2026-09-20T10:00:26Zhttps://dspace.mit.edu/server/oai/requestoai:dspace.mit.edu:1721.1/1037222026-06-16T18:53:48Zcom_1721.1_7582com_1721.1_7581col_1721.1_131022
Anne E. White.
Sung, Choongki
Massachusetts Institute of Technology. Department of Nuclear Science and Engineering.
Massachusetts Institute of Technology. Department of Nuclear Science and Engineering
2016-07-18T20:04:06Z
2016-07-18T20:04:06Z
2015
2015
http://hdl.handle.net/1721.1/103722
953415980
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Nuclear Science and Engineering, 2015.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 463-478).
The comprehensive analysis was performed to study turbulent transport in Alcator CMod plasmas in this thesis. A new Correlation Electron Cyclotron Emission (CECE) diagnostic was designed and installed as a part of this thesis work. Using this diagnostic, we measured local T fluctuations in r/a >/~ 0.75 in C-Mod for the first time. This thesis work provided new information about the Ohmic confinement transition, from the linear to the saturated confinement regime with the increase in average density. It was found that Te fluctuations near the edge (r/a0~.85) tend to decrease across the Ohmic confinement transition. Although the Ohmic confinement transition has been considered predominantly as a result of the linear turbulence mode transition, we found no changes in the dominant turbulence mode across this transition via gyrokinetic analysis using the code, GYRO. The GYRO simulations performed near the edge reproduce experimental ion heat flux and Te fluctuations, but electron heat flux was under-predicted. Considering that both ion heat flux and the T fluctuations mainly come from ion scale turbulence, the under-prediction of electron heat flux suggests the importance of electron scale turbulence. Intrinsic rotation reversals in C-Mod plasmas were studied in this thesis. Similar changes in electron temperature fluctuations, the reduction of Te fluctuations near the edge, were observed across RF rotation reversals and Ohmic rotation reversals. The gyrokinetic and self-similarity analyses also showed similarities between rotation reversals in Ohmic and RF heated discharges. These observations suggest that the physics of Ohmic confinement transition and the rotation reversal can be applied to the physics of rotation reversal in RF heated discharges. This thesis also found the reduction of Te fluctuations inside pedestal region with the transition from low to high energy confinement regime, which indicates the changes in core turbulence are correlated with the global energy confinement.
by Choongki Sung.
Ph.D.
478 pages
eng
Massachusetts Institute of Technology
M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.
http://dspace.mit.edu/handle/1721.1/7582
Nuclear Science and Engineering.
Experimental study of turbulent heat transport in Alcator C-Mod
Thesis
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<Abstract>The comprehensive analysis was performed to study turbulent transport in Alcator CMod plasmas in this thesis. A new Correlation Electron Cyclotron Emission (CECE) diagnostic was designed and installed as a part of this thesis work. Using this diagnostic, we measured local T fluctuations in r/a >/~ 0.75 in C-Mod for the first time. This thesis work provided new information about the Ohmic confinement transition, from the linear to the saturated confinement regime with the increase in average density. It was found that Te fluctuations near the edge (r/a0~.85) tend to decrease across the Ohmic confinement transition. Although the Ohmic confinement transition has been considered predominantly as a result of the linear turbulence mode transition, we found no changes in the dominant turbulence mode across this transition via gyrokinetic analysis using the code, GYRO. The GYRO simulations performed near the edge reproduce experimental ion heat flux and Te fluctuations, but electron heat flux was under-predicted. Considering that both ion heat flux and the T fluctuations mainly come from ion scale turbulence, the under-prediction of electron heat flux suggests the importance of electron scale turbulence. Intrinsic rotation reversals in C-Mod plasmas were studied in this thesis. Similar changes in electron temperature fluctuations, the reduction of Te fluctuations near the edge, were observed across RF rotation reversals and Ohmic rotation reversals. The gyrokinetic and self-similarity analyses also showed similarities between rotation reversals in Ohmic and RF heated discharges. These observations suggest that the physics of Ohmic confinement transition and the rotation reversal can be applied to the physics of rotation reversal in RF heated discharges. This thesis also found the reduction of Te fluctuations inside pedestal region with the transition from low to high energy confinement regime, which indicates the changes in core turbulence are correlated with the global energy confinement.</Abstract>
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