bluuebunny/crossref_metadata_2025 huggingface dataset:
Prediction of Equilibrium Properties for Nearly Normal Model Turbulence
Authors: Meecham W. C. , Su M. -Y.
Published: February 2004

The first two terms of the Cameron-Martin-Wiener representation for turbulence are employed to examine the expected characteristics of the Burgers' model equation for initial-value problems. The representation employs the basic white noise process, nontime varying, and the characteristics of the expansion at later time are found. The equations are integrated more completely than in earlier works, and it is seen that so long as the initial spectra are not too far from equilibrium spectra the representation is adequate to a couple of correlation times. For greater time it would be necessary to employ higher-order terms or to turn to time-dependent white noise processes in the expansion. It is shown that it is possible to use a single white noise process to examine equilibrium characteristics for the model turbulence. Without further approximation, the by now familiar energy spectrum is derived, E ∼ k−2. Other recent work relating to the Cameron-Martin-Wiener expansion is reviewed critically.
Structure of Shock Waves with Nonequilibrium Radiation and Ionization
Authors: Nelson H. F. , Goulard R.
Published: February 2004

The investigations of this study are concerned with: (1) the physical processes that occur in the precursor and in the nonequilibrium region behind a strong shock wave during its approach to equilibrium in an argonlike gas; (2) the influence of different atom-atom collisional rates in the relaxation region on the precursor; and (3) the cause of precursor ionization, which in this study has been assumed to be the photoionization of both the ground and excited states. The argonlike gas is regarded as a combination of two gases; one consisting of electrons and the other of atoms and ions. Temperature differences between the two gases affect both the approach to equilibrium behind the shock wave and the precursor. Just behind the shock wave, the electron gas is cold relative to the atom gas. Farther into the relaxation region, the electron temperature approaches that of the atom gas, and thermal equilibrium is reached. Shortly thereafter, ionizational equilibrium is reached, and the gas begins to cool by the emission of excited-state radiation until it reaches its final steady state. The precursor ionization depends directly on the ratio of radiative to convective energy; thus, decreasing the ambient pressure increases both the extent and magnitude of the precursor. Increasing the atom-atom cross section increases the precursor ionization; however, changing the atom-atom cross section does not affect the extent of the precursor.
Electron Loss Processes in Air Afterglows
Authors: Dobrov W. I. , MacDonald A. D.
Published: February 2004

A modified microwave cavity technique was used to measure the decay rates of electron densities in air afterglows. Measurements of low-duty cycle or single discharges which were not affected by the discharge products of preceding events were obtained by monitoring the shifts of the resonant frequencies. Results of measurements in late afterglows show that one loss mechanism can be described by an effective ambipolar diffusion coefficient representing participation of two positive ions in the process; the ions being most likely O2+ and NO+. The other loss mechanism is due to two-body attachment of electrons, the likely attaching specie being NO2. The measurements on two different x-band cavities in the pressure range 0.1-10.0 Torr for ambipolar diffusion yielded: Da,eff p = 122 ± 18cm2/sec Torr and for attachment: hav1 = (4.9 ± 0.15) × 103sec−1Torr−1.
Near-Surface Electron Temperature of Weakly Ionized Plasma According to Kinetic Theory
Authors: Chung Paul M.
Published: February 2004

Properties of electrons near absorbing and emitting surfaces are studied for weakly ionized plasmas by analyzing the Boltzmann equation governing the electrons. For simplicity, it is assumed that the electric field intensity is given a priori. It is shown that there exists a “nonequilibrium absorption layer,” near the surface, wherein the kinetic distribution of electrons is completely out of equilibrium for all values of the mean free path, when the surface is highly absorbent with small or no electron emission. This layer is responsible for the large electron temperature jump at the surface, and it governs the electron temperature profile through the continuum as well as the rarefied plasmas. From the analysis it is found that the simple surface boundary condition for the continuum electron energy equation previously employed by the present author is correct when there is no surface emission. A similar simple surface boundary condition is deduced for surfaces with given finite emission rates.
Solitary Waves in a Warm Collision-Free Plasma
Authors: Krall Nicholas A.
Published: February 2004

The effect of finite temperature on the width of a magnetic solitary wave is calculated by expanding the Vlasov equation. The calculation is valid when this width exceeds the ion gyroradius but is less than the electron gyroradius.
Lorentz Model and Time-Dependent Diffusion
Authors: Huchital D. A. , Hollinger H. B. , Holt E. H.
Published: February 2004

The formalism required to treat the time-dependent diffusion of the light particles of a Lorentzian fluid from a given initial state is developed at the microscopic level in terms of an appropriate solution of the Boltzmann equation. Comparison is made with the results obtained from the alternative macroscopic approaches based on Fick's law and the telegrapher's equation. It is shown that the development via the Boltzmann equation leads to a microscopic telegrapher's equation. A solution is also presented for the case where a potential gradient is applied.
Effect of Charged Particle-Neutral Collisions on Collective Thomson Scattering
Authors: Gorog I.
Published: February 2004

