bluuebunny/crossref_metadata_2025 huggingface dataset:
Upper Hybrid Resonance Scattering by Nonuniform Plasma Columns
Authors: Greenwald Raymond , Boley Forrest I.
Published: February 2004

Extraordinary mode scattering spectra in the vicinity of upper hybrid resonance are calculated for an infinitely long, radially inhomogenous, magnetoplasma column. The wave fields are determined inside the plasma column by a numerical solution of the full set of Maxwell's equations. The results indicate that enhanced scattering is limited to the range of upper hybrid frequencies of the column, that the shape of the resonance spectrum is strongly dependent on the shape of the density profile, and that the presence of a glass sleeve about the plasma column can completely change the shape of the resonance spectrum. Experimental scattering spectra and density profile measurements have been obtained from a thermally ionized potassium plasma column enclosed in a Pyrex tube and shunting a section of waveguide. The profile was measured with Langmuir probes. The spectrum predicted by the modified profile was found to be in very good agreement with an experimental spectrum obtained while the density measurements were being made.
Further Investigation of the Dual Solutions of the Greenspan-Carrier Equations
Authors: Bramley J. S.
Published: February 2004

The numerical solutions of the boundary layer equations associated with aligned magnetohydrodynamic flow past a semi-infinite flat plate are unique when the plate is thick, but nonunique for a thin plate. The present works bridges the gap.
Decay of Homogeneous Turbulence
Authors: Rosen Gerald
Published: February 2004

Statistical similarity for low-order ensemble averages of local velocity-dependent quantities implies a closed-form expression for the specific kinetic energy σ the observed decay laws σ ∝ (t − t0)−1 and σ ∝ (t − t0)minus5/2 follow for the initial and final periods.
Closure for Stochastically Distributed Reactants
Authors: O'Brien Edward E. , Eng Ronald M.
Published: February 2004

A closure is presented for the problem of the decay of reactants which obey an Rth-order equation, 1 ≤ R ≤ 3. Predictions of the closure are in agreement with an exact stochastic solution for a typical initial probability density.
Zero Diffusivity Invariance for Turbulent Chemical Reaction
Authors: Hill James C.
Published: February 2004

Two approaches for turbulent chemical reactions are suggested that preserve O'Brien's invariance and give the exact decay rates for zero diffusivity.
Blast Waves and Scaling Laws
Authors: Jones Donald L.
Published: February 2004

Spherical blast wave scaling is studied with the intermediate strength formalism. Simple scaling relations rarely exist, but the intermediate strength equations permit a direct comparison of arrival times and front overpressures for different explosions.
Ionizing Shocks Incident upon a Transverse Magnetic Field
Authors: Bout Dmitri A. , Post Richard S. , Presby Herman
Published: February 2004

The interaction of an ionizing shock wave incident upon a transverse magnetic field was investigated. The interaction results in slowing the transmitted shock and forming a reflected one. The magnetic field is compressed by the shock and decreases behind the shock.
Validity of the Electrostatic Approximation
Authors: Montgomery David
Published: February 2004

Criteria are derived for the existence of normal modes in a magnetized plasma for which |≇ × E|≪|≇·E|. The condition is different from the frequently quoted condition of thermal pressure ≪ magnetic pressure.
Drift Velocities in a Time-Dependent Electric Field
Authors: Gelman Harry
Published: February 2004

Generalized expressions are derived for the Hall, polarization, and Pedersen drift velocitites, which are valid in a static magnetic field and an electric field with arbitrary time dependence.
Ordinary-Mode Electromagnetic Instability in High-β Plasmas
Authors: Davidson R. C. , Wu C. S.
Published: February 2004

An absolute instability associated with electromagnetic waves propagating perpendicular to an external magnetic field is discussed. A lower bound on the growth rate is found and it is shown that growth rates may be of the order of the electron cyclotron frequency.
Theta Pinch Behavior for Very Early Times
Authors: Miller Bennett
Published: February 2004

A two-dimensional model of a theta pinch is used to analyze the buildup of the drive current on the surface of the plasma. The analysis shows that the usual asymmetric method of feeding energy into the plasma can produce significant azimuthal asymmetries in the current distribution.
Dispersion and Damping of Electrostatic Ion Waves in a Uniform Magnetic Field
Authors: Hirose A. , Alexeff I. , Jones W. D.
Published: February 2004

Dispersion and electron Landau damping of electrostatic ion waves in a magnetically supported plasma have been experimentally investigated for propagation angles 0° ≤θ≤90° and frequencies 0.2ωci ≲ ω ≲ 3ωci. For the most part, good agreement with theory is found.
Wave-Wave Coupling in Ion Wave Propagation
Authors: Ohnuma Toshiro , Hatta Yoshisuke
Published: February 2004

In the propagation of two ion waves (frequencies f1 and f2) the signal of f1 − f2 is found to grow spacially in some region, contrary to the monotonic damping of the waves of f1 and f2, which is explained as a wave-wave coupling among ion waves.
Internal Wave Wakes of a Body Moving in a Stratified Fluid
Authors: Keller Joseph B. , Munk Walter H.
Published: February 2004

