H-MODE THRESHOLD AND DYNAMICS IN THE NATIONAL SPHERICAL TORUS EXPERIMENT
- H-MODE THRESHOLD AND DYNAMICS IN THE NATIONAL SPHERICAL TORUS EXPERIMENT
- Bush, CE; Bell, MG; Bell, RE; Boedo, J; Fredrickson, ED; Kaye, SM; Kubota, S; LeBlanc, BP; Maingi, R; Maqueda, RJ; Sabbagh, SA; Soukhanovskii, VA; Stutman, D; Swain, DW; Wilgen, JB; Zweben, SJ; Davis, WM; Gates, DA; Johnson, DW; Kaita, R; Kugel, HW; Lee, KC; Mastrovito, D; Medley, S; Menard, JE; Mueller, D; Ono, M; Paoletti, F; Park, H; Paul, SJ; Peng, YKM; Raman, R; Roney, PG; Roquemore, AL; Skinner, CH; Synakowski, EJ; Taylor, G
- Date Issued
- AMER INST PHYSICS
- Edge parameters play a critical role in high confinement mode (H-mode) access, which is a key component of discharge optimization in present day toroidal confinement experiments and the design of next generation devices. Because the edge magnetic topology of a spherical torus (ST) differs from a conventional aspect ratio tokamak, H-modes in STs exhibit important differences compared with tokamaks. The dependence of the National Spherical Torus Experiment (NSTX) [C. Neumeyer , Fusion Eng. Des. 54, 275 (2001)] edge plasma on heating power, including the low confinement mode (L-mode) to H-mode (L-H) transition requirements and the occurrence of edge-localized modes (ELMs), and on divertor configuration is quantified. Comparisons between good L-modes and H-modes show greater differences in the ion channel than the electron channel. The threshold power for the H-mode transition in NSTX is generally above the predictions of a recent International Tokamak Experimental Reactor (ITER) [ITER Physics Basis Editors, Nucl. Fusion 39, 2175 (1999)] scaling. Correlations of transition and ELM phenomena with turbulent fluctuations revealed by gas puff imaging and reflectometry are observed. In both single-null and double-null divertor discharges, the density peaks off-axis, sometimes developing prominent "ears" which can be sustained for many energy confinement times, tau(E), in the absence of ELMs. A wide variety of ELM behavior is observed, and ELM characteristics depend on configuration and fueling. (C) 2003 American Institute of Physics.
- Article Type
- PHYSICS OF PLASMAS, vol. 10, no. 5, page. 1755 - 1764, 2003-05
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