The effect of charged particle-neutral collisions on the spectrum of electromagnetic radiation scattered by the free electrons in plasmas is investigated. The calculations are restricted to the regime where λe ≫ k−1 > λD, where λe is the mean free path for electron, k is the magnitude of the scattering k vector, and λD is the Debye length. The spectral density of the electron density fluctuations is computed from the Vlasov equation with the aid of a relaxational collision model. The results thus obtained correspond to Salpeter's expressions with a finite damping constant. The effect of collisions with neutrals on the central ion peak is found to be small in most laser scattering experiments. The effect of collisions on the electron wings, however, is much stronger. Approximate analytical estimates and more accurate numerical evaluation of the scattering cross section suggest that electron-neutral collisions may enhance the scattering from the longitudinal electron waves.
Dependence of Shock-Tube Boundary Layers on Shock Strength
Authors: Sturtevant B. , Okamura T. T.
Published: February 2004

Using familiar considerations of vorticity transport, the essential behavior of shock-tube boundary layers is explicitly exhibited; the nearly constant functions that cannot be calculated analytically are evaluated numerically and compared with Mirels' correlations.
Measurement of Velocity Space Diffusion using the Plasma Wave Echo
Authors: Jensen T. H. , Malmberg J. H. , O'Neil T. M.
Published: February 2004

The diffusion of plasma electrons in velocity space has been measured using the plasma wave echo as an experimental tool. The measurements were made for velocity space diffusion due to noise impressed on the plasma and that due to background noise.
Experimental Study of Thermal Convection in a Vertical Cylinder of Mercury Heated from Below
Authors: Verhoeven J. D.
Published: February 2004

Very precise temperature measurements have been made on a vertical circular column of liquid mercury, and also a mercury-zinc alloy, heated from below. In both pure mercury and the alloy, two types of temperature oscillations, indicating two modes of time-dependent fluid flow, were observed. The first oscillatory mode appeared at a Rayleigh number 10% higher than the critical Rayleigh number for the onset of fluid flow predicted by linear stability theory. At higher Rayleigh numbers this mode disappeared and the second oscillatory mode, having a shorter period, began at Rayleigh numbers 30% above the critical value. Both types of temperature oscillations are consistent with a pulsed mode of fluid flow. Attempts to detect the predicted, steady, antisymmetric flow at the onset of fluid motion by means of lateral temperature measurements were unsuccessful.
Strong Blowing across a Couette-Poiseuille Shear Flow
Authors: Inger G. R.
Published: February 2004

A theoretical study of mass injection into laminar viscous flows is made using an idealized Couette-Poiseuille shear flow model. Emphasis is placed on an examination of the massive blowing regime. Closed-form solutions are obtained in a unified form applicable to either two-dimensional or axisymmetric flow including heat transfer and the effects of both axial and blowing-induced lateral pressure gradients. The analysis shows that shear layer blowoff from the blown surface occurs for sufficiently strong injection, and that its onset is appreciably delayed by three-dimensional relief effects. The flow in this asymptotic regime has a two-layered structure whose basic character depends critically on whether or not an axial pressure gradient is present. The flow work effect of the blowing-induced lateral pressure gradients is also shown to influence the structure of the temperature field if the injection kinetic energy is sufficiently large.
Buoyant Ekman Layer
Authors: Hsueh Y.
Published: February 2004

The solution of a steady-state, baroclinic boundary layer over a two-dimensional terrain in an f plane is obtained. The boundary-layer thickness is found to be dependent on both the stability S = αmg[(Tm/H) + (g/cp)] (4Ω2L)−1 and the terrain slope. For a given terrain slope α and Prandtl number σ = ν/k, a critical value of the stability parameter S is found to exist and be equal to −(α2σ)−1, beyond which the O(1) boundary layer disappears completely. Except for neutral stability, the solution conserves up-slope (or down-slope) mass transport when the free-stream thermal wind is parallel to the ridges, reflecting the fact that the boundary layer is “leak free.” When the free stream possesses a small cross-ridge component, the Ekman suction is necessarily nonzero even under nonneutral conditions, so that the influx from the interior may be accommodated.
Effect of Dielectrophoretic Forces on the Bénard Instability
Authors: Turnbull R. J.
Published: February 2004

When a fluid is heated from below, there is a critical temperature gradient above which the fluid becomes unstable and convection results. The effect of dielectrophoretic forces on this critical temperature gradient is studied. Dielectrophoretic forces are caused by an electric field and a gradient in dielectric constant. The principle of exchange of stabilities is shown to hold for a certain set of boundary conditions. Variational principles are derived for various boundary conditions. These variational principles and the Galerkin method are then used to find approximate solutions for the critical temperature gradient as a function of the wavelength and the electric field.
Electron Temperature Effects in Fast Magnetohydrodynamic Shock Waves
Authors: Leonard B. P.
Published: February 2004

