[en] Radiative recombination transitions into the ground state of cooled bare and hydrogen-like uranium ions were measured at the storage ring ESR. By comparing the corresponding x-ray centroid energies, this technique allows for a direct measurement of the electron-electron contribution to the ionization potential in the heaviest he-like ions. For the two-electron contribution to the ionization potential of he-like uranium we obtain a value of 2248 ± 9 eV. This represents the most accurate determination of two-electron effects in the domain of high-Z he-like ions and the accuracy reaches already the size of the specific two-electron radiative QED corrections. (orig.)

[en] Full text: In the current presentation an overview about the envisioned program of the atomic physics research collaboration SPARC (Stored Particle Atomic Research Collaboration, http://wwwlinux. gsi.de/ sparc) at the future GSI accelerator facility will be given. This program can be associated mainly with four types of experimental studies: Highly relativistic heavy ions will be employed for a wide range of collision studies involving photons, electrons and atoms, and exploiting the large Doppler boost and the rapidly varying fields in those reactions. High-energy beams will be utilized for achieving high stages of ionization up to bare uranium nuclei. Fundamental atomic physics studies and model-independent determination of nuclear quantities with stable as well as radioactive atoms in well-defined charge states will be performed, applying atomic physics methods. An important scenario for this class of experiments will be the slowing-down, trapping and cooling of particles in ion traps. Low energy beams of high Z few-electron ions from an additional 'low energy' storage ring ('LSR') behind the NESR will be employed for collisions characterized by very large Sommerfeld parameters q/v

[en] We have studied the $K$-shell excitation of He-like uranium (${\mathbf{\text{U}}}^{90+}$) in relativistic collisions with hydrogen and argon atoms. Performing measurements with different targets, as well as with different collision energies, enabled us to explore the proton- (nucleus-) impact excitation as well as the electron-impact excitation process for the heaviest He-like ion. The large fine-structure splitting in uranium allowed us to partially resolve excitation into different L-shell levels. State-of-the-art relativistic calculations which include excitation mechanisms due to the interaction with both protons (nucleus) and electrons are in good agreement with the experimental findings. Moreover, our experimental data clearly demonstrate the importance of including the generalized Breit interaction in the treatment of the electron-impact excitation process.

[en] In this contribution, a brief overview of the Stored Particle Atomic physics Research Collaboration scientific program at the upcoming Facility for Antiproton and Ion Research (FAIR) is given. The program comprises a very broad range of research topics addressing atomic structure and dynamics in hitherto unexplored regimes, light–matter interactions, lepton pair production phenomena, precision tests of quantum electrodynamics and standard model in the regime of extreme fields and many more. We also present the current strategy for the realization of the envisioned physics program within the modularized start version (MSV) of FAIR. (paper)

No abstract available

[en] The new international accelerator Facility for Antiproton and Ion Research (FAIR) which is currently under construction in Darmstadt has key features that offer a wide range of exciting new opportunities in the field of atomic physics and related fields. The facility will provide highest intensities of relativistic beams of both stable and unstable heavy nuclei, in combination with the strong electromagnetic fields generated by high-power lasers, thus allowing to widen atomic physics research into completely new domains. In the current contribution, a short overview of the SPARC (Stored Particle Atomic physics Research Collaboration) research programme at the FAIR facility is given. Furthermore, we present the current strategy for the realization of the envisioned SPARC physics programme at the modularized start version of the FAIR facility. (paper)

[en] We present the current status in experimental investigations of the heaviest hydrogen-like systems at the Experimental Storage Ring (ESR) at GSI Darmstadt. Together with the most recent theoretical predictions the present experimental result provides a test of the leading quantum electrodynamical (QED) contributions on a percent level. In addition, the planned future experimental studies and related developments devoted to high-resolution spectroscopy of the ground-state in high-Z hydrogen-like systems are reviewed.

[en] We studied the angular distribution of the X-ray emission associated with KLL-RTE for H-like U⁹¹⁺ ions colliding with quasi-free electrons from an H₂ target. In this resonant transfer and excitation process an intermediate doubly excited He-like U^90+** with two electrons in the L-shell is produced by electron-electron interaction; this exotic state decays by the emission of two photons, a Kα-hypersatellite and a Kα-satellite X-ray. According to the different j values (1/2 and 3/2) for the L-shell electrons three different KLL-RTE resonance groups can be distinguished by the corresponding ion energies. At the three resonance energies and one off-resonance energy (116.6, 124.9, 133.1 and 102.0 MeV/u, respectively) X-ray spectra were taken simultaneously at seven different observation angles. The Kα2 satellite lines (j=1/2-j=1/2 transitions) are isotropic, whereas the Kα1 hypersatellite lines (3/2-1/2 transitions) for the second resonance display a pronounced anisotropy pointing to a strong alignment of the involved doubly excited states. Our data agree with full relativistic theory in its general features

[en] For the current X-ray spectroscopy program at the ESR storage ring (GSI-Darmstadt) a position sensitive germanium detector system has been completed. The position sensitive structure of the detector has been realized on an area of 47 mm x 23.4 mm by an array of 200 strips (200 μm wide and 23.4 mm long) separated by 35 μm wide grooves etched through boron implanted contact. The thickness of the detector inclusive a 0.6 mm thick Li-diffused rear contact amounts to 4.1 mm. Each strip has been joined to a preamplifier placed outside the cryostat with printed leads inside the flexible Kapton foil. The energy resolution of the strips has been about 1.8 keV [FWHM] for 60 keV photons. Coincidences between neighbouring strips were measured whereby a time resolution of 70 ns [FWHM] was obtained. First preliminary results obtained with the detector mounted at the transmission X-ray spectrometer FOCAL demonstrated that an energy resolution better than 100 eV is achievable together with a high detection efficiency. Along with a new kind of X-ray spectrometer this detector may play a keyrole for the next step of high precision X-ray experiments, aiming on a precise test of quantum electrodynamics in the heaviest one-electron systems such as hydrogenlike uranium. (orig.)

[en] X-ray spectra following radiative recombination of free electrons with bare uranium ions (U⁹²⁺) were measured at the electron cooler of the ESR storage ring. The most intense lines observed in the spectra can be attributed to the characteristic Lyman ground-state transitions and to the recombination of free electrons into the K-shell of the ions. Our experiment was carried out by utilizing the deceleration technique which leads to a considerable reduction of the uncertainties associated with Doppler corrections. This, in combination with the 0 observation geometry, allowed us to determine the ground-state Lamb shift in hydrogen-like uranium (U⁹¹⁺) from the observed X-ray lines with an accuracy of 1%. The present result is about 3 times more precise than the most accurate value available up to now and provides the most stringent test of bound-state quantum electrodynamics for one-electron systems in the strong-field regime. (orig.)