bluuebunny/crossref_metadata_2025 huggingface dataset:
Super-Alfvénic flow and collision free shock wave in a plasma wind tunnel
Authors: Kuriki Kyoichi , Inutake Masaaki
Published: February 2004

A super-Alfvénic and supersonic flow in a plasma wind tunnel were studied experimentally. The wind tunnel was constructed for the studies of the magnetohydrodynamic shock waves and wakes, and has features such as quasisteady flow and low fluctuation level. The Alfvén Mach number MA and ion acoustic Mach number M covered in the present experiment are MA = 1−4 and M = 2−6 A standing shock wave was found downstream of the magnetic-nozzle exit. The shock wave is collision free and the normal of the wavefront is parallel to the magnetic field. Macroscopic features of the shock wave were discussed with reference to the theoretical predictions of the magnetohydrodynamic and collision-free shock waves.
Hypersonic flows generated by parabolic and paraboloidal shock waves
Authors: Schwartz Leonard W.
Published: February 2004

A computer algorithm has been developed to determine the bluntbody flow fields supporting symmetric parabolic and paraboloidal shock waves at infinite free stream Mach number. Solutions are expressed in an analytic form as high-order power series, in the coordinate normal to the shock, whose coefficients can be determined exactly. Analytic continuation is provided by the use of Padé approximants. Test cases provide solutions of very high accuracy. In the axisymmetric case for γ = 75 the solution has been found far downstream where it agrees with the modified blast-wave results. For plane flow, on the other hand, a limit line appears within the shock layer, a short distance past the sonic line suggesting the presence of an imbedded shock. Local solutions in the downstream limit are discussed.
Electric field driven flute instabilities in a nonuniform collisional plasma
Authors: D'lppolito Daniel A. , Krall Nicholas A.
Published: February 2004

The stability of a magnetically confined nonuniform plasma column with a radial electric field is examined with a linear single-fluid theory including the effects of rotation, ion-neutral collisions and finite Larmor radius stabilization. The transition from the Rayleigh-Taylor instability in the collisionless limit to the Simon neutral-drag instability in the collision-dominated limit, and the effect of collisions on finite Larmor radius stabilization, is studied in detail. A numerical example is given and the application of the theory to experiments is discussed.
Turbulence in a cusp Q device
Authors: D'Angelo N. , Pécseli H. L. , Petersen P. I.
Published: February 2004

Spectral measurements are reported of plasma turbulence in the Cs plasma of a Q device, modified to a magnetic cusp geometry. The excitation mechanism for the fluctuations appears to be the centrifugal instability discussed by Chen. A transition from an f−5 to an f−3 power spectrum is observed as one moves from the hot plates to the midplane of the cusp.
Coherent production of energetic electrons in anomalous reflection and absorption of intense laser light
Authors: Manheimer Wallace M. , Klein H. H.
Published: February 2004

The rate at which electrons are transported from the body to the nonthermal tail of the distribution function in the nonlinear stage of reflective and absorptive parametric instabilities is computed. The calculation is performed by conserving energy and momentum between waves and particles in the nonlinear regime. For the case of reflection, the reflection coefficient and energy flux of nonthermal particles are computed. It is found that the principal effect of the trapped electrons is to increase the density gradient length scale by as much as a factor of twenty five, at given reflection coefficient. For absorption, the rate of production of energetic particles is found. Also, the transport of energetic particles into the core of a laser fusion plasma is examined.
Equilibrium of a toroidal plasma
Authors: Sudano J. Pantuso
Published: February 2004

A class of exact magnetohydrodynamic toroidal equilibrium solutions is found, which holds good for arbitrary aspect ratio.
Strong ion heating in a magnetic neutral point discharge
Authors: Ohyabu N. , Okamura S. , Kawashima N.
Published: February 2004

A sudden anomalous increase in the plasma resistivity at a magnetic neutral point is observed which results in fast energy dissipation and strong plasma heating. It appears earlier and its magnitude increases as (1) the plasma density is decreased, (ii) the discharge plasma current is increased, or (iii) the external quadrupole magnetic field is increased. When the sharp rise in the resistivity appears, the electron and ion temperatures rise abruptly up to the range of several keV within 0.5 μsec and about 10% of the initial energy stored in the capacitor (for the plasma current excitation) is converted into the ion thermal energy. This strong and efficient ion heating cannot be explained by a simple classical process and the role of turbulent waves should be important.
Magnetic field annihilation in a reversed-field current layer
Authors: Chen Y. G. , Chervin R. M. , Robertson S. , Taussig R. T.
Published: February 2004

Reversed-field current layer evolution with magnetic field annihilation is examined numerically using single-fluid, two-temperature, magnetohydrodynamic equations with anisotropic, classical transport properties. Self-pinching occurs with magnetic field reversal in the current layer. Very high local plasma temperatures and density are produced in the pinched current layer and magnetic field diffusion is inhibited. Numerical results are compared with experimental data.
Theory and experiment on radio-frequency plugging of magnetically confined plasma in an open-ended system
Authors: Watari Tetsuo , Hiroe Shinji , Sato Teruyuki , Ichimaru Setsuo
Published: February 2004

