Wide Pedestal Quiescent H-mode Plasmas in DIII-D Tokamak

Conference · Fri Jun 15 04:00:00 EDT 2018

OSTI ID:1462701

Chen, Xi ^[1]; Burrell, K.H. ^[2]; Osborne, T.H. ^[2]; Barada, K. ^[3]; Ernst, D.R. ^[4]; Chrystal, C. ^[2]; Grierson, B.A. ^[5]; McKee, G.R. ^[6]; Odstrcil, T. ^[4]; Paz-Soldan, C.P. ^[2]; Petty, C.C. ^[2]; Rhodes, T.L. ^[7]; Rost, J.C. ^[4]; Solomon, W.M. ^[2]; Wilks, T.M. ^[4]; Yan, Z. ^[6]; Zeng, L. ^[7]

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1. General Atomics, La Jolla, CA (United States); General Atomics
2. General Atomics, La Jolla, CA (United States)
3. University of California - Los Angeles
4. Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)
5. Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
6. University of Wisconsin Madison
7. University of California Los Angeles

Quiescent H-mode (QH-mode) is a naturally ELM-stable high performance operation mode which has been obtained in DIII-D, ASDEX Upgrade, JET, and JT-60U [1 and references within]. The additional transport to maintain constant density and radiation is provided by the benign coherent edge harmonic oscillations mode (EHO) [2] which is thought to be a kink/peeling mode [3]. A new QH-mode regime with enhanced pedestal has been discovered in DIII-D at reactor-relevant low torque and collisionality [4]. The regime was originally found in conventional QH-mode when the counter-Ip neutral beam torque drops to ~2Nm in double null plasma shapes. It is referred to as ‘wide-pedestal QH-mode’ because the pedestal width exceeds the EPED kinetic ballooning mode (KBM) limit [5]. Across the transition from QH to wide-pedestal QH, the pedestal electron pressure generally increases by 60% and widens by 50% and the plasma confinement (ITER Hy98y2) rises by 40%. The onset of broadband edge MHD modes and micro-turbulence accompanied with a lower ExB shear in this region is a common feature of the wide-pedestal QH, instead of EHO. It is conjectured that the increased transport provided by these edge modes reduces the pedestal gradients resulting in a higher pedestal while still remaining below the ELM-limit.

• Research Organization: General Atomics
• Sponsoring Organization: USDOE
• DOE Contract Number: FC02-04ER54698
• OSTI ID: 1462701
• Country of Publication: United States
• Language: English