bluuebunny/crossref_metadata_2025 huggingface dataset:
Application of the Continuum Theory to Nematic Liquid Crystals
Authors: Tseng H. C. , Silver Dayton L. , Finlayson Bruce A.
Published: February 2004

The apparent viscosity of nematic p-azoxyanisole in Poiseuille flow at 122°C is calculated by numerically solving the differential equation derived by Atkin which is based on the continuum theory of Ericksen and Leslie for nematic liquid crystals. The theory requires knowledge of seven independent material properties, which are determined from experimental measurements of Miesowicz, Marinin and Zwetkoff, Zwetkoff, and the Orsay Liquid Crystal Group. Parodi's relation is used to show that in cases where there are conflicting data, some data are inconsistent with Onsager's reciprocal relation. The calculations are compared with the Poiseuille flow experiments of Fisher and Fredrickson.
Theory of Sound Propagation in Mixtures of Monatomic Gases
Authors: Foch James D. , Uhlenbeck George E. , Losa Manuel Fuentes
Published: February 2004

Plane wave solutions are sought for the coupled, linearized Boltzmann equations governing sound propagation in a binary mixture. The solvability criteria for the ensuing matrix integral equation determine the dispersion law for sound propagation. In zeroth-order the Laplace sound velocity is obtained, and in first order the Kohler absorption is recovered. In second order an initial sound dispersion is found which could only be calculated from hydrodynamics if the analog of the Burnett equations for mixtures were known. As a preliminary guide to experiments, the absorption and dispersion in helium-argon mixtures are calculated through super-super-Burnett order on the assumption that each of the three interatomic forces is an inverse fifth-power repulsion
Shock-Wave Structure using Nonlinear Model Boltzmann Equations
Authors: Segal Ben M. , Ferziger Joel H.
Published: February 2004

The structure of strong plane shock waves in a perfect monatomic gas was studied using four nonlinear models of the Boltzmann equation. The models involved the use of a simplified collision operator with velocity-independent collision frequency, in place of the complicated Boltzmann collision operator. The models employed were the BGK and ellipsoidal models developed by earlier authors, and the polynomial and trimodal gain function models developed during the work. An exact set of moment equations was derived for the density, velocity, temperature, viscous stress, and heat flux within the shock. This set was reduced to a pair of coupled nonlinear integral equations and solved using specially adapted numerical techniques. A new and simple Gauss-Seidel iteration was developed during the work and found to be as efficient as the best earlier iteration methods. Extensive comparisons were made of the model results with Monte Carlo solutions, and significant aspects of the comparisons are discussed.
Shock-Induced Dynamics of a Low-Density Heated-Fluid Element
Authors: Hamernik Roger P. , Dosanjh Darshan S.
Published: February 2004

The dynamic behavior of a two-dimensional, heated, turbulent fluid element which is instantaneously set into motion relative to its surroundings by the passage of a reflected shock wave has been studied in a shock tube. It is demonstrated that the dynamics of this fluid element are similar to those encountered in the study of gravitational thermals, and that the shock tube may be used to extend the range of experimental parameters under which “thermal-like” phenomena can be investigated. An exploding wire was used to generate the clearly defined heated element. Data obtained from high-speed (22 000 pictures/sec) interferograms indicate that the effective radius (re) of the heated element varies linearly with its horizontal displacement (x), i.e., re = αx, where α, the entrainment coefficient, is a constant. The coefficient α is shown to vary approximately linearly in the range 0.15 ≲ α ≲ 0.50 with increasing shock strength. The observed temporal growth of the heated element was compared with that predicted analytically from a semiempirical application of the mass and momentum conservation relations.
Analytical Solutions for Straight Oblique Shock Waves in Radiating Gases
Authors: Finkleman David
Published: February 2004

Analytical expressions are obtained for flow fields about two-dimensional walls which support straight shock waves. Results are interpreted in terms of shock displacement upon bodies with straight surfaces. Linear spectral bands and grey body emission are considered.
Ion Temperature Diagnostic Using a High Power Alternating Current Probe
Authors: Rubinstein J. , Laframboise J. G.
Published: February 2004

A method is presented for using a probe to measure ion temperature in a plasma. The method involves applying a strong rf alternating potential to the probe, of sufficient amplitude to drive electrons away from it via a nonlinear effect which acts preferentially on them. The ion current, essentially unaffected, can then be seen separately and the usual retarding potential technique can be used to measure ion temperature. The method requires electron motion to be sufficiently collisionless. Self-consistent sheath profiles are calculated in order to show that there exists a useful range of driving frequencies and amplitudes over which the dc potential is ion repelling and monotonic and hence the ion current is exponential in probe dc potential. Since the ion and electron fluxes to the probe can simultaneously be made very small, the technique should permit measurements in some environments which would otherwise overheat and destroy probes. An ion heating mechanism based on the electron repulsion effect is also proposed.
Nonequilibrium Energy Constants Associated with Large-Amplitude Electron Whistlers
Authors: Davidson Ronald C. , Hammer David A.
Published: February 2004

Two independent energy constants are derived for arbitrary-amplitude electron whistler distrubances propagating parallel to a uniform magnetic field B0. These constants exhibit precisely how energy is partitioned between the fields and the components of plasma kinetic energy perpendicular and parallel to B0.
Scattering Function of a Soft Collision Plasma
Authors: Cheng Chiang S. , McLennan James A.
Published: February 2004

