bluuebunny/crossref_metadata_2025 huggingface dataset:
Some Inertial Modifications of the Linear Viscous Theory of Steady Rotating Fluid Flows
Authors: Barcilon Victor
Published: February 2004

Some inertial modifications of the linear theory of steady homogeneous rotating fluid flows are investigated. More specifically, nonlinear modification of boundary layers, and in particular, of Stewartson layers are examined in connection with (i) a uniform flow past a cylinder and (ii) flows due to uniform source-sink distribution.
Perturbed Two-Phase Cylindrical Type Flows
Authors: Healy J. Val
Published: February 2004

The flow of an ideal fluid, containing small spherical particles, past a cylinder and a flat plate of finite width standing normal to the stream, is treated by the method of small perturbations. The perturbed equations for arbitrary initial particle density k0 are difficult to solve, even numerically. When the further assumption of small k0 is made, the problem is simplified considerably. For this case the nonlinear equation governing the particle streamlines is given in differential form. The equation governing the particle density distribution is solved by the method of characteristics and the result given in integral form. The Runge–Kutta method is used to obtain numerical solutions and the results are presented graphically. Conformal mapping and analysis are used to find the particle streamlines and density distribution k for the flow past a flat plate of finite width. For both bodies a particle-free zone exists, whose size depends only on the particle Stokes' number, and in all cases the particle density increases monotonically along the particle streamlines in the downstream direction. The critical particle Stokes' number is found to be 0.125 for the cylinder and 0.25 for the plate.
Lagrangian Statistics from Numerically Integrated Turbulent Shear Flow
Authors: Deardorff J. W. , Peskin R. L.
Published: February 2004

Lagrangian turbulence statistics were obtained from a three-dimensional numerical model of plane Poiseuille flow at large Reynolds number. Single-particle Lagrangian correlations were computed and compared with Eulerian space correlations. Although the curves were not self-similar, a dimensionless scale ratio defined at the e-folding time was comparable to Eulerian-Lagrangian scale ratios found in the literature. The numerically obtained mean-square particle displacements exhibited correct short- and long-time behavior. Mean-square particle separations were analyzed, and two-particle Lagrangian velocity correlations taken at the same time were more persistent than Lagrangian autocorrelations. A semiempirical functional form was constructed for the two-particle velocity correlations which yielded two-particle distance correlations in good agreement with those of the numerical model. The effect of mean shear on downstream separation was examined. Results indicate a t3 or steeper dependence for downstream mean-square separation 〈(xa − xb)2〉, with strong shear and Reynolds stress. Batchelor's similarity law, namely, that 〈(xaj − xbj)2〉 ∝ εt3 in directions not controlled by shear, is postulated for the direction of shear when shear generates ε. This postulate was tested numerically and found to be consistent.
Density Fluctuations and Longitudinal Conductivity of a Weakly Ionized Turbulent Plasma in a Magnetic Field
Authors: Tsukishima T. , Mase A. , Takeda S.
Published: February 2004

The collision frequency νt of an electron with turbulent waves is found to increase linearly with the mean square of the density fluctuation of the electrons in a turbulent positive column. νt becomes as large as 10 times the electron-neutral collision frequency νen.
Nonlinear Ion-Acoustic Waves in a Vlasov Plasma
Authors: Gary S. Peter
Published: February 2004

Nonlinear ion-acoustic waves in a collisionless, Maxwellian, electron-ion plasma are considered in an initial-value problem. The changes in the second order, spatially homogeneous parts of the distribution functions are calculated in the long time limit, and are used to modify the linear dielectric function. For Ti ∼ Te, it is shown that nonlinear electron contributions are much more important than corresponding ion terms, and the zero electron mass approximation is not valid for calculating nonlinear damping in this case. The decrease in the magnitude of the damping decrement in the long time limit is obtained.
Collisional Coupling of Neutral- to Plasma-Acoustic Waves in a Diffuse Layer
Authors: Woo James C. , Kahalas Sheldon L.
Published: February 2004

If a neutral acoustic wave propagates into an inhomogeneous, partially ionized region whose particle density is decreasing and whose ionization density (starting from zero) is increasing in the direction of propagation, then the neutral acoustic wave, propagating in the neutral component of the gas, excites an ion acoustic wave by collisional coupling. If the neutral gas and plasma are in thermal equilibrium, the two waves are in phase, so that an ion wave of significant amplitude will be excited, while the neutral wave is strongly dispersed. The ion wave amplitude has a maximum in the frequency domain at a period of about 1 min, consistent with experimental observations of certain traveling disturbances in the lower ionosphere.
Electrostatic Electron-Ion Streaming Instability
Authors: Wong H. V.
Published: February 2004

When electrons drift relative to ions across a magnetic field, the field-free instabilities can still persist. However, new possibilities for collective instabilities occur. In particular, an electrostatic instability with growth rate γ ∼ (me/mi)1/4Ωe can develop when ωpe ≫ Ωe, Te > Ti, and the electron drift velocity is less than the electron thermal velocity. This is due to the coupling of a Doppler-shifted ion mode and the electron cyclotron mode.
Dynamic Stabilization and the Rayleigh-Taylor Instability
Authors: Wesson John
Published: February 2004