The interaction between magnetic and electron temperature effects is analyzed in the simplest nontrivial case of fast magnetohydrodynamic shock waves in a slightly ionized plasma. This interaction occurs because the magnetic structure and the associated Joule heating are dependent on the variation of electrical conductivity; the latter is affected by the electron temperature structure which depends in turn on the amount of Joule heating in the magnetic layer. The ionization is assumed to be frozen and so slight that the heavy particle structure (including a viscous subshock) is independent of that of the electrons. For negligible Hall currents a nonuniform coordinate stretching formally decouples the magnetic equation from the electron temperature system; the resulting two-point boundary-value problem is solved by matching asymptotic expansions in the outer magnetic layer and intermediate thermal layer when the respective length scales differ by a factor of about 3. The fine structure of the inner subshock region is not considered. Joule dissipation preheats the electrons in the upstream magnetic layer. Near the subshock the effect of a sudden compression of the electrons due to charge coupling with the heavy ions is diffused by thermal conduction, and there is a collisional relaxation zone downstream.
Anomalous Friction Due to Microturbulence
Authors: Drummond W. E. , Sloan M. L.
Published: February 2004

The effects of a stochastic electric field of high frequency and phase velocity on the dynamics of a low-velocity particle is studied. It has been shown that the effect of such fields, to second order in the electric field strength, is to introduce an anisotropic drag force into the equations of the particle dynamics which, as in the collisional case, is linearly related to the particle velocity and vanishes when the autocorrelation time of the statistical electric field vanishes.
Influence of the Self-Induced Magnetic Field on the Stability of a Plasma Column in a Longitudinal Magnetic Field
Authors: Paranjape B. V. , Seale D. , Ng K. C. , Johnson Roy R.
Published: February 2004

The Kadomtstev and Nedospasov theory of the helical instability of a positive column is extended to include force arising from the self-induced magnetic field, which pulls the plasma to the center. The effect is considered only to lowest order. It is predicted that an unstable positive column at critical longitudinal magnetic field will become stable if the electric current is increased. Modifications in frequency and wavelength associated with the increased current are derived.
Coaxial Snowplow Discharge
Authors: Butler T. D. , Henins I. , Jahoda F. C. , Marshall J. , Morse R. L.
Published: February 2004

The development of a coaxial plasma discharge in an initially uniform gas filling has been studied experimentally and theoretically. In the experiment, the usual outer coaxial electrode was replaced by a current return at the rear of the system, permitting unobstructed access to the discharge for the diagnostics. These diagnostics were image converter photography, magnetic probes, and holographic interferometry. The theory consists of two parts: two-dimensional (axisymmetric) time-dependent fluid computations and a supplementary analytic model, both of which assume that the vacuum magnetic field and the plasma are separated by a sharp interface; the experiments and computations are in good agreement on all gross features of the discharge leading up to the formation of a plasma focus and bubblelike structure in the shock front at the outer end of this focus.
Intrinsic Transport Theorem
Authors: Kiehn R. M. , Pierce J. F.
Published: February 2004

Cartan's method of exterior differential forms is used to generate an intrinsic transport theorem for continuous media.
Electron Temperature of a Partially Ionized Gas in an Electric Field
Authors: Robben F.
Published: February 2004

The effect of higher-order corrections in the Chapman-Enskog theory on the electron temperature is discussed, and some results are given for plasmas with power-law cross sections.
Mode Conversion in a Weakly Inhomogeneous Collisionless Magnetoplasma
Authors: Tang Ting-wei
Published: February 2004

The propagation of an extraordinary wave in a weakly inhomogeneous collisionless magnetoplasma is first studied in the cold plasma approximation. As the cold plasma theory breaks down near the upper hybrid resonance, a fourth-order warm plasma field equation is derived and its solutions obtained in integral form. Connection formulas based on the asymptotic expansion of the integral solutions by the method of saddle-point integration are deduced. These connection formulas are then applied to the problem of mode conversion between extraordinary waves and electrostatic plasma waves across the upper hybrid resonance.
Negative Mass Instabilities
Authors: Callen J. D. , Horton C. W.
Published: February 2004

Previous studies of negative mass instabilities are extended, for particles which do not encircle the axis of symmetry, to include the effects of thermal spreading in the ion velocity distribution, particle drifts, a new finite ion Larmor radius effect due to radial variations in the magnetic field B, and particle mirroring (bounce effects). For large anisotropies (T⊥ ≫ T∥) thermal spreading of the velocity distribution is found to introduce a low-density threshold and often to remove the cutoff of the instabilities at high densities. A (radial) min-B configuration is found to have a stabilizing effect on the longest (azimuthal) wavelength modes. Also, stabilization of the fastest growing modes is predicted if the velocity distribution is reasonably isotropic: T∥/T⊥ ≳ 4ai/L (ai is the ion Larmor radius, L is the scale length of magnetic field variation).
Heat Transfer Effects on Supersonic Wake Transition
Authors: Demetriades Anthony
Published: February 2004

Transition to turbulence in a two-dimensional supersonic wake has been studied for a series of model temperatures elevated above the stagnation temperature. Such heat transfer was found to delay transition greatly.
Upper and Lower Bounds on the Shear Stress of a Rarefied Gas
Authors: Strieder William
Published: February 2004

A variational lower bound on the shear stress in plane Couette flow is presented for the linearized Bhatnagar-Gross-Krook kinetic equation. Along with a variational upper bound developed by Cercignani and Pagani, it permits a “squeeze” on the values of the shear stress.
Numerical Solutions of the Compressible Navier-Stokes Equations for the Laminar Near Wake
Authors: Allen J. S. , Cheng S. I.
Published: February 2004