The effects of collisions on the scattering function of a fully ionized gas, and on the related functions describing conductivity and energy loss of a test particle are discussed using a simplified Fokker-Planck collision model which preserves certain important features of the long-range small angle soft collisions. The dispersion relations are discussed in detail, and explicit calculations are carried out for the scattering function and the energy-loss function in the long-wavelength approximation when the wavelength is longer than the mean free path and the Debye length. The damped plasma oscillation poles dominate the energy-loss function while for the scattering function the ambipolar diffusion dominates the low-frequency region.
Attenuation Due to Scatter in Random Media
Authors: Guthart H. , Graf K. A.
Published: February 2004

A summary of calculations is presented to show the merit of a phenomenological model for calculating scatter from a turbulent plasma. The model was applied to two experiments at 9 and 31 GHz as well as an experiment at 16 GHz. These experiments indicated in an empirical way the magnitude of the attenuation coefficient due to scatter. These coefficients were significantly different for the experiments considered. Consequently a new method for calculating the attenuation due to scatter was outlined and shown to be effective. While this calculation is not rigorous it does establish a useful relation between plasma parameters and the attenuation coefficient due to scatter.
Spectral Dependence of Diffusion in a Magnetized Plasma
Authors: Hsuan Hulbert C. S.
Published: February 2004

The problem of random walk of charged particles across a magnetic field is studied using a generalized Langevin formulation. The diffusion coefficient is found to be independent of B, inversely proportional to B, or inversely proportional to B2, depending upon the electric field fluctuation spectra.
Electron Cyclotron Drift Instability and Turbulence
Authors: Forslund D. , Morse R. , Nielson C. , Fu J.
Published: February 2004

The linear theory of the electron-cyclotron drift instability, including off angle and collisional effects, is discussed in the context of applications to controlled fusion and collisionless shocks. With the help of numerical simulations it is then shown in detail that a strong nonlinear development of the instability causes anomalous resistance to current flow perpendicular to magnetic field lines, which is large enough to be consistent with the anomalous diffusion seen in these applications. In particular a repeated trapping and untrapping of electrons in combined electrostatic-magnetic wells is an essential part of the nonlinear resistive heating process. A relatively steady resistance and turbulence level is seen, in contrast with the short burst of turbulence produced by many magnetic field free beam plasma instabilities.
A Stability Mechanism for the Ion-Acoustic Waves
Authors: Krishan S. , Selim A. A.
Published: February 2004

The nonlinear frequency shift in the growing ion-acoustic wave and the linear and nonlinear effects associated with resonance ωq − v·q = 0, are investigated and their stabilizing influence discussed.
Beam-Generated Collisionless Ion-Acoustic Shocks
Authors: Sakanaka P. H.
Published: February 2004

A numerical study of a one-dimensional collisionless ion-acoustic shock generated by an injection of a plasma beam is presented. The electrons are assumed to be hot and isothermal, and obey the Boltzmann distribution; the ions are described by the Vlasov equation which is solved by a direct finite difference scheme. There is a threshold beam velocity ubm, above which shock is not generated. ubm is a function of the beam-background density ratio and the electron-ion temperature ratio, and is larger than the limit of the ion-ion two-stream instability uts. For beam velocities ranging from zero to uts a shock is observed followed by a region of fully developed two-stream instability. For beam velocities between uts and ubm, a shock and a phase-space vortex are formed and in between them a quiescent region grows. A stable two-stream remains behind the vortex.
Neoclassical Diffusion in Axisymmetric Torus in the “Intermediate Region”
Authors: Bhadra Dilip K. , Liu Chuan S. , Ohkawa Tihiro
Published: February 2004

Neoclassical diffusion in the “intermediate” region of a toroidal plasma is studied using an asymptotic solution to the Fokker-Planck equation with a small parameter νc/νt (νc, νt being the collision and transit frequencies, respectively). The diffusion coefficient is given by D = D0[1 + a(νc/νt)1/2 − b(νc/νt) ⃛] with D0 = (π/2)1/2(2πρe/lR) (ρe2Ωe); a is a small number which vanishes when the radial electric field is neglected; b is a positive quantity of the order of unity. Thus, the diffusion coefficient in the “intermediate” region tends to decrease as collision frequency increases.
Experimental and Two-Dimensional Computational Study of End Losses from a Theta Pinch
Authors: Bodin H. A. B. , McCartan J. , Pasco I. K. , Schneider W. H.
Published: February 2004

A theoretical and experimental study of axial plasma flow and end losses in a θ pinch with a collisional 100-eV plasma with β on axis of 0.7 is described. The predictions of a magnetohydrodynamic code which is two-dimensional in radius and axial length were compared with data from a θ pinch with a coil 8 m long, which gives stable times of some tens of microseconds and good axial resolution. The radial density distribution was measured at four axial positions and its spatial and temporal evolution during the loss process agreed with the computed results. Rarefaction waves were found numerically, and the propagation velocity on a given flux tube agreed with the analytic expression. The computed and measured line density also agreed, and fell sequentially at different axial positions. The results showed that particle flow on a given flux tube depends on the local values of beta and sound speed. Higher-β plasma on the axis is lost more slowly than the plasma as a whole.
Investigation of Magnetic Field Errors in the Supported Spherator
Authors: Okabayashi M. , Freeman R.
Published: February 2004

