bluuebunny/crossref_metadata_2025 huggingface dataset:
Turbulently heated distribution functions and perturbed orbit theory
Authors: Katz J. I. , Weinstock Jerome , Kruer W. L. , DeGroot J. S. , Faehl R. J.
Published: February 2004

The perturbed orbit plasma-turbulence theory of Dupree and Weinstock predicts the evolution of the electron-distribution function according to a diffusion equation. The electric field spectrum in one-dimensional electrostatic simulations of the modified two-stream instability is used to obtain the theoretical diffusion coefficient. The diffused distribution function is compared with the actual distribution function in the simulation as a test of the theory.
Filamentation and trapping of electromagnetic radiation in plasmas
Authors: Kaw P. , Schmidt G. , Wilcox T.
Published: February 2004

It is shown that an electromagnetic wave interacting with a plasma is subject to instabilities leading to light filamentation. Nonlinear solutions for light filaments and light trapping are also investigated.
Pitot tube errors in dilute polymer solutions
Authors: Berman N. S. , Gurney G. B. , George W. K.
Published: February 2004

The onset of Pitot tube errors in fresh and degraded solutions of Polyox WSR 301 was found to be related to drag reduction onset. A linear dependence of the pressure error on strain rate, U / D, is also noted.
Low speed calibration formula for vortex shedding from cylinders
Authors: Kohan S. , Schwarz W. H.
Published: February 2004

Calibration formulas are presented for the shedding of vorticies from cylinders at low speeds.
Spin-up from rest: Limitations of the Wedemeyer model
Authors: Watkins William B. , Hussey R. G.
Published: February 2004

The Wedemeyer model for the spin-up from rest of a homogeneous fluid in a cylindrical container is examined experimentally and numerically. The validity of the model is shown to depend on the Ekman number, the container aspect ratio, the radial position, and the nearness to solid body rotation.
Discrete spectrum basic to kinetic theory
Authors: Siewert C. E. , Burniston E. E. , Thomas J. R.
Published: February 2004

The theory of complex variables is used to establish explicit solutions to the transcendental equation that defines the discrete spectrum for a model problem in the kinetic theory of gases.
Developing velocity profiles in a magnetohydrodynamic duct
Authors: Koegler S. S. , Thomson W. J.
Published: February 2004

A laser Doppler velocimeter is used to measure the velocities for a developing magnetohydrodynamic flow under laminar flow conditions. It is found that entrance effects propagate upstream and exert considerable influence on the distance required to attain fully developed flow.
Pressure profiles of a plasma in hydromagnetic equilibrium
Authors: Hall Laurence S. , Haste G. R.
Published: February 2004

Measurement of total pressure (or any pressure component) along a magnetic field line determines the full pressure tensor of a plasma in equilibrium. This is applied to an electron-cyclotron-resonance produced plasma, yielding the pressure anisotropy and stability limits of the given experimental device.
Representation of dielectric function of magnetized plasma
Authors: Johnston George L.
Published: February 2004

A representation of the dielectric function of a uniform magnetized plasma with bi-Maxwellian or model loss-cone distribution functions, which is convenient for computational purposes in the case of large temperature anisotropy or propagation at large angles with the magnetic field, is presented.
Nonequilibrium thermodynamic relation between the diffusion and conductivity tensors in a magnetized plasma
Authors: Corkum P. B.
Published: February 2004

The general relation between the particle diffusion and the electrical conductivity tensors of a plasma in an external magnetic field of arbitrary strength is derived. It is shown that they are not independent quantities from the point of view of nonequilibrium thermodynamics.
Parametric decay near the lower-hybrid resonance
Authors: Fidone I.
Published: February 2004

Spatial parametric decay of a wave with frequency near the lower-hybrid frequency is investigated. A three-wave problem is considered with special emphasis on the effect of the mismatch of the wave vectors on the saturation amplitude of the excited waves and the characteristic length of conversion.
Resistivity of ST tokamak
Authors: Ross David W. , Cardwell George L.
Published: February 2004

The magnetic diffusion equation is solved for discharges in the ST tokamak, eliminating the need to define plasma lumped circuit parameters. Agreement with experiment is obtained if the mean ionic charge increases by 50% from the measured value during the first 25 msec.
Plasma losses to an octupole hoop
Authors: Drake J. R.
Published: February 2004

Plasma losses to the unsupported hoops of a toroidal octupole magnetic field were experimentally measured with striped, particle collectors and found to be 5 to 100 times smaller than calculated Bohm diffusion fluxes.
Half-space problems in the kinetic theory of gases
Authors: Siewert C. E. , Thomas J. R.
Published: February 2004

The elementary solutions of the linearized and decomposed BGK equation are used to solve evaporation and heat-conduction problems in a half-space, and values of the microscopic and macroscopic temperature and density slip coefficients are reported, along with the complete temperature and density profiles.
Viscous effects in Rayleigh-Taylor instability
Authors: Plesset Milton S. , Whipple Christopher G.
Published: February 2004

