bluuebunny/crossref_metadata_2025 huggingface dataset:
Observation of ion heating near cyclotron harmonics using a radio frequency modulated electron beam
Authors: Hsieh C. L. , Lieberman M. A. , Shepp T. A.
Published: February 2004

Ion heating near the ion cyclotron frequency and its harmonics has been observed using a modulated electron beam injected into the low-density afterglow of a beam-generated plasma. Ion energies of 200 eV for He, 500 eV for D, and 700 eV for H have been measured.
Parametric effects as the mechanism for energy spreading in wave number space of the drift instability
Authors: Chu T. K. , Hendel H. W. , Simonen T. C.
Published: February 2004

By a feedback method, the wave-energy spreading in wave number space of the drift instability in the transition from oscillatory to turbulent regime is shown to be parametrically driven by linearly unstable modes.
Infinite-β limit of the drift instability
Authors: El-Nadi A. , Rosenbluth Marshall N.
Published: February 2004

Drift waves can be excited in a uniform pressure very high-β plasma because of the existing density and temperature gradients. The growth rate is calculated and an estimate for the resulting diffusion is given.
Suitability of the waveguide probe technique for measuring electron plasma temperature
Authors: Singer A. , Minkowski J. M.
Published: February 2004

It is shown that it is frequently not meaningful to compare the temperatures of shock-heated plasma determined by means of a waveguide probe with the electron plasma temperatures predicted by shock-wave theory. A numerical example is given, using published data for argon.
Effect of a Coriolis force on the stability of plane Poiseuille flow
Authors: Wollkind R. , DiPrima R. C.
Published: February 2004

The stability of an exact solution of the Navier-Stokes equations for the flow between two parallel horizontal plates due to a constant reduced pressure gradient in a system rotating about a vertical axis is studied. For zero rotation the stability problem reduces to the classical Orr-Sommerfeld equation for the stability of plane Poiseuille flow. The variation of the critical Reynolds number with rotation is determined by an expansion procedure for small values of the dimensionless rotation parameter (Taylor number). The effect of small rotation is destabilizing. By using known results for the stability of the Ekman boundary layer an asymptotic result for the critical Reynolds number is obtained for large values of the Taylor number.
Spatial instability of a jet
Authors: Keller Joseph B. , Rubinow S. I. , Tu Y. O.
Published: February 2004

The instability of a circular cylindrical jet of liquid in air is studied on the assumption that the wavenumber k of the disturbance is complex while its frequency σ is real. This implies that the disturbance grows with distance along the jet, but that it does not grow with time. The occurence of such disturbances is called spatial instability, in contrast to the temporal instability studied by Rayleigh and others, in which k is real and σ is complex. It is found that there are infinitely many unstable modes for the axially symmetric case and also for each of the asymmetric cases. In the case of high velocity jets, one of these modes for the symmetric case corresponds to the mode Rayleigh found. However, it is not the most rapidly growing mode. Both analytical and numerical solutions of the dispersion equation are given for k as a function of σ and of the dimensionless jet velocity.
Thermal oscillations in convecting fluids
Authors: Hurle D. T. J. , Jakeman E.
Published: February 2004

The occurrence of thermal oscillations in a wedge-shaped Bénard cell containing water-methanol mixtures is described and evidence is presented to suggest that the oscillations arise from an instability in the roll-cell convection produced by the wedge shape. Steady oscillations observed recently in a Benard cell containing water-ethanol mixtures have been attributed to the Soret effect and this suggestion is critically discussed.
Isochoric turbulent mixing of two rapidly reacting chemical species with chemical heat release
Authors: Dopazo César , O'Brien Edward E.
Published: February 2004

The temperature and concentration fields produced by turbulent mixing of two reactants undergoing a one-step, very rapid, irreversible, exothermic reaction are studied. Temperature and concentration fields decay in two stages: kinetically driven and diffusion controlled. Stochastic solutions are derived for the first stage, the asymptotic state of which displays all the characteristics of species segregration. In particlar, only a weak correlation between the concentration and temperature fields is generated in the first stage. For the special case of equal mass diffusivities and a Lewis number of one the solution to the second stage is obtained in terms of the solution of a nonreacting binary mixing problem. An approximate solution for Lewis numbers different from one is proposed. The temperature field seems to decay with an effective thermal diffusivity determined by the smaller of the molecular mass and thermal diffusivities.
Biasing correction for individual realization of laser anemometer measurements in turbulent flows
Authors: McLaughlin D. K. , Tiederman W. G.
Published: February 2004

In turbulent flow situations the histograms constructed in the individual realization mode of laser anemometry are biased. The biasing occurs because a larger than average volume of fluid, and hence a larger than average number of scattering centers, pass through the probe volume during periods when the velocity is faster than the mean. Similarly, a smaller volume of fluid and a smaller number of scattering particles pass through the probe volume during periods when the velocity is slower than the mean. The proper weighting function needed to correct the biased data is the inverse of the instantaneous velocity vector. However, an analysis using turbulent flow models show that corrections based only upon the streamwise component of the velocity vector are adequate for many flow situations.
Construction of linearized kinetic models for gaseous mixtures and molecular gases
Authors: McCormack Francis J.
Published: February 2004