Equations are derived for the wake produced by a source of waves moving in any dispersive homogeneous anisotropic medium. The behavior of the wake far from the source and near the source path are examined in detail. Then, internal waves in a stratified fluid with a thermocline of finite thickness are considered. The dispersion equations for all the propagating modes, of which there are infinitely many, are found. They are used in the preceding formulas to determine the wakes produced by an object moving horizontally with constant velocity in such a stratified fluid. A novel feature of these wakes is that the wavefronts of each of them have cusps spaced periodically along the path of the source.
Damping of Solitary Waves
Authors: Ott E. , Sudan R. N.
Published: February 2004

The Korteweg-de Vries equation is modified to include energy dissipation. In the cases treated the dissipative term is the Fourier transform of the linear damping. The effect of a small amount of such dissipation on the time evolution of a solitary wave is obtained.
Effect of Viscosity on Long Waves in Shallow Water
Authors: Bloor M. I. G.
Published: February 2004

A linearized theory is used to investigate the effect of viscosity on long gravity waves in shallow water. The propagation of an initial disturbance to the surface is considered and an asymptotic solution to this problem is obtained.
Three-Dimensional Long Waves on a Liquid Film
Authors: Roskes G. J.
Published: February 2004

The equations of motion for three-dimensional long waves on a liquid film are formulated, and the equation for the surface height is derived. The interaction between two- and three-dimensional waves is considered.
Kinetic Moment Equations for a Gas of Polyatomic Molecules with Many Internal Degrees of Freedom
Authors: McCormack Francis J.
Published: February 2004

The 17-moment approximation in the kinetic theory of polyatomic gases is extended to include gases whose molecules may possess many internal degrees of freedom. A closed set of moment equations is derived and their application to near equilibrium and relaxation type flows is considered. The role of complex collisions and the connection between the relaxation times and the volume viscosity are discussed.
Slip and Creep in Polyatomic Gas Mixtures
Authors: Annis B. K. , Mason E. A.
Published: February 2004

Explicit expressions are obtained for viscous slip, thermal creep, and diffusive slip in polyatomic gas mixtures through the use of the “dusty-gas” model. The most significant result is that the thermal creep depends only on the translational parts of the thermal conductivity and thermal diffusion coefficients. The multicomponent generalization is obtained, but is complicated for diffusive slip.
Transient Couette Flow of Rarefied Binary Gas Mixtures
Authors: Koura Katsuhisa
Published: February 2004

The transient Couette flow problem of rarefied binary gas mixtures is studied for the nonlinear case, Mi ≥ 1: one of the plates with equal plate temperatures is accelerated impulsively. The method of solution is the Monte Carlo method. The physical space is divided into macroscopically small cells. The change in the distribution function in a cell during a time interval Δt, which should be sufficiently small in comparison with the characteristic times (τD)iα, (τF)iα, and (τC)ij, is obtained by following the test particles for each molecular event through the event; i.e., molecular drift, external force, or molecular collision. The flow field is calculated for Maxwellian molecules and the range of Knudsen number Kn ≥ 0.1 (from free molecular to transition flow regime). The relaxation phenomena of a gas mixture with the boundary effects are observed. Of particular interest are an epochal relaxation due to the molecule-surface collision and the temperature “overshoot” near the moving plate. The steady-state solutions, which are obtained from the long-time results, are also presented. The effects of Knudsen number, mixture ratio, and gas-surface interaction are investigated, and the separation phenomena between the species are observed.
Weak Shock Generation According to the Energy-Conserving Bhatnagar-Gross-Krook Kinetic Equation
Authors: Mason Rodney J.
Published: February 2004

The early-time, linearized impulsive piston problem is solved analytically for a gas obeying the energy-conserving Bhatnagar-Gross-Krook equation. The piston is adiabatic by reflecting particles specularly. Exact solutions for the density, mean velocity, and temperature are obtained as simple quadratures which are evaluated numerically. Flow features are related to the properties of certain “γ figures.” Density near the piston is found to rise and then fall as the early, near free-molecular flow converts to a transient thermal boundary layer and emerging viscous-acoustic front. A temperature maximum is observed traveling first at the isothermal sound speed and then slowing to half the adiabatic sound speed as the post-front profile flattens. Comparisons are made with a previous isothermal BGK study and with Moran and Shen's results for the linearized Navier-Stokes equations. Agreement with the latter results down to transition times proves the value of retaining high frequency components in a Navier-Stokes description of the flow.
Interaction of an Ionizing Shock Wave with a Transverse Magnetic Field
Authors: Bout Dmitri A. , Gross Robert A.
Published: February 2004

A strong ionizing shock wave penetrating a transverse magnetic field is analyzed. The distribution of magnetic field behind the shock front is obtained. It is shown that for a steady-state magnetic field ahead of the shock front, at high magnetic Reynolds numbers, the field is swept along as a contact discontinuity initiated at the moment the shock enters into the field. For a magnetic field ahead of the shock front increasing rapidly in time, the field behind the shock front decreases sharply with the distance. The interaction of the incident shock with the magnetic field results in forming a reflected shock and a transmitted shock whose speed is less than that of the incident shock. The value of the magnetic field is found for which reflection of the incident shock is similar to the reflection from a solid wall.
Effect of Inelastic Collisions on Electron Transport Coefficients
Authors: Fox R. L.
Published: February 2004