A simple, physical approximation is developed for the effect of viscosity for stable interfacial waves and for the unstable interfacial waves which correspond to Rayleigh-Taylor instability. The approximate picture is rigorously justified for the interface between a heavy fluid (e.g., water) and a light fluid (e.g., air) with negligible dynamic effect. The approximate picture may also be rigorously justified for the case of two fluids for which the differences in density and viscosity are small. The treatment of the interfacial waves may easily be extended to the case where one of the fluids has a small thickness; that is, the case in which one of the fluids is bounded by a free surface or by a rigid wall. The theory is used to give an explanation of the bioconvective patterns which have been observed with cultures of microorganisms which have negative geotaxis. Since such organisms tend to collect at the surface of a culture and since they are heavier than water, the conditions for Rayleigh-Taylor instability are met. It is shown that the observed patterns are quite accurately explained by the theory. Similar observations with a viscous liquid loaded with small glass spheres are described. A behavior similar to the bioconvective patterns with microorganisms is found and the results are also explained quantitatively by Rayleigh-Taylor instability theory for a continuous medium with viscosity.
Theory of two-dimensional turbulence
Authors: Dupree Thomas H.
Published: February 2004

The two-dimensional Navier-Stokes equation and the drift approximation to the Vlasov equation are equivalent. An analytical theory of the turbulent state of this system is developed which contains no ad hoc assumptions. The theory is not strictly valid for the largest eddies and in the inertial range is restricted to large Reynolds numbers. A vorticity flow to large wavenumbers and an energy flow to small wavenumbers is predicted. In the inertial range the theory has a similarity solution whose spectrum agrees with that obtained from dimensional arguments. Diffusion coefficients are derived and the extension to shear turbulence and more general plasma turbulence is discussed.
Neoclassical diffusion in an l = 3 stellarator
Authors: Connor J. W. , Hastie R. J.
Published: February 2004

Neoclassical diffusion in a stellarator is investigated in detail by introducing a consistent expansion in λ1/3 (where λ is the inverse aspect ratio of the torus) for the magnetic fields and particle distribution function. As a result of the expansion, the various characteristic bounce and transit frequencies of the particle orbits appear in different orders, and various regimes of collision frequency (analogous to the “banana”, and “plateau” regimes of the axisymmetric analysis) are considered separately. It is found that over most of the range of collision frequencies the diffusion is the same as that of an equivalent axisymmetric configuration with the sole role of the helical fields being that of supplying the rotational transform. At sufficiently low collision frequencies particle trapping in the helical field modulations becomes important and localized particle diffusion dominates. Expressions for the diffusion flux and ion heat flux are derived in this limit.
Helical plasma structure observed in a hard-core theta pinch
Authors: Düchs D.F. , Dixon R.H. , Elton R.C.
Published: February 2004

Through the addition of an axial current-carrying conductor (hard core), helical fields and magnetic shear have been added to the elongated toroidal plasma generated in a θ-pinch device operated with antiparallel bias field. Two-dimensional (r, z) photographs indicate the presence, from the beginning of the discharge, of a persistent luminous helical structure imbedded in the annular plasma.
Laser plasma heating in a strong magnetic field
Authors: Martineau J.
Published: February 2004

The heating of a deuterium plasma created from solid granule (∼ 100 μ diam; ∼ 1017 particles) confined by strong magnetic fields B0 up to 1 G is studied. Taking into account the inverse bremsstrahlung absorption process, an inhomogeneous hydrodynamic model is used to describe the plasma dynamics. The skin depth due to the diffusion of the magnetic field inside the plasma is calculated. Ohmic heating is taken into account. The magnetic body force for a diffusion plasma is given by J × B while for the infinite conductivity model the force is calculated from the magnetic pressure B02/2μ0 on the plasma boundary. The efficiencies for CO2 lasers and neodymium glass lasers are compared. It is important to feed energy slowly to obtain a high efficiency of incident laser energy to the plasma thermal energy.
Treatment of the magnetically deflected, wall-stabilized arc by means of Green's functions
Authors: Raeder J. , Seeger G. , Gorenflo H. H.
Published: February 2004

Based on the conservation equations for mass density, momentum, and energy, the coupled distributions of viscous flow and temperature in a wall-stabilized arc in a transverse magnetic field are calculated. By means of Green's function of the biharmonic and the Laplace operator, respectively, the relevant equations are converted to integral equations which can be solved by an alternating iteration procedure. Examples are given for an argon arc and are compared with the experimental results.
Self-consistent equilibria and current limitation in relativistic electron beams
Authors: Auer P. L.
Published: February 2004

Several classes of self-consistent equilibria are examined with a view toward establishing their general character. It is found that within the context of self-consistent equilibria current limitation in the sense of Alfvén and Lawson is not present per se. Practical considerations, however, would argue that this limit has rather broad validity in the strictly relativistic regime providing externally generated magnetic fields are absent. An example of potential practical interest in which field reversal occurs inside the beam while the bulk of it remains nearly force-free is discussed in some detail.
Irreversible interaction between cumulants in homogeneous, isotropic, two-dimensional turbulence theory
Authors: André Jean-Claude
Published: February 2004

