A segment of a field coil, a toroidal field coil, and a method of manufacturing is provided. The segment of a field coil is for use in a superconducting electromagnet. The segment includes an assembly for carrying electrical current in a coil of a magnet. The assembly includes a pre-formed housing comprising a channel configured to retain high temperature superconductor (HTS) tape, the channel including at least one pre-formed curved section. The assembly further includes a plurality of layers of HTS tape fixed within the channel. Wherein the pre-formed curved section has a radius of curvature which is less than a total thickness of the layers of HTS tape in that section divided by twice a maximum permitted strain of the HTS tape.