The ultra-powerful magnets that confine fusion plasma — from the legacy Nb3Sn technology in ITER to the revolutionary REBCO high-temperature superconductors enabling compact fusion reactors.
ReviewedLast reviewed: 9 Aug 2026·Category: Glossary
Why Superconducting?
Fusion reactors require magnetic fields of 5–20+ tesla sustained continuously. Resistive (copper) magnets would consume hundreds of megawatts of electrical power just for the field coils, making net energy gain impossible. Superconducting magnets carry current with zero resistance, consuming power only for cryogenic cooling (typically <1% of the equivalent resistive power).[1]
Two generations: (1) Low-temperature superconductors (LTS): NbTi (operating at 4.5 K, fields up to ~8 T) and Nb3Sn (4.5 K, up to ~12–13 T). Used in ITER, JT-60SA, KSTAR, and W7-X. (2) High-temperature superconductors (HTS): REBCO tape (operating at 20–30 K, fields exceeding 20 T). Used by CFS (SPARC), Tokamak Energy (ST40), and most private fusion companies.
HTS Revolution
REBCO (Rare Earth Barium Copper Oxide) tape has transformed fusion reactor design. By enabling fields of 20 T and above, HTS magnets allow tokamaks to be built at roughly one-quarter the linear dimensions of ITER while maintaining equivalent plasma performance (since fusion power scales as B4). CFS demonstrated a 20-tesla HTS magnet in September 2021.[2]
Engineering Challenges
Key challenges include: manufacturing long lengths of HTS tape with consistent quality; managing the mechanical stresses at 20 T (forces exceeding 10 MN per coil); protecting against quench (loss of superconductivity); and designing joints and connections for demountable magnets that allow sector maintenance.[3]
Sources
Sborchia, C. et al. "Design and specifications of the ITER TF coils." IEEE Transactions on Applied Superconductivity, 18, 463, 2008.
Whyte, D.G. et al. "Smaller and sooner: exploiting high magnetic fields from new superconductors for a more attractive path to fusion energy." Journal of Fusion Energy, 35, 41–53, 2016.
Creely, A.J. et al. "Overview of the SPARC tokamak." Journal of Plasma Physics, 86, 865860502, 2020.