An open refrigerator cooled superconducting magnet for the special purpose of magnetic resonance imaging

A 10 K refrigerator cooled superconducting magnet with an open-ended, C-shaped iron core was developed and tested for the special purpose of magnetic resonance imaging. The magnet employs a single Nb3Sn tape superconducting coil and an open-ended iron loop. The superconducting coil Is cooled and maintained at the 10 K operational temperature by a Gifford-McMahon (G-M) cryocooler. The magnetic field in the iron open gap is used for magnetic resonance imaging. The field homogeneity is achieved by contoured iron pole faces and specially developed passive shimming procedures. We have achieved less than 1 ppm/hour field stability and a 29 ppm field homogeneity over a 10 cm diameter spherical volume. High quality images have been produced using this magnet