The hierarchy describing homogeneous and isotropic two-dimensional turbulence is used to show that one of the effects of (n + 1)-th order cumulants is to introduce a turbulent relaxation frequency (or eddy-damping rate) in the equation for the rate of change of n-th order cumulants. As a result, it is possible to construct a Markovian eddy-damped (n + 1)-th order cumulant-discard approximation in which the eddy-damping rate simulates the irreversibility due to the infinite serie of cumulants with order greater than n. In the case of our Markovian eddy-damped quasi-normal approximation the governing equations for the evolution of the energy spectrum are compared to those of stochastic models like the generalized random phase approximation or the self-consistent field approximation.
Electrostatic cyclotron harmonic wave instabilities in beam-plasma systems
Authors: Mizuno Katsuhiro , Tanaka Shigetoshi
Published: February 2004

The cyclotron harmonic wave instabilities of a weak electron beam and a warm plasma system having a finite cross section in a finite magnetic field are investigated. Experimentally, it is shown, by using a test wave method, that the unstable cyclotron harmonic waves are observed in each cyclotron harmonic band and their dispersion curves have harmonic structure. Theoretical studies show that the observed instabilities are ascribed to the Cerenkov and cyclotron excitations (normal and anomalous Doppler effects), where the negative energy waves on the beam are coupled to the obliquely propagating cyclotron harmonic waves in the warm plasma in a magnetic field.
Toroidal drift of a collisionless plasma
Authors: Ejima S. , Marshall T.C. , Schlesinger S.P.
Published: February 2004

The toroidal drift of a collisionless plasma flowing along a curved magnetic field has been directly observed. The experiment was done using a low density plasma generated in a small single-ended Q machine. The magnetic lines were bent into an arc of a circle with curvature adjustable by additional magnetic windings, designed for smooth line curvature with the aid of a stereoscopic computer-graphics device; the magnetic geometry was also determined by a weak electron beam. The polarization field in the plasma was short-circuited by the presence of the hot ionizer which terminated one end of the plasma. The toroidal drift was observed experimentally by a movable battery of 45 probe wires mounted in an insulator which terminated the other end of the plasma. The plasma potential and plasma density were measured with this and displayed quantitatively using a fast analog-digital data printer. The experimental data correlated satisfactorily with a two-fluid theory in which the curvature drift was modeled by an effective gravitational force.
Toroidal equilibrium of current-carrying plasmas
Authors: Yoshikawa S.
Published: February 2004

A general method was developed to determine a toroidal equilibrium of plasmas, once a cylindrically symmetric linear solution is known. Arbitrary current distribution can be treated. The application to an equilibrium calculation to toroidal E layer is also given. This azimuthally symmetric toroidal E layer has an advantage of stable configuration with poloidal magnetic field comparable to the toroidal magnetic field offering the possibility of high β toroidal plasma containment.
Stabilization of the collisionless trapped-particle instability by shaping of the tokamak cross section
Authors: Glasser A. H. , Frieman E. A. , Yoshikawa S.
Published: February 2004

Distortion of the cross sections of a tokamak has been suggested as a means of improving Ohmic heating and raising β. The effects of such distortion on the collisionless, electrostatic trapped-particle mode have been investigated and it is found that under certain conditions a maximum-J configuration can be approached. Results are presented for finite elliptic and triangular distortions, indicating significant stabilization.
Interchange destabilization by incomplete line-tying
Authors: Prater Ronald
Published: February 2004

A theory is presented for a plasma unstable to the interchange mode which shows that longitudinal current flow to conducting end plates can be destabilizing if the sheath impedance at the end plates is large or if the growth rate is small. This destabilizing effect is experimentally verified in a multipole-mirror device. For large growth rates, a stability criterion on the cold background plasma density is derived and compared with several experiments in the literature.
Stabilization of ion acoustic waves by electron trapping
Authors: Albright Norman W.
Published: February 2004

The unstable ion acoustic waves resulting from a beam of electrons entering a plasma are considered. A test wave is introduced in the region of unstable waves through the same boundary where the beam enters the plasma. This test wave has an amplitude much larger than the noise. The growth rate of this wave including the effects of electron trapping and collisions is calculated, and it is found that such a test wave will stabilize by electron trapping.
Polarization of plasma wave resonances in an axial magnetic field
Authors: Willis J. W. , Nickel J. C.
Published: February 2004

The splitting of the Tonks-Dattner resonances in an axial magnetic field is considered. It is found that the higher-order resonances are split and decompose into left- and right-circularly polarized modes. Experiments at higher magnetic fields are described in which the Buchsbaum-Hasegawa resonances are also observed. These resonances appear to be right-circularly polarized.
Approach to the origin of turbulence on the basis of two-point kinetic theory
Authors: Tsugé Shunichi
Published: February 2004