Most problems in the dynamic stabilization of plasmas have been treated in a sharp boundary limit. The stability of an incompressible liquid and of a low-β plasma, having continuous density profiles, is considered here. The destabilizing force is gravity, and stability is sought by oscillating the system in a direction parallel to this force. In the case of a liquid, long wavelengths are stabilized but short wavelengths remain unstable. In the case of a plasma, it is found that modes which are unstable with dynamic stabilization alone or finite Larmor radius effects alone can be stabilized by the presence of both.
Energy and Particle Loss from a Short Theta Pinch
Authors: Jones W. B. , Goldman L. M. , Kilb R. W. , Bingham R. L.
Published: February 2004

The axial and temporal variation of the electron density and temperature have been measured in a 0.5-m-long theta pinch with a 14.5-μsec half-cycle duration by means of laser light scattering. The plasma diameter and diamagnetic flux signal were also measured. A fairly flat peak of the electron temperature of ∼ 160 eV is found from 2 to 6 μsec inside the mirror coil. The density is more sharply peaked, both in axial and temporal variation, with a maximum of 3.2 × 1016electrons/cm3 at the centerplane from 3 to 4 μsec. The predominant energy loss is the energy transport associated with the particle loss (e-folding time of 1.5 μsec) in this relatively short theta pinch, but electron heat conductivity does result in an energy loss of 50-150 eV/μsec per electron. Ion-electron heat transfer from the hotter ions to the cooler electrons nearly balances the electron heat flow. From the electron temperature and density profiles and using the electron momentum balance equation, the plasma potential was derived and found to be approximately 450 V at the centerplane from 2 to 6 μsec. A magnetohydrodynamic model computation for this experiment has been made which shows that the parallel electron heat conductivity as given by Spitzer and Landshoff is correct to no worse than a factor of 10, and possibly a factor of 3. The computations also show that the amount of magnetic flux trapped in the plasma cannot be constant but either decreases with time or is nonuniformly imbedded in the plasma at the end of the initial implosion.
Stability of Trans-Alfvénic Ionizing Shock Waves
Authors: Leonard B. P.
Published: February 2004

Unlike trans-Alfvénic shock waves in a preionized gas, trans-Alfvénic ionizing shock waves may exist. A shock wave of this type is able to stably absorb a rotational Alfvén disturbance into its structure, thereby giving rise, in general, to a perturbed “skew” shock.
Dynamic Stabilization of the m = 1 Instability in a Bumpy Theta Pinch
Authors: Berge G.
Published: February 2004

Both theoretically and experimentally a bumpy theta pinch is known to be hydromagnetically unstable. The possibility of dynamic stabilization of this configuration is discussed. The results show that stability can be achieved in this way. The plasma column is assumed to be separated from a vacuum magnetic field by a sharp boundary. The analysis is based on a generalization of the hydromagnetic energy principle. Within the framework of this theory a sufficient condition for stability is obtained for the m = 1 mode. This condition contains the amplitude of the unstable bulge, the frequency and amplitude of the forced oscillations, and the characteristic lengths and speeds in the system. The condition shows that stability is obtained for sufficiently large amplitude in the oscillatory magnetic field. The case of β = 1 and “arbitrary” m numbers is also briefly reviewed.
Stability of a Submerged Jet
Authors: Nakaya C. , Hasegawa E.
Published: February 2004

A new method is presented of investigating the stability of a submerged jet. It is shown that steady perturbation appears for a certain value of total momentum flux of the jet.
Oscillations of a Weakly Inhomogeneous Plasma with Collisions
Authors: Bajwa G. S. , Srivastava K. M.
Published: February 2004

The oscillations are damped when the collision term is incorporated in the study of the oscillations of a weakly inhomogeneous plasma. It has also been established that the resonance and cutoff frequencies are not identical for zero curvature of the field lines.
Ion Acoustic Wave Propagation near the Ion Cyclotron Frequency
Authors: Ceglio Natale M. , Lidsky Lawrence M.
Published: February 2004

An experimental investigation of ion acoustic wave propagation near the ion cyclotron frequency is described. The acoustic wave was found to propagate along the plasma column in other than a plane wave mode, but no cyclotron resonance effects were observed.
Interaction of Three Plasma Waves in a Cylindrical Waveguide
Authors: Spithas E. N. , Manheimer Wallace M.
Published: February 2004

Three-wave interaction in a cold, collisionless, uniform plasma filling a circular waveguide is studied. Selection rules and matrix elements are obtained.
Effects of Collisions on Spatial Plasma Wave Echoes
Authors: Ichikawa Yoshi H. , Suzuki Takehiko
Published: February 2004

Collisional effects of spatial plasma wave echoes are studied for an electron plasma on the basis of simple collision models. It is shown that the central structure of the spatial wave echo may be determined by the saddle point contribution of the free-streaming plasma particles.
Nonequilibrium Theory of Fluid Fluctuations
Authors: Hinton F. L.
Published: February 2004

A generalization of previously existing theories of fluctuations in dilute monotonic gases is obtained which describes nonequilibrium states with spatial gradients. A kinetic description of the fluctuations is first derived, and the reduction to the fluid limit is then carried out. The theory can be used to describe the enhanced fluctuations which are expected to occur near the onset of hydrodynamic instabilities.
Effects of Electron Emission on Electrostatic Probes at Arbitrary Pressures
Authors: Chang Kuo Wei , Bienkowski George K.
Published: February 2004

