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in subjects: "Fluctuations"

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The interpretation of reflectometry measurements of plasma fluctuations

Wave reflections from density fluctuations with magnitudes and frequencies typical of drift waves have been investigated. Both drift waves and the reflected phase and amplitude depend on the density gradient scale length, and this common feature implies that both the angular deviation of a normally propagating wave and the phase change on reflection are of order unity. Thus the surface will always appear rough'' and amplitude variations will always be large. For smaller amplitude waves numerica… more

Date: October 1, 1991

Creator: Bretz, N.

Item Type: Report

Partner: UNT Libraries Government Documents Department

open access

Application of optical fluctuation diagnostics to transport studies in high temperature tokamak plasmas

First data was obtained from the TFTR BES system in May 1990, after the prototype 4-channel system with photomultiplier detectors from PBX-M was transferred to the TFTR Hot Cell. The system was expanded to 16 spatial channels during the Summer 1990 run period, and data of interest was obtained near the end of the run in October 1990. The most attention has been given to a radial profile data set obtained for an L-mode plasma condition in TFTR, where we characterized the nature of the long-wavel… more

Date: January 1, 1991

Creator: Fonck, R.J.

Item Type: Report

Partner: UNT Libraries Government Documents Department

open access

Statistical fluctuations in heavy-ion collisions

The relevance of the statistical equilibrium limit to the description of substantially relaxed degrees of freedom is discussed. Fluctuations are considered specifically in the following processes: the correlation between entrance-channel angular momentum and exit-channel kinetic energy; the sharing of the dissipated kinetic energy between the two fragments; the magnitude and the alignment of the fragment angular momentum including the effect of shell structure. It is found that statistical fluc… more

Date: February 1, 1982

Creator: Moretto, Luciano G.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Torque ripple in a Darrieus, vertical axis wind turbine

Interaction between a steady wind and a rotating, Darrieus, vertical axis wind turbine produces time periodic aerodynamic loads which cause time dependent torque variations, referred to as torque ripple, to occur in the mechanical link between the turbine and the electrical generator. There is concern for the effect of torque ripple upon fatigue life of drive train components and upon power quality. An analytical solution characterizing the phenomenon of torque ripple has been obtained which is… more

Date: January 1, 1980

Creator: Reuter, R.C. Jr.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Pseudorapidity densities and fluctuations in central sup 32 S interactions at 200A GeV

Observations of heavy ion interactions at the highest available accelerator energies provide essential information for the analysis and interpretation of cosmic ray interactions. We report on an experiment in which emulsion chamber detectors were exposed to beams of 200A GeV {sup 32}S ions at the CERN SPS. We present statistical features of pseudorapidity distributions from central collisions in the experimental sample and compare them with the predictions from the Lund Model (FRITIOF) which co… more

Date: January 1, 1990

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Electrostatic turbulence and transport in the RFP edge

This thesis details measurements of electrostatic turbulence and transport in the Madison Symmetric Torus reversed field pinch. The electrostatic fluctuation levels are found to be large, with {tilde n}{sub e}/n{sub e} {approximately} 30%--55% and {tilde T}{sub e}/T{sub e} {approximately} 15%--40%. The frequency and wavenumber spectra are broad, with {Delta}n {approximately} 70--150 and {Delta}m {approximately} 3--6, and differ from measured magnetic fluctuation spectra. The transport inferred … more

Date: May 1, 1992

Creator: Spragins, C.W.

Item Type: Report

Partner: UNT Libraries Government Documents Department

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The structure of perturbative quantum gravity on a de Sitter background

Classical gravitation on de Sitter space suffers from a linearization instability. One consequence is that the response to a spatially localized distribution of positive energy cannot be globally regular. We use this fact to show that no causal Green's function can give the correct linearized response to certain bilocalized distributions, even though these distributions obey the constraints of linearization stability. We avoid the problem by working on the open submanifold spanned by conformal … more

Date: May 1, 1992

Creator: Tsamis, N. C. & Woodward, R. P.

