bluuebunny/crossref_metadata_2025 huggingface dataset:
Oblique Reflection of a Plane Impulsive Electromagnetic Wave from a Plasma Half-Space
Authors: Wait James R.
Published: February 2004

Using the known steady-state solution, the transient response of the reflected wave for an incident wave of impulse wave shape is derived. It is indicated that the response “rings” at the plasma frequency divided by the cosine of the angle of incidence.
Low-Frequency Interchange Stability of Plasmas from the Maximum Entropy Conditions
Authors: Santini F.
Published: February 2004

The conditions for the stability of a low-pressure plasma equilibrium against low-frequency interchange modes, including trapped particle modes, are also conditions for a maximum of the entropy functional introduced in preceding papers.
Propagation of Two Ion Waves
Authors: Ohnuma Toshiro , Hatta Yoshisuke
Published: February 2004

Wave-wave coupling among three or four ion wave modes is treated.
Temporal Plasma Echoes
Authors: Baker John C. , Oldham William J. B.
Published: February 2004

Results are given from a computer experiment conducted on a 9000-particle plasma to test the theoretical prediction of temporal echoes. The second-order echo is found at the time and wavenumber as predicted by the theory.
Determination of the Density Profile in a Plasma Slab
Authors: Baldwin David E. , Kaufman Allan N.
Published: February 2004

A simple formula is derived, for the direct determination of the electron density profile of a symmetric plasma slab, in terms of the arc resistance of the slab as a function of frequency. The cold-plasma approximation is used.
Local Boiling and Cavitation in Heat-Induced Counterflow of He II
Authors: Broadwell James E. , Liepmann Hans W.
Published: February 2004

Local boiling, cavitation, and cavitation collapse have been observed in the heat induced counter-flow of He II in a convergent-divergent nozzle. These observations are described and shown to be qualitatively and quantitatively in agreement with the two fluid equations supplemented by the Gorter-Mellink force.
Sources and Sinks at the Axis of a Viscous Rotating Fluid
Authors: Pao Hsien-Ping , Kao Timothy W.
Published: February 2004

Theoretical and experimental investigations have been made for the problem of a source or sink at the axis of a viscous, incompressible, steady, unbounded rotating fluid. For the sake of generality, the theoretical portion of this paper also includes a uniform axial velocity. It is found that the velocity distributions have similarity forms at the distant wake along the axis of rotation using the Fourier transform technique. An inverse coordinate expansion technique is then used. This procedure not only brings out the nature of the approximation very clearly but also allows higher-order solutions to be calculated. The zeroth-order solution indicates that there exists a withdrawal viscous core which grows in radius with the axial distance x* from the sink at the rate x*1/3. The first-order solutions are also calculated. The experimental results agree very well with the theoretical predictions.
Stability of Convective Flow in a Porous Medium
Authors: Westbrook D. R.
Published: February 2004

A universal criterion for the stability under arbitrary disturbances of the convective flow of a fluid in a porous medium is obtained in terms of a Reynolds number and a Rayleigh number for the flow. It is also shown that stability bounds obtained by small perturbation methods are equally good bounds under arbitrary disturbances.
Free-Molecule Expansion Polynomials and Sound Propagation in Rarefied Gases
Authors: Hanson F. B. , Morse T. F.
Published: February 2004

In the asymptotic evaluation of certain integrals in the method of Kahn and Mintzer describing high-frequency sound propagation, certain errors occur. These have been described and corrected in an attempt to obtain a valid description of sound dispersion and attenuation over a wide range of frequencies. However, the corrected asymptotic results fail to yield physically acceptable modes of propagation for all values of the rarefaction parameter τ = p/ωμ. Only for small values of the rarefraction parameter (the high-frequency limit) are suitable descriptions of experimental results obtainable. The physical and mathematical reasons for the failure of free molecule expansion polynomials to predict continuum sound modes are discussed.
Nearly Free Flow through an Orifice
Authors: Rotenberg A. , Weitzner H.
Published: February 2004

In the case of steady flow out of an orifice into an originally evacuated half-space, a method is given for obtaining the first correction to free flow for the net outflow through the orifice for the class of collision functions B(θ, V) cut off or made regular near θ = π/2. An explicit computation is described for hard-sphere molecules and the resultant fractional correction is 1 + 0.145/K where K is the Knudsen number. The coefficient 0.145 is about 30% lower than the current best data for argon.
Physical Model of Hydrodynamic Turbulence
Authors: Parker E. N.
Published: February 2004

A model for statistically isotropic homogeneous turbulence in an incompressible fluid is constructed, representing the turbulence as a superposition of individual vortex sheets. Each vortex sheet moves in the velocity field of the other sheets which have larger scale. Each sheet is stretched out, and intensified, until obliterated by viscosity at high wavenumber. The rate of stretching is related to the symmetric part of the strain tensor ∂νi/∂κj, which is postulated to be statistically independent of the antisymmetric part. Representing the turbulence by the usual energy spectrum function F(k) leads to a set of integrodifferential equations. Solution of the equations gives a spectrum which is in close agreement with experimental spectra of turbulence over both the inertial and viscous subranges, suggesting that the model may be of some real physical interest. The model is sufficiently explicit so as to give information on the correlation between different Fourier components of the turbulence. The calculations give the probability of finding a particular value of the vorticity or velocity at a given position and time in the turbulent field.
Anomalous Resistivity from Drift Waves in a Magnetoplasma Shock Wave
Authors: Woods L. C.
Published: February 2004

