A toroidal field coil for use in a tokamak, the toroidal field coil comprising a central column comprising high temperature superconducting, HTS, material and a plurality of return limbs, each return limb comprising: a quenchable section (122,802) comprising superconducting material, the quenchable section being configured to contribute towards a magnetic field of the toroidal field coil; two high temperature superconducting, HTS, sections (112,801) comprising HTS material, wherein the HTS sections electrically connect the quenchable section to the central column and are in series with the central column and the quenchable section; and a quenching system associated with the quenchable section and configured to quench the quenchable section; the toroidal field coil further comprising: a quench protection system 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; a cooling system configured to cool each quenchable section to a temperature at which the superconducting material is superconducting; wherein 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 enough that the temperature of the quenched part of the HTS section remains below a second predetermined temperature. a quenchable section (122,802) comprising superconducting material, the quenchable section being configured to contribute towards a magnetic field of the toroidal field coil; two high temperature superconducting, HTS, sections (112,801) comprising HTS material, wherein the HTS sections electrically connect the quenchable section to the central column and are in series with the central column and the quenchable section; and a quenching system associated with the quenchable section and configured to quench the quenchable section; the toroidal field coil further comprising: a quench protection system 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; a cooling system configured to cool each quenchable section to a temperature at which the superconducting material is superconducting; a quench protection system 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; a cooling system configured to cool each quenchable section to a temperature at which the superconducting material is superconducting; wherein 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 enough that the temperature of the quenched part of the HTS section remains below a second predetermined temperature.