Design of the TF Coil for a Tokamak Fusion Power Reactor with YBCO Tape Superconductors

A low aspect ratio tokamak, VECTOR was designed by Japan Atomic Energy Research Institute (JAERI) to provide the high cost performance necessary for a commercial power reactor. The maximum magnetic field within the winding of the toroidal field (TF) coil is about 20 T. The applicability of high temperature superconductor YBCO tape to the TF coil conductor is considered. YBCO tape is well known to have higher critical current density. However, YBCO tape has magnetic instability due to flux jumps. The magnetic field at which the first flux jump occurs is estimated to be 6.8 T at 33 K. Therefore, to prevent flux jumps, the winding is divided into three (higher, middle and lower field) winding packs and the maximum self magnetic field produced by each winding pack is less than 6.8 T. The low field winding pack is cooled first down to 33 K and operated up to its nominal current. In this case, the middle and higher field winding packs are maintained above 90 K. Next, in similar process the middle pack is operated. Finally, the higher pack is operated, and 20 T is generated without flux jump. The nominal current for every winding pack is 40 kA. Thus it is possible to apply YBCO tape to the TF coil and YBCO tape will be expected to play an important role in the realization of tokomak fusion power reactors with low construction and operation costs, and high performance plasma