| Summary: | Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2013. === This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. === Cataloged from student-submitted PDF version of thesis. === Includes bibliographical references (p. 201-210). === Usually when sufficient heating power is injected, tokamak plasma will make an abrupt transition into a state with improved confinement, known as the high-confinement mode, or H-mode. Given the greatly enhanced fusion yield, H-mode is foreseen as the baseline scenario for the future plasma operation of the International Thermonuclear Experimental Reactor (ITER). Many research efforts have been given to understand the criteria for H-mode access. To further contribute to this research, a primary focus of this thesis is characterizing the H-mode access conditions in the Alcator C-Mod tokamak, across a broad range of plasma density, magnetic field, and plasma current. In addition, dedicated experiments were designed and executed on C-Mod, to explore the effects of divertor geometry, ICRF resonance location, and main ion species on H-mode access conditions. Results from these experiments will be included in this thesis. The underlying physics of H-mode access is very complex, and the critical mechanisms remain largely unresolved. To promote our understanding, some models proposed for the H-mode transition are tested, using well documented local plasma conditions, obtained in C-Mod experiments. In particular, this thesis pioneers the test of a recently developed model for H-mode threshold power predictions. === by Yunxing Ma. === Ph.D.
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