Equations for the fluctuation correlation in an incompressible shear flow are derived on the basis of kinetic theory, utilizing the two-point distribution function which obeys the BBGKY hierarchy equation truncated with the hypothesis of “ternary” molecular chaos. The step from the molecular to the hydrodynamic description is accomplished by a moment expansion which is a two-point version of the thirteen-moment method, and which leads to a series of correlation equations, viz., the two-point counterparts of the continuity equation, the Navier-Stokes equation, etc. For almost parallel shearing flows the two-point equation is separable and reduces to two Orr-Sommerfeld equations with different physical implications. Solution of an eigenvalue problem for the Blasius boundary layer is obtained in a certain parallelism to the classical stability theory, and is used for predicting the transition Reynolds number of a “quiescent” Blasius flow in which thermodynamic fluctuations alone are the initiating mechanism. Also, the calculated spatial growth rate of fluctuation agrees with the Schubauer-Klebanoff experiment, which gives an account of unexplained experimental evidence that the fluctuation complex (turbulence bursts plus the Tollmien-Schlichting wave), as a whole, obeys a certain linear theory.
On the theory of electrostatic confinement of plasmas with ion injection
Authors: Hu K. M. , Klevans E. H.
Published: February 2004

A theoretical model of a spherical electrostatic confinement device with ion injection is presented. It is assumed that the potential inside the accelerating cathode (inner wall) forms a virtual anode, and that a deep well for ion trapping exists inside this virtual anode. Particle distribution functions, composed of beams and trapped particles moving radially, are constructed which are consistent with the potential profile. The conditions needed for large ion trapping in the center are explicitly developed and their relationship to the fusion experiments of Hirsch are discussed.
Computer simulation of radiofrequency confinement of a plasma
Authors: Hatch Albert J. , Shohet J. L.
Published: February 2004

Computer simulation methods have been used to investigate the confinement of lowdensity plasmas in nonuniform rf electromagnetic fields. The basic problem is to obtain a numerical solution of the equations of motion of a single charged particle in two-dimensional cross sections of both confining and nonconfining electromagnetic field configurations in a resonant cavity. The occurrence of confinement in a quadrupole electric mode of a cavity is demonstrated and the Φ quasipotential well theory of rf confinement is verified. The problem is then extended to large equal numbers of positively and negatively charged particles and the particle-in-cell method is used to include the effects of the self-consistent fields. The effects of finite initial temperature and of starting conditions are investigated. Confinement effects are observed in a quadrupole electric mode for initial temperatures corresponding to energies less than the depth of the Φ well.
Distinction between collective and ballistic contributions in low-frequency perturbation in a Q machine
Authors: Watanabe S. , Oishi M. , Tanaca H.
Published: February 2004

An experimental distinction is presented between the contributions due to the collective and ballistic modes of low-frequency disturbances excited by a grid in the equal temperature plasma of a Q machine. The collective mode (ion wave) velocity must slow down with increasing electron drift velocity, while the ballistic mode must have a constant velocity irrespective of the electron drift velocity. The ballistic mode was always overwhelmingly excited in the experiment. A small wave of rather low frequency of an ion wave nature was observed only when the electron drift velocity was close to the critical one for the ion wave instability. Experimentally, we may conclude that, in general, in Q machines the ion wave which is excited by a grid and accompanied by ion Landau damping is practically invisible, being buried in the ballistic mode in agreement with an analysis of the dielectric function and also with a computer simulation.
Generalized spherical vortex for nonhomogeneous fluids
Authors: Hains F. D.
Published: February 2004

Inviscid incompressible spherical vortex flows with continuous velocity and velocity gradients at the sphere boundary are presented as a function of the velocity at the center of the sphere. Results for the vorticity and velocity components are compared with the classical Hill's spherical vortex.
Onset of drag reduction in dilute polymer solutions
Authors: Berman N.S. , George W.K.
Published: February 2004

The onset of drag reduction is observed in a 0.635 cm (0.25 in.) turbulent pipe flow for dilute solutions of Polyox WSR N-80 in three different glycerine-water solutions. The time scale onset hypothesis is found to be much more consistent with the data than the length scale onset hypothesis.
Electromagnetic instability in high-β plasmas with generalized distribution functions
Authors: Buti B.
Published: February 2004

Electromagnetic instability of waves propagating transverse to the external magnetic field of an anisotropic high-β plasma governed by generalized non-Maxwellian distribution functions is discussed. The region of instability is much smaller compared with that for Maxwellian plasma.
Behavior of Bernstein waves propagating obliquely to the magnetic field in a beam-plasma system
Authors: Idehara T. , Takeda M. , Ishida Y.
Published: February 2004

An obliquely propagating Bernstein wave excited by a coaxial antenna is amplified by inverse Landau damping in a beam-plasma system. The perpendicular components of the phase velocity are directed inward and/or outward from the beam region, corresponding to the backward and forward waves, respectively.
Diagnostic measurements of currents and magnetic fields in axisymmetric plasmas
Authors: Hartman C. W. , Hooper E. B.
Published: February 2004

The azimuthal current and magnetic flux in an axisymmetric torus or mirror are related to the (anisotropic) plasma pressure. Measurements by a Rogowski loop and a flux loop can be used to determine the spatially averaged components of pressure along and across the magnetic field.
Uniqueness of mean turbulent flows
Authors: Warsi Z. U. A.
Published: February 2004

