bluuebunny/crossref_metadata_2025 huggingface dataset:
Flow Velocity Measurements in a T Tube
Authors: Strachan J. D. , Ahlborn B. , Huni J. P.
Published: February 2004

The flow velocity of a T-tube plasma has been measured by recording the attenuation of a known shock wave propagating through the T-tube flow. This technique yields results with typical accuracies of 0.1 km/sec which is about 10% of the velocity of the probing shock. The interpretation of the results invites a comparison of the T-tube flow field with an overexpanded detonation or breakdown wave in the high-velocity regime and with a radiation driven shock front in the low-velocity regime.
Revision and Test of the Quasilinear Theory
Authors: Burns Thomas , Knorr Georg
Published: February 2004

The quasilinear theory is revised analytically and its consequences are tested by a numerical simulation for a one-dimensional periodic electron plasma with discrete electrostatic modes. The theory is formulated for unstable and damped modes and a series of constants of motion derived. The numerical model is a Vlasov-Poisson system where the mode-mode coupling terms have been omitted. The result is that the predictions of our analytical theory are confirmed by simulation. For all cases considered there are always several modes which are initially unstable, but become damped at a later time so that an inclusion of damped modes in the theory is absolutely necessary.
Electrostatic Stability Theory of Tokamaks from Two-Component Fluid Equations
Authors: Horton C. W. , Varma R. K.
Published: February 2004

The electrostatic stability theory of tokamak plasmas is developed from the two-component fluid equations. The consistent treatment of the collisional equations with the transport processes from Coulomb scattering shows the relative importance of the transport processes of resistivity, viscosity, the thermoelectric effect, and thermal conduction in the several plasma modes. The plasma modes derived from the electrostatic equations are the sound waves, the drift wave, and thermal modes. The growth rates are given as functions of the driving forces of the tokamak current, the density gradient, and the temperature gradients. At finite aspect ratio, the equations describing the current driven drift-sound waves are solved for the toroidal shift in the growth rate. In addition to the gradient-B drifts previously modeled by a periodic gravity, it is shown that consistency requires inclusion of the plasma compression due to the modulation of the parallel and perpendicular fluxes in the nonuniform magnetic field.
Anomalous Reflection and Transmission of Cyclotron Waves
Authors: Marsh J.
Published: February 2004

A formalism is developed to describe the propagation along a slowly varying magnetic field of purely transverse cyclotron waves. By an expansion of the coupled set of Vlasov-Maxwell equations, a one-dimensional wave equation is derived, which is applied to the case where the field configuration is a magnetic mirror with small field variation which includes points of cyclotron resonance where the local gyrofrequency is equal to the wave frequency. An investigation is made of the processes whereby particles trapped in the mirror field can cause anomalous transmission and reflection of the wave by a nonlocal mechanism. It is found that the nonlocal processes are most significant when the function which gives the total phase difference observed by a trapped particle on its orbit between the point of damping of the incident wave and that of excitation of the transmitted or reflected wave is stationary with respect to both the energy and magnetic moment of the particle.
Theory and Simulation of the Beam Cyclotron Instability
Authors: Lampe M. , Manheimer W. M. , McBride J. B. , Orens J. H. , Papadopoulos K. , Shanny R. , Sudan R. N.
Published: February 2004

A detailed theory in conjunction with the results of computer simulation experiments is presented for the beam cyclotron instability. The main results are (1) After a period of exponential quasilinear development, turbulent wave-particle interactions cause cross-field diffusion of the electrons which smears out the electron gyroresonances. This occurs at a level of turbulence which scales as Σκ(| Eκ |2/4πN0Te)∼(Ωe/ωe)2(Ωe/kve), where Ωe and ωe are the electron cyclotron and plasma frequencies, and results in a transition to ordinary ion sound modes that would occur in an unmagnetized plasma. The magnetic field serves to reduce the effects of electron trapping. (2) This level of turbulence appears to have virtually no effect on long wavelength fluid modes. (3) At this level the instability stabilizes if ordinary ion sound is stable due to ion Landau damping. For cold ions it continues to develop at the slower ion acoustic growth rate until the fields become strong enough to trap the ions. After the fields saturate, further plasma heating is much slower than exponential.
Electron Cyclotron Heating as Resonant Diffusion
Authors: Eldridge Owen
Published: February 2004

The heating of electrons by externally applied microwave fields is treated as a resonant diffusion in velocity space. The diffusion is calculated directly from electron orbits with the microwave fields considered to be small perturbations. The motion of an electron is found to be adiabatic outside resonant zones where the microwave frequency matches the cyclotron frequency. Heating rates are found which are independent of collisional time scales if the correlation length of the external fields is long enough; several wavelengths are required. Finite cyclotron radius effects are included to find the dominant contribution to scattering into the loss cone of a plasma in a mirror field and spatial diffusion rates. The theory is found to agree qualitatively with experiment, but relativistic dynamics must be used for a detailed comparison.
Conductivity of a Two-Dimensional Guiding Center Plasma
Authors: Montgomery David , Tappert Frederick
Published: February 2004

