Deconvolving the roles of E × B shear and pedestal structure in the energy confinement quality of super H-mode experiements

Garofalo, Andrea M.; Solomon, Wayne M.; Knölker, M.; Osborne, Tom H.; Chrystal, Colin; Petty, Craig C.; Ding, Siye; Grierson, Brian A.; Laggner, Florian M.; Jian, Xiang; Holland, Christopher; Marinoni, Alessandro

doi:10.1088/1741-4326/ac4d63

Deconvolving the roles of E × B shear and pedestal structure in the energy confinement quality of super H-mode experiements

Journal Article · Tue Mar 15 00:00:00 EDT 2022 · Nuclear Fusion

DOI:https://doi.org/10.1088/1741-4326/ac4d63· OSTI ID:1844607

^[1]; Solomon, Wayne M. ^[2]; ^[2]; Osborne, Tom H. ^[2]; ^[2]; ^[2]; ^[3]; ^[4]; Laggner, Florian M. ^[4]; Jian, Xiang ^[5]; ^[5]; Marinoni, Alessandro ^[6]

General Atomics, San Diego, CA (United States); General Atomics
General Atomics, San Diego, CA (United States)
Oak Ridge Associated Univ., Oak Ridge, TN (United States)
Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
Univ. of California, San Diego, CA (United States)
Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)

Analysis of “super H-mode” experiments on DIII-D has put forward that high plasma toroidal rotation, not high pedestal, plays the essential role in achieving energy confinement quality H_98y2>>1. Recently, super H-mode experiments with variable input torque have confirmed that high rotation shear discharges have very high levels of H_98y2 (>1.5), independent of the pedestal height, and that high pedestal discharges with low rotation shear have levels of H_98y2 only slightly above 1 (≤1.2). Although some increase in stored energy with higher pedestal occurs, the energy confinement quality mainly depends on the toroidal rotation shear, which varies according to different levels of injected neutral beam torque per particle. Here, quasi-linear gyrofluid modeling achieves a good match of the experiment when including the E×B shear; without including plasma rotation, the modeling predicts a confinement quality consistent with the empirical observation of H_98y2~1.2 at low rotation. Nonlinear gyrokinetic transport modeling shows that the effect of E×B turbulence stabilization is far larger than other mechanisms, such as the so-called hot-ion stabilization (T_i/T_e) effect. Consistent with these experimental and modeling results are previous simulations of the ITER Baseline Scenario using a super H-mode pedestal solution, which showed the potential to exceed the Q=10 target if the pedestal density could be increased above the Greenwald limit. A close look at these simulations reveals that the predicted energy confinement quality is below 1 even at the highest pedestal pressure. The improvement in Q at higher pedestal density is due to the improved fusion power generation at the higher core density associated with higher pedestal density, not to an improved energy confinement quality.

View Accepted Manuscript (DOE)

Research Organization:: General Atomics, San Diego, CA (United States)

Sponsoring Organization:: USDOE

Grant/Contract Number:: FC02-04ER54698; AC02-09CH11466; SC0010685; SC0018287; SC0016154

OSTI ID:: 1844607

Journal Information:: Nuclear Fusion, Journal Name: Nuclear Fusion Journal Issue: 5 Vol. 62; ISSN 0029-5515

Publisher:: IOP ScienceCopyright Statement

Country of Publication:: United States

Language:: English

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