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Runaway electrons during a coil quench in stellarators

Pavel Aleynikov*, Per Helander, and Håkan M. Smith

  • *Contact author: pavel.aleynikov@ipp.mpg.de
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Phys. Rev. Applied 25, 024065 – Published 20 February, 2026

DOI: https://doi.org/10.1103/v4s5-p4fr

Abstract

It is shown that avalanches of runaway electrons can arise in stellarators, even if there is no net toroidal current in the plasma or the magnetic-field coils, if the current in the latter varies rapidly enough, e.g., due to a superconductor quench. In present-day devices such as W7-X, significant runaway generation is theoretically possible only at very low gas or plasma density in the vacuum vessel, e.g., between discharges, if a seed population of free electrons is present. In reactor-scale stellarators, more dangerous runaway generation may occur both between discharges and during low-density plasma operation. Since a radiation-induced seed population is necessarily present in an activated device, an accidental coil ramp-down could convert substantial magnetic energy into wall-damaging runaway currents. There is, however, much more time to mitigate such events than in tokamak disruptions.

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References (28)

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Outline

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Phys. Rev. Applied 25, 024065– Published 20 February, 2026
  • Received 19 September 2025
  • Revised 19 December 2025
  • Accepted 2 January 2026
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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. Open access publication funded by Max Planck Society.

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