The source of the anomalous resistivity that broadens shock fronts in a near-collisionless plasma is attributed to the drift-wave instability driven by the strong electron temperature gradients in the front. Whistler-type waves propagating through the electrons in the plane of the shock front are treated by the fluid equations, with the ions kept unperturbed. The fastest growing unstable waves are found to propagate normal to the magnetic field, for which case the whistlers degenerate to convected waves. Resistivity is introduced such that it exactly cancels the growth rate due to the gradients, and the calculation is made self-consistent by using this resistivity to deduce the magnitude of the gradient. The main results are simple formulas for the anomalous collision frequency and the resistive shock thickness λη. It is found that λη ≃ (Te2/mev1)1/2 (c/ωpe), where the subscripts 1 and 2 refer to conditions upstream and downstream of the shock, and v is the component of plasma velocity normal to the stationary shock. This result is found to be in reasonable agreement with the few available experimental results.
Propagation of Coherent Magnetohydrodynamic Waves
Authors: Liu C. H.
Published: February 2004

The propagation properties of coherent magnetohydrodynamic waves in the presence of plasma density fluctuations are investigated. A perturbation technique borrowed from quantum field theory (renormalization procedure) is used to solve the stochastic wave equation. Effective propagation and attenuation constants are derived for propagation of plane coherent magnetohydrodynamic waves. It is found that, in general, the phase velocity will be less than the Alfvén velocity and there will be attenuation (or damping) of the waves due to the random mixing of phase.
Double-Toroidal Hydromagnetic-Equilibrium Configurations within a Perfectly Conducting Sphere
Authors: Morikawa G. K.
Published: February 2004

A one-parameter family of exact hydromagnetic-equilibrium solutions is found describing a plasma of finite pressure (0 ≤ β ≤ 1) confined by a force-free magnetic field contained within a perfectly conducting sphere.
Nonstationary Properties of a Marginally Stable Plasma
Authors: Hatori Tadatsugu
Published: February 2004

Temporal behavior of some physical quantities is investigated for the system of electron plasma and injected beam with fixed velocity distributions. The fluctuation of the electric field with the critical wavenumber k0 (defined by γko = 0) grows secularly; the velocity diffusion coefficient for v0 (defined by ωko = k0·v0) grows in proportion to log t; the rate of energy loss by the beam approaches the enhanced value as t−1/2.
Modification of the Quasilinear Theory by the Spontaneous Emission of Plasma Waves
Authors: Nunez P. , Rand S.
Published: February 2004

The transfer of energy between an electron beam and longitudinal waves in a collisionless plasma has been studied. The quasilinear theory, with the inclusion of the spontaneous emission of wave energy, is used. Numerical solutions of the resulting equations are obtained and compared with those of the quasilinear theory.
Higher-Order Corrections to the Theory of the Guiding Center Plasma
Authors: Wilson Gerald E.
Published: February 2004

The theory of the guiding center plasma is extended to include previously neglected terms proportional to the particle mass-to-charge ratio m/e. To do this it is necessary to obtain a correspondingly accurate solution of the single charged particle equation of motion. Then, one may define a conservation equation for the time average particle motion or, equivalently, for guiding centers. This equation is combined with a macroscopic momentum equation through the use of a generalized Ohm's law. Adding Maxwell's equations, the result is a self-consistent set of higher-order equations describing the behavior of the guiding center plasma. These equations are then linearized in small perturbations about a uniform equilibrium configuration to obtain stability criteria. The results show that these criteria are the same as those of the lowest-order system.
Constants of the Linearized Motion of Vlasov Plasmas
Authors: Felderhof B. U.
Published: February 2004

It is shown that the symmetry properties of a time-independent solution of the set of Vlasov's and Maxwell's equations naturally leads to constants of the motion of the linearized equations. The constants corresponding to invariance under translations in time and to invariance under spatial translations and rotations are explicitly obtained.
Resonant Scattering of Cyclotron Harmonic Plasma Waves
Authors: Porkolab M. , Chang R. P. H.
Published: February 2004

Experimental results are presented which show that resonant mode coupling can be the dominant process in the scattering of cyclotron harmonic waves (or Bernstein modes). The important and new feature of the present work is that, in addition to confirming the frequency (energy) conservation relation ω1 + ω2 = ω3, the wavenumber (momentum) conservation relation k1 + k2 = k3 is also shown to be satisfied in accord with the requirements of resonant mode coupling [where ω1(k1) and ω2(k2) refer to the incident waves and ω3(k3) to the product wave]. Since all three waves participating in the scattering process are cyclotron harmonic waves, the present work provides an important technique for studying the symmetry relations which govern wave-wave scattering processes in a magnetic field.
Numerical Simulation of Axisymmetric, Collisionless, Finite-β Plasma
Authors: Dickman D. O. , Morse R. L. , Nielson C. W.
Published: February 2004