The theory of the rf plugging of a magnetically confined plasma in an open-ended system is presented; it takes explicit account of the collective effect brought about by the dynamic screening action of the plasma. The theory predicts a maximum efficiency of the rf plugging at an optimum frequency corresponding to a zero of the longitudinal dielectric constant. The plugging efficiency is calculated as a function of the plasma density, the strength of the rf field, and the intensity of the magnetic field. These theoretical predictions are compared with experimetal observations, demonstrating satisfactory agreement in over-all features. The results provide a useful scaling law associated with the concept of the rf confinement. The theory also offers an explanation for the discrepancy between the experimental values of the optimum frequency and those predicted by a conventional theory based on an individual-particle model.
Ion acceleration in a plasma focus
Authors: Gary S. Peter
Published: February 2004

The electric and magnetic fields associated with anomalous diffusion to the axis of a linear plasma discharge are used to compute representative ion trajectories. Substantial axial acceleration of the ions is demonstrated.
Nonresonant plasma heating by a single mode, beam-plasma instability
Authors: Conrad J. R. , Levine J. S. , Walsh J. E.
Published: February 2004

The variation of plasma temperature with the frequency and intensity of a single mode in a beam-plasma system has been measured. The results agree with the quasi-linear theory of the beam-plasma interaction.
Shock wave structures in weakly ionized gases using the Krook kinetic model
Authors: Masuda M. , Ikui T. , Murakami T.
Published: February 2004

The structures of the normal shock waves in weakly ionized nonequilibrium flows have been analyzed by the Krook kinetic models using the Maxwellian or the ellipsoidal distribution functions, and the calculated results were compared with those obtained from the bimodal approximations.
Unsteady magnetic boundary layer flow of power-law fluids
Authors: Djukic Djordje S.
Published: February 2004

The Galerkin approximation technique is used to solve the flow problem of an infinite plate immersed in a non-Newtonian power law fluid in the presence of a constant transverse magnetic field. The velocity outside the boundary layer depends exponentially on time.
Nonlinear evolution of parallel-propagating hydromagnetic waves
Authors: Cohen Ronald H. , Kulsrud Russell M.
Published: February 2004

The nonlinear evolution of plane hydromagnetic fluctuations propagating along the unperturbed magnetic field direction is considered. From an expansion of the ideal magnetohydrodynamic equations and the hydromagnetic shock jump conditions, it is shown that a wave in which the magnitude of the magnetic field is nonconstant steepens into a shock and subsequently evolves toward a purely Alfvénic fluctuations of lower mean energy density. Explicit expressions are derived for the asymptotic state and for the characteristic lines which describe the evolution toward that state. A class of fluctuations which includes linearly polarized waves is shown to evolve into rotational discontinuities. The results are applied to observations of hydromagnetic fluctuations in the solar wind.
Observations of the stable equilibrium and classical diffusion of field reversing relativistic electron coils
Authors: Phelps D. A. , Smith A. C. , Woodall D. M. , Meger R. A. , Fleischmann H. H.
Published: February 2004

Observations of high current relativistic electron coils are presented and interpreted theoretically. Electron coil self-magnetic field strengths up to almost twice that of the external magnetic field at the mirror center are observed. Lifetimes up to 30 μsec are related to the classical diffusion of electron coils in a stable equilibrium state. The diffusion mechanism is verified as inelastic small angle scattering of the relativistic electrons from a neutral gas background.
Randomization of the gyration phase through binary collisions
Authors: Momota Hiromu , Takizuka Tomonori
Published: February 2004

A criterion for the gyration phase being well randomized through binary collisions for a bounce motion of a charged particle in a magnetic mirror is investigated theoretically. The resultant criterion is seen to be easily satisfied even for the case of very rare collisions.
Kinetic theory of the resistive torque on a rotating cylinder
Authors: Gervois A. , Pomeau Y.
Published: February 2004

The resistive torque exerted upon a rotating cylinder by a rarefied gas may be computed by an expansion in powers of the inverse Knudsen number. The first correction diverges logarithmically, and the renormalized theory should replace the argument of the divergent logarithm by the Knudsen number.
Induced magnetic field for the Rayleigh motion of an insulated plate
Authors: Wilks Graham
Published: February 2004

The impulsive motion of an insulated plate in a transverse magnetic field is examined for fluids of small magnetic Prandtl number.
Stagnation-point flow in a rotating fluid
Authors: Davis R. W. , Ludford G. S. S.
Published: February 2004

The exact solution of the Navier-Stokes equations originated by von Kármán is shown to apply even when a stagnation-point flow is added. The numerical integration is carried through in five special cases, chosen for their relevance to previous work of Hömann, of Hannah, and of Benton as well as the “coffee-tin experiment” which started the investigation.
Kinetic theory approach to the vapor-phase phenomena in a nonequilibrium condensation process
Authors: Gajewski P. , Kulicki A. , Wiśniewski M. , Zgorzelski M.
Published: February 2004

