bluuebunny/crossref_metadata_2025 huggingface dataset:
Nonlinear Interaction of Electromagnetic Waves in a Cold Magnetized Plasma
Authors: Etievant C. , Ossakow S. , Ozizmir E. , Su C. H. , Fidone I.
Published: February 2004

The nonlinear interaction of electromagnetic waves propagating in a cold plasma across a magnetic field is investigated. The amplitude of the generated wave is evaluated, and numerical computations are given for two cases of interest: (a) the interaction of an extraordinary wave with an ordinary wave leading to the generation of an ordinary wave; (b) the interaction of two ordinary waves leading to the generation of an extraordinary wave. The results show that under appropriate conditions the detection of generated wave is feasible and the scheme should provide a diagnostic method for measuring the local density and its fluctuations in magnetized plasmas.
Overstable Modes due to Resistivity Gradients in a Current-Carrying Plasma Slab
Authors: Pridmore-Brown D. C.
Published: February 2004

A preliminary study is made of overstable modes due to resistivity gradients in a current-carrying plasma slab. A restricted set of solutions satisfying a constant pressure assumption is found for the magnetohydrodynamic equations. These solutions turn out to be overstable in a certain range of the resistivity.
Plasma Current Density and Equilibrium of Magnetically Trapped Particles
Authors: Siambis John G.
Published: February 2004

The current density of a low-density collisionless plasma, confined in static equilibrium by a strong externally applied static magnetic field, is obtained in the limit of adiabatic motion for the charged particles. When there is no net streaming, to zero order in ε: the mass-to-charge ratio, along the field lines of the magnetic field, then the current density is of first order in ε, and its component along the field line is produced by three contributions. The first is due to the shear drift of the guiding centers along the field line. The second is due to the zero-order drift of the guiding centers along the field line, and the velocity space asymmetry in the first-order correction to the lowest-order distribution function. This asymmetry is due to the shear in the field lines. The third contribution is due to the component of the curl of the magnetization along the field line and is also related to the shear. A local macroscopic equilibrium relation for the gradient of the pressure is obtained from the divergence of the current density.
Anisotropic Temperature Plasma Instabilities
Authors: Kalman G. , Montes C. , Quemada D.
Published: February 2004

An anisotropic plasma exhibits a transverse instability due to the mutual attraction of the microscopic current elements. A detailed study is made of this instability in an electron-ion plasma without any external magnetic field. The system is characterized by a temperature tensor and described by a quasi-Maxwellian distribution function. The dielectric tensor for such a system is calculated and then the dispersion relation is considered. It is found that there are two unstable modes: (i) a purely transverse mode and (ii) a coupled or transverse-longitudinal mode. The latter separates into two branches: (a) the first is an essentially unstable quasitransverse mode, (b) the second is the quasi-longitudinal ion acoustic mode driven into instability through its interaction with the quasitransverse mode. Growth rate, k and angular dependence, domain of instability, and polarization are analyzed in detail.
Turbulent Heating of Plasma in a Mirror
Authors: Jensen T. H. , Scott F. R.
Published: February 2004

By the discharge of condensers, a current is driven axially through a plasma column located in a mirror field. The maximum value of the current is typically 5000 A and the frequency typically 1 Mc/sec. It is found that under a variety of circumstances, 3-4% of the energy initially stored in condensers is transferred to perpendicular energy of the plasma. A substantial part of the energy is transferred to ions. The ion energy spectrum has been measured in one case and within experimental error found Maxwellian with a temperature close to 500 eV. Measurements of x rays emitted when a tantalum target is placed in the plasma show that very few high-energy electrons (> 5keV) are present except while the axial current flows. It is found that the energy transferred to the plasma is proportional to the square of the maximum current; this suggests that efficiencies higher than 4% may be obtained.
Direct Measurement of Nonclassical Particle Losses in a Linear Quadrupole
Authors: Palladino R. W. , Yoshikawa S.
Published: February 2004

In a linear quadrupole plasma containment device, lacking internal supports for the current conductors, the flux of charged particles from the main plasma volume is measured directly. With rf-produced plasmas (ne between 1010 − 1012cm−3, Te ̃ 10 eV, Ti < 1 eV), the end losses are only a small fraction of the total losses. Most of the plasma is lost outwards in a direction perpendicular to the current conductors (radial loss). With gun-injected plasmas, the radial loss is usually smaller than the end loss but is still nonclassical.
Coherent Forward Scattering of Microwaves from Density Fluctuations in Alkali Plasmas
Authors: Iannuzzi M. , Magistrelli F. , Piperno F.
Published: February 2004

An experimental study has been carried out on coherent forward scattering of microwaves from ion acoustic waves in alkali plasmas in a nonlinear regime. The experimental apparatus allowed quantitative measurements to be made with good accuracy. Geometrical and diffraction effects have been avoided by using a plasma filled waveguide. The dependence of scattering cross section on the amplitude of ion acoustic waves and on the frequency of the incident radiation has been studied in detail. The experimental results are in good agreement with the theoretical results.
Similar Solutions for Unsteady Magnetohydrodynamic Couette Flow
Authors: Sluyter Marshall M.
Published: February 2004

