Present and future experiments with stored exotic nuclei at relativistic energies

Pioneering experiments with stored and cooled exotic nuclei at relativistic energies have been performed using the combination of the fragment separator FRS with the storage-cooler ring ESR. Exotic nuclei created in peripheral collisions are spatially separated in-flight and injected into the storage ring for high-precision mass and unique lifetime measurements. Lifetimes of stored bare and few-electron nuclei have been measured to study the influence of the electron density on the β decay. This condition, relevant for stellar plasma, can now be systematically investigated in the laboratory for the first time. Characteristic experiments of the present FRS-ESR system are presented and perspectives for a next-generation facility are briefly outlined.