Development of indirect-cooling radiation-resistant magnets

In a high-intensity proton beam facility, beam line element downstream of a production target are exposed to a huge amount of radiation and heat. Heat problem of magnets can be solved by installing a beam collimator between the target and the magnets. However, beam pipes are closer to the beam than the magnet poles and more difficult to cool sufficiently without tritium production. Therefore, the magnets are placed in a large vacuum chamber, instead of using vacuum pipes located within the pole gaps. We have adopted indirect-cooling mineral-insulation-cable (MIC) coils for these magnets. They have the great advantages that the mechanical strength and the insulation performance can be significantly improved by avoiding the use of ceramic insulation pipes, because electric circuits are completely separated from water pass. We have tested magnet operation in vacuum using a test coil made of 1000-A class solid-conductor MICs and stainless-steel tubes. By improving the structure of end parts of MICs and increasing their emissivity, we have successfully fed the current of DC 1000 A to the solid-conductor MIC coil in vacuum. (author)