A new generation of superconducting magnets built from materials like REBCO tape that operate at higher temperatures and produce stronger magnetic fields, potentially enabling smaller, faster-to-build fusion reactors.
For decades, fusion magnets relied on low-temperature superconductors (LTS) such as NbTi and Nb3Sn, limited to ~11–13 T. High-temperature superconductors (HTS) retain superconductivity at higher temperatures (20–77 K) and can carry substantial current even above 20 T.[1]
REBCO (rare-earth barium copper oxide) tape can carry engineering current densities exceeding 500 A/mm² at 20 T and 20 K, far surpassing any LTS material.[2]
Fusion power density scales as β2B4. A device with 20 T on-coil field (roughly double ITER’s) can produce comparable fusion power in a substantially smaller machine. This is the central argument behind compact tokamak concepts such as SPARC.[3]
Quench detection: HTS magnets propagate thermal disturbances much more slowly than LTS. Joint technology: Demountable joints must carry thousands of amperes with resistance below 1 nΩ. Stress management: At 20 T, Lorentz forces are roughly four times those in ITER’s coils.[4]
In September 2021, Commonwealth Fusion Systems demonstrated a large-bore HTS magnet reaching 20 T, a verified milestone. Multiple manufacturers deliver kilometer-length REBCO tapes, though cost remains significant.[3]