Working Group for the High Resolution Spectrometer (S800) at FRIB

The S800 Spectrograph

About the Group

To join visit: and create a new account (bottom-right of the page). On the next page, select " Join Working Group for the High Resolution Spectrometer (S800) at FRIB" when filling in the form.

The Working Group aims to explore, develop and design the necessary infrastructure for experiments at FRIB that utilize the High-Resolution Spectrometer (S800) with fast rare isotope beams and advocates the needs for the science program with the spectrometer at FRIB to the community.  In addition, the group is working on the case for, and the design of a High-Rigidity Spectrometer (up to 7-8 Tm).

The following people serve as spokespersons for the working group: Daniel Bazin (NSCL), Paul Fallon (LBNL), Alexandra Gade (NSCL/MSU), Ingo Wiedenhoever (FSU), Michael Thoennessen (NSCL/MSU), Jim Brown ( and Remco Zegers (NSCL/MSU).


The Science

A wide variety of topics can be studied at S800 Spectrograph, using different types of reactions such as knock-out, transfer and charge-exchange reactions, inelastic scattering and Coulomb excitations. Furthermore, lifetime measurements can be performed using a plunger device and time-of-flight mass measurements can be carried out utilizing the high momentum resolution of the S800. These reactions will be amongst the main tools employed at FRIB to obtain detailed information about rare isotopes and their nuclear structure and the implication for astrophysics.

For certain types of experiments, such as the investigation of neutron unbound states, the momentum resolution is not so important, but being able to run at higher rigidities than possible with the S800 (4 Tm) is. To facilitate such studies at FRIB, the specifications for a high-rigidity (8 Tm), large (momentum/angular) acceptance spectrometer are being considered, which would essentially be an upgrade of the current Sweeper magnet. A high-rigidity device is also important for some experiments that are currently ran at the S800, as the S800 can only bend nuclei with a rigidity of maximal 4 Tm. At FRIB maximum RI beam production rates will be achieved at higher rigidities that are 1.5-2 times higher.


Our Equipment

The S800 spectrograph combines both high resolution and high acceptance in a single device and is specially designed for reaction studies with rare isotope beams. Its large acceptances both in solid angle (20 msr) and momentum (5%) are well adapted to the large emittances of secondary beams produced by projectile fragmentation. The high resolution is achieved via an analytical reconstruction method in which aberrations are calculated a priori from the magnetic field maps and used directly to correct the raw data. For that purpose, high resolution tracking detectors are placed in the focal plane of the S800 spectrometer. In addition, an ion-chamber and several layers of plastic scintillation detectors are used for particle identification (a segmented hodoscope for use in the focal plane is currently being developed). The spectrograph is installed vertically on a carriage that can rotate from 0° to 60°, although most experiments with rare isotope beams are run at 0°. Its maximum rigidity is limited to 4 Teslameter (Tm). The S800 is preceded by an analysis line that allows for different optical modes of operations, either focusing or dispersion matched.

The S800 spectrograph is often run with secondary detector systems, such as the Segmented Germanium Array (SeGA), the High Resolution Array (HiRA) and more recently the Caesium Iodide Array (CAESAR). Additional detection systems are being developed, such as the Low Energy Neutron Detector Array (LENDA).  Furthermore, several types of beam tracking and timing detectors can be employed in the analysis line to reduce uncertainties related to beam emittances.

Together with these auxiliary devices, the S800 spectrometer is an excellent device for performing the next generation of rare isotope beam experiments at FRIB. Nevertheless, experiments at FRIB require careful consideration of the available equipment and upgrades and improvements need to be studied and developed so that the most interesting and exciting experiments can be performed when FRIB goes online.

Some information about the sweeper magnet, currently being used together with the Modular Neutron Array (MoNA) can be found here:



News & Announcements

High Rigidity Spectrometer Workshop July 11, 2014 at NSCL/MSU.

See workshop site:

Registration: Registration Form

The workshop is aimed at discussing the science program, as well as the design and construction of the High Rigidity Spectrometer (HRS) and associated infrastructure stationed at the Facility of Rare Isotope Beams (FRIB).

Update report for FRIB SAC finalized and submitted

The Update report for the FRIB SAC has been submitted. Thank you for your input. The final version can be found under this website's resources.

Call for update by FRIB SAC

The working group received a call (see below) by the FRIB Scientific Advisory Committee for an update on the working group activities. A draft document has been sent around and can also be found under resources on this website. Please send comments by January 24, 2011 to Remco Zegers (zegers at nscl