The phenomenon of one-dimensional steady condensation of pure vapor at the plane surface of a liquid is considered from the kinetic theory viewpoint. The vapor is treated as a perfect gas without internal degrees of freedom. For the description of this problem the full nonlinear BGK model equation is used. For the solution of the BGK model equation the method of discrete ordinates is applied. The calculations are carried out for water vapor. As a result the temperature and density distributions in the vapor phase are obtained and also for a given temperature difference the net condensation molecular flux rate is determined, depending on the condensation and evaporation coefficients which are treated as parameters.
Application of line reversal method to measurement of shock flow electron temperature
Authors: Jeanmaire Peter
Published: February 2004

The electron temperature of a shock tube magnetohydrodynamic plasma was measured by the line-reversal method. In order to reduce the influence of self-reversal in the cool boundary layer on the measurement, the use of nonresonance lines of the potassium seeding was first explored theoretically, then confirmed by experiment. Best suited lines were selected by integrating the radiative transfer equation over both the wavelength and the width of the shock tube assuming a boundary-layer temperature profile. A lower limit to the population density of the upper level of the selected transition (4p-6s) was found from the rate equation for this level. The electron temperature distribution along the plasma column was measured using Moutet's double beam version of the line-reversal method. The measurements show good correspondence between the temporal evolution of the electron temperature in the center of the flow and the generator current. The discrepancy between the measured electron temperature and the gas temperature calculated from the shock Mach number is explained by the occurrence of nonequilibrium ionization.
Viscosity-dominated convective plasma diffusion
Authors: Okuda Hideo
Published: February 2004

It is shown that, in addition to the classical (D⊥ ∼ B−2), plateau (D⊥ ∼ B0), and Bohm (D⊥ ∼ B−1) diffusions, there is a new region of diffusion between the classical and the plateau regions where the diffusion increases with increasing the magnetic field. In this region, the lifetime of the convective cells is determined by the ion collisional viscosity and, therefore, this region is important for a plasma with large ion mass.
Formation of nonthermal ion tails in the ion acoustic instability
Authors: Manheimer Wallace M. , Flynn Robert W.
Published: February 2004

The rate at which ions are transported from the body to the nonthermal tail of the distribution function during the nonlinear stage of the ion acoustic instability is calculated self-consistently. The nonlinear stage is characterized by a very small growth rate and a tail whose population increases slowly in time. The calculation is done by conserving the energy and momentum of ions, electrons, and electrostatic fields in the linear and nonlinear regime. These two conservation laws give rise to two equations for growth rate and phase velocity.
Drifting oscillating two-stream instability
Authors: Johnston George L.
Published: February 2004

The theory of parametric excitation of plasma waves is applied to a plasma in which there is a static drift between electrons and ions. For appropriate values of drift speed and elevated electron-ion temperature ratio, there exists a solution of the dispersion relation and a threshold for instability at a frequency which is close to zero in the electron frame. This instability occurs for pump frequencies which are slightly below the Bohm-Gross frequency. It has some similarities to the oscillating two-stream instability in a plasma in which there is no static drift. An approximate analytic solution of the dispersion relation in the neighborhood of zero frequency is obtained.
Space-time interaction of opposed transverse waves in a plasma
Authors: Cohen Bruce I.
Published: February 2004

The interaction of two opposed, intense electromagnetic waves, whose difference frequency approximates the plasma frequency, is studied. Plasma heating ensues. Energy is transferred to the lower-frequency wave throughout a uniform plasma, but only in a resonance zone in a nonuniform plasma.
Frequency shift due to resonant particle diffusion in velocity space
Authors: Bornatic Marino
Published: February 2004

The shift in the frequency of an electrostatic mode due to modification of the ensemble average orbits is considered for an ensemble of electrostatically turbulent, unmagnetized plasmas.
Approximations to diffusion in a random velocity field
Authors: Thiebaux M. L.
Published: February 2004

The diffusion of a marked fluid particle is considered in a random incompressible, isotropic velocity field, stationary in space and time. The integrodifferential equations proposed earlier by Bourret and Saffman, for the time evolution of the probability density of marked fluid particles, are introduced and solutions are found for a Gaussian Lagrangian covariance function. An improved equation is derived by including the effects of higher-order moments. Solutions are found to be in good agreement with independent results based on fluid particle diffusion in a multivariate-normal field.
Viscous incompressible flow between eccentric coaxially rotating spheres
Authors: Munson B. R.
Published: February 2004

The motion of a viscous fluid contained between two eccentric rotating spheres is obtained as a perturbation solution valid through first-order terms in the Reynolds number and second-order terms in a parameter describing the eccentricity.
Finite-amplitude instability of the compressible laminar wake: Comparison with experiments
Authors: Liu J. T. C. , Gururaj P. M.
Published: February 2004