Similar solutions are obtained for the unsteady magnetohydrodynamic Couette flow with suction. Both uniform and time-dependent magnetic fields are considered. It is shown that the magnetohydrodynamic flows can be obtained through the analysis of viscous flow.
Structure of Turbulent Hydromagnetic Channel Flows
Authors: Harris L. P.
Published: February 2004

The predictions of velocity profiles in hydromagnetic channel flows derived during an earlier study compare satisfactorily with recent experimental measurements of Brouillette and Lykoudis.
General Two-Dimensional Steady Magnetogasdynamic Flows
Authors: Lynn Y. M.
Published: February 2004

Essential features of general two-dimensional steady magneto-gasdynamic flows are shown. For the special class of zero transverse electric field flow, new invariants along streamlines and their intrinsic properties are given.
Ion Wave Reflections as Observed in a “Perturbed” Plasma
Authors: Aksornkitti S. , Hsuan H. C. S. , Lonngren K. E. , Alexeff I.
Published: February 2004

The experimental observation of the reflection of ion acoustic waves from a negatively biased grid immersed in a plasma is reported. Reflection is detected only in the region where the plasma is “perturbed.”
Turbulence Measurements in an Axisymmetric Compressible Wake
Authors: Demetriades Anthony
Published: February 2004

The turbulence characteristics of an axisymmetric wake shed by a very slender body at Mach 3 have been measured with the hot-wire anemometer. The region covered began at transition, located immediately downstream of the model, and ended about 100 virtual (momentum) wake diameters downstream. By using computer-aided corrections to the anemometer frequency response, maps of the temperature and axial velocity fluctuations, their cross correlations, spectral density, and autocorrelation macroscales were obtained as a function of the axial and radial coordinates. Beyond 40 wake diameters from the virtual origin, dynamic equilibration forces these distributions into seemingly selfpreserving forms. These forms are identical with their incompressible counterparts except for a coordinate transformation already suggested by the dynamic equilibrium hypothesis and the Reynolds analogy typical of adiabatic flows. The density macroscale is numerically smaller than that of the velocity, although they both approximate the transverse wake scale. Away from the axis, both the fluctuation magnitudes and their spectral densities are apparently disorted by signals associated with the intermittent boundary, which is thought to be weakly periodic with a wavelength on the order of the wake diameter.
Long Waves in a Stratified Fluid over a Channel of Arbitrary Cross Section
Authors: Shen M. C.
Published: February 2004

A theory of unsteady long waves in a stratified fluid over a channel of arbitrary cross section is proposed. The results obtained are general enough to meet any practical purpose, but rather simple in application. A formula is first derived to determine the wave speed in relation to any given density profile, current speed, and cross section of the channel. The wave form is then prescribed by a set of three time-dependent equations, depending upon the relationship among the longitudinal length, wave amplitude, and time scales. The theory predicts the occurrence of various types of internal waves at the depth where the rate of change of the density profile is the largest in the increasing direction of depth, and with slight modification, the method developed is applied to the case of a fluid with infinite height or a fixed boundary, where density stratification plays an indispensable role.
Integral of Motion for Centered Unsteady Flows
Authors: Lee T. S.
Published: February 2004

For general centered self-similar unsteady flows separated by a shock wave from an unsteady ambient medium, the profile distributions of physical variables are, in general, obtainable by purely numerical means only. However, one integral of motion based on mass and energy conservation relations is found to exist universally, except in the singular case where the ambient density decay exponent falls on the geometry expansion index. This work formally derives and presents this integral in closed form.
Mass Spectrometric Sampling in Shock-Tube Studies
Authors: Wang C. P.
Published: February 2004

The mass spectrometer has frequently been employed to study chemical kinetics and ionization processes. The difficulty encountered is the sampling process, i.e., the transfer of a sample of gaseous or ionized species from a high-temperature and high-pressure reactive region, into the operating pressure of a mass spectrometer, 10−5 mm Hg, with the fewest reactions and changes of composition. The sampling process in the shock tube is further complicated by the nonsteady, nonuniform, cool, and dense end-wall thermal layer. A detailed study of ions (or gaseous species) diffusing through the thermal layer and expanding through an orifice to a free-molecular jet, and the reactions which occur during the process, is carried out using a simplified model. The agreement between the simplified model results and the experimental results promises the possibility of obtaining quantitative measurement by this sampling process.
Closure for Stochastically Distributed Second-Order Reactants
Authors: O'Brien Edward E.
Published: February 2004

A closure at the third-order moment is presented for the problem of the decay of reactants which obey a second-order equation, and whose initial description is given stochastically. The closure satisfies prescribed realizability conditions for all possible initial assignments of the mean, the mean square fluctuations, and third-order moments of the concentration field. The closure is applied in two typical examples, and in each case the results agree satisfactorily with exact stochastic solutions.
Free Convection in a Rotating Medium
Authors: Samuels Michael R.
Published: February 2004

