Scientific Case

Working Group



The Department of Energy, Office of Science, Office of Nuclear Physics approved Critical Decision 1 (CD-1: Approve Alternative Selection and Cost Range for the High Rigidity Spectrometer Research Project) for the HRS Project on September 18, 2020.


The High Rigidity Spectrometer (HRS) will be the centerpiece experimental tool of the Facility for Rare-Isotope Beams (FRIB) fast-beam program. The fast-beam program at FRIB has tremendous discovery potential, enabling experiments with beam intensities of few ions per second or less through the luminosity afforded by thick targets. The high magnetic rigidity of the HRS (8 Tm) will match the rigidities for which rare-isotope production yields at the FRIB fragment separator are maximum across the entire chart of nuclei and enable experiments with the most exotic, neutron-rich nuclei available at FRIB.

The figure on the right provides a schematic overview of the scope of the HRS at FRIB and integration example with other detector systems. The HRS consists of two main elements: the High-Transmission Beam Line (HTBL) and the Spectrometer Section. Rare isotopes beams are transported from the FRIB fragment separator through the HTBL to the target position at the HRS. The first element of the HRS after the target station is the sweeper dipole, which diverts charged particles toward a focusing beam line that transports particles to the spectrometer dipoles and the focal plane detectors. The spectrometer dipoles provide the precise exit channel characterization with momentum and particle identification resolutions required for the broad scientific program with the HRS.

Also shown in the figure are the Gamma-Ray Energy Tracking Array (GRETA) and the Modular Neutron Array (MoNA-LISA). There are many other state-of-the-art detectors that have been developed by the User Community that will be used in combination with the HRS to achieve the scientific objectives of FRIB.