A CRYOCOOLER COOLED 6T NBTI SUPERCONDUCTING MAGNET WITH ROOM-TEMPERATURE BORE OF 220MM

We are developing a cryocooler cooled 6T superconducting magnet withou t liquid helium and/or liquid nitrogen. This magnet, which is directly cooled by two 4K Gifford-McMahon(GM) cryocoolers in vacuum, consists of an graded NbTi coil, Bi-based oxide superconducting current leads a nd a persistent current switch. The coil is made using two types of Nb Ti wires and a copper bobbin, The coil with an inner diameter of 260mm , an outer diameter of 329mm, and a height of 334mm, is impregnated wi th grease to ensure a good heat conduction. The operating current for central field of 6T in the 220mm room temperature bore is 152A. A mech anical persistent current switch is used to limit the load from the sw itch Into the 4K GM cryocooler. Designed temperature of the magnet is 4.9 K at the operating current of 152 A.