Low Energy Ion Ring

Low Energy Ion Ring. The Low Energy Ion Ring was a specialized synchrotron storage ring constructed at the European Organization for Nuclear Research (CERN) laboratory. Its primary function was to decelerate and cool beams of lead ions produced by the CERN Heavy Ion Programme for experiments in atomic physics and nuclear physics. Operating from 1994 until its decommissioning in 2002, it played a crucial role in preparing low-energy, high-quality ion beams for the internal-target experiment at the CERN Intersecting Storage Rings facility.

Overview

The ring was conceived as a key component of the CERN Heavy Ion Programme, designed to interface between the primary ion source complex and the experimental areas. It accepted pulsed beams of partially stripped lead ions from the CERN Linear Accelerator 3 and employed sophisticated techniques to reduce their energy and phase-space volume. This process was essential for experiments requiring precise collisions at very low energies, such as those studying electron-ion recombination processes and the properties of highly charged ions. Its operation supported a dedicated research program that complemented the high-energy collision studies conducted at the Super Proton Synchrotron and later the Large Hadron Collider.

Design and Operation

The machine was a racetrack-shaped synchrotron with a circumference of approximately 78 meters, utilizing a magnetic lattice of dipole magnets and quadrupole magnets for beam steering and focusing. Its core operational principle involved capturing a batch of ions from CERN Linear Accelerator 3, then using radio frequency systems to decelerate them from an injection energy of 4.2 MeV per nucleon down to a variable final energy as low as 4.3 MeV total for fully stripped lead. To counteract beam heating and emittance growth during this process, the ring implemented an electron cooling system, where the ion beam was merged with a cold electron beam to reduce its momentum spread. This combination of deceleration and cooling produced beams of exceptional quality for precision measurements.

Scientific Applications

The primary user facility was the internal gas-jet target installed in one of its straight sections, which facilitated collisions between the cooled ion beam and atoms of hydrogen, helium, or other gases. This setup enabled groundbreaking studies in atomic physics, particularly the measurement of electron-ion recombination rates for very heavy, highly charged ions—processes critical for understanding astrophysical plasmas and the dynamics of stellar evolution. Further experiments investigated nuclear physics phenomena at low energies, such as the behavior of exotic nuclei and fundamental interactions in quantum electrodynamics. The data collected provided stringent tests for theoretical models from institutions like the Max Planck Institute for Nuclear Physics and the University of Giessen.

Technical Specifications

The accelerator achieved a maximum magnetic rigidity of 3.2 Tesla-meters and could store ions with a charge-to-mass ratio (q/A) up to 0.5. Its electron cooling system operated with a 10-20 keV electron beam, achieving cooling times on the order of seconds and dramatically reducing beam momentum spread. The ring's vacuum system maintained an ultra-high pressure below 10⁻¹¹ mbar to minimize beam loss from interactions with residual gas. It could deliver decelerated beams to its internal target with intensities exceeding 10⁸ ions per pulse, enabling statistically significant measurements of low-probability collision processes.

History and Development

The project was approved in 1991, with construction taking place from 1993 to 1994 in the former CERN Intersecting Storage Rings experimental hall. It was largely built using recycled components, including magnets and vacuum chambers, from its predecessor, the Low Energy Antiproton Ring, which had concluded its research program for the CP violation experiments. The first beam was successfully decelerated and cooled in late 1994. Throughout its operational lifetime, it served a dedicated international collaboration, with key contributions from researchers at CERN, the University of Aarhus, and the GSI Helmholtz Centre for Heavy Ion Research. The ring was decommissioned in 2002 to make space for the installation of the Extra Low ENergy Antiproton ring, a new decelerator for antimatter experiments. Its legacy persists in the data it produced and the accelerator techniques it refined for low-energy ion beam physics.

Category:Particle accelerators Category:CERN Category:Nuclear physics