Potential Methods for Improving Pedestal Temperatures and Fusion Performance

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The physics of the tokamak edge is very complicated, and the scaling of the H-mode transport barrier pedestal has significant uncertainties. Evidence from the largest tokamaks appears to support a model in which the H-mode pedestal width scales linearly with the poloidal gyroradius and the gradient scales with ideal MHD ballooning limits. However, there appears to be significant variability in the data from different tokamaks, including observations on DIII-D that indicate a regime where the pedestal is in second stability and the width is independent of poloidal gyroradius, which would give a more favorable scaling to reactor scales. An important ... continued below

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159 Kilobytes pages

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Hammett, G.W.; Kotschenreuther, M.; Beer, M.A. & Dorland, W. October 1, 1999.

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Description

The physics of the tokamak edge is very complicated, and the scaling of the H-mode transport barrier pedestal has significant uncertainties. Evidence from the largest tokamaks appears to support a model in which the H-mode pedestal width scales linearly with the poloidal gyroradius and the gradient scales with ideal MHD ballooning limits. However, there appears to be significant variability in the data from different tokamaks, including observations on DIII-D that indicate a regime where the pedestal is in second stability and the width is independent of poloidal gyroradius, which would give a more favorable scaling to reactor scales. An important question is the role of the bootstrap current in the pedestal, and another is how far can the improvements in edge stability be p shed with higher triangularity and elongation. Even with the more pessimistic model, where the pedestal width is proportional to the poloidal gyroradius, the results presented here suggest that pedestal temperatures, and thus the fusion performance, may be significantly improved by designs with stronger plasma shaping higher triangularity and elongation, moderate density peaking, and higher magnetic field (and thus reduced size), such as in ARIES-RS, FIRE, and some of the new ITER-RC designs.

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159 Kilobytes pages

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INIS; OSTI as DE00013836

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  • Other Information: PBD: 1 Oct 1999

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  • Report No.: PPPL-3360
  • Grant Number: AC02-76CH03073
  • DOI: 10.2172/13836 | External Link
  • Office of Scientific & Technical Information Report Number: 13836
  • Archival Resource Key: ark:/67531/metadc619797

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  • October 1, 1999

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  • June 16, 2015, 7:43 a.m.

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  • April 15, 2016, 9:51 p.m.

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Hammett, G.W.; Kotschenreuther, M.; Beer, M.A. & Dorland, W. Potential Methods for Improving Pedestal Temperatures and Fusion Performance, report, October 1, 1999; Princeton, New Jersey. (digital.library.unt.edu/ark:/67531/metadc619797/: accessed September 24, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.