The Kubo method is used to calculate the electrical conductivity of a two-dimensional, strongly magnetized plasma. The particles interact through (logarithmic) electrostatic potentials and move with their guiding center drift velocities (Taylor-McNamara model). The thermal equilibrium dc conductivity can be evaluated analytically, but the ac conductivity involves numerical solution of a differential equation. Both conductivities fall off as the inverse first power of the magnetic field strength.
Neutron Energy and Flux Distributions from a Crossed-Field Acceleration Model of Plasma Focus and Z-Pinch Discharges
Authors: Bernstein M. J. , Comisar G. G.
Published: February 2004

Anisotropic distributions of neutron fluxes and neutron energy spectra are calculated for D-D reactions in self-pinching discharges, particularly for a plasma focus. A generalized beam-target model is assumed where (1) high-energy deuterons have angular distributions consistent with a crossed-field acceleration mechanism, and (2) these energetic deuterons undergo fusion collisions primarily with stationary target ions. Energy distributions of ions proportional to Ed−3 in the range from 50 to as high as 600 keV give computed results agreeing with many experimental observations at laboratory angles of 0°, 90°, and 180°. These ion-energy distributions can account for a 50-to 100-fold increase in neutron yield when a deuterium-tritium gas mixture is used.
Plasma Magnetization and the Determination of Hydromagnetic Equilibrium
Authors: Hall Laurence S.
Published: February 2004

Equilibrium of a plasma and a magnetic field is determined through a plasma magnetization M with both local and nonlocal contributions. The equations of equilibrium are thus posed in soluble form, ∇ × H = 0 and ∇·B = 0 with B = H+4πM, possible previously only when pressures depended on | B | alone.
Frequency Shift Due to Trapped Particles
Authors: Dewar R. L.
Published: February 2004

The time asymptotic distribution functions corresponding to adiabatic and sudden excitation of an electrostatic wave are calculated. These distributions are compared and used to calculate the nonlinear response of the plasma, and Poisson's equation is used to find a nonlinear dispersion relation.
General Recurrence Relation for Use in Evaluating Moments of the Integrand of the Plasma Dispersion Function
Authors: Goodrich Lewis C. , Durney Carl H. , Grow Richard W.
Published: February 2004

A derivation is given of a general recurrence relation which allows one to evaluate moments of the integrand of the plasma dispersion function is terms of the plasma dispersion function itself, without the laborious algebraic manipulations which are used otherwise.
Prandtl Number Dependence of the Stability of a Stratified Free Shear Layer
Authors: Miller J. R. , Gage K. S.
Published: February 2004

A fundamental result of linear inviscid theory for stratified parallel shear flow guarantees stability when the local Richardson number exceeds 0.25 throughout the flow. By extending a numerical study by Maslowe and Thompson, the authors have demonstrated instability for a viscous shear layer at low Prandtl number even with the Richardson number greater than 0.25.
Variable Mesh Numerical Method for Solving the Orr-Sommerfeld Equation
Authors: Hughes Thomas H.
Published: February 2004

A numerical method using a nonuniform mesh spacing has been developed for solving the Orr-Sommerfield equation and has been used to explore a puzzling detail in the curve of neutral stability at large values of the Reynolds number. The numerical method consists of the usual finite-difference method, an automatically determined variable mesh, and a modified eigenvalue-search-procedure. For plane Poiseuille flow it is demonstrated that the kink in the curve of neutral stability is a feature of solutions of the Orr-Sommerfeld equation and not just a deficiency in the asymptotic analysis as previously suggested.
Some Inertial Wave Sideband Instabilities
Authors: Roskes G. J.
Published: February 2004

Equations describing the behavior of weakly nonlinear slowly varying inertial waves in an unbounded inviscid fluid are derived. A balance between nonlinearity and dispersion is considered. For this balance, sideband instabilities are investigated for two cases. Case 1: Sideband wavenumber vectors K are chosen to be perpendicular to the rotation vector Ω̂ (so that Ω̂·K = 0), and sideband instabilities are found for waves with a wavenumber vector k lying within 35° of the rotation vector. Case 2: K is chosen so that 4(Ω̂·K)2 = ε2(cg·K)2 | K |2, where ε is a measure of the nonlinearity, and cg is the group velocity of the wave. Instability is found for all waves.
Sea-Surface Slope and Equilibrium Wind-Wave Spectra
Authors: Wu Jin
Published: February 2004

The measured mean-square slope of the sea surface is shown to vary logarithmically with the wind velocity, and the rates of variation change with different boundary-layer regimes of the wind. Based on mean-square slope data, the form of a newly proposed equilibrium wind-wave spectrum for the capillary range is verified, the spectral coefficients for both gravity and capillary ranges are determined, and the cutoff wavenumber for the slope data is shown to be much smaller than the neutrally stable wavenumber obtained from laminar model. Finally, an approximate correlation is presented between the mean-square slope and the roughness height of the sea surface, implying that the growth of small waves is mainly due to the direct action of the wind.
Thermohaline Instability and Salt Fingers in a Porous Medium
Authors: Taunton J. W. , Lightfoot E. N. , Green Theodore
Published: February 2004

