Speaker
Description
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 electron coolers and those employing quasi-free electrons of gas-jet targets. Compared to the latter, the absence of a target nucleus enables unambiguous studies of processes, which are otherwise masked by competing reactions with the target nucleus. As compared to an electron cooler, the interaction region of a transverse target is spatially well localized. This facilitates X-ray and electron spectroscopy with relatively large solid angles. Over the last years, a specially tailored electron-target for heavy-ion storage rings was developed and built at the University of Giessen in cooperation with GSI. Its scientific prospects have been outlined in the CRYRING@ESR Physics Book 1.
The project benefits from decades-long experience of single-pass electron-ion-collision experiments [2-4]. The target is equipped with a versatile electron gun that is optimized for an operation in storage rings. The electron gun can be fully retracted from the storage ring to a position behind a gate valve. One of the specific design criteria was a rather large opening for the ion beam in order to accommodate ion injection into the storage ring on different orbits. First electron-ion beam experiments showed that in total only up to 20\% of ions are lost due to the electron target which is a great success.
The electron target creates a ribbon-shaped high-intensity electron beam with energies up to 12.5~keV (lab system).
The multi-electrode assembly offers a decoupling of electron energy and electron density, which is beneficial for the ultra-high vacuum conditions in the ring. It also offers a quasi-constant electron density over large energy ranges. We report on the latest achievements during the commissioning beamtimes of the electron target at the CRYRING@ESR. The evaluation of the performence and operation behaviour is ongoing.
This research was supported by the ErUM-FSP APPA (BMBF grant nos. 05P15RGFAA, 05P19RGFA1, 05P21RGFA1, 05P24RG2),
https://fsp-appa.fair-center.eu.
References
1 Lestinsky M et al. 2016 Eur. Phys. J Spec. Top.
225 797
[2] Ebinger B et al. 2017 Nucl. Instrum. Methods B
408 317
[3] Jin F et al. 2024 Eur. Phys. J. D 78 68
[4] D¨ohring B M et al. 2025 Atoms 13(2) 14
