−3) and substantial growth rates are found for parameters of interest for present and future tokamaks.
End loss from a collision dominated theta pinch plasma
Authors: McKenna K. F. , York T. M.
Published: March 2003

The plasma parameters and end loss in a collision-dominated theta pinch plasma have been investigated photographically, interferometrically, with axially arrayed diamagnetic probes and with a local pressure sensitive diagnostic. The compressed plasma (nemax∼1017 cm−3, Te=Ti∼45 eV) is highly stable for a period of approximately 9 μsec; the end-loss process is examined over this time interval. The development of a plasma throat region has been identified at an axial position of approximately one coil diameter within the theta pinch coil ends. The existence of inward propagating rarefaction waves is indicated from the plasma temperature time history. The plasma end-loss rate derived from local pressure measurements indicates an initial period of rapid particle loss followed by a period of gradual decay in the loss rate. The experimentally observed end-loss time is in excellent agreement with the prediction of a recent numerical magnetohydrodynamic computation.
Neoclassical transport of a multi-species plasma in a mixed regime with several collisional species
Authors: Gelbard Ely M. , Hirshman Steven P.
Published: March 2003

Neoclassical transport coefficients are derived for a multi-species plasma in a mixed regime, with several banana-plateau species, a, and several Pfirsch–Schlüter species, z. It is assumed that ma≪mz, but the masses are otherwise arbitrary.
Magnetic extraction of runaway electrons from a tokamak plasma
Authors: Stone D. S. , Richards B.
Published: March 2003

A short (∼0.5 msec) localized vertical magnetic field (∼200 G) is used to extract runaway electrons from a tokamak plasma without affecting the thermal component of the plasma. This effect is documented with measurements of the hard x-ray and suprathermal microwave emission from the torus.
Some properties of internal waves
Authors: Case K. M.
Published: March 2003

General properties of linearized internal waves are developed in preparation for a treatment of nonlinear waves. Two sets of results are obtained. The first pertain to propagation in an arbitrary stability stratified medium. The second set refer to the case when the Boussinesq approximation is made. Special attention is paid to the completeness of the normal modes and their use in solving initial value problems. Some novel sum rules are obtained. The principal tools of the investigations are two variational principles.
Three-dimensional natural convection motion in a confined porous medium
Authors: Zebib A. , Kassoy D. R.
Published: March 2003

Weakly nonlinear analysis is used to calculate the possible two- and three-dimensional convection patterns in a rectangular parallelepiped of saturated porous media when the horizontal dimensions are integral multiples of the vertical dimension. A two-term expansion for the Nusselt number is found for values of the Rayleigh number close to the critical values. It is shown that the two-dimensional roll configurations transfer heat more effectively than does the three-dimensional pattern of motion when the Rayleigh number is just above the critical value.
Magnetic flux diffusion in imploding liquid liners
Authors: Cooper A. L. , Book D. L.
Published: March 2003

Calculations have been made of the rate at which confined magnetic flux compressed by an imploding cylindrical liquid metal liner diffuses into the latter because of finite electrical resistivity. The diffused magnetic field profile and associated magnetic energy and Joule heating are also calculated. In the limit of high magnetic Reynolds number Rm, the skin depth, total diffused flux, and associated energy scale like Rm−1/2. It is shown that cylindrical liner motion mitigates the diffusion calculated in slab models, owing to the reduction in the surface area through which the flux must diffuse. The influence of the form of the liner motion on the results is displayed.
Nonlinear development of lower hybrid cones
Authors: Pereira N. R. , Sen A. , Bers A.
Published: March 2003

The instability of a planar lower hybrid soliton to transverse long wavelength perturbations is investigated numerically. Initially, a kink-like deformation grows in agreement with linear analysis. In the nonlinear regime the soliton breaks up into bunches which move apart and spread the energy throughout the plasma.
Enhanced transport across laser generated magnetic fields
Authors: Max Claire Ellen , Manheimer Wallace M. , Thomson J. J.
Published: March 2003

Laser generated mega-Gauss magnetic fields may have a disordered small-scale structure, because many different field generation mechanisms are operating simultaneously. Electron cross-field transport in such fields is studied, concentrating on three specific nonclassical transport processes: resonant scattering, field line wandering, and an analog of neoclassical diffusion. Each of these mechanisms seems capable of producing cross-field transport rates significantly faster than the classical values for a mega-Gauss magnetic field, yet considerably slower than the classical value for a field-free plasma.
On the motion of a nearly spherical bubble in a viscous liquid
Authors: Ceschia M. , Nabergoj R.
Published: March 2003

The equations of motion of a nearly spherical bubble immersed in an incompressible and viscous liquid are deduced using the Lagrangian procedure with a dissipation function. The results appear valid for only slightly viscous liquids.
Expectation of an exponential function of an integral
Authors: Lumley John L.
Published: March 2003

Appropriately restricted,the normalized integral of a stationary process asymptotically approaches a Gaussian distribution, but the expectation of the exponential function of the unnormalized integral does not have the value anticipated from this fact. An example is given, applicable to turbulence.
General dispersion relation for nonpotential ion harmonic waves propagating in plasmas with arbitrary β
Authors: Stéfant R. J.
Published: March 2003

The dispersion relation for nonpotential ion harmonic waves propagating at any angle to the magnetic field in plasmas with arbitrary β is derived for ω/kz≫Vi, where ω/kz is the parallel phase velocity and Vi is the ion thermal speed. It is shown that these slow waves can propagate in plasmas when the electron plasma pressure to magnetic pressure ratio βe, is much less than 1 and only in the wavenumber range k≳ (Πe/c)(ω/Ωecosϑ)1/2, where Πe is the plasma frequency, Ωe is the electron gyrofrequency, c is the velocity of light, and ϑ is the propagation angle. Finally, a comparison between the properties of these slow waves and those of the fast electromagnetic ones, is given.
Nonlinear instability of electromagnetic drift waves
Authors: Mima Kunioki , Hasegawa Akira
Published: March 2003

