bluuebunny/crossref_metadata_2025 huggingface dataset:
Nonlinear gyrokinetic equations for low-frequency electromagnetic waves in general plasma equilibria
Authors: Frieman E. A. , Chen Liu
Published: March 2003

A nonlinear gyrokinetic formalism for low-frequency (less than the cyclotron frequency) microscopic electromagnetic perturbations in general magnetic field configurations is developed. The nonlinear equations thus derived are valid in the strong-turbulence regime and contain effects due to finite Larmor radius, plasma inhomogeneities, and magnetic field geometries. The specific case of axisymmetric tokamaks is then considered and a model nonlinear equation is derived for electrostatic drift waves. Also, applying the formalism to the shear Alfvén wave heating scheme, it is found that nonlinear ion Landau damping of kinetic shear-Alfvén waves is modified, both qualitatively and quantitatively, by the diamagnetic drift effects. In particular, wave energy is found to cascade in wavenumber instead of frequency.
The high-β universal drift mode
Authors: Hastings Daniel E. , McCune James E.
Published: March 2003

A linear kinetic analysis of the universal drift mode, valid for arbitrary values of β( = 8πp/B2), is presented. The three high-β effects on the universal, ∇B drifting particles, coupling to the drift Alfvén wave and compressional magnetic fluctuations are examined in detail. For small values of β, the drift wave behavior is dominated by coupling to the Alfvén wave, while for β∼O(1) the wave behavior is determined by ∇B effects. For most plasma and wave parameters, the mode is stable for βi⩾7%. The stabilization mechanism is the Alfvén induced frequency downshift which reduces the parallel phase velocity of the wave until the (slightly) ∇B broadened ion Landau resonance damps the wave. For ηe( = ∂ ln Tc/∂ ln N)≳0, a peculiar case is found where the mode remains unstable for βi⩽0(50%). This is caused by the ∇B frequency upshift coupled with inverse transit time damping.
Axisymmetric magnetohydrodynamic equilibria in local polar coordinates
Authors: Clemente R. A.
Published: March 2003

The Grad–Shafranov equation for an ideal magnetohydrodynamic axisymmetric toroidal configuration is solved analytically in a local polar coordinate system using a novel method which produces solutions valid up to the second order in the inverse aspect ratio expansion.
Effects of electrostatic trapping on neoclassical impurity transport in a collision-dominated plasma
Authors: Chang C. S. , Hazeltine R. D.
Published: March 2003

It has been shown by Hazeltine and Ware that the existence of a reasonable high-Z impurity species can produce electrostatic trapping and drift comparable to the magnetic effects, assuming that the main plasma components are in the plateau regime. The calculation is extended to the collisional regime, modeling the edge region of the tokamak column and significant modification to the neoclassical impurity transport coefficients is found. A fluid approach is developed and the transport coefficients are found to be nonlinear in density and temperature gradients.
A generalization of the Rayleigh–Plesset equation of bubble dynamics
Authors: Prosperetti Andrea
Published: March 2003

The classical Rayleigh-Plesset equation of spherical bubble dynamics in an incompressible liquid is generalized to include the non-Newtonian behavior of the liquid and mass exchange processes at the bubble interface.
Effects of an inhomogeneous impurity distribution in a field-reversed theta pinch
Authors: Greve P. , Haumann J. , Kunze H.-J. , Ullrich L. K.
Published: March 2003

A 140-kJ theta-pinch device originally constructed for spectroscopic investigations of highly ionized atoms is described. Atoms of solid elements are introduced into the initial plasma by laser-driven ablation from solid targets. The stability of the field-reversed plasma configuration is investigated with and without impurities. An inhomogeneous impurity distribution leads to the ejection of the plasma as a whole. This phenomenon is interpreted as the result of asymmetric field line reconnection at the ends.
Electromagnetic oscillating two-stream instability of plasma waves
Authors: Tripathi V. K. , Liu C. S.
Published: March 2003

Near the resonance (ωo≊ωp) a high-amplitude plasma wave decays into a purely growing electromagnetic perturbation and two Langmuir wave sidebands. The growth rate of the instability γ≃ωpk20v20/ 8k2v2e for a Langmuir pump wave of finite wavenumber k0≳kve/c and the threshold due to the finite extent, x0, of the pump is v20/v2e≳4k2v2e(k2x0+β)/ ω2pβx0; v0 and ve are the oscillatory and thermal velocities of electrons and β is the x component of propagation vector k of the perturbation. This instability may be a possible source of spontaneous generation of random magnetic field in laser-produced plasmas.
Resistive magnetic tearing in a finite length pinch
Authors: Mok Yung , Van Hoven Gerard
Published: March 2003

The effects of axial boundary conditions on the tearing mode of a cylindrical pinch are described. A flexible inertial ’’line-tying’’ model is used to restrict the available perturbations of a force-free current-channel equilibrium, similar to that in a reversed-field pinch. The resistively unstable mode is found to be azimuthally symmetric (m = 0), and the external (ideal) and internal (resistive) solutions are detailed, the latter being found by a unique numerical procedure. The solutions can be either ’’constant-ψ’’ or fast growing, depending on the width of the current channel. Threshold behavior and subsequent growth rates are calculated. Finally, an application of this reconnection mechanism to the flare instability of a narrow solar coronal loop is described.
Self-similar oscillations of a Z pinch
Authors: Felber F. S.
Published: March 2003

