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

Author(s): Snyder, PB; Hughes, JW; Osborne, TH; Paz-Soldan, C; Solomon, WM; et al

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Abstract: 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.
Publication Date: 2019
Citation: Snyder, PB, Hughes, JW, Osborne, TH, Paz-Soldan, C, Solomon, WM, Knolker, M, Eldon, D, Evans, T, Golfinopoulos, T, Grierson, BA, Groebner, RJ, Hubbard, AE, Kolemen, E, Labombard, B, Laggner, FM, Meneghini, O, Mordijck, S, Petrie, T, Scott, S, Wang, HQ, Wilson, HR, Zhu, YB. (2019). High fusion performance in Super H-mode experiments on Alcator C-Mod and DIII-D. Nuclear Fusion, 59 (10.1088/1741-4326/ab235b
DOI: doi:10.1088/1741-4326/ab235b
Type of Material: Journal Article
Journal/Proceeding Title: Nuclear Fusion
Version: Final published version. This is an open access article.

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