bluuebunny/crossref_metadata_2025 huggingface dataset:
Nonlinear analysis of laminar boundary layer flow over a periodic wavy surface
Authors: Bordner Gary L.
Published: March 2003

The problem of laminar, incompressible flow over a periodic wavy surface is treated as a first-order perturbation to the boundary layer flow on a flat surface. The analysis demonstrates that some nonlinear terms in the disturbance boundary-layer equations are first order if the wave amplitude and disturbance sublayer thickness are comparable in magnitude. Further, the theory predicts that the nonlinear effects are confined to the thin sublayer adjacent to the wavy surface. Computer-generated, nonlinear solutions are presented for sinusoidal waves with a range of wave amplitudes, including cases with local separated flow regions.
Nearly extensional flows
Authors: Pountney D. C. , Walters K.
Published: March 2003

Constitutive equations appropriate to nearly extensional flows are derived. The main conclusion is that three functionals are required in contrast to the thirteen involved in the corresponding case of nearly viscometric flows.
Velocity slip of gas mixtures in free jet expansions
Authors: Raghuraman P. , Davidovits P.
Published: March 2003

A theoretical model is presented for calculating the species velocity of a gas mixture expanding as a free jet through a sonic orifice into vacuum. Calculations were done for two systems (a) a binary gas mixture of argon seeded in helium, and (b) a ternary mixture of uranium hexafluoride isotopes seeded in helium. The results are compared with previous calculations and with experiments.
Distorted quasi-equilibrium distribution functions in isotropic plasmas containing metastable atoms. Application to helium
Authors: Peyraud Nelly
Published: March 2003

The influence of metastable atoms on the equilibrium distribution function of an isotropic plasma is studied. It is shown that there is a quasi-stationary solution to this problem resulting from the balance between electron-electron interactions, inelastic and super-elastic collisions. The distribution function is composed of thermal Maxwellian electrons and of a bump at the excitation energy potential of the metastables. Evaluation of the electronic density in this bump is made for the case of helium.
Beam generation in foil-less diodes
Authors: Chen J. , Lovelace R. V.
Published: March 2003

A study is made of the generation of intense relativistic electron beams in rectangular and cylindrical foil-less diodes. The diode space charge is treated self-consistently. The electron emission from the cathode is assumed to be space-charge-limited. A strong axial magnetic field is assumed to prevent the electrons from reaching the anode surface(s) directly, and to constrain the electron motion to be approximately one-dimensional. A useful dimensionless measure of the diode potential φc is ε≈[mec2/(eφc)]1/2, with me and e the electron rest mass and charge, and c the speed of light. Properties of the diodes are first analyzed in the ultra-relativistic limit, ε=0, where the condition for space-charge-limited emission gives rise to a linear singular integral equation. This equation is solved for rectangular diode geometry, and the solutions are studied in detail. In particular, the diode impedance is independent of φc, and the beams are, in general, hollow. The beam particle kinetic energy flux, Γp, decreases as the beam width, b, increases; for b=a, Γp=0, where a is the diode width. A treatment of the diodes is then given for small but nonzero values of ε. For finite ε, there is a nonrelativistic Child–Langmuir sheath of thickness ≈εa at the cathode surface. For b=a, Γp is shown to be proportional to φc3/2.
Interaction of 1.06 μm laser radiation with variable Z̃ targets
Authors: Shay H. D. , Haas R. A. , Kruer W. L. , Boyle M. J. , Phillion D. W. , Rupert V. C. , Kornblum H. N. , Rainer F. , Slivinsky V. W. , Koppel L. N. , Richards L. , Tirsell K. G.
Published: March 2003

Parylene (C8H8) and tungsten-glass (W2O/P2O5) disks have been irradiated with 150–400 psec Nd:YAG-glass laser pulses focused to diameters of 250–300 μm with flux levels in the 1013–1015 W/cm2 range. An extensive array of diagnostics was used to measure the temporal and energy distributions of the focused laser light at the target, the angular distribution of the scattered laser light, the x-ray spatial and spectral emission characteristics, and the emitted ion and electron distributions. Analysis of the experimental results indicates that the laser-plasma interaction was characterized by a variety of collective phenomena which appeared stronger in the tungsten-glass experiments.
Upper-bound current to a cylindrical probe in a collisionless magnetoplasma
Authors: Rubinstein J. , Laframboise J. G.
Published: March 2003

Upper bounds are presented for ion or electron collection by a cylindrical electrostatic probe inclined at an angle to a uniform magnetic field. Over a wide range of conditions, these bounds are better than those derived earlier by Laframboise and Rubinstein.
Relaxation of initial probability density functions in the turbulent convection of scalar fields
Authors: Dopazo Cesar
Published: March 2003

The evolution of an initially binary (zero unity) scalar field undergoing turbulent and molecular mixing is studied in terms of conservation equations for the probability density function of the scalar property. Attention is focused on the relaxation of the dynamic system to a state independent of the intial conditions. A few existing methods are discussed and evaluated and a new mechanistic model is proposed. Classical iteration techniques are used to obtain an equation for the single point probability density and the unperturbed Green’s function. It is suggested that use of the true Green’s function or perturbed propagator of the system might be necessary in order to obtain the correct evolution of the probability density function.
Shear stabilization of the Rayleigh–Taylor modes
Authors: Hameiri Eliezer
Published: March 2003

