Extension of ELM suppression window using <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>n</mml:mi> </mml:mrow> <mml:mo>=</mml:mo> <mml:mn>4</mml:mn> </mml:math> RMPs in EAST
Pengcheng Xie, Youwen Sun, Qun Ma, S. Gu, Yueqiang Liu, M. Jia, A. Loarte, X. Wu, Yuyang Chang, Tianqi Jia, Tao Zhang, Z. Zhou, Qing Zang, Bo Lyu, Shengyu Fu, Hui Sheng, Cheng Ye, Hua Yang, Huihui Wang, the EAST Team
Abstract
Abstract The q 95 window for Type-I edge localized modes (ELMs) suppression using n = 4 even parity resonant magnetic perturbations (RMPs) has been significantly expanded to the ranges [3.9, 4.1] and [4.2, 4.8] in EAST while maintaining good confinement, 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 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mi>q</mml:mi> <mml:mrow> <mml:mn>95</mml:mn> </mml:mrow> </mml:msub> <mml:mo>=</mml:mo> <mml:mn>3.7</mml:mn> <mml:mo>±</mml:mo> <mml:mn>0.1</mml:mn> </mml:math> . Here, n represents the toroidal mode number of the applied RMPs and q 95 is the safety factor at <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mn>95</mml:mn> <mml:mi mathvariant="normal">%</mml:mi> </mml:math> of the normalized poloidal magnetic flux. During ELM suppression, there is only a slight drop in the plasma stored energy and density ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mo>⩽</mml:mo> <mml:mn>10</mml:mn> <mml:mi>%</mml:mi> </mml:mrow> </mml:math> ). 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 q 95 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 q 95 windows for plasma response. The Chirikov parameter taking into account plasma response near the pedestal top, which measures plasma edge stochasticity, significantly increases when q 95 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.