7th Asia-Pacific Conference on Plasma Physics, 12Nov. -17 Nov., 2023, Nagoya, Japan

Turbulent transport of impurity ions with hollow density profiles in tokamak
devicesM. K. Han1,2, W. L. Zhong2, J. Q. Dong2,3,*, Z. X. Wang2,*, X. L. Zou4,*, W. Horton5, Y. Shen2, A. P.
Sun2, J. L. Wang1, J. M. Gao2, B. B. Feng2, C. Y. Chen2, G. L. Xiao2, Z. B. Shi2, D. L. Yu2, X. Q.
Ji2, C. F. Dong2, K. R. Fang2, L. F. Wang2, Y. Xiao3, M. Xu2 and X. R. Duan2
Key Laboratory of Materials Modification by Beams of the Ministry of Education, School ofPhysics, Dalian University of Technology, Dalian 116024, China
2Southwestern Institute of Physics, Chengdu 610041, China
3Institute for Fusion Theory and Simulation, Zhejiang University, Hangzhou 310027, China
4CEA, IRFM, F-13108 Saint-Paul-lez-Durance, France
5
Institute for Fusion Studies, The University of Texas, Austin, TX 78712, United States of America
e-mail: hanmingkun@swip.ac.cn
1Hollow density profiles (HDPs) of impurity ions widelyobserved in advanced tokamaks and helical devices
indicate that steep temperature gradients of main ionsand electrons are beneficial for the sustainment of HDPs
of impurity ions. However, the underlying physicalmechanism for sustaining such profiles remains unsolved.
Such profiles are desirable for present experiments andfuture fusion reactors due to preventing impurity
accumulation in the core, reducing the heat load on thedivertor, and improving confinement. This talk reports
systematic theoretical and experimental investigations of
the sustaining mechanisms of hollow impurity ion
density profiles. It proposes that the dominant role ofimpurity mode (IM) in the transport of impurity ionswith HDPs, and the temperature gradient screening
effects on turbulent transport as the mechanism for thesustainment of HDPs of impurity ions. A comparison
with the impurity injection experiment in HL-2A wasperformed and reasonable agreement has been observed.
Reduction of the peaking factor of impurity density
profiles caused by the increase of electron density
gradient observed in the experiment is evidenced in turnwith theory. It is important shows that the IM produces

significant heat transport even when the temperature
profiles are relatively flat. We find the temperature ratio
effects, Te/Ti (τi) and Te/Tz (τz), are quite opposite on
linear instability but are similar in quasilinear particle
and heat transport. These results suggest that IM may
cause damage to fusion energy gaining in future fusion
devices, which are accompanied by high temperature
ratios (τz and τi). Based on our simulation and experiment
investigation, it is shown that I-mode characterized by alow electron density gradient and steep temperature
gradient is expected to be favorable for sustaining HDPs
of impurity ions. Furthermore, mitigation of edge
localized mode and improvement of confinement havealso been found in HL-2A when impurity ions are
injected into the edge.
References[1]Coppi B. et al., Phys. Rev. Lett 17 (1966) 377.
[2]Dong J. Q. et al., Phys. Plasmas 4 (1997) 755.
[3]Zhong W. L. et al., Phys. Rev. Lett 117(2016) 045001.
[4]Ida K. et al, Nucl. Fusion 59 (2019) 056029.
[5]Zhong W. L. et al Nucl. Fusion 59 (2019) 076033.
[6]Han M. K. et al, Nucl. Fusion 61 (2021) 046010.

Figure 1 Contour plots of the normalized total heat fluxes of various elementary particles, (a) for IMs with C6+ in thetwo-dimensional plane of (τi, ks) for τz=1 (b) and (τz, ks) for τi=1, respectively.