Beam lifetimes of stored ${\mathrm{U}}^{28+}$ ions with energies between 10 and $180\mathrm{MeV}/\mathrm{u}$ were measured in the heavy ion synchrotron SIS18 and in the experimental storage ring (ESR) of the GSI accelerator facility. By using the internal gas jet target of the ESR, it was possible to obtain projectile ionization cross sections for collisions with ${\mathrm{H}}_2$ and ${\mathrm{N}}_2$ from the lifetime data. The experimental cross sections are compared to theoretical data predicted by the $n$-body classical-trajectory Monte Carlo (CTMC) method of Olson et al. and to calculations of Shevelko et al. using the LOSS-R code. In addition, both theoretical approaches are probed by using the resulting cross sections as input parameters for the STRAHLSIM code, which models the beam losses and, consequently, the lifetimes in the heavy ion synchrotron SIS18. Both the cross section measurement and the SIS18 lifetime study indicate that the LOSS-R code cross sections are in better agreement with the experimental results than the $n$-body CTMC calculations.

Using novel metallic magnetic calorimeter detectors at the CRYRING@ESR, we recorded x-ray spectra of stored and electron cooled heliumlike uranium ( U 90 + ) with an unmatched spectral resolution of close to 90 eV. This allowed for an accurate determination of the energies of all four components of the K α transitions in U 90 + . We find good agreement with state-of-the-art bound-state QED calculations for the strong-field regime. Our results do not support any systematic deviation between experiment and theory in heliumlike systems, the presence of which was subject of intense debates in recent years.

We report on the first integration of novel magnetic microcalorimeter detectors (MMCs), developed within SPARC (Stored Particles Atomic Physics Research Collaboration), into the experimental environment of storage rings at GSI ^{6 6} GSI Helmholtzzentrum für Schwerionenforschung GmbH, Planckstraße 1, 64 291 Darmstadt. , Darmstadt, namely at the electron cooler of CRYRING@ESR. Two of these detector systems were positioned at the 0° and 180° view ports of the cooler section to obtain high-resolution x-ray spectra originating from a stored beam of hydrogen-like uranium interacting with the cooler electrons. While previous test measurements with microcalorimeters at the accelerator facility of GSI were conducted in the mode of well-established stand-alone operation, for the present experiment we implemented several notable modifications to exploit the full potential of this type of detector for precision x-ray spectroscopy of stored heavy ions. Among these are a new readout system compatible with the multi branch system data acquisition platform of GSI, the synchronization of a quasi-continuous energy calibration with the operation cycle of the accelerator facility, as well as the first exploitation of the maXs detectors’ time resolution to apply coincidence conditions for the detection of photons and charge-changed ions.