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Characterization of Transition to Detachment of Magnetic Confinement Plasmas via Data Driven Approach in LHD

Yugo ISOBE¹⁾, Hiroshi YAMADA¹⁾, Tatsuya YOKOYAMA²⁾, Masahiro KOBAYASHI^1,3), Yasuhiko IGARASHI⁴⁾, Yoshiro NARUSHIMA^3,5), Yuki TAKEMURA^3,5), Chihiro SUZUKI^3,5), Ryuichi SAKAMOTO^3,5)

1)

Graduate School of Frontier Sciences, The University of Tokyo, Kashiwa, Chiba 277-8561, Japan

2)

National Institutes of Quantum Science and Technology, Naka 311-0193, Japan

3)

National Institute for Fusion Science, National Institutes of Natural Sciences, Toki 509-5292, Japan

4)

Tsukuba University, Tsukuba 305-8573, Japan

5)

The Graduate University for Advanced Studies, SOKENDAI, Toki 509-5292, Japan

(Received 13 November 2024 / Accepted 26 January 2025 / Published 8 April 2025)

Abstract

The transition condition from an attached state to a detached state of magnetic confinement plasmas has been investigated by a data-drive approach in LHD. This transition is defined as a binary classification problem of two states, and Support Vector Machine together with Exhaust Search has been applied. The boundary between detachment and attachment in the physical parameter space has been identified as a decision function comprising radiation and heating power, magnetic field and the resonant magnetic flux. While resonant magnetic perturbation (RMP) secures stable detached plasmas, it has been found that the featured parameter is not externally applied RMP itself but the plasma response to RMP. The present approach gives a robust separation boundary even for the extended operation with radiation enhancement by neon gas puff. Anomaly detection with a singular value decomposition has been also applied to the temporal behavior and identified pre- and post-relationships of each physical parameter in time. Emissions from carbon impurities with low ionization potential start to change prior to the RMP penetration and then the drop of ion saturation current, that is the transition to detachment, happens. These temporal sequences do not necessarily mean causality but are helpful for approach to physical inference.

Copyright (c) 2025 The Japan Society of Plasma Science and Nuclear Fusion Research

Keywords

detached plasma, resonant magnetic perturbation, large helical device, support vector machine, anomaly detection

DOI: 10.1585/pfr.20.1402024

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