The effect of slight asymmetry of the magnetic field in an azimuthally symmetric toroidal machine is investigated in the spherator by applying an additional uniform horizontal magnetic field. The azimuthal distribution of plasma loss across the magnetic field is varied by changing the direction and the strength of the additional horizontal magnetic field. Numerical calculations are carried out and possible initial field error is discussed by comparing the experimental results and an analytical calculation. By canceling the initial field error with the additional magnetic field, the particle loss becomes uniform in the azimuthal direction, but no significant change is observed in the confinement time in the argon afterglow plasma.
Further Comparison of Theory and Experiment for Decay of Homogeneous Turbulence
Authors: Deissler R. G.
Published: February 2004

An analysis for the decay of homogeneous turbulence from a given initial state is compared with the water-channel data of Ling and Huang. Good agreement is indicated.
Density Distribution in a High-Pressure Gas Jet Measured by Laser-Induced Gas Breakdown
Authors: Neusser H. J. , Puell H.
Published: February 2004

A novel technique for measuring the density distribution in a freely expanding, high pressure, gas jet is reported. Using the pressure dependence of threshold power for laser-induced gas breakdown the density gradients within the gas jet were determined with high spatial resolution.
Virtual Plasma Wave Echoes
Authors: Brackbill J. U.
Published: February 2004

“Virtual” temporal echoes which are predicted by the theory of Gould and O'Neil are seen in the results of a numerical simulation of plasma wave echoes by the distribution pushing method and are shown to be observable if the pulse interval and the lifetime of the primary response are comparable.
Qualitative Model for Turbulent Intermittency
Authors: Spiegel E. A.
Published: February 2004

It is proposed that turbulence can be regarded as a fluid of excitations moving through the actual (or laminar) fluid. Governing equations for this two-fluid system are written down and they are analogous to the Landau equations for superfluidity. These equations admit waves of turbulent intensity which, it is suggested, form the basis of an interpretation of turbulent intermittency. Other qualitative features are suggested by the model and one in particular, the turbomechanical effect, appears to be related to turbulent entrainment and is proposed as an experimental test of the model.
Convection in a Box of Porous Material Saturated with Fluid
Authors: Beck J. L.
Published: February 2004

The true critical Rayleigh number for the onset of a convective flow of a fluid in a rectangular box of porous material heated from below is found for various box geometries. The preferred cellular mode of the motion at Rayleigh numbers just above the critical is determined. In contrast with the established results for the similar problem in a continuous fluid, the roll (a cell with only two nonzero velocity components) is not the only cellular mode and the roll axis direction is such that there is the greatest degree of “squareness” in the cross section of each roll. The invalidity of a frequently used form of Darcy's law and the present form of the energy method for the stability of flows in which fluid crosses the boundaries is discussed.
Propagation and Growth of Shock Waves in Inhomogeneous Fluids
Authors: Nunziato J. W. , Walsh E. K.
Published: February 2004

The propagation of a shock discontinuity into a fluid region at rest with a spatially dependent density and entropy distribution is considered. Representing the shock wave as a propagating singular surface, a differential equation is derived for the strength of the shock in terms of the density gradient behind the shock and a “critical density gradient.” The growth and decay behavior of the wave is discussed for two different conditions ahead of the wave and it is found that, under certain circumstances, a characteristic shock strength may exist which markedly affects the character of the critical density gradient (and thus the growth and decay behavior of the wave).
Boundary Layer Closure in the Conical Shock Tube
Authors: Connor Joseph G.
Published: February 2004

The characteristics of the shock front produced in the Naval Ordnance Laboratory explosive driven conical shock tube differ both from those of its free-air analog and those of the shock in a conventional shock tube. The presence of walls makes it different from a free-air spherical explosion shock; the fact that it is in a diverging rough-walled cone makes it different from the conventional tube shock. Measurements of dynamic pressure and opacity of the gases behind the front and light output from the explosion gases were made near the wall of a conical tube at various distances from the site of an explosion. Results are interpreted in terms of turbulent boundary layer closure.
Modeling Theory of the Linearized Collision Operator for a Gas Mixture
Authors: Boley C. D. , Yip Sidney
Published: February 2004

Kinetic models are developed for the linearized Boltzmann collision operator which describes the collisions between different kinds of molecules. From the known eigentheory of this operator and the method of Gross and Jackson, a sequence of increasingly more accurate model operators is generated. All of the models satisfy the conservation laws, and all except the single-relaxation time model lead to the proper transport coefficients. Explicit expressions are given for some models, including the simplest one compatible with hydrodynamics. In the context of the present development, a unified discussion of the linearized versions of several existing models is given.
Evaluation of Rotational Temperature at High Vibrational Temperature in Electron Beam Fluorescence Technique
Authors: Ho Wing-Chuen , Schweiger Gustav
Published: February 2004

