Fusion magnet quench risk increase with irradiation damage
Open accessAbstract
Superconducting material enables fusion reactor magnet concepts to operate with current densities that would melt materials with non-zero resistance. The application of superconducting material is considered essential for net-positive power machines. Catastrophic damage can occur when superconductivity is lost and the current generates heat. This scenario is called a quench. Stabilizer material carries the magnet current (typically copper) during a quench and is the focus of this work. Irradiation-induced defects store energy in the Cu crystalline lattice. The presence of defects reduces thermal conductivity (thermally insulating the superconductor), electrical conductivity (increasing temperature ramp rate during a quench), and specific heat capacity (increasing thermodynamic instability). The release of stored energy in the magnet materials, in combination with the magnet material property changes, has the potential to cause extreme off-normal events in superconducting magnets that worsen with fluence. Stored energy can be released causing local heating and increasing the risk of a quench. For example, following irradiation at 4.6 K and a fluence of 0.45×10 18 n cm−2, an energy release of 0.023 J g−1 was measured from Cu when increased in temperature from 10 K to 18 K, which would have been enough energy to create the same temperature increase spontaneously. Extrapolations of experimental data are used to estimate when spontaneous heating can occur due to the release of energy stored in irradiation-induced defects. Critical fluence values are estimated between 1.74×10 18 n cm−2 and 2.85×10 19 n cm−2 for neutron irradiation of Cu at a temperature of 20 K. In-situ cryogenic calorimetry experiments, operated at high-temperature-ramp rates on irradiated magnet materials, could offer certainty for fusion magnet system designers. Periodic annealing of defects through controlled temperature cycling will be essential in fusion power plants to manage the increasing risk of quench as the superconducting magnets accumulate dose. The ideal frequency and dynamics of these maintenance temperature cycles will be established with further experimental examination.
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At cryogenic temperatures below 50 K, defect migration is minimized, so defect clusters are more stable and rarely recombine.
“At cryogenic temperatures below 50 K, defect migration is minimized, meaning clusters are more stable and rarely recombine [45, 46].”
From A facility for thermo-mechanical characterization of fusion magnet materials during cryogenic ion irradiation (2025) · cites this paper as [45]
Section 4 (page unavailable) says decreasing temperature reduces interstitial–vacancy interactions, supporting reduced recombination at lower temperatures. But section 3 says Frenkel pairs anneal below 45 K and complex defect structures anneal above 45 K. The source therefore does not support a blanket claim that defects rarely recombine throughout the range below 50 K. (LLM, conf=0.86)
Experimental — accuracy not yet measuredIn metals and alloys like Cu-110, irradiation-induced lattice vacancies and interstitials form defect clusters within the microstructure.
“In metals and alloys like Cu-110, irradiation-induced lattice vacancies and interstitials form defect clusters within the microstructure.”
From A facility for thermo-mechanical characterization of fusion magnet materials during cryogenic ion irradiation (2025) · cites this paper as [45]
Section 3 (Stored energy release; page unavailable) says Frenkel pairs agglomerate into defect structures, and section 4 (Defect saturation; page unavailable) describes irradiation-produced interstitials, vacancies, and structures remaining in the lattice. The paper discusses copper but does not identify Cu-110 specifically, so the claim's material-specific example is not directly supported. (LLM, conf=0.85)
Experimental — accuracy not yet measured
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Aurora, A., Devitre, A. R., Wylie, A. P. C., Rajagopal, J. A., & Short, M. P. (2025) · Nuclear Fusion · doi:10.1088/1741-4326/add74e · Cited by 1 · see citing works
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“These initial findings indicate that more comprehensive property evolution studies are necessary to prove existing assumptions regarding cop-per’s cryostability and quench protection candidacy under cryogenic irradiation [45].”
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Neutron Irradiation Experiments to Support Fusion Blanket Development
Taylor, C. N., Calderoni, P., Yu, X., Fischer, D. X., Fuerst, T. F., & Weisberg, D. B. (2026) · IEEE Transactions on Plasma Science · doi:10.1109/tps.2026.3730331
- Authors
- John, J. M., Gilbert, M. R., & Hardie, C. D.
- Affiliations
- United Kingdom Atomic Energy Authority (GB)
- Corresponding author
- John, Jacob M.
- Venue
- Nuclear Fusion
- Publisher
- IOP Publishing
- Published
- 2025-03-12
- Volume
- 65
- Issue
- 4
- Pages
- 046013
- ISSN
- 0029-5515 (ISSN-L)
- 1741-4326
- OpenAlex
- W4407202907
- Cited by
- 5
- References
- 35
- Citations by year
- 2026: 4 · 2025: 1
- FWCI
- 1.22
- Type
- journal article
- Language
- en
- Open access
- gold
- doi.org
- Licence
- Locations
- Nuclear Fusion (publishedVersion, cc-by)
- DOAJ (DOAJ: Directory of Open Access Journals) (submittedVersion, cc-by-sa)
- Funders
- Research Councils UK (EP/W006839/1)
- Topics
- Physical Sciences › Engineering › Biomedical Engineering › Superconducting Materials and Applications
- Physical Sciences › Materials Science › Materials Chemistry › Fusion materials and technologies
- Physical Sciences › Physics and Astronomy › Nuclear and High Energy Physics › Magnetic confinement fusion research
- Keywords
- fusion reactor magnets, superconducting magnets, radiation damage, copper stabilizer, neutron irradiation, radiation-induced defects, stored energy release, spontaneous heating, critical fluence, thermal conductivity, electrical conductivity, specific heat, defect annealing, thermal cycling
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