A numerical simulation method for time-dependent, axisymmetric, collisionless, finite-β plasma is described and applied to mirror modes in θ pinches and to rotational and tearing modes in Astron. It is shown that the mirror modes cause an increase of axial thermal velocities and the long time development of a gross bumpy structure in the θ-pinch plasma. The Astron plasma layer first develops tearing modes in agreement with linear theory, but at later times the wavelength of this mode increases by coalescence until the plasma is completely reassembled.
Drifts and Purification of a Fast Plasma Injected into a Double Bend Magnetic Field
Authors: Colomès J. , Véron D.
Published: February 2004

Drifts of plasma moving in a curved magnetic field are studied experimentally. Depolarization currents of the plasma are measured directly and compared with the values deduced from the distribution of the ion density at a given time. The curvature drift is used to remove fast heavy impurities. The electric drift is used to separate the fast component from the slow component of the plasma puff.
Critical β from Stellarator and Scyllac Expansions
Authors: Grad Harold , Weitzner Harold
Published: February 2004

Toroidal equilibria with helical windings have been studied using two scalings, low β and finite β. A transfer of stability (critical β) found by one expansion is automatically invisible using the other. New stable regions are found with each expansion.
Plasma Diagnostics with Ionized Barium and Tunable Dye Lasers
Authors: Dimock D. , Hinnov E. , Johnson L. C.
Published: February 2004

Resonance fluorescence and optical pumping techniques using tunable dye lasers permit the measurement of density, ion temperature, electron temperature, and ion drifts, over a wide range of density in barium, or barium doped plasmas.
Separation and Flow Reversal in Swirling Flows in Circular Ducts
Authors: Lavan Z. , Nielsen H. , Fejer A. A.
Published: February 2004

The swirling motion of a laminar incompressible viscous flow in a circular duct is studied. The duct consists of two smoothly joined sections, one stationary and the other rotating with a constant angular velocity. A linearized analytical solution, valid for flows having small Reynolds numbers and large swirl ratios, is developed. Solutions for a wider range of Reynolds numbers and swirl ratios are obtained by numerically solving the discretized angular momentum and vorticity transport equations. The occurrence of flow reversal on the axis and near the tube wall is studied, in particular, and conditions for incipient flow reversal are established.
Finite-Amplitude Instability of the Compressible Laminar Wake. Weakly Nonlinear Theory
Authors: Liu J. T. C.
Published: February 2004

An extension of the Lees-Gold linear theory to a theory of finite-amplitude instability of two-dimensional compressible wake flows is presented. Use is made of the amazing similarity between the experimentally observed transition region of certain high-speed wakes and that of the low-speed Sato-Kuriki wake. A Fourier expansion procedure, similar to that of the Stuart-Watson low-speed finite-amplitude instability theory, is used. The mean flow is distorted by the disturbance correlations. A local analysis of the disturbances is made. The Landau amplitude equation is, as in the incompressible theory, again required to solve the problem. The fundamental disturbance component satisfies the Lees-Lin inviscid (spatial) pressure equation. The first harmonic component also satisfies such an equation but with nonhomogeneous terms due to nonlinear interactions. The fundamental distortion function and the modified disturbance growth rate come from the nonhomogeneous third-order problem. This is solved through the use of the smallness of the amplification rate far downstream for a fixed frequency, which leads to an orthogonality condition appropriate to the compressible problem. The streamwise, exponential growth of the disturbance amplitude is limited by nonlinearity.
Hole Theory of Cavitation Nucleation
Authors: Finch R. D.
Published: February 2004

Previous estimates of the tensile strengths of various liquids, based on the hole theory, were much higher than empirical values. It is pointed out that these estimates did not take account of the pressure gradients which exist under typical experimental conditions. Such gradients will cause holes to drift and accumulate leading to much lower theoretical tensile strengths.
Symmetry Properties of Cameron-Martin-Wiener Kernels
Authors: Siegel Armand , Kahng Woo-Hyung
Published: February 2004

The symmetry properties of the Cameron-Martin-Wiener (Wiener-Hermite) kernels are investigated in the isotropic velocity field as required for the invariance of the velocity distribution of the field under rigid rotation and reflection. As a sufficient condition for the invariance, it is found that the even kernels must be isotropic true tensors, and the odd kernels (i) isotropic true tensors or (ii) isotropic pseudotensors. In incompressible turbulent flow, it is shown that the odd kernels must be isotropic pseudotensors. Assuming that the nonlinear term of Burgers' equation can be treated as a perturbation in the very late decay stage, it is shown that the energy spectrum density must vanish at zero wavenumber in order to get a valid physical model of turbulence. Applying the above conclusion, it is seen that the odd kernels in the Burgers' model must be odd functions, which suggests that the model thus obtained is the one-dimensional counterpart of turbulent flow which is incompressible.
Application of the Wiener-Hermite Expansion to the Diffusion of a Passive Scalar in a Homogeneous Turbulent Flow
Authors: Saffman P. G.
Published: February 2004