A simple method of construction of linearized kinetic models is proposed which is based upon the equivalence of moments of the Nth-order modeled collision operator and the moments of the full collision operator calculated with the Nth-order approximation to the distribution function. This method is used to construct a third-order model of the linearized cross-collision operator for a general multicomponent monatomic gaseous mixture, not restricted to Maxwell molecules. In addition, this method is used to extend the Hanson-Morse diatomic gas model of the Wang Chang-Uhlenbeck collision operator to a polyatomic gas. Also presented is a new method of formally extending the Gross-Jackson modeling procedure to multicomponent monatomic mixtures. It is shown that the method of constructing mixture models based on the equivalence of moments is identical to this new procedure. In addition, the Gross-Jackson modeling procedure recently developed for mixtures by Boley and Yip is analyzed. It is shown that, under a certain weak restriction, their method is equivalent to the simpler Gross-Jackson procedure — and leads to the same expression for the Nth-order model, except for the manner of specification of the constant in the diagonal approximation.
Approximate solutions of the Boltzmann equation for shock waves
Authors: Sather Norman F.
Published: February 2004

Several approximate solutions of the Boltzmann equation for shock waves are shown to be applications of the method of weighted residuals. Values of shock thicknesses obtained by these methods are compared, and a systematic procedure for improving the accuracy of the general method is suggested.
Constitutive relations associated with the Mott-Smith distribution function
Authors: Nathenson M. , Baganoff D.
Published: February 2004

It is shown that the distribution function assumed by Mott-Smith determines a unique relation between heat flux, stress, and fluid velocity given by q = (3/2)τu, i.e., it provides a constitutive relation for heat flux, and it also determines a simple expression for the ratio of third-order central moments Q = 〈C x3 〉 / 〈C x C 2〉. These expressions allow the equation of transfer for cx2 to be cast in a form that yields a nonlinear constitutive relation for stress. The results obtained from the Mott-Smith ansatz are compared with the theory of Baganoff and Nathenson and results from a numerical solution of the Boltzmann equation for shock-wave structure obtained by Hicks and Yen.
Heat transfer between parallel plates with arbitrary surface accommodation
Authors: Thomas J. R. , Chang T. S. , Siewert C. E.
Published: February 2004

Elementary solutions of the coupled pair of integrodifferential equations arising from the decomposition of the linearized BGK equation in the kinetic theory of gases are used to solve the problem of heat transfer between parallel plates with arbitrary surface accommodation. A coupled pair of Fredholm equations is derived, and rapidly convergent iterative solutions are constructed. These solutions are then used to obtain accurate values of the heat flux between the plates and the temperature and density profiles, for various values of the accommodation coefficient and inverse Knudsen number. Numerical results for the heat flux are presented and compared to existing variational solutions. Also, explicit results for the temperature and density profiles are given.
Nonsimilar blast waves with transparent gas radiation
Authors: Erickson Gary G. , Olfe D. B.
Published: February 2004

Analytical and numerical calculations are carried out for an initially adiabatic blast wave in which the effect of transparent gas radiation increases as the temperature decreases. After a radiative cooling time is reached, a very dense shell of gas rapidly forms behind the shock front, and a cooling wave slowly progresses through the hot interior gas. The cooling wave reduces the interior pressure, resulting in an attenuation of the shock-front velocity. For a specific heat ratio γ near unity the shock velocity will remain near the adiabatic value, whereas for γ = 5/3 the shock velocity will approach the value for a momentum-conserving shell, as predicted by some authors.
Measurement of electrical conductivity of argon at high pressure
Authors: Bauder U. , Devoto R. S. , Mukherjee D.
Published: February 2004

Measurements have been carried out of the current, electric field strength, and radial temperature distribution in a 5 mm diam. wall-stabilized electric arc in argon at pressures from 1-200 atm. These data have been analyzed to determine the electrical conductivity as a function of temperature and pressure. The results are in reasonable accord with other measurements to 10 atm and with theory.
Electron wave breakdown of helium
Authors: Blais Roger N. , Fowler R. G.
Published: February 2004

A revision of the electrostatic gas breakdown wave apparatus used by Haberstich and Winn has been employed to generate waves for studies of wave speed, and electron temperature and density behind the wave front. The measurements were carried out in helium at applied electrode voltages from 6 to 42 kV of both polarities and over a pressure range of 0.3 to 30.0 Torr. Nuclear data-handling techniques were adapted to the measurement of the wave speeds to increase the accuracy of the data. Good over-all agreememt is obtained with the theory of Shelton.
Laminar electrostatic shock waves generated by an ion beam
Authors: Ikezi H. , Kamimura T. , Kako M. , Lonngren K. E.
Published: February 2004

Strong laminar electrostatic shock waves have been experimentally observed when an ion beam is injected into a collisionless plasma. The structure of the shock is qualitatively different from one with a trailing wave train. A density depression follows behind the shock front, and no trailing wave train due to wave dispersion is found. A significant amount of ions reflected from and transmitted through the shock front form a precursor. The critical Mach number above which no shock is formed is found to be 1.5. Numerical simulations reported here reproduce the experimental observations very well. An analysis based on the water-bag model accounts for the observed value of the critical ion-beam velocity which gives the critical Mach number. It also points out that the reflected ions play an essential role in the persistence of the shock.
Microscopic theory of the transition from ambipolar to free diffusion
Authors: Numano Masahiro
Published: February 2004