The influence of vibrational temperature on the rotational distribution function in nitrogen has been investigated. The rotational temperature TR is calculated for various vibrational temperatures Tv and compared with the calculations, where the influence of Tv is neglected.
Numerical Calculation of the Lunar Wake in a Magnetohydrodynamic Model
Authors: Beers Brian Lee
Published: February 2004

Following previous interpretation, a model is developed which has the solar wind flowing directly into the lunar surface and the magnetic field passing unimpeded through the moon. The collapse of the plasma void behind the moon is calculated numerically using the equations of magnetohydrodynamics. The model is three-dimensional, allowing complete calculations to be made without special restrictions on the magnetic field direction. A cursory quantitative comparison with data shows agreement to be satisfactory. The calculations indicate that the rate of collapse of the void does not depend strongly on the solar wind-magnetic field angle. The penumbral decrease depends very strongly on both the solar wind-magnetic field angle and the angle of passage through the wake.
Hydromagnetic Flow between Two Rotating Disks with Noncoincident Parallel Axes of Rotation
Authors: Mohanty Hemanta Kumar
Published: February 2004

Magnetohydrodynamic flow between two disks, rotating with the same angular velocity Ω about two different axes, a distance a apart, has been studied under the action of a uniform axial magnetic field. An exact solution of the equations of motion is obtained in a simple closed form. It is found that the torque, experienced by the disks, increases due to the magnetic field. For large values of the governing parameters, thin boundary layers are formed at the disks.
Schrödinger-Like Equations for the Nonadiabatic Escape of Charged Particles
Authors: Varma R. K. , Horton C. W.
Published: February 2004

The Schrödinger-like equations for the nonadiabatic escape of charged particles from magnetic mirror traps are derived starting from the integral equation for the evolution of the quantum mechanical wavefunction for the problem. A connection is thus established between the wavefunction of quantum mechanics and the wavefunction describing the nonadiabatic behavior. At the same time, the derivation of these equations given here justifies the ansatz used in an earlier derivation.
Structure of Ion Acoustic Solitons and Shock Waves in a Two-Component Plasma
Authors: White Roscoe B. , Fried Burton D. , Coroniti Ferdinand V.
Published: February 2004

Time-independent solitary waves and shocks are investigated in a two-component plasma using a fluid model and kinetic theory. It is found that very small concentrations of a light ion can drastically alter the structure, changing the potential maximum φm by an order of magnitude. For a fixed Mach number, a critical density ratio of light to heavy ions is found at which φm changes discontinuously from a value large enough to reflect the light ions to one which allows them to traverse the shock front and enter the downstream flow. The downstream oscillatory structure normally seen in a shock is completely quenched by dissipation due to light ion reflection at concentrations of 3-8% He in an Ar plasma for typical Te/Ti and Mach number values.
Probabilistic Model of Plasma Turbulence
Authors: Benford Gregory , Thomson J. J.
Published: February 2004

To obtain convergent series in plasma turbulence theory, it is necessary to include the effects of the turbulent fields in the particle propagator. The assumptions and different approaches of previous workers, notably Dupree, Rudakov and Tsytovich, and Weinstock, are clarified. Their results may be obtained by a simple assumption: that particles in phase space diffuse in a Markovian way under the action of the stochastic turbulent fields. From statistical arguments similar to those of Weinstock, a quite general expression for the diffusion coefficient D(V) emerges. This result holds without assuming weak turbulence if the wave spectrum is sufficiently broad. From the Markovian view above there follows immediately, without involved calculation, the familar expression for D(V) found by Dupree. Using probabilistic arguments, the particle propagator for a broad-band spectrum is calculated, allowing statistical spreading of trajectories in both position and velocity. This is identical to the usual method of obtaining a Green's function from a differential equation, but simpler. This new approach is valid whenever the turbulence is sufficiently broad-banded.
Conservation of Quasiparticles in Weakly Turbulent Plasmas
Authors: Bloomberg H. W.
Published: February 2004

An expansion making use of the eikonal is shown to yield a solution to the equations of a general weak turbulent plasma which is weakly dependent on space and time. The method is used to derive a quasiparticle conservation equation for quasistatic perturbations of Vlasov plasmas with general equilibrium field configurations.
Nonlinear Theory of Density Fluctuations in Turbulent Plasmas
Authors: Sleeper Arthur M. , Weinstock Jerome
Published: February 2004

The level of rms density fluctuations in a turbulent plasma, saturated by modified particle orbits, are theoretically found to obey a remarkably general, but simple, formula. The results are obtained independently of the form of the dispersion relation and are therefore applicable to turbulence arising from a broad class of instabilities. The restrictions on the ratios between gyro, collision, and mode frequencies are explicitly given. Both the collisional and collisionless cases are discussed, and shown to be consistent with a variety of experiments.
Nonlinear Interaction of a Small Cold Beam and a Plasma. Part II
Authors: O'Neil T. M. , Winfrey J. H.
Published: February 2004