In the closure problem of the theory of turbulent mean flows, the unknown correlations have to be expressed in terms of the other field variables. Estimates for the behavior of the unknowns, both for the steady and nonsteady flows, have been obtained which insure uniqueness of solutions.
Entrainment in turbulent wake flows
Authors: Menkes J. , Sreedhar Rao , Hindman Carlton
Published: February 2004

The stability of an axisymmetric turbulent wake produced behind a stationary sphere in a fluid moving with uniform velocity is investigated. The dispersion relation indicates that the interface is unstable at all wave numbers, if the wake is treated as a viscous medium. From the dispersion relation the surface-strain energy density spectrum of a known initial disturbance is obtained. The dynamic similarity of the distributions of the phase velocity and the surface-strain energy density at high Reynolds number is demonstrated. From the energy equation one obtains a critical wavenumber beyond which the energy transport to the wake through the interface is cut off. A critical time is obtained based on the assumption that the momentum deficit in the wake is due to the viscous drag. The critical time and the critical wavenumber are used to explain the existence of an entrainment cycle.
Spatial waves in turbulent jets
Authors: Chan Y. Y.
Published: February 2004

Measurements of the spatial development of disturbance pressure waves in a low-speed axisymmetric turbulent free jet have been carried out. The results show that the wavenumbers of the pressure waves increase monotonically, while the phase velocities decrease as the Strouhal number of the jet increases. The pressure disturbance grows to a maximum at some distance downstream from the nozzle and then decays. The distributions of the amplitude of the pressure waves along the jet are similar if the data are plotted against a normalized distance St x/D. The most amplified mode is at a Strouhal number of 0.5 for the shear layer and 0.35 for the center line. The wave characteristics follow closely the linear stability theory of an inviscid diverged shear flow.
Asymptotic solution of the nonlinear Boltzmann equation for unsteady gas flows
Authors: Hu Pung Nien
Published: February 2004

The one-dimensional unsteady flow problem in the kinetic theory of gases is studied, based directly on the nonlinear Boltzmann equation. Using a singular perturbation technique with a single scaling of time and length, a unified asymptotic theory is developed. It is shown that for any given smooth initial condition, the gas motion can be decomposed into five modes. For the first-order quantities, these five modes of motion are independent of one another. The three diffusion modes are linear, governed by the diffusion equation for the unsteady heat and shear flows, while the two wave modes are nonlinear, governed by the Burgers equation for the evolution of shock and nonlinear waves in a dissipative medium. The coupling (nonlinear effects) among the five modes starts to appear in higher order. The solution of the distribution function up to the second order is obtained. The difference and relation between the present theory and the theories of Hilbert, of Chapman and Enskog, and of Grad are also discussed.
Calculation for the wake of a small cylinder under ionospheric satellite conditions
Authors: Woodroffe J. A. , Sonin Ain A.
Published: February 2004

A method is outlined for the calculation of the wakes of small cylinders in hypersonic, collision-free, cold-ion plasma flow. No applied magnetic field is considered. Results are presented for a cylinder with a radius of 0.005 Debye lengths in a flow with a Mach number (based on the ion-acoustic speed) of 8, and a comparison is made with available experimental data.
Shock loading on a submerged structure
Authors: Chen Michael Hsiang-teh , Collins Richard
Published: February 2004

The problem of propagation of a two-dimensional shock wave in water over a submerged rigid structure (semicylinder) due to a nearby underwater explosion has been solved numerically using a method of characteristics based upon a curvilinear co-ordinate system fixed in successive shock wave positions. Maximum surface pressures occur at the transition from regular to irregular reflection, and nonlinear theory appears essential there, even for shocks of Mach number close to unity. Results are given for a range of explosive strengths, distances from the structure, and structural dimensions.
Translational nonequilibrium in free jet expansions
Authors: Cattolica R. , Robben F. , Talbot L. , Willis D. R.
Published: February 2004

The velocity distribution function for helium in translational nonequilibrium in hypersonic free jet expansions has been investigated with an electron beam fluorescence technique. A unique computer controlled Fabry-Perot interferometer and data acquisition system has been used to observe the 5015.67 Å radiation from the 31 P-21 S transition in helium. From the spectral structure, the Doppler broadening and shift of the line due to the velocity distribution function can be determined. With this technique parallel and perpendicular gas kinetic temperatures, mean flow velocity, and relative density measurements were made along the centerline of the free jet, from near equilibrium conditions through the midpoint of transition (T‖/T⊥ = 2.0). A comparison with kinetic theory predictions of the temperatures and velocity distribution functions indicate that the adoption of the ellipsoidal model, although sufficient for fitting the measured distribution function, is inadequate for determining the parallel temperature. The experimental data have been compared with a Navier-Stokes theory, with moment solutions of the Boltzmann equation, and a rarefication parameter suggested from previous Monte Carlo calculations. Determination of an effective hardsphere diameter from the experimental data is also presented.
Strong shock structure
Authors: Lohn P. D. , Lundgren T. S.
Published: February 2004