Detailed numerical results and comparison with wind tunnel experiments are presented. These include the nonlinear unstable region of the wake behind adiabatic and heated flat plates, the far wake of cooled and adiabatic wedges, and the bow-shock generated outer wake of an adiabatic circular cylinder. In general, it is found that disturbance energy production is primarily contributed by the Reynolds shear stress integral. However, the development of mean flow kinetic and thermal energy fluxes is primarily contributed by their respective streamwise diffusion fluxes due to the disturbance density fluctuation. The peaking of the averaged disturbance kinetic energy and the extent of mean flow decay is, in terms of the appropriately scaled streamwise distance, hastened by either (i) an increase of the Reynolds number for the same body geometry and surface thermal conditions; (ii) surface cooling for the same body geometry and Reynolds number; or (iii) an increase in the body length for the same wedge angle, Reynolds number, and surface thermal conditions.
Energy stability of a general viscoelastic simple fluid heated from below
Authors: Carmi S. , Sokolov M.
Published: February 2004

The energy theory is applied to investigate the stability of a general viscoelastic simple fluid heated from below. The linear theory predicts overstability for this configuration and the present energy results provide a sufficient condition for stability which coincides with the linear limit for the Newtonian case.
Transport in axisymmetric plasmas
Authors: Bernstein Ira B.
Published: February 2004

The general case of transport in axisymmetric fully ionized quasineutral plasmas is formulated for systems immersed in a strong magnetic field and close to local kinetic equilibrium. The particle density and temperature for each species, which depend on position only via the magnetic streamfunction, obey a closed system of transport equations involving coefficients which can be optimally computed via minimax variational principles. The electric field is eliminated from the transport equations, apart from the electrostatic potential which is obtained from a rate equation, as is the toroidal magnetic field. The magnetic streamfunction is determined by an elliptic boundary value problem. The theory goes over to previous work in the limit where the frequency associated with the guiding center motion of a representative particle in the absence of collisions is much greater than the collision frequency, and vice versa.
Convection in a horizontal porous gap
Authors: Wolanski E. J.
Published: February 2004

The criterion for the onset of the convective flow in a thin horizontal saturated porous gap heated from below, is a function of the appropriate boundary conditions, but no subcritical instability arises.
Rayleigh-Taylor instability in the “shallow-water” approximation
Authors: Book D. L. , Ott Edward
Published: February 2004

The nonlinear evolution of the Rayleigh-Taylor instability in the long wavelength limit is investigated for an incompressible fluid supported against gravity (or inertial forces) by a massless fluid and bounded above by a rigid wall. This limit is characterized by L ≫ η, where L is a horizontal scale length and η is the thickness of the dense fluid. In plane geometry, the equations are identical to those of shallow water theory, but with the sign of the gravitational acceleration reversed. They are rewritten in the Riabouchinsky (gas-dynamic analogy) formulation and solved numerically. The shallow water approximation permits a solution for the motion of the interface without reference to the detailed motion of fluid in the interior.
Resolution of the electric shock tube precursor into component causes
Authors: Mills J. I. , Naraghi M. , Fowler R. G.
Published: February 2004

Previous investigations of the electric shock tube precursor demonstrated a method for distinguishing between any wave precursors and photo-preionization accompanied by light scattering. Continuation of this research has led to characterization of the chief element in the wave precursor as a modified potential (breakdown) wave supported by voltages generated by electromagnetic induction in the ground circuit. Although electric forces must be present for its existence, the unusual properties of the precursor derive from the auxiliary support it receives from the driver plasma by transport processes. After this potential wave precursor has been completely suppressed there remains a small residual component of the total precursor phenomenon composed of simple electron diffusion ahead of the main shock.
Laser-induced instabilities in homogeneous plasmas
Authors: Jorna Siebe
Published: February 2004

A linearized theory is presented for the dominant instabilities in a laser-driven homogeneous plasma. The distinction between convective and absolute instabilities, and their effect on thresholds in finite plasmas, is especially emphasized. Thus, it is found that the effective thresholds for stimulated Brillouin and Raman scattering are higher than those generally quoted. The analysis is further extended to two dimensions, and it is shown that stimulated Brillouin scattering is primarily excited in the backward direction. The broader backscattering profile for stimulated Raman scattering exhibits a cutoff angle approaching 90° near a “critical” surface at one-fourth the critical density. At this density a strong instability is predicted corresponding to the excitation of Langmuir waves.
Nonlinear theory of the collisional drift-wave instability
Authors: Monticello Donald A. , Simon A.
Published: February 2004

Experiments have shown the existence of a steadily oscillating drift mode above a critical magnetic field, Bc, in fully ionized Q machines. The amplitude and frequency shift of this mode are calculated as a function of Δ = (B − Bc)/Bc for small Δ. The self-consistent analysis includes temperature variation and shows that non-linear saturation is due to flattening of the density gradient by zero-frequency harmonic generation. The results are compared with experiment and show good agreement.
Hydromagnetic stability of a current-carrying pinch with noncircular cross section
Authors: Laval G. , Pellat R. , Soule J. S.
Published: February 2004

The hydrodynamic stability of a free-boundary pinch with noncircular cross section is investigated. The analysis is restricted to nonflute modes. The stability conditions for a pinch with elliptical cross section and flat current density are obtained. For arbitrary shapes and current profiles, an asymptotic stability criterion is given for kink and tearing modes of large azimuthal wavenumbers.
Effect of magnetic field space perturbations in toroidal plasmas in the intermediate diffusion regime
Authors: Casati G. , Lazzaro E. , Orefice A.
Published: February 2004

