Development of Large-Current Indirectly Cooled Radiation-Resistant Magnets

This paper reports developments of indirectly cooled radiation-resistant magnet coils, which can be loaded with 2000-A dc. This current capacity is required for the most upstream magnets of a new high-momentum beam line to be constructed in the future extension of the J-PARC hadron experimental facility. Indirectly cooled coils using solid-conductor-type mineral insulation cables (MICs) and stainless-steel water pipes were adopted to achieve high radiation hardness. MICs were sandwiched by independent cooling water pipes and stacked in a casing, and the entire coil assembly was filled with solder. However, the maximum load applied to the indirectly cooled MIC coils was limited to 1000-A dc, mainly owing to a heat problem at the end parts of the coils. In pursuit of the required current capability, we have carried out load tests using a test sample of the end parts, which consists of MIC current leads and a copper bus bar connecting the MIC conductors, instead of a whole MIC coil. By improving the structure of the end parts, we have succeeded to operate the test piece stably with 2000-A dc in a vacuum.