The Experimental Storage Ring (ESR) enables the storage of charged particles at relativistic speeds over a wide range of masses and energies. The primary focus is on highly charged heavy ions and radioactive beams produced in the Fragment Separator (FRS). All ions used in the ESR are accelerated to the required energies in the Heavy Ion Synchrotron (SIS) before being transferred to the ESR.A key feature of the ESR is the ability to improve the quality of the stored beam by several orders of magnitude through phase-space cooling, utilizing both electron cooling and stochastic cooling. For experiments with stored beams, an internal gas target is integrated into one of the ESR's straight sections.Another essential capability of the ESR is decelerating highly charged ion and fragment beams—produced at high energies—down to low energies. These decelerated beams can be used for in-ring experiments or extracted from the storage ring. Extraction options include a slow extraction method for experiments on external targets and a fast extraction method, which routes the low-energy ions to the CRYRING or the HITRAP linear accelerator for further deceleration.Because storing highly charged ions—especially at low energies—requires an exceptional vacuum, the ESR is equipped with a UHV system capable of reaching pressures in the range of 10¹¹.

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