Stress Analysis of a 7 T Actively Shielded Superconducting Magnet for Animal MRI

A two-dimensional (2D) axisymmetric finite-element-analysis (FEA) structural model has been developed to evaluate the mechanical stability though the processes of winding, cooling and charging of a 7 T actively shielded superconducting magnet for animal MRI. The magnet has a warm bore diameter of 210 mm. It consists of five concentric solenoids with each made of epoxy-impregnated NbTi/Cu windings. To improve the accuracy of analysis while keeping the mesh sizes within an acceptable level, the epoxy-impregnated composite coils are simulated by the equivalent uniform windings with their smeared material properties being obtained by an FEA based homogenization method. The influence on the field homogeneity of the mechanical deformations owing to winding tension, warm-to-cold contraction and the Lorentz forces is also analysed.