An extension of the analysis of Nield is made to more completely characterize the onset of convection in an infinite horizontal porous medium stratified by temperature and concentration. Comparisons are made with thermohaline convection in Newtonian fluids. Major differences lie in the concentration Rayleigh number dependence of the wavenumber at the marginal state of overstability and the dependence of the horizontal wavenumber in the “salt finger” region of stationary convection on both temperature and concentration Rayleigh numbers. Suggestions of geological applications and laboratory verification using a Hele-Shaw cell are presented.
Numerical Investigation of the Stability of a Shock-Accelerated Interface between Two Fluids
Authors: Meyer K. A. , Blewett P. J.
Published: February 2004

Recent experiments by Meshkov have demonstrated that a shock-accelerated perturbed surface separating two gases of different densities is unstable for shocks traveling from the lighter gas to the heavier gas and vice versa. Using a two-dimensional Lagrangian hydrodynamic code, the authors show qualitative agreement with Meshkov's experiments. Experiment, numerical calculations, and linear analysis are compared. Good agreement was obtained between numerical calculations and linear analysis.
Ion-Exosphere with Asymmetric Velocity Distribution
Authors: Lemaire J. , Scherer M.
Published: February 2004

The number density, the particle flux, the momentum fluxes, and the energy flux are calculated in a model ion exosphere with an open magnetic field, for an asymmetric Maxwellian velocity distribution (i.e., ∼exp[−β(v−u)2]). Numerical calculations for the polar ionosphere of the earth show that this asymmetry does not qualitatively affect the results obtained with a symmetric velocity distribution function (u = 0), i.e., the protons are accelerated outward and escape with a supersonic flow speed.
Transition from Free-Molecule to Continuum Flow in an Annulus
Authors: Maegley Wendel J. , Berman A. S.
Published: February 2004

Results of precise measurements of the pressure dependence of the flow of gases through annuli of various radius ratio are presented. The data cover a range of Knudsen numbers for about 0.01 to 450. The depth of the Knudsen minimum is found to vary markedly with radius ratio and increases as the radius ratio increases. (Radius ratio is defined as the ratio of inside to outside radii). About 50% of the total change in the depth of the Kundsen minimum occurring between flat plates (radius ratio = 1.0) and capillaries (radius ratio = 0) is effected by a 13% change in radius ratio from 1.0 to 0.8711. Previously observed deviations from classical kinetic theory are verified; and, in particular, in the free-molecule and near free-molecule regimes, the flows are found to be lower than those predicted based on diffuse scattering of gas molecules from the annulus wall. The data are generally found to be in good agreement with flows predicted by the BGK and variational techniques presented by Berman and Maegley [Phys. Fluids 15, 772 (1972)].
Nonlinear Heat Conduction in Rarefied Gases Confined between Concentric Cylinders and Spheres
Authors: Lou Y. S. , Shih T. K.
Published: February 2004

Heat conduction problems in rarefied gases confined within the solid boundaries of two concentric cylinders and spheres have been studied using the four moment method. A two-sided velocity distribution function is assumed for the gas. The two number densities and the two temperatures in the distribution are the four unknowns of the problem. Unlike previous analyses, a series expansion of these four unknowns in terms of the temperature difference is introduced to account for problems with finite temperature differences. Closed-form solutions are thus obtainable. An example of a calculation is presented for cases retaining the second-order terms in the expansion. The results show that the heat conduction ratio of Q/Qfm, where Qfm is the heat conduction rate at the free molecular limit, is a function of the temperature difference ε. Previous results of small temperature difference are recovered by taking the limit of ε→0.
Electrohydrodynamic Cellular Bulk Convection Induced by a Temperature Gradient
Authors: Lee Chung-Oh , Kim Moon-Uhn , Kim Dong-Il
Published: February 2004

A gradient in electric conductivity generally results if a temperature gradient is imposed on a slightly conducting liquid. It is shown that if the liquid layer between two rigid boundaries is subjected to a standing electric potential wave, charges are induced in the bulk and the charges interact with the imposed electric field to produce a cellular liquid motion. A theoretical model is developed for the cell streamlines, and the distribution of electric potentials. The theoretical results are shown to be in agreement with the experimental observations.
Numerical Study of Strong Plasma Shock Waves Produced in an Electromagnetic Shock Tube
Authors: Schneider S. H.
Published: February 2004

A set of two-fluid Navier-Stokes equations with classical physical transport coefficients is used to compute the evolution and structure of collisional plasma shock waves in an electromagnetic shock tube. Shock speeds up to 200 cm/μsec and shocked-plasma temperatures of the order of kilovolts are studied. A strong transverse bias magnetic field is employed, which significantly alters the size and shape of the shock profiles, when compared with the zero bias field case. The wave structure is different from that of a two-fluid gas-dynamic shock without transverse magnetic field. Especially significant is the effect of the small ion Larmor radius in reducing the gasdynamic shock thickness by at least an order of magnitude in the transverse shock case, which permits collisional shocks to have thicknesses much smaller than the post-shock mean free path. These collisional shock waves produce very hot ions, the ion temperature increasing with shock speed, although the formation time and distances also increase substantially with shock speed. Generally, the results compare favorably with electromagnetic shock tube experimental data.
Three-Dimensional Plasma Diffusion in a Very Strong Magnetic Field
Authors: Montgomery David , Liu C.-S. , Vahala George
Published: February 2004

