High-temperature superconducting (HTS) magnets are electromagnets wound from rare-earth barium copper oxide (REBCO) tape that carry enormous currents without resistance at temperatures around 20 kelvin, producing magnetic fields far stronger than conventional superconductors allow.
In magnetic-confinement fusion, field strength is the decisive variable: the power density of a 📝tokamak plasma rises roughly with the fourth power of its magnetic field, so doubling the field shrinks the machine needed for the same fusion output by an order of magnitude. Conventional low-temperature superconductors saturate near 12 tesla; REBCO tape, commercialized in the 2010s, removed that ceiling and opened a path to compact, economical fusion machines.
In September 2021, 📝Commonwealth Fusion Systems and the 📝MIT Plasma Science and Fusion Center demonstrated the SPARC 📝toroidal field model coil, a full-scale HTS fusion magnet, sustaining a field of 20 tesla — the strongest high-temperature superconducting fusion magnet built to that date and the milestone on which the company's 📝SPARC and 📝ARC reactor program rests. CFS manufactures these magnets at scale at its Devens, Massachusetts campus, building on earlier advances such as the VIPER superconducting cable.