A 1 T, 0.33 m bore superconducting magnet operating with cryocoolers at 12 K [for MRI]

The application of small cryocoolers to cooling a superconducting magnet at 12 K has important advantages, especially for small and medium-size magnets. Simple construction and a helium-free magnet system were obtained. The demonstration magnet developed is a six-coil system with a volume of 75 L and can be regarded as a 1:3 scale MRI magnet. With a current of 100 A, a 1-T central field is generated with a maximum of 1.9 T in the windings. The magnet consists of six coil formers and five aluminum spacing rings, providing easy service and disassembly. The superconductor, a 0.6-mm-diameter Nb₃Sn wire, is wound on the thin-walled stainless steel coil formers, after which the coil is heat treated and vacuum impregnated. Afterwards, the coil system is assembled and the electrical and thermal connections are made. At an operating temperature of the demonstration magnet of 12 K the test coil reached its nominal current after a few training quenches