Analysis of mechanical stress due to winding pretension in a 1.5 T superconducting MRI magnet

The paper presents the analysis of stresses due to winding tension in a 1.5 T MRI magnet with a clear bore of ∼1 m and an outer diameter of ∼1.8 m. The magnet has four pairs of symmetric coils arranged over a length of ∼1.5 m. The stringent requirement of field homogeneity makes it critical to design a structurally stable magnet system. It is essential to evaluate the 3-dimensional stresses that would be generated in the magnet during winding, cool down and operation. The bobbin structure also has to be designed so as to reduce the relative movements of theeight superconducting coils, which otherwise can adversely affect the field homogeneity at the Field of View (FOV). The bobbin will be made of aluminium 5083 alloy, while the magnet winding will be a composite structure which consists of NbTi, copper and polyester insulation. The paper discusses the stress distribution over the aluminium bobbin and the coil caused due to winding tension applied during magnet winding. The article also discusses the element death and birth method in FEA to accurately simulate the winding process.