Annual Meeting of the ErUM-FSP APPA 2026

For photon energies from several tens of keV up to a few MeV, Compton polarimetry is an indispensable tool to gain insight into subtle details of fundamental radiative processes in atomic physics. Within the SPARC collaboration [1] several segmented semiconductor detectors have been developed that are well suited for application as efficient Compton polarimeters. For photon emission processes...

Study of electronic processes (ionization, excita-tion and capture) in ion-ion collisions is experimen-tally very challenging. So far, such collisions have been performed mainly in the low-energy regime (typically at center‐of‐mass energies ≾ a few 100 keV) where the charge transfer is by far the dominant process. Specific experimental conditions are required to perform absolute cross section...

The transverse electron target at the CRYRING has recently been commissioned successfully. It will allow investigating interactions between heavy ions and a collimated beam of monoenergetic electrons, including the emission of X-rays from radiative electron capture. For ions of low and medium nuclear charges, the X-ray transitions lie in the energy range of 1 – 50 keV. To determine the...

Electron-ion collision experiments in a
merged beams geometry (electron cooler) are
well established at ion storage rings. A complete
new range of experiments is possible if the geometry is changed to a crossed-beams setup in 90° angle between the electron and ion beams employing a dedicated free-electron target. The target
bridges the gap between low-collision-energy experiments in...

An active plasma lens is a device used to focus charged particle beams by means of a gas discharge initiated in a capillary aligned with the beam axis. The high current carried by the discharge plasma generates a strong azimuthal magnetic field, causing the charged particles traversing the plasma to experience a focusing Lorentz force.

Plasma lenses are particularly suited for...

Using the electron-ion crossed-beams technique, we have measured absolute cross sections for electron impact single ionization of Xe$^{12+}$ and Xe$^{13+}$ ions, and double ionization of Xe$^{12+}$, Xe$^{13+}$ and Xe$^{14+}$ ions. In addition we have performed corresponding calculations using a hybrid level-to-level and subconfiguration-average distorted wave approach. We find excellent...

Plasma lenses, created by gas discharges along the beam axis of charged particle beams, provide a compact and efficient approach to magnetic focusing. High currents initiated between ring electrodes generate azimuthal magnetic fields via Ampère's law, enabling symmetric focusing in both transverse planes. Compared to conventional solenoids and quadrupoles, plasma lenses achieve substantially...

As a first completed facility of the FAIR project, the heavy ion storage ring CRYRING@ESR is in operation since 2020 and is serving as experiment platform for the SPARC collaboration. The ring is optimized for low-energy storage and beam cooling, and with access to all ion species available from the GSI accelerator chain or from a local RFQ injector. This offers a unique access to study the...

Bunched relativistic ion beams with a narrow momentum distribution are essential for precision experiments at modern accelerator facilities. Laser cooling presents a promising approach to further reduce the relative momentum distribution of such ion beams.

This work presents the two high power UV laser systems, one pulsed and one cw, for laser cooling of relativistic bunched ion beams at...

The energy deposition of ions in water generates pressure waves, known as ionoacoustic signals. Ionoacoustic detection offers EMP-resilient diagnostics for (ultra-) short ion bunches over a broad dynamic range, enabling single-shot measurements of beam energy, dose, size, and position. We present recent developments of the I-BEAT detector as an online acoustic monitor for charged-particle...

The energy-resolved merged beams recombination rate coefficient α(E) for dielectronic recombination (DR) of O2+ has been measured on an absolute scale in the energy range from 0 to 45 eV. The experimental data comprises all ∆N=0 DR series associated with 2s → 2p core excitations and the lowest ∆N=1 DR series limits associated with 2p → 3s and 2p → 3d core excitations. In addition, we have...

In recent years, Metallic Magnetic Calorimeters (MMC) have emerged as excellent single photon detectors, exhibiting a broad spectral acceptance, ranging from a few to hundreds of keV, combined with a high energy resolution of $E/\Delta E (FWHM) \approx 6000$ [J. Geist. PhD thesis, 2020]. In combination with their fast rise time, they represent a superb tool for fundamental research in atomic...

Dielectronic recombination of N-like Ne was studied using a merged-
beams setup at CRYRING@ESR for collision energies from 0 to 25
eV. The measured energy-dependent recombination rate coefficient in-
cludes all ΔN=0 DR resonances from 2s to 2p core excitations was
compared with results from theoretical calculations. The ion beam
contained roughly equal fractions of ions in the...

As the upgrades of accelerator facilities are pushing the frontiers of high-intensity and high-energy particle beams, there is a demand for reliable beam extraction techniques into high-pressurized target areas with little impact on the beam properties. A promising technique that allows the extraction of such ion beams is the plasma window [1]. It is based on a cascaded arc discharge that...

S. Schippers, C. Brandau, S. Fuchs, M. Lestinsky, S.-X. Wang, C. Y. Zhang, N. R. Badnell, A. Borovik Jr., M. Fogle, V. Hannen, Z. Harman, P.-M. Hillenbrand, E. B. Menz, Y. Zhang, Z. Andelkovic, F. Herfurth, R. Heß, A. Kalinin, C. Kozhuharov, C. Krantz, S. Litvinov, B. Lorentz, U. Spillmann, M. Steck, G. Vorobyev, D. Banas, S. Fritzsche, E. Lindroth, X. Ma, A. Müller, R. Schuch, A....

The ARTEMIS experiment at the HITRAP facility situated at GSI, Darmstadt, focuses on precision measurements of electron magnetic moments in highly charged ions as a benchmark QED test in extreme fields. The experiment utilises a homogeneous magnetic field of 7 T with a harmonic electrostatic field which enables ion densities of up to 10e6 cm−3 to be stored for several days. The trap is equipped...

The heavy-ion synchrotron SIS100 is (at) the heart of the Facility for Antiproton and Ion Research (FAIR) in Darmstadt, Germany. It is designed to accelerate intense beams of heavy highly charged ions up to relativistic velocities and to deliver them to unique physics experiments, such as those planned by the APPA/SPARC collaboration. In order to cool these extreme ion beams, "bunched beam...

Transition energy measurements in heavy, few-electron ions are unique tools to test bound-state quantum electrodynamics (QED) in extremely high Coulomb fields, where perturbative methods cannot be implemented. By accurately measuring the relative energies between $2p_{3/2} \to 2s_{1/2}$ transitions (of an energy of about 4.5 keV) in two-, three-, and four-electron uranium ions, we were able,...