Design and Experimental Study of a Model Magnet for Spiral-Sector FFAG Accelerators

A project to develop fundamental technologies for accelerator magnets using high-T
_c
superconductors is currently underway. In this project, conceptual design studies of fixed-field alternating gradient (FFAG) accelerators for carbon cancer therapy and for accelerator-driven subcritical reactors have been carried out. To establish technologies for cryocooler-cooled high-T
_c
superconducting (HTS) accelerator magnets wound with coated conductors, a downscaled model magnet system for a spiral-sector FFAG accelerator has been developed. A model magnet consisting of multiple coils with complicated shapes, including a negative-bend part or a 3-D bent part, was designed to demonstrate the generation of an asymmetrical magnetic field on the midplane of the magnet bore. One issue is how to wind coils for the accelerator magnets by using tape-shaped coated conductors, which have anisotropic bending flexibility between the flatwise and edgewise directions. Another issue is the effects of the characteristic features of the coated conductors on the accuracy of the magnetic field. The field precision of coils wound with coated conductors is considered to be influenced by the dimensional accuracy of the YBCO tapes and coils, as well as the magnetization of the HTS layer. This paper describes the design and fabrication of YBa
₂
Cu
₃
O
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coils for the model magnet, as well as disturbance factors of the field of the HTS magnet and the effect of dimensional variations of the YBCO coil on the magnetic field.