Numerical solutions of finite difference approximations to the compressible Navier-Stokes equations have been calculated for the steady two-dimensional flow of a supersonic stream and boundary layer over a rectangular base. The configuration represents a model problem for the laminar near wake of a blunt-based body. Solutions have been obtained for a range of Reynolds numbers (based on the base half-height and the inflow conditions) less than 1000 at Mach numbers between 2 and 4. Both the cases of an adiabatic wall and a constant wall temperature have been computed. The important features of the flow, such as the expansion around the corner, the separation of the boundary layer, the recirculation region, the recompression, and the formation of the wake shock, are illustrated in the results. Also shown are the changes in the solutions with the variation of the Reynolds number, the Mach number, and the wall temperature conditions.
Experiments with Shock-Heated Molecular Beams
Authors: Spence D. , Dolder K. T.
Published: February 2004

Shock-heated molecular beams have been produced in an apparatus similar in principle to that described by Skinner and Moyzis. Probes were used to measure particle velocities in shock-heated beams of argon, oxygen, and mixtures of these gases with helium. Good agreement was found between experimental and theoretical values. The velocity in a beam derived from a 5% mixture of argon with helium corresponded to an argon energy of 3.6 eV. Mass spectrometric measurements were made of the dissociation in shock-heated beams of argon mixed with either hydrogen or oxygen. Complete dissociation of hydrogen or oxygen was obtained by shock heating mixtures containing about 10% of these gases with argon. Excellent agreement between theory and experiment was found for the degree of dissociation of hydrogen, but there was substantial disagreement in the case of oxygen. It is suggested that this may be due to the variation with temperature of the dissociative ionization cross section of oxygen.
Stability of Crosshatched Wave Patterns in Thin Liquid Films Adjacent to Supersonic Streams
Authors: Nachtsheim Philip R.
Published: February 2004

Oblique wave formation giving rise to a crosshatched wave pattern in the melt layer of a body in supersonic flow is examined. The three-dimensional disturbance equations of the liquid including the effects of viscosity are formulated. The disturbance motion of the supersonic gas stream is taken into account neglecting viscosity. Three-dimensional disturbances are considered for which the flow is supersonic in the direction normal to the wave fronts and for which energy is fed into the disturbance motion of the liquid from the external gas flow through the pressure variation of the Mach waves at the interface. Numerical results are presented for waves in the liquid for a range of liquid Reynolds numbers. Analytic results in closed form are presented for a highly viscous melt layer. The connection between the dispersion relation presented for thin liquid films and the dispersion relation presented by earlier investigators for liquids of infinite depth is established. It is demonstrated that the inclusion of a finite depth for a viscous liquid leads to a lower cutoff wavenumber. Furthermore, it is shown that this cutoff is present even for initially quiescent liquid films as it is for films in shearing motion. For initially quiescent liquid films the results are correlated in terms of a single parameter.
Nonlinear Landau Damping of Ion Acoustic Modes
Authors: Sloan M. L. , Drummond W. E.
Published: February 2004

The time development of the ion acoustic modes of a hot electron plasma drifting through a cold ion beam is investigated. The nonlinear dynamics of the wave are governed by nonlinear Landau damping, resonant wave-wave scattering being forbidden. Owing to the adiabatic nature of the electrons, nonlinear Landau damping on the electrons is the dominant nonlinear process rather than ion nonlinear damping, contrary to the results of Kadomtsev. This error brings the anomalous resistivity formula of Sagdeev into serious question.
Nonlinear Theory of the Positive Column Spiral Instability
Authors: Shiau J. N. , Simon Albert
Published: February 2004

A previous calculation of the positive column spiral instability is extended to include mode-coupling terms as well as mixtures of He+ and He2+. At any given pressure, the theoretical results for pure He+ and for pure He2+ always bracket the experimental observation. The exact mixture necessary for agreement varies with pressure in the expected manner.
Feedback Stabilization of a High-β, Sharp-Boundaried Plasma Column with Helical Fields
Authors: Ribe F. L. , Rosenbluth M. N.
Published: February 2004

A sharp-boundaried, high-β stellarator of l-fold helical symmetry (plasma radius a, periodicity length 2π/h) is magnetohydrodynamically unstable, particularly to the m = 1, long-wavelength mode. For this mode the instability is driven by l ± 1 fields introduced by the unstable displacement ξ. Compensating fields (or, equivalently, plasma distortions) to counteract the instability can be introduced externally and controlled by a feedback arrangement. Estimates of the required external currents are given. The self-adjointness property of the magnetohydrodynamic energy-principle operator is used to derive the general relationship between the external fields and the unstable motion. Since perturbation theory is used, the question arises whether the normal mode with feedback differs appreciably from that without feedback for large feedback. The mode may be driven to a pure interchange, which is not subject to feedback control. In the stellarator this mode is stable above a critical β [of order (ha)2 for l = 1], and linear feedback stabilization is apparently possible in this case.
Multiple Scattering and Energy Loss of a Fast Test Electron Beam in a Plasma
Authors: Lampe Martin
Published: February 2004

