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

Demonstration of divertor stationary heat flux control during RMP ELM
suppression in EAST
M. Jia1, Y. Sun1, A. Loarte2, H. Yang1, Q. Ma1, P. Xie1, G. Chen1, 3, X. Wu1, S. Gu4, K. Li1,Y. Liang5, R. Liang1, C. A. Paz-Soldan6, J. Qian1, B. Shen1, H.H. Wang1, B. Wan1, S. Xu5, Q. Zang1,L. Zhang1
1
Institute of Plasma Physics, Chinese Academy of Sciences, China, 2 ITER Organization, France,3Donghua University, China, 4 Oak Ridge Associated Universities, USA,
5Forschungszentrum Jülich, Germany, 6 Columbia University, New York, United States of America
e-mail: jiamanni@ipp.ac.cn
Compatibility of divertor stationary heat flux control byimpurity injection with the type-I edge localized modes(ELMs) suppression by resonant magnetic perturbations(RMPs) has been demonstrated in EAST. A clear
reduction of divertor heat flux on the original strike lines
can be observed after carbon impurity being injectedduring ELM suppression. While the change of heat fluxes
onto the splitting strike line is not significant. At the sametime, good confinements of both energy and particles aremaintained. The advantages of using n=4 RMPs arefurther confirmed.
An example of the effective heat flux reduction byimpurity injection during n = 4 RMP ELM suppression isshown in Fig. 1. Here n is the toroidal mode number of theRMP field. Another shot #115755 without impurity
injection is shown as comparison. To address the ITER
concerned issues on characterization and control ofstationary divertor power fluxes with RMP fields [1],these experiments are operated in low input torqueplasmas, which are close to the ITER equivalent torque1.1 Nm in EAST [2] with the edge safety factor at 95% ofnormalized poloidal flux q95 ~ 4, the line averaged plasma
density ne ~ 3×1019 m-3 and the normalized plasma beta βN~ 1.5. Both of the two shots achieve ELM suppression by
the n = 4 RMP field with even parity except for someoccasionally appeared single ELMs. The RMP coil current
are 3.5 kA in #115793, which is higher than that in#115755. As a result, the suppression is relatively stablein #115793 with less occasionally appeared ELM spikes.
In #115793, CD4 gas is injected from 4 s to 6 s from thevalve on the low field side target of the newly upgradedtungsten lower divertor module. The heat flux splitting
can be observed after RMP application, which isconsistent with the numerical modelling. An effective
reduction on heat flux to the original strike point at about
L ~ 30 mm can be distinguished after 4s in #115793. Here
L is the distance to the divertor corner in the poloidal
direction. The change of heat fluxes onto the splitting
strike line is not significant.
The plasma confinement is well maintained with CD4
injection during ELM suppression. The carbon radiation
is effectively increased but localized near the divertor
target and the slight increase in plasma density iscontributed to the fueling effect by injecting CD4. It
indicates that the carbon impurity can be well screened by
the edge stochastic layer formed by the n = 4 RMP field.
Although previous EAST experiments have shown thecompatibility of divertor heat flux reduction by neon
impurity injection with the n = 2 RMP field [3], there wereabout 30% drop in the energy confinement, which is not
an attractive result for ITER. Such good energy
confinement with edge localized impurity radiation during
ELM suppression further increases the confidence inusing high n RMPs in future ITER application. To expand
the physics understanding for integrated divertor and heat
flux control, modeling of plasma response to RMP as wellas the three-dimensional plasma and neutral particle
transport modelling using EMC3-EIRENE would address
new understanding of 3D edge transport and divertor heat
flux profiles. More detailed discussions of modelling andanalysis will be addressed in this presentation. As a result,the advantages of using n=4 RMPs is further confirmed
not only in ELM suppression but also in the compatibility
with integrated divertor flux control, which is attractivefor ITER and future devices.

Figure 1. The effective heat flux reduction by CD4
injection in EAST #115793 discharge and the comparison
with another discharge #115755 without any impurity
injection. (a)(b)References[1] A.Loarte et. al. Nuclear Fusion 54, 033007 (2014)[2] Sun Y et al, Nuclear Fusion 61, 106037 (2021)[3] Jia M. et al, Nuclear Fusion 61,106023 (2021)