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Your search keyword '"Edlund, E. M."' showing total 28 results
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28 results on '"Edlund, E. M."'

1. Reynolds number scaling of influence of boundary layers on the global behavior of laboratory quasi-Keplerian flows

Author

Edlund, E. M. and Ji, H.

Subjects
Physics - Fluid Dynamics, Astrophysics - Instrumentation and Methods for Astrophysics
Abstract

We present measurements of quasi-Keplerian flows in a Taylor-Couette device that identify the boundary conditions required to generate near-ideal flows that exhibit self-similarity under scaling of the Reynolds number. These experiments are contrasted with alternate boundary configurations that result in flows that progressively deviate from ideal Couette rotation as the Reynolds number is increased. These behaviors are quantitatively explained in terms of the tendency to generate global Ekman circulation and the balance of angular momentum fluxes through the axial and radial boundary layers.

Published
2014
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2. Localized phase contrast imaging at the Wendelstein 7-X stellarator.

Author

Hansen, S. K., Porkolab, M., Bähner, J.-P., Stechow, A. von, Grulke, O., and Edlund, E. M.

Subjects
PLASMA confinement, ELECTRON density, PLASMA waves, FOCAL planes, PLASMA density
Abstract

In its basic form, phase contrast imaging (PCI) provides line-integrated measurements of electron density fluctuations in plasmas. As turbulent fluctuations in magnetically confined plasmas have wave vectors almost perpendicular to the background magnetic field, the signals scattered by fluctuations from different parts of the PCI line-of-sight (LoS) are spatially separated in focal planes of the plasma. This allows localized PCI measurements by placing a mask in such a plane, to only permit signals from specific parts of the LoS to reach the PCI detectors. The present paper describes modeling and design of localization masks for the PCI system at the Wendelstein 7-X (W7-X) stellarator as well as the first results obtained using the masks in the recent long-pulse W7-X experimental campaign. During this project, we have extended the theory describing the mask response within the Fraunhofer diffraction model. As a novel development, we show from first principles that the mask response is determined by the fraction of power of the scattered beam spots that passes the mask. These insights have been used to select the W7-X mask design, consisting of a circular cutout, allowing the unscattered beam spot to pass the mask, with wedges covering a fixed angular range outside the central cutout. In the recent W7-X experimental campaign, the masks have verified the location of the main turbulence features observed by the PCI system and provided new information about the location of short-wavelength magnetohydrodynamic modes. [ABSTRACT FROM AUTHOR]

Published
2024
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3. Energetic particle instabilities in fusion plasmas

Author

Sharapov, S E, Alper, B, Berk, H L, Borba, D N, Breizman, B N, Challis, C D, Classen, I G J, Edlund, E M, Eriksson, J, Fasoli, A, Fredrickson, E D, Fu, G Y, Garcia-Munoz, M, Gassner, T, Ghantous, K, Goloborodko, V, Gorelenkov, N N, Gryaznevich, M P, Hacquin, S, Heidbrink, W W, Hellesen, C, Kiptily, V G, Kramer, G J, Lauber, P, Lilley, M K, Lisak, M, Nabais, F, Nazikian, R, Nyqvist, R, Osakabe, M, von Thun, C Perez, Pinches, S D, Podesta, M, Porkolab, M, Shinohara, K, Schoepf, K, Todo, Y, Toi, K, Van Zeeland, M A, Voitsekhovich, I, White, R B, Yavorskij, V, TG, ITPA EP, and Contributors, JET-EFDA

Subjects
Physics - Plasma Physics
Abstract

Remarkable progress has been made in diagnosing energetic particle instabilities on present-day machines and in establishing a theoretical framework for describing them. This overview describes the much improved diagnostics of Alfven instabilities and modelling tools developed world-wide, and discusses progress in interpreting the observed phenomena. A multi-machine comparison is presented giving information on the performance of both diagnostics and modelling tools for different plasma conditions outlining expectations for ITER based on our present knowledge., Comment: 37 pages, 20 figures

Published
2013
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12. Nonlinear gyrokinetic simulations of the I-mode high confinement regime and comparisons with experimenta)

Author

White, A. E., primary, Howard, N. T., additional, Creely, A. J., additional, Chilenski, M. A., additional, Greenwald, M., additional, Hubbard, A. E., additional, Hughes, J. W., additional, Marmar, E., additional, Rice, J. E., additional, Sierchio, J. M., additional, Sung, C., additional, Walk, J. R., additional, Whyte, D. G., additional, Mikkelsen, D. R., additional, Edlund, E. M., additional, Kung, C., additional, Holland, C., additional, Candy, J., additional, Petty, C. C., additional, Reinke, M. L., additional, and Theiler, C., additional

Published
2015
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22. Diagnostic Systems on Alcator C-Mod

Author

Basse, N. P., primary, Dominguez, A., additional, Edlund, E. M., additional, Fiore, C. L., additional, Granetz, R. S., additional, Hubbard, A. E., additional, Hughes, J. W., additional, Hutchinson, I. H., additional, Irby, J. H., additional, LaBombard, B., additional, Lin, L., additional, Lin, Y., additional, Lipschultz, B., additional, Liptac, J. E., additional, Marmar, E. S., additional, Mossessian, D. A., additional, Parker, R. R., additional, Porkolab, M., additional, Rice, J. E., additional, Snipes, J. A., additional, Tang, V., additional, Terry, J. L., additional, Wolfe, S. M., additional, Wukitch, S. J., additional, Zhurovich, K., additional, Bravenec, R. V., additional, Phillips, P. E., additional, Rowan, W. L., additional, Kramer, G. J., additional, Schilling, G., additional, Scott, S. D., additional, and Zweben, S. J., additional

