AbstractThe Large Helical Device is a nuclear fusion experimental device with superconducting magnets. Designs for constructing the helical and poloidal coils, the cryostat and the helical-coil winding machine are now being carried out. The helical coils have a magnetic energy of 1600 MJ and an overall current density of 53 A/mm2 in phase-II. Its rated current is 21.2 kA in phase-I, and the maximum magnetic field in the helical-coil winding in phase-I is calculated to be 6.9 T. Three pairs of poloidal coils are cooled by forced-flow supercritical helium because of the requirement of no metal coil vessel. The magnetomotive force of one inner vertical poloidal coil (IV coil) is 5.0 MA, and its stored energy is 80 MJ. The maximum magnetic field of the two IV coils only is calculated to be 5.8 T. The type of superconductor for the IV coils is a cable-in-conduit conductor.