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

Effects of drift on the tungsten impurity accumulation in the core of tokamak
during insert gas seeding
Chaofeng Sang*, Yihan Wu, Yilin Wang, Qingrui Zhou, Yuchen Luo, Dezhen Wang
School of physics, Dalian University of Technology*e-mail (speaker): sang@dlut.edu.cnTungsten (W) is taken as the main candidate for theplasma-facing materials (PFMs) of the future fusion
devices such as ITER, DEMO and CFETR. However, as
high-Z impurity, W is incompatible with the main plasma
due to its strong bremsstrahlung radiation. The
acceptable central concentration of W should be strictly
controlled below 10−5 in ITER. Therefore, theunderstanding of the W impurity accumulation in thecore plasma and its main influencing factor becomes to
one of the most important issues in fusion community. It
is well known that the classical drift flow has great
impact on the edge plasma, e.g. causing the in-out
divertor asymmetry, which may influence the W target
erosion. Meanwhile, the plasma flow and drift alsochange the transport of the W impurity. These together
alter the W accumulation in the core. However, theinvestigation of the role of drifts on the W accumulationis still hard. On one hand, the fluid model requires huge
computational
resources
andfacesnumerical
convergence problem. On the other hand, the widelyused guiding center approximation 2D Monte Carlo suchas DIVIMP does not include drifts naturally.
In this report, we present the investigation of the W
impurity accumulation in the core plasma with theconsideration of classical drifts. A two-dimensional
impurity transport code based on the guiding center
approximation and full-orbit is developed [1,2], which
has been validated by the benchmark against DIVIMP[4]. Three methods, fluid code SOLPS-ITER [3], theguiding center approximation code [1], and full-orbit
code [2], are used in the presented work to show thedifference and limitations of each model. The
background plasma during Ne and Ar seeding of EAST
are provided by the SOLPS-ITER modeling [3]. The
simulation shows that the guiding center approximation
model can be applied to simulate drifts effectively via

adding the drift velocity manually. While the qualitative
difference between the guiding center approximation andfull-orbit methods on the W impurity transport isillustrated.
The drifts play important role on the W impurity
distribution. The simulation results indicate that drift
could influence W transport via W impurity retention andredistribution in the divertor, and the leakage from thedivertor. In forward Bt, the eroded W flux at the outertarget is increased remarkably. Drifts drive the W
impurity from the common flux region of the outerdivertor to the private-flux region and inner divertor, thus,leading to the strong poloidal asymmetry. Both W source
and transport alter the W impurity penetration rate andinfluences the concentration in the core region. The
effects of Bt direction on the W accumulation is also
evaluated in different divertor operation regimes. The
present work will improve the understanding of the W
impurity behavior to suppress W impurity accumulationin the core.

References[1] Y. Wu et al., Nucl. Mater. Energy 33 (2022) 101297[2] C. Sang et al., 29th IAEA Fusion Energy Conference,
2023. 10. 16-21, London UK[3] Y. Wang et al., Nucl. Fusion 63 (2023) 096024[4] Q. Zhou et al., Nucl. Mater. Energy 25 (2020)
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