A method is described for determining the maximum contribution of inelastic collisions to the transport properties of electrons in neutral and partially ionized gases. The inelastic collision cross sections are obtained from asymptotic expressions. The calculation was carried out for electron diffusion in neutral argon and lithium vapor and for the electrical conductivity of argon. The inelastic contribution to the diffusion coefficient displays a similar behavior for both the gases considered. The effect of inelastic collisions on the electrical conductivity was found to be less than 1% over the temperature range from 5000°K to 25 000°K.
Experimental Total and Total Line Radiation of Nitrogen, Oxygen, and Argon Plasmas
Authors: Krey R. U. , Morris J. C.
Published: February 2004

Total radiation measurements for nitrogen, oxygen, and argon plasmas are presented for 2000Å < λ < 60 000Å and for temperatures from 9000 to 15 000°K. These data are compared to previous measurements for the total continuum and to theoretical calculations for the total line radiation. The line radiation was found to be of the same order of magnitude as the total continuum. Taking into account the effect of absorption in the total radiation measurements, a lower limit is obtained for the accuracy of theoretical total line radiation calculations.
Reducing Experimental Langmuir Probe Data to Obtain a Comparison with Collisionless Probe Theory
Authors: Battle E. L. , Bell R. B.
Published: February 2004

The technique developed by Sonin for using the collisionless probe theory of Laframboise to obtain charged particle number density is here refined and extended to measurements of plasma potential. All necessary curves are given and the technique is applied to the reduction of experimental data taken in a glow discharge in argon in order to illustrate the method.
Critical Condition for the Electrothermal Instability in a Partially Ionized Plasma
Authors: Hiramoto Tatsumi
Published: February 2004

It is known that an electrothermal instability arises in nonequilibrium partially ionized plasmas subjected to crossed electric and sufficiently high magnetic fields. A linear theory is applied to investigate the properties of instability waves in the vicinity of the critical condition, considering the damping factor due to electronic heat conduction and radiative transfer, and also the phase shift between the variations in the electron temperature and density. There are two kinds of electrothermal instabilities: One is the normal ionization instability, and the other is a radiative instability, which can arise even in the case of no magnetic field. In the former, the largest growth rate occurs for a wave with the wavelength comparable to the characteristic length of the device. The latter has sufficiently long wavelengths compared with the length of the device. The critical Hall parameter below which instabilities do not arise increases as the size of the device containing plasmas becomes larger or the plasma pressure rises.
Hydromagnetic Oscillations of a Tangential Discontinuity in the Chew, Goldberger, and Low Approximation
Authors: Duhau S. , Gratton F. , Gratton J.
Published: February 2004

The differential equation for linear modes of oscillation of plane parallel flows of plasmas along an external magnetic field in the Chew, Goldberger, and Low approximation is obtained. Properties of modes for a tangential discontinuity are studied for the case when the surface is modulated along the magnetic field. Overstable modes found by other authors are shown to be spurious. Regions of existence of modes, proper frequencies, and spatial dependence of the perturbation are given. It is found that, broadly speaking, low β plasmas should be free of surface instabilities for all values of the flow velocity, whereas high β plasmas can be unstable if the flow velocity is nearly sonic. Changes in the anisotropy do not substantially affect the general picture of the problem.
Plasma Production with a Multibeam Laser System
Authors: Mead S. W.
Published: February 2004

A multibeam laser system has been used to produce spherical plasmas whose energies and growth rates have been compared with the results of machine computations. The laser system is designed to provide twelve simultaneous laser pulses that can be focused symmetrically on a common point in a gas-filled target chamber. Under typical operating conditions, a total energy of about 2 J in approximately 10 nsec was directed at targets of deuterium, hydrogen, and helium at atmospheric pressure. A multiple pulse schlieren system, utilizing light from the laser oscillator, was used to measure the growth rates of the shock waves associated with the expanding plasmas. The data were compared with computational results obtained using a one-dimensional machine code which treats the formation, heating, and hydrodynamic development of laser-produced plasmas. The measured growth rates are found to be in quite good agreement with the computed results and with the behavior expected on the basis of Taylor's blast wave theory.
Electrostatic Plasma Instabilities Excited by a High-Frequency Electric Field
Authors: Sanmartin Juan R.
Published: February 2004

The electrostatic plasma waves excited by a uniform, alternating electric field of arbitrary intensity are studied on the basis of the Vlasov equation; their dispersion relation, which involves the determinant of either of two infinite matrices, is derived. For ω0 ≫ ωpi (ω0 being the applied frequency and ωpi the ion plasma frequency) the waves may be classified in two groups, each satisfying a simple condition; this allows writing the dispersion relation in closed form. Both groups coalesce (resonance) if (a) ω0 ≈ ωpe/r (r any integer) and (b) the wavenumber k is small. A nonoscillatory instability is found; its distinction from the DuBois-Goldman instability and its physical origin are discussed. Conditions for its excitation (in particular, upper limits to ω0,k, and k·vE, vE being the field-induced electron velocity), and simple equations for the growth rate are given off-resonance and at ω0 ≈ ωpi. The dependence of both threshold and maximum growth rate on various parameters is discussed, and the results are compared with those of Silin and Nishikawa. The threshold at ω0 ≈ ωpi/r,r ≠ 1, is studied.
Comparison of Dupree's Perturbation Theory for Plasma Turbulence with Quasilinear Theory
Authors: Gratzl H.
Published: February 2004