The thermal equilibrium coefficient of spatial diffusion transverse to a strong uniform dc magnetic field is calculated for a fully ionized plasma. The particles are assumed to move transverse to the field only as a consequence of the E × B drift, but to move freely parallel to it. The particles interact only electrostatically. The calculation is done at large, but fixed and finite, plasma volume. It is shown that, as B→∞, the leading term of the coefficient of transverse spatial diffusion falls off as O(1/B), but contains a multiplicative factor which goes to zero as the plasma volume becomes infinite. The method of calculation fails for unbounded plasmas.
Nonlinear Frequency Shift of a Plasma Wave
Authors: Dewar R. L. , Lindl J.
Published: February 2004

The effect of nonlinearity on the dispersion relation of an electron plasma wave is investigated experimentally by numerical simulation, and theoretically by perturbation expansion and use of Hamilton's variational principle. The simulation was carried out using a one-dimensional water bag distribution of finite-size electrons, and the theory takes this into account by using a fluid-type Lagrangian with a non-local field-particle interaction. The first-order (in wave energy) correction coefficient in the nonlinear dispersion relation was measured as a function of wavelength, and reasonable agreement was found with the theory in both the traveling and the standing wave cases.
Absorption of an Electromagnetic Wave Normally Incident on a Warm Plasma
Authors: Arumi F. N. , Oakes M. E.
Published: February 2004

A theoretical analysis of an electromagnetic wave incident on a warm, homogeneous plasma half-space is reported. A static magnetic field is parallel to the plasma surface. Collisions are included to discuss several experiments; however, the approach is not restricted to collision-dominated systems. Particular attention is given to the plasma-vacuum boundary conditions.
Collisional Theory of Shock and Nonlinear Waves in a Plasma
Authors: Hu Pung Nien
Published: February 2004

The unsteady state problem of weak nonlinear plasma waves in the presence of a perpendicular magnetic field is studied, based on a system of moment equations of Boltzmann equations for electrons and ions. This system, rigorously closed and obtained by proper scalings in time and space with respect to the wave strength, describes a fully ionized plasma with all possible dissipative mechanisms including electron and ion viscosity, coupled electron and ion heat conduction, thermal diffusion and resistivity, as well as all the distinct Hall effects. In all the plasma parameter ranges, it is found that the evolution of weak nonlinear waves is governed by the Burgers equation, subject to given initial and boundary conditions. The formation of a shock wave and the evolution of a compression pulse are studied in detail. The transit time and distance for a fully developed shock wave are obtained, both being complicated functions of plasma parameters. In some parameter ranges, the transit time is smaller than the electron self-collision time while the transit distance is smaller than the mean free path. The time scale for the evolution of a compression pulse depends strongly on its initial width. A steady shock front will shortly appear if the initial width of the pulse is large compared with the thickness of a steady shock wave. On the other hand, the pulse will immediately decay if its initial width is small compared with the thickness of a steady shock wave. Depending on the parameter range, the thickness of a steady state shock wave can be larger than, comparable to, or smaller than the mean free path. Eventually, however, a compression pulse becomes self-similar, with its amplitude decaying as 1/t1/2 and its width spreading as t1/2. The inclusion of the electron inertia effect leads to the Korteweg-de Vries-Burgers equation which covers a wide range of wave profiles.
Magnetostatic Equilibria of Finite-Pressure Minimum-B Plasma Configurations
Authors: Hall Laurence S.
Published: February 2004

Magnetostatic equilibria for a broad class of plasma conditions are shown to correspond to solutions of the equations ∇·B = 0, ∇× H =0, where B = μ H. Magnetohydrodynamic stability then corresponds to satisfaction of the criteria H>0 and dH/dB>0, where B = |B | and H =μ−1B. Equilibria are studied for a variety of plasma distributions taken as functions of total energy and magnetic moment and in the most general cases, the coordinates of a line of magnetic flux. A new result is the determination of a relationship between well depth and the maximum pressure for magnetohydrodynamic stability which puts an upper limit on the well depth to achieve given pressure when the value of the maximum field strength is fixed. For so-called collisional distributions, if p is the total pressure at the center and B0 is the maximum magnetic field, β̃ = 8πp/B02<0.2, and the mirror ratio to achieve maximum β̃ may not exceed 1.8. More general equilibria, where the pressures are functions of field lines as well, cannot improve the results and may be even more unstable.
Nonlinear Saturation of Parametric Instability: Basic Theory and Application to the Ionosphere
Authors: DuBois D. F. , Goldman M. V.
Published: February 2004

A calculation is presented of the nonlinear level of Langmuir and acoustic wave plasma fluctuations excited by parametric decay instability, and saturated by induced scattering of the plasma waves from dynamically screened ions (low-frequency spontaneous emission). This is found to be an important weak turbulence saturation mechanism for instabilities excited parametrically in the ionosphere. The cross section for incoherent scattering from the excited waves is obtained and comparisons are made with recent experiments.
Ekman Layer on a Porous Plate
Authors: Gupta A. S.
Published: February 2004

An exact solution of the steady three-dimensional Navier-Stokes equations is obtained for the case of flow past a porous plate at zero incidence in a rotating frame of reference. For uniform suction at the plate, an asymptotic profile exists for the velocity distribution.
Numerical Examination of Two-Species Reactions in Final Period Turbulence
Authors: O'Brien Edward E. , Lin C.-H.
Published: February 2004