Published
2007
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24. Characterization of core and edge turbulence in L- and enhanced Dα H-mode Alcator C-Mod plasmas

Author

Basse, N. P., primary, Edlund, E. M., additional, Ernst, D. R., additional, Fiore, C. L., additional, Greenwald, M. J., additional, Hubbard, A. E., additional, Hughes, J. W., additional, Irby, J. H., additional, Lin, L., additional, Lin, Y., additional, Marmar, E. S., additional, Mossessian, D. A., additional, Porkolab, M., additional, Rice, J. E., additional, Snipes, J. A., additional, Stillerman, J. A., additional, Terry, J. L., additional, Wolfe, S. M., additional, Wukitch, S. J., additional, Zhurovich, K., additional, Kramer, G. J., additional, and Mikkelsen, D. R., additional

Published
2005
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25. Measurements of Mode Converted Ion Cyclotron Wave with Phase Contrast Imaging in Alcator C-Mod and Comparisons with Synthetic PCI Simulations in TORIC.

Author

Tsujii, N., Porkolab, M., Edlund, E. M., Lin, L., Lin, Y., Wright, J. C., and Wukitch, S. J.

Subjects
ION cyclotron resonance spectrometry, ELECTRON beams, ELECTROMAGNETIC waves, PHYSICAL measurements, LASER beams
Abstract

Mode converted ion cyclotron wave (ICW) has been observed with phase contrast imaging (PCI) in D-3He plasmas in Alcator C-Mod [1, 2]. The measurements were carried out with the optical heterodyne technique using acousto-optic modulators which modulate the CO2 laser beam intensity near the ion cyclotron frequency [3]. With recently improved calibration of the PCI system using a calibrated sound wave source, the measurements have been compared with the full-wave code TORIC, as interpreted by a synthetic diagnostic. Because of the line-integrated nature of the PCI signal, the predictions are sensitive to the exact wave field pattern. The simulations are found to be in qualitative agreement with the measurements. [ABSTRACT FROM AUTHOR]

Published
2009
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26. Free magnetohydrodynamic shear layers in the presence of rotation and magnetic field.

Author

Spence, E. J., Roach, A. H., Edlund, E. M., Sloboda, P., and Ji, H.

Subjects
MAGNETOHYDRODYNAMICS, SHEAR flow, ROTATIONAL motion, MAGNETIC fields, HYDRODYNAMICS, STABILITY (Mechanics), COMPUTER simulation
Abstract

We present an experimental and numerical study of hydrodynamic and magnetohydrodynamic free shear layers and their stability. We first examine the experimental measurement of globally unstable hydrodynamic shear layers in the presence of rotation and their range of instability. These are compared to numerical simulations, which are used to explain the modification of the shear layer, and thus the critical Rossby number for stability. Magnetic fields are then applied to these scenarios and globally unstable magnetohydrodynamic shear layers generated. These too are compared to numerical simulations showing behavior consistent with the hydrodynamic case and previously reported measurements. [ABSTRACT FROM AUTHOR]

Published
2012
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27. Characterization of core and edge turbulence in L- and enhanced Dα H-mode Alcator C-Mod plasmas.

Author

Basse, N. P., Edlund, E. M., Ernst, D. R., Fiore, C. L., Greenwald, M. J., Hubbard, A. E., Hughes, J. W., Irby, J. H., Lin, L., Lin, Y., Marmar, E. S., Mossessian, D. A., Porkolab, M., Rice, J. E., Snipes, J. A., Stillerman, J. A., Terry, J. L., Wolfe, S. M., Wukitch, S. J., and Zhurovich, K.

Subjects
*PLASMA gases, *TURBULENCE, *MAGNETIC fields, *MAGNETICS, *PARTICLES (Nuclear physics), *FLUID dynamics
Abstract

The recently upgraded phase-contrast imaging (PCI) diagnostic is used to characterize the transition from the low (L) to the enhanced Dα (EDA) high (H) confinement mode in Alcator C-Mod [I. H. Hutchinson, R. Boivin, F. Bombarda et al., Phys. Plasmas 1, 1511 (1994)] plasmas. PCI yields information on line integrated density fluctuations along vertical chords. The number of channels has been increased from 12 to 32 and the sampling rate from 1 MHz to 10 MHz. This expansion of diagnostic capabilities is used to study broadband turbulence in L and EDA H mode and to analyze the quasicoherent (QC) mode associated with EDA H mode. Changes in broadband turbulence at the transition from L to EDA H mode can be interpreted as an effect of the Doppler rotation of the bulk plasma. Additional fluctuation measurements of Dα light and the poloidal magnetic field show features correlated with PCI in two different frequency ranges at the transition. The backtransition from EDA H to L mode, the so-called enhanced neutron (EN) mode, is investigated by new high frequency (132 and 140 GHz) reflectometer channels operating in the ordinary (O) mode. This additional hardware has been installed in an effort to study localized turbulence associated with internal transport barriers (ITBs). The EN mode is a suitable candidate for this study, since an ITB exists transiently as the outer density decreases much faster than the core density in this mode. The fact that the density decays from the outside inward allows us to study fluctuations progressing towards the plasma core. Our results mark the first localized observation of the QC mode at medium density: 2.2×1020 m-3 (132 GHz). Correlating the reflectometry measurements with other fluctuating quantities provides some insight regarding the causality of the EN-mode development. [ABSTRACT FROM AUTHOR]

Published
2005
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