Low Energy Ion Ring


The Low Energy Ion Ring is a particle accelerator at CERN used to accelerate ions from the LINAC 3 to the Proton Synchrotron to provide ions for collisions within the Large Hadron Collider.

History

LEIR was converted from a previous machine the Low Energy Antiproton Ring ; a facility to decelerate and store antiprotons and to deliver them to experiments; the last LEAR antiproton run has taken place in 1996. LEIR was first proposed in 1993 but it wasn't until 2003 that work to transform the old experiment into the new accelerator was started. The upgrade took just over two years being commissioned in October 2005 and tested for 4 months. In Autumn 2006 it was used to re-commission the PS to handle ions and then again a year later it was used to re-commission the SPS. However, it wasn't until November 2010, five years later, that it successfully carried out its primary role to provide the lead ions to the LHC for its first ion collisions..
During 2017, LEIR was running with xenon ions sending them normally to SPS and, exceptionally, they were sent to LHC for one day of physics. In 2018, the machine is running again with lead ions and had the objective to reach an LIU performance of more than charges extracted. The 6th of June 2018 that performance was achieved and also a new extraction record of charges was accomplished.

Operation

LEIR takes long bunches of lead-208 ions from the LINAC 3, and splits them into 4 bunches. Each bunch contains lead ions which are accelerated from per nucleon to per nucleon before passing them through to the PS for storage.
The most important function of LEIR is not acceleration, but electron cooling to reduce the emittance of the ion beam in order maintain high luminosity of the final LHC beam. Each group of two bunches takes about 2.5 seconds to accelerate and cool, so with the LHC using 592 bunches of ions, it takes around 10 minutes for a complete fill of the LHC for operations.