A single-wave model was previously used to construct a properly scaled universal solution for the initial nonlinear interaction between a small cold beam and a plasma. Two experimentally motivated extensions of the single-wave model are now related back to this universal solution. The first extension shows that although the universal solution was originally obtained for boundary conditions where the wave grows temporally, it is, with proper scaling, equally valid for the more realistic boundary conditions in which the wave grows spatially from the point where the beam enters the plasma. The second extension concerns the statistical properties of the single-wave model. The universal solution is generalized so that it depends analytically on the initial phase and amplitude of the single wave, and the ensemble average of this generalized solution is then taken over all possible values of the initial phase and amplitude. This is a straightforward average of the solution over the initial conditions, and it does not rely on the random phase approximation usually invoked in the theory of weak turbulence. The ensemble average corresponds to the typical experimental practice of time averaging the received signal, provided the ergodic theorem applies.
Magnetohydrodynamic Equilibria in Sharply Curved Axisymmetric Devices
Authors: Callen J. D. , Dory R. A.
Published: February 2004

Ideal magnetohydrodynamic equilibria in current-carrying diffuse toroidal pinches of circular cross section (tokamaks) are studied numerically to determine possible limitations on β = 8πp/B2. Equilibrium considerations alone give no limitations even for β∼1 or βp≃βq2A2∼A2, but the stability requirement q>1 for magnetohydrodynamic kink modes does limit β. The best case found has β∼0.1 with q>1, A = 3, and βp∼2.
Magnetohydrodynamic Channel Flow with an Arbitrary Inlet Velocity Profile
Authors: Chen T. S. , Chen G. L.
Published: February 2004

The laminar flow development in a magnetohydrodynamic channel with an arbitrary velocity distribution at the inlet is analyzed by the linearization method. The present analysis is simple and gives accurate results for the velocity distribution and pressure drop.
Weak Inhomogeneity Formalism as Applied to the Bernstein Modes
Authors: Tang Ting-wei , Sivasubramanian A.
Published: February 2004

Bernstein modes propagating in the direction of the number density gradient are studied. The resulting field equation is compared with that found from an exact integral equation obtained by Fourier-transform techniques. The weak inhomogeneity formalism is shown to be accurate only to the order λ/L.
Asymptotic Solution of Landau's Dispersion Equation
Authors: Canosa José
Published: February 2004

The asymptotic solution of Landau's dispersion equation valid for long wavelengths has been obtained analytically to an arbitrary order of accuracy, thus improving Landau's first-order solution and Jackson's second-order solution.
Comments on “Laser-Induced Anomalous Heating of a Plasma”
Authors: Meyer Harry C. , Shatas Romas A.
Published: February 2004

Thresholds for the onset of parametric and two-stream instabilities for the 10.6 μm CO2 laser interacting with critically dense low-Z plasma at 1 keV electron temperature are estimated to occur, respectively, at 1012 and 1011 W cm−2.
Time Scales and Correlations in a Turbulent Boundary Layer
Authors: Blackwelder Ron F. , Kovasznay Leslie S. G.
Published: February 2004

Space-time correlations with large streamwise separation were obtained in a turbulent boundary layer with a zero-pressure gradient. The auto and cross correlations of the velocities u and υ with streamwise spatial separation distances up to 20 boundary layer thicknesses revealed a difference in their structure and decay rate. Using conditional averaging techniques, the velocity product, uυ, was sampled in both the turbulent and nonturbulent zones. Further conditional sampling led to an average picture of the velocities in the interfacial bulges. Near the wall the space-time correlation results are consistent with the idea of retarded fluid being ejected outward from the wall region and influencing the intermittent region.
Soret Driven Instability
Authors: Platten J. K. , Chavepeyer G.
Published: February 2004

The conditions of overstability are given for the two-component Bénard problem with thermal diffusion. Overstable motions can only occur for negative values of the Soret coefficient and moreover, the latter must exceed, in modulus, a critical value.
Overstability of Dielectrophoretic Poiseuille Flow in a Thin Annulus
Authors: Savkar S. D.
Published: February 2004

The stability of dielectrophoretic forced convection in a thin annulus at low Reynolds numbers is examined. Approximate calculations based on a linearized perturbation analysis, using axially directed Poiseuille base flow, show that the resultant secondary (transverse roll cell) flow pattern is overstable. It is also argued that the overstability is the consequence of the even content of the base flow and that an odd base flow would spawn a stationary secondary flow. The parametric influence of increasing Reynolds and Prandtl numbers is such as to increase the stability of the base flow. However, beyond a certain Reynolds number, the neutral stability curves for the two modes cross and longitudinal roll cells appear to be the more likely mode at higher Reynolds numbers. The nondimensional parameter governing the dielectrophoretic effects is identified in analogy to the Rayleigh number, and it appears that the stability is potential governed rather than electric field strength governed.
Knudsen Flow in a Tube with Arbitrary Gas-Wall Interaction
Authors: McCormick N. J. , Kuščer I.
Published: February 2004

The flow of a highly rarefied gas in a cylindrical tube is obtained in terms of accommodation coefficients. As a consequence of the geometry, two new coefficients are introduced. The mechanocaloric and thermal transpiration effects are also briefly discussed.
Numerical Simulation of the Harris Instability in Two Dimensions
Authors: Gitomer S. J. , Forslund D. W. , Rudsinski L.
Published: February 2004