The stochastic expansion of Cameron, Martin, and Wiener is used for the velocity and concentration fields in a homogeneous turbulent flow convecting a passive scalar. The expansion is truncated and analytical solutions are obtained for the concentration field with the velocity distribution given and molecular diffusion neglected. For diffusion from a point source, the effective diffusivity is found in terms of Eulerian velocity correlations. For a statistically homogeneous scalar distribution, the spectrum function is determined in terms of the energy spectrum function. When the Prandtl number is large, the results obtained do not agree with the predictions of the universal equilibrium hypothesis.
Burgers' Turbulence Models
Authors: Case K. M. , Chiu S. C.
Published: February 2004

A detailed investigation of the stability of the solutions and the growth of secondary solutions beyond the critical points is carried out for the Burgers' model equations. It is found that the transitions at some critical points are very much like the intuitive description given by Landau; however, the possibility of finite jumps is also encountered.
Electron Temperature Distribution across a Shock Wave in a Partially Ionized Gas
Authors: Murty S. S. R.
Published: February 2004

The electron temperature structure in a weakly ionized plasma is studied allowing the degree of ionization to vary across the shock wave. The values of the electron temperature and the downstream equilibrium temperature obtained with variable ionization are less than those for frozen ionization. The electron temperature rises sharply behind the shock for variable ionization while a gradual increase is predicted by frozen ionization.
Dispersion and Stability of Moving Striations
Authors: Garscadden A. , Bletzinger P. , Simonen T. C.
Published: February 2004

Experiments are reported on the waves of ionization which can be excited in the low- and medium-pressure discharge in argon, neon, and a mercury-argon mixture. The glow to arc transition and the change from a forward wave to a backward wave of ionization were studied in detail using a space-time display which immediately reveals the dispersion of the waves. Evidence is also presented for the transition from a convective to an absolute instability. A comparison is made with the Pekarek-Krejci theory of moving striations and using Derfler's stability criteria, calculations are presented to show that this theory predicts both forward and backward waves which can be stable, convectively unstable, or absolutely unstable.
Solutions of the Linearized Equations of Magnetohydrodynamics in Nonhomogeneous Magnetic Fields
Authors: Infeld Eryk
Published: February 2004

Earlier results, concerning the conditions when the solutions of the linearized equations of magnetohydrodynamics are exact, are extended. Only a partial answer to the question is still possible for varying initial fields. An exact solution is given as an illustration. This solution might be useful as a model for investigating the effect of currents on Alfvén waves in the radiation belts.
Surface Waves in Hot Plasmas
Authors: Guernsey Ralph L.
Published: February 2004

The solution of the initial value problem for a semi-infinite Vlasov plasma, with no applied fields, is given. In the long-wavelength limit, in addition to the usual plasma waves, terms corresponding to surface plasma waves, for which the dispersion relation is given, are found.
Stationary Equilibrium of a Two-Dimensional Plasma in a Magnetic Field
Authors: Yoshikawa S. , Barrault M. R.
Published: February 2004

Equilibrium of plasmas in a uniform magnetic field is considered with E × B plasma motion perpendicular to the magnetic field and gravitational field (simulating magnetic field curvature). It is concluded that the equilibrium of moving plasmas in the absence of current parallel to the magnetic field is limited to a very small class of configurations even without the gravitational field. With the motion of plasma included, the plasma equilibrium other than the plasma pressure, p = p(U) where U is the gravitational potential, can be constructed. Finally, the implication of the plasma motion for the increase of the resistive diffusion is considered. It is shown that under a large-Larmor-radius configuration, the resistive diffusion could be increased over the classical rate by an amount proportional to the square of the length of a device over the plasma radius.
Drift Wave Instability in General Magnetic Field Configurations
Authors: Siambis John G.
Published: February 2004

A method is presented for the investigation of the propagation and stability properties of drift waves driven by a density gradient and other low-frequency electrostatic waves in realistic magnetic field configurations confining a low-pressure plasma in static equilibrium. At the outset the method utilizes the guiding-center motion and associated invariants of the charged patricle in order to obtain the perturbation in the charge density in terms of the electrostatic potential associated with the wave. For linear stellarator-and levitron-type fields of infinite axial extent, unstable, nonseverely localized, normal modes are found in contrast to the severely localized modes of planar slab geometry with simulated shear. The imposition of boundary conditions on the linear stellarator-type field to simulate a closed toroidal field yields standing waves along the magnetic field line and high m numbers (short wavelength) for the azimuthal field transverse to the magnetic field line. The rapid helical winding, around the hard core, of the field lines of the linear levitron-type field of infinite axial extent constrains the maximum wavelength along the field line to a single helical turn, a constraint which leads to high m numbers for the azimuthal field. In both the case of the linear stellarator field with identified ends and the case of the linear levitron field of infinite axial extent, the stabilizing effect of shear is manifested by short transverse wavelengths for the drift wave leading to reduced anomalous diffusion.
Experimental Investigation of the Ion-Ion Hybrid Resonance
Authors: Baird A. W. , Swanson D. G.
Published: February 2004

An experiment is described in which the ion-ion hybrid resonance is observed and studied. The theory of a cool, partially ionized plasma in a magnetic field is given, and dispersion characteristics of a wave launched in a bounded two-ion species plasma near the resonance are investigated. Computer results showing the behavior of the attenuation coefficient of the launched wave as a function of density, magnetic field, resistivity, density ratio of the ions, and frequency are given. The apparatus for generating a highly ionized pulsed plasma and for launching and detecting a wave in the plasma is described. The attenuation coefficient has been measured for a variety of plasma conditions; this data has been fitted to the predicted theory with generally good agreement using values of plasma density and temperature which are characteristic of the type of discharge used.
Resistive Loading by a Finite Plasma Cylinder near the Lower Hybrid Resonance
Authors: Skipping C. R. , Oakes M. E. , Schlüter H.
Published: February 2004