A new analytic, self-similar solution of the equations of ideal magnetohydrodynamics describes cylindrically symmetric plasmas conducting constant current. The solution indicates that an adiabatic Z pinch oscillates radially with a period typically of the order of a few acoustic transit times. A stability analysis, which shows the growth rate of the sausage instability to be a saturating function of wavenumber, suggests that the oscillations are observable.
Kinetic description of Alfvén wave heating
Authors: Ross David W. , Chen G. L. , Mahajan Swadesh M.
Published: March 2003

Heating of tokamak plasmas by Alfvén waves is studied by means of a linearized kinetic model which takes into account electron inertia and Landau damping, finite ion gyroradius, the equilibrium current, and magnetic shear. In cylindrical geometry, a fourth-order set of differential equations in r for the perturbed fields Er and E⊥ is solved numerically for modes driven by a sheet current of single helicity and frequency ω, located between the plasma edge and a conducting wall. Realistic profiles of density, temperature, and safety factor are employed. The energy deposition and density fluctuations as functions of r and the total impedance to be expected in experiments on the pretext tokamak are computed, and optimum conditions for heating are investigated. Mode conversion to the kinetic Alfvén wave and its damping are observed in the computed solutions. The plasma impedance is sensitive to the profiles and mode numbers chosen, and, with two exceptions, is consistent with previous work based on magnetohydrodynamics. Kinetic effects can produce ’’high Q’’ resonant absorption, both for frequencies below the Alfvén continuum (corresponding to discrete stable kink modes) and for frequencies such that the Alfvén resonance approaches the plasma edge (corresponding to normal modes of the kinetic shear wave in cold plasma).
Ponderomotive force effects on slow-wave coupling
Authors: Wilson J. R. , Wong K. L.
Published: March 2003

Localized plasma density depressions are observed to form near a multi-ring slow-wave structure when the value of the nonlinearity parameter, s = ω2pe‖Ez‖2/8πω2nκT, is of order unity. Consequent changes in the wave propagation and coupling efficiency are reported. For large enough values of s, the coupling efficiency may be reduced by 50% from the linear value.
Nonlinear aspects of wave propagation near the upper-hybrid mode conversion layer
Authors: Chan V. S. , Chiu S. C.
Published: March 2003

It has been found that the effect of self-modulation by a large-amplitude wave can significantly modify the mode conversion process at the upper-hybrid resonance. Under the condition ω2pe<3Ω2c, an incoming extraordinary plane wave of sufficiently large amplitude can be mode converted to soliton-like hot plasma waves. These waves can build up to very high intensities and allow nonlinear processes, such as parametric decay which is otherwise not possible due to high excitation thresholds, to occur close to the upper-hybrid resonance. The investigation involves determining the modulational stability of the incoming extraordinary wave using the warm fluid model, and the hot plasma wave using the Vlasov model. An equation governing wave propagation in a nonuniform plasma taking into account the effect of self-modulation is derived. This equation is analyzed to obtain the physical picture described.
Space charge waves in a cylindrical waveguide with arbitrary wall impedance
Authors: Uhm Han S.
Published: March 2003

Properties of the space charge waves in a solid relativistic electron beam propagating in a cylindrical waveguide are investigated, including the important influence of arbitrary wall impedance. The stability analysis is carried out within the framework of the linearized Vlasov–Maxwell equations. In order to examine the influence of axial momentum spread on stability behavior, it is assumed that all electrons have a Lorentzian distribution in the axial canonical momentum. One of the most important features of the analysis is that, for short axial wavelength perturbations, the eigenfunction can be described by a Bessel function. Moreover, the condition for zero phase velocity of the space charge wave is also obtained, in connection with collective ion acceleration. Space charge wave properties for a dielectric loaded waveguide are also investigated. For the appropriate choice of the dielectric constant ε and thickness of the dielectric material, it is shown that strong mode-coupling occurs, exhibiting the growth rate of instability comparable to the beam plasma frequency. The physical mechanism of instability is Cerenkov radiation.
Resistive interchange modes in reversed-field pinches
Authors: Finn John M. , Manheimer Wallace M.
Published: March 2003

A new regime is found in which the growth rate of the resistive interchange mode in cylindrical geometry is considerably smaller than previously believed. This stabilization is due to coupling to the external, tearing stable, region. Considering the crossover point from the conventional resistive interchange to the new regime as a critical beta, βc, it is found that βc∼7% for classical resistivity with Te = 10 eV, in agreement with recent numerical studies. However, βc scales as T−3/5e, giving βc∼1% for Tc = 1 keV. Marginally stable pressure profiles for totally localized modes in the Bessel function model for a reversed-field pinch are also computed, and show that for tearing stable equilibria the central pressure may be up to 400 times the pressure at the wall.
Theory of plasma injection into a magnetic field
Authors: Peter William , Rostoker Norman
Published: March 2003

Analytic and self-consistent solutions for the propagation of a low-beta, large-gyroradius plasma across a transverse magnetic field are derived. It is shown that if ω2pi/Ω2i≫(M/m)1/2, the beam can propagate into the field by means of an E×B plasma drift. The cross-field velocity of the plasma in this case is found to be very nearly equal to the beam injection velocity u0. The theory is discussed with reference to recent proof-of-principle experiments on cross-field propagation.
Allowable discontinuities in a Gerstner wave field
Authors: Mollo-Christensen Erik
Published: March 2003

