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For photon energies from several 10 keV up to a few MeV Compton polarimetry is an indispensable tool to gain insight into subtle details of fundamental atomic radiative processes. Within the SPARC collaboration several segmented semiconductor detectors are developed that are well suited for application as efficient Compton polarimeters. In this report, these recent developments are reviewed and it is discussed how Compton polarimetry can be employed at the upcoming Gamma Factory. [ABSTRACT FROM AUTHOR]

A theoretical investigation of the elastic resonant scattering of photons by ultra–relativistic and partially stripped ions is presented. Particular attention in the study is given to the angular distribution and polarization of scattered photons as "seen" in both the ion‐rest and laboratory reference frames. In order to evaluate these angular and polarization properties, the irreducible polarization tensor approach is combined with the density matrix theory. If, furthermore, the ion–photon coupling is treated within the electric dipole approximation, this framework enables one to obtain simple analytical expressions for both the emission pattern and the polarization Stokes parameters of the outgoing radiation. These (analytical) expressions for the nS0→n′P1→nS0$n S_0 \rightarrow n^{\prime } P_1 \rightarrow n S_0$, nS1/2→n′P1/2→nS1/2$n S_{1/2} \rightarrow n^{\prime } P_{1/2} \rightarrow n S_{1/2}$, and nS1/2→n′P3/2→nS1/2$n S_{1/2} \rightarrow n^{\prime } P_{3/2} \rightarrow n S_{1/2}$ transitions are displayed and analyzed , that are of interest for the Gamma Factory project and whose realization is currently under discussion at CERN. Based on the performed analysis, it is demonstrated that the resonantly scattered photons can be strongly (linearly or circularly) polarized, and that this polarization can be well controlled by adjusting either the emission angle and/or the polarization state of the incident radiation. Moreover, the potential of the photon scattering for measuring the spin‐polarization of ion beams is also discussed in detail. [ABSTRACT FROM AUTHOR]

A theoretical investigation of the resonant elastic scattering of laser photons by ultra‐relativistic partially stripped ions, that is the core process of the Gamma Factory project, is presented. Special emphasis in the study is placed on the angular distribution and polarization of scattered photons as observed in the collider and ion‐rest reference frames. In order to describe these (angular and polarization) properties for arbitrary relativistic many‐electron ion, the general approach, based on the application of irreducible polarization tensors, is laid down. By making use of the polarization tensors, the scattering of both conventional plane‐wave‐ and twisted (or vortex) photons is explored in detail. For the former case, it is shown how the propagation directions and polarization states of incident and outgoing photons are related to each other for the nS0→n′P1→nS0$n S_{0} \rightarrow n^{\prime } P_{1} \rightarrow n S_{0}$, nS1/2→n′P1/2→nS1/2$n S_{1/2} \rightarrow n^{\prime } P_{1/2} \rightarrow n S_{1/2}$, and nS1/2→n′P3/2→nS1/2$n S_{1/2} \rightarrow n^{\prime } P_{3/2} \rightarrow n S_{1/2}$ resonant transitions. For the scattering of initially twisted light that carries non‐zero orbital angular momentum, the angular distribution of secondary photons is explored and the conditions under which they are also twisted are discussed. [ABSTRACT FROM AUTHOR]

Recent progress in quantum electrodynamics (QED) calculations of highly charged ions is reviewed. The theoretical predictions for the binding energies, the hyperfine splittings, and the g factors are presented and compared with available experimental data. Special attention is paid to tests of bound-state QED at strong field regime. Future prospects for tests of QED at the strongest electric and magnetic fields as well as for determination of the fine structure constant and the nuclear magnetic moments with heavy ions are discussed. [ABSTRACT FROM AUTHOR]