The transition from ambipolar to free electron diffusion was investigated by making use of the expression for the diffusion coefficient in terms of the velocity autocorrelation function. It was assumed that the electron mean free path is much smaller than the plasma dimension. The diffusion coefficient was obtained from Vlasov-Boltzmann type kinetic equations, assuming a BGK model for the terms representing collisions between charged particles and the neutrals. It was found that when the Debye length is much shorter than the plasma dimension, the diffusion is ambipolar and that as the Debye length increases there is transition to free diffusion. The diffusion coefficient obtained was compared with the machine calculation results by Allis and Rose, and a fairly good agreement between them was found. The effect of a magnetic field on the transition of diffusion across the magnetic field was also investigated.
Interaction of force-free fields with external circuits
Authors: Kadish A. , Zwart J. W. A.
Published: February 2004

The interaction of a perfectly conducting force-free magnetic field with external circuits during the adiabatic compression of a perfectly conducting column is studied in a slab geometry. It is shown that the circuit equations of a cylindrical screw pinch discharge together with an initially specified magnetic field determine a unique motion of the plasma, provided the E × B vector is initially inward. It is found that after a finite time, the model breaks down. Estimates for this time, which correspond to the self-crowbarring time of the plasma, are obtained. Exact nonlinear solutions are obtained for special initial discharges.
Equilibrium and stability of mirror-confined nonneutral E layers
Authors: Davidson Ronald C. , Drobot Adam T. , Kapetanakos C. A.
Published: February 2004

The steady-state Vlasov-Maxwell equations are used to study the equilibrium properties of a nonneutral E layer confined both axially and radially, by a static external mirror field, mirror field, B0ext(x). Equilibrium properties are calculated for the electron distribution function fe0 (H , P θ) in which all electrons have the same total energy (H) and the same canonical angular momentum (P θ), i.e., fe0 (H , P θ) = N0δ(H − H0)δ(Pθ − P0), where N 0, H 0, and P 0 are positive constants. For a low-density E layer, the electrostatic potential energy of an electron, − e φ0(r , z ), is small in comparison with H 0. Neglecting terms of order |e φ0(r , z)/ H 0|, a closed zero-order expression for the r - z boundary of the E layer is obtained. Iterating, the equilibrium electrostatic potential φ0(r , z) is then computed to lowest order, together with O [e φ0(r , z) / H0] corrections to the boundary of the E layer. Computer simulation experiments are used to investigate electrostatic stability properties for the case of azimuthally symmetric perturbations (∂/∂θ = 0). The code allows only r and z spatial variations but self-consistently follows the three velocity components of 6264 macroparticles. When the electrons are initially loaded close to the equilibrium state described by fe0(H , Pθ) = N 0δ(H − H 0)δ(P θ − P 0), the E layer is observed to achieve a stable quasisteady configuration in about 15 ωp e−1 with negligible particle loss out the mirrors.
Spectrum of electrostatic field fluctuations in a bounded beam plasma system
Authors: Diaz C. J. , Walsh J. E. , Conrad J. R.
Published: February 2004

A theoretical study of the electrostatic field fluctuations of a bounded beam plasma system in the regime below threshold for growing oscillations is presented. The spectrum exhibits a triplet structure in the neighborhood of the beam line. The structure is predicted on the basis of the electrostatic wave emission model and the behavior of the dispersion relation for the bonded system.
Scattering in a stable beam-plasma system
Authors: Diaz C. J. , Conrad J. R. , Walsh J. E.
Published: February 2004

A Fokker-Planck equation is used to describe the random walk of the particles in stable electron beam driven fluctuations. The resulting kinetic equation is a bounded version of the Balescu-Lenard equation. The ion velocity distribution relaxation rates calculated on the basis of this equation exhibit a resonant structure for velocities near synchronism with the phase velocities of the modes predicted by the dispersion relation.
Heating of magnetized plasmas by a large-amplitude low-frequency electric field
Authors: Chen Liu , Birdsall C. K.
Published: February 2004

Plasma electron and ion heating due to a large-amplitude oscillating electric field E 0 applied normal to a steady magnetic field B 0 has been followed in detail, by one-dimensional computer simulations. The large oscillating drift velocity (E 0/B 0 > ν e ) at low frequency (ωci ≪ ω0 ≃ ωpi ≪ ωce ) sets up instabilities due to the periodic electron E / B drift through the ions, which then cause rapid heating. For waves propagating across B0(k · B̂ 0 = k ‖ = 0), the instability is a Buneman-type upper-hybrid two-stream instability. Electron perpendicular thermal velocity is increased to ∼E0/B0 with little ion heating. For obliquely propagating waves (k ‖ ≠ 0), there is an additional instability, the modified two-stream instability. For small k ‖ [roughly, k ‖/k ≲ (m e / m i )(1/2)], the upper-hybrid instability dominates and the heating is similar to the k ‖ = 0 case but with a small amount of electron parallel heating. As k ‖ increases, however, the modified two-stream instability becomes dominant. Electron parallel thermal velocity is increased to ≃ (E 0/B 0)(k /k ‖). Strong ion (perpendicular) heating also occurs with the ion thermal velocity at wave saturation near (E 0/ B 0)(me / mi )(3/4)(k /k‖)(3/2). Comparison with similar work for B 0 = 0 shows that addition of B 0 is best for ion heating, improving KTi by (mi /me)(1/2). Possible applications of these results to laboratory experiments are also discussed.
Heating of the relativistic electron plasma in a levitated spherator
Authors: Shohet J. L. , Chen K. , Okabayashi M.
Published: February 2004