Velocity discontinuity surfaces can be inserted at will in a Gerstner edge wave on an inclined boundary in a rotating fluid.
Experimental test of modulation theory and stochasticity of nonlinear oscillations
Authors: Dimonte Guy
Published: March 2003

The initial nonlinear evolution of two unstable waves in a cold beam-plasma system can be described by a single wave with a slow modulated amplitude and phase. The modulational calculation is tested quantitatively on the analogous wave-particle interaction in a traveling wave tube. The model is found to be valid for one autocorrelation time following the onset of nonlinearities. Stochastic behavior follows the breakdown of the modulational approximation, i.e., after one autocorrelation time, in agreement with reasonance overlap theory.
Finite β effects on the nonlinear evolution of the (m = 1; n = 1) mode in tokamaks
Authors: Holmes J. A. , Carreras B. A. , Hicks H. R. , Lynch V. E. , Rothe K. E.
Published: March 2003

The stability and evolution of ISX-B-like plasmas are numerically studied using a reduced set of resistive magnetohydrodynamic equations. For a sequence of equilibria stable to ideal modes, the n = 1 mode changes from a tearing branch to a pressure-driven branch as βp is increased. When this mode is unstable at low β, it is just the (m = 1; n = 1) tearing mode. Higher n modes also become linearly unstable with increasing βp; they are essentially pressure-driven and have ballooning character. For low values of β, the instability is best described as a βp distortion of the (m = 1; n = 1) tearing mode. This mode drives many other helicities through toroidal and nonlinear couplings. As βp is increased, the growth of the m = 1 island slows down in time, going from exponential to linear before reconnection occurs. If βp is large enough, the island saturates without reconnection. A broad spectrum of other modes, driven by the (m = 1; n = 1) instability, is produced. These results agree with some observed features of magnetohydrodynamic activity in ISX-B.
Effect of collisions on dc magnetic-field generation in a plasma by resonance absorption of light
Authors: Adam J. C. , Gourdin-Servenière A. , Mora P. , Pellat R.
Published: March 2003

The importance of collisional ponderomotive effects on dc magnetic field generation is stressed. Computer simulations show that a weak rate of collision is sufficient to completely modify dc magnetic field generation in the resonant absorption of light, as compared with previous collisionless simulations. The agreement with theoretical predictions is shown.
Effect of turbulent diffusion on collisionless tearing instabilities
Authors: Meiss J. D. , Hazeltine R. D. , Diamond P. H. , Mahajan S. M.
Published: March 2003

The direct interaction approximation is used to obtain the kinetic electron response in the presence of drift-wave turbulence. Primary effects on the tearing mode equations are a diffusive broadening of the conductivity and an anomalous perpendicular viscosity. The first has a negligible effect on collisionless current channel modes. The viscous term, however, produces significant stabilization of the m = 1 mode for levels of turbulence much smaller than those expected.
Some nonlinear properties of drift-cyclotron modes
Authors: Cohen Bruce I. , Maron Neil , Smith Gary R.
Published: March 2003

The nonlinear evolution of the drift-cyclotron instability has been investigated by means of analytical perturbation theory and computer simulations with a particle-fluid hybrid code. The nonlinear modification of the electrostatic ion response in the presence of a single drift-cyclotron mode is calculated. It is determined that a nonlinear shift in the effective ion cyclotron frequency can stabilize long-wavelength modes (kai∼N/κai, ω≊ω*≊Nωci, N = ±1, ±2, ...) at fairly small amplitudes of the electrostatic potential ‖eφ/Ti‖∼(me/mi+ω2ci/ ω2pi)1/2κai, where ω* is the ion diamagnetic drift frequency, ai is the ion gyroradius, Ti is the ion temperature, and κ−1 is the density-gradient scale length. These saturated states exhibit nonlinear oscillations, and analysis indicates that these states are stable to perturbations arising from other long-wavelength drift-cyclotron modes. A shift of the ion cyclotron frequency is not the dominant nonlinear feature in the case of more unstable short-wavelength modes [kai∼(me/mi+ω2ci /ω2pi)−1/2, ω≊Nωci∼ω*/2], and the nonlinear ion response is much more difficult to calculate. Simulations indicate that the short-wavelength modes eventually trap ions, as has been seen in previous simulations of ion cyclotron instabilities and the closely related lower-hybrid drift instability.
Warm relativistic electron fluid
Authors: Newcomb William A.
Published: March 2003

Equations of motion are derived for a warm relativistic collisionless electron fluid. In particular, the appropriate modification of the adiabatic equation of state is given. Use of the modified equation of state is illustrated by a calculation of the thermal correction to the zero-temperature electron susceptibility tensor.
Trapped particle induced ion solitary waves in a magnetized plasma
Authors: Bujarbarua S. , Yu M. Y.
Published: March 2003

Solitary ion acoustic and ion cyclotron waves due to the trapped electron nonlinearity are investigated for a magnetized plasma. The solitons obtained are narrower than those due to the convective nonlinearity.
Energy principle with global invariants
Authors: Bhattacharjee A. , Dewar R. L.
Published: March 2003