The effect of flow shear on the stability of rotating ideal magnetohydrodynamic equilibria is investigated. It is found that a large enough shear can sometimes completely stabilize the flute(k=0) modes. The most notable result is a theorem which provides for an analytical determination of the exact number of unstable modes. A weaker sufficient condition for stability is also derived.
Heating of a fully ionized collision-free plasma with a high amplitude compressional wave
Authors: Läuter R. , Stampa A. , Tuczek H. , Wulf H. O.
Published: March 2003

A plasma source is described, which produces a fully ionized, collision-free and magnetized initial plasma with a low content of contaminations and good homogeneity in linear geometry. The plasma is subjected to a high frequency field with frequencies near 2 ωci. Measurements show that the external field is coupled effectively to the compressional wave which transfers its energy to the plasma by some collisionless dissipation mechanism. The observed phenomenon show no resonance at multiples of the ion cyclotron frequency and the temperature is higher than expected from direct resonance of the particles at ω=2ωci; it is assumed that turbulent effects are responsible which are excited by electron-ion drifts smaller than the thermal velocity of the ions.
Magnetic field distribution and image field index for short axial length E layers
Authors: Woodall D. M. , Lovelace R. V. , Meger R. A. , Fleischmann H. H. , Berk H.L.
Published: March 2003

A study is made of the influence of different current density distributions on the magnetic field distributions and effective image field indices for axially short astron E layers or rings. Significant differences are found between the newly calculated values of the image index and those derived from long-layer models. For short axial lengths, which correspond to most observed electron rings, both the magnetic field distributions and the effective image indices do not depend strongly on the current distribution within the ring. Good agreement is found between the theoretical stability limits implied by the presented field indices and the ’’dump’’ levels observed in the RECE-Berta experiment.
Solutions to the mass continuity equation obtained by introducing a change of variable
Authors: Tempelman Wayne
Published: March 2003

For a one-dimensional flow situation involving a source, a simple closed form solution for the mass density is obtained for the mass continuity equation by introducing a change in variable. Instead of functionalizing the flow in terms of the velocity, the starting time or transit time is used. This type of functionalization allows the individual trajectories to be obtained by algebraic or geometric means, avoiding the nonclosed form solution associated with integrating the velocity. For a time varying system, the integrals of mass, momentum, and energy all involve the mass density expression. By eliminating the mass density expression from these integrals and expressing the velocity in terms of one of the new time parameters, a set of equations is obtained which may be easier to solve than the original set of equations.
Studies of ion-acoustic wave properties by pulsed CO2 laser scattering
Authors: Watterson R. L. , Peratt A. L. , Derfler H.
Published: March 2003

The dispersion of ion-acoustic plasma waves is investigated using pulsed CO2 laser scattering and homodyne detection techniques. Broadening of the scattered spectrum due to spatial wave damping is demonstrated.
Comparison of a correlation term-discard closure for decaying homogeneous turbulence with experiment
Authors: Deissler R. G.
Published: March 2003

Turbulence decay is calculated by using experimental initial conditions and discarding quadruple-correlation terms in the correlation equations. Agreement with experiment is good only for moderately small times, but there are no perceptible negative spectral energies even at large times.
Magnetohydroelectric waves in a fluid dielectric
Authors: De Bibhas R.
Published: March 2003

A theoretical wave behavior in a magnetized fluid dielectric is deduced. The wave consists of oscillations of magnetic, kinetic, and electrostatic energies.
Laminar boundary layer on an impulsively started rotating sphere
Authors: Dennis S. C. R. , Ingham D. B.
Published: March 2003

The problem of determining the development with time of the flow of a viscous incompressible fluid outside a rotating sphere is considered. The sphere is started impulsively from rest to rotate with constant angular velocity about a diameter. The motion is governed by a coupled set of three nonlinear time-dependent partial differential equations which are solved by first employing the semi-analytical method of series truncation to reduce the number of independent variables by one and then solving numerically a finite set of partial differential equations in one space variable and the time. The calculations have been carried out on the assumption that the Reynolds number is very large. The physical properties of the flow are calculated as functions of the time and compared with existing solutions for large and small times. A radial jet is found to develop with time near the equator of the sphere as a consequence of the collision of the boundary layers.
Exact solitary ion acoustic waves in a magnetoplasma
Authors: Ray Dipankar
Published: March 2003

Solitary ion acoustic waves in a magnetoplasma have been studied by Shukla and Yu [J. Math. Phys. 19, 2506 (1978)]. A more rigorous study confirms the conditions that Shukla and Yu said would be necessary for humps. However, it is shown that a density cavity is also possible in the limiting case.
Nonlinear evolution of the bump-on-tail instability
Authors: Shoucri Magdi M.
Published: March 2003

The nonlinear evolution of a bump-on-tail Maxwellian distribution function, to an initially unstable perturbation, is studied numerically. The results indicate that the time asymptotic solution is a Bernstein–Greene–Kruskal equilibrium.
Stability effects of external conducting sheets on magnetically contained plasmas
Authors: Weston V. H.
Published: March 2003

