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Deceleration of Accelerator-Produced and In-Trap Electron Cooling of Highly Charged Ions

S. Rausch1,2,*, Z. Andelkovic3, S. Fedotova3, W. Geithner3, F. Herfurth3, M. Horst1,2, J. Ködel1, K. Mohr1,2, D. Neidherr3 et al.

W. Nörtershäuser1,2, N. Stallkamp3,4, S. Trotsenko3, G. Vorobjev3, and D. Zisis1,2

  • *Contact author: s.rausch@gsi.de
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Phys. Rev. X 16, 031022 – Published 29 July, 2026

DOI: https://doi.org/10.1103/961c-j3p5

Abstract

The most efficient and most versatile technique for producing highly charged ions (HCI) with high atomic numbers is electron stripping in-flight at high kinetic energies. While this requires relativistic velocities, many experiments call for trapped or at least slowly moving ions. For example, studies of fundamental interactions would significantly improve in precision when performed in an ion trap while studies on slow HCI for material science are not yet feasible due to the lack of availability. The goal of the HITRAP project at the GSI Helmholtzzentrum für Schwerionenforschung GmbH is to decelerate accelerator-produced heavy HCI and prepare them in a Penning trap via electron cooling for subsequent experiments. We present the trapping of accelerator-produced HCI. Fully stripped Ar3618+ were decelerated from the production energy of 45  MeV/u to 6  keV/u followed by trapping in the HITRAP Cooling Trap for the duration of several seconds. The Cooling Trap is a nested Penning trap that allows for the simultaneous storage of HCI ions with a cold electron plasma. It was commissioned with HCI from a local electron beam ion source, which led to the first observation of electron cooling of highly charged ions in a Penning trap, marking a significant advancement in the field. These developments constitute a major step toward a worldwide unique facility with unparalleled capabilities in heavy-ion research and already enable the first experimental studies at HITRAP.

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Studying heavy highly charged ions provides insights into various fields such as fundamental atomic and nuclear physics, material physics, and astrophysics, but achieving the highest precision requires trapping ions that are conventionally produced at high kinetic energies through in-flight electron stripping. We established a technology at the HITRAP facility to bridge this gap by decelerating accelerator-produced ions from their production energy and subsequently confining them in a Penning trap. Inside the trap, we implemented electron cooling by simultaneously storing ions with a cold electron plasma, allowing the ions to transfer their kinetic energy to the electrons via Coulomb interaction. Combining both techniques will provide heavy highly charged ions for subsequent precision experiments without the energy broadening typically associated with their production at high velocity. We expect these advancements to facilitate a wide range of experiments such as the most stringent tests of quantum electrodynamics using heavy ions at rest.

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Phys. Rev. X 16, 031022– Published 29 July, 2026
  • Received 11 July 2025
  • Accepted 13 May 2026
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