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

Journal Article · · Nuclear Fusion
ORCiD logo [1];  [1]; ORCiD logo [1];  [1]; ORCiD logo [1]; ORCiD logo [1]; ORCiD logo [2]; ORCiD logo [3];  [3];  [4]; ORCiD logo [4];  [5]
  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)
+ Show Author Affiliations

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 H98y2>>1. Recently, super H-mode experiments with variable input torque have confirmed that high rotation shear discharges have very high levels of H98y2 (>1.5), independent of the pedestal height, and that high pedestal discharges with low rotation shear have levels of H98y2 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 H98y2~1.2 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 (Ti/Te) 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.

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, Vol. 62, Issue 5; ISSN 0029-5515
Publisher:
IOP ScienceCopyright Statement
Country of Publication:
United States
Language:
English

References (28)

Integrated modeling applications for tokamak experiments with OMFIT journal July 2015
On the stability and stationarity of the Super H-mode combined with an ion transport barrier in the core journal January 2021
Experimental Study of the Ion Critical-Gradient Length and Stiffness Level and the Impact of Rotation in the JET Tokamak journal April 2009
The role of toroidal rotation in the very high energy confinement quality observed in super H-mode experiments on DIII-D journal November 2021
Tokamak profile prediction using direct gyrokinetic and neoclassical simulation journal June 2009
Flow shear induced fluctuation suppression in finite aspect ratio shaped tokamak plasma journal May 1995
Density limits in toroidal plasmas journal July 2002
Access to a New Plasma Edge State with High Density and Pressures using the Quiescent H Mode journal September 2014
Investigation of physical processes limiting plasma density in high confinement mode discharges on DIII-D journal May 1997
On the very high energy confinement observed in super H-mode DIII-D experiments journal January 2020
Exploration of the Super H-mode regime on DIII-D and potential advantages for burning plasma devices journal March 2016
Experimental challenges to stiffness as a transport paradigm journal January 2018
Examination of stiff ion temperature gradient mode physics in simulations of DIII-D H-mode transport journal May 2021
Self-consistent core-pedestal transport simulations with neural network accelerated models journal July 2017
Impact of plasma triangularity and collisionality on electron heat transport in TCV L-mode plasmas journal June 2007
Access to high beta advanced inductive plasmas at low injected torque journal September 2013
Nonlinear Stabilization of Tokamak Microturbulence by Fast Ions journal October 2013
Chapter 2: Plasma confinement and transport journal December 1999
The H-mode density limit in the full tungsten ASDEX Upgrade tokamak journal November 2014
Predicting the rotation profile in ITER journal January 2020
Development and validation of a predictive model for the pedestal height journal May 2009
Study of the density limit with pellet fuelling in JT-60 journal October 1991
A theory-based transport model with comprehensive physics journal May 2007
Influence of toroidal rotation on transport and stability in hybrid scenario plasmas in DIII-D journal May 2008
Super H-mode: theoretical prediction and initial observations of a new high performance regime for tokamak operation journal July 2015
Full linearized Fokker–Planck collisions in neoclassical transport simulations journal December 2011
Scaling studies of the high mode pedestal journal May 1998
Understanding the core confinement in DIII-D super-H experiments by transport modeling journal June 2022

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