Development of Saddle-Shaped Coils Using Coated Conductors for Accelerator Magnets
A project to develop fundamental technologies for accelerator magnets using high-Tc superconductors is currently underway. The primary applications in this project are fixed field alternating gradient (FFAG) accelerators for carbon cancer therapy systems and accelerator-driven subcritical reactors. One of the challenging issues in this study is to accomplish the complicated coil shape required for the accelerator magnets using YBa2Cu3Ox (YBCO) coated conductors. An asymmetric, three-dimensional winding structure has been designed for the main ring of an FFAG accelerator, but the anisotropic bending flexibility of coated conductors is constrained because of their tape-like shape. To demonstrate a suitable winding technology for a three-dimensional coil using coated conductors, a prototype winding machine with a two-axis motion mechanism was constructed. Based on the present design of the FFAG magnet, a saddle-shaped coil wound on a curved surface with a radius of 700 mm was designed. A 100-turn coil was wound by the winding machine using an approximately 90 m length of 3 mm-wide YBCO coated conductor made by the IBAD-MOCVD method. The coil was impregnated with epoxy resin, and the voltage-current (V-I) characteristics were evaluated in a liquid nitrogen environment. From the V-I characteristics in an electric field region of 10-9V/cm, an index value of above 20 was obtained, which means that the superconducting properties were not degraded.