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

Study of impurity tungsten transport and suppression in EAST Tokamak
H. M. Zhang1, B. Lyu1,2, Z. C. Lin1,2, X. D. Yang1, Y. C. Shen3, H. J. Ji1,2, F. D Wang1, J. Fu1, Y.
Fan1,4, C. Zeng1,4, B. Sun1,4, S. Y. Dai5
1

Institute of Plasma Physics, Chinese Academy of Sciences
School of Physics, University of Science and Technology of China
3
School of Physics and Materials Engineering, Hefei Normal University
4
School of Physics and Materials Engineering, South China University
5
School of Physics, Dalian University of Technology
e-mail (speaker): hmzhang@ipp.ac.cn
2

The impurity in fusion plasmas is generally produced
by an interaction between edge plasmas and plasma facing
components in the vacuum vessel, e.g., divertor plates,
first wall and radio-frequency antennas. Impurity
accumulation in core plasma can dilute the density of fuelions, cool down the plasma, degrade the confinement
performance and even result in plasma disruption. In
particular, accumulation of heavy impurities such as
tungsten (W) can breaks the energy balance through thehuge radiation loss in the core region since the radiation
loss power is a function of the atomic number. Since W
divertor plates are used in ITER, suppression of W
concertation in core plasma has become one of the mostcritical technique challenges for the steady-state operation.
ITER-like tungsten divertor has been used in EAST.
Even wall conditioning methods, such as Lithium coating,are applied, plasma disruptions caused by impurity W
accumulation also frequently happen during the EAST
experimental campaign. The disruption not only degrade
the first wall condition, but also threaten the device safety.
Suppression of impurity W in the core region also
becomes one the most important issues for achieving
long-pulse operations in EAST. In this study, therefore,both on-axis electron cyclotron resonance heating(ECRH) and resonant magnetic perturbation (RMP) areapplied to suppress impurity W accumulation in EAST.
Impurity transport is also studied under the conditions ofECRH and RMP.
In EAST, space-resolved extreme ultraviolet (EUV)
spectroscopy and X-ray crystal spectroscopy (XCS) havebeen developed to observe the spatial distribution andtemporal behavior of core impurity emissions [1].
Recently, in order to obtain the W concertation in EAST
plasma, absolute intensity calibration is conducted for theXCS system. Besides, Abel inversion technique is also
developed for obtaining the radial profile of W44+ ionsconcentration [2]. In this study, the radial profiles of W
LXV (3.9095 Å) emissions are used to analyze the W
behavior in the core region.
Firstly, the effects of on-axis ECRH on W emissions
are studied with the help of EUV and XCS systems. As
shown in Fig.1, the W concentration dramaticallydecrease as ECRH applied. Then, the behavior of Wemissions is also study under the condition of applying
both on-axis ECRH and RMP. It is observed that theimpurity W concentration in the core region of EAST
plasma can be further reduced as RMP is supplied [2]. The
impurity suppression efficiency of RMP is also studied
against the RMP strength and RMP mode number.
The impurity transport behavior is also studied with
one-dimensional impurity transport code STRAHL [4]. As
the on-axis ECRH heating is applied, the diffusion
coefficient in 0<ρ<0.6 region are enhanced significantly.
However, the value of inward convective velocity
decreases at the same time. When the RMP is further
applied, the inward convective velocity further decreases
and even turns outward in the region of ρ > 0.5. It isthought that the on-axis ECRH and RMP increase theturbulence intensity in the core region, which changes thediffusion coefficient and the convective velocity of W ions.
The reverse of the convective velocity may also contributeto the suppression of W concentration in core impurity
density.
References[1] Y. C. Shen, X.W. Du, W. Zhang, et. al., , Nuclear
Instruments and Methods in Physics Research A 700, 86–90 (2013).
[2] Z. C. Lin, H. M. Zhang, F. D. Wang, et. al., Phys.
Plasmas 30, 032505 (2023).
[3] G. Vogel, H.M. Zhang, Y.C. Shen, et. al, , IEEE
Transactions on Plasma Science, 46, 1350 – 1355 (2018).
[4] G. Vogel, H. M. Zhang, Y. C. Shen, et. al, J. Plasma
Phys. 87, 905870213 (2021).

w/o ECRH

with ECRH

Fig. 1 The concentration profile of W44+ ions shows dramatic
decrease in the core region as ECRH is applied.