A comparison of the effect of different configurations of the outer conducting surface on the stability of a cylindrical circular plasma of radius a and length L is made. As opposed to the usual configuration of a concentric circular outer conductor, ’’fins’’ or radial conducting surfaces lying on the field lines with the nearest edge a distance c from the center of the plasma are considered. The comparison procedure is based upon estimating the difference of the perturbed energy integrals for the various configurations. The usual surface perturbations of the form exp[i (kz±nϑ)], k∼0 are treated. Fins of zero thickness have no effect on the n = 0 mode; however, they do tend to stabilize the important n = 1 mode. For a/c sufficiently small, radial planes ϑ = 0, π, and ±π/2 tend to have the same stabilization effect on the n = 1 mode as a concentric outer cylinder of radius b, where b∼√2c. The interaction between the opposite fins was taken into account.
Effect of convection on magnetohydrodynamic kink stability
Authors: Dagazian R. Y.
Published: March 2003

A magnetohydrodynamic boundary layer analysis is performed treating the effect of the convective term of the equation of motion near the singular surface. The nonlinear equations in this region are separable; the time evolution of the solution is determined by the Riccati equation and nonlinear harmonics are generated at wavenumbers which are multiples of the fundamental. This solution is matched to the linear solution in the outer region yielding modes reminiscent of resistive instabilities which nevertheless are not normal modes of the system.
Electrostatic bounce modes in mirror plasmas
Authors: Sharp William M. , Berk H. L. , Nielsen Carl E.
Published: March 2003

Bounce modes are plasma waves which result from the coherent bounce motion of trapped particles. Such modes can occur in mirror devices when the relative spread in electron bounce frequencies is small. When electron bounce modes have perpendicular wavelengths comparable to typical ion gyroradii and frequencies near the ion gyrofrequency or some harmonic, they couple effectively with the ions and can be destabilized by a loss-cone ion distribution. A one-dimensional integral dispersion equation for electron bounce modes in a mirror plasma is derived and solved numerically for the wave eigenfrequencies. Predicted threshold densities for bounce mode instabilities in the Baseball I and Baseball II devices are compared with experimental values. Good agreement is found for Baseball II, but in Baseball I the predicted thresholds are consistently below observed values.
Some solutions pertaining to the resonant interaction of long and short waves
Authors: Ma Yan-Chow , Redekopp L. G.
Published: March 2003

The evolution equations describing the interaction of long and short waves when they are resonantly coupled are discussed. Envelope-pulse soliton solutions of these equations are constructed using the method of Hirota and the existence of a breather state is shown. The wavetrain modulational characteristics and envelope-hole solitary wave solutions are also presented.
Response of a tokamak plasma to particle and momentum sources
Authors: Stacey W. M. , Sigmar D. J.
Published: March 2003

The response of an axisymmetric toroidal tokamak plasma to first-order particle and momentum sources is investigated. The momentum sources drive coupled poloidal and toroidal mass flows and electrostatic field evolution which relax to asymptotic values on a time scale characteristic of the dominant viscous or external drag mechanism. The asymptotic steady-state momentum balance provides the necessary condition to completely determine the ambipolar potential, the particle fluxes, and currents in the flux surfaces and, hence, to determine transport fluxes across flux surfaces. Transport fluxes are driven across flux surfaces both by interspecies collisional momentum exchange, the usual case, and by momentum exchange between the plasma and external sources and/or drags. A generalized Ohm’s law is obtained and used to determine how particle and momentum sources drive parallel currents and alter the evolution of the q profile. The theory is formulated for arbitrary plasma cross sections, beta, and collision regimes.
The interaction of 1.06 μm laser radiation with high Z disk targets
Authors: Rosen M. D. , Phillion D. W. , Rupert V. C. , Mead W. C. , Kruer William L. , Thomson J. J. , Kornblum H. N. , Slivinsky V. W. , Caporaso G. J. , Boyle M. J. , Tirsell K. G.
Published: March 2003

Gold disks have been irradiated with 1.06 μm laser light at intensities between 7 × 1013 and 3 × 1015 W/cm2, and pulse lengths between 200 and 1000 psec. Due to the high Z and long pulse, inverse bremsstrahlung becomes an important absorption mechanism and competes strongly with resonance absorption and stimulated scattering. In addition to measured absorptions, data on the temporal, spatial, angular, and spectral characteristics of the x-ray emission are presented. Temporally and spectrally resolved back-reflected light, and polarization-dependent sidescattered light are detected, providing estimates for the amount of stimulated scattering and of the coronal electron temperature. Inhibited electron thermal conduction and nonlocal thermodynamic equilibrium ionization physics play key roles in bringing numerical simulations of these experiments into agreement with all of the above-mentioned data.
Nonlinear behavior and turbulence spectra of drift waves and Rossby waves
Authors: Hasegawa Akira , Maclennan Carol G. , Kodama Yuji
Published: March 2003