Item Type: Report

Partner: UNT Libraries Government Documents Department

open access

Vortices associated with toroidal ion temperature gradient driven fluctuations

The three nonlinear hydrodynamic equations for potential, parallel ion velocity and ion pressure used in simulations of the toroidal ion temperature gradient driven fluctuations and transport in a shear magnetic field are analyzed for coherent vortex structures. Two types of vortex structures are found: one type for weak shear that is a generalization of the usual modon vortex construction and the second type of solution for strong magnetic shear where the convective nonlinearity in the paralle… more

Date: May 1, 1992

Creator: Horton, W. (Texas Univ., Austin, TX (United States). Inst. for Fusion Studies); Jovanovic, D. (Belgrade Univ. (Yugoslavia). Inst. za Fiziku) & Rasmussen, J.J. (Association Euratom-Risoe National Lab., Roskilde (Denmark))

Item Type: Report

Partner: UNT Libraries Government Documents Department

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Static and dynamic spin fluctuations in the spin glass doping regime in La sub 2-x Sr sub x CuO sub 4+y

We review the results of neutron scattering studies of the static and dynamic spin fluctuations crystals of La{sub 2-x}Sr{sub x}CuO{sub 4+{delta}} in the doping regime intermediate between the Neel and superconducting regions. In this regime the in-plane resistance is linear in temperature down to {approximately}80 K with a crossover due to logarithmic conductance effects at lower temperatures. The static spin correlations are well-described by a simple model in which the inverse correlation le… more

Date: January 1, 1991

Creator: Birgeneau, R.J.; Belk, N.; Kastner, M.A.; Keimer, B. (Massachusetts Inst. of Tech., Cambridge, MA (United States). Dept. of Physics); Endoh, Y. (Tohoku Univ., Sendai (Japan). Dept. of Physics); Erwin, R.W. (National Inst. of Standards and Technology, Gaithersburg, MD (United States)) et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Security assessment of power systems including energy storage and with the integration of wind energy. Progress report, October 1, 1979-December 31, 1979

Progress in wind energy studies is reported. During this quarter two areas were pursued: wind turbulence models and their effect on unsteady shaft torque of horizontal machines; and reduced order aerodynamic models of wind machines. (LCL)

Date: January 1, 1980

Creator: Carroll, D P & Krause, P C

Item Type: Report

Partner: UNT Libraries Government Documents Department

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Microstructural evolution in fast-neutron-irradiated austenitic stainless steels

The present work has focused on the specific problem of fast-neutron-induced radiation damage to austenitic stainless steels. These steels are used as structural materials in current fast fission reactors and are proposed for use in future fusion reactors. Two primary components of the radiation damage are atomic displacements (in units of displacements per atom, or dpa) and the generation of helium by nuclear transmutation reactions. The radiation environment can be characterized by the ratio … more

Date: December 1, 1987

Creator: Stoller, R.E.

Item Type: Report

Partner: UNT Libraries Government Documents Department

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Interaction of bootstrap-current-driven magnetic islands

The formation and interaction of fluctuating neoclassical pressure gradient driven magnetic islands is examined. The interaction of magnetic islands produces a stochastic region around the separatrices of the islands. This interaction causes the island pressure profile to be broadened, reducing the island bootstrap current and drive for the magnetic island. A model is presented that describes the magnetic topology as a bath of interacting magnetic islands with low to medium poloidal mode number… more

Date: October 1, 1991

Creator: Hegna, C. C. & Callen, J. D.