Noncyclotron resonant microwave heating preferentially heats relativistic electrons in a plasma. In the FM-1 device, a levitated spherator, plasma may be produced by cyclotron resonant microwave heating at a base pressure of 3 × 10−8 Torr in helium. Under these conditions, plasma lifetimes are of the order of 100 sec. Nonresonant microwave heating at power levels of up to 1.5 kW produced electron temperatures of up to 900 keV with 4 MeV electrons not at all uncommon, as measured by wall bremsstrahlung produced at the limiter. Anomlaous loss mechanisms drop the energy to about 140 keV within 200 msec after the turnoff of the nonresonant heating, and the temperature remains roughly this value for 100 sec. Nonresonant heating at the cyclotron harmonics is as efficient as heating below the fundamental, which is explained by observing that synchrotron emission may be used to compute the nonresonant absorption.
Parametric excitation of ion-acoustic waves by a high-frequency electric field
Authors: Stowe D. W. , Böhmer H.
Published: February 2004

The theory of parametric coexcitation of ion-acoustic and electron plasma waves by a high-frequency electric field is reviewed. Numerical calculations of the parametric excitation are reported which include the effect of steady-state drift velocities and plasma-neutral collisions to simulate an actual physical situation. The solutions are compared with experimental results obtained by the interaction of a 1.5-GHz electromagnetic signal with a low-pressure helium discharge.
Theory of double resonance parametric excitation in plasmas
Authors: Arnush Donald , Nishikawa K. , Fried Burton D. , Kennel Charles F. , Wong A. Y.
Published: February 2004

Parametric instabilities in a plasma driven by a long wavelength electric field with two “pump” frequencies ω1 and ω2 which lie near the resonant frequency for Langmuir oscillations, their difference Δ = ω1 − ω2 being chosen close to a low frequency resonance, linear or nonlinear, at Ω − i Γ are studied. A general dispersion relation in terms of linear susceptibilities, χ, is derived by retaining, on a selective basis, terms of fourth order in the pump amplitudes. Illustrative calculations are carried out using resonant fluid approximations for the χ. The most interesting cases occur when Δ = Ω or Δ = 2Ω. A lowering of the net power threshold for instability is found in both cases, when the linear damping rate of the electronic wave is large compared with Ω. In addition, a coupling between the “decay” and “oscillating two-stream” instabilities occurs when Δ = Ω, the threshold for exciting the latter with the ω2 pump being arbitrarily small when the ω1 pump amplitude is near the usual decay instability threshold.
Computer simulation of the saturation of the parametric instability in the weak turbulence regime
Authors: Godfrey Brendan B. , Taggart Keith A. , Rhoades Clifford E.
Published: February 2004

The theory of nonlinear saturation of the parametric decay instability in the weak turbulence limit is developed, and the resulting kinetic equation solved numerically for a variety of cases. These solutions are compared with the results of a series of computer simulations. Agreement is found to be good only for pump powers below threshold, with the reason for partial failure above threshold unclear. The validity of the random phase approximation is also discussed. A summary of computational methods is provided.
Nonlinear saturation of parametric instabilities: Spectrum of turbulence and enhanced collision frequency
Authors: Weinstock Jerome , Bezzerides B.
Published: February 2004

The nonlinear saturated state of parametric instabilities driven by an externally applied electromagnetic pump field oscillating near the plasma frequency is considered. For short wave lengths or strong pump fields, modifications of electron and ion orbits are the dominant saturation mechanism. A calculation is made of the saturated spectrum of Langmuir waves excited by the decay instability for T e ≈ T i. The spectrum is found to be broad in angle, in the absence of a magnetic field, and this has been confirmed by computer simulations. A calculation has also been made of the enhanced collision frequency and heating rate ν*. It is found that: (a) ν* increases rapidly with pump intensity when the intensity is small, (b) ν* increases very slowly, logarithmically, with intensity when the intensity is large, and (c) ν* significantly depends on whether the ratio of matching wave number to Debye wave number is greater or less than 0.2. These predictions have all been confirmed by computer simulations and by a laboratory experiment. A previous calculation for the saturation of the decay and oscillating two-stream instabilities with T e ≥ T i was limited to just the total fluctuation energy at saturation.
Turbulence in electrostatic ion-acoustic shocks
Authors: Means R. W. , Coroniti F. V. , Wong A. Y. , White R. B.
Published: February 2004