The realistic situation of slight, space-dependent magnetic perturbations superimposed on the usual magnetic field in axisymmetric toroidal machines is treated on the basis of kinetic equations in the drift approximation. It is shown that the radial component of such perturbations may cause an enhanced plasma loss.
Turbulent dispersion of ion cyclotron waves: Theory and experiment
Authors: Benford Gregory , Rynn Nathan , Thomson J. J. , Williamson W. S.
Published: February 2004

Particles in or near resonance with a plasma wave undergo perturbations of their equilibrium orbits due to stochastic fields. This contributes added diffusion damping to any wave in the plasma. In a steady-state experiment this mechanism can cause the saturation of a wave. A theory of the current-driven ion cyclotron instability modified by turbulent damping based on addition of a damping term to the linear dispersion relation is presented. The turbulent damping is interpreted as an upper bound on the linewidth of the wave. As current varies, the frequency and line width of the mode alter. Once the frequency of the ion cyclotron wave is lowered to nearly the ion cyclotron frequency, mode coupling to an ion-acoustic wave seems to occur, damping the oscillations. Until this point, detailed predictions of theory agree well with experiment.
Straight and toroidal plasma equilibria with an intense relativistic electron current component
Authors: Mondelli Alfred , Ott Edward
Published: February 2004

The equilibrium of an axisymmetric, large aspect-ratio, finite temperature toroidal plasma enclosed by a perfectly conducting toroidal container is studied analytically. The new feature of the analysis is the presence of a relativistic electron beam which circulates around the torus thus producing a poloidal magnetic field in addition to the external field and the field created by currents in the plasma. This problem may be of interest in connection with recent toroidal beam injection experiments at Cornell University and in tokamaks. The equilibria are obtained from the relativistic virial theorem. Specific examples are given wherein the plasma pressure is characterized by its dependence on the magnetic flux function and the relativistic electron beam is characterized by an electron distribution function which is a delta function in energy and canonical momentum in the toroidal direction.
Behavior of interfacial tension near the tricritical point of the 3He-4He system
Authors: Papoular M.
Published: February 2004

From scaling arguments, the interfacial tension of the 3He−4He system is expected to vanish as (Tc − T)2, as the tricritical point is approached.
Bifurcation of elliptic equilibrium
Authors: Strauss H. R.
Published: February 2004

The magnetohydrodynamic equilibrium of an elliptical, cylindrical plasma, with uniform current density, is not uniquely determined by the boundary conditions.
Scaling laws for condensation in nozzle flows
Authors: Hagena Otto F.
Published: February 2004

Scaling laws are derived which define the source parameters (temperature, pressure, and nozzle size) of all those nozzle flows that show the same condensation effects for a given gas or gas mixture.
Fluctuation-dissipation theorems on the basis of hydrodynamic propagators
Authors: Szu H. H. , Szu S. C. , Hermans J. J.
Published: February 2004

Hydrodynamic propagators of forces are formulated and studied in the following cases: for uniform temperature, neglecting convection or using Oseen's linearization, with or without compressibility, and also for nonuniform temperature. Discussions and comparisons are given wherever possible. Such a propagator formalism is useful in cases of hydrodynamic interactions among solid bodies, as well as thermodynamic fluctuation forces. It is found that the velocity correlation functions describe a source with time-dependent or -independent Oseen propagators. The correlation of pressure fluctuations, which exists even in the absence of dissipation, agrees with the result derived from the relaxation function of the mechanical fluctuation-dissipation theorem, as well as with the thermodynamic equilibrium correlation. The correlation of temperature fluctuations describes a diffusion process of the variance κ/ρ0cp when cp = cν. In accordance with Curie's principle of nonequilibrium thermodynamics, it is found that the transverse vector field is not coupled to the scalar fields. Finally, a possible comparison with a wind tunnel experiment on temperature fluctuations is indicated.
Collective contributions to the electric microfield distribution in a turbulent plasma
Authors: Spatschek K. -H.
Published: February 2004

The electric microfield distribution for weakly turbulent electron-ion systems is calculated using an individual-collective approach. The possibility of separation into collective ion, collective electron, and individual contributions due to electrons and ions is discussed. Analytical expressions for the collective electron and the collective ion microfield distribution are presented in terms of the turbulent spectrum. The results for the total distribution in the case of ion-sound turbulence show significant deviations compared with those of plasmas in thermodynamic equilibrium.
Parametric instability arising in inhomogeneous plasmas
Authors: Whitfield D. W. A.
Published: February 2004

A new, electrostatic, one-dimensional plasma instability is described. It arises when an external electric field is applied to a cold plasma in which both species have initial density perturbations. Both computer simulations and fluid calculations have revealed the instability, which, for sufficiently large perturbations, has a growth rate greater than the two-stream instability.
Mode coupling description of ocean wave dynamics
Authors: West Bruce J. , Watson Kenneth M. , Thomson J. Alex
Published: February 2004