A systematic investigation of the effects on probe response caused by electrons emitted with a half-Maxwellian distribution is performed. In the absence of collisions a theory for spherical and cylindrical probes in a plasma of infinite extent is formulated, based on orbit calculations. A simple method is developed which greatly facilitates the solution of the space-charge-limited emission problem. The structure of the resulting double sheath is analyzed in detail. Effects of trapped particles are found to be unimportant under practical situations. Solutions of current-voltage characteristics and space-charge-limited current are presented for the case of thermionic emission. Theories in the transitional and continuum regimes for a spherical probe in a weakly ionized gas are formulated by the moment method. For a dense plasma with a free fall sheath the emission is usually both space charge and diffusion limited.
Adiabatic Wall Solutions for the Hypersonic Compressible Laminar Boundary-Layer Equations
Authors: Rogers David F.
Published: February 2004

Similar solutions for the laminar compressible boundary layer are presented for zero heat transfer at the wall and Prandtl number equal to 0.723. The maximum adiabatic wall temperature ratio is found to occur at the separation point. The effects of Prandtl numbers from 0.5 ≤ σ ≤ 1.0 on the maximum adiabatic wall temperature ratio and the pressure gradient parameter at the separation point are presented. In contrast to Stewartson's conclusion for the general compressible boundary layer, numerical evidence indicates that the hypersonic similar compressible boundary layer does not exhibit singular behavior when the shear and heat transfer at the surface are simultaneously zero.
Chemical Reaction in a Turbulent Flow Field with Uniform Velocity Gradient
Authors: Chung Paul M.
Published: February 2004

A simplified statistical theory is developed which describes the chemically reacting, turbulent shear flows in a tractable manner. This theory, which is based on the concept of the generalized Brownian motion, instead of Navier-Stokes equation, is completely self-containing provided that the molecular Schmidt number is of order one and that the local turbulence Reynolds number is sufficiently large. The latter requirement restricts the theory to the flow region outside of the laminar sublayers. The homologous flow and concentration fields are first analyzed for the chemically frozen case. From the analyses, the relationships between the mean velocity and concentration gradients, and the Reynolds stress, turbulence energy, turbulent transport of chemical species, and the mean square fluctuation of the species concentration are established. Comparison of the present results with the available experimental data is made, which shows a satisfactory agreement. The nonequilibrium chemical reaction is then analyzed and is found to create an inhomogeneity in the concentration field which, among other things, causes the mean square fluctuation to vary nonuniformly with respect to the Damkohler number and the flow region.
Turbulent Mixing at the Contact Surface in a Driven Shock Wave
Authors: Levine M. A.
Published: February 2004

In a shock tube, with a bursting diaphragm, the separation of the test gas from the driver gas at the contact surface does not always occur. In this paper helium-argon test gas mixtures are used with a helium driver to explore the role of the ratio of average molecular weight on the formation of the contact surface. The results are correlated with a theory that supposes turbulent mixing due to a Rayleigh-Taylor instability, and a criterion or L ratio is defined which predicts when the turbulent mixing is sufficient to destroy the hot gas sample of the pure test gas.
Aspects of the Structure of Strong Shock Waves
Authors: Bird G. A.
Published: February 2004

The direct simulation Monte Carlo method has been used to study the structure of strong shock waves in a gas of point center of repulsion molecules. The values obtained for the maximum density slope thicknesses agree with the predictions of the Mott-Smith method. The results for the effect of molecular model on the rate of change of this thickness with shock Mach number are in agreement with the common prediction of the Mott-Smith and Navier-Stokes theories. The velocity distribution function within the wave is illustrated by computer display photographs with the molecules represented as dots in the plane of longitudinal and lateral velocity. This also gives qualitative support to the bimodal model. However, it is found that the density profile has a significant degree of asymmetry, contrary to the bimodal prediction. Results are also presented for the profiles of the higher moments of the distribution function.
Test Particle Method in Kinetic Theory of a Plasma
Authors: Matsuda Kyoko
Published: February 2004

A general relationship has been found between many body correlation functions and the conditional probability functions which describe the shield clouds surrounding test particles. This is the generalization of Rostoker's superposition principle. The relationship is useful because the problem of kinetic theory is reduced to determining the conditional probability functions, which essentially involves only the Vlasov equation.
Turbulence in the Positive Column
Authors: Halseth Martin W. , Pyle Robert V.
Published: February 2004

An oscillation that is helical in shape is known to be present when an axial magnetic field applied to the positive column of a glow discharge is greater than the critical magnetic field Bc for the onset of the current convective instability. According to a theory proposed by Kadomtsev, this oscillation will be replaced by a turbulent spectrum of oscillations when the field is several times Bc. In this experiment with a helium plasma the magnetic field has been raised to as much as 20 times Bc to determine if and to what degree random oscillations characteristic of strong turbulence will replace the helical instability. It was found that strong turbulence dominated the positive column when the magnetic field was greater than 15 times the critical field. The radial mixing length as determined from spatial correlations with movable Langmuir probes and the radial density profile were found to agree with the results calculated from Kadomtsev's theory for strong turbulence. Particle transport rates calculated from the theories of Dupree and Kadomtsev for a turbulent plasma agree within a factor of 2 with the values deduced from this experiment.
Theory of Stability of Large Periodic Plasma Waves
Authors: Goldman Martin V.
Published: February 2004