A theoretical study is carried out for the resistive loading of a finite wave-generating coil concentric with a uniform plasma which is immersed in an axial magnetic field and bounded by conducting end plates. The solutions are used to make a numerical and analytic study of the influence of coupling resonances on resistive loading near the lower hybrid resonance. For proper values of the plasma parameters the coupling resonances are strong and completely mask the hybrid resonance. The higher-order Fourier components of the wave may contribute substantially to the loading resistance affecting both its magnitude and the location of the resonance minima.
Plasma Injection and Trapping in a Caulked Stuffed Cusp Magnetic Field
Authors: Burkhardt Louis C. , DiMarco Joseph N. , Karr Hugh J.
Published: February 2004

A minimum-average-B-stable toroidal magnetic well with high shear is obtained from the combined fields of a solenoid, axial conductors, and an internal ring conductor. Results of measurements of the injection and trapping of high-energy plasma from a coaxial gun are described. The confinement times are dependent on both particle energy and magnetic field. The density e-folding time is independent of the ion velocity under conditions of low shear and well depth. As they are increased the e-folding time varies roughly as 1/vi2. Trapped 0.9-keV plasma decays with an e-folding time that increases by a factor of 6 to 110 μsec as shear and magnetic well depth increase. The initial density of the plasma (0.5 to 3 keV) is ∼ 5 × 1011 cm−3 for field magnitudes resulting in a 40-μsec lifetime of 0.9-keV deuterons. This lifetime is independent of density over the range from ∼ 5 × 1011 cm−3 to 109 cm−3. The range of magnetic field magnitude is limited by the decreasing amount of plasma injected from the gun with increasing magnetic fields. The maximum lifetime of 110 μsec is commensurate with the combined effects of the ∼ 370 μsec support lifetime, a calculated ∼ 1000-μsec charge exchange time, and an anomalous lifetime of ∼ 190 μsec. A search for fluctuating electric fields that might be associated with such an anomalous loss shows the presence of low-amplitude 2-MHz oscillations but their possible role as a loss mechanism is not identified.
Flute Fluctuations in a Linear Quadrupole Device
Authors: Rusbridge M. G. , Meservey E. B.
Published: February 2004

Flute fluctuations have been studied in an afterglow discharge in a linear quadrupole device. They are observed outside the critical surface; inside, their amplitude is unobservably small. The results support the stability criterion including adiabatic effects. The phase velocity and growth rate of the fluctuations outside the critical surface have been measured and compared with a simple linear theory; significant differences from the theory are found, some of which can be explained qualitatively by a more elaborate linear theory. It is not clear, however, whether this theory would account for the differences or whether nonlinear effects are also important. The radial transport of plasma due to these fluctuations is estimated and compared with the observed loss rate, but it is shown that some other mechanisms must exist for transporting plasma from the stable region across the critical surface.
Plasma Confinement in a Toroidal Quadrupole
Authors: Yoshikawa Masaji , Ohkawa Tihiro , Schupp Arthur A.
Published: February 2004

The confinement of plasma in a toroidal quadrupole configuration is studied. The plasma parameters are, ion temperature = 50 eV, electron temperature = 6 eV, and plasma density 1013-107 cm−3. The confinement times in terms of Bohm diffusion time range from 20 to 40. The loss of the plasma is to the walls. The plasma fluctuations which are present in large amplitudes are the most likely cause of plasma loss. The superposition of a toroidal field reduces the plasma loss.
Shock Ionization Kinetics of Pure Nitrogen
Authors: Bentley S. B.
Published: February 2004

The ionization-rate limiting processes behind strong shock waves in pure nitrogen are studied by variation of the coefficients for the kinetic processes in the fluid dynamic equations representing a one-dimensional shock wave.
Electrohydrodynamic Secondary Flow
Authors: Ramadan O. E. , Soo S. L.
Published: February 2004

Secondary flow in an electrostatic precipitator in the form of electric wind takes the form of jets emitted from corona wires. Depending on the magnitude of electric Reynolds number of the systems, jet speed may reach several times that of mean gas flow.
Electron Temperatures from He I Intensity Measurements
Authors: Johnson L. C. , Hinnov E.
Published: February 2004

Data are presented relating the intensity of the λ 5876 Å line of He I to electron temperature for use in electron thermometry of plasmas in the range 2 eV ≲ Te ≲ 10eV and 1010cm−3 ≲ ne ≲ 1014cm−3.
Optical Measurements of Effects of Collisional Drift Waves on Plasma Density in Barium Plasmas
Authors: Johnson L. C. , Chu T. K. , Hendel H. , Hinnov E.
Published: February 2004

Effects of the collisional drift wave and of the presence of a Langmuir probe on plasma density in a Q-device barium plasma are investigated by means of independent measurements of local ion densities with the method of resonance fluorescence.
Stability of Spatially Periodic Supercritical Flows in Hydrodynamics
Authors: Kogelman S. , DiPrima R. C.
Published: February 2004

