An overview of the experiments conducted at the ESR in the last beam time running periods will be given. The big number of proposals submitted to the G-PAC in 2024 illustrates an exiting future of the storage ring program at GSI. The presentation will be concluded by an outlook to the planned studies in 2026/2027.
Lead-205 initially looks like a very promising candidate to be used as a chronometer for the early Solar System due to its unique position among astrophysically short-lived radionuclides as an s-only isotope probing the termination of the s process [1]. Unfortunately, the 2.3 keV 1/2− first excited state in $^{205}$Pb reduces the half-life in stellar environments by around 6 orders of...
It has been more than two decades since the first experimental demonstrations of the generation of relativistic electron beams produced by the interaction of ultra intense laser pulses with plasma [1]. Ever since, several research groups worldwide invested considerable effort towards detailing the Physics behind the mechanism of Laser Wakefield Acceleration (LWFA), that drives the formation...
The electrostatic Cryogenic Storage Ring (CSR) at the Max Planck Institute for Nuclear Physics in Heidelberg offers unique possibilities to study electron recombination of internally cold molecular ions as well as low-charged heavy atomic ions. The CSR provides a cryogenic environment with vacuum chamber temperatures < 10 K, resulting in a low residual gas density. This enables storage of ion...
Electron spectroscopy has long been a cornerstone for studying the dynamics of ion-atom/molecule collisions [1], offering detailed insight into fundamental processes such as electron capture, ionization, and excitation [2-4]. Extending electron spectroscopy to ion-ion collisions — where both collision partners are charged — is an emerging and largely unexplored frontier. Such studies enable...
Neon, one of the most abundant elements in the universe, is frequently observed in the spectroscopic data of many astrophysical objects. Dielectronic recombination (DR) is a key process for the charge state distribution in astrophysical plasma environments. It is initiated by the resonant capture of a free electron with simultaneous excitation of a bound electron and completed by the emission...
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 $1 – 50 \, \mathrm{keV}$. To...
C. Brandau$^{1,2}$, A. Borovik Jr.$^{1}$, B. M. Döhring$^{1,3}$, D. Banas$^{4}$, J. Glorius$^{2}$, A. Gumberidze$^{2}$, E. O. Hanu$^{2,5,6}$, P.-M. Hillenbrand$^{1,2}$, P. Jagodzinski$^{4,7}$, A. Kalinin$^{2}$, A. Krishnan$^{2,8}$, M. Lestinsky$^{2}$, M. Looshorn$^{1,3}$, E. B. Menz$^{2}$, U. Spillmann$^{2}$, K. Szary$^{4}$, R. Tyagi$^{9}$, J. Viehmann$^{9}$, S.-X. Wang$^{1,3}$, S....
The Highly charged Ions TRAP (HITRAP) located at the GSI, Darmstadt, is a facility for deceleration and cooling of ions that are produced at the accelerator complex thereby providing heavy, highly charged ions at low velocities and small energy distributions. Ion bunches consisting up to $10^{8}$ ions are injected into HITRAP at energies of 4 Mev/u from the Experimental Storage Ring (ESR),...
In modern charged particle collider research, increasing the number of investigated events requires beams with high-quality characteristics, particularly high brightness and low velocity spread. This can be achieved using beam cooling techniques. The most well-known among them is electron cooling, which involves colliding fast charged particles with a cold electron beam, resulting in a...
An Electron Beam Ion Trap (EBIT) provides highly charged ions (HCI) for spectroscopy and other experiments. To this end, a nearly monoenergetic electron beam is used. In interactions with the electrons from the beam, neutral atoms or positively charged ions can be stripped of bound electrons by means of electron impact ionisation. The electron beam originates at a so-called “electron gun”, is...
Electron-ion collision spectroscopy is a very successful approach for studying the properties of highly-charged ions [1], in particular if low-energy dielectronic recombination (DR) resonances are scrutinized. The heavy-ion storage ring CRYRING@ESR at the international FAIR facility in Darmstadt, Germany, is especially attractive for dielectronic recombination studies, since it is equipped...
Interaction of high-intensity lasers with highly charged atomic ions is
widely explored field in theory while there is still a lack in experimental data.
In the past, several experiments have analyzed high-intensity laser
ionization of gases. However, experiments of relativistic laser beams
targeting highly charged ions would allow for addressing only the
weakest bound electron in the...
Precision studies of the weak interaction in atomic systems offer sensitive tests of the Standard Model and open avenues for exploring physics beyond it. Although the landmark atomic parity violation (APV) measurements in cesium represent a key reference in the field [1], further studies are necessary. Currently, two complementary experimental approaches are being pursued: (1) large-scale...