A variational principle is proposed for constructing equilibria with minimum energy in a toroidal plasma. The total energy is minimized subject to global invariants which act as constraints during relaxation of the plasma. These global integrals of motion are preserved exactly for all ideal motions and approximately for a wide class of resistive motions. We assume, specifically, that relaxation of the plasma is dominated by a tearing mode of single helicity. Equilibria with realistic current density and pressure profiles may be constructed in this theory, which is also used here to study current penetration in tokamaks. The second variation of the free energy functional is computed. It is shown that if the second variation of any equilibrium constructed in this theory is positive, the equilibrium satisfies the necessary and sufficient conditions for ideal stability.
Comments on ‘‘Linear waves and instabilities on magnetically insulated gap’’
Authors: Winterberg F.
Published: March 2003

A comment on linear waves and instabilities on magnetically insulated gap is presented. (AIP)
The meandering fall of paper ribbons
Authors: Bejan Adrian
Published: March 2003

This paper discusses experimental observations of the meandering fall of light-weight tissue paper ribbons. The photographs show that the ribbons assume a sinusoidal shape with a unique wavelength which scales with the thickness of the airstream entrained by the ribbon.
Reply to the comments of F. Winterberg
Authors: Swegle John
Published: March 2003

A comment on the comment of magnetically insulated ion diodes is presented. (AIP)
Particle transport in field-reversed configurations
Authors: Tuszewski M. , Linford R. K.
Published: March 2003

Particle transport in field-reversed configurations is investigated using a one-dimensional, nondecaying, magnetic field structure. The radial profiles are constrained to satisfy an average β condition from two-dimensional equilibrium and a boundary condition at the separatrix to model the balance between closed and open-field-line transport. When applied to the FRX-B experimental data and to the projected performance of the FRX-C device, this model suggests that the particle confinement times obtained with anomalous lower-hybrid-drift transport are in good agreement with the available numerical and experimental data. Larger values of confinement times can be achieved by increasing the ratio of the separatrix radius to the conducting wall radius. Even larger increases in lifetimes might be obtained by improving the open-field-line confinement.
Boundary conditons on the envelope function of convective rolls close to onset
Authors: Cross M. C.
Published: March 2003

Boundary conditions are derived for the envelope function of convective rolls approaching a rigid sidewall at an arbitrary orientation. This generalizes previous results for parallel and perpendicular rolls. It provides the first step in a study of the convective pattern to be expected close to onset in Rayleigh–Benard cells of any cross section, and allows consideration of more complicated patterns in rectangular or circular cross sections.
Beam-plasma instability in the presence of low-frequency turbulence
Authors: Goldman Martin V. , DuBois D. F.
Published: March 2003

General equations are derived for a linear beam-plasma instability in the presence of low-frequency turbulence. Within a ’’quasilinear’’ statistical approximation, these equations contain Langmuir waves scattering, diffusion, resonant and nonresonant anomalous absorption, and a ’’plasma laser’’ effect. It is proposed that naturally occurring density irregularities in the solar wind may stabilize the beam-unstable Langmuir waves which occur during Type III solar radio emissions.
Stokes drag on a flat annular ring
Authors: Roger R. P. , Hussey R. G.
Published: March 2003

A surface distribution of point forces has been used to calculate the Stokes flow drag on a thin flat ring moving either parallel to or perpendicular to the axis of rotational symmetry. The results for motion parallel to the axis are confirmed by experiment. The drag is found to depend primarily upon the outside diameter of the ring and to be relatively insensitive to the inside diameter, in contrast to measurements at high Reynolds number. When the inside diameter is zero, the results agree with the known exact solutions for the circular disk.
Steady flow in a sudden expansion at high Reynolds numbers
Authors: Acrivos Andreas , Schrader Mark L.
Published: March 2003

The sudden expansion of a laminar flow in a two-dimensional channel is examined theoretically in the limit of large Reynolds number R. Previous investigators found, from experiment and from numerical solutions of the equations of motion, that a region of closed streamlines is formed whose streamwise length is linearly related to R for R = O(102). It is desired to determine if the steady solutions to the Navier–Stokes equations continue to exhibit this relationship indefinitely for increasing R. Since solutions are sought for which the longitudinal length scale is O(R) and that in the tranvserse direction is O(1), the equations of motion reduce to the boundary-layer equations as R→∞. These equations are solved numerically using a finite difference technique for selected values of λ, the ratio of the upstream channel half-width to the step height. Steady solutions are found for all values of λ when the inlet velocity profile is parabolic. However, a uniform inlet velocity profile yields steady solutions with an O(R) wake length only for λ⩽λc = 1.54. Analogous results apply in the axisymmetric case for which λc is found to be equal 3.67.
Stability of convection rolls in the presence of a vertical magnetic field
Authors: Busse F. H. , Clever R. M.
Published: March 2003

The stability of two-dimensional convection rolls in a horizontal fluid layer heated from below with rigid boundaries is investigated theoretically for the case when a vertical magnetic field permeates the layer. It is assumed that the magnetic diffusivity is large compared with the thermal and viscous diffusivities of the fluid. Low Prandtl numbers are emphasized in order to make the analysis directly applicable to experiments on convection in mercury and liquid sodium. The theory predicts that the onset of the oscillatory instability of convection rolls is delayed by the effects of the magnetic field and that the parameter range over which steady rolls are stable increases with the magnetic field strength. In the parameter regime investigated, there does not seem to exist a new mode of instability introduced by magnetic forces. It is also found that the magnetic field tends to increase the efficiency of the convective heat transport thereby conpensating in part for the delay in the onset of convection caused by the stabilizing effect on the Lorentz force.
Viscous decay of long internal solitary waves
Authors: Leone C. , Segur Harvey , Hammack J. L.
Published: March 2003