Recently, Eckhaus developed a theory for a class of nonlinear stability problems which can be formulated in terms of a scalar partial differential equation with quadratic nonlinearities. It is demonstrated that Eckhaus' work on the development and stability of periodic solutions can be extended to a class of nonlinear matrix partial differential equations. The equations governing axisymmetric viscous flow between concentric rotating cylinders belong to the class of equations considered. When the Taylor number T is slightly above the minimum critical value Tc there exists an interval of possible equilibrium flows (Taylor-vortex flows) growing out of the instability of Couette flow. It is shown that within the interval of possible Taylor-vortex flows, there exists a subinterval of stable vortex flows.
Theory of a Probe in a Strong Magnetic Field
Authors: Sanmartin Juan R.
Published: February 2004

An asymptotic analysis of the Langmuir-probe problem in a quiescent, fully ionized plasma in a strong magnetic field is performed, for electron cyclotron radius and Debye length much smaller than probe radius, and this not larger than either ion cyclotron radius or mean free path. It is found that the electric potential, which is not confined to a sheath, controls the diffusion far from the probe; inside the magnetic tube bounded by the probe cross section the potential overshoots to a large value before decaying to its value in the body of the plasma. The electron current is independent of the shape of the body along the field and increases with ion temperature; due to the overshoot in the potential, (1) the current at negative voltages does not vary exponentially, (2) its magnitude is strongly reduced by the field, and (3) the usual sharp knee at space potential, disappears. In the regions of the C-V diagram studied the ion current is negligible or unaffected by the field. Some numerical results are presented. The theory, which fails beyond certain positive voltage, yields useful results for weak fields, too.
Oscillations of a Weakly Inhomogeneous Plasma
Authors: Bajwa G. S. , Srivastava K. M.
Published: February 2004

An attempt has been made to study the oscillations of a collisionless, incompressible plasma, immersed in a weakly inhomogeneous magnetic field. Analysis is based on the use of an orthogonal curvilinear coordinate system. It is found that for ω ≪ ωci, radio signals will suffer least-possible attenuation when k ≫ 0.53146 − 10−4 T2, where ωci is the ion cyclotron frequency, k is the wave vector perpendicular to both the magnetic field and its gradient, and T is the kinetic temperature. Discussions are also extended to the complex frequencies, and expressions for resonance, as well as for cutoff frequencies, are derived.
Capillary Stability of a Hollow Inviscid Cylinder
Authors: Dumbleton J. H. , Hermans J. J.
Published: February 2004

The application of Rayleigh's treatment of capillary stability to the case of an inviscid liquid bounded by two concentric circular cylindrical surfaces leads to a characteristic equation from which the following predictions can be made. The system is stable for disturbances that do not have cylindrical symmetry. It is stable (unstable) for disturbances with cylindrical symmetry when the wavelength of the disturbance in axial direction is less (greater) than the circumference of the inner surface. There are always two modes of deformation. In the special case of a thin-walled cylinder these two modes are symmetric and antisymmetric, respectively. When the wavelength of the disturbance is varied in such a manner that there is a transition from stable to unstable conditions, then at the same time there is a transition from symmetric to antisymmetric mode or vice versa. It is shown, further, that when one mode is stable and the other unstable, the stable mode is a deformation for which the total surface area of the system is increased by the disturbance, while the unstable mode corresponds to decreased surface area.
Effect of Fokker-Planck Collisions on Plasma Wave Echoes
Authors: Johnston George L.
Published: February 2004

The effect on plasma wave echoes of Coulomb collisions described by a complete Fokker-Planck collision term is determined theoretically by application, in first and second orders, of the particular integral of a linearized kinetic equation which is capable of describing a Fokker-Planck collisional kinetic equation in the resonant region.
Plasma Convection and Particle Loss
Authors: Harries W. L.
Published: February 2004

Afterglow plasmas in a linear quadrupole showed the same anomalous loss rate from a region where density fluctuations were undetectable (peak-to-peak fluctuation/average density < 1%) as from turbulent regions. The possibility that convective cells may be responsible for the anomalous loss from the quiescent region is discussed.
Compressible Resistive “Tearing” Instability in the Hard-Core Pinch
Authors: Lister G. G. , Hosking R. J.
Published: February 2004

The influence of compressibility on the real growth rates of the resistive “tearing” instability in the hard-core pinch is considered. Numerical calculations indicate that the growth rates differ little for the chosen physical parameters from those given by incompressible theory. The difference is considerably less than an order of magnitude. Inclusion of terms involving the perturbed field in the direction of the field is found to have the most noticeable stabilizing effect particularly when the ratio of azimuthal to axial field is increased. In many cases, the high m modes are found to be the more unstable.
Physical Model of Cyclotron Damping
Authors: Lutomirski R. F.
Published: February 2004