A method is developed for examining the stability of a large-amplitude periodic Bernstein-Greene-Kruskal wave, E0, in a collisionless plasma. Vlasov's equation is integrated by the method of characteristics to yield a polarization charge density response ρ1, linear in a small-amplitude field E1, but nonlinear in E0. The susceptibility linking ρ1 and E1 is expressed in terms of the exact orbits of trapped and untrapped particles in the field E0, distributed in energy according to an assumed Bernstein-Greene-Kruskal distribution function f0. These susceptibilities couple the Fourier components of E1 in the usual mode-coupling fashion, but trapping effects are now included. For fields E0 which are not too large, the mode-coupling problem reduces to finding the zeroes of a 2 × 2 or 3 × 3 determinant. Trapped electron distribution functions which are localized at the bottom of the potential energy troughts of E0 give the growing side-band instability of Kruer, Dawson, and Sudan.
Low-Density Plasma Sheath in the Presence of a Weak Magnetic Field
Authors: Caron Paul R.
Published: February 2004

The theory of the collisionless plasma sheath with a weak magnetic field is presented. Both planar and cylindrical geometries are considered. Two forms for the ion-electron pair generation function are considered—a constant function and a function which is proportional to electron density. These are applicable to beam-generated plasmas and to positive columns. Numerical results are given for the plasma limit when the generation function is constant.
Obstacle Induced Convection in a Toroidal Octupole
Authors: Schmidt J. A. , Schmidt G. L.
Published: February 2004

The effects of hoop supports and other obstacles penetrating the plasma containment region of a toroidal octupole were determined. Obstacles produced large scale convective cells which move plasma toward the field boundary at the azimuth of the obstacles and toward the separatrix at other azimuths. Under certain obstacle bias conditions, 3 V floating potential steps were observed across a dummy support along with 100% density steps. The density step showed an exponential dependence on the obstacle bias potential. A model is discussed which predicts the observed properties of the potential and density steps. Electron cooling at the obstacle was also detected.
Direct Correlation Function in Space and Time
Authors: Lado F.
Published: February 2004

A new, simpler derivation is presented of the equation suggested by Percus and Yevick to define the generalized direct correlation function in space and time. In addition, an explicit, though formal, definition of this function is given.
Thermal Relaxation in One- and Two-Dimensional Plasma Models
Authors: Montgomery David , Nielson C. W.
Published: February 2004

Thermal relaxation of stable one- and two-dimensional plasmas is followed in time by particle-in-cell numerical computation. The predicted dependences of relaxation rate on plasma parameter are observed.
Nonlinear Dynamics of a Single Nonharmonic Loss-Cone Flute Mode
Authors: Bodner S. E.
Published: February 2004

Previous analysis at the cyclotron harmonics indicated that particles would move in closed isolated eddies with a maximum change in kv⊥/Ω of π. At other frequencies a degeneracy is removed and some of the particles become untrapped.
Theory of the Positive Column Including Electron-Ion Recombination
Authors: Lindgren R. G. , Gavalas G. R.
Published: February 2004

A theoretical study of the effect of electron-ion recombination on the voltage-current characteristic of the positive column of a glow discharge is presented. In the absence of recombination, as the current increases the voltage decreases and reaches a constant value. In the presence of recombination and at sufficiently high currents, the voltage increases with increasing current.
Multiple Pseudowaves Produced by a Single Voltage Pulse
Authors: Alexeff I. , Jones W. D. , Widner M.
Published: February 2004

A multiple pseudowave—or a series of fast ion bursts—is generated when a short negative voltage pulse is placed on a transparent grid immersed in a plasma. The phenomenon resembles, but is not, a damped wave train. Using a single-particle model, it is shown that multiple pseudowaves can be explained in terms of ions trapped and oscillating in the ion sheath formed around the grid by the negative voltage pulse. A pulsed grid used in this manner constitutes a simple diagnostic technique for measuring plasma density.
Shock and Current Sheet Structure in a Theta-Pinch Configuration
Authors: Alidières M. , Aymar R. , Koechlin F. , Jourdan P. , Samain A.
Published: February 2004

The structure of a current sheet during the compression of an argon plasma with no bias field is studied in a theta-pinch configuration. The profiles of magnetic field, particle density, mean velocity, and temperature are measured. No perturbation in front of the sheet is observed. It is shown that the initial gas passes through the sheet, emerging downstream, with a small relative velocity. During this acceleration process, the ion and electron temperatures remain small. The initial energy of ions relative to the sheet is thoroughly converted into thermal electron energy and in turn is radiated away through excitation of argon ions. The plasma motion, as well as the structure of the sheet, can be explained using fluid equations and Ohm's law. These equations are similar to those which govern the structure of a transverse shock wave with the resistivity as the only dissipative process.
Vlasov Equilibria and Stability of an Electron Gas
Authors: Davidson Ronald C. , Krall Nicholas A.
Published: February 2004