Numerical techniques have been used to study natural convection in a fluid subjected to axial rotation. Axisymmetrical flows were studied in two different geometries for a variety of rotational speeds. For case I (R1 = 1.0, R2 = 2.5, H = 3.0), the computed flow patterns were qualitatively compared with those which would be expected from the basic rules of physics, and good agreement was obtained. Rotational speeds between Ω = 0, and Ω = 20 were studied for a Grashoff number of 3000. Increased rotational speed was found to decrease the over-all heat transfer rate. For case II (R1 = 1.0, R2 = 4.0, H = 1.0), rotational speeds of Ω = 0.0 to Ω = 40.0 were studied at a Grashoff number of 400. At low rotational speeds, a single convection cell was found, however, at higher rotational speeds, the single cell became unstable, and changed to a two-celled pattern. This transition resulted in a slight increase in the over-all heat transfer rate.
Toroidal and Poloidal Field Representation for Convective Flow within a Sphere
Authors: Sherman Michael
Published: February 2004

In spherical regions, an arbitrary solenoidal velocity field can be developed into a series of toroidal and poloidal fields. These fundamental vector fields, expressed in terms of spherical Bessel functions and spherical harmonics, have certain orthogonality properties which prove useful in treating convective flow problems within spheres. The utility of this velocity field representation is demonstrated by considering the stability of a nonuniformly heated fluid in a spherical cavity. A variational principle is presented, equivalent to the eigenvalue problem for the critical Rayleigh number (the stability criterion). This principle forms the basis for an approximate method of determining upper bounds to the critical Rayleigh number. It is found that a class of three-dimensional disturbances is more unstable than either the simplest poloidal (axisymmetric) disturbance mode or the simplest toroidal (two-dimensional) disturbance mode. The numerical results are compared with previously published analyses.
Stability of a Fluid Layer with Time-Dependent Density Gradients
Authors: Mahler E. G. , Schechter R. S. , Wissler E. H.
Published: February 2004

The stability of a fluid layer with adverse time-dependent density gradients is examined by two computational techniques. The most direct solution, that of integrating the time-dependent equations, is compared with the results obtained by invoking the often used quasistationary state approximation. It is seen that this latter approximation is not valid if the instability stems from a sudden change in the concentration or temperature at one surface of the fluid layer. The particular problem studied here is that of a liquid film resting on an impermeable wall with gas absorption into the liquid. In this case the system evolves from one stable state to another with the essential problem being to assess the stability of the system during its evolution between these stable states. It is shown that a single critical Rayleigh number does not exist as in the usual case with linear time-independent density gradients, but that the critical Rayleigh number depends, to some extent, on intangible factors such as the initial perturbation magnitude and the mode of observation.
Heat and Mass Transfer from Small Spheres and Cylinders Freely Suspended in Shear Flow
Authors: Frankel Neil A. , Acrivos Andreas
Published: February 2004

The problem of heat and mass transfer from small spheres and cylinders freely suspended in a shear flow is considered in the limit of Reynolds number Re → 0. Asymptotic formulas are derived which relate the Nusselt number Nu to the Péclet number Pe in the limit Pe → 0, and for the case of the cylinder, Pe → ∞. At high Pe, the Nusselt number is found to approach a constant value, whereas, at low Pe it is shown to increase with Pe12 for the sphere and with —(log Pe)−1 for the cylinder. These results indicate the existence of a fundamental difference at high Pe between the shear flow problem studied here and the corresponding classical problem of uniform flow at infinity.
Asymptotic Behavior of Diffusion of Tangential Velocity Discontinuity in Rarefied Gas
Authors: Sone Yoshio
Published: February 2004

A treatment of the diffusion of a tangential discontinuity in flow velocity is given for the linearized Boltzmann-Krook equation, with emphasis on the asymptotic behavior for large values of time. The connection with the general asymptotic theory of Grad is also discussed.
Exponential Repulsive Potential. II. Third Virial Coefficient
Authors: Bruch Ludwig W.
Published: February 2004

The classical third virial coefficient and its first quantum correction are evaluated analytically for the exponential repulsive potential. The classical integral for the Morse potential is treated approximately. The results are compared with the classical second virial coefficients for these models.
Plasma Virial and Equations of State for a Plasma
Authors: Liboff Richard L. , Lie Tae-Journ
Published: February 2004

The virial theorem for a plasma is formulated within a particle framework. The result is applicable to isotropic, anisotropic, and quasirelativistic systems. The form reveals the negative quality of the time derivative of the virial in addition to the structure of the particle-particle inductance tensor. A tensoral virial theorem is formulated for anisotropic systems. Equations of state for magnetoactive idealized plasma configurations are derived.
Investigation of Kinetic Models for Gas Mixtures
Authors: Walker E. L. , Tanenbaum B. Samuel
Published: February 2004

The collision integrals of various kinetic models are compared to those of the Boltzmann binary-collision operator for gas mixtures. It is found that the Holway ellipsoidal model is unable to reproduce the Boltzmann result for the partial heat-flow collision integral [δ(12maca2ca)]ab when ma ≫ mb. The Gross-Krook and Sirovich models are found to be in serious disagreement with the Boltzmann operator with regard to the partial traceless-pressure and heat-flow collision integrals.
Transport Equations for a Weakly Ionized Electron Gas
Authors: Walker E. L. , Tanenbaum B. Samuel
Published: February 2004