The structure of an infinitely strong shock in a gas of rigid spheres is investigated. A bimodal form is proposed for the molecular velocity distribution function. Solutions are developed using moment methods. The error in satisfaction of the Boltzmann equation is developed and used both to evaluate moment solutions and to approximate a minimum error solution.
Electrohydrodynamic stability of dielectric liquids during transient regime of space-charge-limited injection
Authors: Atten P.
Published: February 2004

A critical examination is undertaken of experiments performed in order to verify electro-hydrodynamic stability criterion of an insulating liquid subjected to a unipolar space-charge-limited injection. It appears that the comparison between predicted and measured values is meaningless because the theory is valid for a stationary state of conduction while experiments have been carried out under transient conditions. The stability of space-charge-limited current during the transient regime is investigated using the quasistationary approach to evaluate the growth rate and the amplification factor of the velocity perturbation. It is shown that the experimental results do not agree with theory; the measured criteria are clearly lower than the expected ones. It is suggested that this discrepancy might be attributed to phenomena related to the injection mechanisms.
Brownian motion of charged particles in a magnetic field
Authors:   Karmeshu
Published: February 2004

The Brownian motion of charged particles in the presence of a magnetic field is studied on the basis of the generalized Langevin equation including a finite relaxation time of the random force. It is found that the introduction of a finite relaxation time for the random force correlation inhibits diffusion although the form of the diffusion coefficient is unaltered and the elements of the velocity autocorrelation matrix depict damped oscillatory behavior.
Hydrostatic profile of ferrofluid around a vertical current-carrying wire
Authors: Krueger David A. , Jones Thomas B.
Published: February 2004

The classical Langevin theory for noninteracting magnetic particles together with an interfacial force balance of hydrostatic pressures and Maxwell stresses is found to describe the experimental results of Neuringer and Rosensweig for the hydrostatic profile of ferrofluid around a vertical current-carrying wire. If r is the distance from the center of the wire, the fluid height varies as r−2 for small magnetic fields, where the ferrofluid is magnetically linear, and as r−1 for large magnetic fields, where the ferrofluid is in saturation. The experimentally obtained r−4/3 dependence is an intermediate behavior between the linear and saturation magnetization regimes of the ferrofluid. No fundamental significance is attributable to the 43 power law. To obtain the r−4/3 dependence over as large a range of r values as found experimentally, it is necessary to use a realistic distribution of particle sizes.
Nonlinear properties of high amplitude ionization waves
Authors: Grabec I.
Published: February 2004

Nonlinear equations describing the state of a weakly ionized plasma in an unstable positive column are derived from a set of hydrodynamic equations, the Poisson equation, and the ionization frequency equation for the direct ionization process. In order to find the solution of the initial value problem, an iterative method is applied. Numerically solved examples show that unstable ionization waves develop into high amplitude relaxation waves—striations. From the calculated distributions of the governing physical quantities particle-like properties of high amplitude striations are established. A nonlinear interaction between striations leading to their collision is noted. The explosive nature of ionization instability is found to be most pronounced at low ionization losses of electron energy. A quantitative, as well as qualitative agreement between calculated and experimental data is obtained.
Nonlinear theory of electron neutralization waves in ion beams with dissipation
Authors: Wilhelm H. E.
Published: February 2004

An analytical theory of nonlinear neutralization waves generated by injection of electrons from a grid in the direction of a homogeneous ion beam of uniform velocity and infinite extension is presented. The electrons are assumed to interact with the ions through the self-consistent space charge field and by strong collective interactions, while diffusion in the pressure gradient is disregarded (zero-temperature approximation). The associated nonlinear boundary-value problem is solved in closed form by means of a von Mises transformation. It is shown that the electron gas moves into the ion space in the form of a discontinuous neutralization wave, which exhibits a periodic field structure (incomplete neutralization). This periodic wave structure is damped out by intercomponent momentum transfer, i.e., after a few relaxation lengths a quasineutral plasma results. The relaxation scale in space agrees with neutralization experiments of rarefied ion beams if the collective momentum transfer between the electron and ion streams is assumed to be of the Buneman type.
Parametric excitation by magnetosonic waves in a multispecies plasma
Authors: Sperling J. L. , Perkins F. W.
Published: February 2004

A magnetosonic pump wave propagating in a plasma with two ion species decays into two electrostatic ion-cyclotron modes at a threshold significantly less than those needed to excite parametric or modified two-stream instabilities in a single-species plasma when Te/Ti > 1. The pump wave frequency must somewhat exceed the sum of the ion gyrofrequencies.
Magnetohydrodynamic equilibria for a bumpy axisymmetric plasma column
Authors: Golovato S. N. , Shohet J. L. , Tataronis J. A.
Published: February 2004

Solutions to the nonlinear ideal magnetohydrodynamic equilibrium equations are numerically computed for the case of an infinitely long axisymmetric plasma column. Boundary conditions are imposed which force the axial variation of the configuration to be sinusoidal thus giving rise to “bumpy” flux surfaces. Current is allowed in both the axial direction and in the direction of the ignorable coordinate. It is found that the depth of penetration into the plasma of the bumpiness increases when the axial current or the plasma β is increased. The effect of the presence of a perfectly conducting wall of constant radius together with a limiter of variable radius on the equilibria is also investigated. Applications to present and proposed tokamak experiments are made.
Sufficient stability criteria for plasma equilibria with tensor pressure
Authors: Spies G. O. , Nelson D. B.
Published: February 2004

