Test of the ITER-like resonant magnetic perturbation configurations for edge-localized mode crash suppression on KSTAR

Abstract

KSTAR has demonstrated divertor heat flux broadening during edge-localized-mode (ELM)-crash-suppression using ITER-like 3-row resonant magnetic perturbation (RMP) for the first time. To address a couple of critical issues in ITER RMP, robust ELM-crash-suppression methodology has been explored at low q95 and established in KSTAR using low-n RMPs. Taking full advantage of the ITER-like 3-row in-vessel control coils (IVCC) in KSTAR, a set of intentionally misaligned RMP configurations (IMC) was tested to investigate whether or not IMC could be compatible with ELM-crashsuppression, while minimizing electromagnetic loads on RMP coils. As a result, the ITER-like 3-row IMCs were found not only to have been compatible with the ELM-crash-suppression, but also to have broadened the heat flux in the vicinity of the outer strike point on divertor. In comparison, the 2-row RMPs have rarely affected the near scrape-off-layer (SOL) heat flux despite slightly broadened profile change in the far-SOL. Since the divertor heat flux broadening reflects the dispersal of the peaked near-SOL heat flux, the experimental outcome is quite favorable to the ITER choice of 3-rows, instead of 2-rows. Nonetheless, since the IMC-driven broadening observed in the attached plasmas in KSTAR might appear substantially different in the partially detached plasmas in ITER, additional investigation has been conducted to see if RMP-driven, ELMcrash-suppression could be compatible with detached plasmas. Although no detached plasmas have been identified with ELM-crash-suppression yet, significantly reduced divertor heat flux was confirmed in high density, ELM-crash-suppressed plasmas at q95=3.8 using n=2 RMPs. These new findings elevate the confidence level about the ITER RMP system, while the remaining uncertainties need to be further clarified using the 3-row IVCCs in KSTAR. As long as mode-locking percussion is minimized along with a quick recovery of wall conditions, the access to the targeted q95 (~ 3) for ITER is foreseen to be feasible in KSTAR.

Summary of the 27th IAEA Fusion Energy Conference in the categories of EX/W, EX/D, and ICC

“…The dynamic control of heat flux profile at the divertor target plate using the perturbation magnetic field of RMP was reported from DIII-D [27,28] and KSTAR [29]. Figure 16 ( these mixed toroidal harmonic cases are observed.…”

“…Variation of the heat flux pattern at different phasing is also reported in KSTAR. 6(a) in [28] and figure 6 in [29]).…”

“…Here the heat flux is normalized with a peak value. (Adapted from figure 4(a) figure6(a) in[28] and figure6in[29]).…”

Pedestal electron collisionality and toroidal rotation during ELM-crash suppression phase under n = 1 RMP in KSTAR

“…For a decade, the KSTAR has conducted a variety of n ¼ 1 RMP experiments related to the ELM-crash control and physics, resulting in the first demonstration of n ¼ 1 RMP ELM-crash suppression, 3 the exploration of the effect of RMP coil phasing on ELM-crash control, 5,20 the first observation of divertor heat flux broadening in intentionally misaligned RMP configurations, 5,6,19 evidence of the interaction between RMP-driven turbulence and ELM structures, 4 and direct measurement of the perpendicular flow changes at the onset of ELM-crash suppression. 7 A database for RMP experiments has been constructed to summarize the results of KSTAR RMP experiments.…”

“…18 KSTAR has provided results to understand the physics and effects of RMP-driven ELM-crash suppression based on the high reproducibility of the suppression. [4][5][6][7]19,20 In KSTAR, the RMP-driven ELM-crash suppression phase is highly sustainable, in that the longest suppression phase was stably sustained up to the time scale of wall saturation by deuterium fuel ($30 s). 6 Therefore, KSTAR provides one of the best testbeds to address the remaining uncertainties of ELM-crash control in ITER.…”