For a tenuous monoenergetic electron beam incident on a quiescent plasma, the number and mean energy loss of electrons scattered through angle θ are calculated. The beam density is assumed so low that the collision frequency exceeds the growth rate of unstable plasma oscillations, preventing the development of a two-stream instability. The resulting test particle quantum Lenard-Balescu equation is solved. In the very-small-θ, multiple scattering regime, the energy loss rate becomes approximately independent of θ, but is about 20% smaller than the “stopping power,” or energy loss rate averaged over θ. Dynamic shielding effects, especially Cerenkov emission of plasma oscillations, contribute significantly to the energy loss rate. Also in the multiple scattering regime, the distribution over θ is approximately Gaussian, as has been shown by other workers, and dynamic shielding results only in small new corrections, principally to the width of the Gaussian. The transition to single scattering, which begins at θ ≳ 5° for parameters considered, is also studied. In the single scattering regime, the distribution over θ is non-Gaussian, and the energy loss depends strongly on θ. The calculation is quantitatively accurate only for θ ≲ 20°.
Viscous Flow in Angle Sectors
Authors: Rotem Zeëv , Ratkowsky D. A. , Neilson J. E.
Published: February 2004

Viscous flows in cavities having the cross-sectional shape of circular angle sectors are considered. The complete range of angles from π/12 to π is investigated numerically, using a new approximation method. The occurrence of higher-order vortices in the corner region is verified and numerical values for both the stream function and location of vortex centers are obtained. Experimental data were taken for sectors with three different opening angles.
Sound Attenuation in a Condensing Vapor
Authors: Marble Frank E. , Wooten David C.
Published: February 2004

The process of acoustic attenuation in a condensing medium is investigated using a continuumlike formulation that allows for the phase-exchange process. The liquid phase is assumed sufficiently disperse so that the field may be treated as a continuum. The elementary relaxation processes associated with droplet velocity, temperature, and vapor pressure equilibration are equally important in determining the attenuation when vapor, liquid, and inert gas mass fractions are of the same order. When the liquid mass fraction is small, however, a strong attenuation band appears at low frequencies. This attenuation process involves a coupled relaxation process in which heat transfer and vaporization processes combine to change the temperature of the relatively large gas mass. This attenuation band (i) centers on a frequency that is proportional to the concentration of liquid, and (ii) has a maximum value that varies directly as the concentration of condensible vapor and roughly as the square of the latent heat of vaporization. When the concentrations of liquid and condensible vapor are both small, the low-frequency attenuation band is nearly isolated and may be described in a convenient analytical manner.
Direct Simulation and the Boltzmann Equation
Authors: Bird G. A.
Published: February 2004

The direct simulation Monte Carlo method for the numerical solution of problems in rarefied gas dynamics is described and discussed. It is shown that the procedures adopted in this method can be directly related to the Boltzmann equation and that the two are entirely consistent. It is concluded that the results obtained from the method constitute a solution of the Boltzmann equation.
Trapped Low Frequency Waves Propagating along a Warm Plasma Cylinder
Authors: Klevans E. H. , Mitchell J. D.
Published: February 2004

Trapped low frequency ion modes propagating along a warm plasma cylinder imbedded in a dielectric are studied. The dispersion relation is given allowing for arbitrary azimuthal dependence. Computer solutions are presented for dipole modes. Symmetric modes are also studied for comparison with experiments. It is found that the electron temperature needed to fit the data is lower than that predicted by probes. A heuristic model used by previous authors is shown to be an approximate solution of the exact dispersion relation. Finally, the feasibility of observing dipole modes is discussed.
Transverse Wave Instability—Driven by Shear Flow in an Unmagnetized Plasma
Authors: Albright Norman W.
Published: February 2004

An unmagnetized collisionless plasma, subjected to shear flow, develops temperature anisotropy which causes unstable magnetic waves to grow. Equations for such a plasma have been numerically integrated in time. It is found that a steady state is approached which has constant phase relations between different spatial components of the magnetic field. Stabilization occurs when the ion gyroradius is equal to the typical wavelength of the magnetic waves. The coefficient of viscosity for this state depends on the local velocity gradient and on the density.
Backward-Scattering Instability of Cyclotron Harmonic Waves in Nonlinear Decay Processes
Authors: Chang R. P. H. , Porkolab M.
Published: February 2004

Experimental results are presented which demonstrate that a finite-amplitude traveling cyclotron harmonic wave may decay into two similar waves by the process of resonant mode-mode coupling. The results presented here are restricted to cases where the group velocity of one of the perturbed waves is in the opposite direction from that of the other perturbed wave. The important feature of this process is that considerable growth, both in time and space, can occur for the perturbed waves. The spatial growth of these waves is observed, and the wave amplitudes are in qualitative agreement with theory. Furthermore, the experiments provide a quantitative measure of the resonant mode-mode coupling coefficient for waves that propagate perpendicularly to the magnetic field in a warm plasma.
Response of a Weakly Ionized Plasma to Turbulent Gas Flow
Authors: Garosi G. A. , Bekefi G. , Schulz Michael
Published: February 2004

