Construction and excitation tests of superconducting coils for the 28 GHz ECR ion source

A superconducting coil assembly for a 28 GHz ECR ion source at the RIKEN RI beam factory was constructed and its excitation tests were carried out. The coil assembly consists of a set of sextupole coils and six solenoids to generate a confinement magnetic field. All the coils use a NbTi conductor and are bath-cooled in liquid helium. The maximum magnetic field on the coils is 7.4 T. The characteristic feature of this coil system is that the six solenoids can generate a flat region in the axial confinement magnetic field. A large radial magnetic field due to this solenoid configuration is accordingly provided on the sextupole coils, and an inhomogeneous, strong expansion force is generated on the sextupole coils; this makes the design and fabrication of the sextupole coil assembly difficult. The coil winding began at a factory of Mitsubishi Electric Corporation in January 2008. After all the coils were wound and assembled, the excitation tests were performed in June 2008. (author)