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

Edge plasma transport in three-dimensional magnetic topology
S.C. Liu1, Y. Liang1, P. Drews2, N. Yan1, M. Jia1, G.S. Li1, Y. Sun1, L. Wang1, G.S. Xu1, X. Gao1,X.Z. Gong1 and EAST Team1

Institute of Plasma Physics, Chinese Academy of Sciences; 2 Forschungszentrum Jülich GmbHE-mail: Shaocheng.liu@ipp.ac.cn
In tokamaks, the edge transport barrier collapses
during the eruption of edge localized mode (ELM);
simultaneously, a large amount of heat and particles
ejected into the scrape-off layer (SOL) could lead to
extremely high instantaneous heat flux on divertor
target. This is a critical challenge for the first-wallmaterials in ITER and fusion reactors. As
demonstrated by many tokamaks, resonant magnetic
perturbation (RMP) is an effective method to control
ELMs. Understanding of edge plasma transport
during the application of RMP is crucial for theinterpretation of ELM control physics, because edgetransport could directly impact the plasma
confinement and divertor heat load. To investigatethe common physical mechanism of edge plasmatransport in 3D magnetic topology, a series ofexperiments are conducted in EAST tokamak andW7-X stellarator. In the plasma conditions close tothe ITER Q=10 scenario in EAST, ELMs are fully
suppressed by 𝑛 = 4 RMP, exhibiting clear
existences of low-frequency turbulence (<30 kHz)and an electromagnetic mode at 120 kHz. The
former propagates in the ion diamagnetic drift
direction with 𝑘𝜃 𝜌𝑠 ≈ 0.1-0.35 and contributes tomost of the outward heat and particle fluxes; thelatter propagates in the electron diamagnetic drift
direction with 𝑘𝜃 𝜌𝑠 ≈ 0.01-0.035 and contributes
to weak outward transport. A set of CGYRO

simulations suggests that the 120 kHz mode is theMTM and the low-frequency turbulence is the ITG
mode, which is consistent with the experimental
fingerprints. When ELMs are strongly mitigated by
𝑛 = 1 RMP, broadband turbulence (<50 kHz)dominates the outward particle flux and helps tomaintain the ELM mitigation. In the island divertor
configurations of W7-X, the radial turbulent heatand particle fluxes strongly depend on the localmagnetic topology and electron density, revealing
two distinct transport patterns: a broadband
turbulence dominant region in the island and a
low-frequency dominant region in the inner SOL.
From the findings in EAST and W7-X, turbulence
could drive significant radial transport in 3D
magnetic topology, and the dominant turbulence
depends on the local magnetic topology and plasma
profiles, which provides a physical means to control
the cross-field transport and divertor heat flux
actively.

References[1] Liu S. C. et al 2023 Nucl. Fusion 63 042003;[2] Liu S. C. et al 2020 Nucl. Fusion 60 082001;[3] Liu S. C. et al 2019 Nucl. Fusion 59 066001;[4] Liu S. C. et al 2020 Phys. Plasmas 27 122504.

Figure 1. Radial turbulent particle flux in the frequency space for the ELMy phase (a) and ELM suppression phase with𝑛 = 4 RMP (b) at the outer midplane; (c) radial turbulent particle flux; (d) radial turbulent heat flux; (e) SOL electron
density. The positive 𝛤𝑟 signifies the outward particle flux, while the negative value means the inward particle flux.
The shaded regions in (c), (d) and (e) denote the standard deviation of particle flux and electron density, respectively.