Sufficient stability criteria are derived which are valid in various situations for which an energy principle holds, i.e., tensor or scalar pressure, collisionless or collisional dynamics, toroidal or open-ended geometry, conducting or insulating walls, closed or ergodic magnetic field lines. These criteria reduce to well known ones in toroidal equilibria with scalar pressure. They are close to necessary criteria in low beta equilibria allowing for interchanges. Various well known favorable properties (viz., good curvature, magnetic well, negative υ″, line-tying) are recovered by considering special classes of equilibria. Since, in general, none of these properties appears to be crucial, the present criteria are capable of yielding a variety of hitherto unknown stably confined equilibria.
Properties of magnetically confined plasma equilibria
Authors: Spies G. O. , Nelson D. B.
Published: February 2004

Certain well known properties of toroidal magnetohydrostatic equilibria with scalar pressure are shown to carry over to a class of equilibria with tensor pressure including openended equilibria with free ends. This class is characterized by the existence of a particular family of surfaces which, because of their analogy to the pressure surfaces of equilibria with scalar pressure, are called “generalized pressure surfaces.”
Effect of the temperature gradient on the ordinary mode electromagnetic instability in a high-beta plasma
Authors: Nambu Mitsuhiro
Published: February 2004

The effect of nonuniformities of temperature, magnetic field, and number density on the ordinary mode with temperature anisotropy is investigated. It is shown that in a high-β plasma the new and much stronger instability due to electron wave resonance with temperature gradient and temperature anisotropy occurs. The ordinary mode instability in an inhomogeneous plasma is possible under the condition T⊥,e (electron perpendicular temperature) > T‖,e (electron parallel temperature), in contrast to the previous results T‖,e > T⊥,e. The pitch angle diffusion of particles is also investigated.
Cusp confinement of high-beta plasmas produced by a laser pulse from a freely-falling deuterium ice pellet
Authors: Kitsunezaki Akio , Tanimoto Mitsumori , Sekiguchi Tadashi
Published: February 2004

Preliminary results of the experimental determination of the particle loss aperture sizes of the spindle cusp magnetic bottle for laser-produced high-beta deuterium plasmas are presented. The fully ionized dense plasma (with maximum density ∼1016 cm−3 and ion energy ∼200 V) is produced at the null-field center of the magnetic bottle, from a freely falling isolated deuterium ice pellet by a focused giant laser pulse. In preparation, the free expansion of laser-produced plasma has been studied experimentally, and the results indicate that the plasmas produced can maintain the fully ionized condition with prescribed plasma parameters until it expands to a certain prescribed volume if the combination of the physical parameters is properly chosen by considering the electron-ion recombination as one of the important factors. The experimental results of cusp confinement for the plasma thus produced suggest that the loss aperture size of the ring cusp is much smaller than the local ion gyroradius, in sharp contrast with other results thus far reported. Although the determination of the point cusp aperture radius is less complete, the rough estimates show that it is also smaller than the ion gyro-radius.
Capped probe for ion temperature diagnostic in a magnetized plasma
Authors: Sato Masumi
Published: February 2004

A simple ion temperature measurement method in a magnetic field using an electrostatic capped probe is presented and tested. The probe with the axis oriented parallel with the magnetic field is a small cylinder whose flat tip is insulated with a cap to inhibit electron inflow parallel to the field. The ion collector current, essentially less affected, becomes comparable to or larger than the saturation electron current, and the usual retarding potential technique can be used to measure ion temperature. Measurements were made in a diffused helium plasma with the density 1010 ∼ 1013 cm−3 at the gas pressure ∼mTorr and the field 0.8 ∼ 3.5 kG. Ion temperatures obtained are 0.8 ∼ 2 eV, which nearly equal electron temperatures, and are compared with data from the ion probe and Doppler profile measurements. Availabilities of the method and limiting conditions for the temperature determination are also discussed.
Numerical study of effect of pressure gradient on stability of an incompressible boundary layer
Authors: Saxena S. K. , Bose T. K.
Published: February 2004

The effect of pressure gradient on the stability of two dimensional, laminar, incompressible boundary layer flow has been investigated numerically using filtered and orthonormalized integration techniques and the results have been compared with Schlichting's calculations.
Nonlinear breakup of a liquid jet
Authors: Lafrance Pierre
Published: February 2004

A third-order perturbation analysis was carried out to study the capillary instability of an inviscid, incompressible liquid jet of circular cross section. The results were used in a computer simulation of breakup, and it was found that the theory is in agreement with the experimental data of Rutland and Jameson.
Limiting current for hollow rotating beams
Authors: Poukey J. W. , Freeman J. R.
Published: February 2004

A theoretical limit is derived for the z-directed current which can be transmitted through a conducting boundary by a hollow beam of electrons. The result generalizes previous work, and is supported by computer simulations.
Field penetration into a plasma with nonlinear conductivity
Authors: Lonngren K. E. , Ames W. F. , Hirose A. , Thomas J.
Published: February 2004