A plasma with a prescribed zero-order distribution function, imbedded in a uniform magnetic field, is assumed to be perturbed by an electromagnetic wave propagating parallel to the field. For small amplitude waves (i.e., a whistler wave), the interaction between the wave and the plasma is computed directly from the single-particle equations of motion. The method readily reveals which particles dominate the interaction and yields insight into the damping mechanism. In contrast to conventional treatments of the problem via the Vlasov equation, the period of time one must wait for the asymptotic forms to be valid is readily obtained by the present method.
Relativistic Kinetic Equations for Plasma, Coulomb Fields, and Radiation
Authors: Lerche I.
Published: February 2004

Equations are derived for the correlations between particles and fields in a plasma. The plasma may be relativistic or thermal; there may exist external electric and magnetic fields as well as the induced fields. The equations place particles, longitudinal (i.e., Coulomb) fields, and radiation fields all on the same footing. The equations represent the relativistically generalized chain of kinetic equations. The chain is “solved” to first order in a generalization of the Rosenbluth and Rostoker expansion scheme. In lowest order the relativistic Vlasov equation and the relativistic one-oscillator statistical Maxwell equations result. In first order, correlation equations are obtained which demonstrate that particle-particle, particle-wave, and wave-wave correlations are all of the same order in general. A method is given for solving the first-order equations. The equations are sufficiently general that bremmstrahlung, synchrotron, and cyclotron radiation, radiative diffusion, particle diffusion, etc., can be extracted, although some effort might be required to elucidate any specific effect in view of the complexity of the resulting equations.
Viscosity of Dilute Uniform Suspensions of Uniform Spheres
Authors: Greenstein Teddy , Happel John
Published: February 2004

A formula for the relative viscosity of a dilute suspension of uniform spherical particles for the case of Poiseuille flow is deduced by studying the motion of a sphere suspended in a parabolic field in a cylindrical tube, and summing the individual additional pressure drops (caused by the presence of the sphere) for a uniform suspension of particles. The mathematical form of higher approximations is also discussed.
Reverse Current Induced by Injection of a Relativistic Electron Beam into a Pinched Plasma
Authors: Cox James L. , Bennett Willard H.
Published: February 2004

A macroscopic treatment of the current induced in a dense pinched plasma because of its penetration by a relativistic electron beam of finite length is presented. The behavior of the plasma is described by the generalized Ohm's law which takes account of the inertia of the plasma electrons in addition to collisions between the plasma electrons and ions. Under some conditions, the current density induced in the plasma is found to contain both longitudinal and transverse (radial) plasma oscillations. The total induced current flowing in the axial direction due to an injected pulse which varies slowly during times on the order of magnitude of the time in which the plasma can respond significantly to the beam disturbance is also calculated and investigated for the following three cases: (1) νm ≪ωp, (2) νm ∼2ωp, and (3) νm ≫ωp, where νm is the frequency of momentum transfer collisions between plasma electrons and ions and ωp is the electron plasma frequency of the plasma electrons. In case 1, it is found that the induced current is nearly equal in magnitude and opposite in direction to the beam current and that it lies almost entirely within the beam channel over the entire length of the beam pulse. These conclusions are consistent with the results of some recently reported experiments which satisfy the conditions of case 1. The induced current in case 1 also contains an oscillatory component with a frequency near the plasma frequency of the plasma electrons. This contribution to the induced current is not significant for the experiments considered, and this conclusion is also consistent with observation. The results of case 3 are equivalent to the results obtained by treating the plasma as a simple Ohmic medium.
Rotational Effects in a High-Beta Plasma Confined by a Longitudinal Magnetic Field
Authors: Stainer Howard M.
Published: February 2004

A theoretical study of structured plasma puffs produced in a two-coil theta-pinch gun is presented. The puffs are fired into a drift tube containing a longitudinal magnetic field and their subsequent behavior analyzed. Electron-electron and ion-ion collision times are short enough so that scalar pressures (P = nkT) can be used. Ion-electron collision times, however, are of the duration of the experiment or longer so that the two-fluid moment equations can be employed. An idealized model for the plasma puffs is proposed in which the ion fluid rotates as a rigid body in one direction about the longitudinal axis and the electron fluid rotates in the opposite direction. This high-β model yields self-consistent equilibrium density and magnetic field profiles, stemming from a balance among thermal, magnetic, centrifugal, and electrostatic forces, that are compatible with observation. It is shown that magnetic pick-up loop signals can be analyzed to ascertain the temperature, peak density, angular momentum, etc., of the plasma as it travels down the tube and a sample calculation is presented. The model thereby provides a self-consistent high-β approach to plasma-magnetic field interaction.
Nonlinear Couette Flows with Temperature-Dependent Viscosity
Authors: Nihoul Jacques C. J.
Published: February 2004

An exact unique solution of the nonlinear temperature and velocity fields equations is obtained for plane and circular Couette flows and for a large class of temperature dependence laws of the viscosity and the heat conductivity.
Observation of Current Diffusion in an Electromagnetic Shock Tube
Authors: Levine Leslie S.
Published: February 2004

Experimental observations have been made in an electromagnetic shock tube of the diffusion of the magnetic piston into the current free post-shock gas upstream of it.
Two-Wavelength Holographic Interferometry of Partially Ionized Plasmas
Authors: Jeffries R. A.
Published: February 2004