A formula for the viscous decay of a long internal solitary wave, propagating into a quiescent fluid in a two-layer model was derived. The result is analogous to Keulegan’s (1948) formula for the viscous decay of long surface waves. The requirement of quiescent fluid ahead of the wave is important, as indicated by a comparison with experiments.
Weakly nonlinear steady gravity-capillary waves
Authors: Ma Yan-Chow
Published: March 2003

The phenomenon of three-dimensional capillary gravity waves on deep water is considered. The solution is obtained by bifurcation from a two-dimensional wave into three-dimensional waves composed of the two-dimensional wave plus a pair of oblique waves. The streamwise period of the three-dimensional waves is doubled, and there is another period in the spanwise direction. The speed and the stability of the three-dimensional waves are discussed.
A model for the skewness of the temperature derivative in a turbulent boundary layer
Authors: Subramanian C. S. , Antonia R. A.
Published: March 2003

A simple model of temperature, based on conditional averages associated with the coherent temperature fronts, yields a distribution of the temperature derivative skewness in reasonable agreement with measurements.
Limiting particle streamline in the flow of a gas–particle mixture through an axially symmetric nozzle
Authors: Ishii R. , Kawasaki K.
Published: March 2003

The flow of gas–particle mixtures through an axially symmetric nozzle is analyzed. The particle behavior is considered under the condition where the velocity and temperature lags are small. Particular attention is paid to the particle streamlines, and the problem is solved only for the particle streamlines in the first approximation. It is rigorously proved that, when the impingement of the particles on the nozzle wall occurs in the supersonic region, there is an upper limiting point (line) in the wall region where the particles can impinge. The location of this point (line) does not depend on the particle size, but only on the nozzle geometry and the equilibrium reservoir conditions.
Nonlinear ion-acoustic waves in weak magnetic fields
Authors: Laedke E. W. , Spatschek K. H.
Published: March 2003

The two-dimensional dynamics of nonlinear ion-acoustic waves in plasmas are considered. A new nonlinear equation is found which is valid for unmagnetized as well as magnetized plasmas. For exactly vanishing magnetic fields, the Kadomtsev–Petviashvili equation is recovered; for weak magnetic fields, however, the dynamics are qualitatively different from that equation, depending on amplitude. With increasing magnetic field, the new equation becomes similar (but not identical) to the Zakharov–Kuznetsov equation which was derived for very strong magnetic fields. The stability behavior of plane solitons propagating along the magnetic field is also discussed. The transition from stable to unstable behavior and some quantitative new results for the instability growth rates are presented.
Effects of curvature of the magnetic field on drift-dissipative instability of a nonuniform plasma
Authors: Shivamoggi Bhimsen K.
Published: March 2003

A study is made of the effects of curvature of the magnetic field on the drift-dissipative instability of a nonuniform plasma. It is found that inward curvature of the static magnetic field stabilizes the drift instability produced by the particle collisions.
Energy transport equations for a bumpy torus
Authors: Pao Young-ping
Published: March 2003

Energy equations are derived from kinetic theory for plasmas in a bumpy torus. It is shown that the work done by the poloidal electric field on the precession motion of the particles should not appear in the energy equation. Both finite- and low-β cases are examined.
Kinetic theory of neutrals in a bounded plasma slab with inhomogeneous temperature and density profile
Authors: Tendler M. B. , Ågren O.
Published: March 2003

The transport of neutral hydrogen atoms in a hydrogen plasma slab is considered. The influence of the inhomogeneous ion temperature profile on the neutral density and distribution is discussed as well as the influence of the neutral edge energy, charge exchange, and ionization rates. The analytical solutions for the neutral density and distribution function are obtained and compared with the numerical results. The effects due to the inhomogeneous temperature profile are discussed. The recommen-dations from the viewpoint of the effects mentioned previously for the purposes of the cold-gas mantle system have been given.
Effect of low-frequency density fluctuations on ion cyclotron waves
Authors: Ono Masayuki
Published: March 2003

Scattering of waves in the ion cyclotron range of frequencies by low-frequency fluctuations is analyzed in the weak turbulence approximation. Finite-ion-Larmor radius, multi-ion species, ion-drift motion, and electromagnetic terms are included in the wave kinetic equation. Conditions for significant scattering have been identified for the fast wave as well as for externally launched ion Bernstein waves. Implications for the ion cyclotron range of frequency heating in tokamak plasmas are discussed.
Energy gains of a wall-confined fusion cycle
Authors: Kmetyk Lubomyra Nadia , Gross Robert A.
Published: March 2003

