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Gas-filled stopping cells are used at accelerator laboratories for the thermalization of high-energy radioactive ion beams. Common challenges of many stopping cells are a high molecular background of extracted ions and limitations of extraction efficiency due to space-charge effects. At the FRS Ion Catcher at GSI, a new technique for removal of ionized molecules prior to their extraction out of the stopping cell has been developed. This technique utilizes the RF carpet for the separation of atomic ions from molecular contaminant ions through their difference in ion mobility. Results from the successful implementation and test during an experiment with a 600 MeV/u 124Xe primary beam are presented. Suppression of molecular contaminants by three orders of magnitude has been demonstrated. Essentially background-free measurement conditions with less than 1 % of background events within a mass-to-charge range of 25 u/e have been achieved. The technique can also be used to reduce the space-charge effects at the extraction nozzle and in the downstream beamline, thus ensuring high efficiency of ion transport and highly-accurate measurements under space-charge-free conditions. Image 1 • Extraction of thermalized ions out of a gas-filled stopping cell with an RF carpet. • Atomic and molecular ions can be separated with the RF carpet by their ion mobility. • Suppression of molecular background by three orders of magnitude with the RF carpet. • Removal of space charge prior to extraction of ions out of the stopping cell. [ABSTRACT FROM AUTHOR]

The access to exotic nuclei at radioactive ion beam facilities is crucial for the state of the art research across several fields of physics such as in nuclear structure, the understanding of fundamental interactions and nuclear astrophysics. The particle identification is of high importance, besides the challenging production of these rare and short-lived nuclei. At in-flight facilities, the particle identification is based on measuring the time-of-flight, energy-deposition and magnetic rigidity. These quantities are calibrated to convert them into A/Q and Z of the ions. To ensure a correct calibration, the unambiguous identification, also called tagging, of one species is necessary. Here, we present a novel tagging method by high-resolution mass measurements using an MR-TOF-MS after thermalization of the ions in a cryogenic stopping cell. The method was successfully established and tested at the fragment separator FRS at GSI with the FRS Ion Catcher in experiments using different FRS operation modes. [ABSTRACT FROM AUTHOR]

A complex, long-range experimental program for the production of neutron-rich nuclei via multi-nucleon transfer (MNT) reactions and spontaneous fission (SF) inside the Cryogenic Stopping Cell (CSC) of the FRS Ion Catcher facility at GSI has been suggested and is under development. A key component is a new experimental set-up, consisting of a modified DC cage, a target-wheel, a beam-dump and a space charge suppression system. This setup replaces the standard electrode structure of the CSC, enabling generation of radioactive isotope beams by in-cell MNT reactions inside the CSC and the efficient and fast extraction of ions produced by MNT reactions or spontaneous fission. Furthermore, the system allows to do experiments with beams from the FRS with much higher rates and shorter half-lives. We present the specifications, design and production of this device. We also present the technical solution adopted against the space charge effect and the simulations that validate it. [ABSTRACT FROM AUTHOR]