In a weakly turbulent plasma Dupree's perturbation theory adds a new nonlinear interaction to the quasilinear equations. The new term is not a higher order correction of the quasilinear theory as others that are recovered by Dupree's theory.
Theory of Strong Turbulence in Plasmas
Authors: Ichimaru Setsuo
Published: February 2004

A theory of fluctuations which may be applicable to a plasma in any of the three states, namely, the quiescent, weakly turbulent, and strongly turbulent states, is obtained from an exact solution of the second equation of the Bogoliubov-Born-Green-Kirkwood-Yvon hierarchy for the stationary values of the pair correlation function. A salient feature of the theory is an explicit recognition of the fact that the effective interactions between two particles may be drastically modified because of the presence of strong correlations in a turbulent plasma. As a consequence of such a modification a significant change in the frequency wavenumber dispersion relationship of the collective mode may take place in such a way that the fluctuations with macroscopic intensities can coexist in a stable manner with the given single-particle distributions; this point is specifically illustrated by means of two examples (the cold beam-plasma system and the ion-acoustic wave instability) of turbulent plasmas. The possible existence of size effects in the plasma turbulence is also discussed.
Plasma Wave Echo in a Weakly Turbulent Plasma
Authors: Ichikawa Yoshi H. , Sanuki H.
Published: February 2004

The effects of turbulent fluctuations on the plasma wave echo have been investigated for a one-dimensional weakly turbulent electron plasma. It has been found that the interaction between electrons and fluctuations gives rise to (i) damping of the plasma echo, (ii) shift of the maximum position of plasma echo, and (iii) suppression of the peak intensity of plasma echo.
Velocity Diffusion in Resonantly Perturbed Magnetic Field
Authors: Clarke J. F. , Lidsky L. M.
Published: February 2004

Charged particle motion in perturbed magnetic fields can often be described as a random walk on a constant energy surface in velocity space. The particle–field interaction is strongest in “resonant perturbations”—those for which the characteristic wavenumber of the field perturbation is related to υ‖, the velocity of the particle along the direction of the average magnetic field, by kυ‖ = ω, where ω is the cyclotron frequency in the average field. Such fields occur (for example) as the magnetic component of slow transverse plasma waves. The random walk is usually described by a Fokker–Planck equation whose coefficients depend on the square of the perturbation field strength. Under certain conditions, this description is incorrect. If the field amplitude is strong enough to affect the phase correlation between the field and the particle before this correlation is destroyed by fluctuations in the field, the Fokker–Planck coefficients take on half-integral power dependences on the perturbation field strength. This behavior depends only on the relative magnitudes of the correlation times and occurs in an exactly analogous fashion for electrostatic perturbations. A criterion for determining the importance of this effect in particular cases is developed and compared with the results of a computer experiment.
Equilibrium Diffusion in a Toroidal Resistive Plasma
Authors: Stringer T. E.
Published: February 2004

The equilibrium equations are solved, including resistivity, parallel viscosity, and a radial electric field. A resonance effect occurs when the frequency of the electric rotation about the minor axis approaches the frequency of a natural plasma mode. For arbitrary steady electric fields the ion and electron diffusion rates are unequal, and the space charge inevitably builds up until the two rates equalize. In most conditions of interest, this ambipolar electric field is close to the resonance value, and the ambipolar diffusion rate is much larger than the Pfirsch and Schlüter rate.
Resonances and Wave Conversion below the Second Electron Cyclotron Harmonic
Authors: Kuehl H. H. , O'Brien B. B. , Stewart G. E.
Published: February 2004

A theory is given describing the conversion of fast-to-slow waves and vice versa, propagating perpendicular to a static magnetic field in a planar geometry for frequencies near and below the second electron cyclotron harmonic. The half-space and slab are treated with collisional effects included. It is shown that the power conversion between the two wave types is directly proportional to the scale length of the density gradient at the point in the plasma where the hybrid resonance condition is satisfied provided this scale length is small compared to a free-space wavelength. In spite of the small coupling, appreciable interaction is shown to take place between a transverse wave incident on a plasma slab and the longitudinal wave when a resonance condition exists for the longitudinal wave. The linewidth of the resonances is found to depend on both the density gradient near the hybrid resonance points and collisional effects.
Plasma Behavior in a Toroidal High-β Device
Authors: Gallagher Charles C. , Combes Lewis S. , Levine Morton A.
Published: February 2004

