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

Abstract

Abstract The integrated Resonant Magnetic Perturbation (RMP)-based Edge-Localized Mode (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 ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mi>β</mml:mi> <mml:mrow> <mml:mtext>N</mml:mtext> </mml:mrow> </mml:msub> </mml:math> ) is introduced as a metric for plasma performance. The integrated process incorporates the latest achievements in the RMP technique to enhance <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mi>β</mml:mi> <mml:mrow> <mml:mtext>N</mml:mtext> </mml:mrow> </mml:msub> </mml:math> 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 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mi>β</mml:mi> <mml:mrow> <mml:mtext>N</mml:mtext> </mml:mrow> </mml:msub> </mml:math> by over 10% compared to the conventional onset. During the RMP phase, the adaptive feedback RMP ELM controller, demonstrating its performance in previous experiments, plays a crucial role in maximizing <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mi>β</mml:mi> <mml:mrow> <mml:mtext>N</mml:mtext> </mml:mrow> </mml:msub> </mml:math> during the suppression phase and sustaining the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mi>β</mml:mi> <mml:mrow> <mml:mtext>N</mml:mtext> </mml:mrow> </mml:msub> </mml:math> -enhanced suppression state by optimizing the RMP strength. The integrated process achieves <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mi>β</mml:mi> <mml:mrow> <mml:mtext>N</mml:mtext> </mml:mrow> </mml:msub> </mml:math> 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 ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mi>β</mml:mi> <mml:mrow> <mml:mtext>N</mml:mtext> </mml:mrow> </mml:msub> </mml:math> = 2.8), and maintains the suppression phase above the lower limit of target <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mi>β</mml:mi> <mml:mrow> <mml:mtext>N</mml:mtext> </mml:mrow> </mml:msub> </mml:math> (= 2.4) for ∼4 s (∼60 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mi>τ</mml:mi> <mml:mrow> <mml:mtext>E</mml:mtext> </mml:mrow> </mml:msub> </mml:math> ). In addition to <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mi>β</mml:mi> <mml:mrow> <mml:mtext>N</mml:mtext> </mml:mrow> </mml:msub> </mml:math> enhancement, the integrated process demonstrates quicker restoration of the suppression phase and recovery of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mi>β</mml:mi> <mml:mrow> <mml:mtext>N</mml:mtext> </mml:mrow> </mml:msub> </mml:math> 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 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mi>β</mml:mi> <mml:mrow> <mml:mtext>N</mml:mtext> </mml:mrow> </mml:msub> </mml:math> and the electron temperature.

Topics & Concepts