The electrostatic Harris instability arising from a bi-Maxwellian electron velocity distribution in the presence of a uniform magnetic field is studied linearly by numerically solving the electrostatic dispersion relation and nonlinearly by two dimensional electrostatic numerical simulation. Contour plots of growth rate in k⊥ − k‖ space for a range of ωp/Ωc and T⊥/T‖ are used to summarize the linear theory. With the initial conditions T⊥ ≠ 0 and T‖ = 0 the numerical simulations show the nonlinear development with T‖ increasing the T⊥ decreasing until T⊥/T‖∼3 which is the practical stability boundary from linear theory. The saturation level of the electrostatic field energy is very small being 0.06% of the total kinetic energy consistent with the predictions of a simple nonlinear theory.
Effects of Parallel Wavelength on the Collisional Drift Instability
Authors: Schlitt L. G. , Hendel H. W.
Published: February 2004

An extensive investigation of the dependence of drift wave characteristics upon parallel wavelength in collisional potassium Q-machine plasmas is presented. Results are compared with a two-fluid slab-model theory which includes the effects of parallel resistivity and thermal conductivity for electrons and Larmor radius, collisional viscosity, and motion parallel to the magnetic field for ions. The general stability characteristics of the drift wave are confirmed: stability at low magnetic field (B/k⊥≲0.4 kG·cm) due to ion viscosity, stability at both long- and short-parallel wavelength (λ‖ ≳ 200 and λ‖≲100 cm, respectively) due to the combined effects of ion viscosity and parallel electron fluid expansion and stability of individual modes at high magnetic field (B/k⊥ ≈ 1 kG·cm, λ‖ ≈ 100 cm) due to ion parallel motion. Quantitative agreement between experiment and theory is demonstrated for the detailed parametric dependences of instability onset, complex frequency, and oscillation amplitude on parallel wavelength, magnetic field, and density.
Transverse Velocity Shear Instabilities within a Magnetically Confined Plasma
Authors: Jassby D. L.
Published: February 2004

Strong shear in the plasma rotation is produced in the interior of a magnetically confined Q-machine plasma column by means of an externally controlled nonuniform radial electric field. Coherent low-frequency oscillations are observed localized in the velocity shear layer, which contains up to seven ion gyroradii. The observed oscillations are shown to result from the transverse Kelvin-Helmholtz instability by the good agreement with finite-Larmor-radius fluid theory for the mode frequencies, radial dependences of the potential and density fluctuations, and the mode structure at large magnetic field and small rotation. At large electric fields the low-frequency Kelvin-Helmholtz modes are completely suppressed. Simultaneously, there appear oscillations with ω>̃ωc, whose properties are described by the fluid equations when extended to arbitrary rotation and wave frequencies.
Trapped-Ion Instabilities in Ion-Acoustic Wave
Authors: Ikezi H. , Kiwamoto Y. , Nishikawa K. , Mima K.
Published: February 2004

Growth of two types of sideband waves has been observed experimentally when a relatively large-amplitude ion-acoustic wave propagates in a collisionless plasma having the electron-to-ion temperature ratio Te/Ti≈20. The observed frequency spectrum and growth rate, as well as the frequency and amplitude ranges of the large-amplitude wave for which the sideband wave growth is observed are in good agreement with the theory of trapped particle instabilities. The sidebands extract the energy from the large-amplitude wave and cause it to be heavily damped.
Plasma Heating by Large-Amplitude, Low-Frequency Electric Fields
Authors: Kruer W. L. , Katz J. , Byers J. , DeGroot J.
Published: February 2004

Computer simulations of plasmas driven by large-amplitude electric fields oscillating near the ion plasma frequency are presented. The large field excites an instability which leads to an efficient heating of the plasma. This is an instantaneous electron-ion two-stream instability due to the slowly oscillating drift between electrons and ions. A simple theory gives the instability properties and the observed plasma heating.
Resonances in the Collisionless Heating of a Plasma by Transit Time Magnetic Pumping
Authors: Lashmore-Davies C. N. , May R. M.
Published: February 2004

Using a general expression for the power absorbed by transit time magnetic pumping, the resonances in the heating, due to the three low-frequency electromagnetic waves which can propagate in a plasma in a magnetic field, are calculated. The strengths and widths of the three resonances are compared under conditions where the electrons absorb most of the power. The ion-acoustic resonance is the broadest and the magneto-acoustic (or compressional Alfvén) the strongest. The Alfvén (or shear Alfvén) wave is undamped when cyclotron damping and terms of order ω2/ωci2 are neglected. However, when terms of order ω2/ωci2 are included, the Alfvén wave is shown to have a stronger resonance than the ion-acoustic wave. Numerical results have also been obtained for the magneto-acoustic resonance under conditions where the ions are also heated and the width of the resonance is much broader than for pure electron heating.
Deuterium-Tritium Heating to Thermonuclear Temperatures by Means of Ion-Ion Collisions in the Presence of Intense Laser Radiation
Authors: Mjolsness R. C. , Ruppel H. M.
Published: February 2004