The stability of a cusp magnetic field has been combined with the low loss rate of a closed field configuration in a series of three small toroidal devices designed for plasma containment. In operation, a pinch partly stabilized by an axial magnetic field, is produced prior to application of the containing cusp field. The axial stabilizing field of the pinch is then trapped by the plasma so that closed field lines are maintained within the plasma while the cusp is excluded from the plasma. There is no evidence of turbulence and the device exhibits a loss rate an order of magnitude below that to be expected from the same device operated as a minimum-B configuration without field trapping. Containment time is dependent on the decay rate of the applied cusp field. Maximum value of β within the plasma exceeds 2 and β remains above 1 for 15 μsec. Electron densities and temperatures exceed 1016 cm−3 and 105 °K, respectively.
Behavior of a Cold Ion Plasma in a Toroidal Octupole
Authors: Sprott J. C.
Published: February 2004

By raising the background hydrogen gas pressure to ∼10−4 Torr and injecting 10-100 kW of 700-9000 MHz microwave power for ∼100 μsec, an afterglow plasma with n ∼ 109−1011 cm−3 and kTi < kTe ∼ 1 eV can be produced in the Wisconsin toroidal octupole. The particle lifetime is ∼3 msec, or somewhat longer than for a hot ion, gun injected plasma, and most (∼80%) of the plasma is lost to the hoops. The electron temperature decays rapidly as a result of inelastic electron-neutral collisions. By changing the magnetic field strength and microwave frequency, the density distribution can be varied, and a variety of fluctuations produced. These fluctuations do not appear to be an important source of plasma loss.
Integration of the Lagrangian-History Approximation to Burgers' Equation
Authors: Walton John J.
Published: February 2004

Using an initial smoothed random velocity distribution a comparison is made between results obtained by direct integration of Burgers' equation and those obtained by application of Kraichnan's Lagrangian-history direct-interaction approximation to this equation.
Droplet Agglomeration Induced by Weak Shock Waves
Authors: Temkin S.
Published: February 2004

It has been proposed that cloud droplet growth may be induced by weak shock waves. This possibility is presently under experimental investigation, and preliminary results are reported here which support the proposed growth mechanism.
Single-Particle Diffusion Due to Magnetically Guarded Hangers in a Toroidal Octupole
Authors: Erickson C. W.
Published: February 2004

Scattering of single particles by field perturbations due to magnetically guarded hangers may cause losses to walls and hoops commensurate with losses to unshielded supports.
Experimental Investigation of a Laminar Two-Dimensional Plane Wall Jet
Authors: Bajura R. A. , Szewczyk Albin A.
Published: February 2004

An experimental investigation was made of a two-dimensional wall jet at low Reynolds numbers with small natural disturbances in the jet. The main characteristics of the laminar regime are in agreement with theoretical results. The stability of the flow was studied for the Reynolds number range of 270-770. Longitudinal velocity fluctuations exhibited two regions of greatest amplitude, one region on each side of the maximum velocity peak. Growth of these fluctuations was found to be in agreement with linear stability theory. The disturbance region farthest from the wall appeared to dominate the stability of the velocity profiles. A characteristic frequency of the disturbance varied directly with the local maximum velocity and inversely with the local boundary layer thickness.
Velocity Profiles in Steady and Unsteady Rotating Flows for a Finite Cylindrical Geometry
Authors: Bien F. , Penner S. S.
Published: February 2004

Experimental determinations have been made of tangential velocity profiles in liquid water under conditions of steady and unsteady rotating flows for low (4 to 5) and high (1000) Reynolds numbers. Velocity measurements were performed by using the laser-Doppler velocimeter in various finite cylindrical arrangements with one stationary and one rotating disk. The steady velocity profiles (at appreciable distances from the cylindrical wall) have been found to be in excellent agreement with theoretical predictions based on solutions of the requisite boundary-value problems for cylinders of infinite radius. The observed unsteady velocity profiles (at appreciable distances from the cylindrical wall) for impulsive slow-down and impulsive start-up at small Reynolds numbers (R) are well accounted for by using a linearized theory for an axisymmetric configuration of infinite radial extent. For large values of R, no large differences were observed in the characteristic slow-down times at different radial locations (away from the cylindrical wall). The experimentally observed tangential velocity profiles for impulsive start-up show characteristic development times that are sensitive functions of the finite radial extent used in the geometric arrangement. Speed-up times decrease as the radial distance from the point of observation to the confining cylinder is reduced. In geometric arrangements in which only the cylinder radius was varied, characteristic development times for tangential motion were found to be a function of the dimensionless ratio measuring the radial distance to the wall divided by the cylinder radius.
Turbulence Measurements in a Supersonic Two-Dimensional Wake
Authors: Demetriades Anthony
Published: February 2004

Turbulence measurements have been made in the supersonic wake behind a two-dimensional flat plate held at zero incidence and heat transfer rate. The constant-current hot-wire anemometer has been used to record the distributions of density and axial velocity fluctuations and their cross-correlation in this wake. Once past an initial relaxation distance of about 900 wake thicknesses the values of these fluctuations measured on the centerplane are in good agreement with predictions based on low-speed behavior, energy conservation, and turbulent energy similarity. In the lateral direction the similarity behavior does not wholly conform to the same predictions, however; it is suggested that this departure is due to the low model Reynolds number of about 600. The longitudinal macroscale of the density is smaller than that of the velocity; they were both found to be smaller than 0.10 the wake thickness. The spectra were distorted by a prominence of wavelength slightly smaller than the wake thickness, which is tentatively attributed to a weak periodicity of the turbulent front.
Laser Planogram Measurements of Turbulent Mixing Statistics in the Near Wake of a Supersonic Cone
Authors: Schneiderman A. M. , Sutton G. W.
Published: February 2004

