Radiation-Resistant Magnets for J-PARC

Several species of radiation-resistant magnets were developed for J-PARC, a Japanese brand-new high-intensity accelerator complex, whose maximum beam power reaches 1 MW. The first development was polyimide insulation magnets. The ordinal epoxy resin was replaced by polyimide resin in order to improve its radiation lifetime up to 4 × 10
⁸
Gy. Most accelerator magnets of J-PARC were assembled with polyimide insulation coils. Peripherals of polyimide insulation magnets, such as insulation water tubes, water valves, water gaskets, etc., were replaced also by ones made of inorganic materials. The second development was mineral insulation magnets. Magnet excitation coils were made of “Mineral Insulation Cable (MIC).” The copper conductor of MIC was surrounded by a thin MgO insulation layer, and the MgO layer was covered by a copper sheath. Several sizes of MIC cross section were developed for large and small magnets with various maximum currents from 1000 to 3000 A. Peripherals of magnets assembled with MIC coils were also made of completely inorganic materials. These MIC magnets were used at the downstream part of beam loss points such as the secondary particle production target of Hadron Experimental Facility. The R&D stories of the radiation-resistant magnets, including the present status of the magnet operation, are briefly summarized.