Extension of ELM suppression window using n = 4 RMPs in EAST

Abstract

The q95 window for Type-I Edge Localized Modes (ELMs) suppression using n=4 even parity Resonant Magnetic Perturbations (RMPs) has been significantly expanded to a range from 3.9 to 4.8 in EAST, which is demonstrated to be reliable and repeatable over the last two years. This window is significantly wider than the previous one achieved using n=4 odd parity RMPs, which is around q95=3.7±0.1. Here, n represents the toroidal mode number of the applied RMPs and q95 is the safety factor at 95% of the normalized poloidal magnetic flux. During ELM suppression, there is only a slight drop in the plasma stored energy and density (≤10%). The comparison of changes in the pedestal profiles suggests that ELM suppression is achieved when the pedestal gradient is kept lower than a threshold. This wide q95 window for ELM suppression is consistent with the prediction made by MARS-F modeling prior to the experiment, which located it at one of the resonant q95 windows for plasma response. The Chirikov parameter taking into account plasma response near the pedestal top, which measures plasma edge stochasticity, significantly increases when q95 exceeds 4, mainly due to the denser neighboring rational surfaces. The modeling of plasma response reveals a strong coupling between resonant and non-resonant components across the pedestal region, which is a characteristic of the kink-peeling like response observed during RMP-ELM suppression in previous studies on EAST. These promising results demonstrate the reliability of ELM suppression using the n=4 RMPs in EAST and expand the physical understanding on ELM suppression mechanism.

Dynamic control of divertor heat flux during n = 4 resonant magnetic perturbation edge localized mode suppression by small variation of q 95 in EAST

“…As shown in figure 2(a), simulation results demonstrate that the stochastic layer width varies with odd and even RMP configurations, exhibiting peaks during q 95 increases. Applying the MARS-F code to consider plasma response effects reveals peaks in the stochastic layer width, showing qualitative agreement with the existence of q 95 windows in experiments [10,37,39], as shown in figure 2(b). These results establish a strong link between simulated stochastic layer widths and ELM suppression windows, highlighting the crucial role of plasma response in understanding the ELM suppression mechanism.…”

“…The MARS-F code [36] is one of the most widely used codes for modeling the linear plasma responses to the applied RMP field. In EAST experiments with various RMP applications, the modeling with the plasma response calculated by MARS-F can well predict the ELM control windows as discussed in [10,37], as well as the distribution of divertor heat and particle fluxes on the divertor target [29,30]. The MARS-F code is also used in this work.…”

Plasma performance and operational space with an RMP-ELM suppressed edge

“…In the range of q 95 4.8-6.2 is also where AUG first discovered strong ELM mitigation [85]. Note very recent EAST data, taken after the compilation of this database, has extended n = 4 RMP-ELM suppression to q 95 ≈3 [86] and q 95 >4, with different q 95 gap sensitivity observed [87]. Also interesting is the generic accessibility of a window between q 95 = 3-4.…”