At the FRS Ion Catcher at GSI/FAIR, projectile and fission fragments are produced at relativistic energies at the FRS, separated in-flight, range-focused, slowed-down and thermalized in a cryogenic stopping cell and transmitted to a multiple-reflection time-of-flight mass spectrometer (MR-TOF-MS). The MR-TOF-MS can perform direct mass measurements of exotic nuclei, to provide an isobarically and isomerically clean beam for further experiments, and as a versatile diagnostics device to monitor the production, separation and manipulation of exotic nuclei.

The MR-TOF-MS is an extremely versatile device with mass resolving power beyond 600,000 (FWHM), high transmission efficiency and ion capacity, and high mass accuracy (better than 1E-7). The excitation energies of isomers and isomeric ratios were measured and, for the first time, an isomeric beam was prepared using an MR-TOF-MS. The unique combination of performance parameters make the MR-TOF-MS the system of choice for measuring the masses of very exotic nuclei and for the search for new long-lived isomeric states.

Currently a next-generation cryogenic stopping cell is under construction for the Low-Eergy Branch at FAIR. This system will allow access to even more exotic nuclei, because it has a faster extraction, higher efficiency and can handle orders of magnitude higher rates.

Based on these concepts, an ion catcher is designed to form together with the liquid lithium target at SARAF-II the most powerful source for fission products in the next decade. Already now a rich physics program has been developed for spontaneous fission with the FRS Ion Catcher.