Development of a 3 T–250 mm Bore Magnet System

The authors had reported components´ development of 3 T-250 mm bore MgB₂ magnet system. Pre-reacted MgB₂ tape wire with copper lamination had n-value related problem due to raw Boron particle size inequality, but it had been corrected. Long MgB₂ wires over 3 km had been supplied. All six component coils were made with a wet winding procedure. They were tested individually with the same cooling scheme of conduction cooling as the actual magnet assembly. Though all coils could be ramped to some extent, some coils showed fairly large remnant voltage. Since the voltage distribution over the coil was not even, the uniformity along the wire length may not be good enough. The stability of the coil was verified by its no training performance even with fast ramping. The magnet assembly and its test with conduction cooling were planned. I_c of the superconducting joint with this pre-reacted wire was doubled during past one year´s development.