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Title: Scenario development for high βp low torque plasma with qmin above 2 and large-radius internal transport barrier in DIII-D

A recent experiment on DIII-D, which was conducted by the joint research team from DIII-D and EAST, has extended the previous high βp, high qmin regime, which has been tested in the 2013 DIII-D/EAST joint experiment, to inductive operation at higher plasma current (Ip=0.8 MA) and significantly higher normalized fusion performance (G = H89βN/=q$$2\atop{95}$$ = 0.16). The experiment aims at exploring high performance scenario with qmin > 2 and reduced torque for long pulse operation, which can be potentially extrapolated to EAST. The effort was largely motivated by the interest in developing a feasible scenario for long-pulse high performance operation with low torque on EAST. Very high confinement, H89 = 3.5 or H98,y2 = 2.1 with βN ~ 3.0, has been achieved transiently in this experiment together with qmin > 2 and reduced NBI torque (3~5 N-m). The excellent confinement is associated with the spontaneous formation of an internal transport barrier (ITB) in plasmas with Ip=0.8 MA at large minor radius (normalized p ~ 0.7) in all channels (ne, Te, Ti, VΦ, especially strong in the Te channel). Fluctuation measurements show a significant reduction in the fluctuation levels, including AE modes and broadband turbulence, at the location where an ITB forms. Linear gyrokinetic simulations also support the decrease of the growth rate of the most unstable mode during strong ITB formation. The simulation implies that strong suppression of turbulence and a positive feedback loop may be active in this process and is responsible for the spontaneous formation of large-radius ITB. Finally, in an unstable ITB phase, an ELM crash is observed to have a positive effect on transient formation of large-radius ITB. The formation of this kind of ITB is found to have a shielding (protecting) effect on the core plasma while isolating the perturbation due to ELM crash.
Authors:
 [1] ;  [1] ;  [2] ;  [3] ;  [4] ;  [1] ;  [3] ;  [5] ;  [6] ;  [6] ;  [7] ;  [1] ;  [1]
  1. Chinese Academy of Sciences (CAS), Anhui, Hefei (China). Inst. of Plasma Physics
  2. Zhejiang Univ., Hangzhou (China). Inst. for Fusion Theory and Simulation
  3. General Atomics, San Diego, CA (United States)
  4. Soochow Univ., Suzhou, Jiangsu (China)
  5. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
  6. Univ. of Wisconsin, Madison, WI (United States)
  7. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Publication Date:
Grant/Contract Number:
FC02-04ER54698; 11575248; 11305209; 2015GB103001; 2015GB102004; 2015GB101000
Type:
Accepted Manuscript
Journal Name:
Nuclear Fusion
Additional Journal Information:
Journal Volume: 57; Journal Issue: 2; Related Information: S. Ding, G.S. Xu, Q. Wang, W.M. Solomon, Y. Zhao, X. Gong, A.M. Garofalo, C.T. Holcomb, G. McKee, Z. Yan, H.Q. Wang, J. Qian, and B.N. Wan, "Scenario development for high Bp low torque plasma with qmin above 2 and large-radius internal transport barrier in DIII-D," Nucl. Fusion 57, 022016 (2017).; Journal ID: ISSN 0029-5515
Publisher:
IOP Science
Research Org:
General Atomics, San Diego, CA (United States)
Sponsoring Org:
USDOE Office of Science (SC); National Natural Science Foundation of China (NNSFC); Chinese Academy of Sciences
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY
OSTI Identifier:
1372052
Alternate Identifier(s):
OSTI ID: 1327549