Three types of collisionless electrostatic ion-acoustic shocks are investigated using the University of California, Los Angeles, double plasma device: (a) laminar shocks; (b) small amplitude turbulent shocks in which the turbulence is confined to be upstream of the shock potential jump; and (c) large amplitude turbulent shocks in which the wave turbulence occurs throughout the shock transition. The wave turbulence is generated by ions which are reflected from the shock potential; linear theory spatial growth increments agree with experimental values. The experimental relationship between the shock Mach number and the shock potential is shown to be inconsistent with theoretical shock models which assume that the electrons are isothermal. Theoretical calculations which assume a trapped electron equation of a state and a turbulently flattened velocity distribution function for the reflected ions yields a Mach number vs potential relationship in agreement with experiment.
Ion streaming instabilities with application to collisionless shock wave structure
Authors: Golden Kenneth I. , Linson Lewis M. , Mani Siva A.
Published: February 2004

The electromagnetic dispersion relation for two counterstreaming ion beams of arbitrary relative strength flowing parallel to a dc magnetic field is derived. The beams flow through a stationary electron background and the dispersion relation in the fluid approximation is unaffected by the electron thermal pressure. Magnetic effects on the ion beams are included, but the electrons are treated as a magnetized fluid, me → 0. The dispersion relation is solved with a zero net current condition applied and the regions of instability in the k − U space (U is the relative velocity between the two ion beams) are presented. These results are extensions of Kovner's analysis for weak beams. The parameters are then chosen to be applicable for parallel shocks. It is found that unstable waves with zero group velocity in the shock frame can exist near the leading edge of the shock for upstream Alfvén Mach numbers greater than 5.5. It is suggested that this mechanism could generate sufficient turbulence within the shock layer to scatter the incoming ions and create the required dissipation for intermediate strength shocks.
The drift shock
Authors: Newcomb W. A.
Published: February 2004

An example is analyzed of shock formation by a nonlinear drift wave in a guiding-center plasma (slow-drift ordering).
Electric field and motion of flux lines in an inductively driven multipole
Authors: Evans Kenneth
Published: February 2004

A calculation of the electric field in an inductively driven multipole is presented. The gap, which destroys the azimuthal symmetry, is explicitly taken into account. The motion of the flux lines as they come in the gap and spread around the machine is determined. Most of the results are derived for a simplified, linear model of a multipole, which is taken to be periodic to better represent a toroid. The plasma is taken to be a dielectric with a slowly varying dielectric constant which is calculated from the second-order drifts for electric and magnetic fields which are both time varying. The electric field is taken to have a sinusoidal variation of the same frequency as the magnetic field pulse plus an additional variation because of the time-changing dielectric properties. The resulting picture is in good agreement with experimental measurements on both of the Wisconsin octupoles.
Interpretation of plasma confinement minima near the resonance surface in a stellarator
Authors: Okuda Hideo , Dawson John M.
Published: February 2004

The observed plasma confinement minima which occur near the resonant values of ι (rational fractions for the rotational transform) in a stellarator may be interpreted in terms of plasma diffusion due to convective cells. Both theoretical estimates and numerical simulation give reasonable qualitative and quantitative agreement with the experimental observations.
Confinement properties in levitated spherator
Authors: Okabayashi M. , Ripin B. , Schmidt J. , Yoshikawa S.
Published: February 2004

In the levitated spherator, a plasma confinement time of 150 ∼ 200 msec was obtained at a plasma density of 2 × 1011cm−3 and an electron temperature of 1 eV. This confinement time is 1/3−1/6 of the classical decay time. It was observed that the confinement time increased with an increase in the electron temperature in the range of 0.1 to 5.0 eV. At higher electron temperature the plasma decay time was reduced with an increase in the electron temperature.
Variable fluid properties in Bénard convection
Authors: Davenport Ian F.
Published: February 2004

The effect of variation of the coefficient of thermal expansion through a fluid with a linear temperature gradient at the onset of Bénard convection can be resolved in terms of a nonlinear density profile.
Drag coefficients and the generalized Boltzmann equation
Authors: Dorfman J. R. , Kuperman W. A. , Sengers J. V. , McClure C. F.
Published: February 2004

There is a close relation between the Knudsen number dependence of the drag coefficient for a macroscopic body in a gas stream, and the density dependence of the transport coefficients for moderately dense gases in both two and three dimensions.
Propagation characteristics of whistler instabilities
Authors: Hall Laurence S. , Scharer John E.
Published: February 2004

The characteristic properties of the electromagnetic wave instability driven by an electron thermal anisotropy are presented in terms of asymptotic pulse shapes computed for typical laboratory parameters. Maximum spatial growth rates for the convective regime are also given.
Phenomena in unsteady rotating flows for a finite cylindrical geometry
Authors: Innes G. de R.
Published: February 2004

Further interpretation of experimental data is presented for spin-up from rest and spin-down to rest in a stationary cylindrical chamber with one endwall free to rotate.
Inviscid dynamics of two-dimensional turbulence
Authors: Fox Douglas G. , Orszag Steven A.
Published: February 2004

The nature of equilibrium states of inviscid two-dimensional “turbulence” is discussed. Results of numerical simulations are presented to clarify the theory.
Test of spectral energy transfer models of turbulence decay
Authors: Orszag Steven A. , Raila Donald S.
Published: February 2004