An arc discharge struck in a stream of flowing argon gas is studied as the flow is increased from the laminar regime to the regime of fully developed pipe turbulence, with Reynolds numbers (Re) ranging from zero to 6300. The properties of the discharge such as the density and density fluctuations, temperature, and electric field are measured with Langmuir-type probes. The discharge is found to respond strongly to the turbulent fluctuations of the un-ionized background gas. With increasing Reynolds number, plasma density fluctuations go up, the plasma column expands, and certain transport coefficients of the discharge rise well above their classical values. In particular, at Re = 6300, the plasma loss rate exceeds the expected classical value by about an order of magnitude. The observed phenomena can be understood in terms of relatively basic physical models.
Plasma Heating with Combined Radio-Frequency and Steady Magnetic Fields
Authors: Kofoid M. J.
Published: February 2004

Measurements were made of the power W p transferred into 5 cm diam cylindrical discharges in noble gases at p = 1μ−500μ pressure, using an axial sinusoidal 0.5 mc/sec magnetic field of intensity B∼ and a superimposed parallel steady magnetic field of intensity B0. With a fixed B∼, W p, passed through a maximum as B0 was increased from zero; W p decreased to a negligible value when B0 was increased to several times the value required for maximum W p. All the test results support the premise that, aside from some Ohmic heating by annular current flow, the only energy transfer process that was important when B∼ was less than B0 was magnetic pumping. The degree of ionization in the test plasmas was ≤ 17%. The test conditions reasonably complied with the restrictions of the large-amplitude magnetic pumping theory of Gerwin for power transfer into a fully ionized gas; only fair agreement between the predictions of his theory and the results of these experiments could be established.
Magnetic Field Confinement of Laser Irradiated Solid Particle Plasmas
Authors: Haught Alan F. , Polk Donald H. , Fader Walter J.
Published: February 2004

Laser irradiation of a small solid particle of lithium hydride in vacuum results in the generation of a spherically symmetric, isolated, highly ionized plasma. Experimental studies with such plasmas formed within mirror and minimum-B magnetic field up to 8 kG show that the expanding plasma can be captured by the magnetic field and the expansion kinetic energy thermalized, in agreement with a simple magnetohydrodynamic model of the plasma-magnetic field interaction. In the experiments, the major plasma loss occurs through the mirror loss cones, and mass spectrometer measurements show rapid escape of the highly ionized lithium followed by a more gradual decay of hydrogen indicating a scattering mechanism for the plasma decay. Plasmas with densities of 3 × 1013 cm−3 at temperatures of 100 eV are confined for lifetimes up to 150 μsec in a minimum-B field compared with the 0.3 μsec lifetime associated with the free plasma expansion. Both the magnitude and the temperature dependence of the plasma decay from a minimum-B containment field are consistent with plasma loss by Coulomb collisional scattering into the magnetic field loss cones.
Correlation of Diffusion Data in Grid Turbulence
Authors: Krasnoff E. , Peskin R. L.
Published: February 2004

The Langevin model for diffusion in grid turbulence is shown to be consistent with self-preservation of the decaying Lagrangian velocity field. Calculated dispersion is in excellent agreement with existing test results for diffusion of heat from a line source.
High Temperature Viscosity Ratios for Krypton
Authors: Goldblatt M. , Guevara F. A. , McInteer B. B.
Published: February 2004

The temperature dependence of the coefficient of viscosity relative to its value at 283°K has been determined for krypton at atmospheric pressure over a temperature range of 1100-2000°K.
Contributions to Nonequilibrium Thermodynamics. II. Fluctuation Theory for the Boltzmann Equation
Authors: Fox Ronald Forrest , Uhlenbeck George E.
Published: February 2004

The theory of the nonequilibrium phenomena in a dilute gas as described by the Boltzmann equation is extended in order to also include the fluctuations of the distribution function of the molecules. It is shown that in a first approximation this extension leads to the Landau-Lifshitz fluctuation terms in the hydrodynamical equations.
First-Order Treatment of Higher-Order Boundary-Layer Effects
Authors: Lewis Clark H.
Published: February 2004

The effects of transverse curvature, shock-generated external vorticity, boundary-layer displacement, and wall slip and temperature jump are considered as first-order boundary-layer effects. The classical boundary-layer equations were modified to include the higher-order effects, and flows over a 9-deg half-angle blunt cone were considered at M∞ = 9 and 18. Comparisons are made with second-order theory and experimental data. Primary interest is given to predicting the higher-order effects on zero-lift drag and comparsion with experimental data. Range of applicability of higher-order boundary-layer theory is indicated based upon the ability to predict zero-lift drag. Vorticity was the dominant higher-order effect, and the theory is most applicable to relatively short slender bodies. At very low Reynolds numbers, strong coupling of the higher-order effects was found to exist.
Viscous Flow through Porous Media. III. Upper Bounds on the Permeability for a Simple Random Geometry
Authors: Weissberg Harold L. , Prager Stephen
Published: February 2004

The variational treatment developed previously is applied to a porous medium constructed of randomly overlapping spheres. Upper bounds on the permeability are obtained for flow both in the absence and in the presence of slip. In the limit of zero solid fraction, these bounds approach the exact permeability in each case.
Electrostatic Probe in a Reacting Gas
Authors: Carrier G. F. , Fendell F. E.
Published: February 2004

