Influence of plasma shaping on <i>n</i>  = 4 RMP response in EAST

Abstract The effect of plasma shaping on the n = 4 resonant magnetic perturbation (RMP) response in EAST is investigated using the resistive magnetohydrodynamic code MARS-F (Liu et al 2010 Phys. Plasmas 17 122502) under both upper and lower single null (USN and LSN) configurations, with the aim of guiding experimental shaping strategies for enhanced control of edge-localized mode (ELM). Upper and lower triangularity ( δ U , δ L ) or elongation ( κ U , κ L ) are varied independently via a coordinate transformation that closely mimics the experimental shaping, while key equilibrium parameters are held fixed. The simulations reveal that increasing the triangularity or elongation on the X-point side (upper in USN, lower in LSN) consistently enhances the edge plasma response, as characterized by increased resonant radial field ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mi>b</mml:mi> <mml:mrow> <mml:mi>res</mml:mi> <mml:mo>,</mml:mo> <mml:mi>outer</mml:mi> </mml:mrow> </mml:msub> </mml:mrow> </mml:math> ), stronger edge peeling response ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mi>A</mml:mi> <mml:mrow> <mml:mi>peel</mml:mi> </mml:mrow> </mml:msub> </mml:mrow> </mml:math> ), and intensified surface displacement near the X-point ( ξ X ), all of which are favorable for ELM suppression. Conversely, increasing shaping parameters on the non-X-point side (lower in USN, upper in LSN) weaken these responses. The optimal RMP coil phasing for maximizing plasma response exhibits an approximately linear dependence on the shaping parameters, with greater sensitivity to variations on the X-point side. Notably, when plasma shaping on X-point side is weak, the optimal phasing derived from ξ X deviates from those based on <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mi>b</mml:mi> <mml:mrow> <mml:mi>res</mml:mi> <mml:mo>,</mml:mo> <mml:mi>outer</mml:mi> </mml:mrow> </mml:msub> </mml:mrow> </mml:math> and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mi>A</mml:mi> <mml:mrow> <mml:mi>peel</mml:mi> </mml:mrow> </mml:msub> </mml:mrow> </mml:math> , suggesting increased complexity in determining the optimal phasing for experiment; in contrast, such divergence does not occur when shaping is varied on the non-X-point side. The shaping variation approach proposed in this work offers a theoretical basis for optimizing plasma geometry and RMP configuration to improve ELM control efficiency in future fusion reactors.