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

On pedestal fluctuations in H-modes without large ELMs during the transition
to a detached tungsten divertor in EAST
R. Chen1, Y. Ye2, G.S. Xu1 and L. Wang1
1
Institute of Plasma Physics, Chinese Academy of Sciences, Hefei 230031, China
2
Institute of Energy, Hefei Comprehensive National Science Center, Hefei 230031, Chinae-mail (speaker): chenran@ipp.ac.cn
Simultaneous control of the damaging erosion inducedby the transient and steady-state heat/particle fluxes onthe divertor target material is one of the critical issues fornext-step magnetic fusion devices. Studying on thepedestal fluctuations in small/no ELM H-modes may
provide important insights into sustainment of large
ELM elimination when compatible with a radiative
divertor.
H-mode operation without large edge-localized modes
has been achieved in EAST with an ITER-like tungsten
divertor, while being compatible with the partial andpronounced detachment in divertor, via either rampingup of bulk density or injection of low/high-Z impurities.
The pedestal characteristics during the transition fromthe attached to the detached divertor and the reversedtransition (detached to attached) under different
detachment methods are studied in detail, where theevolution of multi fluctuating structures commonlyresiding in the H-mode pedestal of EAST (edge coherentmode (ECM) [1], magnetic coherent mode (MCM) [2] andhigh frequency mode (HFM) [3]) is highlighted.
It is found that in the pronounced detachment which
EAST has successfully achieved at the auxiliary heating
power Psource = 2–6 MW, the ECM tends to disappear
either by ramping plasma density up or by impurity

Heating
Psource (MW)Edge coherent mode
Magnetic coherentmodeHigh-frequency
mode

injection in the divertor, while evolutions of the MCM
and the HFM behaviors are not uniform, as summarizedin Table 1[4]. Further analysis shows that in addition tothe pressure gradient which is considered as a primary
free energy source for the pedestal instabilities including
the ECM, the MCM and the HFM, the pedestal
collisionality also appears to play a crucial role inaffecting the ECM amplitude, and subsequently
influencing the MCM and the HFM intensities possibly
via re-allocating free energy among the three modes
In addition, the radial structures of ECM, MCM andHFM are detected, for the first time, in one discharge.
The ECM peak position is localized in the steep gradientregion, while the MCM and the HFM peak positions areslightly more radially outside than the ECM, but still
within the separatrix. Distinct from the ECM and theMCM, the HFM seems to exhibit a non-monotonousradial distribution of intensity, and even be detectable inthe SOL region.
References[1] H.Q. Wang et al Phys. Rev. Lett. 112 185004 (2014)[2] R. Chen et al Nucl. Fusion 58 112004 (2018)[3] H. Lan et al Phys. Plasmas 26 122505 (2019)[4] Y. Ye et al Nucl. Fusion 61 126050 (2021)

Pronounced detachment induced by

Pronounced detachment induced byramping-up plasma density

injecting impurity

Low heating
2–4

High heating
4–6

Plasma confinement degrades
severely, ECM, MCM and HFM all
disappear

Low heating
2–4
Disappear

High heating
4–6
Disappear

Disappear

WeakenDisappear, weaken or

Weakeneven enhance

Table 1. The relative amplitude of ECM, MCM and HFM in the pronounced detachment at EAST.