A spherical perfectly catalytic conductor with negative potential bias lies in a quiescent slightly ionized gas whose density is large enough to warrant the use of continuum theory. The Debye number ε, the ratio of the Debye length to the conductor radius, is small. Principal attention is given to the case, amenable to asymptotic analysis, of probe potential ψp > 0(ln ε). The relation between the current collected by the probe and the electrode potential is sought; the current virtually saturates (increases very slowly relative to increases in applied potential difference) for ψp ≫ 0(ln ε). A reconstruction of the chemically frozen case with three novel features is furnished: a transformation of variables that renders the transition-zone equations almost uniformly valid; a very accurate, easily obtained closed-form approximation to the solution of the resulting boundary-value problem; and a current-potential relationship that is derived on the basis of the gross behavior of this approximate closed-form solution. Then the increase in current is determined for the case of finite-rate gas-phase ionization and recombination in which the negative-charge carrier is an electron and in which an electron does not serve as the third body for recombination. It is found that ionization can play a role in a thick sheath in addition to the more conventional effect of both ionization and recombination in the quasineutral region. When an electron serves as the third body for recombination, the sheath is frozen.
General Solution for the Linearized Ekman-Hartmann Layer on a Spherical Boundary
Authors: Loper David E.
Published: February 2004

A general solution for the linearized, hydromagnetic Ekman-Hartmann boundary layer on a spherical boundary is presented. The fluid is assumed to be incompressible, viscous, electrically conducting, and in a state of motion close to rigid body rotation. The conductivity of the boundary is unspecified and an arbitrary magnetic field permeates the fluid and boundary. The solution obtained is found to be independent of both the conductivity of the boundary and the magnetic field components parallel to the boundary. If the magnetic field is assumed to be frozen into the fluid outside the boundary layer, the general solution may be integrated for large time to obtain a stationary solution. It is found that hydromagnetic effects preclude the possibility of boundary-layer breakdown whenever a local normal magnetic field exists.
Steady Hydromagnetic Boundary Layer near a Rotating, Electrically Conducting Plate
Authors: Loper David E.
Published: February 2004

Gilman and Benton's study of the steady fluid motions and magnetic fields induced by a differentially rotating, electrically insulating infinite flat plate in the presence of a uniform magnetic field is generalized by allowing the electrical conductivity of the plate to be an arbitrary function of distance from the fluid-plate interface. It is found that the important measure of the conductivity of the plate is the ratio of plate conductance to conductance of a layer of fluid whose thickness is one Ekman depth. The form of the steady Ekman-Hartmann layer is found to be completely independent of the conductivity of the plate. The steady perturbation magnetic field within the plate is found to be entirely azimuthal and its magnitude is directly proportional to the conductance ratio. For values of parameters approximating conditions within the earth, the perturbation field may not be small. This azimuthal field causes an axial electric current to be drawn into the plate from the fluid, effectively strenghtening the coupling between fluid and plate. If the conductance ratio is large, as it is within the earth, spin-up is accomplished primarily by this current and the Ekman-Hartmann layer no longer plays a dominant role in coupling the fluid with its boundary.
Plasma Confinement in a High Magnetic Field Toroidal Quadrupole
Authors: Lubin M. J. , Friedman W. , Roberts M. , Alexeff I.
Published: February 2004

Plasma (n < 1011 cm−3, Te < 100 eV) in the ∮  dl/B stable region shows two decay times, τfast (20 μsec) followed by τslow (120 μsec, at constant Te). Where Debye length exceeds electron Larmor radius, τ ∼ B2 with particle loss mainly radial, below that field, τ ∼ B1/3.
Thermal Instability with Radiative Transfer
Authors: Christophorides C. , Davis Stephen H.
Published: February 2004

Linear stability theory is applied to determine the effects of radiative transfer in the thermal convection of a thin fluid layer bounded by rigid horizontal planes and heated from below. The critical values (for instability of the motionless fluid) of the Rayleigh number and wavenumber are computed for a gray, transparent medium including the effect of nonlinear initial temperature profiles. Limited results are given for the whole range of optical thickness showing that molecular heat conduction is negligible in the whole range except when the optical thickness approaches zero (a nonuniform limit). An estimate for the convective heat transport in a transparent medium is made using the “shape assumption” and compared with nonradiative convection.
Initial Stages of Axisymmetric Shock-on-Shock Interaction for Blunt Bodies
Authors: Moran John P.
Published: February 2004

A study is made of the transient flow in the shock layer of a blunt-nosed axisymmetric body which, while moving supersonically at zero angle of attack, is intercepted head-on by a plane blast wave. The analysis is based on Taylor-series expansion in space and time of the flow variables and of the shapes of the shocks and contact surfaces. Coefficients of the series are determined numerically from recursion relations derived by substituting the series into the exact three-dimensional equations of motion and jump conditions. The series are continued analytically beyond their natural region of convergence by recasting them as continued fractions. Comparisons of results obtained from successive truncations of the series show them to be sufficiently accurate to provide checks on the accuracy of more approximate methods. Although the present results are restricted to the initial stages of the interaction, they include the value and time derivative of the stagnation-point pressure immediately after blast-wave impingement. Also included in the results is a new approach, based on approximation theory and quasilinearization, to the adaptation of solutions of the inverse blunt-body problem to the direct problem, whose solution is required to determine the initial steady-state flow.
Diagram Techniques for Determining the Conductivity of a Liquid Metal
Authors: Neal T.
Published: February 2004