Calculations of energy gain are made for a wall-confined deuterium–tritium fusion cycle. Plasma, first heated by strong shock waves, re-expands to completely fill a cylindrical cavity. An azimuthal magnetic field, everywhere parallel to the walls, provides thermal insulation. The energy input is evaluated by solving the transverse magnetohydrodynamic shock wave equations. The fusion energy yield is determined by the competition between fusion burn, radiation, and wall cooling. A one-dimensional initial value code is used to evaluate the plasma energy loss rates and the fusion burn. Two-dimensional loss mechanisms are estimated using a modified form of the one-dimensional model. Energy gain ratios of twenty are calculated for a cylinder whose characteristic size L is less than one meter. Energy breakeven is found for L∼0.2 m, with an energy input of 1.9 MJ at a power of 8.8 TW.
Nonexistence of quasilaminar equilibria in cylindrical magnetically insulated lines
Authors: Swegle J. A.
Published: March 2003

It has previously been shown for nonrelativistic voltages (i.e., much less than 500 kV) that a quasilaminar, cold-fluid, magnetically insulated equilibrium does not exist on coaxial cylindrical lines for which (1) the magnetic field is azimuthal, (2) electron emission at the cathode is space- charge-limited, and (3) the cathode lies within the anode. Since it is expected to encounter this configuration frequently in practice, and because such lines typically operate at voltages above 500 kV, the previous analysis has been extended to take account of relativistic and sheath diamagnetic effects. Despite their inclusion it is found that the nonexistence of this type of equilibrium state continues to hold at the higher voltage levels.
Spanwise correlation of temperature in a turbulent boundary layer
Authors: Rajagopalan S. , Subramanian C. S. , Antonia R. A. , Chambers A. J.
Published: March 2003

Conventional correlations of temperature in the spanwise direction of a turbulent boundary layer indicate a length scale which is independent of Reynolds number and of the order of the boundary layer thickness.
One-dimensional stability of self-similar converging flows
Authors: Lazarus Roger B.
Published: March 2003

A necessary condition for the asymptotic approach of symmetric converging flows to a self- similar form is the stability of the one-dimensional partial differential equations when linearized about the appropriate similarity solutions. For the converging shock problem, and (for sufficiently large adiabatic exponent γ) also for the collapsing free-surface problem, it is found that (1) the standard, analytic similarity solution is positively stable with respect to symmetric (one- dimensional) perturbations, and (2) that all other similarity solutions are positively unstable. For the free-surface problem when γ is small, there seem to be three regimes: neutral stability, instability of all solutions, and stability of a degenerate solution.
The effect of curvature at the detachment point of a fluid sheet from a rigid boundary
Authors: Naghdi P. M. , Rubin M. B.
Published: March 2003

The effect of curvature at the detachment point (the point at which the flow separates from a rigid boundary) of flow of an incompressible, inviscid fluid sheet under the action of gravity over a rounded edge is studied. The fluid sheet flows upstream over a level bottom which joins smoothly with a rounded bed leading to a free overfall downstream. A nonlinear steady state solution of the problem is obtained, partially by a numerical procedure, which differs significantly from the corresponding known solutions for flow over a vertical bed. The location of the detachment point (rather than being specified) is determined as part of the solution and is found to be dependent on both the values of far upstream depth and far upstream Froude number.
Influence of the velocity ratio on the spatial instability of mixing layers
Authors: Monkewitz Peter A. , Huerre Patrick
Published: March 2003

The linear spatial instability of the tanh and Blasius mixing layers is studied for different values of the ratio between the difference and the sum of the velocities of the two co-flowing streams. The growth rate, phase velocity, and perturbation velocity distributions are determined numerically and the results are compared with expansions for small shear or low frequency. It is found that the maximum growth rate is approximately proportional to the velocity ratio. This is shown to be consistent with the observed variation of shear layer spreading rate with velocity ratio and with a recent model of flight effects on jet mixing noise.
Correlations of squared velocity and temperature derivatives in a turbulent plane jet
Authors: Antonia R. A. , Rajagopalan S. , Browne L. W. B. , Chambers A. J.
Published: March 2003

Correlations, in a turbulent plane jet, of squared time derivatives of three components of velocity and of squared time and spatial derivatives of temperature indicate a value for the exponent μ of about 0.2 for velocity and 0.25 for temperature.
Theory of a spheroidal probe in low-density continuum plasmas
Authors: Kamitsuma M. , Teii S.
Published: March 2003

A spheroidal probe theory for a low-density continuum plasma, i.e., one where the electron density is Ne ≲108 cm−3 and the gas pressure is P≳1 Torr has been developed using a spheroidal coordinate system in order to properly take into account the effect of the finite length of the probe. The numerical results of both the electron- and the ion-current characteristics are obtained for various values of Rp/λD ranging from 0 to 1, ε = Ti/Te from 0.1 to 1, and Cp = Lp/2Rp from 1 to 100, where λD is the Debye length, Rp and Lp are the probe radius and the probe length, Ti and Te are the ion and the electron temperature, respectively. Using these results, new methods to determine the electron temperature and the plasma space potential (consequently, the electron density) by practical measurements are also proposed and discussed.
Temperature gradient and electric field driven electrostatic instabilities
Authors: Morrison Philip J. , Ionson James A.
Published: March 2003

