We have successfully constructed an 18.1 T superconducting magnet conductively cooled by a GM/JT cryocooler. The double-pancake insert using Ag-sheathed Bi 2Sr 2Ca 2Cu 3O 10 (Bi2223) tape with stainless steel reinforcement tape generated 2.5 T in a 15.6 T background magnet. In order to develop a cryogen-free high-field superconducting magnet producing over 20 T, an YBa 2Cu 3O 7 (Y123) coated conductor insert is intended for upgrading the cryogen-free 18 T superconducting magnet. The Bi2223 insert, whose size is 176 mm outer diameter, 90 mm inner diameter, and 252 mm coil height, is now excited at 162 A operation current, and will be replaced by a new Y123 insert. We have already confirmed excellent mechanical properties of 1000 MPa hoop stress tolerance for Y123 coated conductor tape with Hastelloy substrate. This means that we no longer need stainless steel reinforcement for the insert. As a result, an Y123 insert with almost the same size as the Bi2223 insert is designed to generate 7.5 T at 187 A, because the number of turns can be improved extremely. A cryogenfree 23 T superconducting magnet can sufficiently be developed for a long-term experiment at a constant high magnetic field.
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