Design study of superconducting coils for the fusion DEMO plant at JAERI

A design study of the TF coil for the fusion DEMO plant at JAERI is in progress. A major issue is to estimate the maximum fields generated by the TF coils for three tokamak options and two conductor options. Three tokamak options are proposed varying the aspect ratio and the role of the CS coil. Two kinds of conductors using advanced superconducting materials are candidates for the TF coils: Nb3Al and high temperature superconductor (HTS). In order to evaluate achievable magnetic fields, a simple method was adopted to calculate mechanical properties. The estimated maximum fields are 17–20 T by the HTS conductor and 16–17 T by the Nb3Al conductor. There is a possibility of a 0.7 T enhancement using grading of Nb3Al winding.