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Your search keyword '"Edlund, E. M."' showing total 11 results
Start Over Author "Edlund, E. M." Publication Year Range Last 10 years
11 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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9. 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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