The Grad 13-moment method (using separate zero-order species flow velocities and temperatures) is used to calculate the electron traceless pressure Pe and heat flow qe for a weakly ionized gas in a dc magnetic field. Electron-neutral collisions are assumed to dominate and the “transport approximation” is used to obtain expressions for Pe and qe using arbitrary inverse power interparticle force laws. The results, under most conditions, show terms that are similar to the usual expressions for a simple gas except that the electron viscosity and thermal conductivity involve the electron-neutral collision frequency ven rather than the electron self-collision frequency. In addition, there are terms in qe proportional to any differences in the zero-order electron and neutral flow velocities and temperatures. Finally, it is noted that the electron-neutral interparticle force law has very little effect on the form of the results (although it is important in determining the explicit value for νen).
Kinetic Theory of Highly Nonequilibrium Plasmas
Authors: Yen James T.
Published: February 2004

Nonequilibrium plasma states involving nonsmall current densities and/or enhanced electron temperatures are studied by taking 13 moments of the Boltzmann equation and using a new approach. New and nonlinear collisional terms are found for the basic equations. The electrical conductivity is calculated for the fully ionized case under no applied magnetic field: It first decreases slowly from the Spitzer-Härm value, then turns sharply around and finally increases as a cubic power in the current density. The sharp turn-around is located roughly at the electron sonic point. Regarding the supersonic states it is observed that they can be reached and maintained as steady states if the local electric field is properly reduced below the critical runaway field ∈c and is limited to the steady-state value. Some associated instabilities and ways of stabilization are discussed. It is also observed that unsteady “run-away” will occur when ∈c is exceeded, as emphasized by Dreicer. The possibility of an insurmountable “electron sonic barrier” is indicated. Experimental studies are urged.
Dynamic Behavior of Imploding Magnetically Driven Axisymmetric Slug-Type Plasma Sheets
Authors: Guman William J.
Published: February 2004

The dynamic behavior of magnetically driven axisymmetric plasma sheets of negligible thickness is examined by postulating a simplified two-dimensional plasma sheet model. The equations of motion in the axial and radial directions are derived in Lagrangian form for the general case of time-varying current. For the case of constant current, the general solution of the equations of motion is obtained. These equations of motion are solved for three different types of small sinusoidal perturbations of a cylindrical implosion. The plasma sheet configurations, particle trajectories, and surface mass density variations are presented for representative examples.
Test-Particle Propagator and Its Application to the Decay of Plasma Wave Echoes
Authors: Hinton F. L. , Oberman C.
Published: February 2004

The conditional probability density W (x, v, t | x0, v0, t0) describing the motion of a test particle satisfies a kinetic-type equation, which was first systematically discussed by Rostoker for stable plasmas and was generalized by Rogister and Oberman to describe weakly tubulent plasmas. A systematic expansion for the solution of this equation is presented which is valid for short times on the kinetic time scale. However, these times are of sufficient length to describe the decay of plasma wave echoes due to collisions or weak turbulence.
Radial Density Distribution in a Wide Unstable Plasma Column
Authors: Ventrice Carl A. , Massey C. G.
Published: February 2004

The positive column of an argon discharge is investigated in the presence of a longitudinal magnetic field using a triple electrostatic probe. A wide chamber with a magnetic field length to radius ratio of six is used. The existence of an instability is confirmed. The variation of the radial density distribution with magnetic field is observed to be in qualitative agreement with the theory of Holter and Johnson. In addition, the electron temperature is observed to increase with increasing magnetic field. Repeated experiments show that the instability does not always develop even when the magnetic field is increased to six times the theoretical value of the critical field. Under this condition the variation of the radial density distribution with magnetic field is observed to be in qualitative agreement with the results of Bickerton and von Engel.
One-Dimensional Plasma Model in the Presence of a Magnetic Field
Authors: Hasegawa Akira , Okuda Hideo
Published: February 2004

A new sheet model is developed which is suitable for studying one-dimensional electromagneto-kinetic disturbances propagating with an arbitrary angle to an applied magnetic field. The model is a generalization of the sheet charge-type models previously considered. The concept of a retardationless electromagnetic field is introduced to provide the coupling between the sheet charges and currents. Some examples of wave propagation using the model are shown which compare very well with those predicted from the dispersion relation.
Two-Dimensional Theta-Pinch Dynamics with Transverse Magnetic Fields
Authors: Düchs Diethelm
Published: February 2004

The complete set of equations for the two-fluid model of a fully ionized plasma, the parameters of which depend on two spatial dimensions and time, is solved by a computer program. This program is applied to the problem of plasma rotation in a theta pinch caused by transverse multipole fields. The results show that the plasma does not rotate like a cylindrical rigid body, rather the velocity varies strongly with azimuth. Moreover, the rotation changes direction along the radius. Therefore, transfer of angular momentum from outside is not necessary for the existence of rotation. Even in small transverse fields (B ∼ 500 G) the rise time for the angular velocity is of the order of 10−7 sec and very short compared with those obtained from previous theoretical models.
Bremsstrahlung and Scattering at Harmonics of the Plasma Frequency
Authors: Manheimer Wallace M.
Published: February 2004

