Felix Martin Kröger
Abstract: For decelerated bare lead ions at a low beam energy of 10 MeV/u, the x-ray emission associated with radiative recombination (RR) at threshold energies has been studied at the electron cooler of CRYRING@ESR at GSI, Darmstadt. In our experiment, we observed the full x-ray emission pattern by utilizing dedicated x-ray detection chambers installed at 0∘ and 180∘ observation geometry. Most remarkably, no line distortion effects due to delayed emission are present in the well-defined x-ray spectra, spanning a wide range of x-ray energies (from about 5 to 100 keV), which enables us to identify fine-structure resolved Lyman, Balmer, and Paschen x-ray lines along with the RR transitions into the K, L, and M shells of the ions. For comparison with theory, an elaborate theoretical model is established taking into account the initial population distribution via RR for all atomic levels up to Rydberg states with principal quantum number n=165 in combination with time-dependent feeding transitions. Within the statistical accuracy, the experimental data are in very good agreement with the results of rigorous relativistic predictions. Most notably, this comparison sheds light on the contribution of prompt and delayed x-ray emission (up to 70 ns) to the observed x-ray spectra, originating in particular from yrast transitions into inner shells.
Abstract: The electron-capture process was studied for Xe54+ colliding with H2 molecules at the internal gas target of the Experimental Storage Ring (ESR) at GSI, Darmstadt. Cross-section values for electron capture into excited projectile states were deduced from the observed emission cross section of Lyman radiation, being emitted by the hydrogenlike ions subsequent to the capture of a target electron. The ion beam energy range was varied between 5.5 and 30.9 MeV/u by applying the deceleration mode of the ESR. Thus, electron-capture data were recorded at the intermediate and, in particular, the low-collision-energy regime, well below the beam energy necessary to produce bare xenon ions. The obtained data are found to be in reasonable qualitative agreement with theoretical approaches, while a commonly applied empirical formula significantly overestimates the experimental findings.
Abstract: We present charge‐state evolution studies for Pb⁵⁴⁺ ion beams passing through stripper foils at relativistic energies of 5.9 GeV/u. The purpose of this investigation is to determine the optimum target material and non‐equilibrium thickness for the efficient production of few‐electron lead ions, that is, Pb⁸⁰⁺ and Pb⁸¹⁺, at the present European Organization for Nuclear Research, CERN, accelerator facility at energies as high as 5.9 GeV/u. Based on these predictions, an Al stripper foil has been selected for a proof‐of‐principle measurement in the frame of the Gamma Factory study group. The experimental data confirms a substantial yield of non‐bare Pb ions. In addition, a charge‐state evolution study for the production of Li‐like lead ions Pb⁷⁹⁺ is presented, which will be subject of a follow‐up experiment in the near future.
Friedrich-Schiller-Universität Jena, Physikalisch-Astronomische Fakultät (2018)
Abstract: In this work charge state distributions of heavy ions have been calculated for the production of effective stripper foils for heavy ion acceleration facilities. In this context, the FAIR facility at GSI and the proposed Gamma Factory at CERN are presented, where the use of partially stripped, relativistic ions will be of special interest for upcoming experiments. To determine the charge state distribution as a function of penetration depth, various programmes have been applied, depending on the respective energy regime. For stripping scenarios in the lower energy regime, the GLOBAL code was applied, that allows to take into account up to twenty-eight projectile electrons for energies up to 2000 MeV/u. Since the GSI/FAIR facility can accelerate even low-charged uranium ions up to 2700 MeV/u, and the Gamma Factory at CERN considers a stripping scenario at 5900 MeV/u, another programme was needed. This is why for the stripping scenarios in the high energy regime, first the well-known CHARGE code was used. However, even though it can operate in the very high energy regime, it only takes into account bare, hydrogen- and heliumlike projectile charge states. To overcome this limitation, the recently developed BREIT code was verified and used for stripping scenarios in the high energy regime. As this code has no built-in treatment of the various charge-changing processes, it needs a multitude of information about the electron capture and loss cross sections as input parameters. Thus, for the calculation of charge state distributions with the BREIT code, cross sections were computed by well-tested theories and codes. The BREIT code together with the codes for the cross section computation were then applied for two studies: first for an exemplification study for the upcoming GSI/FAIR facility to show the practicability of the BREIT code together with the cross section programmes, and then for a study to find optimal stripper foils for the Gamma Factory study group at the CERN facility, in order to efficiently produce Pb⁸⁰⁺ and Pb⁸¹⁺ ions from a Pb⁵⁴⁺ beam before entering the LHC. Furthermore, experimental data of a beam time at ESR at GSI in 2016 was analysed, where a Xe⁵⁴⁺ ion beam of several MeV/u was colliding with a hydrogen gas target. The data allowed the derivation of experimental NRC cross sections, and it was shown that the predictions of the EIKONAL code are in good agreement with these cross sections in an energy range most relevant for upcoming experiments at CRYRING@GSI.