Diagrammatic perturbation techniques can be used to solve a general transport equation. These techniques are developed for the case of a correlated scattering system and the simple formula for the electrical resistivity of a liquid metal is obtained. Corrections to this formula are obtained in the form of a perturbation series whose convergence depends on the strength of the ion-electron potential and the density of ions. The convergence of this series and the corrections it represents are investigated for the case of liquid sodium.
Rotational Relaxation in Nonpolar Diatomic Gases
Authors: Lordi John A. , Mates Robert E.
Published: February 2004

The rotational-translational energy transfer in collisions between homonuclear diatomic molecules and the rotational relaxation time in diatomic gases have been investigated classically. Using Parker's model for the intermolecular potential, numerical solutions were obtained for the rotational-energy transfer in individual collisions. The method of solution for the collision trajectories has been combined with a Monte Carlo integration procedure to evaluate the transport properties for diatomic gases. The formal kinetic-theory expressions derived by Wang Chang, Uhlenbeck, and Taxman for the transport coefficients of gases with internal energy states were used. Results are presented for the shear viscosity, thermal conductivity, and rotational relaxation time in N2 which compare favorably with experimental values. Results are included for both a coplanar and three-dimensional collision model. Approximate solutions for the rotational-energy transfer in coplanar collisions and the rotational relaxation time are also presented. The approximate expression for the relaxation time agrees well with the Monte Carlo calculation and with experimental data for N2 and O2. The effect of unequal rotational and translational temperatures was also studied and found to be significant.
Effects of Nonelastic Collisions in Partially Ionized Gases I. Analytical Solutions and Results
Authors: Shaw J. F. , Mitchner M. , Kruger C. H.
Published: February 2004

A self-consistent solution of the coupled free-electron Boltzmann equation and the rate equations for the populations of the excited levels of a monatomic gas is presented, taking into account both nonelastic collisions and radiation losses. Appropriate forms of these equations for a monatomic, partially ionized gas are obtained. Approximate forms of the Boltzmann equation including the effects of nonelastic collisions, are solved analytically to obtain the distribution function. These solutions coupled with an approximate rate equation yield algebraic formulas for the first excited level population. The coupled Boltzmann equation and the rate equations for a model atom provide a qualitative model for predicting the first excited level population, the distribution function, and either the steady-state electron number density, or the net ionization rate. Results based on this model are presented, and include a discussion of the conditions necessary for the validity of the Saha equation at the electron temperature. It is concluded that the effects of nonelastic collisions and radiation loss are largest at low electron number densities and large radiation escape parameters.
Modification of the Quasilinear Theory by Two-Body Collisions
Authors: Nunez P. , Rand S.
Published: February 2004

The transfer of energy from the particles of an electron beam to longitudinal plasma waves has been studied. The quasilinear theory, with the inclusion of collision effects, is used. A comparison of the effect of two-body collisions and random wave-particle interactions on the evolution of the distribution function is made. Numerical solutions of the resulting equations are obtained.
Electron Beam Measurement of Ion Acoustic Wave Propagation
Authors: Goldan Paul D. , Leavens William M.
Published: February 2004

Ion acoustic wave propagation, near the sheath developed at a plasma-wall boundary, has been investigated in a low-pressure (∼ 5 × 10−4 Torr) argon plasma by an electron beam probing technique. Waves propagating into the plasma are found to have velocities ∼ 2 × 105 cm/sec, increasing with distance from the wall. The results are consistent with an analysis in terms of an ion free-fall model of the sheath. The model also makes plausible the observed zero reflection coefficient for small ion acoustic disturbances at the plasma boundary.
Relativistic Nonlinear Propagation of Laser Beams in Cold Overdense Plasmas
Authors: Kaw Predhiman , Dawson John
Published: February 2004

The nonlinear propagation of a very intense laser beam in a cold overdense plasma is analytically investigated; the laser beam is assumed to be intense enough to cause the directed component of electron velocity to be comparable to the velocity of light. Special attention has been given to the case when coupled longitudinal-cum-transverse modes propagate in the plasma. An interesting result is that the beam can readily propagate through the overdense plasma, in contrast to what would be expected on the basis of a linear theory of laser propagation.
Knudsen Flow through a Long Circular Tube
Authors: Pao Young-ping , Tchao Jeanne
Published: February 2004

Asymptotic solutions are obtained for the Knudsen flow through a long circular tube.
Velocity Distribution Measurements for Near-Free Molecule Flow through an Orifice
Authors: Lou Yeong-Suei , Stickney Robert E.
Published: February 2004

A time-of-flight technique has been used to measure the velocity distribution of the flow of cesium atoms from a sharp-edged orifice in the near-free molecule regime, 0.4 ≤ λ/D ≤ 18, for pressure ratios that are essentially infinite.