Low-n stability and plasma response to RMP in various STEP scenarios

Liu, Yueqiang; Chen, Xi; Li, Zeyu; Saarelma, Samuli; Tang, Tengfei; Xia, Guoliang

doi:10.1088/1361-6587/adf462

Low-n stability and plasma response to RMP in various STEP scenarios

Journal Article · Tue Aug 05 00:00:00 EDT 2025 · Plasma Physics and Controlled Fusion

DOI:https://doi.org/10.1088/1361-6587/adf462· OSTI ID:2998641

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General Atomics, San Diego, CA (United States)
United Kingdom Atomic Energy Authority, Oxon (United Kingdom)

The low-n (n is the toroidal mode number) magnetohydrodynamic (MHD) stability and plasma response are numerically investigated for various scenarios designed for STEP, that are relevant for the H-mode pedestal analysis. Control of the edge-localized modes (ELMs) with externally applied resonant magnetic perturbations (RMPs) is considered. Optimization of the ELM control coil current configuration, based on the computed plasma MHD response and well-established figures of merit validated on present-day experiments, finds reasonable robustness of a fixed coil phasing (for a given n-number) to control ELMs in all five STEP plasmas considered. Based on certain semi-empirical criteria, the required coil current to achieve ELM suppression is estimated to be about 10–20 kAt with the n = 1 or 2 RMP configuration and about 100–200 kAt for the n = 4 RMP. Systematic linear stability calculations are used to map out stability windows for the low-n kink-peeling modes, in terms of the ideal-wall location and variation of the edge safety factor q₉₅ with respect to the target design. The kink-peeling stability boundary is found to be generally sensitive to the q₉₅ variation, which has implications for achieving the quiescent H-mode regime in STEP. Full toroidal quasilinear initial-value simulations for these STEP plasmas find that generation of the edge-harmonic oscillations (EHOs) depends sensitively on the plasma scenario, the initial linear stability of the kink-peeling modes, the initial plasma toroidal flow and q₉₅. In general, it is easier (more robust) to access the EHO-regime for two of the cases considered with smaller plasma volume and higher on-axis safety factor. Finally, quasilinear simulations find robust density pumpout due to applied RMPs in these STEP plasmas, but the effect on the plasma toroidal flow varies among different cases.

View Accepted Manuscript (DOE)

Research Organization:: General Atomics, San Diego, CA (United States)

Sponsoring Organization:: UKIFS; USDOE Office of Science (SC), Fusion Energy Sciences (FES)

Grant/Contract Number:: SC0018992

OSTI ID:: 2998641

Journal Information:: Plasma Physics and Controlled Fusion, Journal Name: Plasma Physics and Controlled Fusion Journal Issue: 8 Vol. 67; ISSN 0741-3335; ISSN 1361-6587

Publisher:: IOP PublishingCopyright Statement

Country of Publication:: United States

Language:: English

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