H-mode pedestal and threshold studies over an expanded operating space on Alcator C-Mod

Journal Article · Tue May 15 04:00:00 EDT 2007 · Physics of Plasmas

DOI:https://doi.org/10.1063/1.2714297· OSTI ID:20975048

Hubbard, A E; Hughes, J W; Cziegler, I; LaBombard, B; Lin, Y; McDermott, R; Rice, J E; Snipes, J A; Terry, J L; Wolfe, S M; Wukitch, S ^[1]; Bespamyatnov, I O; Rowan, W L ^[2]; Biewer, T ^[3]

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1. Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, Massachusetts 02129 (United States)
2. Fusion Research Center, University of Texas at Austin, Austin, Texas 78712 (United States)
3. Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, Tennessee 37831 (United States)

This paper reports on studies of the edge transport barrier and transition threshold of the high confinement (H) mode of operation on the Alcator C-Mod tokamak [I. H. Hutchinson et al., Phys. Plasmas 1, 1511 (1994)], over a wide range of toroidal field (2.6-7.86 T) and plasma current (0.4-1.7 MA). The H-mode power threshold and edge temperature at the transition increase with field. Barrier widths, pressure limits, and confinement are nearly independent of field at constant current, but the operational space at high B shifts toward higher temperature and lower density and collisionality. Experiments with reversed field and current show that scrape-off-layer flows in the high-field side depend primarily on configuration. In configurations with the Bx{nabla}B drift away from the active X-point, these flows lead to more countercurrent core rotation, which apparently contributes to higher H-mode thresholds. In the unfavorable case, edge temperature thresholds are higher, and slow evolution of profiles indicates a reduction in thermal transport prior to the transition in particle confinement. Pedestal temperatures in this case are also higher than in the favorable configuration. Both high-field and reversed-field results suggest that parameters at the L-H transition are influencing the evolution and parameters of the H-mode pedestal.

• OSTI ID: 20975048
• Journal Information: Physics of Plasmas, Journal Name: Physics of Plasmas Journal Issue: 5 Vol. 14; ISSN PHPAEN; ISSN 1070-664X
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
ALCATOR DEVICE
COLLISIONS
CONFIGURATION
ELECTRIC CURRENTS
ELECTRON TEMPERATURE
H-MODE PLASMA CONFINEMENT
ION TEMPERATURE
MAGNETOHYDRODYNAMICS
PLASMA
PLASMA DENSITY
PLASMA SCRAPE-OFF LAYER