Design of Coil-Dominated Quadrupole Triplet for High Rigidity Isotope Beams

Iron-dominated superconducting magnets are one of the most popular and most used design choices for superconducting magnetic quadrupoles for accelerator systems. While the iron yoke and pole tips are economic and effective in shaping the field, the large amount of iron also leads to certain drawbacks, namely, unwanted harmonics from the sextupole correctors nested inside of quadrupole iron pole tips. Additional problems include the cryogenic design challenges of the iron yoke being part of the cold mass, and the mechanical challenges of mounting the sextupole and octupole. The Facility for Rare Isotope Beams (FRIB) plans to implement a coil-dominated cosine-theta type quadrupole as a future upgrade, and the advantages of using an iron-free quadrupole, along with the methods and choices of the design and the approach for the planned fabrication, as well as current status of the project are overviewed in this paper.