The laser heating of deuterium and tritium ions by small angle D-T collisions is calculated assuming that ion distribution functions are displaced Maxwellians with average velocity determined by the laser electric field. For all conditions of high radiation intensity the ion temperature will increase as t2/5 to good approximation. The heating times are of the order of t∼10−9(E0/1010 esu)−2(n/1021 cm−3)−1(λ/10−4 cm)−2 × (T/108 K)5/2 sec. At high laser fluxes this mechanism dominates electron-ion heat transfer by several orders of magnitude and results in substantial heating of ions in adjacent nonlaser irradiated plasma, through ion-ion heat conduction. The heating rate is examined for a plasma of two arbitrary ion species. The heating rate is sensitive to ion masses and charges, and it appears that the above heating time can be shortened by as many as three to five orders of magnitude. A D-T plasma may be brought to thermonuclear temperatures by this mechanism, but this requires laser fluxes and laser energies two to three orders of magnitude larger than currently available.
Spontaneous Excitation of the Long-Wave Ion-Cyclotron and Ion-Acoustic Oscillations in Fully Ionized Plasmas
Authors: Milić B.
Published: February 2004

For model wavelengths longer than the electron mean free path, the damping coefficients of both longitudinal ion-cyclotron and ion-acoustic waves are close to zero. As in the collisionless plasma these coefficients may become negative provided that the electron drift velocity exceeds some threshold value, due to the normal Doppler effect. The threshold drift for both modes mentioned is evaluated, assuming that the plasma is fully ionized, i.e., using one-particle distribution function formalism and kinetic equations with Landau collision integrals. It is shown that the spontaneous excitation of the ion-cyclotron oscillations first sets in at the long wave limit, as the electron drift is gradually augmented. On the contrary, spontaneous excitation of ion-acoustic waves is first noted at short wavelengths. Conditions of existence of the long wave limits for both modes are discussed.
Interaction of a Streaming Plasma with a Magnetic Mirror
Authors: Kramer William R. , Siambis John G.
Published: February 2004

The interaction between a supersonically streaming plasma and a spatially increasing longitudinal magnetic field is investigated experimentally. The object of the experiment is to obtain qualitative and quantitative data on this interaction and, in particular, the transition from supersonic to subsonic flow and the attendant shock formation. It is shown that for distances in excess of 50 cm from the gun, where the plasma beam is formed, to the peak of the mirror field and for values of peak mirror field exceeding 3 kG, a supersonic-subsonic flow transition does occur and a shock is formed. The helium plasma beam is produced by a conical theta-pinch gun driven by a capacitor bank with a stored energy of 2.5 kJ. Measurements are made of the plasma density, temperature, and streaming velocity. The experimental results are compared to and found in qualitative agreement with an existing theory which predicts the parameter values for the formation of a shock in a related geometry.
Helical Field Experiments on a Three-Meter Theta Pinch
Authors: Thomas K. S. , Harder C. R. , Quinn W. E. , Siemon R. E.
Published: February 2004

Small helical fields have been added to the main compression field of a 3-m long theta pinch, both by grooving the main compression coil and by adding helical windings driven by capacitor banks. The equilibrium and stability of the theta-pinch plasma column and the interference force produced by a combination of helical fields have been studied and are found to be in agreement with theory.
Model Equation of Turbulent Shear Flow
Authors: Jeng Dah-Teng
Published: February 2004

Some statistical characteristics of a Burgers-type model system for shear-flow turbulence are studied here. It is found that this mathematical model could be a realistic model for certain types of wall turbulence.
Measurements of Reynolds Shear Stress Fluctuations in a Turbulent Boundary Layer
Authors: Antonia R. A.
Published: February 2004

Measurements in both smooth and rough wall boundary layers show that the rms of the Reynolds shear stress fluctuation is approximately twice the wall shear stress value in the region close to the wall and equal to about three times the local shear stress throughout most of the smooth wall layer.
Alfvén Waves in Inhomogeneous Magnetic Fields
Authors: Uberoi C.
Published: February 2004

It has been found that the rigorous and general treatment of electrostatic oscillations in a cold plasma of nonuniform density given by Barston can be extended to the case of Alfvén waves in an ideal fluid in the presence of a class of inhomogeneous magnetic fields.
Systematic Derivation of the Wave Kinetic Equation for a Homogeneous Plasma
Authors: Swift Daniel W.
Published: February 2004

The wave kinetic equation for waves in a homogeneous plasma is derived from Maxwell's equations and the linearized solution of the Vlasov equation.
Nonlinear Evolution of Loss-Cone Flute Modes
Authors: Eldridge Owen , Crume E. C. , Meier H. K.
Published: February 2004

An analytic theory is developed that explains the results of a recent computer simulation of loss-cone flute modes.
Ion-Acoustic Instability of a Collisional Plasma with Nonstationary Equilibrium
Authors: McBride J. B. , Chu T. K.
Published: February 2004

A long-wavelength ion-acoustic instability of a fully ionized, two-temperature (Te>Ti), collisional plasma without sources and sinks is of no practical importance since it can e fold, at most, only once before Te≃Ti due to collisional relaxation of the two-temperature equilibrium.
Free Boundary Solution of a Current-Carrying Plasma
Authors: Yoshikawa S.
Published: February 2004

The effect of the externally imposed field error on the shape of the current-carrying plasma is considered. It is found that the ratio of the perturbation to the plasma size is of the order of Be/(Bam), where Be is the perturbed field and Ba is the field of the plasma current.
Induced viscosity changes in a polarizable liquid
Authors: Yun C. K. , Fredrickson A. G.
Published: February 2004