Two representative spectral energy transfer models of turbulence are tested by comparison with recent numerical simulations of three-dimensional, homogeneous, isotropic turbulence. Heisenberg's eddy viscosity gives generally good results, while Leith's diffusion approximation is less satisfactory, at least for decay from the Gaussian initial conditions of the computer experiments.
Eddy viscosity models for free turbulent flows
Authors: Lundgren T. S. , Wang F. C.
Published: February 2004

The structure of the turbulent interface is studied by means of several eddy viscosity models. A detailed analysis results in boundary conditions across the interface. These are applied to the solution of the turbulent Rayleigh shear flow problem.
System of vortices in rotating liquid helium
Authors: Su C. H.
Published: February 2004

The Hamiltonian of a system of N vortex lines moving in an incompressible fluid contained in a circular cylinder is given. The equilibrium state of vortices is constructed through minimization of the energy of the system with the constraints of constancy of number of vortices and their total angular momentum. One and only one assumption is used throughout this work, that pair correlation between vortices is neglected. In equilibrium, the system of vortices rotates uniformly with respect to the central axis of the cylinder. The fluid does not rotate as a solid body, only approaches solid rotation as N→∞. Continuous distribution functions of vortices are found for all N > 1. For N = 1, the distribution is a delta function at the central axis of the cylinder. As N increases the distribution spreads out; in the limit N→∞, it becomes uniform throughout except for a thin layer of order N−1/2 approaching the wall where the density goes to zero rapidly but continuously and remains zero up to the wall. The vortex-free region next to the wall has a thickness varying from 1 − 1/√2 for N = 2 to 1/√N for large N.
Stability of a curved gas-liquid interface
Authors: Berghmans Jan
Published: February 2004

A localized perturbation technique is used to study the stability of a paraboloidal interface. Surface tension effects are considered but viscosity is neglected in the analysis. It is found that instability can occur for certain displacements of the interface. The results of this theoretical analysis are applied to the stability of the interface of a gas jet impinging on a liquid. A linear relationship between the critical jet strength and surface tension is obtained. This agrees with the experimental observations.
Effect of finite mean free path on the diffusion around a convex obstacle
Authors: Brunn P. , Berman A. S. , Prager S.
Published: February 2004

It is well known that the steady-state flow of a gas past a solid obstacle immersed in a space filled with isotropic scattering centers can be represented by an integral equation for the collision density distribution. Asymptotic expansions are developed for the gas flux in the form of a power series in the mean free path λ, the leading term representing the continuum diffusion limit. The method replaces the original integral equation with a series of problems, each requiring the solution of a Poisson equation with inhomogeneous terms of increasing complexity. The case of a spherical obstacle of radius R is treated explicitly; two iterations give the reduction in the flux correct to order λ2. It is found that at moderate λ the sphere acts as though its radius had increased by 3λ/16R.
Electron temperature measurements along a stagnation point streamline
Authors: Nishida Michio , Sugimoto Shuji
Published: February 2004

Experimental observations of the electron temperature profile along a stagnation point streamline have been found to be in good agreement with the theory developed for the case where the interaction between an electron thermal layer and a viscous shock layer was considered. The electron temperature measurements have been carried out with the Langmuir probe technique in an argon plasma flow.
Establishment of partial local thermal equilibrium in transient and inhomogeneous plasmas
Authors: Engelhardt W.
Published: February 2004

New formulas for relevant relaxation times and relaxation lengths for the establishment of partial local thermal equilibrium are presented taking into consideration the influence of the ground state on the population of the excited levels and on the energy distribution of the free electron gas.
X-Ray and electron spectra from the double inverse pinch device
Authors: Baum P. J. , Bratenahl A. , White R. S.
Published: February 2004

X-ray measurements are reported for the double inverse pinch device (Mark I) which develops an X-type neutral point through argon plasma flow. An x-ray pulse ( E>3 keV) is observed at a critical phase of field line reconnection. Differential absorber measurements with two proportional counters indicate an x-ray energy spectrum of the form (dN / dE)E = aE−s, where S is 3.0±0.2 and a is (1.4±0.7) ×106 (keV)3.0. E is the energy, expressed in keV. The proportional counters are also operated in the Ross filter (K-edge) mode. The x rays appear to be produced by thick target bremsstrahlung of the electrons on the copper anode in the immediate area of the X-type neutral point. An electron energy spectrum of the form (dN / dE) E = bE−γ where γ 4.0±0.2 is and b is (6.8±3.4) × 104 (keV)4.0 is deduced from the x ray spectrum. The x-ray signal starts less than 0.2 μsec after the resitivity minimum and continues for less than 0.25 μsec. The results suggest that runaway electrons are produced then later braked probably by the same wave-particle interactions that have been considered responsible for the current disruption at the neutral point.
Origin of hot ions observed in a modified Penning discharge
Authors: Roth J. Reece
Published: February 2004

