Mechanical Stress Analysis of Zero-Boil-Off Cryostat for a 1.5 T MRI magnet

Abstract

A whole-body 1.5T superconducting MRI magnet is operated in 4.2K inside a zero-boil-off helium cryogenic vessel i.e. cryostat. The cryostat has horizontal bore of 850 mm used as the patient bore. The cryostat houses the 1.5T superconducting magnet in a coaxial position maintaining a high degree of alignment along with the gradient coil, the birdcage RF coil necessary for any MRI scanner. A set of support link having low thermal conductivity and higher mechanical strength would provide structural support to the cold mass at 4.2K which includes the superconducting magnet, helium vessel. A two stage 4.2K G-M cryocooler is used to recondense helium to achieve a 'zero boil-off' condition. The helium vessel and the vacuum vessel of the cryostat experience stresses during the normal operation, transportation etc. The ASME B&PV Code and the Finite Element Analysis has been used for the engineering design and stress analysis of cryostat. The modal analysis of the cryostat has been done during the transportation of the cryostat. The seismic behaviour of the cryostat has also been analyzed extensively for a 1.5T MRI cryostat