Spectrum cascade in drift wave turbulence in a magnetized plasma as well as Rossby wave turbulence in an atmospheric pressure system are studied based on a three-wave decay process derivable from the model equation applicable to both cases. The decay in the three-way interaction occurs to smaller and larger values of ‖k‖. In a region of large wavenumbers this leads to the dual cascade; the energy spectrum cascades to smaller ‖k‖ and the enstrophy spectrum to larger ‖k‖, similar to the case of two-dimensional Navier–Stokes turbulence. In a small wavenumber region a resonant three-wave decay process dominates the cascade process, and an anisotropic spectrum develops. As a consequence of the cascade, zonal flows in the direction perpendicular to the direction of inhomogeneity appear which presents a potential implication for the particle confinement in a turbulent plasma.
Mode coupling of modulational instabilities
Authors: Himmell Lewis C.
Published: March 2003

A general formalism is developed to described the nonlinear evolution associated with the parametric decay of an intense, coherent electromagnetic wave into an electrostatic wave, its second harmonic, and scattered electromagnetic waves in a homogeneous plasma. It is assumed that all waves are coherent, and that the system is in a regime in which pump depletion may be neglected. Two classes of solutions are found. One class is explosively unstable, while the other consists of growing aperiodic oscillations. The evolution of modulational modes is discussed.
Coalescence of magnetic islands
Authors: Pritchett P. L. , Wu C. C.
Published: March 2003

A detailed numerical analysis has been conducted of the instability described by Finn and Kaw in which parallel currents in neighboring islands tend to coalesce into larger units. The existence of this coalescence instability in the ideal magnetohydrodynamic limit is confirmed, but no evidence is found for a threshold in island width. The linear growth rates are found to be rapid compared with those for purely resistive processes, and the linear mode structure has only a weak dependence on resistivity. In the nonlinear regime, saturation of the mode in the ideal case is observed due to flux piling up at the X point, while in the nonideal case the merging process is observed to proceed to completetion.
Unified theory of tearing modes
Authors: Mahajan Swadesh M. , Hazeltine R. D. , Strauss H. R. , Ross David W.
Published: March 2003

A unified theory of tearing modes in slab geometry is presented. All known results are readily derived from our general dispersion relations. Several new results are derived and discussed, and the inter-relatonship between various tearing modes is established.
Stochastic ion heating by a lower hybrid wave: II
Authors: Karney Charles F. F.
Published: March 2003

The motion of an ion in a coherent lower hybrid wave (characterized by ‖k∥‖<<‖k⊥‖ and ω≳≳Ωi) in a tokamak plasma is studied. For ions satisfying v⊥≳ω/k⊥, the Lorentz force law for the ions is reduced to a set of difference equations which give the Larmor radius and phase of an ion on one cyclotron orbit in terms of these quantities a cyclotron period earlier. These equations exhibit stochastic behavior when the wave amplitude exceeds a threshold. The stochasticity threshold is given a simple physical interpretation. In addition, the difference equations are used to derive a diffusion equation governing the heating of the ions above the stochasticity threshold. Far above the stochasticity threshold, ion Landau damping is recovered. By including the effects of collisions, the heating rate for the bulk ions is obtained.
Spectral characteristics of vortex breakdown flowfields
Authors: Garg A. K. , Leibovich S.
Published: March 2003

Laser-Doppler anemometer measurements upstream and in the wakes of vortex breakdowns of bubble and spiral types are described. Spectral analysis of the data indicates prominent oscillations in the wakes at less than 10 Hz. These oscillations correspond closely to theoretical predictions of the linearly most unstable normal modes of the time-averaged mean flow profiles. The oscillations are more energetic, and vortex core expansions are greater for flows with a bubble form of vortex breakdown, which is therefore regarded as the stronger form of breakdown.
Free oscillation in a rotating spherical shell
Authors: London S. , Shen M. C.
Published: March 2003

Free oscillations of an incompressible inviscid fluid in a rotating spherical shell are studied by means of the ray method, which is different from the conventional approach. Axisymmetric modes covering the whole sphere and asymmetric modes trapped in equatorial regions bounded by critical circles of constant latitude as well as in regions off the equator bounded by caustics are discovered. The anomalies at poles and critical circles of the ray method expansion are removed by means of uniform asymptotic expansions. The equations for the resonance frequencies of each of the various modes of oscillation are studied numerically.
Stability of a Stokes’ layer of a dusty gas
Authors: Drew Donald A.
Published: March 2003

The stability of a Stokes’ layer of a particle-fluid mixture is discussed. A set of coupled Orr–Sommerfeld equations governing the evolution of infinitesimal disturbances is derived. For low concentrations of coarse dust, it is found that for sufficiently large values of the particle relaxation time, the flow is unstable. Decreasing the particle relaxation time (by increasing the drag) eventually stabilizes the flow.
Convective cells and transport in toroidal plasmas
Authors: Hassam A. B. , Kulsrud R. M.
Published: March 2003

