A toroidal field coil comprising a central column, a plurality of return limbs, a quench protection system, and a cooling system. The central column comprises IITS material. Each return limb comprises a quenchable section, two IITS sections, and a quenching 5 system. The quenchable section comprises superconducting material, and is configured to contribute towards a magnetic field of the toroidal field coil. The IITS sections comprise IITS material. The IITS sections electrically connect the quenchable section to the central column and are in series with the central column and the quenchable section. The quenching system is associated with the quenchable section 10 and configured to quench the quenchable section. The quench protection system is configured to detect quenches in the toroidal field coil and, in response to detection of a quench, cause the quenching system to quench the superconducting material in one or more of the quenchable sections in order to dump energy from the toroidal field coil into the one or more quenchable sections. The cooling system is configured to cool each 15 quenchable section to a temperature at which the superconducting material is superconducting. Each quenchable section has a heat capacity sufficient to cause a temperature of the quenchable section to remain below a first predetermined temperature when energy is dumped from the toroidal field coil into the quenchable section, and a resistivity sufficient to cause decay of the magnet's current quickly 20 enough that the temperature of the quenched part of the HTS section remains below a second predetermined temperature.