The velocity potential and surface displacement for deep ocean waves are expanded in a set of eigenmodes of the linearized wave equations. Nonlinear effects are then represented by mode coupling. The important processes are related to resonances. A numerical computation is given to illustrate the diffusing of energy in wavenumber space, phase locking, and the Benjamin-Feir experiment.
Planing of a flat plate at high Froude number
Authors: Ting L. , Keller J. B.
Published: February 2004

The planing of a plate of width L with velocity U at high Froude number [U / (gL)1/2≫ 1] on the surface of an incompressible fluid is considered. The solution of this problem by Green [A. E. Green, Proc. Cambridge Phil. Soc. 32, 67 (1936)] which omits gravity (g = 0), is inadequate because it yields a one-parameter family of solutions rather than a single solution. In addition, it yields a free surface height which tends to — ∞ far from the plate. These two defects are removed by treating Green's solution as the leading term in an inner expansion of the flow. An appropriate outer expansion is constructed by using the linear theory of surface waves with a suitable pressure distribution moving along the free surface. Matching of the two solutions determines the free parameter in the inner expansion, and yields the correct behavior of the free surface far from the plate. From the solution, graphs of the lift coefficient of the plate are obtained. An important feature of the solution is the inclusion of the effect of the impact on the free surface of the jet thrown up by the plate.
Angular motions of freely falling spheroidal hailstone models
Authors: Kry P. R. , List Roland
Published: February 2004

The free fall behavior of rotating oblate spheroids with Reynolds numbers of 4 × 104 to 4 × 105 is studied by solving semiempirical Eulerian equations of motion which use a quasistatic approximation for aerodynamic forces and torques. The angular motions are classified in terms of solutions to the restricted set of equations in which the center of mass falls uniformly. One class of solutions, named symmetric gyration, is relevant for studies of the symmetric growth of hailstones because symmetrically equivalent points on the surface of a spheroid are equally exposed to the flow. For large hailstones with horizontal total angular momentum, critical frequencies sufficient for symmetric gyration are in the range of 2-6 Hz (Strouhal numbers 0.005 to 0.01), they increase with increasing axis ratio, decrease with size, and are independent of the density ratio spheroid/air. Solutions to the full equations of motion show that the rotational energy of a symmetrically gyrating spheroid increases with time. This results in an increase in nutational amplitude which depends on the spheroid, its spin rate and its nutation amplitude. Such an effect occurs because the horizontal velocity, which tends to align with the horizontal major axis, causes the aerodynamic torque to have an oscillating vertical component in phase with the oscillating angular velocity about the vertical. A similar interaction prevents a steady helical motion.
Stability of Poiseuille flow in a thin elastic tube
Authors: Garg V. K. , Rouleau W. T.
Published: February 2004

It is shown that an elastic tube can cause instability of Poiseuille flow to infinitesimal axisymmetric disturbances, unlike a rigid tube in which the flow is always stable. Neutral curves are determined for both temporal and spatial stability. The region of instability are large for small values of Young's modulus E, but become smaller with increasing E. For E > 690 N/cm2(1000 psi), the flow is stable at all Reynolds numbers, and the eigenvalues for the least stable modes are nearly the same as have been found for rigid tubes.
Statistical mechanics of “negative temperature” states
Authors: Montgomery David , Joyce Glenn
Published: February 2004

The dynamics of two-dimensional interacting “line” vortices is identical to that of the two-dimensional electrostatic guiding center plasma. Both are Hamiltonian systems and are therefore susceptible to statistical mechanical treatments. The predictions of the microcanonical ensemble are explored for this sytem. Interest focuses primarily on the regime in which the interaction energy is high enough to be above the Onsager “negative temperature” threshold. Calculations of the probability distribution for a component, by means of the central limit theorem, are carried out in the manner of Khinchin. The probability distribution of a component reduces to the usual Gibbs distribution in the regime of positive temperatures, and is still explicitly calculable for negative temperatures. The negative temperature states are neither quiescent nor spatially uniform. Expressions for the temperature are explicitly provided in terms of the total particle energy and particle number. A BBGKY hierarchy can be derived for both temperature regimes. A Vlasov approximation on the first pair of BBGKY equations leads to the differential equation (two dimensions) ∇2ψ +sinh ψ = 0. The charge (vortex) density has an expectation value proportional to ∇2ψ. Numerical simulations involving solutions of the equations of motion of 4008 particles are presented.
Determination of the speed ratio for a body moving in a collisionless gas
Authors: Pack D. C. , Sharp J. M.
Published: February 2004