Item Type: Report

Partner: UNT Libraries Government Documents Department

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Phase space distribution of particles near an isolated difference resonance

We have studied the phase space distribution of beam particles near an isolated difference resonance. The numerical simulation has shown that the distribution can quickly settle down to a final state if its initial state is Gaussian. The final state can be treated as a stationary state as long as the high order fluctuation can be neglected. From the Liouville equation, the emittances of beam particles are calculated approximately. There is a good agreement between analytical and numerical resul… more

Date: January 1, 1991

Creator: Shi, Jicong; Huang, Yunxiang & Ohnuma, Shoroku.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Effects of shear on vortex shedding patterns in high Reynolds number flow: an experimental study

Vortex shedding has been identified as a potential major source of loading on the Ocean Thermal Energy Conversion (OTEC) Plant Cold Water Pipe (CWP). To gain a better understanding of the vortex shedding phenomena, a series of model tests has been conducted. The results of this investigation are presented. The effects of current shear on vortex shedding patterns in high Reynolds number (R/sub e/) flow around a circular cylinder used to model the OTEC CWP are addressed. Tests were conducted in a… more

Date: unknown

Item Type: Report

Partner: UNT Libraries Government Documents Department

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Role of rotational degrees of freedom in heavy-ion collisions

The degrees of freedom affected by the angular momentum are identified. The relevance of the equilibrium fluctuations in a diffusive evolution of the system is discussed. The statistical limit is described and chosen as a reference for comparing with experiment. The rigid rotation regime is shown to be reached in a variety of reactions. The fragment spin alignment is measured from ..gamma..-ray multiplicities and anisotropies as well as from sequential fission angular distributions. Good agreem… more

Date: April 1, 1982

Creator: Moretto, Luciano G.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Thermal and quantal isospin and spin fluctuations in heavy ion reactions

The isobaric charge distributions are discussed in terms of quantal and classical isospin fluctuations. The roles of mass asymmetry and of the higher giant isovector modes are treated within the framework of a cylinder model that is worked out exactly. Spin fluctuations are considered first in terms of quantal fluctuations in a cylinder model and second in terms of thermal fluctuations in a two-sphere model. The results are applied to the calculation of in- and out-of-plane angular distribution… more

Date: January 1, 1980

Creator: Moretto, Luciano G.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Edge gradient and safety factor effects on electrostatic turbulent transport in tokamaks

Electrostatic turbulence and transport measurements are performed on the Tokapole-II tokamak at the University of Wisconsin-Madison, as the safety-factor and the edge equilibrium gradients and varied substantially. Tokapole-II is a poloidal divertor tokamak capable of operating at a wide range of safety factors due to its unique magnetic limiter configuration. It also has retractable material limiters in a large scrape-off region, which permits the study of edge boundary conditions like density… more

Date: May 1, 1992

Creator: Tan, Ing Hwie.

Item Type: Report

Partner: UNT Libraries Government Documents Department

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MHD computation of feedback of resistive-shell instabilities in the reversed field pinch

MHD computation demonstrates that feedback can sustain reversal and reduce loop voltage in resistive-shell reversed field pinch (RFP) plasmas. Edge feedback on {approximately}2R/a tearing modes resonant near axis is found to restore plasma parameters to nearly their levels with a close-fitting conducting shell. When original dynamo modes are stabilized, neighboring tearing modes grow to maintain the RFP dynamo more efficiently. This suggests that experimentally observed limits on RFP pulselengt… more

Date: May 1, 1992

Creator: Zita, E.J.; Prager, S.C. (Wisconsin Univ., Madison, WI (United States). Plasma Physics Research); Ho, Y.L. & Schnack, D.D (Science Applications International Corp., San Diego, CA (United States))

Item Type: Report

Partner: UNT Libraries Government Documents Department

open access

On the causes of compositional order in the Ni sub c Pt sub (1-c) alloys

We review, briefly, the arguments which gave rise to the current controversy concerning the origin of compositional order in Ni{sub c}Pt{sub 1-c} alloys. We note that strain fluctuations play an important role in determining the state of compositional order in this system and outline a theoretical framework that takes account of them. 29 refs., 4 figs.