Self-consistent Vlasov equilibria with space charge are constructed for a pure electron gas radially confined in a uniform external magnetic field. A sufficient condition is obtained for the stability of these nonuniform equilibria to electrostatic perturbations. For the case in which the electron density is constant in the column interior, the dispersion relations for small-amplitude interior perturbations, electrostatic and electromagnetic, are shown to be similar in structure to the corresponding results for a neutral plasma. Algorithms are given for obtaining electron gas stability information from the neutral plasma literature.
Observation of Plasma Effects on the Synchrotron Emission from a Hot Electron Plasma
Authors: Blanken R. A.
Published: February 2004

It has been observed that the presence of a dense magnetized background plasma can greatly influence the synchrotron emission associated with relativistic electrons. The plasmas studied are produced by electron cyclotron resonance heating in a magnetic mirror geometry. After microwave turnoff, when the background plasma is not present, the usual synchrotron radiation associated with a tenuous distribution of relativistic electrons is observed; during microwave heating when a dense magnetized background plasma is present, the synchrotron intensity may be considerably decreased from the vacuum intensity. The largest decreases are observed at frequencies below the nonrelativistic electron gyrofrequency ωc, in qualitative agreement with the predictions of a test particle model for the synchrotron emission process. The decreases near nωc are due to the absorption of the synchrotron extraordinary mode via cyclotron damping in the finite temperature background plasma. At frequencies above the upper hybrid frequency ωuh(ωuh2 = ωp2+ωc2 the decrease arises because the synchrotron emission occurs into a cutoff mode of the background plasma.
Autocorrelation Measurements in the Near Wake of Square Cylinders in Turbulent Free Streams
Authors: Mujumdar A. S. , Douglas W. J. M.
Published: February 2004

Eddy-shedding frequencies were measured for square cylinders in cross flow of turbulent air streams of different intensities and scales. The Strouhal number was found to remain almost constant at 0.130 in the Reynolds number range studied.
Modified Discrete Ordinate Approach in Rarefied Gas Dynamics
Authors: Su Chih-Lan , Springer R. W.
Published: February 2004

An improved discrete ordinate approach involving the Willis integral iteration is tested by application to linearized cylindrical Couette flow. The results agree well with those previously published.
Effect of Kinetic Energy Corrections on Degree of Ionization
Authors: Wright T. P. , Theimer O. H.
Published: February 2004

A Saha equation is derived for a system exhibiting a classical kinetic energy correction. The resulting form of the degree of ionization has a correction term which may be experimentally observable.
Simplified Derivation of the Condition for Electrothermal Instability
Authors: Gilpin R. R.
Published: February 2004

The electrothermal instability is interpreted in terms of a generalized form of the classical condition for instability in a gas discharge, that is, if dE/dJ ≤ 0, instability occurs.
Gravitational Instability of a Rotating Anisotropic Plasma with Hall's Effect
Authors: Ariel P. D.
Published: February 2004

For perturbations parallel to a magnetic field, the Hall effect together with rotation suppresses the wavelength band for which the overstability can occur. Criteria of instability are derived for perturbations transverse to the magnetic field.
Electron Cyclotron Resonance Heating in a Q Machine
Authors: Soures J. , Lubin M. J.
Published: February 2004

An experimental method of achieving ratios of Te/Ti > 10 in a single-ended Q machine, utilizing pulsed x-band microwave power, is presented.
Role of Elasticity on the Stability of Stratified Flow of Viscoelastic Fluids
Authors: Li Chin-Hsiu
Published: February 2004

The stability of two-layer flow of viscoelastic fluids down an inclined plane is studied. It is found that elasticity of liquids plays an equally important role in stabilizing and destabilizing the flow for the interfacial mode of disturbances. This elasticity mainly destabilizes the flow for the free-surface mode of disturbance. The stabilizing effect of the elasticity is a feature of discretely stratified flow in which the instability of the flow is governed by long surface or interfacial waves.
Effect of Thermal Radiation on the Propagation of Plane Shock Waves
Authors: Wang C. P.
Published: February 2004

A study is made of the effect of thermal radiation on the propagation of plane shock waves produced by an infinite, plane and moving wall. Governing equations of one-dimensional, nonsteady and radiating gas flow are formulated, and solutions are found by using the perturbation technique and the method of characteristics. To display the essential features of the radiation effect a few cases, optically thick gas, optically thin gas, perfect absorbing wall, and perfect reflecting wall, are studied in detail. For the case of large time and a perfectly absorbing wall, the profiles of temperature, pressure, and density (or shock structure) resemble those of steady radiation-resisted shock waves. Application of these solutions to the shock tube problems is also discussed.
Photographic Observations of the Retrograde Rotation of an Arc Discharge
Authors: Murphree David L. , Carter Richard P.
Published: February 2004

Observations have been obtained through high-speed photography on the dynamics of the magnetically induced retrograde rotation of a low-pressure argon arc discharge. Two distinctly different cases of retrograde motion were observed. In one case, the cathode spots form an apparently continuous cathodic arc region; in the second case, groups of discrete cathode spots exist. The behavior of the positive column for the two cases is dissimilar. The mode of retrograde rotation which occurs is determined by the applied magnetic field strength.
Convective Cells in a Quiescent Plasma Region
Authors: Harries W. L.
Published: February 2004

