Patent ID: 7714574

Claim:
A superconducting magnet comprising: a superconducting coil for circulating a persistent current to generate a static magnetic field; a refrigerant container for containing the superconducting coil and a refrigerant for cooling the superconducting coil below a critical temperature of the superconducting coil; a vacuum container for housing the refrigerant container and holding the refrigerant container in a vacuum state; a radiation shield between an outer surface of the refrigerant container and an inner surface of the vacuum container; a refrigerator for re-liquefying the refrigerant vaporized inside the refrigerant container, comprising: at least two regenerative refrigerant stages including: a first regenerative refrigerant for reciprocating between the outer surface of the refrigerant container and an inner surface of the radiation shield to cool a vaporized refrigerant; and a second regenerative refrigerant for reciprocating between an outer surface of the radiation shield and the inner surface of the vacuum container to cool the radiation shield and the first regenerative refrigerant; and a dynamic magnetic field shield that is an electric good conductor and arranged around the first regenerative refrigerant along a motion axis of the first regenerative refrigerant, wherein a direction of the motion axis is aligned with a direction of a magnetic force line of the static magnetic field at the first regenerative refrigerant.