LAUSR

Abstract The image quality in a MRI magnet greatly depends on the mechanical, thermal and electromagnetic performance of the thermal shield in presence of any time varying field. A detailed analysis on the mechanical resonance frequency, temperature distribution and the eddy current distribution on a thermal shield of a zero-boil-off cryostat for 1.5 T MRI magnet system is presented. Five combination of aluminum alloys using AA1100, AA5083-O, AA6061-T6 are considered for the analysis. The mechanical natural resonance frequency of shield is studied for its various length and the radial thickness varying in the range of 1-10 mm of the thermal shield. The resonance frequency of the AA1100 bore tube is found to varying in the range of 1.9 kHz -5.2 kHz. The overall temperature non-uniformity of 8.5 K is achieved in the binary shield made of AA1100 for the outer shell and the bore tube and AA6061-T6 for the endplates. The temperature non-uniformity achieved in the imaging length of 45cm of the bore tube is 0.034 K. The eddy current induced along the imaging length of the bore tube is 1.7% of the peak eddy current onto the shield during a quench in the magnet. The highest eddy current of ∼ 2490 A/cm2 is generated on the bore tube for the binary shield made of AA1100 for the outer shell and the bore tube and AA5083-O for the endplates .