Periodic spatial variations of density and potential were observed in the quiescent region of a plasma, in the magnetohydrodynamically stable region of a linear multipole. The variations were of the order of 50%, and were both radial and along the axial direction z, along which the magnetic field configuration was approximately invariant. Measurements of E/B velocities, as well as of particle flux, revealed drift velocities in closed vortices or convective cells, with the drift kinetic energy as high as 30% of the electron thermal energy. The cells persisted in the afterglow for at least a millisecond, roughly the plasma containment time. The axial dimension of the cells depended on the spatial variation of the input power density during ionization and heating; radially they extended from the stagnation point to near ψc [where ∂(§ dl/B)/∂ψ = 0], where there were large fluctuations of density and potential with time. The density in the quiescent region decayed at about the same rate as the density in the region of temporal fluctuations. The effect of convective cells on plasma loss is discussed.
Well-Posedness Criteria for One-Dimensional Unsteady Flow of an Anisotropic Plasma
Authors: Lynn Y. M.
Published: February 2004

The local well-posedness criteria are: 2 + β ≥ β‖ ≥ ζ − (ζ2 − 13β2 tan2θ)1/2, where ζ = (1 + β) sec2θ − 12β, β and β‖ denote ratios of perpendicular and parallel pressures, respectively, to the magnetic pressure, and θ is the angle from the direction of spatial variation to that of magnetic field. They should be satisfied at each instant and in every transverse plane throughout any stable one-dimensional unsteady flow of an anisotropic plasma.
Optical Mixing in a Magnetoactive Plasma
Authors: Weyl Guy
Published: February 2004

The nonlinear interactions of two electromagnetic waves resulting in the excitation of electrostatic oscillations of a homogeneous plasma in a strong magnetic field are studied. Starting from the cold plasma equations for electrons, and neglecting ion motions, a general expression for the second-order density perturbation of the plasma in the presence of two first-order electromagnetic waves is derived. One basic assumption made is that the frequencies of the electromagnetic waves are much larger than the plasma frequency and than the electron cyclotron frequency. The second-order density perturbation is explicitly calculated in the two cases where the difference frequency and wave vector of the interacting waves satisfy the dispersion relation for plasma oscillations and for the upper hybrid resonance. The scattering cross section for electromagnetic radiation per electron due to the excited electrostatic oscillation is calculated and compared to cross section due to thermal fluctuations. The results are applied to a laboratory Q device using ruby lasers as sources of the electromagnetic waves and to an ionospheric plasma using radio waves. The effect of finite beamwidth and of nonuniform plasma density is also considered. It is found that the excited oscillations near either of the two resonances considered in the ionosphere should easily be observed by use of a satellite receiving part of the scattered radiation. This method of excitation and detection is suggested for sounding of ionospheric plasmas.
Effect of Initial Condition on Weak Homogeneous Turbulence with Uniform Shear
Authors: Deissler R. G.
Published: February 2004

The initial condition for a previous analysis of turbulence with shear is modified to give a finite initial energy. The total energy increases for finite periods, during which turbulence production exceeds dissipation. For large times the turbulence decays.
Laminar Hydromagnetic Flow between Concentric Rotating Cylinders
Authors: Lin Sheng Hsiung
Published: February 2004

An analytic solution for the general laminar hydromagnetic flow between concentric rotating cylinders is presented. The general solution agrees with that of the nonmagnetic special case.
Instabilities in Finite Beam-Plasma Systems
Authors: Evans Kenneth , Jackson E. Atlee
Published: February 2004

The relationship between the temporal growth of linear fluctuations in a finite beam-plasma system, and the spatial growth of the resulting stationary oscillations is discussed.
Effects of Introducing Supports in a Levitated Toroidal Quadrupole
Authors: Stirling W. L. , Roberts M. , Alexeff I.
Published: February 2004

The effect of introducing supports into a levitated toroidal quadrupole is determined. Using double probe techniques, no measurable effect on the probe flux, electron temperature, or plasma lifetime, for a support size less than 5 mil diam was found.
Occurrence of Finite-Amplitude Surface Waves on Falling Liquid Films
Authors: Gjevik B.
Published: February 2004

The linearized stability problem for a steady parallel flow of a thin viscous fluid layer flowing down an inclined plane has been investigated by several authors. When the volume flux exceeds a critical value, the steady parallel flow is known to be unstable. In order to explain the development of steady surface waves on such a flow, finite-amplitude effects must be considered. The growth of a linear unstable periodic perturbation and its nonlinear interaction with higher harmonics are studied. For small volume fluxes and fluids with sufficiently strong surface tension, such as water and alcohol, it is shown that for a flow down a vertical plane a steady finite-amplitude surface wave will develop. The transient development of the finite-amplitude waves is investigated by numerical integration. Numerical values for wave velocities and amplitudes are given. The dependence of the wave form on the wavelength of the initial perturbation is also discussed.
Onset of Convection in a Porous Channel with Net Through Flow
Authors: Sutton Frances M.
Published: February 2004