An expression is derived for the bremsstrahlung intensity at the n + m harmonic of the plasma frequency ωp and for incoherent scattering intensity at the incident frequency ν plus or minus nωp. The bremsstrahlung intensity at 3ωp and incoherent scattering intensity at ν ± 2ωp is explicitly calculated. The intensity is shown to be very small unless the plasma is highly turbulent.
Bremsstrahlung of a Fully Ionized Plasma in the Infrared
Authors: Bogen P. , Rusbüldt D.
Published: February 2004

The frequency dependence of the bremsstrahlung for hv ≪ kT and ν > 2νp (where νp is the plasma frequency) has been measured and compared with theory. Experiments have been carried out on a theta pinch with the following data: 14 τ = 0.75 μsec, Bmax = 45 kG, T ∼ 106 °K, Ne ∼ 3 × 1017cm−3. The intensity between 0.25 μ and 25 μ has been measured with a time resolution of 20 nsec, using an InAs photodiode and a copper-doped germanium photoresistive detector in the infrared, and a photomultiplier in the visible and uv domains. It was verified that the emission signals observed side-on were at all times and for all wavelengths practically proportional to one another; shape differences observed end-on resulted almost certainly from refractive index effects. The experiments confirm the theoretical prediction, that the Gaunt factor should vary by a factor of 2 in the investigated wavelength domain. No influence of three-body encounters or nonthermal radiation has been detected.
Synchrotron Radiation Experiments with a Hot Electron Plasma
Authors: Sesnic S. , Lichtenberg A. J. , Trivelpiece A. W. , Tuma D.
Published: February 2004

The synchrotron radiation emitted parallel and perpendicular to the magnetic axis of a “hot electron” plasma (Te = 80 keV) confined in a 50-kG magnetic mirror field has been measured in the 4−0.2mm wavelength region of the electromagnetic spectrum by means of a spectrometer system capable of determining the absolute intensity of the synchrotron radiation. The experimental spectrum agrees with the theoretical spectrum based on single-particle emission and a two-dimensional Maxwellian distribution for the plasma electrons. The electron temperature and density predicted by the measured spectrum agrees with other methods of measurement of these quantities.
“Single-Ended” Q-Device
Authors: Decker John A.
Published: February 2004

The equilibrium theory of the Q-device is extended to the “single-ended” configuration by use of an approximate model which only considers source and axial loss terms and ignores cold-end-plate phenomena. Numerical calculations which explicitly include alkali-metal adsorption effects at the ionizer surface are compared with single-ended Q-device operating data. The surprisingly good agreement between the predictions of this simplified model and the observations for axial magnetic fields above about 2 kG—with the exception of an unexplained anomaly at a cesium flux of 1017cm−2.sec−1—indicates that the “single-ended” Q-device is remarkably insensitive to cold-end and plasmacolumn conditions.
Observation of Fluctuations in the Plasma Confined in the Toroidal Octopole
Authors: Ohkawa Tihiro , Yoshikawa Masaji
Published: February 2004

Observations of the fluctuations by electrostatic and magnetic probes are made in the toroidal octopole device. The plasma density is varied from 5 × 108cm−3 to 1010cm−3. The ion and electron temperatures are approximately 100 and 6 eV, respectively. The fluctuations exist only where the density gradient is large. The amplitude of the potential fluctuation is less than one-hundredth of the electron temperature at the strongest magnetic field. A transmission experiment is performed to obtain the dispersion relation of the waves. Qualitative comparison with linear theory on instabilities singles out the drift cyclotron instability as consistent with the observations. Quantitative comparison with the computed dispersion relation is also made on the dependence on the magnetic field and the plasma density. The rate of transport of the plasma across the magnetic field estimated from the fluctuation amplitudes is orders of magnitude smaller than the rate obtained from the ion confinement time. The amplitudes can be reduced when the magnetic field is increased or when a small toroidal field is applied.
Direct Correlation Function in Space and Time
Authors: Percus J. K. , Yevick G. J.
Published: February 2004

The partition function of a classical many-body system is formally extended to space-time. The total space-time correlation function is expressed in terms of a time-dependent direct correlation ĉ(x, t).
Direct Computation of the Functional Integral Expression for the Correlation Function of the Turbulent Velocity Field
Authors: Hosokawa Iwao
Published: February 2004

The time-dependent functional integral expression for the field correlation, which is derived exactly from the well-known Hopf functional formalism for turbulence, is numerically estimated by the Monte Carlo quadrature for Burgers' model of turbulence.
Two-Dimensional Magnetohydrodynamic Turbulence
Authors: Robinson D. C.
Published: February 2004

For a system governed by a generalized Ohm's law, an arbitrary velocity field cannot independently maintain magnetic field fluctuations in a two-dimensional situation.
Visualization of Plasma Flutes in a Q-Machine
Authors: Cataldo Joseph C. , Jen Norman C.
Published: February 2004

