Patent ID: 7924011

Claim:
A cryocooler assembly having a rare-earth regenerator for recondensing of a cooling liquid for cooling of a superconductive magnet or for directly cooling the superconductive magnet coils of a magnetic resonance imaging apparatus, wherein the cryocooler assembly comprises a shield of ferromagnetic material at least partially surrounding the rare-earth regenerator, wherein the rare-earth regenerator is adapted to move between a cold region and a hotter region, wherein the shield of ferromagnetic material is adapted to generate a magnetic field between the cold and hotter region from the magnetic field of the superconductive magnet so that the magnetic field induces a magnetic moment in the rare-earth regenerator which compensates for a change of the magnetic moment of the rare-earth regenerator caused by the movement of the rare-earth regenerator between the cold region and the hotter region, wherein the shield of ferromagnetic material is arranged so that the cross sectional area enclosed by the inner surface of the shield is of circular form and so that the cross sectional area enclosed by the outer surface of the shield is of elliptical form.