The properties of convective cells and the diffusion resulting from such cells are significantly influenced by an inhomogeneity in the external confining magnetic field, such as that in toroidal plasmas. It is shown, first, that the zero-frequency convective cell of the homogeneous medium (vortex) is transformed into the interchange flute mode in the presence of the field inhomogeneity. For stable interchange profiles, this has the effect of reducing the step size of the diffusion process. Second, in an inhomogeneous field, convective motions damp by magnetic pumping at a rate typically much faster than perpendicular viscous damping. This reduces the lifetime of the cell. The convective diffusion in the presence of a field inhomogeneity is estimated. For a thermal background, this diffusion is shown to be substantially smaller than classical diffusion. The influence of the field inhomogeneity is also shown to be significant for nonthermal backgrounds.
Radial expansion of a self-pinched beam with distributed energy
Authors: Haftel M. I. , Lampe Martin , Aviles J. B.
Published: March 2003

The structure and radial expansion of a relativistic particle beam are calculated in the presence of Coulomb scattering. The beam is assumed to be self-pinched and paraxial, but to have a distribution in energy. For the case in which the beam energy spread is small enough to satisfy (βγ)minβ−1γ−1≳1/2, solutions are found in which the entire beam expands self-similarly at an exponential rate proportional to β−1γ−1, where β≡v/c, γ−2≡1−β2, and the bar denotes the average over γ. The beam profile is calculated exactly in this case. If the inequality is not satisfied, low-γ particles expand faster than the main beam, at an exponential rate proportional to (2βγ)−1. Approximate time-dependent solutions, including initial transients, are presented for both cases.
Instability condition for confined waves with ergodic ray trajectories
Authors: Ott Edward
Published: March 2003

Unstable plasma waves which follow ergodic ray trajectories in a confined region are considered. It is argued that under certain circumstances, application of the ergodic theorem yields a useful method for calculating growth rates and stability thresholds.
Generalized procedure for exact solutions in magnetohydrodynamics
Authors: Shivamoggi Bhimsen K. , Uberoi Mahinder S.
Published: March 2003

Lin’s procedure is generalized to obtain Uberoi’s results as a special case. Uberoi’s solution is shown to be valid for fluids with infinite as well as finite electrical conductivity. It is also possible to build some dependence on the coordinate perpendicular to the plane of flow into this solution.
Total dispersion of a scalar quantity in turbulent flow
Authors: Chevray R. , Venkataramani K. S.
Published: March 2003

A general approach to the problem of the dispersion of a scalar quantity in a turbulent flow is given. The essential feature of this formulation is the consideration of the motion of isoconcentration surfaces. Use of this continuum kinematic concept, while preserving the exact results for both the limiting cases of zero molecular diffusivity and no fluid motion, enables the study of the dispersion of scalar quantities, like heat, without the use of physical concepts which are inconsistent with the continuum field description. It is shown that the effect of the interaction of the molecular and turbulent diffusion processes is such that the total dispersion of the scalar is less than the sum of the individual dispersions due to fluid motion alone and the direct effect of molecular diffusivity. Of the two terms arising from the interaction, the first one obtained by a simple approximation to the position field is identical to that obtained by an entirely different method. The additional term which was not found in the earlier studies varies as the square of the time. A preliminary extension to the dispersion of a specie of negligible molecular diffusivity undergoing a first-order chemical reaction shows that this method can also be extended to other related problems.
On soliton amplification
Authors: Leibovich S. , Randall J. D.
Published: March 2003

A modified Korteweg–de Vries equation that permits wave amplification or damping is considered. A ’’terminal similariry’’ solution is identified for large times in amplified systems. This asymptotic result is confirmed by a series of numerical computations.
Confinement of a plasma column by ablation fronts from cold gas plugs
Authors: Liese Wolfgang , Ahlborn Boye , Armstrong Bruce
Published: March 2003

A cylindrical plasma column of about 1–2 eV temperature and ne ≈ 1016 cm−3 is confined and compressed in the axial direction by an ablation front supported with a specific power in the range W/ρ1 = 108–5×109 W cm/g. Pressure and particle velocity are measured as a function of W/ρ1 and compared with model predictions.
Self-similar expansion of a plasma into a vacuum
Authors: Mora Patrick , Pellat R.
Published: March 2003

The Boltzmann equilibrium for electrons has been an ad-hoc assumption of previous work about self-similar plasma expansion in vacuum. Using Boltzmann’s relation, one finds a linear electrostatic potential as a solution of the self-similar expansion. It is first shown that in such a potential, the electron behavior is exactly solvable. As a result, one finds that the exact electron density differs substantially from the Boltzmann equilibrium for moderate values of the self-similar parameter. The complete calculations of the self-similar expansion, without any assumption about the equation of state of the electrons, is presented. It is shown, in particular, that half the electron density depletion in logarithmic units is compensated for by the self-consistent modification of the electric potential. Finally, the effect is analyzed in terms of energy exchange between the electrons and the ions in the expansion.
Kinetic theory of evolution of anisotropic plasmas
Authors: Pao Young-ping
Published: March 2003

A kinetic theory is constructed to evaluate the evolution and motion of an anisotropic axisymmetric plasma caused by collisional effects and pressure anisotropy. The relationship to neoclassical transport theory is also discussed.
Vlasov-fluid stability of a rigidly rotating theta pinch
Authors: Seyler C. E.
Published: March 2003

