Design of a Model Sector Magnet for the RIKEN Superconducting Ring Cyclotron

In the RIKEN RI Beam Factory project, it is planned to build two superconducting ring cyclotrons, SRC-4 and SRC-6, as post accelerators of the existing cyclotron. This paper reports on a model sector magnet for the second cyclotron, SRC-6. The SRC-6 has been designed to consist of six superconducting sector magnets. Its main features are as follows: the mean injection and extraction radii are 3.56 m and 5.36 m, respectively; the sector angle is 25 degrees; the maximum magnetic field is 4.3 T; the total stored energy is 450 MJ; the maximum ampere-turn of mail coil is 6 MA for each magnet; the main coil is cooled by the liquid-He bath cooling method and designed to be cryogenically stable. The sector magnet is characterized by adopting the cold-pole method, in which the electromagnetic force on the coil is supported by the pole piece. The coil vessel is fixed to the pole piece, which is separated from a yoke and cooled down together with the main coil. A full scale model is to be built to make sure the design of sector magnet. Its detailed structure such as the coil vessel, the cold pole and the coil winding will be presented.