The determination of the speed ratio for a body in flight in a rarefied medium is very difficult. One possible approach is to bleed gas through two tubes at different orientations to the mean flow and to try to relate the speed ratio to the pressure ratio obtained from measurements made in the gauge volumes. The equations relating these ratios have been developed for collisionless Maxwellian flow past a plane wall in which are set molecularly rough tubes at angles ±β to the normal to the wall. Calculations have been carried out to find the pressure ratios for speed ratios S = 12, 1, 2, 3, 4, and 6 for β = 14 π rad and ratios of tube length to radius l/a = 1, 2, 4, 6, 8, 12, and 16. These results show that the longer tubes are advantageous in giving a greater rate of change of pressure ratio for speed ratios not in excess of 2, but for higher speed ratios the pressure ratio becomes rather insensitive to change in such tubes. For a range of speed ratios up to 6 it would be necessary to restrict l/a to a value in the neighborhood of unity. Results are also included for the probability of ultimate transmission of molecules from points on the tube walls into the gauge volume and for the density of direct impact from the free stream onto the tube walls.
Stability of a current-carrying fluid with a free surface in a transverse magnetic field
Authors: Wang Chung-Yi
Published: February 2004

The stability of a viscous, incompressible, electrically conducting fluid with a free surface in a transverse magnetic field is investigated. A horizontal layer of fluid is set in motion by the combined action of the horizontal electric current and a vertically imposed magnetic field. An eigenvalue problem is formulated for infinitesimal disturbances and is solved by the regular perturbation method. It is found that if the electromagnetic effects are sufficient to overcome the stabilizing effect of gravity, the flow is unstable. The instability is due to the stratification of electric conductivity and to the longitudinal Lorentz force. Topological features of the (c1)i curves for various cases are depicted. The roles played by the electric current as well as the magnetic field on the stability of the flow system are discussed briefly.
Field-generating thermal instability in laser-heated plasmas
Authors: Tidman D. A. , Shanny R. A.
Published: February 2004

The intense thermal energy flux emanating from the critical layer in laser-produced plasmas is shown to generate an instability that derives from the magnetic field dependence of the thermal conductivity. This implies that B fields, with their attendant nonuniform heating effects, will occur even in uniformly irradiated spherical pellets or plane slabs. These fields may play a role in attempts to compress pellets for fusion, for example, by being partially trapped and amplified by compression in the interior of a pellet.
Raman and Brillouin scattering of electromagnetic waves in inhomogeneous plasmas
Authors: Liu C. S. , Rosenbluth Marshall N. , White Roscoe B.
Published: February 2004

Raman and Brillouin scattering of an electromagnetic wave in an inhomogeneous, expanding plasma are studied. Application to laser-pellet irradiation is considered.
Effect of collisions on the plasma line of the electron density fluctuation spectrum
Authors: Swift Daniel W.
Published: February 2004

The Klimontovich-Dupree formalism is used to investigate the effect of electron-neutral collisions on the plasma line of the electron density fluctuation spectrum. The Fourier transform of the fluctuation electron number density is calculated by integrating along electron trajectories consisting of straight-line segments joined at electron-neutral scattering sites. It is shown that the scattering process itself results in the excitation of plasma oscillations and contributes to the plasma line intensity. The electron density autocorrelation is calculated by ensemble averaging over the initial positions and velocities of all the electrons in the system and averaging over a transition probability describing the electron-neutral collisions. The transition probability is expanded as a power series in the collision frequency. The plasma line spectrum is calculated in the limit that the electron travels many wavelengths between collisions. The principal result of this is that collisions enhance the intensity of the plasma line by as much as a factor of six when the collision frequency exceeds the Landau damping decrement. This result is of most interest in attempts to observe the electron plasma line with the incoherent-scatter radar in the E-region of the ionosphere when the electron density is enhanced by auroral bombardment.
Theory of the negative electrostatic potential well in spherical geometry
Authors: Swanson D. A. , Cherrington B. E. , Verdeyen J. T.
Published: February 2004

A theoretical analysis has been made of the negative electrostatic potential well formed by electron injection in spherical geometry. Poisson's equation has been modified to include spreads in the total energy of the injected electrons as well as spreads in their angular energies. Solutions have been obtained for both rectangular and Boltzmann distributions in total and angular energy. The resulting solutions agree very well with the experimental data, showing a potential well of approximately parabolic radial dependence whose depth depends essentially linearly on the injected current and whose well depth is relatively independent of the anode voltage for a constant anode current.
Effect of magnetic line fanning on microinstabilities in minimum-β wells
Authors: Baldwin D. E.
Published: February 2004

The fanning of magnetic lines in a minimum-B mirror machine creates distortion of the constant phase surfaces of ion-cyclotron loss cone modes. This distortion can stabilize infinite-medium modes which occur for narrow bands of k⊥.
First-order reactant in homogeneous turbulence before the final period of decay
Authors: Kumar Prem , Patel S. R.
Published: February 2004

Following Deissler's approach the concentration fluctuation of a dilute contaminant undergoing a first-order chemical reaction is studied. Two-, three-, and four-point correlation equations have been obtained and to make the set of equations determinate, the terms containing quintuple correlations are neglected in comparison to those containing lower-order correlation terms. The solution obtained gives the state of concentration fluctuation in a homogeneous turbulence between its initial and final periods.
Convective rolls driven by internal heat sources
Authors: Peckover R. S. , Hutchinson I. H.
Published: February 2004

