Suppression of edge localized mode crashes by multi-spectral non-axisymmetric fields in KSTAR

Abstract

Among various edge localized mode (ELM) crash control methods, only non-axisymmetric magnetic perturbations (NAMPs) yield complete suppression of ELM crashes beyond their mitigation, and thus attract more attention than others. No other devices except KSTAR, DIII-D, and recently EAST have successfully achieved complete suppression with NAMPs. The underlying physics mechanisms of these successful ELM crash suppressions in a non-axisymmetric field environment, however, still remain uncertain. In this work, we investigate the ELM crash suppression characteristics of the KSTAR ELMy H-mode discharges in a controlled multi-spectral field environment, created by both n = 2 middle reference and n = 1 top/bottom proxy in-vessel control coils. Interestingly, the attempts have produced a set of contradictory findings, one expected (ELM crash suppression enhancement with the addition of n = 1 to the n = 2 field at relatively low heating discharges) and another unexpected (ELM crash suppression degradation at relatively high heating discharges) from the earlier findings in DIII-D. This contradiction indicates the dependence of the ELM crash suppression characteristics on the heating level and the associated kink-like plasma responses. Preliminary linear resistive MHD plasma response simulation shows the unexpected suppression performance degradation to be likely caused by the dominance of kink-like plasma responses over the island gap-filling effects.

Simulation study of fast ion losses associated with the rotating n = 1 resonant magnetic perturbations in KSTAR

“…One such method involves applying 3D magnetic field perturbations through a set of external coils [5][6][7][8]. In KSTAR, ELM mitigation and suppression has been attempted via external 3D magnetic field perturbations [9][10][11][12].…”

Control of edge localized modes by pedestal deposited impurity in the HL-2A tokamak

“…Numerous efforts have been dedicated to explore the effective techniques for ELM control and many techniques have been developed. Existing methods for ELM control include resonant magnetic perturbations (RMPs) [10][11][12][13][14][15][16][17][18][19][20], supersonic molecular beam injection (SMBI) [8,[21][22][23][24], small pellet pacing [3,[25][26][27][28][29][30], fast vertical jogs of the plasma columns [31,32], and lower hybrid current drive (LHCD) [33][34][35]. ELM control has been achieved with RMPs in JET [14,17], DIII-D [6,10], ASDEX Upgrade [11], MAST [13,16,28], and KSTAR [12,18], with pellet pacing in DIII-D [3] and ASDEX Upgrade [7,[25][26][27][28][29][30], with SMBI in HL-2A [8,…”

Nonlinear simulation of ELM dynamics in the presence of resonant magnetic perturbations

“…The occurrence of edge localized modes (ELMs) during the H mode operation of a tokamak remains a serious concern for future devices like ITER because of their potential deleterious effects on the plasma facing components and divertor plates. These finite-amplitude perturbations of the plasma edge region which originate due to MHD instabilities driven by steep pressure gradients or edge plasma currents present during an H-mode have therefore been the subject of much theoretical and experimental studies over the past several years [1][2][3][4][5][6][7][8][9]. While the linear characteristics of these modes have been extensively modelled and attributed to the excitation of peeling/ballooning modes, their nonlinear dynamics is quite complex and far from being fully understood.…”