The stability of a rigidly rotating theta pinch is investigated using the Vlasov-fluid model. The main differences between the present and the asymptotic theory are due to the effect of resonant ions present in the exact Vlasov-fliud equations. An analytical explanation of the resonant ion effects is given.
Parametric instabilities and ion heating in a two ion-species plasma
Authors: Lin C. C. , Lin A. T. , Okuda H.
Published: March 2003

Parametric instabilities and the associated ion heating in the presence of two-ion species have been studied using a one-dimensional, quasi-neutral particle simulation model. At an early stage the heating is due to trapping or resonance heating of the decay waves. When the average Larmor radius reaches half the excited electrostatic wavelength, the heating becomes stochastic.
Production and flow of plasma in ion beams
Authors: Hooper E. B. , Anderson O. A. , Willmann P. A.
Published: March 2003

Steady plasma flow is analyzed for the case where a positive- or negative-ion beam penetrates and ionizes background gas (or vapor). The work of previous authors is extended to treat nonuniform beam densities that fall to low values at the transverse plasma boundary, and to include gas densities that are nonuniform along the beam axis. These nonuniformities give a two-dimensional plasma flow problem that is analyzed using a fluid model. The effect of unusually low gas density on the plasma flow is discussed; for negative-ion beams, the electron density becomes much smaller than the beam density and space-charge neutralization is maintained by a reduction in plasma flow. When there is a large local gas density, as in a gas cell, the resulting high electron density is also localized to the same region by the nature of the flow.
Axial eigenmodes for long −λ∥ waves in plasmas bounded by sheaths
Authors: Chen Francis F.
Published: March 2003

Waves such as drift waves and lower hybrid oscillations in a plasma are sensitive to the degree to which charge neutrality can be maintained by electron flow along the magnetic field. When the plasma is bounded axially, the sheath conditions on the end plates determine the parallel wavelength. It is found that the nature of the bounded modes depends on whether the motion of electrons is resistive or inertial. If it is resistive, the sheath matching conditions can be satisfied by standing waves with the proper wavelength. If it is inertial, pure standing waves are not possible; there must also be a variation of phase along B. Application is made to two-ion hybrid waves in connection with isotope separation.
Stabilization of trapped-electron shear-Alfvén instabilities by temperature gradient
Authors: Ross David W. , Mahajan Swadesh M. , Hazeltine R. D. , Strauss H. R.
Published: March 2003

Localized shear-Alfvén modes with large m numbers are shown, numerically, to be strongly damped by the collisionless electron response in the presence of a temperature gradient. The trapped-electron drift-tearing instability is stabilized by this effect in a tokamak unless the inverse aspect ratio exceeds a critical value, typically between 0.1 and 0.2. Analytical models demonstrate the scaling of these results with plasma parameters.
Diocotron instability of a relativistic hollow electron beam
Authors: Uhm Han S. , Siambis John G.
Published: March 2003

The diocotron stability properties of a relativistic hollow electron beam are investigated within the framework of the macroscopic, cold fluid model, in which the electron motion is assumed to be laminar. The stability analysis is carried out for the case of a sharp boundary density profile, including the important influence of relativistic effects and fractional charge neutralization on the stability behavior. It is found that the growth rate of instability is proportional to 1/γb2, thereby being reduced considerably by increasing the electron energy γbmc2. Moreover, the fractional charge neutralization plays a significant role in the stability behavior, particularly for the relativistic electron beam.
Ponderomotive effects and magnetic field generation in radiation plasma interaction
Authors: Mora Patrick , Pellat R.
Published: March 2003

A kinetic theory of ponderomotive effects and magnetic field generation is presented. For a comparison with standard fluid theories, explicit equations for momentum and energy conservations are established. As an example, it is shown that collisions do not lead to the usual resistive drag. In the important case of magnetic field generation via resonant absorption, three regimes with different behavior are found. In the collision-dominated regime of the parameters, the main source of the magnetic field is the off-diagonal terms of the particle pressure tensor. An intermediate regime appears when the nonlinear effects are collisionless and the amplitude of electromagnetic field due to the resonance absorption mechanism is limited by the plasma resistivity. In the collisionless regime, the validity of published results is extended by a self-consistent nonlinear calculation. As a result, the distribution function of electrons may include suprathermal tails, and the magnetic field generated does not appear explicitly in the formula.
Magnetosheath effects on cylindrical Langmuir probes
Authors: Szuszczewicz Edward P. , Takacs Peter Z.
Published: March 2003

The response of cylindrical Langmuir probes in magnetoplasmas is studied from a perspective which focuses on the relative magnitudes of Larmor radius and sheath size. The approach results in a classification for magnetic field effects which involves not only the magnetic field strength but also the plasma parameters of density, temperature, and the applied probe potential. It is specifically shown that a 0.25 G field can have similar effects on the current collection properties of the probe in an ionospheric plasma (Ne≈106 cm−3) as a 30 kG field would have in a hot, dense laboratory plasma (Ne≈1015 cm−3). The classifications are found to agree with new experimental results collected in an ionospheric plasma. The data also show: (a) the effects of probe orientation on electron current collection from magnetoplasmas; (b) that these effects can be important even when the electron Larmor radius is larger than the radius of the probe; and (c) that substantial magnetic field effects occur when the probe’s sheath is comparable to or greater than the Larmor radius.
Natural transition frequency of Hagen–Poiseuille flow
Authors: Maki Hiroshi
Published: March 2003

