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10-15 May 2021
Nice, France
Europe/Vienna timezone
The Conference will be held virtually from 10-15 May 2021

Study of ITB formation and sustainment with optimized current profiles in the high-performance steady state plasma on EAST

11 May 2021, 14:00
4h 45m
Nice, France

Nice, France

Regular Poster Magnetic Fusion Experiments P2 Posters 2

Speaker

Prof. HAIQING LIU (Institute of Plasma Physics, Chinese Academy of Sciences)

Description

Recently, improved high-performance plasma operation has been significantly extended towards more ITER and CFETR related high beta steady-state regime with optimization of current profile (βP ~ 2.5 & βN ~ 1.9 with ITB +ETB of using RF & NB and βP ~ 1.9 & βN ~ 1.5 with eITB + ETB of using pure RF) on EAST 1. The ITB formation and sustainment company with optimization of the current profiles, which seem to be due to different MHD-modes, similar with other devices 2. The mechanisms of linking the observed changes in MHD-behaviour and current profile seem to play an important role for ITB formation and sustainment in high beta steady state plasma on EAST.
First demonstration of a  >100 s time scale long-pulse steady-state scenario with a good plasma performance (H98(y2) ~ 1.1, with eITB) has been achieved on EAST using the pure radio frequency (RF) power heating and current drive. A typical discharge, with NB injection based on the >100 s long pulse discharge parameter, is shown in Figure 1. Better confinement was obtained with flat central safety factor q~1 profile, with a flat boundary is about 0.2 m, and sawtooth-free in plasma discharges, accompanied by a long live mode (LLM) with a few times of current relaxation time. The LLM is localized in the core with the amplitude (10-20 Gauss) directly measured by Faraday-effect based polarimetry, and mode number (1,1) is determined by toroidally and poloidally separate diagnostics. The helical displacement of LLM is estimated to be as large as 2-3 cm, implying helical structure in the core may play an important role in current relaxation to sustain flat q profile. The measured local peaking radial magnetic fluctuation of LLM is ~90 Gauss, which is at least 10% equilibrium poloidal magnetic field inside q=1 surface, suggesting a 3D equilibrium topology.
The ITB and ETB are both observed with an optimizied flat central q profile in the long-pulse high βN operation, as shown in Figure 2. The ITB of ion temperature, electron temperature and electron density has been obtained simultaneously during the fishbone event. And the ITB+ETB discharges sustain a few seconds with the long live fishbone in the H-mode discharge 80496, the central q profile is flat and q ~ 1 inside ρ<0.3. The sustainment of internal transport barrier of electron density is accompanied with m/n =1/1 fishbone while it has no fishbone in the phase without ITB at t = 3.7 s. Further analysis shows that the m/n =1/1 fishbone signals located at the region of ρ=0.3 which is consistent with central flat q profile and ITB region of electron density. The formation and sustainment of the central flat q profile could be associated with the presence of the fishbone mode. Also, relationship between the formation of ITB and fishbone in EAST high βN ELMy H-mode discharge is confirmed in discharge 56933 in ref. 1. This current clamping effect is similar with other hybrid scenarios like in other devices. It suggests that some no-linear coupling exist between the MHD behaviors and the current profiles. The peak of the stored energy during the full shot revealed that the plasma was well constrained.
The 1/1 mode almost exists during the entire discharge period for improved H mode on EAST, and is a common phenomenon for many similar shots, which is similar to the LLM found on ASDEX-U and MAST 2. The over driven off axis current and fast transport of current from the core area give rise to larger difference between qmin and q=1 rational surfaces, which makes the internal mode with low m,n number more hard to be driven unstable. The combination of ECRH and LHCD plays an important role in sustaining flat q profile to avoid sawtooth crash. The 1/1 mode might play important role in shaping current density profile and sustaining the ITB in the high-performance plasma on EAST. The detailed process or mechanism based on internal measurements about how those modes can affect current profile is still missing. It is speculated that 1/1 modes may have interactions with background turbulence and play a role in current relaxation to sustain flat q profile and high-performance plasma with ITB..
1 X. Gao et al., Nucl. Fusion 57 056021(2017); B.N.Wan, et al., Nucl. Fusion 59 112003(2019); X. Z.Gong, et al., Nucl. Fusion 59 086030(2019).
2 J.Stober et al., Nucl. Fusion 47 728(2007); E. Joffrin et al., Nucl. Fusion 43 1167(2003); I Chapman et al., Nucl. Fusion 50 045007(2010).
Time history of high beta discharge #70177 with RF & NB (a-e), and Fourier spectra of the Faraday angle signals (f-h).

Kinetic profiles (a-d), q profiles (e) and the electron density gradient contour-plot (f) and the m/n =1/1 fishbone (g) analysis with ITB discharge #80496.

Affiliation Institute of Plasma Physics, Chinese Academy of Sciences
Country or International Organization China

Primary authors

Prof. HAIQING LIU (Institute of Plasma Physics, Chinese Academy of Sciences) Mr Yuqi Chu (Institute of Plasma Physics, Chinese Academy of Sciences) wenzhe mao (University of Science and Technology of China) Mr hui Lian (Institute of Plasma Physics, Chinese Academy of Sciences) Mr shouxin wang (Institute of Plasma Physics, Chinese Academy of Sciences) Shoubiao Zhang (Institute of Plasma Physics,Chinese Academy of Sciences, Hefei 230031, China) Jinping Qian (Institute of plasma physics, Chinese academy of sciences) Dr yao yang (Institute of Plasma Physics, Chinese Academy of Sciences) Dr Long Zeng (Institute of Plasma Physics, Chinese Academy of Sciences) Prof. Jinlin Xie (University of Science and Technology of China) Yinxian Jie (Institute of Plasma Physics, Chinese Academy of Sciences) Xiang Gao (Institute of Plasma Physics, Chinese Academy of Sciences) Xianzu Gong (Insititute of Plasma Physics, Chinese Academy Sciences) Weixing Ding (University of Science and Technology of China) Kazuaki Hanada (Advanced Fusion Research Center, Research Institute for Applied Mechanics, Kyushu University) Prof. yunfeng liang (Institute of Plasma Physics, Chinese Academy of Sciences) Nong Xiang (Institute of plasma physics, Chinese academy of science) Xiaodong ZHANG (Institute of Plasma Physics, Chinese Academy of Sciences) Prof. Baonian Wan (Institute of Plasma Physics, Chinese Academy of Sciences) the EAST Team

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