Comparison of Nb₃Sn and NbTi Superconductor Magnet ITER Devices

The TETRA tokamak systems code is used to compare designs for the International Thermonuclear Experimental Reactor (ITER) that use Nb₃Sn and NbTi superconductor magnets. Similar minimum-cost devices are found with both types of conductors when superfluid helium (He-II) is used in conjunction with the NbTi. The cost of using NbTi with He-I cooling is much higher than that of using Nb₃Sn or NbTi with He-II cooling. Generally, the minimum-cost devices occur for peak fields at the toroidal field coil of about 11.5–13 T, depending on the physics requirements. Sensitivities to the allowable stress level indicate strong cost increases when the stress is reduced from the nominal 600-MPa level and weaker cost benefits when the stress is allowed to reach higher levels.