High Rigidity Spectrometer (HRS)

The proposed High Rigidity Spectrometer (HRS) will substantially increase FRIB’s scientific reach and productivity and address the overarching intellectual challenges from the 2015 Nuclear Science Advisory Committee (NSAC) Long Range Plan and the National Research Council Decadal Study. Eleven of the 17 NSAC Rare-Isotope Beam Taskforce benchmarks which were introduced to characterize the scientific research of a rare-isotope facility, require the use of fast beams at FRIB and benefit from the experimental program that will be performed at the HRS.

The HRS is proposed as the first major addition to FRIB’s experimental facilities. It consists of two segments: the High-Transmission Beam Line (HTBL) and the Spectrometer Section. The HTBL transports rare isotope beams from the Advanced Rare Isotope Separator (ARIS) fragment separator to the reaction target stationed at the entrance of the Spectrometer Section. ARIS delivers specific rare isotope beam (RIB) to the fragment separator focal plane. From there, RIBs are delivered to experimental areas including HRS, the decay station, and the S800 spectrograph.

At the Spectrometer Section, charged reaction products created at the target are analyzed. A wide variety of high-impact ancillary detector systems developed by the nuclear science community for experiments at FRIB will be used in combination with the HRS, such as the Gamma-Ray Energy Tracking Array (GRETA) and the Modular Neutron Array (MoNA-LISA).


The HRS project scope includes the design, procurement, installation, and commissioning of the technical elements including the magnets and concomitant  diagnostics, controls, power supplies, and cryogenic ancillary systems. MSU is constructing the conventional facilities with anticipated beneficial occupancy at the end of 2019. HRS achieved Critical Decision 0 (CD-0) in November 2018 as part of the U.S. Department of Energy’s staged project approval process. CD-0 documents that a mission need, such as a scientific goal or a new capability, requiring material investment exists.

A Conceptual Design Report (CDR) has been developed with input from the FRIB user community.

Science HRS will enable

The key characteristic of the proposed HRS is its ability to accommodate rare-isotope beams up to magnetic rigidities of 8 Tesla meters (Tm). That matches the rigidities at which the rare-isotope production in the Advanced Rare Isotope Separator is optimized for isotopes across the chart of nuclei, even with an envisioned FRIB upgrade to 400 MeV/u, or FRIB400.

Consequently, experiments with the HRS will greatly increase the sensitivity of the scientific program at FRIB, in particular for experiments with the most neutron-rich isotopes that have the highest potential for discovery.

The HRS will increase experimental productivity by up to a factor of 100. The gain factors in luminosity are over what will be possible with existing spectrometers at NSCL (S800 spectrograph and sweeper magnet) that have a maximum magnetic rigidity of 4 Tm.

The largest luminosity gains are achieved for the most neutron-rich species, including many of the nuclei that in the path of the astrophysical r process.


The scientific case for HRS has been developed by a collaboration of scientists from 18 U.S. universities, Argonne National Laboratory, Lawrence Berkeley National Laboratory, and Los Alamos National Laboratory. Learn more about HRS at hrs.lbl.gov.

Significant contributions to the HRS project efforts have been made by more than 20 U.S. institutions as well as those in Canada, Europe, and Japan.