Numerical integration of a proposed closure approximation yields results consistent with analytical predictions for very rapid two-species reactions in final period turbulence.
Computer Studies of Collionless Damping of a Large Amplitude Whistler Wave
Authors: Ossakow S. L. , Haber I. , Sudan R. N.
Published: February 2004

Computer simulation of a single large amplitude whistler wave propagating in a plasma has been carried out. Such a wave shows an initial linear damping, then a regrowth and amplitude oscillation, and finally settles to a constant amplitude value; all in good agreement with theory.
Scattering of Electromagnetic Waves from a Turbulent Plasma Slab
Authors: Liu C. H.
Published: February 2004

Scattering of electromagnetic waves from a turbulent plasma slab is studied. Part of the effects of the multiple scattering is taken into account. The reflection coefficient is found to be increased and its variation with respect to the slab thickness is smoothed out by the random scattering.
Microwave Scattering from Underdense and Overdense Turbulent Plasmas
Authors: Attwood David
Published: February 2004

Experimental results of microwave scattering from a turbulent plasma are presented. As electron density is increased beyond the critical value, a transfer from volume to surface scattering is observed. Overdense scattering is characteristic of a cylinder displaying orientation fluctuations.
Comparison of the Low-Frequency Eigenmodes of a Cylindrical Plasma with Experimental Parametrically Excited Plasmas
Authors: Fredericks R. M. , Asmussen J.
Published: February 2004

The low-frequency eigenfrequencies and electron temperatures of a cylindrical plasma are calculated and are compared with experimental parametrically excited plasma cylinders. The agreement between theory and experiment indicates that certain refinements of the theory must be made.
Nearly Free-Molecular Channel Flow at Finite Pressure Ratio
Authors: Wang P. Y. , Yu E. Y.
Published: February 2004

The problem of nearly free-molecular flow of a gas from one reservoir to another through a two-dimensional channel is studied. The width of the channel is much smaller than the length which is of the order of the mean free path of the gas. The ratio of the equilibrium pressures in the reservoirs is finite, whereas the equilibrium temperatures are the same. The fundamental solution of the linear Boltzmann equation is used for the evaluation of total mass flow rate. The result is presented in the form of an asymptotic series, of which the first-order terms are of the order of α ln α and α, where α is the inverse Knudsen number. Computations shows that the first-order terms, which represent intermolecular collisions in the counter flows, have a net negative value. The total mass flow rapidly decreases as the length of the channel increases.
Slip Coefficients for General Gas-Surface Interaction
Authors: Klinc Tomaž , Kuščer Ivan
Published: February 2004

The velocity and the temperature slip coefficients are evaluated for general gas-surface scattering kernels by a variational method. The results are expressed in terms of a set of accommodation coefficients.
Falkner-Skan Problem in Magnetohydrodynamics
Authors: Hildyard Lewis T.
Published: February 2004

The Falkner-Skan problem is extended to magnetohydrodynamic flow past a nonconducting body by imposing a magnetic field whose lines of force are parallel to the undisturbed streamlines. The magnetic-field boundary condition used by Gribben is shown to be inappropriate and results in the form of asymptotic series for large and small values of the magnetic Prandtl number are obtained. Numerical integration is used to establish the validity of the series in each case.
Stability Criterion for the Bluff-Body Stabilized Electrodeless Arc
Authors: Martin R. E. , Keefer D. R.
Published: February 2004

It has been found that the electrodeless arc can be stabilized in the presence of flow by placing a bluff body in the entrance stream. A two-stream boundary layer analysis, analogous to that used in combustion theory, is used to calculate an attachment length, the distance required to heat the entering stream to the arc temperature. The criterion for stability is that the attachment length is less than the length of the recirculation cell formed in the wake of the bluff body. Calculations are made for conditions typical of an atmospheric pressure arc in argon. It is found that the attachment length is approximately a linear function of the ratio of flow velocity to power density.
Onset Point of Ionization
Authors: Murty S. S. R. , Serou P.
Published: February 2004

It is shown that precursor photoionization is capable of creating electron number densities large enough to virtually eliminate the atom-atom collision region and the Mach number at which the above phenomenon occurs is calculated for a few initial pressures and temperatures for argon.
Magnetohydrodynamic Turbulence Experiments in a Transverse Magnetic Field
Authors: Kellam John M.
Published: February 2004

Random fluctuations in a transverse magnetic field caused by a helium plasma produced in an arc discharge were measured with magnetic probes. Ensemble averaged power spectra of these fluctuations followed a power law over the frequency range from about 0.2 to 1 MHz, the exponents varying from −11/3 to −19/3. The time average of the fluctuation intensity parallel to the external magnetic field increased nearly linearly with the imposed field up to about 1000 G. Stronger magnetic fields inhibited these fluctuations and retarded the flow of the plasma. Integral and microscales were in the range of 40 to 100 mm and 20 to 40 mm, respectively. The random fluctuations in the magnetic field may have been due partly to random inhomogeneities in the conductivity of the plasma and only partly to vortical turbulence. Magnetic and conductivity probes indicated the presence of substantial electrical conductivity ahead of the luminous plasma. This conductivity was reduced by increasing magnetic field, interpreted as involving an electron flux.
Optical Measurements of the Degree of Turbulence of a Gun Plasma
Authors: Matt D. R. , Scott F. R.
Published: February 2004