When Hagen–Poiseuille flow is naturally changed from laminar to turbulent, frequencies of pressure fluctuation in the transition region are measured by means of highly sensitive pressure transducers installed at the inner wall of the circular pipe. The frequency of the pressure wave at minimum transition Reynolds number nearly agrees with the frequency corresponding to the minimum critical Reynolds number for the neutral stability curve obtained experimentally by azimuthal disturbance.
Axial flow in trailing line vortices
Authors: Uberoi Mahinder S. , Shivamoggi Bhimsen K. , Chen Sin-Sung
Published: March 2003

Axial flow in the core of a laminar steady trailing vortex from the tip of a semi-infinite wing is analyzed assuming small departure of the axial velocity from the free-stream velocity. It is further assumed that the axial pressure gradient is determined by the swirl velocities of an ideal infinite line vortex in which the radial and the associated axial velocity variations are neglected in the equation for the angular momentum. The axial and lateral variations of the axial velocity depend on the strength of the vortex and initial axial velocity distribution which must be specified at some station behind the wing except at the virtual origin of the vortex where a nonintegrable singularity exists. Numerical solutions for the axial velocity are obtained using the axial pressure gradient given by the line vortex and analytical solutions are obtained using an equivalent axial pressure gradient with good agreement between the two sets of axial velocity distributions. Resolution of the previous uncertainties in this field is given which were due to the unrecognized singularity at the virtual origin of the vortex. Using the calculated axial velocity the neglected radial and the associated axial fluxes of angular momentum are determined and the limits of validity of the theory presented here in terms of a suitably defined vortex Reynolds number and a nondimensional distance measured from the virtual origin of the vortex are given.
Stationary striations in an argon plasma as a bifurcation phenomenon
Authors: Goldstein Ronald A. , Huerta Manuel A. , Nearing James C.
Published: March 2003

The formation of stationary striations in an argon plasma due to the development of an instability is studied using the equations for the competing plasma population species. The nonlinear dynamic stability of the system is analyzed using a two-time perturbation procedure. The unstable uniform steady state bifurcates to a new state with a sinusoidal density variation in space leading to the formation of balls of glowing plasma. This is analogous to phenomena of structure formation that appear in chemical reactions and biological processes.
Stability of axisymmetric field-reversed equilibria of arbitrary ion gyroradius
Authors: Sudan R. N. , Rosenbluth M. N.
Published: March 2003

An  energy principle  is developed that leads to sufficient conditions for treating the low frequency stability of axisymmetric, field-reversed equilibria, e.g., ion rings, ϑ pinches, and field reversed mirrors. Particles that carry the azimuthal current are described in the Vlasov formalism allowing for arbitrary gyroradius while the background plasma is approximated by the two-fluid equations. Two special cases, viz., a long, thin P layer and a thin ion ring of large aspect ratio, are examined in detail.
Parametric decay of lower hybrid waves in a plasma: Effect of ion nonlinearity
Authors: Tripathi V. K. , Liu C. S. , Grebogi C.
Published: March 2003

The contribution of ion nonlinearity to the coupling coefficients for parametric decay, quasi-mode decay, oscillating two-stream instability, and modulational instability of a lower hybrid pump (k0≠0) has been obtained by solving the full Vlasov equation for magnetized ions. It is seen that the contribution of ions is important only for decay into a Bernstein wave of short perpendicular wavelength (ω≫kzve, k⊥ρi≫1). A comparative study of various channels of decay reveals that the oscillating two-stream instability and nonlinear Landau damping by electrons are the predominant channels in the high density region. Modulational instability and the decay into an ion acoustic wave are seen to be irrelevant to tokamaks.
Computer simulation of nonlinear interaction between a cold beam and a weakly collisional plasma
Authors: Abe Hirotada , Fukumasa Osamu , Itatani Ryohei , Naitou Hiroshi
Published: March 2003

The spatial growth of the instability and the nonlinear interaction between a small cold beam and a warm background plasma are examined by means of particle simulation. Up to the first maximum in the amplitude oscillation of the wave, quantitative measurements confirm the predictions based on the single wave model: the magnitude of the growth rate, monochromaticity of the unstable mode, the maximum wave amplitude, and the phase space orbits of the beam electrons. After the first maximum of the wave amplitude, the spatial dependence of the wave amplitude cannot be explained by the single wave model predictions and the wave power is anomalously overdamped by a factor of 0.1 smaller than the predicted value in the first minimum. The extended single wave model equations suggest that this anomalous phenomenon is caused by weak collisions of the order of ν/ωp∼10−3 within the background plasma.
Turbulent heating studies in a tokamak
Authors: Mascheroni P. L. , Krall N. A. , Bengtson R. , Kochanski T. , Jancarik J. , Phillips P. , Stinnett R.
Published: March 2003

