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High fusion performance in Super H-mode experiments on Alcator C-Mod and DIII-D

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  • P. B. Snyder
  • J. W. Hughes
  • T. H. Osborne
  • C. Paz-Soldan
  • W. M. Solomon
  • M. Knolker
  • D. Eldon
  • T. Evans
  • T. Golfinopoulos
  • B. A. Grierson
  • R. J. Groebner
  • A. E. Hubbard
  • E. Kolemen
  • B. Labombard
  • F. M. Laggner
  • O. Meneghini
  • S. Mordijck
  • T. Petrie
  • S. Scott
  • H.Q. Wang
  • Y. B. Zhu


Publication details

JournalNuclear Fusion
DateAccepted/In press - 21 May 2019
DatePublished (current) - 24 Jun 2019
Issue number8
Original languageEnglish


The 'Super H-Mode' regime is predicted to enable pedestal height and fusion performance substantially higher than standard H-Mode operation. This regime exists due to a bifurcation of the pedestal pressure, as a function of density, that is predicted by the EPED model to occur in strongly shaped plasmas above a critical pedestal density. Experiments on Alcator C-Mod and DIII-D have achieved access to the Super H-Mode (and Near Super H) regime, and obtained very high pedestal pressure, including the highest achieved on a tokamak (p ped ∼ 80 kPa) in C-Mod experiments operating near the ITER magnetic field. DIII-D Super H experiments have demonstrated strong performance, including the highest stored energy in the present configuration of DIII-D (W ∼ 2.2-3.2 MJ), while utilizing only about half of the available heating power (P heat ∼ 7-12 MW). These DIII-D experiments have obtained the highest value of peak fusion gain, Q DT,equiv ∼ 0.5, achieved on a medium scale (R < 2 m) tokamak. Sustained high performance operation (β N ∼ 2.9, H98 ∼ 1.6) has been achieved utilizing n = 3 magnetic perturbations for density and impurity control. Pedestal and global confinement has been maintained in the presence of deuterium and nitrogen gas puffing, which enables a more radiative divertor condition. A pair of simple performance metrics is developed to assess and compare regimes. Super H-Mode access is predicted for ITER and expected, based on both theoretical prediction and observed normalized performance, to allow ITER to achieve its goals (Q = 10) at I p < 15 MA, and to potentially enable more compact, cost effective pilot plant and reactor designs.

Bibliographical note

© 2019 IAEA, Vienna

    Research areas

  • Alcator C-Mod, DIII-D, EPED, fusion gain, pedestal, Super H Mode, tokamak

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