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

Investigation the impact of carbon impurity radiation on density limitin limiter and divertor configurations on J-TEXT

X. Xu1, Z.P. Chen1,*, Q.H. Yang1, J.M. Wang1, J.L. Guo1, Y.H. Wang1, X.L. Zhang2, Z.Y. Jin1, W.
Yan1, L. Gao1, Z.J. Yang1, X.Q. Zhang1, and J-TEXT Team
1
International Joint Research Laboratory of Magnetic Confinement Fusion and Plasma Physics,
State Key Laboratory of Advanced Electromagnetic Engineering and Technology, School ofElectrical and Electronic Engineering, Huazhong University of Science and Technology, Wuhan
430074, People’s Republic of China
2Southwestern Institute of Physics, Chengdu, Chinae-mail (speaker): xxu@hust.edu.cn, * zpchen@hust.edu.cn
High-density operation is a crucial aspect of achieving
efficient and sustainable fusion reactions in tokamak
devices like ITER[1]. However, the operational region ofstable tokamak discharges is limited towards high plasma
density due to the phenomenon known as the density limit(DL). The DL is a critical issue in tokamak research, andcooling of the plasma edge thought to be a key element,
which can lead to current shrinking, strong
magnetohydrodynamic (MHD) activity, and ultimately,plasma disruptions[2]. Understanding the density limit isessential for successful and reliable operation of future
fusion devices.
This investigation presents the impact of carbon impurity
radiation in the density limit in different magnetic field
configurations on the J-TEXT tokamak. The study focuseson the edge plasma cooling and its effects on triggering
the mode locking of the precursor 2/1 tearing mode (TM)before reaching the density limit. Experiments wereconducted in various magnetic field configurations,including the normal limiter, HFS-limiter, and HFS-MSN
divertor configurations[3], with different carbon impurity
concentrations introduced by methane gas injection fromthe high-field-side (HFS), as shown on the left of Figure
1. The edge plasma parameters, such as electron
temperature and density, were closely monitored as theplasma approached the density limit.
The introduction of carbon impurities resulted in stronger
core radiation and enhanced cooling of the boundary

region, affecting the temperature profiles near the q=3
surface. The study also revealed that the electron
temperature near the q=3 surface exhibited similarities
across all magnetic configurations as the density limit
approached, as shown in Fig 1(a, b, c). However,significant differences were observed near the Last Closed
Flux Surface (LCFS), indicating the importance of q=3
surface temperature as a key factor in the density limit
discharge.
In conclusion, the investigation sheds light on the criticalrole of carbon impurity radiation and edge plasma coolingin influencing the density limit in different magnetic fieldconfigurations. The findings contribute to thedevelopment of comprehensive models for understanding
and mitigating the density limit in future fusion devices,ensuring their stable and efficient operation at high plasma
densities.
This work is supported by the National MCF Energy
R&D Program under Grant Nos. 2018YFE0310300 and2018YFE0301104.
References[1] E.J. DOYLE, et al., Nucl. Fusion 47(6): S18(2007).
[2] M. Greenwald, et al., Phys. Plasmas 21110501(2014).
[3] Z.P. Chen, et al., Plasma Sci. Technol. 24124008(2022)

Figure 1. Schematic diagram of three magnetic field configurations (left). C III radiation distribution before
approaching the density limit under the normal limiter(a), HFS-limiter(b), and HFS-MSN divertor configurations(c).
The blue vertical dashed line represents the position of the q=3 surface.