The ITER tokamak is housed in a cryostat. This is a large (~14,000m³) evacuated vessel which provides thermal insulation for the superconducting magnets and serves as a second confinement barrier after the vacuum vessel. It consists of a cylindrical section bolted and seal welded to heads at top and bottom.

The cryostat vessel presents a challenge because of the large number (~400) of penetrations to be accommodated whilst remaining leak-tight.

While the vacuum of the cryostat minimises convective heat transfer, thermal shields placed between the cold magnet structure and the warm vessel minimise radiative heat transfer. These shields consist of stainless steel panels cooled by helium gas at 80K. Although in general there is plenty of room for thermal shields, the space between the vessel and the underside of the TF coils is particularly limited, given the relative movement that occurs during operation and the difficult access during assembly.