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.