Transport and performance in DIII-D discharges with weak or negative central magnetic shear

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Discharges exhibiting the highest plasma energy and fusion reactivity yet realized in the DIII-D tokamak have been produced by combining the benefits of a hollow or weakly sheared central current profile with a high confinement (H-mode) edge. In these discharges, low power neutral beam injection heats the electrons during the initial current ramp, and {open_quotes}freezes in{close_quotes} a hollow or flat central current profile. When the neutral beam power is increased, formation of a region of reduced transport and highly peaked profiles in the core often results. Shortly before these plasmas would otherwise disrupt, a transition is triggered from the low ... continued below

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30 p.

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Greenfield, C.M.; Schissel, D.P. & Stallard, B.W. December 1, 1996.

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Discharges exhibiting the highest plasma energy and fusion reactivity yet realized in the DIII-D tokamak have been produced by combining the benefits of a hollow or weakly sheared central current profile with a high confinement (H-mode) edge. In these discharges, low power neutral beam injection heats the electrons during the initial current ramp, and {open_quotes}freezes in{close_quotes} a hollow or flat central current profile. When the neutral beam power is increased, formation of a region of reduced transport and highly peaked profiles in the core often results. Shortly before these plasmas would otherwise disrupt, a transition is triggered from the low (L-mode) to high (H-mode) confinement regimes, thereby broadening the pressure profile and avoiding the disruption. These plasmas continue to evolve until the high performance phase is terminated nondisruptively at much higher {beta}{sub T} (ratio of plasma pressure to toroidal magnetic field pressure) than would be attainable with peaked profiles and an L-mode edge. Transport analysis indicates that in this phase, the ion diffusivity is equivalent to that predicted by Chang-Hinton neoclassical theory over the entire plasma volume. This result is consistent with suppression of turbulence by locally enhanced E x B flow shear, and is supported by observations of reduced fluctuations in the plasma. Calculations of performance in these discharges extrapolated to a deuterium-tritium fuel mixture indicates that such plasmas could produce a DT fusion gain Q{sub DT} = 0.32.

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30 p.

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INIS; OSTI as DE97003727

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  • Meeting of the Division of Plasma Physics of the American Physical Society, Denver, CO (United States), 11-15 Nov 1996

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  • Other: DE97003727
  • Report No.: GA-A--22517
  • Report No.: CONF-961102--6
  • Grant Number: AC03-89ER51114;AC05-96OR22464;FG02-89ER53297;FG05-88ER53266;FG02-92ER54139;W-7405-ENG-48
  • Office of Scientific & Technical Information Report Number: 453999
  • Archival Resource Key: ark:/67531/metadc677682

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  • December 1, 1996

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  • July 25, 2015, 2:21 a.m.

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  • Aug. 3, 2016, 1:57 p.m.

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Greenfield, C.M.; Schissel, D.P. & Stallard, B.W. Transport and performance in DIII-D discharges with weak or negative central magnetic shear, article, December 1, 1996; San Diego, California. (digital.library.unt.edu/ark:/67531/metadc677682/: accessed September 21, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.