The laser planogram technique is a new method for the study of turbulent mixing. It utilizes a pulsed laser and a particulate tracer to determine the spatial mixing field of tagged and untagged fluids. The laser planogram technique is described along with design considerations. As an example of its implementation, laser planogram measurements have been obtained and analyzed to provide turbulent mixing statistics in the wake of a cone at a Mach number of 2.5 and a Reynolds number of 3 × 106. The mean radial concentration profile of tagged material is shown to be a Gaussian in agreement with theory. A k−5/3 spectral dependence on wavenumber is observed which is characteristic of high turbulent Reynolds number flows. Experimental limitations prevent the resolution of the turbulent scale lengths in the present experiment although the integral scale should be easily resolved with increased data length.
Numerical Study of the Burgers' Model of Turbulence Based on the Characteristic Functional Formalism
Authors: Hosokawa Iwao , Yamamoto Kiyoshi
Published: February 2004

The one-dimensional Burgers' model of turbulence is investigated by computing the functional integral expression for the correlation function, based on the Hopf theory of statistical hydromechanics, with the aid of a high-speed computer. The initial probability distribution of the velocity is assumed to be normal with zero mean and with a Gaussian covariance function. The manner in which the energy decay curve changes under variation of the Reynolds number R implies the existence of a certain asymptotic curve for R → ∞. The values obtained for the correlation function at some instants indicate that the inverse-square law for the energy spectrum holds in some wavenumber range for high values of R.
Stability of Liquid Film Flow down an Inclined Plane with Oblique Airflow
Authors: Smith F. I. P.
Published: February 2004

The hydrodynamic stability of a liquid film of uniform thickness and constant viscosity flowing down an inclined plane is examined, subject to a wind stress in some direction on its surface and having insoluble surface contaminants present. The intention is to discover how these two instabilities—that due to gravity and that due to wind stress—are related for a three-dimensional primary flow and to find criteria for the onset of instability. Previous work is discussed in relation to the results.
A Theory of Oriented Fluids
Authors: Kaloni P. N. , DeSilva C. N.
Published: February 2004

The development of a theory for the mechanical behavior of a fluid with deforming substructure is considered. Conservation laws appropriate for a class of oriented fluids, at each point of which are associated three deformable directors, are derived and discussed, and constitutive equations relevant to this class of fluids are given. These equations are then applied to study the behavior of dilute suspensions of both rigid and deformable substructure particles. It is shown that some of the results obtained by previous authors can be derived in a simple manner.
Qualitative Interferometry of Expanding Metal Vapor
Authors: Bennett F. D. , Kahl G. D. , Weber F. N.
Published: February 2004

The metal vapor from a wire exploded in a gas is assumed to be contained between the walls of a hollow cylinder which has boundaries that are linear functions of time. It is shown that the presence of the ambient gas can be ignored in the qualitative descriptions of the flow determined from interferograms. Studies of the single and multiple fringe interferograms expected from such a cylindrical flow are made. Graphical plotting techniques are developed to obtain these expected interferograms and supplementary mathematical relations describing the interferograms are demonstrated. Finally, comparison of interferograms obtained by these methods is made with those interferograms obtained during actual exploding wire experiments.
Effect of the Collision Frequency on Boundary Value Problems in Kinetic Theory
Authors: Sirovich Lawrence , York Harold
Published: February 2004

An approximate method in kinetic theory is applied to a model equation with velocity-dependent collision frequency. The Kramers problem is solved and an expression for the slip coefficient in terms of the collision frequency is obtained. The behavior of the solution in the kinetic layer and the far field is examined. The analytical form of the solution in the kinetic layer is shown to be independent of the collision frequency. In the far field, the solution is seen to contain a nonhydrodynamical term with an analytical form which depends on the asymptotic behavior of the collision frequency for high-speed molecules. An expression for the decay rate of the nonhydrodynamical portion of the solution is given in terms of the collision frequency. This expression is seen to agree with other known results.
Nonequilibrium in Confined-Arc Plasmas
Authors: Kruger Charles H.
Published: February 2004

The nonequilibrium behavior of argon and helium confined-arc plasmas at atmospheric pressure is analyzed in terms of a two-temperature ambipolar-diffusion model. Examination of spectroscopic data for the nonquilibrium arc shows that the free and bound electrons are mutually in equilibrium at a common electron temperature but not in equilibrium with the translational degrees of freedom of the heavy particles; the electron density in the outer portions of the arc may be as much as several orders of magnitude greater than its local thermodynamic-equilibrium value. Integration of the electron continuity equation and the electron and heavy-particle energy equations, with calculated transport properties and recombination coefficients, yields a satisfactory comparison with the measurements.
Test Ion Energy Loss in a Plasma with a Magnetic Field
Authors: May Robert M. , Cramer N. F.
Published: February 2004

