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

Tungsten impurity screening and its control using different gas injection onEAST with full tungsten divertor
R. Ding1, G.L. Xu1, H. Wang1,2, H. Si1, F. Ding1, L. Zhang1, Q. Zhang1,2, K.D. Li1, J.B. Liu1, B.F.
Gao1,2, L.Y. Meng1, H. Xie1, L. Wang1, J.P. Qian1, J. Huang1, J.L. Chen1, X.Z. Gong1, J.G. Li1
1
Institute of Plasma Physics, Chinese Academy of Sciences, Hefei, China, 2 Science Island Branch,
Graduate School of University of Science and Technology of China, Hefei, Chinae-mail (speaker): rding@ipp.ac.cn
Tungsten (W) impurity contamination is a key issue
for long-pulse high-performance plasma operation intokamaks with W plasma-facing materials. To reduce
the W impurity level in the core plasma, it isimportant to understand the physics processes of W
impurity source and edge transport.
Dedicated gas puffing experiments were carried out
on EAST tokamak with full W divertor to achieve
divertor detachment and evaluate the W impurity
transport under different divertor conditions [1]. Neand D2 injection from the divertor target wereobserved to have different impacts on the edge Wscreening. Before the onset of divertor detachment, Ne
seeding increases both the W source and the W
leakage rate, while D2 puffing helps to reinforce the W
screening in the edge plasma. Based on the EAST
experiments, W impurity transport processes from thedivertor target to the core plasma are quantitatively
analyzed by sequential SOLPS-ITER and DIVIMP
simulations [2] with drift velocities included.
Simulation results reveal that, for the D2 puffing cases,
the increase of the friction and the decrease of the ion
temperature gradient force near the divertor target are
the main reason for the enhancement of edge W
screening during the transition from the high recycling
regime to detachment. However, when increasing theNe injection rate, the friction and the ion temperature

gradient force vary little, and a higher Ne
concentration can lead to more W erosion which
finally makes more W leakage to the core plasma. The
E×B drift can dramatically enhance the W leakage
ability for both Bt directions, but the enhancement
effect becomes weaker when the divertor is detached.
With the help of drifts, W leakage from the PFR to theupstream or core plasma by diffusion near the X pointis proved to be significant, especially for the divertor
condition with good SOL screening. Modeling results
also reveal that there exists an impurity flow reversal
in the near-SOL region due to the E×B drift under thepronounced detached condition. This kind of flow
reversal plays an important role in impurity
distribution and will be discussed in the presentation.
The work was supported by the National Natural
Science Foundation of China under Contract Nos.
12022511 and 12005143, the Key Research Programof Frontier Sciences, CAS with Grant No.
ZDBS-LY-SLH010.
References[1] R. Ding et al., Nuclear Materials and Energy 33(2022) 101250[2] H. Wang et al., Nuclear Fusion 62 (2022) 126018

Figure 1 Location of W impurity leakage out of divertor region from SOLPS-DIVIMP modeling for highrecycling regime (a) without drift and (b) with drift, and detachment regime (c) without drift and (d) with drift.
The leakage channels are shown in (e) for high recycling regime and (f) for detachment regime.