The plasma camera has been used to observe flute modes in a single-ended Q-machine. The flutes, rotating in the E × B direction, are irregular extensions of the plasma column and exhibit a convective mass transfer phenomenon by the breaking off of the flutes.
Viscous Drag of Bodies Moving near a Free Surface
Authors: Dugan John P.
Published: February 2004

An integral representation is obtained for the velocity and pressure fields produced by the horizontal motion of two-dimensional bodies below (or on) the free surface of a viscous liquid. This allows consideration of viscous and free surface effects to be incorporated in one model for the prediction of forces on the body. The integral representation is used to consider the simple physical example of the motion of a horizontal flat plate. This illustrates the interaction of viscous and free surface effects since the plate experiences skin friction drag plus drag due to the generation of surface waves by the viscous boundary layer.
Numerical Studies of Viscous Flow around Circular Cylinders
Authors: Hamielec A. E. , Raal J. D.
Published: February 2004

Numerical solutions have been obtained for incompressible Newtonian flow around a circular cylinder for Reynolds numbers of 1, 2, 4, 10, 15, 30, 50, 100, and 500. The results are presented in the form of vorticity and stream function distributions. The solutions allow detailed characterization of the vortex rings. Drag coefficients, pressure distributions, and vortex dimensions are compared with experimental data and with available theoretical predictions for Reynolds numbers up to 50. The agreement with both experimental data and previous theoretical solutions is considered to be excellent.
Nature of the Rotational Discontinuity
Authors: Gerdin G. A. , Sonnerup B. U. Ö.
Published: February 2004

The behavior of a large-amplitude intermediate magnetohydrodynamic wave in the presence of reflected particles is examined. For reflections off its front side, the wave becomes a spreading expansion wave; for reflections off the back side it steepens to a shock wave, i.e., an entropy increase is produced across the wave.
General Weak Turbulence Theory of Resonant Four-Wave Processes
Authors: Davidson Ronald C.
Published: February 2004

The time evolution of wave correlations (cumulants) in a uniformly turbulent ensemble of weakly nonlinear, dispersive systems is discussed. With closure of the hierarchy for wave correlations appropriate to the inclusion of resonant four-wave processes, a kinetic equation for the spectral energy density of the waves is derived in situations where the resonant three-wave decay condition cannot be satisfied. The resulting kinetic equation is a nonlinear integrodifferential equation with driving terms trilinear in the energy density. Some general properties of this equation are discussed including associated conservation relations and the law of increase of entropy.
Electrical Conductivity of Partially Ionized Noble Gases
Authors: Nighan William L.
Published: February 2004

The electrical conductivity of the noble gases—argon, helium, xenon, and krypton—has been calculated for arbitrary degrees of ionization for electron temperatures in the 300-30 000°K range. A variational method elaborated by Robinson and Bernstein was employed in the calculations, along with the electron-atom momentum transfer cross-section values reported by Frost and Phelps. Because of the very low values of the electron-noble-gas atom cross sections near the Ramsauer minimum, Coulomb collisions have been found to influence the conductivity for values of fractional ionization as low as 10−7. For the same reason electron-neutral momentum transfer collisions have been found to be unimportant for values of fractional ionization as low as 10−5, above which the gas behaves as though it were fully ionized. Two limiting degrees of ionization have been defined for each noble gas above or below which the gas can be considered either completely or weakly ionized, respectively. In addition, the influence of electron-electron interactions on the electrical conductivity in the partially ionized regime has been established.
Temperature Relaxation Near the Interface of Two Semi-Infinite Plasmas
Authors: Lin Shao-Chi , Wei Hsin Yi
Published: February 2004

The problem of electron-ion temperature relaxation when two semi-infinite, nonmagnetized plasmas at different initial temperatures were suddenly brought into thermal contact under constant pressure is investigated using the two-fluid model. No current is assumed to flow across the interface, and charge separation is considered only to the extent of a simple correction on effective thermal conductivity (i.e., no plasma oscillation). Viscous stresses associated with induced fluid motion are also neglected. The asymptotic solution for long time after thermal contact is shown to be identical to that in a single-temperature plasma, with effective thermal conductivity equal to approximately [1 + (3me/mi)12] times the local electron thermal conductivity. For a time scale shorter than or comparable to the mean electron-ion collisional energy transfer time tei a self-similar solution is obtained in the form of a double series in ascending powers of the nondimensional time τ = t/tei and of the initial temperature difference parameter ε ≡ (T2−T1)/(T2+T1). It is found that the induced pressure is quite large at early times, suggesting that thermal shock could be a significant source of plasma wave excitation in certain non-steady problems.
Nonlinear Confining and Deconfining Forces Associated with the Interaction of Laser Radiation with Plasma
Authors: Hora Heinrich
Published: February 2004

The nonlinear interaction of an intense light wave with an inhomogeneous plasma produces a macroscopic motion. A rigorous treatment of this interaction based on the ponderomotive force description leads to a general equation of motion. In a plasma with collisions and high electron density, the resulting force density can be interpreted as an expression of the radiation pressure. Below special densities there results a nonlinear collisionless force whose direction is toward decreasing density, and which produces a deconfinement. The magnitude of this force has a polarization dependence only in the third-order terms of the spatial dependence of the density. The total deconfining recoil momentum transferred to the inhomogeneous transition layer is evaluated. The theory of the nonlinear collisionless acceleration is used to explain the experimentally observed properties of the fast part of plasmas produced by lasers from isolated single small aluminum balls and thick solid targets.
Onset of the Helical Instability in Weakly Ionized Discharge Plasmas
Authors: Robertson Harry S. , Currie Edward H.
Published: February 2004