The critical Rayleigh number for convective flow in a porous two-dimensional channel is found when there is a net flow of fluid up through the channel.
Electrohydrodynamic Stability of Space-Charge-Limited Currents in Dielectric Liquids. I. Theoretical Study
Authors: Schneider J. M. , Watson P. K.
Published: February 2004

Liquid motion is often observed when an electric field is applied to a dielectric liquid. An analysis of the steady cellular convection which results when charge is injected uniformly into the free surface of a film of an insulating liquid is discussed. The initial, steady-state current is space-charge-limited. The method of exchange of stabilities is assumed to be valid; velocity and potential perturbations on the initial steady state lead to a characteristic equation which determines the conditions for onset of instability. This characteristic equation is of the seventh order and has nonconstant coefficients. A numerical integration has been performed on the equation and the resulting solutions show that a critical potential exists above which convection will occur. The condition for instability is R = 99 = εV0/μη., where η is the dynamic coefficient of viscosity, μ is the charge carrier mobility, and ε is the permittivity. The dimensionless number R is analogous to the Rayleigh number in hydrodynamics. A numerical calculation of growth rate is given, at values near the critical voltage. Above V crit, positive growth rates are obtained, and below V crit the growth rates are negative.
Time-Dependent Analysis of Population Inversions in an Expanding Gas
Authors: Anderson John D.
Published: February 2004

A time-dependent technique for the numerical solution of convergent-divergent, nonequilibrium nozzle flows has been used to analyze the rapid, vibrational nonequilibrium, supersonic expansion of a mixture of CO2, N2, and H2O, wherein the finite rate molecular energy transfer processes can result in a population inversion between the (001) and (100) vibrational energy levels of CO2. Results for such population inversions are presented. Among these, a comparison has been made between the present results and the recent results of Basov et al.; this comparison indicates that Basov's calculations overestimate the population inversion in an expanding mixture of CO2 and N2. In addition, results are presented from a series of numerical experiments conducted to assess the validity of several simplified methods for computing population inversions.
Nonlinear Stabilization of High-Frequency Instabilities in a Magnetic Field
Authors: Dum Christian T. , Dupree Thomas H.
Published: February 2004

It is shown that the broadening of wave-particle resonances by the random motion of particles in a turbulent electric field may determine the saturation level of a variety of high-frequency instabilities. Secular changes of the guiding center positions, cyclotron radii, and phase angles give rise to resonance broadening and diffusion, similar to that produced by collisional scattering. The field dependent broadening is expressed in terms of resonance functions which replace the familiar resonant denominators of the linear theory. Resonance functions are derived in a simple manner from the solution of a Brownian motion problem, leading to an expression in terms of diffusion coefficients. The close resemblance of the theory to quasilinear theory and the linear theory including collisions allows one to start from a linear stability analysis and then assess the importance of nonlinear effects. This method is illustrated by the determination of the saturation level of cyclotron instabilities from the condition of vanishing nonlinear growth rate.
Theory of Plasma Simulation Using Finite-Size Particles
Authors: Langdon A. Bruce , Birdsall Charles K.
Published: February 2004

The elementary properties of a plasma, in which the small-separation force is smoothed from the Coulomb force, are developed. The modification is considered as being produced by spreading out the charge distribution of a particle to make a particle of finite size R (cloud). These clouds move freely through one another and interact through normal electromagnetic fields. A method to adapt point-particle results for plasma oscillations, shielding, fluctuations, and collisions, is shown, and the modifications to these plasma properties discussed in detail. The relevance of these considerations to computer simulation of plasmas (in which some smoothing is a consequence of the numerical methods used and additional smoothing is sometimes added) is discussed. It is found that smoothing the short wavelength interaction can be used without destroying the desired physics, while suppressing collisional effects and noise at wavelengths < R which are exaggerated in simulation due to the use of far fewer particles than in a real plasma.
Determination of Diffusion Coefficients by Correlation of Microscopic Density Fluctuations
Authors: Mills G. S. , McLane C. K. , Tsukishima T.
Published: February 2004

The cross spectrum of density fluctuations in a radio frequency heated abnormal glow discharge plasma is determined using Langmuir probes as sensors. The form of the cross spectrum and its dependence on probe separation, gas pressure, and electron temperature are in agreement with a theory given by Weinstock for a neutral collision dominated electron gas. If the diffusion coefficient obtained from fitting the theory to experiment is interpreted as an ambipolar diffusion coefficient, it is found to be in satisfactory agreement with that calculated from measured electron and gas temperatures and gas pressure utilizing the known mobility of helium ions in helium.
Current Sheet Structure in a Parallel Plate Rail Gun
Authors: Pert G. J.
Published: February 2004

Experimental measurements of the magnetic and electric field structure in a low-density parallel plate rail-gun discharge are compared with measurements of the electron density and temperature. At a sheet speed of approximately 6 cm/μsec in hydrogen at 0.1 Torr it is found that the sheet snowplows the ambient gas throughout the region of observation. The experiments are made at short times (less than the ionization time) after breakdown, and the gas is only weakly ionized. The results indicate that under these conditions a dissociating but nonionizing shock wave precedes the current sheet. The fields and thermodynamic state measurements are shown to be completely self-consistent.
Functional Dependence of Drag Coefficient of a Sphere on Reynolds Number
Authors: Abraham Farid F.
Published: February 2004

