Sector Magnets for the RIKEN Superconducting

The sector magnets of the K2500-MeV Supercon- ducting Ring Cyclotron (SRC), which is under construction for the RIKEN RI Beam Factory, are described. The SRC consists of six sector magnets, four rf resonators, etc. Each sector magnet is 7.2 m in length and 6 m in height and 800 t (metric ton) in weight; the sector angle is 25 deg. The required maximum magnetic field is 3.8 T. The superconductor for the main and trim coil has a rect- angular shape (8 mm by 15 mm) consisting of a Rutherford-type NbTi cable located at the center of an Al-alloy stabilizer housing. The main coil is bath-cooled and the trim coil is indirectly cooled. Each component of the sector magnet as well as the cryogenic cooling system was completed in the spring of 2003. Index Terms—Bath-cooling and indirect-cooling, sector magnet, superconducting ring cyclotron, superconductor with Al-alloy sta- bilizer. A bird's eye view of the SRC is shown in Fig. 1. The SRC consists mainly of six sector magnets, four main rf (radio fre- quency) resonators, a flattop rf resonator, injection and extrac- tion elements. The valley regions are covered with magnetic shield irons in order to reduce the stray field. Some of the iron slabs of the magnetic shield are bridged on the top and bottom of the valley regions between the sector magnets, and the others are placed vertically between these top and bottom slabs. The total weight of these six falling-U-shaped structures is about 3000 t; the total weight of the SRC amounts to 7800 t. The K-value is 2500 MeV. The outer radius and height of the SRC are 9.2 m and 7.6 m, respectively. The mean injection and extraction radii are 3.56 m and 5.36 m, respectively. The SRC allows us to ac-