7th Asia-Pacific Conference on Plasma Physics, 12-17 Nov, 2023 at Port Messe Nagoya

Breaking of the ion temperature clamping in EAST electron-heated H-mode
plasmas by applying neutral beam injections

Jianwen Liu1,2,3, Qing Zang1,*, Yunfeng Liang1,3,*, Jiale Chen1, Xiaohe Wu1,2, Alexander Knieps3,Jiahui Hu1, Yifei Jin1,2, Bin Zhang1, Yuqi Chu1, Haiqing Liu1, Bo Lyu1, Yanmin Duan1, Miaohui Li1,Yingjie Chen1, Xianzu Gong1 and EAST team1
1
Institute of Plasma Physics, Chinese Academy of Sciences, Hefei 230031, China
2
University of Science and Technology of China, Hefei 230026, China
3
Forschungszentrum Jülich GmbH, Institut für Energie- und Klimaforschung – Plasmaphysik,Partner of the Trilateral Euregio Cluster (TEC), 52425 Jülich, Germany
e-mail (speaker): jianwen.liu@ipp.ac.cn
A major goal of fusion energy research is to heat andconfine ionized gases (i.e. deuterium and tritium) so theyfuse into heavier elements, producing significantly more
power from fusion reactions than power put into theplasma for heating[1]. An essential condition for therealization of fusion reactions is to have a high fusion
triple product (niTiτE), which is extremely dependent on
the temperature of main ions. Therefore, it is critical toraise the ion temperature effectively in the fusion
devices.
At the EAST Tokamak, the ion temperature (T i) is
observed to be clamped[2] around 1.25keV inelectron-heated plasmas, even at core electron
temperatures up to 10 keV (depending on the electron
cyclotron resonance heating - ECRH - power and theplasma density), as shown in Fig.1. This clamping is
caused by turbulence driven transport. Turbulent
transport analysis shows that trapped electron mode(TEM) and electron temperature gradient (ETG) driven
modes are the most unstable modes in the core ofelectron-heated H-mode plasmas. However, recently it
was found that the Ti/Te ratio can increase further withthe fraction of the Neutral Beam Injection (NBI) power,
which leads to a breaking of T i clamping. InNBI-heating-dominant H-mode plasmas, the ion

temperature gradient (ITG) driven modes become themost unstable modes. The growth rate of the ITG modes
increases following the rise of the T i0/Te0 ratio.
Furthermore, a strong and broad internal transport barrier(ITB) can form at the plasma core in high-power NBI
heated H-mode plasmas, which results in steep core T eand Ti profiles, as well as a peaked ne profile. Powerbalance analysis shows a weaker Te profile stiffness at
the core plasma after the formation of ITBs, where T iclamping is broken, and the core T i can increase furtherabove 2 keV, which is 80% higher than the value of Ti
clamping in electron-heated plasmas.
This finding proposes a possible solution to the problemof Ti clamping and demonstrates an advanced
operational regime with formation of a strong and broad
ITB for future fusion plasmas dominated by electron
heating.
References[1] Stott P E Plasma Physics and Controlled Fusion 2005
47 1305-1338[2] Beurskens M N A, Angioni C, Bozhenkov S A, et al.
Nuclear Fusion 2021 62 016015

Figure 1. Variation of core electron temperature (T e0) with core ion temperature (T i0) at (a) electron-heated plasmas and(b) NBI heating dominant plasmas on EAST.