Two-dimensional convection in a layer of volumetrically heated fluid confined between free horizontal boundaries has been studied using numerical experiments. The dependence on the appropriate modified Rayleigh number of the maximum horizontally averaged temperature and of the fraction of thermal flux emerging from the upper surface has been found for RaH ≤ 80 RaHC.
Laminar boundary layer over a body of revolution at extremely high incidence
Authors: Wang K. C.
Published: February 2004

Results of exact, full three-dimensional solutions of the incompressible laminar boundary layer over a prolate spheroid at an extremely high incidence are presented. This extremely high incidence problem is characterized by features reflecting the predominance of the circumferential flow over the meridional flow and, more importantly, by a change of separation pattern from an open type to a closed type. These features include much larger circumferential skin friction than meridional skin friction and that the limiting streamlines are more closely oriented along the parallels.
Flow due to an impulsive rotation of infinite disk
Authors: Katagiri M.
Published: February 2004

Numerical solutions for the extended von Kármán rotating disk problem to the case of impulsive rotation from rest are given and used to discuss the ultimate approach to the steady state.
Diffusion of plasma confined in stellarator with Εt > Εh
Authors: Miyamoto Kenro
Published: February 2004

Diffusions of plasmas confined in the stellarator with εt > εh are considered in the region of very low frequency where εt and εh are the field modulations of toroidal and helical terms. The dependence is different from the opposite case of εh > εt.
Phase relations in isotropic turbulence
Authors: Betchov R. , Lorenzen C.
Published: February 2004

The velocity fluctuations at one point of a strongly turbulent air flow, produced by arrays of jets, are analyzed up to eighth order correlations. The odd order correlations show the proportionality factors already found in grid and boundary layer turbulence. Two numerical models are described, which rely on a simple nonlinear process to attempt to explain the observed results. The first model generates a signal where the relations between the phases of the Fourier components are limited to triplets. Except for short range correlations, the agreement with turbulent results is good. However, in the range of small, but still inertial, eddies, significant differences appear. The second model simulates abrupt jumps in velocity. It gives qualitative agreement through the entire range, thus showing that strong coupling of the phases, by occasional discontinuities can produce the same appearance of weak phase relations in the range of medium to large eddies, as well as the short range behavior.
Transmission of singularities through a shock wave and the sound generation
Authors: Ting Lu
Published: February 2004

The interaction of a plane shock wave of finite strength with a vortex line, point vortex, doublet or quadrupole of weak strength is studied. Based upon the physical condition that a free vortex line cannot support a pressure difference, rules are established which define the change of the linear intensity of the segment of the vortex line after its passage through the shock. The rules for point vortex, doublet, and quadrupole are then established as limiting cases. These rules can be useful for the construction of the solution of the entire flow field and for its physical interpretation. However, the solution can be obtained directly by the technique developed for shock diffraction problems. Explicit solutions and the associated sound generation are obtained for the passage of a point vortex through the shock wave.
Free electron and vibrational temperature nonequilibrium in high temperature nitrogen
Authors: Lazdinis Šarun̄as S. , Petrie S. L.
Published: February 2004

The degree of coupling between free electron and nitrogen vibrational temperatures in weakly ionized nozzle expansions of shock-heated nitrogen has been determined. Free electron temperatures were measured with Langmuir probes while nitrogen vibrational temperatures were determined with a new instrument based on the electron beam technique. The resultant data were analytically correlated by coupling chemical nonequilibrium with nitrogen vibrational and free electron temperature nonequilibrium. It was found that a vibrational loss factor of 7 × 10−4 and an effective translational-rotational loss factor of 4.26 × 10−4 best predicted the measured electron temperature distributions.
Energetic particle distribution in a toroidal plasma with neutral injection heating
Authors: Cordey J. G. , Core W. G. F.
Published: February 2004

The energetic ion distribution resulting from the injection of high-energy neutrals into a toroidal plasma has been derived. An appropriate kinetic equation which contains the angular scattering, friction, and diffusion of the energetic ions by the background particles, charge exchange on the background neutrals, and acceleration of the ions by the electric field has been solved analytically by use of the WKBJ method. Collisions of the energetic ions with the faster moving electrons results in some of the ions increasing their energy above the injection energy. The width of this ``high-energy tail'' is shown to depend upon the electron temperature and the electric field. An estimate of the effect upon the width of this tail of collisions between the energetic ions themselves is also given. Finally, illustrated examples of the various significant physical processes are presented.
Synchronous quenching of drift-wave instability
Authors: Odajima K. , Nishida Y. , Hatta Y.
Published: February 2004

Synchronous quenching of drift-wave instability is investigated experimentally. The measurements show resonance phenomena similar to that of ion-sound instability. The result is quantitatively compared with a phenomenological theory which includes a linear growth and a nonlinear saturation source term.
Saturation of beam-plasma instability in a lossy plasma
Authors: Carr W. , Jones R. , Boyd D. , Manickam J. , Seidl M.
Published: February 2004

For the beam-plasma instability with ω > ωce in the limit of a cold, weak beam effective energy transfer to the plasma is observed. This is found to agree with the one-dimensional beam trapping calculation when linear cyclotron damping is included.