Date: January 1, 1991

Creator: Gyorffy, B.L. (Bristol Univ. (United Kingdom). H.H. Wills Physics Lab.); Pinski, F.J. (Cincinnati Univ., OH (United States). Dept. of Physics); Ginatempo, B. (Messina Univ. (Italy). Ist. di Fisica Teorica); Johnson, D.D. (Sandia National Labs., Albuquerque, NM (United States)); Staunton, J.B. (Warwick Univ., Coventry (United Kingdom). Dept. of Physics); Shelton, W.A. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Overview of recent results from the Advanced Toroidal Facility

An overview of recent experimental results from the Advanced Toroidal Facility (ATF) is presented. Beam-heated plasmas with {bar n}{sub e} of 10{sup 20} m{sup {minus}3} and {tau}{sub E}{asterisk} of {approx}20 ms have been achieved. Thermal collapse of the plasmas is mitigated by wall conditioning and particle fueling. Confinement time scales positively with density and magnetic field, offsetting deterioration with power. Results fit the LHD scaling and the drift wave turbulence scaling. Bootst… more

Date: January 1, 1989

Creator: Anabitarte, E.; Hidalgo-Vera, C. (Centro de Investigaciones Energeticas, Medioambientales y Tecnologicas, Madrid (Spain)); Anderson, F. S. B. (Wisconsin Univ., Madison, WI (USA)); Bell, G. L.; Gandy, R. F. (Auburn Univ., AL (USA)); Bell, J. D. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Longitudinal spin fluctuations in nickel

The longitudinal and transverse spin fluctuations in Ni have been measured below {Tc} by means of polarized neutron scattering in the momentum range 0.06 < q < 0.18 {angstrom}{sup -1}. In transverse scans spin wave peaks at E{sub q} = Dq{sup 2} appear as expected from early measurements performed with unpolarized neutrons. The longitudinal magnetic scattering {sub {chi}L}(q, E), on the other hand, is quasielastic without any signature of inelastic peaks near E{sub q}. The q and T dependences of… more

Date: October 10, 1989

Creator: Boeni, P.; Martinez, J. L. & Tranquada, J. M.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Fast wave current drive: Experimental status and reactor prospects

The fast wave is one of the two possible wave polarizations which propagate according to the basic theory of cold plasmas. It is distinguished from the other (slow wave) branch by having an electric field vector which is mainly orthogonal to the confining magnetic field of the plasma. The plasma and fast wave qualitatively assume different behavior depending on the frequency range of the launched wave. The high frequency fast wave (HFFW), with a frequency (..omega..2..pi.. )approximately) GHz) … more

Date: March 1, 1988

Creator: Ehst, D.A.

Item Type: Report

Partner: UNT Libraries Government Documents Department

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The fast simulation of electromagnetic and hadronic showers

A program for the fast simulation of electromagnetic and hadronic showers using parameterizations for the longitudinal and lateral profile is described. The fluctuations and correlations of the parameters are taken into account in a consistent way. Comparisons with data over a wide energy range are made. 15 refs., 17 figs.

Date: October 1, 1989

Creator: Grindhammer, G.; Rudowicz, M.; Peters, S. (Stanford Linear Accelerator Center, Menlo Park, CA (USA) & Max-Planck-Institut fuer Physik und Astrophysik, Muenchen (Germany, F.R.). Werner-Heisenberg-Inst. fuer Physik)

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Low frequency noise in freely suspended tin films at the superconducting transition. [Spectral density]

The spectral density, S/sub v/(f), of the voltage noise across 1-D current-biased tin films has been measured at the superconducting transition. Each film was freely suspended between two thermal clamps a distance L apart in a vacuum can. A thin layer of lead was evaporated on the outer portion of the films to leave an uncoated middle region of length l. S/sub v/(f) was flat at frequencies below f/sub L/ approximately D/L/sup 2/, where D is the thermal diffusivity. At frequencies between f/sub … more

Date: July 1, 1977

Creator: Ketchen, M.B. & Clarke, J.

Item Type: Article

Partner: UNT Libraries Government Documents Department