A model for bulk plasma (r≲7.5 cm) neglecting an annular region of about 2 cm of the Texas turbulent torus experiment during the rise time of the current (1 μsec) is described. The predicted poloidal and current density profiles show good agreement with the experimental values, and the temperature profiles are within the experimental error. The basic framework is provided by the Maxwell and fluid equations with a self-consistent anomalous collision frequency picture which uses quasi-linear theory and is saturated to agree with particle simulation results. The profiles show a strong skin effect and consequently, lack of heating of the core of the plasma. A significant amount of energy is found in the tail of the electron distribution function.
Steady-state solutions for laser plasmas in planar geometry
Authors: Perez J. D. , Payne G. L.
Published: March 2003

Global steady-state solutions of the plasma hydrodynamic equations in planar geometry are generalized to include heat conduction both in front and in back of the critical surface. Constraints on the plasma parameters which must be satisfied in order to obtain solutions which reflect the important characteristics of the full time-dependent problem are derived. This yields some insight into the dynamics of laser plasmas.
Helmholtz instability of a vortex sheet in uniform shear flow
Authors: Kiya Masaru , Arie Mikio
Published: March 2003

The effect of background vorticity on the instability of a vortex sheet is theoretically described by an inviscid linear stability analysis. The background vorticity increases the growth rate of the deformed vortex sheet whose vorticity is of the same sign as the background vorticity.
Interaction of tearing modes
Authors: Satya Y. , Schmidt G.
Published: March 2003

A fully developed tearing mode modifies the magnetic field profile. The effect of this profile modification on the linear growth rate of a different tearing mode in a slab and cylindrical geometry is investigated.
Ion ring dynamics and angular momentum conservation
Authors: Lovelace R. V.
Published: March 2003

For arbitrary perturbations or changes of an ion-ring plasma system in an axisymmetric container, the total angular momentum of the system is not, in general, a constant of the motion.
Comments on ’’Relaxation processes in plasmas with magnetic field’’
Authors: Kaiser Thomas B.
Published: March 2003

Velocity sapce fokker−planc coefficients obtained in an investigation of the temperature relaxation of a magnetizaed plasma differ from those obtained by other workers in thensor structue. Although the diffusion tensor is in error, it is shown that the relaxation rates are unaffected by the mistake.
Spectrum of curvature radiation from laser heated dense plasmas
Authors: Leubner C.
Published: March 2003

The spectrum of the nonthermal emission arising from the irradiation of a dense plasma by very intense linearly polarized laser light, as recently discussed qualitatively by other authors, is evaluated quantitatively by the method of steepest descents. It turns out that the directional properties of the radiation pattern differ essentially from those expected by invoking an analogy with synchrotron radiation.
Impact of nonequilibrium ionization and recombination processes on the evaluation of laser-produced plasmas
Authors: Matzen M. Keith , Pearlman Jay S.
Published: March 2003

A Lagrangian hydrodynamics code is used to provide the temperature and density parameterization for a coupled set of rate equations which describe the number densities of the ionization stages in a laser-produced, expanding plasma. Comparison of the steady state and rate equation ion density distributions indicates that time delays in the ionization of the plasma can affect x-ray calculations whereas the calculation of the freezing out of the recombination processes in the plasma is necessary to predict signals from ion diagnostics.
Beam-plasma interactions in a filled waveguide immersed in an applied axial magnetic field
Authors: Ottinger P. F. , Guillory J.
Published: March 2003

A fully electromagnetic linear stability analysis is used to investigate beam-plasma interactions in a filled cylindrical conducting waveguide. The system is immersed in a finite applied axial magnetic field, and it assumed that the electron gyroradius is small compared with the waveguide radius. The effects on stability of a small spread in the perpendicular and parallel beam momentum are considered. Particular attention is focused on the two-stream and beam cyclotron instabilities, and it is shown that the cyclotron instability can grow faster than the two-stream instability for ωce≳ωpe when the beam is sufficiently relativistic.
Effects of finite radial beam geometry and magnetic self-fields on beam-plasma interactions in a plasma filled waveguide
Authors: Ottinger P. F. , Guillory J.
Published: March 2003

The stability analysis of a beam-plasma filled waveguide presented previously will be extended to include radial beam geometry effects and azimuthal magnetic self-field effects. Here, the dispersion equations cannot be solved analytically, therefore, the equations must be integrated numerically. Because boundary conditions are specified at both r=0 and r=Rw (i.e., at the conducting wall), this is a two-point boundary value problem and solutions are sought using a generalized shooting method. This shooting technique is described and then used to solve the fully electromagnetic linear dispersion equations, in order to investigate radial beam geometry effects and azimuthal magnetic self-field effects on the wave and stability properties of a bounded beam-plasma system immersed in an applied axial magnetic field.
Motion of three vortices
Authors: Aref Hassan
Published: March 2003

A qualitative analysis of the motion of three point vortices with arbitrary strengths is given. This simplifies and extends recent work by Novikov on the motion of three identical vortices. Using a phase diagram technique, the possible regimes of motion are classified according to the signs of the arithmetic, geometric, and harmonic means of the three vortex strengths. For the special case where the vortex strengths (κ1,κ2,κ3) take the values (+κ,+κ,−κ), the diagram has an interpretation in terms of the scattering of a neutral pair by a single vortex. Quantitative details are presented for this case. If the harmonic mean of the three vortex strengths is zero, the triangle of vortices can collapse to a point in a finite time for certain initial conditions.