The energy loss by a test ion in a plasma in the presence of a homogeneous magnetic field is considered, and numerical results for the magnetic field corrections to the rate of energy loss are presented. This is done for strong fields and for weak fields (i.e., for the electron cyclotron frequency greater than, and less than, the plasma frequency), and for all values of x, the ratio between test ion speed and plasma electron thermal speed; previous work is confined to x ≫ 1 .
Experimental Test of a Kinetic Theory of Tonks-Dattner Resonances
Authors: Ignat D. W.
Published: February 2004

Experiments were performed to test the effectiveness of a recent kinetic theory of plasma wave resonances in a warm inhomogeneous plasma column. The calculation and measurements are compared qualitatively with regard to resonance wave forms and quantitatively with regard to resonance location. An approximate comparison is made with calculations based on velocity moments of the Vlasov equation.
Linear and Nonlinear Theory for Waves in a Plasma Column in a Strong Magnetic Field
Authors: Jensen Torkil H.
Published: February 2004

A linear theory is formulated for electrostatic waves in a plasma column in a strong magnetic field. It is assumed that the electron velocity distribution is independent of space while the plasma density may be an arbitrary function of radius. This condition may be closely matched experimentally. The formalism is closely related to the usual theory of the infinite homogeneous plasma, and like that theory it provides a prescription of how to find the electric potential which results from an externally applied space charge. Therefore, weak nonlinearities may be treated. As an example, the theory for the plasma wave echo with the effects of velocity space diffusion included is extended to the plasma column case. As another example of the use of the formalism, the effect of a weak electron beam added to the plasma column is also calculated.
Surface Waves on a Plasma Half-Space
Authors: Kaw P. K. , McBride J. B.
Published: February 2004

The effect of density gradients and a finite temperature on the dispersion relation for surface waves on a plasma half-space has been investigated analytically. The full set of Maxwell's equations is used to obtain the dispersion of surface waves on a warm homogeneous plasma, thus complementing earlier work on the electrostatic mode. The full surface-wave dispersion relation is then derived for a cold plasma with arbitrary but weak density profile in the WKB limit. Finally, the dispersion of electrostatic surface modes on a cold plasma with a linear density profile of arbitrary strength is obtained. It is shown that when the density variation over a wavelength is very large, a new type of damped surface wave with a frequency higher than the surface plasma frequency is possible.
Coupling of Electrostatic Waves in a Nongyrotropic Plasma
Authors: Eldridge Owen
Published: February 2004

The dispersion relation for small-amplitude electrostatic waves in a nongyrotropic plasma is derived. The equilibrium distribution function is not symmetric in the plane perpendicular to the magnetic field and is necessarily periodic in time. A single electrostatic mode contains a linear superposition of potentials with the same wavelength and damping rate but with different frequencies separated by the cyclotron frequency. The dispersion relation is solved for the case of small asymmetry. The asymmetry then leads to a linear coupling of known modes, with small changes in known dispersion relations.
Experimental Investigation of the Production and Containment of a Laser-Produced Plasma
Authors: Bruneteau J. , Fabre E. , Lamain H. , Vasseur P.
Published: February 2004

The results of optical interferometric measurements in a laser produced plasma are presented. Two processes are studied. First, the quantity of charge in the plasma, as a function of the power density at the focal spot; agreement is found with the theoretical one-dimensional heating model. Second, expansion in a uniform magnetic field. Here, confinement occurs in the first stage and is rapidly perturbed by a large flow of the plasma across the field. This flow is explained by a charge separation when a highly directed velocity exists.
Magnetohydrodynamic Stability of a Diffuse Screw Pinch
Authors: Freidberg J. P.
Published: February 2004

The magnetohydrodynamic stability of a diffuse screw pinch is investigated in an attempt to explain certain discrepancies between experiment and sharp boundary theory. It is found that the stability of a diffuse pinch is fairly sensitive to the Bθ profile and can lead to large differences from the sharp boundary model. By suitably adjusting Bθ in the diffuse profile, the original discrepancy between experiment and theory is removed.
Perpendicularly Propagating Plasma Cyclotron Instabilities Simulated with a One-Dimensional Computer Model
Authors: Byers Jack A. , Grewal Mahesh
Published: February 2004

Perpendicular propagating (k‖ = 0) cyclotron instabilities of velocity distributions f(υ⊥) = δ(υ⊥ − υ0)/2πυ⊥ and similar loss cone distributions with velocity spreads are simulated with a one-dimensional computer model. Essentially noise-free starting conditions are created by loading phase space in a uniform way. Growth starting from machine roundoff levels can be observed at precisely the linear Vlasov theory predictions, up to the saturated level, many orders of magnitude above the starting point. When the growth is dominated by a single wavenumber, the post-saturation time behavior of the electric field is dominated by recurring peaks separated by the cyclotron period. This causes the major frequency components of the nonlinear signal to be at or near harmonics of the cyclotron frequency rather than the linear real frequency, which is nonharmonic. The amplitude of succeeding bursts decays slowly, suggesting the existence of quasistable nonlinear states. A nonlinear instability has also been observed. Furthermore, we have examined another k‖ = 0 instability, a double hump mode arising from the combination of a stable loss cone plus a small amount of cold ions.
Propagation of High Current Relativistic Electron Beams
Authors: Hammer D. A. , Rostoker N.
Published: February 2004

