Helical and poloidal coil R&D in LHD

The development of superconducting coil system for the Large Helical Device (LHD) is summarized. The LHD is a fully superconducting heliotron type fusion experimental device under construction at the National Institute for Fusion Science (NIFS). The superconducting coils for the LHD consist of two helical coils and three pairs of poloidal coils. Their magnetic stored energy is 1.6 GJ and the LHD is one of the largest superconducting systems in the world. To construct such a large scale superconducting coil system, we have not only to accumulate existing technologies but we also have to develop new technologies. The items of research and development for the superconducting coil system of LHD, including the development of superconducting conductors and coils for the helical and the poloidal coils, cooling and excitation tests on a single inner vertical coil for the LHD, are reviewed.