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Effect of Thermal Strain, Induced by Cryogenic Cooling, on a High Homogeneity Superconducting Magnet for MRI Applications

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Title Effect of Thermal Strain, Induced by Cryogenic Cooling, on a High Homogeneity Superconducting Magnet for MRI Applications
 
Creator Thekkethil, Sankar Ram
Rastogi, Vikas
Kar, Soumen
 
Subject Superconducting Magnets
Thermal Strain
Field homogeneity
Cryogenic cooling
 
Description 581-585
The heart of the modern whole body MRI scanners is a superconducting magnet producing the required magnetic field
with high homogeneity. The superconducting magnet operates at 4.2 K (-268.95 oC) and thus is kept dipped in liquid helium
to maintain its superconducting state. This cool down of the multi-coil magnet from room temperature to the LHe
temperature generates thermal strains in the magnet structure which deforms the magnet. These deformations are found to
affect the final magnetic field homogeneity and introduce artifacts in the MR images. We report our results on studies on the
stresses induced in the bobbin and the coils consequent upon cooling the magnet to 4.2 K. The maximum von Mises stress in
the coils is calculated to be 31.3 MPa while in the bobbin it comes out to be 60 MPa. We find that the cool down causes a
relative movement of the coils which in turn degrades the field homogeneity from 5.5 ppm to 278 ppm. The centre field is
found to increase by 60 G is caused by a reduction in the overall cross-section of the coils. The change in homogeneity is
also analysed in terms of Legendre polynomials where we found that the relative displacements of the coils introduce odd
order terms to the polynomial expansion terms which were not present in the original design.
 
Date 2022-11-01T05:31:17Z
2022-11-01T05:31:17Z
2022-10
 
Type Article
 
Identifier 0971-4588 (Print); 0975-1017 (Online)
http://nopr.niscpr.res.in/handle/123456789/60764
https://doi.org/10.56042/ijems.v29i5.52987
 
Language en
 
Publisher NIScPR-CSIR,India
 
Source IJEMS Vol.29(5) [October 2022]