skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

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

Abstract

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.

Authors:
; ; ; ; ; ; ; ; ; ;  [1]; ;  [2];  [3]
  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)
Publication Date:
OSTI Identifier:
20975048
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physics of Plasmas; Journal Volume: 14; Journal Issue: 5; Other Information: DOI: 10.1063/1.2714297; (c) 2007 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
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

Citation Formats

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., Bespamyatnov, I. O., Rowan, W. L., and Biewer, T. H-mode pedestal and threshold studies over an expanded operating space on Alcator C-Mod. United States: N. p., 2007. Web. doi:10.1063/1.2714297.
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., Bespamyatnov, I. O., Rowan, W. L., & Biewer, T. H-mode pedestal and threshold studies over an expanded operating space on Alcator C-Mod. United States. doi:10.1063/1.2714297.
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., Bespamyatnov, I. O., Rowan, W. L., and Biewer, T. Tue . "H-mode pedestal and threshold studies over an expanded operating space on Alcator C-Mod". United States. doi:10.1063/1.2714297.
@article{osti_20975048,
title = {H-mode pedestal and threshold studies over an expanded operating space on Alcator C-Mod},
author = {Hubbard, A. E. and Hughes, J. W. and Cziegler, I. and LaBombard, B. and Lin, Y. and McDermott, R. and Rice, J. E. and Snipes, J. A. and Terry, J. L. and Wolfe, S. M. and Wukitch, S. and Bespamyatnov, I. O. and Rowan, W. L. and Biewer, T.},
abstractNote = {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.},
doi = {10.1063/1.2714297},
journal = {Physics of Plasmas},
number = 5,
volume = 14,
place = {United States},
year = {Tue May 15 00:00:00 EDT 2007},
month = {Tue May 15 00:00:00 EDT 2007}
}