A transient partially ionized plasma has been observed by two-wavelength holographic interferometry. Electron-density measurements of plasmas that are less than fully ionized are possible by use of this diagnostic technique.
Linear and Nonlinear Behavior of Laser Produced Aluminum Plasmas
Authors: Engelhardt A. G. , George T. V. , Hora Heinrich , Pack J. L.
Published: February 2004

Framing camera and energy absorption studies of aluminum plasmas produced from single spheres 50-130 μm in radius indicate linear and nonlinear behavior.
Single-Integral Form of the Dispersion Relation for Waves in a Magnetized Plasma
Authors: Catto Peter J. , Baldwin David E.
Published: February 2004

The dispersion relation for waves in a uniform magnetized plasma is written in a single integral representation. This form should be useful in numerical applications. Examples of model loss-cone and temperature anisotropy distributions are treated.
Diffusion by a Random Velocity Field
Authors: Kraichnan Robert H.
Published: February 2004

Single-particle diffusion in a multivariate-normal, incompressible, stationary, isotropic velocity field is calculated in two and three dimensions by computer simulation and by the direct-interaction approximation. The computer simulations are carried out by storing the velocity field as a set of Fourier components and synthesizing in physical space only along the particle trajectories. The spectra taken for the velocity field are of the form E(k) ∝ δ(k − k0) and E(k) ∝ k4 exp (−2k2/k02) in three dimensions, and E(k) ∝ δ(k − k0) and E(k) ∝ k3 exp (−3k2/2k02) in two dimensions. Both frozen Eulerian fields and fields with Gaussian time correlation are treated. The simulation results agree with Taylor's picture of a classical diffusion process for times long compared with the eddy circulation time, except for the frozen-Eulerian-field runs in two dimensions, where strong trapping effects are found. The direct-interaction approximations for Lagrangian velocity correlation, eddy diffusivity, dispersion, and modal response functions agree well with the computer experiments except where there are trapping effects, which the approximation completely fails to represent.
Weak Fluctuation Modes of an Electrically and Thermally Conducting Viscous Incompressible Fluid in a Homogeneous Magnetic Field
Authors: Stanišić M. M. , Kovasznay L. S. G.
Published: February 2004

A method has been developed in order to extract the fundamental fluctuation modes in a slightly disturbed electrically and thermally conducting viscous incompressible fluid. The method, based on the linearized theory, consists in factorization of a fixed operator. The isolated modes have been studied separately by means of shifting and blurring operators. The theory shows that in the presence of an imposed magnetic field the propagation of the disturbed quantities is nonisotropic.
Linear Perturbation Analysis of the Stability of a Dissociating Fluid
Authors: Wollkind David J. , Frisch H. L.
Published: February 2004

An investigation is made of the stability of an infinite expanse of a dissociating, diatomic fluid to infinitesimal disturbances (fluctuations), using a model due to Lighthill. Initially the fluid is at a uniform temperature and is kept stationary by the external removal of the heat produced by dissociation. The results of the linear perturbation analysis of the normal mode resolution of the disturbances shows that: (1) The non-steady-state chemical quasiequilibrium solution is stable if, and only if, the steady-state chemical equilibrium solution is stable; (2) the steady-state chemical equilibrium solution can be stable if, and only if, the partial derivatives of pressure with respect to density and internal energy with respect to temperature are of the same sign. In particular, for an ideal gas the chemical equilibrium solution is stable for all temperatures and amounts of dissociation. Physically, the criterion establishing this corresponds to the ability of the gas to dissipate effectively the heat produced by dissociation.
Fluid Mechanics of Meteor Trails
Authors: Liu V. C.
Published: February 2004

The initial dispersion of a meteor trail which consists of atoms, ions, etc., evaporated from a hot meteoric body has an important bearing on its detectability via electromagnetic wave scattering. In the contemporary literature, the classical diffusion equation, in one form or another, is often used for an approximate description. This leads to much uncertainty and conceptual difficulty. From the Maxwell-Boltzmann viewpoint of kinetic theory, it is found that a new relation in the form of the telegraph equation can be derived which removes the present difficulties and gives closer agreement with observations.
Intermolecular Forces: Thermal Diffusion and Diffusion in Ar-Kr
Authors: Humphreys A. E. , Mason E. A.
Published: February 2004

Thermal diffusion and diffusion measurements on Ar-85Kr, made by the two-bulb method, are reported for the temperature range 77-600°K. In part of the temperature range there is an unexplained discrepancy between our thermal diffusion data and those of Grew and Mundy, making it no longer clear that the thermal diffusion factor has a positive minimum. However, it is confirmed, by the use of a specially constructed thermal diffusion column, that the thermal diffusion factor is positive between 77 and 90°K. The ordinary diffusion coefficients are in excellent agreement with other work. Notwithstanding the thermal diffusion discrepancy, it is clear that the exp-6, Kihara core, and Morse potential models are not entirely satisfactory.
Variational Principles for a Rarefied Gas Flow past an Arbitrary Three-Dimensional Body
Authors: Su Chih-Lan
Published: February 2004

Variational principles for a rarefied gas flow past an arbitrary three-dimensional isolated body are formulated, based on the linearized BGK equation. Both the constant wall temperature case and adiabatic wall case are considered. It is shown that the stationary values given by these principles are related to physically meaningful quantities such as drag and heat flux. The principles are valid for all Knudsen numbers.