Iron Magnetic Shielding of the Series Connected Hybrid Magnet

The NHMFL presently has three magnet projects using Cable-in-Conduit Conductor (CICC) underway: first for the magnet lab in Tallahassee, FL, second for the Helmholtz Centre Berlin for Materials and Energy (HZB), Germany, and the third for the Spallation Neutron Source (SNS) at the Oak Ridge National Laboratory, TN. The original design of an active shield coil using NbTi superconducting CICC for the NHMFL SCH is replaced by a much lower-cost iron shield composed of 100 mm thick iron-walls positioned symmetrically around the magnet. The SCH fringe field and the effect of iron magnetization on central field homogeneity are discussed under the alternative shield design concept. Nonlinear magneto-static analysis is performed for various shield configurations to ensure the levels of fringe field and the magnetic forces on surrounding instrumentation are acceptable to magnet users. The minimum iron volume and magnetic forces among iron walls are obtained for the design of shield supporting structure. The field uniformity over 1 cm diameter spherical volume (DSV) for both axial and radial directions is examined to meet the design requirements. In addition, effects of current leads, bus bars and surrounding magnets such as the 45-T hybrid to field uniformity are evaluated and the best option for iron shielding is presented.