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

Abstract

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 ifmore » 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.« less

Authors:

Garofalo, Andrea M.  ^[1];

• Search DOE PAGES for author "Garofalo, Andrea M."
• Search DOE PAGES for ORCID "0000-0002-8244-2448"

Solomon, Wayne M. ^[1]; Knölker, M.  ^[1];

• Search DOE PAGES for author "Knölker, M."
• Search DOE PAGES for ORCID "0000-0002-8468-8767"

Osborne, Tom H. ^[1]; Chrystal, Colin  ^[1];

• Search DOE PAGES for author "Chrystal, Colin"
• Search DOE PAGES for ORCID "0000-0003-3049-8658"

Petty, Craig C.  ^[1];

• Search DOE PAGES for author "Petty, Craig C."
• Search DOE PAGES for ORCID "0000-0003-4534-9073"

Ding, Siye  ^[2];

• Search DOE PAGES for author "Ding, Siye"
• Search DOE PAGES for ORCID "0000-0002-1930-0439"

Grierson, Brian A.  ^[3];

• Search DOE PAGES for author "Grierson, Brian A."
• Search DOE PAGES for ORCID "0000-0001-5918-6506"

Laggner, Florian M. ^[3]; Jian, Xiang ^[4]; Holland, Christopher  ^[4];

• Search DOE PAGES for author "Holland, Christopher"
• Search DOE PAGES for ORCID "0000-0001-6029-2306"

Marinoni, Alessandro ^[5]

---

+ Show Author Affiliations

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

Publication Date:

Tue Mar 15 00:00:00 EDT 2022

Research Org.:

General Atomics, San Diego, CA (United States)

Sponsoring Org.:

USDOE

OSTI Identifier:

1844607

Grant/Contract Number:  

FC02-04ER54698; AC02-09CH11466; SC0010685; SC0018287; SC0016154

Resource Type:

Accepted Manuscript

Journal Name:

Nuclear Fusion

Additional Journal Information:

Journal Volume: 62; Journal Issue: 5; Journal ID: ISSN 0029-5515

Publisher:

IOP Science

Country of Publication:

United States

Language:

English

Subject:

70 PLASMA PHYSICS AND FUSION TECHNOLOGY