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

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.