Series-Connected Hybrid Magnetic Shielding Conceptual Design for the Helmholtz Centre Berlin for Materials and Energy

The National High Magnetic Field Laboratory (NHMFL) has been funded to design and construct two series-connected hybrids (SCH), one each for the NHMFL in Tallahassee, FL and the Helmholtz Centre Berlin for Materials and Energy (HZB), Germany. The original designs for both hybrids contained three concentric coils comprising a Nb₃Sn superconducting cable-in-conduit (CIC) main-field outsert coil, a resistive main-field insert coil and a NbTi superconducting CIC shield coil. The fringe field requirements for both facilities were met by designing the NbTi shield coil to match the 9.6 times 10⁶ A-m² dipole moment of the main field coils at an average radius of 1.16 m. Subsequent, alternate magnetic shielding concepts for both hybrids have been investigated with the objective of reducing the anticipated $700 k NbTi shield coil cost. The HZB fringe field requirements were targeted to a local area of concern at the adjacent Spin Echo facility, centered 15.65 m from the hybrid magnet center. An alternate, lower-cost shield concept comprised a set of four smaller shield coils positioned orthogonally around the HZB spin echo facility with a resultant total 85% to 90% reduction in required dipole moment compared to the original NbTi shield coil. The fringe field requirements at the NHMFL were not changed, but a lower-cost iron shielding option (not described here) located around the NHMFL hybrid was found to be a viable alternative. As a result, the NbTi CIC coil can be eliminated from the common superconducting magnet design for both the HZB and the NHMFL SCH´s in favor of viable lower cost shielding options.