Precise studies of the linear polarization for Compton scattered photons open the unique opportunity for a detailed test of the impulse approximation for energetic photon matter interaction. Compton scattering is the inelastic scattering of a photon off an electron, in which the scattered photon carries a lower energy than the incident photon. For scattering off bound electrons, the resulting...
Compton scattering is one of the fundamental processes in light–matter interaction in which an incoming photon is inelastically scattered off an electron. In the energy range from a few keV to several MeV, Compton scattering makes a significant contribution to the light-atom coupling. It therefore has a wide range of important applications across various fields of modern science, from...
M. Tatsch$^1$, B. M. Döhring$^{1, 2}$, K. Huber$^1$, S. Schippers$^{1,2}$
$^1$I. Physikalisches Institut, Justs-Liebig-Universität Gießen, Germany
$^2$Helmholtz Research Academy Hesse for FAIR (HFHF)
The Giessen ion source test bench is an apparatus designed to facilitate an easy adaption to a variety of different ion sources and to provide straightforward control and operation....
The well-known Auger-Meitner (AM) effect has been used extensively to study electron correlations. In ion-atom collisions, the AM process occurs during hard collisions (small impact parameter). It is known that for ions, the energy of AM e$^{-}$ shifts to the low-energy side, in contrast to X-ray energy, which shifts toward the high-energy side. For ion-atom collisions, understanding this...
S. Schippers$^{1,2}$, C. Brandau$^{1,3}$, S. Fuchs$^{1,2}$, M. Lestinsky$^{3}$, S-X. Wang$^{1,2}$, C. Y. Zhang$^{4}$, N. R. Badnell$^{4}$, A. Borovik Jr$^{1,5}$, M. Fogle$^6$, V. Hannen$^7$, Z. Harman$^{8}$, P-M. Hillenbrand$^{1,3}$, E. B. Menz$^{3,5}$, Y. Zhang$^{8,9}$, Z. Andelkovic$^3$, F. Herfurth$^{3}$, R. Heß$^3$, A. Kalinin$^3$, C. Kozhuharov$^3$, C. Krantz$^3$, S. Litvinov$^3$, B....
During the user run 2025 essentially all operation modes of the ESR were used and highlights will be presented: electron cooling, stochastic cooling, stacking, internal experiments and extracted beam experiments with beam delivery to CryRing and HITRAP. The new LSA control system is consolidated in the sense that it offers practically all operation modes covered by the decommissioned legacy...
We briefly report on the first laser excitation of the ground-state hyperfine transition in lithium-like 208Bi80+. The experiment took place at the ESR during the beam-time block at GSI in May 2025 (GPAC-Experiment: G-22-00038). The detection of the transition became possible by combining the laser excitation with dielectronic recombination as (DR) a new detection scheme.
Therefore, the...
The low-lying isomeric state of the $^{229}$Th nucleus has been intensively discussed as a candidate for nuclear clocks. Different approaches are pursued worldwide, either based on Th-doped crystals or lowly charged Th ions. The HITHOR project follows a different approach by utilizing nuclear hyperfine mixing (NHM) in highly-charged hydrogen-like $^{229}$Th$^{89+}$. GSI offers the unique...
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...
Neutron-induced reaction cross sections of short-lived nuclei are crucial for our understanding of nuclear astrophysics and for various applications in nuclear technology. However, direct measurements of these cross sections are extremely challenging or even impossible, due to the difficulty in producing and handling the required radioactive targets.
We are developing a novel approach that,...
The nuclear two-photon or double gamma (2$\gamma$) decay is a rare
second-order electromagnetic process in which an excited nucleus emits two gamma rays simultaneously [1]. Its branching ratio is significantly lower than that of competing first-order processes such as internal conversion, pair creation, or single-photon emission, making its experimental observation extremely challenging....
Electron cooling is a central beam preparation technique at CRYRING@ESR, and has been employed in all beamtimes since re-commissioning of the storage ring at GSI/FAIR in 2020. With the large variety of ion species available from the UNILAC/SIS18/ESR injector chain and from the local ion source, the electron cooler is required to operate at a wide range of beam parameters. Over the years, beam...
Metallic-magnetic microcalorimeter detectors for X-ray precision spectroscopy provide excellent energy
resolution combined with a broad bandwidth acceptance. This opens up new experimental possibilities, in
particular for bound-state QED studies in highly charged ions. Using a pair of such detector systems, we
recently conducted a landmark experiment, as presented in [P. Pfäfflein et al....