The stability of electrostatic waves to thermodynamic and electric potential gradients is investigated. A general instability parameter, ε = 2.6(εE+εp) +0.2εT, is identified which is related to thermodynamic gradients (εp and εT) and internal electric fields (εE). This parameter is evaluated at the instability threshold as a function of Te/Ti for both ion acoustic and electrostatic ion cyclotron waves. The major virtue of this analysis, other than its overall generality, is to show that thermodynamic gradients drive instabilities even when the internal electric field vanishes. This result does not emerge from previous analyses because skewing of the distribution function was not included in the dielectric.
Physical mechanism of wave-particle resonances in a curved magnetic field
Authors: Huba J. D. , Drake J. F.
Published: March 2003

The physical mechanism of wave-particle resonances in a curved magnetic field is investigated. Specifically, the energy exchange process between a wave and resonant curvature drifting particles is discussed (i.e., ω∼k⋅Vc, where Vc = v2∥/RcΩ is the curvature drift, Rc is the radius of curvature of the magnetic field, and Ω is the cyclotron frequency). A general expression for the wave damping/growth rate is derived based upon physical arguments. The theory is applied to the lower-hybrid-drift instability and nonlinear consequences are discussed.
Electron cyclotron heating experiments on the JFT-2 tokamak using an inside launch antenna
Authors: Moeller C. P. , Chan V. S. , La Haye R. J. , Prater R. , Yamamoto T. , Funahashi A. , Hoshino K. , Yamouchi T.
Published: March 2003

An electron cyclotron heating experiment is described in which 28 GHz microwave power is launched from the high field side (inside) of a tokamak discharge from a steerable phased array antenna exciting the extraordinary mode. The central temperature was doubled (from 600 eV to 1200 eV) with a power at the antenna approximately two-thirds the Ohmic input. An oblique launch of the extraordinary mode was found to heat more efficiently and to a higher density than either the perpendicularly launched extraordinary mode or the ordinary mode launched from the outside.
A generalized kinetic energy principle
Authors: Van Dam J. W. , Rosenbluth M. N. , Lee Y. C.
Published: March 2003

Using three single-particle adiabatic invariants, we derive an energy principle which generalizes that for the usual guiding center plasma in order to describe the low-frequency stability of a plasma containing an energetic nonhydromagnetic component (such as the annular electrons in an Elmo Bumpy Torus device).
A sufficient condition for stability of axisymmetric collisionless systems
Authors: Walstead A. E.
Published: March 2003

A sufficient condition for the stability of an axisymmetric mirror machine is obtained using the guiding center plasma model. The criterion is particularly suited to configurations with comparable transverse and longitudinal length scales, so-called short, fat equilibria. Under this ordering, the stabilizing effects of plasma compression is significant. These effects are included through the use of a positive definite lower bound on their contribution to an energy principle.
Free boundary field-reversed configuration (FRC) equilibria in a conducting cylinder
Authors: Spencer Ross L. , Hewett Dennis W.
Published: March 2003

Highly elongated field-reversed configuration (FRC) equilibria are computed in a straight conducting cylinder for the pressure profile p′(ψ) = cH(ψ), where H(x) is the Heaviside function. The equilibria are found by inverting the Grad–Shafranov equation by means of a Green’s function and by solving the resulting nonlinear integral equation. Long equilibria are obtained only for values of the constant c very near a critical value: the equilibria change from 2:1 elongated to infinitely long as c varies by only 0.3%. This criticial value of c is predicted by the average beta condition.
Stabilizing effect of a normal magnetic field on the collisional tearing mode
Authors: Nishikawa K.-I. , Sakai J.
Published: March 2003

A set of coupled eigenmode equations in a current sheet with a normal magnetic field is solved numerically for the collisional tearing mode. It is found that the normal magnetic field has a stabilizing effect. Furthermore, in the case of a very weak normal component, the classical results of Furth, Killeen, and Rosenbluth are recovered.
Radio frequency current generation by waves in toroidal geometry
Authors: Antonsen T. M. , Chu K. R.
Published: March 2003

The quasilinear generation of current by rf wave fields is investigated in toroidal geometry. A general expression is derived for the amount of current generated for a given wave-induced flux of particles. This expression should be of great practical value in assessing the various competing effects on current generation in toroidal geometry and is well-suited for implementation in a toroidal ray tracing code.
One-dimensional turbulent dispersion in convergent and divergent flows
Authors: Faller Alan J. , Mignerey Peter C.
Published: March 2003

A theory is presented that gives an analytical solution to the kinematic interaction of a convergent (or divergent) mean flow and turbulence for spatially constant convergence and homogeneous turbulence of a specified type. The turbulence is characterized by its mean square velocity, ∼(v2), and by its Lagrangian autocorection function. The problem is formally that of the Langevin equation, and analytical solutions for the time dependence of the ensemble-average variance of many fluid tracers are presented. These solutions are compared with numerical solutions obtained by calculating the Lagrangian motion of a large number of tracers.
Application of the Wiener–Hermite expansion to turbulence of moderate Reynolds number
Authors: Lee Chun-Ping , Meecham William C. , Hogge H. D.
Published: March 2003

The Wiener–Hermite expansion with a renormalized, time-dependent moving base is used to calculate the evolution of the energy spectra of several homogeneous, isotropic flows. The results compare well with laboratory experiments and with numerical simulation experiments. Wiener– Hermite calculations have been done previously for high Reynolds numbers by Hogge and Meecham [J. Fluid Mech. 85, 325 (1978)]with some success. In this work moderate Reynolds numbers are treated.
Wave heating models for ion-cyclotron heating in ELMO Bumpy Torus-Scale
Authors: Sperling J. L.
Published: March 2003

