Practical use of a liquid helium-free superconducting magnet

A cryocooler-cooled 4.6 T superconducting magnet with a 38 mm room temperature bore, which consists of a low-T_c Nb₃Sn coil and high-T_c Bi₂Sr₂Ca₂Cu₃O₁₀ current leads, has been working in vacuum for about 18000 cooling hours without trouble. It is found that the high-T_c current leads can hold excellent superconducting properties for a long enough time to be practically used. As a next step, we have succeeded in the construction of a 10.7 T-52 mm room temperature bore and a 5.7 T-220 mm room temperature bore liquid helium-free superconducting magnet.