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New Tokamak Plasma Confinement Regime Realized by Utilizing Small Magnetic Perturbations in the EAST Tokamak

Hui Sheng1,2, Youwen Sun2,*, Alberto Loarte3, Tonghui Shi2, Yingying Li4, Jiale Chen2, Yueqiang Liu5, Yunfeng Liang6, Shaojie Wang1 et al.

Ling Zhang2, Wenmin Zhang2,1, Chengxi Zhou2, Lei Ye2, Shifeng Mao1, Tianqi Jia2, Huihui Wang2, Manni Jia2, Qun Ma2, Xuemin Wu2,1, Pengcheng Xie2, Cheng Ye2, Shuai Gu2, Nan Chu2, Jinping Qian2, Qing Zang2, Haiqing Liu2, Yuqi Chu2, Xuexi Zhang2, Hailin Zhao2, Yanmin Duan2, Jinfang Wang2, Minyou Ye1,†, and Baonian Wan2

  • *Contact author: ywsun@ipp.ac.cn
  • †Contact author: yemy@ustc.edu.cn
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PRX Energy 4, 043012 – Published 19 December, 2025

DOI: https://doi.org/10.1103/jtrr-p41y

Abstract

Achieving sustained high plasma confinement both in the core and at the edge, without crashes due to edge instabilities, is highly desirable for efficient fusion energy production in a tokamak device. However, control of edge instabilities usually results in core plasma confinement degradation. Here we demonstrate a new improved core confinement plasma regime in EAST, characterized by a sustainable internal transport barrier (ITB) and effective control of edge instabilities, both achieved by applying small resonant magnetic field perturbations (RMPs) at just 0.1% of the equilibrium field amplitude. The key is to localize the perturbations at the edge, which can be effectively realized by use of RMPs with high toroidal mode numbers. Nonlinear interaction between the perturbed magnetic fields and plasma, especially tungsten impurities, on different scales plays a key role in lowering the threshold heating power by a factor of 2 for triggering the formation of an ITB to improve core confinement. More importantly, the improved core confinement can be actively controlled by tuning the perturbed field profile. This provides an attractive method and a physical basis for an integrated solution of keeping high core confinement during edge stability control for a future fusion reactor.

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Popular Summary

Realizing practical fusion energy in tokamaks requires simultaneously achieving two essential goals: high plasma confinement for sufficient fusion gain and suppression of edge crash events from edge instabilities for device safety. Historically, these objectives have proved fundamentally incompatible, as stabilizing the edge consistently degraded core performance. This work on the Experimental Advanced Superconducting Tokamak (EAST) overcomes this longstanding trade-off. By applying optimized small magnetic perturbations to the plasma edge, the approach presented here completely suppressed edge crashes while simultaneously enhancing core confinement. The analysis shows that multiscale interactions between perturbations, plasma, and tungsten impurities enable high core confinement. Remarkably, the perturbations reduce the heating power for this enhanced confinement state by 50%. Furthermore, the improved core confinement is sustainable and controllable by adjusting the perturbations. This breakthrough demonstrates a method to achieve both stable edges and high-performing cores, which is critical for the efficient operation of future fusion reactors.

Article Text

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PRX Energy 4, 043012– Published 19 December, 2025
  • Received 1 July 2025
  • Revised 9 October 2025
  • Accepted 19 November 2025
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

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