The High Transmission Beamline Superconducting Magnets for High Rigidity Spectrometer Project at FRIB: Design Status

The High Rigidity Spectrometer (HRS) project is a critical expansion of the Facility for Rare Isotope Beams (FRIB), designed to transport high-emittance rare isotope beams with magnetic rigidities of up to 8 Tesla-meters. The HRS consists of two main segments: the upstream High Transmission Beamline (HTBL) and the downstream Spectrometer Section (SPS). This paper presents the design feature of the HTBL's superconducting magnets, which include eight quadrupole triplets and four dipoles. Two different approaches for the quadrupole magnets are explored: the iron-dominated and coil-dominated designs, each with distinct electromagnetic characteristics and manufacturing techniques incorporating nested higher-order multipoles. The dipole design builds upon the proven technology of FRIB's existing switching dipoles, benchmarked from the National Superconducting Cyclotron Laboratory (NSCL) era. Here, we discuss the advantages and limitations of the proposed design options and their performance to meet HTBL operational requirements. Insights gained through FRIB's design advancements and challenges encountered in developing high-performance superconducting magnets for the HRS project are also presented.