The helical instability in a discharge plasma has been variously reported, sometimes as having an explosive onset, sometimes as reversible. Experiments in cesium are plasmas show that the onset is always explosive provided the ambient noise level is low enough; hysteresis is normally present; and plasma parameters change discontinuously at the onset and extinguishment of the instability. In the presence of noise, however, the onset is reversible and continuous.
Drift Instabilities in a Uniformly Rotating Plasma Cylinder
Authors: Chu T. K. , Coppi B. , Hendel H. W. , Perkins F. W.
Published: February 2004

The dispersion relation for low-frequency, collisional, electrostatic waves in a uniformly rotating plasma cylinder is obtained in terms of several positive-definite bilinear forms whose magnitude may easily be estimated. The effects of ion transverse collisional viscosity, electron parallel resistivity, ion parallel motion, and an equilibrium radial electric field are included in the theory. The close correspondence between the present dispersion relation and the dispersion relation for localized, slab-model modes justifies the use of the latter in the interpretation of Q-machine experiments. Another result is that ion collisional viscosity stabilizes the density-gradient driven drift wave if the axial wavelength λ‖ satisfies λ‖ < 2πσr0 (M/me)1/4, (σ ∼ 0.7; r0 is the density gradient scale length; M, me are the ion and electron masses, respectively). Overstable waves, which are driven by the centrifugal force and which resemble flutes with a finite parallel wavelength, can exist if λ‖ is sufficiently long.
Plasma Fluctuations and Convective Modes
Authors: Kent A. , Taylor J. B.
Published: February 2004

The electric field fluctuations in an inhomogeneous plasma are calculated directly, using a test particle method, and the result interpreted in terms of convective modes. This serves to place the usual convective mode picture on a more secure basis.
Dispersion of the Upper Hybrid Mode in a Spatially Inhomogeneous Plasma
Authors: Pearlstein L. D. , Bhadra D.
Published: February 2004

The dispersion of the normal mode at the upper hybrid frequency propagating parallel to a uniform magnetic field in a spatially inhomogeneous plasma is calculated. For the case where the density varies in a direction perpendicular to the magnetic field, it becomes necessary to solve a fourth-order differential equation for the perturbed potential. The method of solution is a WKB analysis of this equation. A Maxwellian plasma and a Maxwellian plasma with a superimposed beam parallel to the magnetic field are considered. Finally, the relevant dispersion relations are solved using a digital machine, and comparison is made with results of a recent experiment.
Single-Particle Confinement Studies in a Radio-Frequency-Supplemented Magnetic Mirror
Authors: Eubank H. P.
Published: February 2004

An experimental study of electron confinement in magnetic mirror geometry supplemented with rf quasipotential barriers yields confinement times which appear to be a function of gas scattering only. Under minimum scattering conditions (p ≈ 5 × 10−8 Torr), 10-20-eV electrons are observed to undergo several thousand reflections before loss occurs. The magnitude of the quasipotentials and the conditions for onset of nonadiabatic particle behavior are found to be in good agreement with existing theory.
Emmons' Problem According to the Oseen Approximation
Authors: Clarke John F.
Published: February 2004

Conditions near the leading edge of an obstacle which is exuding fuel into a stream of oxidizer are studied by making use of the special properties of the Oseen equations in a parabolic coordinate system.
Anisotropy of Brownian Motion Observed in a Temperature Gradient Gas
Authors: Elrick Richard M.
Published: February 2004

Random motion of submicron oil drops and smoke particles exhibit an anisotropy which appears to be a function of temperature gradient in the suspending gas. The Brownian motion is more significantly altered in a direction perpendicular to the gradient.
Equations for Gas Mixtures. II
Authors: Goldman Edward , Sirovich Lawrence
Published: February 2004

An extension of a previous paper on the equations governing gas mixtures is presented. Revision of the relaxation time of component velocities leads to a new diffusion equation. Various dimensionless parameters of a binary gas are plotted.
Ion and Electron Temperature and Density by Thomson Scattering with a Low Resolution Monochrometer
Authors: Siemon Richard E. , Benford James
Published: February 2004

Experimental results are presented which demonstrate the advantages of doing Thomson scattering with the Salpeter parameter α near unity. A simple method for determining Ti in this region with a low resolution monochrometer is described.
Plasma Flux Transport
Authors: Parkin C. W. , Barach J. P.
Published: February 2004

An electric shock tube has been used in an interaction experiment with a transverse, dc magnetic field. A simple magnetohydrodynamic analysis, assuming a conductivity of 130 mho/cm, emphasizes the importance of tensor conductivity and transverse field diffusion.
Classical Diffusion of a Stationary Toroidal Plasma
Authors: Johnson John L. , von Goeler S.
Published: February 2004