Ions with a Maxwellian energy distribution and kinetic temperatures ranging from below 100 eV to several keV have been observed in a steady-state modified Penning discharge. Observations in the plasma, with capacitive probes at several azimuthal locations, are consistent with the existence of two distinct spokes rotating with different velocities in the sheath between the plasma and the anode ring. The faster (0.3−10 MHz) spoke consists of electrons rotating with the E/B drift velocity. The slow 0.06−0.8 MHz) spoke consists of ions, the measured thermal velocity of which is directly proportional to the spoke velocity. The interaction of the two spokes is apparently responsible for the observed electrostatic “turbulence” and ion thermalization. The anode sheath thickness is smaller than the ion gyrodiameter in this plasma. Thus, the ions are in the electric field of the sheath for only a fraction of their orbit, and their E / B drift (spoke) velocity is smaller than that of the electrons.
Stability of two-dimensional magnetohydrodynamic equilibria
Authors: Freidberg J. P. , Marder B. M.
Published: February 2004

A numerical procedure is presented for computing the stability of high β, diffuse two-dimensional magnetohydrodynamic equilibria. The method is tested on the problem of the bumpy θ pinch with arbitrary size bumpiness.
Characteristic modes of anisotropic two-component plasma
Authors: Georges G. C. , Sakuda Kyohei
Published: February 2004

A convenient formulation is presented for the numerical calculation of the complete set of characteristic modes in a two-component, fluid-model, warm, unbounded, fully ionized, and anisotropic plasma. The anisotropy in this analysis is due to a static background magnetic field. Quantitative plots of the dispersion relations and field polarizations are presented for various modes of the system using an assumed set of typical plasma parameters. An interesting property of the hybrid low-frequency ion mode is shown to display a critical dependence on the angle between the wave propagation vector and the background magnetic field as this angle is varied near 90°.
Boundary problem of anisotropic Vlasov plasma
Authors: Sakuda Kyohei , Palócz István
Published: February 2004

The boundary problem at the interface between vacuum and plasma is studied. The plasma is one component and homogeneous, but anisotropic due to an external static magnetic field. The plasma is described by the linearized Vlasov equation. In order to obtain the field quantities, i.e., first-order electric and magnetic field, and the velocity distribution function, the dyadic Green's function is derived. Then by applying the completeness relationship, the complete set of eigenvectors corresponding to the continuous as well as discrete spectra, are derived. By virtue of the superposition integral, all first-order quantities are obtained, once the expansion coefficients are determined. To obtain the expansion coefficients uniquely, the speculum assumption and outgoing wave condition are used. The reflection coefficients of the left- and right-hand polarized waves are calculated. Because of the different dispersion relations for the two different polarized waves, the two surface impedances are different; therefore, the reflection coefficients are different. The polarizations of the reflected and the transmitted waves depend on the excitation frequency.
Low-frequency parametric instabilities of magnetized plasmas with two ion species
Authors: Ott Edward , McBride John B. , Orens Joseph H.
Published: February 2004

A theoretical and computer simulation treatment is presented of the response of magnetized plasmas with two ion species to low-frequency, electric fields oscillating at ω0 near the lower-hybrid frequency ωlh that shows the existence of parametric instabilities. A new decay instability involving the Buchsbaum two ion resonance occurs for ω0>ωlh, and a purely growing instability occurs for ω0<ωlh. The analysis is valid even when the masses of the ion components are comparable and applies, for example, to deuterium-tritium plasmas. Computer simulation experiments demonstrate the potential importance of these instabilities as ion heating mechanisms.
Electromagnetic instability in interpenetrating electron-ion plasmas
Authors: Chen W. M. , Lai C. S.
Published: February 2004

The electromagnetic instability associated with plasma waves propagating perpendicular to a uniform magnetic field B0 is studied for counterstreaming electron-ion plasmas, based on the linearized Vlasov-Maxwell equations. Owing to the different densities, temperatures, and drift velocities of two plasma streams, the plasma waves can no longer be separated into the ordinary and extraordinary modes. It is found, as in the case of two identical counterstreaming plasmas, that the instability can occur in rather low-β plasmas and the typical growth rate is of the order of the electron cyclotron frequency.
Nonlinear theory of the E × B electron drift instability in high-β plasmas with T i ∼ T e
Authors: Rogister André
Published: February 2004

A nonlinear theory of the E × B electron drift instability for Te∼Ti is developed on the basis of the wave kinetic equation for weakly turbulent plasmas in a uniform magnetic field. It is found that nonlinear electron cyclotron resonances stabilize short wavelength—but destabilize long wavelength modes; the total wave energy, however, is stabilized by this mechanism. In a two-dimensional model (the waves propagate in a narrow fan encompassing the plane orthogonal to B), wave-wave scattering processes can transfer energy from the unstable small k region of the spectrum toward larger k's where nonlinear electron damping dominates. Either balancing the relevant stabilizing and destabilizing processes for small k's, or considering over-all energy balance, predicts that the theoretical turbulence level at k = kD (the inverse of the Debye length) is a few hundred times thermal. The estimated effective electron-ion collision frequency is found to be much too small to explain the anomalous heating observed in collisionless orthogonal shocks suggesting that another instability, not confined to propagate in a narrow fan, is required to explain the anomalous resistance.
Plasma current multipole with a free boundary
Authors: Chu M. S. , Dobrott D.
Published: February 2004

A straight plasma current quadrupole equilibrium, a doublet, with a free boundary and outer conducting walls is examined by means of the static magnetohydrodynamic equations. Analytic expressions for the flux surfaces are obtained for the plasma and the vacuum regions when the axial current density is uniform in the plasma cross section. An internal figure-eight separatrix is obtained when position of the plasma-vacuum interface and the outer conducting wall is appropriately chosen.
Transverse dynamic stabilization of a theta pinch
Authors: Lister G. G. , Troyon F. S. , Weibel E. S.
Published: February 2004

