Eur. Phys. J. Spec. Top.
https://doi.org/10.1140/epjs/s11734-025-01605-z

Review

Technical design report for the cryogenic stopping cell of the Super-FRS at FAIR

¹ II. Physikalisches Institut, Justus-Liebig-Universität Gießen, Gießen, Germany
² GSI Helmholtzzentrum für Schwerionenforschung GmbH, Darmstadt, Germany
³ University of Valencia, Valencia, Spain
⁴ University of Groningen, Groningen, The Netherlands
⁵ University of Edinburgh, Edinburgh, UK
⁶ Helmholtz Research Academy Hesse for FAIR (HFHF), GSI Helmholtz Center for Heavy Ion Research, Campus Gießen, Gießen, Germany
⁷ Extreme Light Infrastructure-Nuclear Physics, Horia Hulubei National Institute for Physics and Nuclear Engineering, Magurele, Romania
⁸ Department of Aerospace Sciences, Politehnica University of Bucharest, Bucharest, Romania
⁹ Institut für Kern- und Teilchenphysik, Technische Universität Dresden, Dresden, Germany
¹⁰ School of Physics and Astronomy, Tel Aviv University, Tel Aviv, Israel
¹¹ Soreq Nuclear Research Center, Yavne, Israel
¹² University of Jyväskylä, Jyväskylä, Finland
¹³ Doctoral School in Engineering and Applications of Lasers and Accelerators, University Polytechnica of Bucharest, Bucharest, Romania
¹⁴ Institute for Analytical Instrumentation, Russian Academy of Sciences, St. Petersburg, Russia
¹⁵ PARTREC & Department of Radiation Oncology, University Medical Center Groningen, Groningen, The Netherlands
¹⁶ Department of Physics, Indian Institute of Technology (Indian School of Mines) Dhanbad, Jharkhand, India

^a W.Plass@gsi.de

Received: 31 December 2024
Accepted: 31 March 2025
Published online: 8 May 2025

Abstract

Precision experiments with thermalized exotic nuclei will be possible at the super-conducting fragment separator Super-FRS at the Facility for Antiproton and Ion Research (FAIR). In the Early Science/First Science programs of FAIR, they will be performed at the focal plane FHF1 of the Super-FRS (in front of the High-Energy Branch) and, at a later stage during First Science++, also at the Low-Energy Branch. Exotic nuclei will be produced in flight and separated in the Super-FRS and their momentum spread will be reduced by energy-bunching. The ions will be further slowed down in a homogeneous degrader, thermalized in a gas-filled stopping cell, and extracted and transferred to the experimental setups. The stopping cell is, thus, a key device for experiments with thermalized exotic nuclei, and its performance characteristics will have a strong impact on the range of nuclides available and their yields, since its stopping and extraction efficiencies and extraction times strongly influence the rate of the extracted nuclei and put a limit on their lifetimes.

In combination with a multiple-reflection time-of-flight mass spectrometer, the stopping cell will enable the measurement of masses, branching ratios, e.g., $\beta$-delayed (multi-)neutron emission probabilities, and lifetimes, as well as the in-cell production of exotic nuclei by multi-nucleon transfer with primary and secondary beams. Moreover, it will be a tool for the absolute calibration of the particle identification in the Super-FRS. Furthermore, using the combination of accurate mass determination with the PID of the Super-FRS on an event-by-event basis, completely new experimental possibilities will become available, such as the identification of millisecond isomers at the Super-FRS and the measurement of the dependence of the isomer-to-ground-state ratios on the production mechanism. These studies will be pursued in the context of the Super-FRS Experiment Collaboration.

At the Low-Energy Branch, high-accuracy mass measurements, in-trap conversion electron and alpha spectroscopy, and trap-assisted spectroscopy will be performed with MATS (Precision Measurements of very short-lived nuclei using an Advanced Trapping System for highly charged ions). Measurements of nuclear spins, magnetic dipole and electric quadrupole moments, and root-mean-square charge radii will be carried out using collinear laser spectroscopy on ions and atoms and beta-NMR experiments with LaSpec (Laser Spectroscopy of short-lived nuclei). These experiments will address a wide scientific field ranging from nuclear structure and nuclear astrophysics to tests of the weak interaction and of the Standard Model.

For the Super-FRS, a stopping cell with an areal density of $20{\text{mg/cm}}^2$ is required, with a cross-section of the stopping volume of $200{\text{cm}}^2$, a high extraction efficiency that is element-independent, an extraction time on the order of 10 ms, and a rate capability of ${10}^7$ ions/s up to a nuclear charge of Z=92. Furthermore, the stopping cell needs to deliver bunches of ions with high purity. No existing stopping cell is capable of reaching these performance characteristics simultaneously. To fulfill these requirements, a novel concept for gas-filled stopping cells has been developed. It is based on the cryogenic stopping cell of the FRS Ion Catcher, and, in addition, it implements the two-stage extraction of the thermalized ions in a direction orthogonal to the incoming ion beam (high-areal-density orthogonal-extraction cryogenic stopping cell, HADO-CSC). This will boost all performance characteristics of the stopping cell and thus remove the performance bottleneck of present stopping cells for the thermalization of exotic nuclei produced at relativistic energies.