Patent ID: 7170377

Claim:
A zero boiloff cryogen cooled recondensing superconducting magnet assembly including superconducting magnet coils suitable for magnetic resonance imaging comprising: a cryogen pressure vessel to contain a liquid cryogen reservoir to provide cryogenic temperatures to said magnet coils for superconducting operation; a vacuum vessel surrounding said pressure vessel and spaced from said pressure vessel; a first thermal shield surrounding said pressure vessel and spaced from said pressure vessel; a second thermal shield surrounding said first thermal shield and spaced from said first thermal shield, said second thermal shield intermediate said vacuum vessel and said first shield; a cryocooler thermally connected by a first and a second thermal interface to said first and second thermal shields, respectively; a recondenser positioned in the space between said pressure vessel and said first thermal shield and thermally connected by a thermal interface to said cryocooler to recondense, back to liquid, cryogen gas provided from said pressure vessel; and means for returning the recondensed liquid cryogen to said pressure vessel; wherein said second thermal shield surrounding said first thermal shield reduces a radiation heat load from said first thermal shield to said pressure vessel lowering boiloff of cryogen gas under conditions of failure or power off of said cryocooler, and wherein sensible heat from said boiloff of cryogen gas cools down a coldhead sleeve of said coldhead, said penetration and said first and second thermal shields.