A toroidal field magnet system for NUWMAK

A conceptual design of a toroidal field coil system is presented for NUWMAK, a compact fusion power reactor. The magnet major radius is 5.13 meters, the minor radius is 3.84 meters and the maximum field in the coil winding is 11.5 Tesla. The magnets are to be cooled with 1.8 K superfluid helium to allow operation at the highest fields present using ductile NbTi instead of brittle Nb3Sn as the superconductor. Various advantages and disadvantages of this design are compared to those of an optional Nb3Sn magnet design operating in 4.2 K pool boiling liquid helium. There are only eight superconducting TF coils, allowing excellent access for maintenance, and the resulting field ripple is trimmed with close-in normal metal coils. These trimming coils do not encircle the plasma but are saddle shaped, and so can be changed out without disturbing the plasma chamber or the TF coils.