REBCO — rare-earth barium copper oxide — is the high-temperature superconductor at the heart of high-field 📝fusion magnets, a ceramic that carries large currents in magnetic fields that shut earlier superconductors down.
The name abbreviates a family of compounds with the formula REBa2Cu3O7, where RE stands for a rare-earth element such as yttrium or gadolinium. The yttrium member, YBCO, was discovered in 1987 and was the first known 📝superconductor with a 📝critical temperature above the boiling point of liquid nitrogen — roughly 90 kelvin, against about 18 kelvin for the best conventional alloys. The near-neighbor distinction is with those low-temperature superconductors, niobium-titanium and niobium-tin: what makes REBCO decisive for magnets is less its warm critical temperature than its behavior in strong fields, where it retains a usable 📝critical current at 20 tesla and beyond while the conventional alloys have long since gone normal.
REBCO is a brittle ceramic that cannot be drawn into wire, so it is manufactured as a coated conductor: a micrometers-thin crystalline film deposited on a flexible metal ribbon — the form known as HTS tape. Cooled to around 20 kelvin, magnets wound from it produce the roughly 20-tesla fields of 📝High-Temperature Superconducting (HTS) Magnets, and because 📝fusion power density rises steeply with field strength, this one material is what makes a net-energy machine as compact as 📝SPARC possible. Two papers trace the material into a magnet: 📝YBCO Wire Production for Fusion reports making it reproducibly at industrial volume, and 📝VIPER: An Industrially Scalable HTS Cable reports turning the tape into a conductor a fusion magnet can actually be wound from.