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Title: Stationary QH-mode plasmas with high and wide pedestal at low rotation on DIII-D

Journal Article · · Nuclear Fusion
 [1];  [1];  [1];  [2];  [3];  [1];  [1];  [4];  [5];  [1];  [6];  [1];  [7];  [3];  [7];  [1];  [1];  [2];  [5]
  1. General Atomics, San Diego, CA (United States)
  2. Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
  3. Univ. of California, Los Angeles, CA (United States)
  4. Univ. of California, Davis, CA (United States)
  5. Univ. of Wisconsin, Madison, WI (United States)
  6. Graduate Univ. for Advanced Studies (SOKENDAI), Kanagawa (Japan)
  7. Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)
+ Show Author Affiliations

A stationary, quiescent H-mode (QH-mode) regime with a wide pedestal and improved confinement at low rotation has been discovered on DIII-D with reactor relevant edge parameters and no ELMs. As the injected neutral beam torque is ramped down and the edge ExB rotation shear reduces, the transition from standard QH to the wide pedestal QH-mode occurs. And at the transition, the coherent edge harmonic oscillations (EHO) that usually regulate the standard QH edge cease and broadband edge MHD modes appear along with a rapid increase in the pedestal pressure height (by ≤60%) and width (by ≤50%). We posit that the enhanced edge turbulence-driven transport, enabled by the lower edge ExB flow shear due to lower torque reduces the pedestal gradient and, combined with the high edge instability limit provided by the balanced double-null plasma shape, permits the development of a broader and thus higher pedestal that is turbulence-transport-limited. Even with the significantly enhanced pedestal pressure, the edge operating point is below the peeling ballooning mode stability boundary and thus without ELMs. Improved transport in the outer core region (0.8≤ρ≤0.9) owing to increased ExB flow shear in that region and the enhanced pedestal boost the overall confinement by up to 45%. Our findings advance the physics basis for developing stationary ELM-free high-confinement operation at low rotation for future burning plasma where similar collisionality and rotation levels are expected.

Research Organization:
General Atomics, San Diego, CA (United States); Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
Sponsoring Organization:
USDOE Office of Science (SC), Fusion Energy Sciences (FES)
Contributing Organization:
the DIII-D Team
Grant/Contract Number:
FC02-04ER54698; FG03-95ER54309; FC02-06ER54873; AC02-09CH11466; FG02-08ER54984; FG02-99ER54531; FG02-08ER54999; FG02-94ER54235
OSTI ID:
1372267
Alternate ID(s):
OSTI ID: 1327560
Journal Information:
Nuclear Fusion, Vol. 57, Issue 2; ISSN 0029-5515
Publisher:
IOP ScienceCopyright Statement
Country of Publication:
United States
Language:
English
Citation Metrics:
Cited by: 7 works
Citation information provided by
Web of Science

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Cited By (4)

A Riccati solution for the ideal MHD plasma response with applications to real-time stability control journal March 2018
Physics of increased edge electron temperature and density turbulence during ELM-free QH-mode operation on DIII-D journal May 2018
Edge state selection by modulating E  ×  B shearing profile in toroidally confined plasmas journal May 2019
Long-lived predator-prey dynamics in the pedestal of near-zero torque high performance DIII-D plasmas journal September 2019

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Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
QH-mode
low rotation
E x B shear
ELM-free
turbulence
pedestal transport