Wave heating of the ELMO Bumpy Torus-Scale (EBT-S) experiment in the ion-cyclotron range of frequencies will be strongly influenced by the geometry of the plasma. In particular, the short finite length of the mirror sections means that the electron bounce frequency is of comparable magnitude to the ion-cyclotron frequency. Consequently, the bouncing motion of trapped particles impacts the electron absorption of wave energy. Furthermore, the varying magnetic field strength along magnetic field lines influences the ion-cyclotron absorption of waves because the ion-cyclotron resonance conditions are satisfied only at discrete points along the field lines. Expressions are given for trapped and passing electron absorption as well as ion-cyclotron absorption. A numerical example is also discussed.
Analytic solution of the two-dimensional Fokker–Planck equation governing stochastic ion heating by a lower-hybrid wave
Authors: Malescio G.
Published: March 2003

The two-dimensional Fokker–Planck equation describing the ion motion in a coherent lower- hybrid wave above the stochasticity threshold is analytically solved. An expression is given for the steady-state power dissipation.
Heat transport properties and dynamics of a cold turbulent plasma blanket
Authors: Anderson D. , Lisak M.
Published: March 2003

An analytic investigation is made of the conductive heat transport properties of a cold plasma blanket, where the heat conductivity has been increased by turbulence due to a current-convective instability.
Return-current-driven instabilities of propagating electron beams
Authors: Uhm Han S. , Lampe Martin
Published: March 2003

A stability analysis is performed for the first nine transverse modes (azimuthal mode number plus radial mode number ⩽3) of a self-pinched relativistic electron beam propagating in a collisional plasma. Only frequencies ω in the range ωτd≪1 are considered, where τd is the dipole magnetic decay length. For such modes, the presence of plasma return current is the only destabilizing mechanism. Paraxial flow, space charge neutrality, and a flat radial profile of beam density are also assumed. Within these limitations, an exact analysis of the linearized Vlasov stability problem is carried out in closed form. For each mode, the instability threshold, growth rate, and conditions for oscillatory versus pure growth are determined. For beams with a moderate return current fraction, the hose, sausage, and axial hollowing modes appear to be particularly dangerous.
Weak turbulence theory of intense beam microwave experiments
Authors: Benford Gregory , Smith Dean F.
Published: March 2003

Recent intense beam experiments in microwave radiation are considered within the context of strong turbulence theory of the beam-plasma instability. A weak turbulence model for radiation at the plasma fundamental gives qualitatively correct power levels and suggests that the radiation itself is an important dynamical entity in the beam-plasma instability. Radiation in the region ω∼2ωp is weak, in agreement with experiment. Plasma inhomogeneities in the experiment of size approximately 0.3 cm can explain the low-frequency emission power level, and its dependence on the plasma density and external magnetic field. Understanding these processes may lead to use of radiation as a versatile diagnostic measurement of beam-plasma systems.
Comments on ‘‘Randomness of low-order models of two-dimensional inviscid dynamics’’
Authors: Lee Jon
Published: March 2003

Randomness of low-order models of two-dimensional invicid dynamics is commented. AIP
Acceleration of multi-species ions in CO2 laser-produced plasmas: Experiments and theory
Authors: Begay Fred , Forslund David W.
Published: March 2003

Experimental and theoretical results on the properties of CO2 laser-induced carbon and polyethylene (CH2) plasmas at laser intensities of ∼1015 W/cm2 are presented. The Thomson parabola technique is used to measure the ion velocity distribution in the underdense expanding plasma which is collisionless and isothermal. A model which treats the problem of the collisionless expansion of an isothermal electrostatic multi-cold-ion quasineutral plasma will be used to interpret the experimental results. Experiments and theory show that the effect of hydrogen in the CH2 target induces a cutoff in the carbon ion velocity distribution. Theory suggests that acceleration field attenuation effects modify the behavior of these plasmas. Data suggest that the space–time evolution of the ion velocity distribution is completed before an ionization-recombination equilibrium is reached. Experimental results from the underdense region are used to estimate plasma parameters near the critical surface, which show that the presence of hydrogen in the target apparently greatly reduces the thermal temperature near the critical surface, probably due to enhanced lateral energy transport.
Reply to comments by Karpman and Maslov
Authors: Ko K. , Kuehl H. H.
Published: March 2003

A reply to the comment on soliton propagation in slowly varying media is presented. (AIP)
The application of kinematic wave theory to wave trains and packets with small dissipation
Authors: Landahl Marten T.
Published: March 2003

The validity of kinematic wave theory for linear waves with small dissipation propagating through a homogeneous medium is examined with the aid of the higher-order theory of Chin. It is shown that both for nondissipative and weakly-dissipative waves the kinematic theory holds with errors of order ε2 for times of order ε−1 times the wave period, where ε is a measure of the nonuniformity of the wave train. For longer times, of order ε−2 times the period, secular terms arise, which makes the theory invalid when wave dispersion becomes vanishingly small. By selecting a complex wavenumber chosen such as to make the group velocity real, it is possible to remove the first-order secular terms and thus produce a modified theory uniformly valid within the longer time period. This modification is also applied to wave trains propagating in a nonhomogeneous medium. General solutions are presented for wave trains or packets of arbitrary initial conditions.