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Axisymmetric Eigenmodes Excited by Alpha Particle Energy Gradients in JET D-T Plasmas

H. J. C. Oliver1, D. King1, Ž. Štancar1, S. E. Sharapov1, D. Banerjee2, T. Barberis3, R. Coelho4, I. Coffey1, M. Dreval5 et al. (JET Contributors*, EUROfusion Tokamak Exploitation Team†)

I. Coffey1, M. Dreval5, M. Fitzgerald1, L. Frassinetti6, C. Giroud1, N. Hawkes1, D. Keeling1, C. C. Kim7, E. Lerche8, F. Porcelli2, and G. Szepesi1 (JET Contributors*, EUROfusion Tokamak Exploitation Team†)

  • *See author list of C. F. Maggi et al., Overview of T and D–T results in JET with ITER-like wall, Nucl. Fusion 64, 112012 (2024).
  • †See author list of E. Joffrin et al., Overview of the EUROfusion tokamak exploitation programme in support of ITER and DEMO, Nucl. Fusion 64, 112019 (2024).
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Phys. Rev. Lett. 136, 055101 – Published 4 February, 2026

DOI: https://doi.org/10.1103/j3cm-5mtm

Abstract

Axisymmetric Alfvén eigenmodes have been observed at the plasma edge in deuterium-tritium (D-T) tokamak plasmas externally heated only by neutral beam injection in JET. The modes were detected only in D-T plasmas, not in pure D plasmas, indicating excitation by fusion-born α particles. The presence of the axisymmetric mode suggests that the modes were driven by positive energy gradients in the α particle distribution rather than radial gradients. The modes are driven by counter-current passing α particles with large orbit widths, allowing core-born α particles to interact with modes at the plasma edge. This reveals an excitation mechanism arising from positive energy gradients produced by the minimum energy required to confine particles at the edge, relevant to all burning plasmas.

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Phys. Rev. Lett. 136, 055101– Published 4 February, 2026
  • Received 23 July 2025
  • Accepted 17 December 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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