A pair of electromagnetic drift waves is shown to be excited simultaneously by an induced Cerénkov emission by electrons. The instability is shown to be explosive. However, its property is different from the ordinary explosive instability involving three wave interactions with a negative energy wave pump. The instability here is excited by the inverted population of electrons (inverse Landau damping) and is less sensitive to the frequency mismatch or dissipation. The nonlinear growth rate is shown to exceed the linear growth rate at a reasonably small level of wave amplitude. A magnetic field perturbation is essential for this process.
Experiments on current-driven three-dimensional ion sound turbulence. Part II: Wave dynamics
Authors: Stenzel R. L.
Published: March 2003

A fast electron beam is injected into an essentially collisionless magnetoplasma. The beam current closes via a field-aligned return current which drives an ion acoustic instability. The observed frequency spectrum is close to that predicted by renormalized turbulence theory. Three-dimensional cross-correlation measurements exhibit a wave vector spectrum extending in magnitude to kλD≳1 and covering in direction a half-space centered around the electron drift. Propagation of phase coherent test waves confirm the three-dimensional character of the instability but also indicate the presence of ion drifts. These can arise from ion trapping in observed large amplitude off-resonant beat modes generated by two obliquely propagating unstable ion acoustic waves.
Theory of turbulence in a homogeneous fluid induced by an oscillating grid
Authors: Long Robert R.
Published: March 2003

A theoretical model of steady turbulence caused by an oscillating grid in a box of homogeneous fluid agrees fairly well with observations of root-mean-square velocity and integral length scale. In the unsteady case the depth of the turbulent layer increases as the square root of time.
Necessary stability criterion for plasma equilibria with tensor pressure
Authors: Nelson D. B. , Spies G. O. , Hedrick C. L.
Published: March 2003

A necessary stability criterion is derived which is valid within ideal magnetohydrodynamics, one-fluid guiding center theory, and double-adiabatic theory. The equilibria considered are such that the magnetic field lines are either closed or intersect insulating end plates. Due to the inclusion of ballooning perturbations, the criterion is stronger than that for stability to line-preserving perturbations; unlike the latter, it is violated in the bulk of the plasma of Elmo bumpy torus-like equilibria. This disagreement with observations suggests that kinetic effects must be included to explain the experiment.
Effect of equilibrium flow on the resistive tearing mode
Authors: Killeen J. , Shestakov A. I.
Published: March 2003

The resistive tearing instability of an incompressible plasma is investigated for the plane sheet pinch in which the equilibrium magnetic field, x̂Bx0+ẑBz0, depends only on y. The usual assumption is to take v0=0, but here the effect of a nonzero v0 is studied. A linear, time-dependent model is used in which perturbations take the form f1(y,t)exp [i (kxx+kzz)]. A new initial-value code has been developed to solve the resulting higher-order system of equations. For a symmetric magnetic equilibrium and modes α<1, where α=a (kx2+ky2)1/2, an exponential growth develops. The growth rate, p=ωτr, is computed as a function of α and S=τr/τh, for several values of v0. The effect is to reduce p for all α, and to reduce the marginal α for instability for values of v0 of the order of the resistive diffusion velocity. Results for larger values of v0 are briefly discussed. For asymmetric tearing, the effect of the diffusion velocity depends on its sign. The velocity may have either a stabilizing or destabilizing influence on both the growth rates and the critical α for instability.
Kinetic theory of m=1 internal instabilities
Authors: Drake J. F.
Published: March 2003

The internal m=1 instability is investigated kinetically over the entire range of collisionality of the plasma using a pitch-angle-scattering collision operator to represent electron-ion collisions. As a function of the ratio of plasma to magnetic pressure β, the ideal magnetohydrodynamic driving energy, and the collisionality, the m=1 mode falls into six basic categories. In the high β (typically βmi/me≳1), low collisionality regime of present tokamak discharges, the Doppler effects associated with electron thermal motion along B strongly modify the structure and growth rate of the instability. Electron thermal effects are found to be negligible, however, when the ideal magnetohydrodynamic driving energy is large. The effect of density and temperature gradients on the instability are also studied. When the electron diamagnetic frequency ω* is large, two distinct modes are typically found, one with ω≃ω* driven by the electron temperature gradient, and a second with ‖ω‖≪ω* driven by the magnetic energy. Simple descriptions of the mode in each of the regimes are presented.
Energy anisotropy instabilities in high-beta plasmas: A comparison of various kinetic and fluid descriptions
Authors: Cayton Thomas E.
Published: March 2003

The Vlasov-fluid model is employed to study linear perturbations of a particular class of magnetized, infinite, homogeneous equilibria. The dispersion properties of waves and anisotropy driven instabilities with frequencies at or below the ion cyclotron frequency are used to compare and contrast the Vlasov-fluid model with other well-known models of a high-beta plasma. Although the various models differ widely in physical content and in the manner in which the dispersion equation is derived, the results obtained from any one of them agree with appropriate limits of all the others. The results illuminate the nature of the anisotropy driven fluid-like instabilities and illustrate their connection to kinetic descriptions that include dispersion due to finite gyroradius effects. For the simple equilibria that have been considered, no reason has been found not to regard the Vlasov-fluid model as an acceptable model of a high-beta plasma.