Theoretical self-consistent relativistic electron beam models are developed which allow the propagation of relativistic electron fluxes in excess of the Alfvén–Lawson critical-current limit for a fully neutralized beam. Development of a simple, fully relativistic, self-consistent equilibrium is described which can carry arbitrarily large currents at or near complete electrostatic neutralization. A discussion of a model for magnetic neutralization is presented wherein it is shown that large numbers of electrons from a background plasma are counterstreaming slowly within the beam so that the net current density in the system, and therefore, the magnetic field, is nearly zero. A solution of an initial-value problem for a beam–plasma system is given which indicates that magnetic neutralization can be expected to occur for plasma densities that are large compared with beam densities. It is found that the application of a strong axial magnetic field to a uniform beam allows propagation regardless of the magnitude of the beam current. Some comparisons are made with recent experimental data.
Flute-Like Instabilities in Plasma with Cylindrical Relativistic Electron Beam
Authors: Striffler C. D. , Kammash T.
Published: February 2004

The linearized, relativistic Vlasov equations are analyzed for the stability of flute-like modes in an infinite, collisionless plasma with a cold background and a relativistic annular electron beam situated in a uniform external magnetic field. Neglecting self-fields, a dispersion equation is obtained for small thickness beams. It is found that oscillations with frequency near harmonics of the gyrofrequency of the relativistic electrons are unstable. The most unstable oscillations are shown to be those with long wavelengths relative to the thickness of the beam. Growth rates and conditions for instability are given for systems where the beam particles are charge neutralized by cold background ions, and when the beam particles are dilute compared with the background species. For rarefied beams, an instability occurs at the hybrid frequency of the background species where the growth rate depends on the beam thickness. As the background density increases, a critical value can be reached where the long-wavelength oscillations are stabilized; and short-wavelength oscillations become most unstable. For these modes growth rates are maximized with respect to the harmonic number ℓ, and beam velocity β = υ/c.
Temperature Gradient Effects and Plasma Confinement in a Q-Device
Authors: Guilino Ernst
Published: February 2004

Azimuthal components of the electric field in Q-machine plasmas may occur if the distribution of temperature over the end plates deviates from rotational symmetry. In this case, Eθ×Bz drifts give rise to plasma loss rates which may be comparable in magnitude to Bohm diffusion. This effect is verified experimentally in a double-ended Q machine. A new heater system for the end plates using rotating cathodes yields temperature distributions which are symmetrical within less than 0.1%. Under these conditions the loss rate is reduced by a factor of 10 to 60 as compared to operation with conventional heater systems.
Application of the Electro-Optical Tracker to Measurements in Fluid Mechanics
Authors: Somerscales E. F. C.
Published: February 2004

A technique is described for the measurement of the falling velocity of small particles through a transparent fluid using an electro-optical tracker. The research had as its main objective the development of a noncontact method of fluid velocity measurement.
Expressions for the Exchange of Energy and Momentum between Gases at Different Temperatures and Velocities
Authors: Carlson Leland A.
Published: February 2004

Closed form expressions for the exchange of energy and momentum resulting from elastic collisions between species characterized by different temperatures and velocities are presented.
An Exact Expression for the Diffusion Slip Velocity in a Binary Gas Mixture
Authors: Lang H. , Loyalka S. K.
Published: February 2004

The method of elementary solutions is used to obtain an exact expression for the diffusion slip velocity for a binary gas mixture as described by a model employed recently by Yalamov, Ivchenko, and Derjagin.
Nonexistence of a Class of Magnetohydrodynamical Toroidal Equilibria
Authors: Tasso H.
Published: February 2004

In the axisymmetric case, it is possible to prove the non-existence of a class of magnetohydrodynamic toroidal equilibria. Resistivity is taken into account, but the motion is incompressible and purely meridional.
Control of an Instability on the Fluid Pendulum with Magnetic Feedback
Authors: Zrnić Dušan S. , Hendricks Charles D. , Crowley Joseph M.
Published: February 2004

A simple model of Rayleigh-Taylor instability on a fluid pendulum and its stabilization under the influence of magnetic fields with and without feedback are discussed.
Model Equations for Magnetohydrodynamic Turbulence—A Gas Dynamic Analogy
Authors: Thomas John H.
Published: February 2004

Model equations for magnetohydrodynamic turbulence previously proposed are shown to have an exact analog in gas dynamics. An analytical solution of the initial value problem and certain general results for the equations are presented.
Initial Comparison of Transform and Particle-in-Cell Methods of Collisionless Plasma Simulation
Authors: Armstrong T. P. , Nielson C. W.
Published: February 2004

Two fundamentally different methods are used to simulate the nonlinear development of a strong two-stream instability. Transform and particle-in-cell simulations are shown to agree for the growth rate and limiting amplitude.
Ion Acoustic Wave Propagation in the Presence of Transverse Inhomogeneity
Authors: Korn P.
Published: February 2004

A criterion is developed which determines when the one-dimensional free space dispersion relation is a valid description for longitudinal propagation along a bounded plasma in the presence of a large axial magnetic field.