Iron dominated 2 T 50° superconducting dipoles for FRIB fragment separator

The Facility for Rare Isotope Beams under construction at Michigan State University, a new national user facility funded by the U. S. Department of Energy Office of Science will provide exotic rare isotope beams at energies of at least 200 MeV/u at a beam power of 400 kW. The proposed FRIB fragment separator has a preseparator consisting of the hot-cell and vertical section in the first stage followed by two more stages. Two large high performance dipole magnets with a 50° bend are required in the vertical section of the preseparator. Both cost and space constraints in the vertical section along with technical scope have pushed the requirement of the superconducting dipole peak field to 2.0 T. The design of a large magnetic gap (0.2 m), superferric dipole with magnetic rigidity as high as 8 T-m and effective length of 3.49 m is presented. The current design is a "warm iron" H-shaped magnet with nominal yoke length of 3.39 m and magnetic half-gap of 0.10 m. The major challenges are tight spaces in the vertical section, the compact coil and cryostat design and the unbalanced forces. The coil design is based on wet wound epoxy impregnated Formvar insulated conductor that provides ample current and temperature margins. This paper also presents the detailed magnet design including coil forces, coil restraint system, coil properties, conductor stability, quench analysis and full mechanical details.