Turbulent electric fields of the order of 7 kV/cm were observed in a plasma from a gun. These values were obtained by measuring the ratio of the forbidden companions of the He I 4471 and He I 4921-Å lines to their corresponding allowed transitions. The electric fields were also observed by examining the shape of the red wing of the He I 4471-Å and the He II 4686-Å lines. The measured plasma charge density of 7 × 1012/cm3 was too low to account for the broadening. The plasma turbulence was determined to be 3% of the electron thermal energy. The observed damping was compatible with spatial linear Landau damping for a mean wavelength 30 times the Debye wavelength.
Conductivity of an Anisothermal Magnetoplasma from a Convergent Kinetic Equation
Authors: Lai Hon-Ming
Published: February 2004

The convergent classical kinetic equation of Kihara and Aono is used to calculate the collisional part of the ac electrical conductivity of a multispecies, anisothermal magnetoplasma in the long wavelength limit. A two-component plasma result is derived, and it shows that at Te/Ti ≳ 103, the Coulomb logarithmic term is no longer dominant.
Conductivity of a Magnetoplasma from a Quantum Mechanical Convergent Kinetic Equation
Authors: Pytte Agnar , Lai Hon-Ming
Published: February 2004

The quantum-mechanical version of Baldwin's convergent kinetic equation is used to calculate the collisional part of the ac electrical conductivity tensor of a multispecies magnetoplasma to second order in the wave vector. Both dominant (Coulomb logarithm) and subdominant terms are calculated exactly to first order in the plasma parameter. Full account is taken of the heavy ion motion.
Microscopic Theory of Conductivity of a Weakly Ionized Plasma
Authors: Chappell W. R. , Williams R. H.
Published: February 2004

Through the use of the microscopic density functions in μ space the conductivity for a weakly ionized plasma can be expressed in terms of a function describing single particle diffusion in the plasma. This diffusion function or transition probability has been shown to obey a linear Boltzmann equation. As a result the approximate solution of the conductivity problem can be accomplished either by modeling the collision term in the kinetic equation or by a stochastic modeling of the diffusion function itself. The two approaches are seen to be completely equivalent.
Near-Steady Oblique Shock Waves in a Collisionless Plasma
Authors: Olson Lynn M.
Published: February 2004

Waves of small amplitude ε which travel at an oblique angle θ to a magnetic field in a cold collisionless plasma and whose head approaches steadiness are studied. The relevant double limit limlimε→0t→∞is treated in terms of appropriate sets of single limits. Near-steady waves which can lead from one equilibrium to another are shown to be possible only at propagation speeds corresponding to Alfvén Mach number 1 or cosθ. In the first case, either the magnetic pressure at the head of the wave decreases monotonically from its initial value and the wave spreads linearly with time, or else the head of the wave consists of a near-periodic train of cnoidal waves, the first crest of which approaches a soliton. For near-normal shocks, the magnetic pressure in the near-periodic wave train always exceeds its initial equilibrium value. But for M cotθ>1, where M = (m+/m−)1/2−(m−/m+)1/2, it always falls short of that value. A transition with precursor wave is shown to be impossible for a cold collisionless plasma. At an Alfvén Mach number cosθ, the only near-steady solution consists of a main wave front followed by an oscillatory tail; on the length scale considered, the electric field transverse to the propagation direction oscillates without bound at the tail.
Cooperative Enhanced Scattering from Nonthermal Theta-Pinch Plasmas
Authors: Stainer Howard M.
Published: February 2004

The conditions under which enhanced scattering of far-infrared laser radiation (337 to 119 μ) can be obtained from theta-pinch plasmas are investigated. The enhanced scattering cross-section results from above-thermal electron density fluctuations that can be produced only by nonthermal electrons in the plasma. The scattering cross section is derived for a plasma in a weak magnetic field (Ωc2≪ωp2) and “rigid rotor” distributions modeling the specific theta pinch plasma are used to calculate the actual cross section. The conditions under which this cross section can become greatly enhanced are then examined. Finally, various types of bremsstrahlung (free-free, magnetic, and nonmagnetic wave-wave) are compared with the scattered power. For typical laser power densities (10 W/cm2, the plasma must be considerably nonthermal for the scattered power to be dominant.
Plasma Capacitor in a Magnetic Field
Authors: Peratt A. L. , Kuehl H. H.
Published: February 2004

Expressions for the electric field and impedance of a planar capacitor containing a warm inhomogeneous magnetized plasma are derived using the electrostatic approximation. The frequency of the excitation field is near and below the second electron cyclotron harmonic while the static magnetic field is parallel to the capacitor plates. The theory, which includes wave coupling and plasma nonuniformity as well as the effects of the ambipolar electric field and the anisotropy of the unperturbed distribution function, shows that the impedance exhibits a resonant structure due to longitudinal waves confined between the two hybrid resonance points. Measurements are taken during the afterglow of a pulsed, low-pressure, argon plasma confined between planar glass walls. These measurements are found to be in good agreement with the theoretical model.
Magnetic Guarding of Octupole Hoop Supports
Authors: Molvik Arthur W.
Published: February 2004