An argument on the drag coefficient of a sphere results in the expression C = C0[1 + δ0/(R)1/2]2where R is Reynolds number, C0δ02 = 24, and δ0 = 9.06This expression is in remarkable agreement with experiment for a wide range of R, i.e., 0 ≤ R ≲ 5000.
Nonlinear Mixing of Ion Acoustic Waves in a Plasma
Authors: Sato Noriyoshi
Published: February 2004

Ion acoustic waves are observed to be generated by non-linear mixing of Landau-damped ion acoustic waves excited externally in a plasma. Their damping is interpreted qualitatively by a simple physical argument.
Theory of Self-Diffusion in Classical Fluids: The Van Hove Self-Correlation Function G8(r, t)
Authors: Akcasu A. Ziya , Corngold Noel , Duderstadt James J.
Published: February 2004

Projection operator techniques have been applied to study the diffusion of a test particle in a classical many-particle system such as a liquid or a plasma. Particular attention has been directed towards the calculation ot the Van Hove self-correlation function Gs(r, t). This calculation proceeds through the development of exact descriptions of Gs(r, t), both in configuration space (analogous to generalized hydrodynamic equations) and phase space (kinetic equations) which are then suitably approximated and solved using either perturbation or modeling methods. These results compare quite favorably with molecular dynamics computer experiments.
Preionization for Collisionless Shock Wave Experiments by Means of Photoionization
Authors: Keilhacker M. , Pecorella F. , Vlases G. C.
Published: February 2004

Strong ultraviolet radiation emitted from a dynamically filled linear z-pinch in xenon is used to ionize low-density molecular hydrogen and the noble gases. The technique produces a homogeneous, current free initial plasma with electron densities of 1012−5 × 1013 cm−3 and temperatures of about 1 eV suitable for collisionless shock wave experiments. The degree of ionization which can be achieved at the center of a 150 cm long test chamber having one light source at each end ranges at 1 mTorr filling pressure from 20% in H2 to 60% in xenon. The absorption of capacitor bank energy by the z pinch and the radiation emitted are estimated. The calculation shows, in agreement with the experimental results, that xenon produces a much higher ionization rate than hydrogen. To get a picture of the space-time dependence of density, electron temperature, and ion temperature in the photoionized gas, the relevant set of coupled differential equations is solved numerically. The calculations show that for conditions resembling those of the experiment the energy equipartition time between electrons and ions can be made shorter than the times for radial diffusion and heat conduction by superimposing an axial magnetic field on the order of 100G.
Experiment on the Interaction between a Plasma and a Neutral Gas
Authors: Danielsson Lars
Published: February 2004

In an experiment where a high velocity plasma stream penetrates a stationary neutral gas cloud in a magnetic field, it is found that the interaction between the plasma and the gas is far more violent than what can be expected from simple atomic interaction theories. The parameters are such that the character of the interaction is collisionless. The observations demonstrate that the plasma is very efficiently retarded as it penetrates into the gas cloud and that the electron energy distribution changes drastically towards higher energies, at least for a part of the population, resulting in partial ionization of the gas. In order to account for the observations it is necessary to assume some kind of collective interaction between the plasma and the neutral gas. The results are analyzed from the point of view of Alfvén's critical velocity hypothesis.
Ion Acoustic Shock Waves
Authors: Biskamp D. , Parkinson D.
Published: February 2004

The one-dimensional hydrodynamic equations for an ion sound system (cold ions, isothermal massless electrons) are solved numerically to study the behavior of nonlinear ion sound waves, in particular, the formation and interaction of shock waves.
Numerical Solution of Dispersion Equation for a Bi-Maxwellian Plasma
Authors: Kito Masafumi , Kaji Ikuo
Published: February 2004

In the presence of a uniform magnetic field, longitudinal oscillations of a plasma with a bi-Maxwellian distribution function are studied numerically. A dispersion equation which involves a function Z(ζ) = π−1/2 ∫ −ωωdxexp(−x2)(x − ζ), where ζ is complex, is derived. A root of the equation is obtained by using a formula which combines the asymptotic expansion of Z(ζ) with the power series of Z(ζ). The real part of roots gives a mode of cold plasma oscillations and modes of multiple oscillations of the cyclotron frequency. These modes are coupled and hybrid modes exist. Instabilities arise along long strips which are along modes of multiple oscillations. If an anisotropy of the bi-Maxwellian distribution is constant, then instabilities are growing while the temperature of the plasma is increasing.
Quasi-Electrostatic Modes in Axisymmetric Tori
Authors: Kim In Kyu , Malik S. K.
Published: February 2004

The effect of the magnetic perturbations on the drift instabilities in the axisymmetric tori is studied. The dispersion relations and growth rates are calculated for the various frequency ranges of physical interest. An unstable mode exists for which the characteristic frequency of the oscillations ω is greater than the electron bounce frequency ωbe. This instability can be suppressed by the average favorable curvature. For the case, ωbe > ω > ωbi, the drift ballooning and drift universal modes are far more unstable than in the electrostatic case. The oscillations are always electrostatic for ω < ωbi.