2026-09-20T08:31:44Zhttps://dspace.mit.edu/server/oai/requestoai:dspace.mit.edu:1721.1/1037052022-01-13T07:54:05Zcom_1721.1_7582com_1721.1_7581col_1721.1_131023
Anne E. White.
Kwak, Daniel (Daniel Joowon)
Massachusetts Institute of Technology. Department of Nuclear Science and Engineering.
Massachusetts Institute of Technology. Department of Nuclear Science and Engineering
2016-07-18T20:02:57Z
2016-07-18T20:02:57Z
2015
2015
http://hdl.handle.net/1721.1/103705
953252937
Thesis: S.M., Massachusetts Institute of Technology, Department of Nuclear Science and Engineering, 2015.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 190-193).
Toroidal rotation, important for suppressing various turbulent modes, mitigating MHD instabilities, and preventing locked modes that cause disruptions, may not be sufficiently generated by external devices in larger devices i.e. ITER. One possible solution is intrinsic rotation, self-generated flow without external momentum input, which has been observed in multiple tokamaks. More specifically, rotation reversals, a sudden change in direction of intrinsic rotation without significant change in global plasma parameters, have also been observed and are not yet fully understood. Studying this phenomenon in ohmic L-mode plasmas presents a rich opportunity to gain better understanding of intrinsic rotation and of momentum transport as a whole. The literature presents many different hypotheses, and this thesis explores three in particular. The first two hypotheses each posits a unique parameter as the primary dependency of reversals - the dominant turbulent mode, or the fastest growing turbulent mode(TEM/ITG), and the local density and temperature profile gradients, especially the electron density gradient, respectively. Other studies state that neoclassical effects cause the reversals and one study in particular presents a 1-D analytical model. Utilizing a new data analysis workflow built around GYRO, a gyrokinetic-Maxwell solver, hundreds of intrinsic rotation shots at Alcator C-Mod can be processed and analyzed without constant user management, which is used to test the three hypotheses. By comparing the rotation gradient u', a proxy variable indicative of the core toroidal intrinsic rotation velocity, to the parameters identified by the hypotheses, little correlation has been found between u' and the dominant turbulence regime and the ion temperature, electron temperature, and electron density profile gradients. The plasma remains ITG-dominated based on linear stability analysis regardless of rotation direction and the local profile gradients are not statistically significant in predicting the u'. Additionally, the experimental results in C-Mod and ASDEX Upgrade have shown strong disagreement with the 1 -D neoclassical model. Strong correlation has been found between u' and the effective collisionality Veff. These findings are inconsistent with previous experimental studies and suggest that further work is required to identify other key dependencies and/or uncover the complex physics and mechanisms at play.
by Daniel (Joowon) Kwak
S.M.
193 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.
Investigation of intrinsic rotation dependencies in Alcator C-Mod using a new data analysis workflow
Thesis
application/pdf
Publication
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<Abstract>Toroidal rotation, important for suppressing various turbulent modes, mitigating MHD instabilities, and preventing locked modes that cause disruptions, may not be sufficiently generated by external devices in larger devices i.e. ITER. One possible solution is intrinsic rotation, self-generated flow without external momentum input, which has been observed in multiple tokamaks. More specifically, rotation reversals, a sudden change in direction of intrinsic rotation without significant change in global plasma parameters, have also been observed and are not yet fully understood. Studying this phenomenon in ohmic L-mode plasmas presents a rich opportunity to gain better understanding of intrinsic rotation and of momentum transport as a whole. The literature presents many different hypotheses, and this thesis explores three in particular. The first two hypotheses each posits a unique parameter as the primary dependency of reversals - the dominant turbulent mode, or the fastest growing turbulent mode(TEM/ITG), and the local density and temperature profile gradients, especially the electron density gradient, respectively. Other studies state that neoclassical effects cause the reversals and one study in particular presents a 1-D analytical model. Utilizing a new data analysis workflow built around GYRO, a gyrokinetic-Maxwell solver, hundreds of intrinsic rotation shots at Alcator C-Mod can be processed and analyzed without constant user management, which is used to test the three hypotheses. By comparing the rotation gradient u', a proxy variable indicative of the core toroidal intrinsic rotation velocity, to the parameters identified by the hypotheses, little correlation has been found between u' and the dominant turbulence regime and the ion temperature, electron temperature, and electron density profile gradients. The plasma remains ITG-dominated based on linear stability analysis regardless of rotation direction and the local profile gradients are not statistically significant in predicting the u'. Additionally, the experimental results in C-Mod and ASDEX Upgrade have shown strong disagreement with the 1 -D neoclassical model. Strong correlation has been found between u' and the effective collisionality Veff. These findings are inconsistent with previous experimental studies and suggest that further work is required to identify other key dependencies and/or uncover the complex physics and mechanisms at play.</Abstract>
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