Magnetic guarding of hoop supports and other obstacles in the Wisconsin octupole reduced the direct loss of plasma to the supports or obstacles by more than an order of magnitude. However, an increased loss rate to the walls and hoops locally around a support offset the reduction in direct loss. Theoretical models based on ion scattering or collective effects were consistent with the magnitude of the increased wall (hoop) loss rate with guarding. But, only the models based on collective effects or associated with the lack of symmetry between each support and the octupole magnetic field were reasonably consistent with the observed scaling of the loss rate with ion temperature and magnetic field.
End Effect in Langmuir Probe Response under Ionospheric Satellite Conditions
Authors: Sanmartin Juan R.
Published: February 2004

A theory is presented for an end effect in the current response of a highly negative, cylindrical Langmuir probe in a collisionless plasma flow. Under conditions where the ratio of probe radius to Debye length is small and the ion-acoustic Mach number is large, the current exhibits a strong peak when the probe axis is brought into alignment with the flow direction. Closed formulas are given for the maximum and angular half-width of the peak, and universal graphical results are presented for the entire peak structure. The theory shows very good agreement with experimental data. The use of the end effect for diagnostic purposes, in particular, for the determination of the ion temperature, is discussed.
Steady Wakes behind Oblate Spheroids: Flow Visualization
Authors: Masliyah Jacob H.
Published: February 2004

Recirculating wakes behind a sphere and three oblate spheroids were photographed for Reynolds numbers from R = 15 to R = 100. The variation with R of the dimensionless wake length for spheroids and the angle of separation for the sphere are compared with existing experimental and numerical results.
Some Electromagnetic Plasma Simulation Methods and Their Noise Properties
Authors: Langdon A. Bruce
Published: February 2004

Several algorithms for incorporating the electromagnetic radiation fields into the numerical simulation of plasmas are examined to clarify their close relations to each other and to explain their relative rates of generation of unwanted radiation field noise.
Ion-Enhanced Diffusion in Quasistable Drift Waves
Authors: Ching Hugh
Published: February 2004

An improved quasilinear theory of drift waves is shown to be capable of accounting for the existence of finite, ion-enhanced diffusion even when the waves are stable and collisions are absent.
Finite Beta Stabilization of the Drift-Cone Instability
Authors: Tang W. M. , Pearlstein L. D. , Berk H. L.
Published: February 2004

An analytic expression giving the drift-cone stability criterion of a finite-beta plasma is derived using a mirror-ratio-dependent loss-cone ion distribution. This is used to determine a beta limit for stability which is found to be insensitive to changes in mirror ratio and plasma temperature.
Instability of Magnetosonic Waves in a Reacting Thermonuclear Plasma
Authors: Tidman D. A.
Published: February 2004

The instability of magnetosonic waves in a reacting thermonuclear plasma is discussed and their growth rate is calculated.
Hot-Electron Equilibrium in the Canted Mirror
Authors: Guest G. E. , Hedrick C. L. , Hogan J. T.
Published: February 2004

A method for determining the distribution function of a high-β hot-electron plasma confined in a canted mirror magnetic trap is discussed and the method is applied to one experimental example.
Depolarization of Singly Scattered Radiation in a Turbulent Plasma
Authors: Halseth M. W. , Sivaprasad K.
Published: February 2004

Single scattering in a weakly inhomogeneous turbulent plasma is examined for angles of incidence greater than the critical angle of the medium. A possible mode for depolarization of backscattered radiation is discussed with the help of the radiative transport equation.
Turbulent Heating and Resistivity in Cool-Electron θ-Pinches
Authors: Krall Nicholas A. , Liewer Paulett C.
Published: February 2004

The turbulent behavior observed in several cool electron (Te≲Ti) experiments is explained by intermediate-frequency, long-wavelength modified two-stream and drift instabilities.
Existence of Variational Principles for the Navier-Stokes Equation
Authors: Finlayson Bruce A.
Published: February 2004

Fréchet differentials are introduced to decide when a classical variational principle exists for a given nonlinear differential equation. The formalism is applied to the steady-state Navier-Stokes equation and the continuity equation, and no variational principle exists unless u × (∇ × u) = 0 or u· ∇u = 0. The concept of an adjoint equation is extended to nonlinear equations and a variational principle is derived for the Navier-Stokes equation and its adjoint.
Use of Streaming Potential Measurements for an Investigation of the Coanda Effect
Authors: Turpin Jim L.
Published: February 2004

The streaming potential technique was adapted for an investigation of the Coanda effect. The attachment distances for two-dimensional submerged, incompressible jets were determined as a function of wall angle and offset. This was done by embedding platinum electrodes in a movable sidewall of a flow model, and determining the electrode pair which exhibited the maximum rms streaming potential fluctuation. Experimentally determined attachment points are presented graphically as a function of wall offset with wall angle as a parameter. It was found that the attachment distance is independent of the nozzle Reynolds number.
Laminar Flow Past a Circle in a Shear Flow
Authors: Jordan Stanley K. , Fromm Jacob E.
Published: February 2004

