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eprslidesmorton.pdf2014-08-15 09:52:20Lucas Morton

Thomson Scattering Measurements of Non-Tearing-Mode Temperature Fluctuations

Author: Lucas A Morton
Requested Type: Poster Only
Submitted: 2014-05-30 09:32:34

Co-authors: D. J. Den Hartog, E. Parke, J.R. Duff, L. Lin

Contact Info:
1150 University Ave
Madison, WI   53706

Abstract Text:
Results of two novel Thomson-scattering-based fluctuation measurements on the MST RFP will be presented. We seek to understand anomalous electron heat transport in the RFP when stochastic magnetic fields are no longer the dominant contributor to transport, such as during improved confinement (PPCD). Previous measurements on MST relied on correlations between the temperature and the edge magnetic signals, demonstrating 15±5 eV temperature fluctuations correlated with the dominant core-resonant tearing mode in 400kA standard plasmas, with similar or smaller amplitudes for other modes as well. By correlating between nearly-simultaneous Thomson scattering electron temperature measurements (made using a tandem laser system), low amplitude plasma electron temperature and density fluctuations can be detected, without reference to the tearing modes. Total fluctuations of up to 35 ± 5 eV are observed in the plasma core during standard MST plasmas. This confirms that activity correlated with tearing modes composes a large share of the electron temperature fluctuations. In PPCD plasmas, the core-resonant tearing modes are known to be reduced by about a factor of three in amplitude, resulting in a corresponding reduction in relative electron temperature fluctuations. Since the equilibrium temperature rises from 350eV in standard plasmas to 1100eV in PPCD (each at 400kA), the absolute fluctuation levels remain similar. Total fluctuations in the core in PPCD are up to 40 ± 20 eV, whereas the tearing-mode correlated fluctuations are up to 30 ± 10 eV. A second novel measurement is the correlation between the Thomson scattering electron temperature and a high-frequency, small-scale density fluctuation detected by the FIR interferometry diagnostic. An upper limit on the FIR-correlated electron temperature fluctuation of 5 eV was found in the edge region where the mode is localized.
*This work supported by the US Department of Energy

Characterization: 4.0

Place with other MST posters.

Workshop on Exploratory Topics in Plasma and Fusion Research (EPR) and US-Japan Compact Torus (CT) Workshop
August 5-8, 2014
Madison, Wisconsin

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