Metallic magnetic calorimeters (MMCs) of the maXs-series, developed within the SPARC collaboration, offer exceptional energy resolving power (up to E/ΔE ≈ 6000 at 60 keV) [1] over a broad spectral range (1–100 keV) with high quantum efficiency and linearity [2], making them ideal for high-precision X-ray spectroscopy in fundamental atomic physics. Their operation, however, requires intricate...
An internal target station featuring a novel design based on previous experiences gained at the ESR has been installed and commissioned in the CRYRING storage ring during 2022. Since then, numerous target experiments utilizing different gases, ranging from hydrogen to xenon, were performed at moderate target densities. However, a considerably higher area density for hydrogen and deuterium was...
DC operation, non-destructive measurement, high sensitivity and direct traceability to the unit ampere are the advantages of CCCs. SQUIDs, superconducting shielding currents and low-temperature flux concentrators made of soft magnetic nanocrystalline alloys allow single cur-rent pulses resolution below 1 nApp and frequency bandwidth from DC of up to 2 MHz De-pending on the application, the DC...
We present recent advancements in the development and simulation studies of a high-resolution asymmetric von Hamos (AvH) spectrometer designed for low-energy X-ray spectroscopy (5–10 keV) at the CRYRING@ESR electron cooler [1]. The spectrometer exploits the unique features of a long linear X-ray source formed by the overlap of cold electron and highly charged ion beams, combined with an...
The interaction of fast ions with molecules of biological interest is a topic of unceasing research interest due to its inherent application to radiation damage of biological tissue [1]. Additionally, such collision systems provide stringent tests for advanced distorted-wave collision theories [2]. Here we report measurements of electron DDCS spectra obtained at zero-degree emission angle with...
On behalf of the SpecTrap collaboration, I will present the physics and status of the SpecTrap experiment located at the HITRAP facility at GSI, Germany. The aim of the experiment is optical and near-optical precision spectroscopy of highly charged ions that are confined and cooled in a dedicated Penning trap. Highly charged ions of interest comprise Bi82+ for further studies in the ARTEMIS...
Quantum logic spectroscopy (QLS) enables optical clocks based on atomic and molecular ions that lack direct laser cooling or state detection transitions [1]. QLS therefore serves as a key technique driving significant advances in optical frequency metrology [2-5]. Heavy hydrogen-like or lithium-like ions offer optical transitions that feature both strong suppression of systematic shifts and...
Atomic physics has long been at the forefront of precision measurement, providing both the tools to define fundamental standards and the sensitivity to probe physics beyond the Standard Model (BSM). Recent advances have allowed us to address open questions in neutrino physics, test the limits of bound-state quantum electrodynamics (QED), and provide benchmark data for astrophysics and plasma...
The advent of quantum sensing x-ray microcalorimeters such as Transition Edge Sensors (TESs) [1] has created exciting new opportunities to push the limits of precision physics in the hard x-ray domain. Thanks to the factor of 50 improvement in energy resolution offered by TESs over high-purity germanium [2, 3], and their high efficiency compared to crystal spectrometers [4], anti-protonic...
Synchotron radiation is widely used to generate intense beams of hard photons [1]. Of particular intrest is the case of electron propagation in a strong magnetic field comparable to the critical Schwinger field, $H_c \approx 4.41 \cdot 10^{13}$ G. In this regime, rapid radiative self-polarization, accompanied by intense emission, is expected to occur on a timescale of femtoseconds. Recently,...
The freezing of a liquid begins with the random formation of a tiny crystalline seed, often consisting of only a few atoms. For over a century, the theory describing this crystal nucleation process has been remarkably difficult to verify experimentally. In our earlier studies with krypton and argon, we observed striking discrepancies between theoretical predictions and measured nucleation...
We present a theoretical study of the Compton scattering of photons by K-shell electrons of a target atom. Special attention is paid to the polarization of the scattered photons for the case when the incident photons are themselves linearly polarized. In order to explore this polarization transfer we employ the S-matrix approach and the density matrix theory. Moreover, the S-matrix results are...
Resonant scattering of laser photons off relativistic ion beams can serve as an effective approach for the generation of high-energy photons, as the relativistic Doppler effect leads to a substantial frequency boost of the scattered photons. This idea is expected to be realized by the Gamma Factory project, supported by CERN’s Physics Beyond Colliders programme. The concept involves the...
In exotic atoms, one or more electrons have been replaced by a heavier exotic particle like a muon or antiproton. These systems are ideal candidates to test strong-field QED since the particle orbits much closer to the nucleus due to its higher mass, thus experiencing stronger fields. Many upcoming experiments will use this fact to improve QED tests in high-$Z$ systems. However, to effectively...
