Design and fabrication of a 7-T force-balanced helical coil

Force-balanced coil (FBC) is a helically wound toroidal coil. The FBC can minimize working stresses by selecting an optimal number of poloidal turns. In order to demonstrate the validity of the FBC concept for high field superconducting magnets, a 7-T force-balanced coil (7-T FBC) was designed. The 7-T FBC will have 270-kJ stored magnetic energy with a major radius of 0.20 m at maximum magnetic field of 7.0 T. This coil is a hand-made coil using NbTi superconductor. The 7-T FBC is designed within an allowable radius whose maximum working stress within an allowable stress of the stabilizer of NbTi strand. Then the winding of the 7-T FBC will be carried out without reinforcing materials for NbTi strand. The experiments will be conducted with pool boiling liquid helium cooling.