A special theory of rectilinear flow of a polarizable liquid is developed by introducing a polarization parameter into the stress-rate-of-strain relationship of the liquid. The viscosity of the liquid is thus dependent on its state of polarization, and this in turn is determined by the shear rate, the strength and direction of any applied electromagnetic field, and the proximity to an interface. Formulas for the effects of these influences on the apparent viscosity are developed for the case of large shear rates. Comparison of these formulas with three published sets of viscometric data—Couette flow with an electric field, Poiseuille flow with a magnetic field, and Poiseuille flow with interfacial effects—on nematic liquid crystals show excellent agreement of the theory with the data.
Effect of velocity dependence of Coulomb logarithm on the solution of the Fokker-Planck equation
Authors: Cooper G. E. , Herman P. T.
Published: February 2004

The error incurred through the customary neglect of the velocity dependence of the Coulomb logarithm was evaluated by reexamining the problem of the deceleration of a test particle in a plasma. Numerical results indicate that a neglect of this velocity dependence results in an underestimation of the energy deposited by a test particle in the ion field of a plasma.
Repeated cascade theory of homogeneous turbulence
Authors: Tchen C. M.
Published: February 2004

The problem of turbulent spectrum engenders two coupled hierarchies: one originates from the development of stress, leading to a transfer function, and the other from the development of an eddy viscosity. In order to incorporate physical roles among scales, the turbulent velocity fluctuation is decomposed into a series of ranks in the increasing order of randomness, contributing successively to energy or stress, eddy viscosity, relaxation frequency, and higher-rank frequencies in the memory chain. As a result, the first hierarchy mentioned above becomes closed at the quadrupole correlation. The second hierarchy governs the eddy viscosities of different ranks, related to relaxation frequencies of such ranks, in the form of a memory chain. It is cut off by an implicit viscous mechanism. For zero wind gradient, the spectrum in the inertial subrange recovers the Kolmogoroff k−5/3 law with a numerical constant 1.58, in good agreement with experiments. For a strong wind gradient, the spectrum in the production subrange has a k−1 law. In the viscous subrange, a law of approach confirming the Heisenberg k−7 power spectrum, and a viscous cut-off in the form of an exponential tail are obtained, insuring the convergence of high-order spectral moments. The critical wavenumbers characteristic of the production, inertia, viscous subranges, and the cutoff are determined, together with their numerical coefficients.
Large-amplitude stabilization of the drift instability
Authors: Ching Hugh
Published: February 2004

A general mechanism of large-amplitude stabilization of the drift instability is investigated. For slab geometry, a drift-wave potential of the form φ = Φ cos(kxx) cos(kyy+kzz−ωt) is used where x is the direction of plasma density inhomogeneity and z is the direction of a uniform field. It is assumed that kx∼ky≫kz and υi≪ω/kz≪υe. Studies of the exact guiding-center particle trajectories in the drift-wave potential show the existence of time-average, y-direction velocities whose magnitudes increase with the amplitude of the drift wave. As the wave grows, these velocities shift parts of the resonance region away from υz = ω/kz and finally into the bulk of the ion distribution. Thus, the original instability is stabilized by strong ion Landau damping. Stabilization will occur around the wave amplitude satisfying the condition, ckxΦ/B=ω/ky.
Effect of compressibility on the stability of a vortex sheet in an ideal magnetofluid
Authors: Duhau S. , Gratton J.
Published: February 2004

The hydromagnetic stability of a vortex sheet with respect to all modulations is examined. A domain of absolute stability not previously noted is found for high compressibility. Stability criteria are given. Onset of instability is related to radiation of hydromagnetic waves.
Pressure limitation in a simple model of a tokamak
Authors: Haas F. A. , Thomas C. Ll.
Published: February 2004

The simple model of a tokamak studied by Strauss is reinvestigated. By defining poloidal β to be the ratio of the integrated pressure to the square of the toroidal current, it is shown that this quantity is bounded.
Parametric excitation of lower hybrid instabilities
Authors: Kaw P. K. , Lee Y. C.
Published: February 2004

The application of a sufficiently intense long wavelength oscillating electric field at the lower hybrid frequency to a plasma with two ion species leads to instability of finite wavelength electron-ion lower hybrid modes and a purely growing modification of the ion-ion hybrid mode.
Asymptotic theory of the Boltzmann equation at large Knudsen number
Authors: Cooper A. L. , Hamel B. B.
Published: February 2004

A study of an asymptotic theory of hyperthermal flow past a blunt object for large Knudsen number is presented. The greatest demands on such a theory are present for flow past two-dimensional bodies. This is because the large lateral extent of the emitted molecules in free molecular flow gives rise to a singularity in the integrated collision frequency of the incoming free stream molecules. This singularity is removed by accounting for the effects of collisions upon the emitted molecules which augments the usual geometric free molecular decay. The method of matched asymptotic expansions is applied to regions near the body and far from the body (one mean free path and greater). For two-dimensional bodies, the surprising result is obtained that the first correction to free molecular flow [Kn−1 ln(Kn)−1] cannot be obtained without explicitly taking into account the collisional effects on the emitted particles in the far region. For three-dimensional bodies, although there is no problem in the determination of the leading term (Kn−1), the evaluation of the next order term [Kn−2 ln(Kn)−1 involves precisely the same difficulties as the leading term for two-dimensional bodies.