A nonlinear diffusion equation describing electric field penetration into a plasma with a nonlinear conductivity has been solved. The penetration time becomes shorter as the non-linearity increases.
Lower hybrid wave conversion for a parabolic density profile
Authors: Fidone I. , Paris R. B.
Published: February 2004

Linear wave conversion at the lower-hybrid layer for a parabolic density profile is investigated. It is found that total conversion of the incident flux in the direction of the density gradient takes place.
Numerical studies of mirror confinement with an end stopper
Authors: McHarg B. B. , Oakes M. E.
Published: February 2004

Numerical studies were made of solutions of the Fokker-Planck equation for a decaying homogeneous plasma in a mirror machine with an end stopper potential field.
Steady supercritical Taylor vortices after sudden starts
Authors: Burkhalter J. E. , Koschmieder E. L.
Published: February 2004

The wavelength of steady Taylor vortices established through a sudden start of the inner cylinder has been studied experimentally. The sudden start procedure gives the fluid a choice in the selection of the wavelength. It was found that the preferred wavelength of singly periodic vortices in the steady state after a sudden start is smaller than the critical wavelength, with a minimum at around T / Tc = 15. When the Taylor number to which the sudden start was made was increased to around 60 Tc, then the preferred wavelength approached the critical wavelength. A wavelength once established through a sudden start did not change its value if afterwards the Taylor number was maintained for a very long time or if the Taylor number was varied over larger intervals, provided the flow was singly periodic. However, this rule does not hold when the critical Taylor number is approached from above with a flow created through a sudden start to a higher Taylor number. In this case the wavelength increases to approach the critical wavelength. Sudden starts to very high Taylor numbers created doubly periodic or turbulent flow with wavelengths larger than the critical wavelength.
Fluid mechanics of colliding plates
Authors: Yih Chia-Shun
Published: February 2004

The flow of air between a plate at rest and another one falling onto it either vertically or by folding is studied, and the infrequency of breakage of glass plates colliding in this way is explained. The falling plate may be two-dimensional, circular, or elliptic, and the results for an elliptic plate give bounds for the motion of a falling rectangular plate.
Rear stagnation-point flow in a rotating fluid
Authors: Davis R. W. , Ludford G. S. S.
Published: February 2004

The exact solution found previously is applied to rear stagnation-point flow imposed on solid-body rotation over a disk. Under normal circumstances, any radial flow reversal which occurs in the boundary layer is suppressed again by the spin up of the fluid outside.
Analysis of laser-induced convection in unconfined fluids and in vertical cylinders
Authors: Vest C. M.
Published: February 2004

Laminar natural convection induced in fluids by absorption of energy from a vertical laser beam is analyzed for two different configurations. In the first configuration, the vertical beam propagates in an unconfined fluid, and is modeled as a line source of thermal energy. Ordinary differential equations are obtained by a similarity analysis of the axisymmetric boundary layer equations, and approximate solutions of them are obtained. In the second configuration, the beam propagates in a fluid confined in a tall, isothermal vertical cylinder, and is assumed to have a Gaussian radial distribution of intensity. An exact solution of the Navier-Stokes and thermal energy equations is obtained for the case of parallel flow. Representative numerical results are presented, and estimates are made of the parametric ranges of validity of the analyses.
Energy stability of modulated flows
Authors: Carmi S.
Published: February 2004

The stability of time-dependent flows is analyzed by the energy theory. Lower bounds as well as optimal results are obtained for modulated Bénard and Taylor problems. It is found that the region of certain stability is reduced because of the basic flow modulation.
Temperature fluctuations in the plane turbulent wake
Authors: LaRue John C. , Libby Paul A.
Published: February 2004

Results are presented of temperature measurements made in the slightly heated, plane turbulent wake at stations 400 and 500 diam downstream from a heated cylinder at a Reynolds number of 2800. The results include transverse distributions of the first four moments of the temperature obtained using both conventional and conditional sampling and averaging techniques, the downstream distribution of the root mean square temperature fluctuations on the wake centerline and the probability density function of the temperature. Additionally, there are obtained, as a function of distance from the interface, temperature moments which indicate that there is a definite thermal structure associated with the interface.
Functional formulation of nonisothermal turbulent reactive flows
Authors: Dopazo César , O'Brien Edward E.
Published: February 2004

The two familiar functional formalisms in turbulence are applied to the simultaneous turbulent mixing and chemical reaction of scalar fields. One-step, second-order, irreversible, exothermic chemical reactions with an Arrhenius-type rate constant are considered. The problem is formally posed in terms of initial and boundary conditions. For the special case of equal mass-diffusivities and a Lewis number of one the functional equations are decoupled into a turbulent binary mixing study and a reactive problem. The Lewis-Kraichnan formalism is used in order to obtain exact functional solutions of the binary mixing case in final period turbulence. Driving forces are included in the thermal energy equation. These solutions are used to obtain detailed information about the binary mixing problem and the behavior of very rapidly reacting species in the final period.