Plasma and Fusion Research

Volume 21, 1202007 (2026)

Rapid Communications

Coherent MHD Behaviour in a Shallow Magnetic Well Configuration in Heliotron J

Sjoerd P. REINHOUDT¹⁾, Kazunobu NAGASAKI²⁾, Josefine H.E. PROLL^1,3), Fumiyoshi KIN²⁾, Shigeru INAGAKI²⁾, Shinji KOBAYASHI²⁾, Shinichiro KADO²⁾

1): Eindhoven University of Technology, Eindhoven 5612AE, The Netherlands
2): Institute of Advanced Energy, Kyoto University, Gokasho, Uji, Kyoto 611-0011, Japan
3): Max Planck Institute for Plasma Physics, Greifswald 17491, Germany

(Received 18 September 2025 / Accepted 4 November 2025 / Published 18 February 2026)

Abstract

This article presents the first experimental results from a novel configuration in Heliotron J, which features a shallow magnetic well in the core of the plasma. A broadband coherent fluctuation of approximately 10 kHz is observed in a low-β electron cyclotron heated (ECH) plasma at rotational transform ι/2π = 0.55 in this configuration, while no mode appears in a deep magnetic well configuration. An electron cyclotron emission measurement shows the mode is excited in the core region where the magnetic well is shallow. This indicates Heliotron J is able to sustain viable plasmas with an edge-hill, although these can be destabilised even at low density and pressure.

Keywords

Heliotron J, magnetic well, magnetic hill, MHD instability

DOI: 10.1585/pfr.21.1202007

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