Patent ID: 7538649

Claim:
A superconducting electromagnet, comprising: a coil vessel for housing a superconducting coil and a cooling medium; a vacuum vessel surrounding the coil vessel; a cryocooler provided outside the vacuum vessel for cooling the cooling medium housed in the coil vessel; a motor for driving the cryocooler; and a magnetic shield for protecting the motor from a magnetic flux of the superconducting coil, wherein the magnetic shield includes a pair of ferromagnetic material plates placed opposite each other across the motor, wherein each of the pair of ferromagnetic material plates has an upper side extending in a direction parallel to a shaft of the motor and being furthest from the vacuum vessel and a lower side extending in the direction parallel to the rotating shaft of the motor and being closest to the vacuum vessel, and wherein a length of the upper side extending in the direction parallel to the shaft of the motor of each of the pair of ferromagnetic plates is longer than a length of the lower side extending in the direction parallel to the shaft of the motor of each of the pair of ferromagnetic plates.