low-temperature superconductor is any of the earlier generation of superconductors, such as niobium-titanium and niobium-tin, that must be cooled to within a few degrees of absolute zero and sustain magnetic fields well below what high-temperature superconductors reach.
The class, abbreviated LTS, covers the metallic superconductors known before the copper-oxide discoveries of 1986. Its two workhorses are niobium-titanium, a ductile alloy with a 📝critical temperature near 9 kelvin, and niobium-tin, a brittle compound that superconducts below about 18 kelvin — both operated in liquid helium at around 4 kelvin. These are mature, well-industrialized materials: they wind the magnets of MRI scanners, particle accelerators such as the Large Hadron Collider, and the 📝toroidal field coils of 📝ITER.
The distinction against the high-temperature 📝superconductor class is what redrew 📝fusion's design space. An LTS magnet is capped by its conductor's 📝critical magnetic field at roughly 12 to 13 tesla in practice, and since fusion performance rises steeply with field strength, machines built on LTS compensate with sheer size — ITER's 📝plasma volume is measured in hundreds of cubic meters. 📝REBCO tape tolerates fields around 20 tesla, which is how 📝High-Temperature Superconducting (HTS) Magnets let a machine roughly one-fortieth ITER's volume, 📝SPARC, pursue the same net-energy goal.