The Pfirsch-Schlüter factor, which measures the enhancement of diffusion due to current along the magnetic field over that associated with diamagnetic current, is calculated for general configurations and applied to specific ones including multipoles.
Improved Plasma Confinement in a Q Machine with Symmetrically Heated End Plates
Authors: Jassby D. L. , Motley R. W.
Published: February 2004

The limiting confinement time of cesium plasma in a Q device has been increased from 20 to 50 msec by making the endplate isotherms circular and concentric.
Experimental Observation of Low-Frequency Oscillations Described by the Plasma Continuity Equations
Authors: Roth J. Reece
Published: February 2004

Low-frequency oscillations in the electron number density of a slightly ionized gas have been experimentally observed over the range 102-105 Hz, and identified with periodic solutions to the neutral and charged particle continuity equations.
Turbulence Theory with a Time-Varying Wiener-Hermite Basis
Authors: Bodner Stephen E.
Published: February 2004

A theory of homogeneous turbulence in an incompressible fluid is formulated. The field variable v(r, t) is expanded in terms of a complete set of an ideal random basis, the first term of which is Gaussian. Since the ideal basis follows the actual fluid motion, there should be no incorrect relation between large and small eddies.
Statistical Theory of Thermal Convection at Large Prandtl Number
Authors: Herring J. R.
Published: February 2004

Three statistical theories of turbulence are applied to thermal convection between infinite slippery plates in the limit of infinite Prandtl number. The range of Rayleigh number R investigated is 657 ≤ R ≤ 1.25 × 104. The theories, which are compared in a series of numerical calculations, are the direct interaction approximation, the quasilinear approximation, and the quasinormal approximation. The direct interaction approximation gives results for the evolution Nusselt number in good agreement with some simple exact solutions to the problem. The flow predicted by this method is very persistent. Turbulence first appears just at critical R and its intensity gradually increases with increasing R. The quasinormal approximation gives satisfactory results for R ≲ 2000, but some of the initial value problems lead to an unphysical negative temperature autocorrelation spectrum for larger R. In none of the initial value problems for R > 2 × 103 did the quasinormal procedure yield a sensible stationary state. The quasilinear approximation appears to upperbound the heat transport given by both the other approximations predicting about 8% larger heat transport than the direct interaction approximation.
Periodic Fluctuation of Chemical Species over a Reactive Surface
Authors: Chung Paul M.
Published: February 2004

The flow of a laminar stream containing a periodic fluctuation of the mass fraction of a chemical species over a flat plate was considered. The fluctuation of the chemical species is assumed to be continuously generated at a point uptream of the plate, and the surface of the plate is assumed to possess a finite catalyticity for the first-order surface reaction of the chemical species. When the wavelength in the inviscid stream is long compared with the distance along the surface, the out-of-phase fluctuation in the boundary layer was found to increase with the Damkohler number, beginning with a finite value when the Damkohler number is zero, and only decrease for very large values of Damkohler number. Thus, the off-phase fluctuation in the boundary layer, particularly near the surface, is maximum for a given fluctuation in the free stream when the surface Damkohler number is finite. When the wavelength in the inviscid stream is very small as compared with the distance along the surface, the fluctuation is confined to the outer portion of the boundary layer. In the limit of the continuously decreasing wavelength (continuously increasing frequency), the momentum boundary-layer edge becomes a singular line across which no fluctuation can penetrate. The regular and the singular perturbation techniques have been employed for the analysis.
Variational Calculation of Transport Coefficients in a Binary Mixture
Authors: Bernstein Ira B.
Published: February 2004

For the case of a binary mixture it is shown that it is possible to formulate the calculation of the coefficients of viscosity, thermal conductivity, thermal diffusivity, and diffusion in terms of variational principles. These are such that a first-order error in the trial function representing the departure of the distribution functions from their local thermal equilibrium values leads to a second-order error in the transport coefficients. For those coefficients which are intrinsically positive the variational method reduces to an absolute maximum principle.
Nonisothermal, Nonstationary Diffusion
Authors: Annis B. K. , Humphreys A. E. , Mason E. A.
Published: February 2004

The theory of nonisothermal, nonstationary diffusion in a two-bulb geometry is corrected and extended. Two major corrections to simple theory are necessary: one for the variation with time of the thermal diffusion ratio, and one for the deviations from a quasistationary state in the connecting tube. All previous treatments of the second correction contain inadequacies serious enough to necessitate revision of many reported diffusion coefficients
Kinetic Description of the Propagation of Plane Sound Waves in a Diatomic Gas
Authors: Hanson F. B. , Morse T. F. , Sirovich L.
Published: February 2004

Plane wave solutions for the propagation of sound in a polyatomic gas have been obtained by employing the method of Sirovich and Thurber for polyatomic kinetic models. An asymptotic analysis valid at small frequencies yields the correct continuum limits for the absorption and speed of propagation, and numerical calculations were made for a wide range of frequencies and at several values of the collision number for the relaxation of internal degrees of freedom. Calculations using values of model parameters suitable for nitrogen, oxygen, and air, over a large range of the rarefaction parameter, are in very good agreement with dispersion and absorption measured in these gases.