Integrated RMP-based ELM-crash-control process for plasma performance enhancement during ELM crash suppression in KSTAR

Abstract

The integrated resonant magnetic perturbation (RMP)-based ELM-crash-control process aims to enhance the plasma performance during the RMP-driven ELM crash suppression, where the RMP induces an unwanted confinement degradation. In this study, the normalized beta (βN) is introduced as a metric for plasma performance. The integrated process incorporates the latest achievements in the RMP technique to enhance βN efficiently. The integrated process triggers the n = 1 edge-localized RMP (ERMP) at the L-H transition timing using the real-time machine learning (ML) classifier. The pre-emptive RMP onset can reduce the required external heating power for achieving the same βN by over 10 % compared to the conventional RMP onset. During the RMP phase, the adaptive feedback RMP ELM controller, demonstrating its performance in previous experiments, plays a crucial role in maximizing βN during the suppression phase and sustaining the βN-enhanced suppression state by optimizing the RMP strength. The integrated process achieves βN up to ~2.65 during the suppression phase, which is ~10 % higher than the previous KSTAR record but ~6 % lower than the target of the K-DEMO first phase (βN = 2.8), and maintains the suppression phase above the lower limit of target βN (= 2.4) for ~4 s (~60 τE). In addition to βN enhancement, the integrated process demonstrates quicker restoration of the suppression phase and recovery of βN compared to the adaptive control with the n = 1 conventional RMP (CRMP). The post-analysis of the experiment shows the localized effect of the ERMP spectrum in radial and the close relationship between the evolution of βN and the electron temperature.

Tailoring tokamak error fields to control plasma instabilities and transport

“…Note that this ERMP example is one of many examples of its safe and efficient ELM suppression in KSTAR. For example, ERMP has improved the plasma confinement of other KSTAR discharges to extend its β N boundary up to β N of 2.65 47 . ERMP also demonstrated n = 1 RMP ELM suppression at ITER relevant q 95 of 3.5 in KSTAR 48 .…”

Highest fusion performance without harmful edge energy bursts in tokamak

“…This adaptive approach exhibits compatibility between RMP ELM suppression and high confinement. Additionally, it provides a robust strategy for achieving stable ELM suppression in long-pulse scenarios 58 (lasting more than 45 s) by minimizing the loss of confinement and non-inductive current fraction 69 . Notably, a remarkable performance ( G ) boost is observed in DIII-D with n RMP = 3 RMPs, showing over a 90% increase from the initial standard ELM-suppressed state.…”

Heuristic predictions of RMP configurations for ELM suppression in ITER burning plasmas and their impact on divertor performance

“…The latter imposes an upper threshold for the applied RMP strength, and this is found to be a particularly strict condition for low n RMPs in KSTAR [35,47,48]. A combined approach for maximizing the edge impact and minimizing the core impact allows for optimal ELM control [49,50]. It has been found that the core-kink response is linked to a large displacement |ξ M | of the plasma boundary at the outboard midplane [30,31,51], and in the following we will use this as a figure of merit for core stability.…”