FEM Modeling of Superconducting Whole Body, Actively Shielded 7 T MRI Magnets Wound Using Nb3Sn Strands

This paper presents the results of a magnetic design study for 7 T, whole body, actively shielded MRI magnet using Nb
₃
Sn conductor. Nb
₃
Sn was used as the conductor to enable the development of short (1.4 m) segmented coil designs, as opposed to the nearly 2 m long compensated solenoid designs needed for NbTi machines. In addition, the use of Nb
₃
Sn will allow a conduction cooled design, if quench is properly managed. We show two designs both with magnetic field homogeneity better than 10 ppm (part-per-million) within DSV (Diameter of Spherical Volume) of 45 cm. Several classes of Nb
₃
Sn strand especially designed for MRI and high field applications were considered as a possible candidate for winding such magnets. The magnets were assumed to achieve maximum on-axis magnetic field of 7 T. For this on-axis field a peak field inside the magnet windings was determined and parameters of the required Nb
₃
Sn strands (such as critical current, engineering current density etc.) calculated. The coil load lines were compared to conductors and we find that such a segment coil design can be achieved with a few classes of existing Nb
₃
Sn conductor. Coil geometry, length of conductor, and overall magnetic performance, and current and thermal margins were discussed. This demonstrates that a viable 7 T whole body MRI is achievable using Nb
₃
Sn conductor.