Structural Integrity of the NHMFL Series-Connected Hybrid Magnet Cryostats

The National High Magnetic Field Laboratory has designed and built cryostats for two series-connected hybrid (SCH) magnets. The first one is for the Helmholtz Center Berlin. Its cryostat is designed to support up to 8 MW of resistive insert inside a water-cooled housing that has a conical warm bore with a 30-degree opening angle and a 5-ton superconducting outsert coil that is housed in a vacuum vessel. Normal operation includes 28 bar of water pressure and 52 kN of side load between the resistive insert coils and the superconducting outsert coils due to a potential 3-mm coil misalignment. Under a fault condition, the resistive coils can generate axial loads of up to 1.1 MN. The second cryostat for the Florida State University SCH houses the same superconducting outsert, but its resistive insert is a high-homogeneity solenoid. The system is designed to support a high-field 14-MW insert, operated at 30-bar water pressure, up to 42-kN side load, and 2.6-MN fault forces. Numerous complex two-dimensional and three-dimensional finite-element models have been developed and used for a systematic optimization of all critical load path items.