The stability of a straight plasma column confined by a static axial magnetic field and a small oscillating transverse magnetic field is discussed. Growth rates for the most important parametric instabilities are obtained. The influence of damping in providing a stabilizing mechanism against these instabilities is discussed, and a set of stability criteria are obtained using a viscous fluid model for the plasma. The possibility of suppressing the fastest growing instability by “wobbling” the frequency of the applied field is also discussed. An order of magnitude calculation for dynamic stabilization of a toroidal plasma is presented.
Plasma diffusion in two dimensions
Authors: Williamson J. H.
Published: February 2004

The nonlinear differential equations describing the interaction of waves in a two-dimensional guiding center plasma form the basis for computer simulation. The method is often more efficient than the particle codes now in use, and it is readily modified to allow direct computation of ensemble averages. It is shown that the electric field correlation and the particle velocity correlation are not equivalent and so estimates of the diffusion coefficient based on the field correlation are pessimistic. Polarization drifts seem to have little effect on the results until ωp exceeds ωc.
Relativistic acceleration of charged particles by superintense laser beams
Authors: Kaw P. K. , Kulsrud R. M.
Published: February 2004

The relativistic motion of charged particles in very intense electromagnetic wave pulses with slowly space-varying amplitude has been analytically investigated. The results of the analysis have been used to discuss the conditions under which currently available lasers can be used for producing MeV electrons in the laboratory.
Critical Reynolds number of the Orr-Sommerfeld equation
Authors: Chock D. P. , Schechter R. S.
Published: February 2004

Using the straightforward Runge-Kutta procedure, the critical Reynolds number for the Orr-Sommerfeld equation has been obtained. The number is 2772.225. The corresponding wavenumber is 1.0205. These values also substantiate the accuracy of the Chebyshev polynomial expansion carried out by Orszag.
Heat conduction between parallel flat plates in binary gas mixtures
Authors: Yeh Bao-Tzang , Frohn Arnold
Published: February 2004

The heat transfer in binary gas mixtures is investigated with the moment method. Using Maxwell's force law an analytical solution is given for small temperature differences.
Cryogenic shock tube
Authors: Liepmann H. W. , Cummings J. C. , Rupert Viviane C.
Published: February 2004

Two shock tubes have been developed which allow for partial or full immersion of the test sections within a cryogenic bath. One tube is used for the study of shock-wave interactions with strong density gradients, and the other to obtain very large shock Mach numbers with ideal gas conditions in all flow regions.
Quasineutral scaling laws
Authors: Elliott C. James
Published: February 2004

Utilizing the Boltzmann equation we develop scaling laws for a quasineutral plasma. Any binary collision process is allowed but radiative processes, three-body collisions, and self-magnetic fields are not allowed. The independent variables appropriate to a cylindrical discharge are given.
Electromagnetic wave instability in a cold electron-ion plasma
Authors: Seshadri S. R.
Published: February 2004

The instability of an electromagnetic wave propagating obliquely to the streaming electrons in an electronion plasma is discussed. The maximum growth rate is found to be essentially the same for all stream directions other than normal to the wave vector.
Whistler waves in a thermal simulation plasma
Authors: Gitomer S. J.
Published: February 2004

Small amplitude whistler waves with K ‖ B have been studied using a numerical simulation. The dispersive properties of these waves agree with linear theory. Nonlinear wave behavior due to magnetic trapping has been observed. The trapping time is in agreement with the Palamadesso and Schmidt theory.
Measurement of Debye length in laser-produced plasma
Authors: Ehler Wayne
Published: February 2004

A technique for measuring the Debye length of an expanded laser produced plasma was devised. With an independent measurement of electron density, the plasma electron temperature could then be ascertained.
Miles mechanism for generation of short-wavelength surface waves
Authors: Siegmann W. L.
Published: February 2004

An energy transfer mechanism which has been explored by Miles and which produces growth of a wave on a fluid boundary is considered theoretically. A simple linear high Reynolds number shear flow model possessing similar energy transfer characteristics is formulated. Two terms in its energy balance equation are estimated using approximation techniques for cases when the location of the point where wavespeed equals shear flow velocity is either close to or distant from the boundary surface. Implications of the approximations for growth of the wave are discussed and are compared with conclusions of Miles, and the importance of the position of the above-mentioned point with respect to the boundary is confirmed.
Flapping of a plane jet
Authors: Goldschmidt V. W. , Bradshaw P.
Published: February 2004

Correlations of the instantaneous velocity fluctuations on opposite sides of a subsonic plane jet have been measured. These indicate that there is a measurable flapping of the jet. The frequency of the flapping is estimated by taking the correlation with one signal delayed in time.
Spiral flow in a porous pipe
Authors: Terrill Robert M. , Thomas Philip W.
Published: February 2004

The equations developed by Prager for fully developed laminar flow with swirl in a porous pipe have been solved numerically. A complete description of the solutions is presented using graphs of the skin-friction and the velocity profiles.