The large vacuum-insulated chamber that surrounds a fusion device’s superconducting magnets, maintaining them at cryogenic temperatures (4–5 K) so they can carry enormous currents with zero resistance.
Superconducting magnets in fusion devices must operate at temperatures near absolute zero — typically 4–5 K for low-temperature superconductors (Nb3Sn, NbTi) or 20–30 K for high-temperature superconductors (REBCO). The cryostat provides thermal insulation between the cryogenic magnet system and the ambient environment by maintaining an intermediate vacuum (10−4 to 10−6 Pa).[1]
A typical fusion cryostat consists of: (1) an outer vacuum vessel providing structural support; (2) multi-layer insulation (MLI) blankets reflecting thermal radiation; (3) actively cooled thermal shields at intermediate temperature (~80 K, cooled by liquid nitrogen or helium gas); and (4) support structures connecting the cold magnets to the warm cryostat wall through low-heat-leak paths.[2]
ITER’s cryogenic plant will be one of the largest in the world, distributing helium at 4.5 K and 80 K to cool the magnets, thermal shields, and cryopumps. The total refrigeration power exceeds 65 kW at 4.5 K equivalent.[3]