A numerical solution of the equations governing time-dependent, viscous, incompressible fluid flow past a circle is presented for Reynolds number 400. The free-stream velocity profile corresponds to the time-averaged flow of a turbulent jet. The location and strength of the jet are adjusted so that the free stream approximates a linear shear flow in the vicinity of the circle. The asymmetry of the free stream causes a shift of the upstream stagnation streamline (the Pitot-tube displacement effect) and small biases in the lift and torque exerted upon the circle. This lift bias is suggested as a contributing factor in the observed stability of raindrops in vertical wind tunnels. Contour plots of the vorticity and stream function are compared with histories of the pressure distribution, drag, lift, torque, and separation angles. These comparisons show how the asymmetry of the free stream manifests itself in terms of fine details within the flow pattern around the circle.
Effects of Couple Stresses on the Stability of Plane Poiseuille Flow
Authors: Jain Jai Kumar , Stokes Vijay Kumar
Published: February 2004

The effects of couple stresses in fluids on the hydrodynamic stability of plane Poiseuille flow have been considered based on the model for fluids proposed by Stokes. Numerical solutions to the problem have been obtained by using an initial-value technique. It has been shown that the critical Reynolds number first decreases and then increases with the increase in couple stresses. The effects of couple stresses on the different flow parameters, which describe the disturbances, have also been determined.
Statistical Characteristics of Reynolds Stress in a Turbulent Boundary Layer
Authors: Gupta A. K. , Kaplan R. E.
Published: February 2004

The first four moments of the Reynolds stress fluctuations uυ(t), and of velocity components u(t) and υ(t) were computed using digital data processing techniques. The results show that over a moderate range of Reynolds number 1900<Reθ<6500 (based on momentum thickness) Reynolds stress fluctuations are intermittent and strongly skewed, while the u and υ fluctuation components separately are not.
“Backward Diffusion” in Turbulent Flow
Authors: Corrsin S.
Published: February 2004

For homogeneous, unsheared, stationary turbulence, it is shown that the dispersion of starting position x0 (at t = 0) for an ensemble of material points which arrive at position x at time t is equal to the dispersion of material points starting at position x, in the same time interval. The question is inspected in both Lagrangian and Eulerian frames.
Use of the Scattering Kernel Approach in Certain Gas Kinetic Problems
Authors: Whipple E. C.
Published: February 2004

The collision gain term of the Boltzmann equation may at times be transformed to a triple integral over the product of the unknown distribution and a scattering kernel in the case of a minor constituent interacting through collisions with a major constituent (scatterer). If isotropy in velocity space may be assumed, the term may be further reduced to an integral over the particle speed. The scattering kernel for hard-sphere collisions has been used in neutron slowing down and thermalization problems, but this approach does not seem to have been used widely in other gas kinetic applications. The transformation is discussed and cast in a form that is applicable to collision models other than hard-sphere scattering and to arbitrary velocity distributions of the scatterers. Kernels are obtained for isotropic constant mean-free-time scattering, and it is shown that kernels for monoenergetic velocity distributions of the scatterers are useful as well as those for Maxwellian and stationary distributions. Use of the scattering kernel approach is illustrated by finding the steady-state velocity distribution of excited atoms that are being produced at a steady rate and that are losing kinetic energy via collisions and their excitation energy by radiation. The solution for Maxwellian scatterers is well approximated at high velocities by the solution for stationary scatterers, and at low velocities by the solution for monoenergetic scatterers.
Thermal Force on Spherical Particles in a Rarefied Gas
Authors: Phillips Warren F.
Published: February 2004

A theoretical analysis is presented for the thermal force exerted on a spherical particle between two flat plates. The case is considered where the Knudsen number KL, based on the plate spacing, is nonzero. The analysis is based on the assumption that the particle radius is much smaller than the plate spacing and the result is valid for all values of KL from zero to infinity. A moment solution to the Boltzmann equation coupled with a two-stream Chapman-Enskog distribution function is employed, and the collision integral is evaluated on the basis of Maxwell molecules.
Space-Charge Dynamics of Liquids
Authors: Zahn Markus , Melcher James R.
Published: February 2004

The propagation and instability characteristics of small-signal electro-fluid-mechanical space-charge and polarization waves in nonhomogeneous fluids are developed. Stratified equilibrium configurations with fluid properties and space-charge density constant within planar, cylindrical, and spherical surfaces, are emphasized. Equilibrium electric fields due both to charges in the fluid and to externally imposed potentials are normal to these surfaces. The liquid is modeled as incompressible, inviscid, and perfectly insulating, with domains of sufficiently high frequency or growth rate to validate the last assumption defined in terms of electrical conductivity or mobility. A general set of relations for perturbation field and flow variables on the perturbed surfaces of fluid layers having constant properties and space charge are derived in each of the configurations. A detailed description of wave dispersion and instability for interactions in the following situations exemplifies how these relations are used in representing a broad class of discretely stratified equilibria: (a) perfectly conducting interface stressed by normal field and bounded from above by fluid supporting uniform space charge; (b) two planar layers of differing properties and space charge; (c) uniformly charged liquid jet; and (d) uniformly charged liquid drop.
Small Disturbance Stability of Plane Poiseuille Flow of Oldroyd Fluid
Authors: Kundu Pijush K.
Published: February 2004

The stability to small disturbances of a plane Poiseuille flow of a viscoelastic liquid has been investigated. The constitutive equation used is that proposed by Oldroyd, which has relaxation times of stress as well as of strain rate. The presence of elasticity has been found to destabilize the flow.