The Low Energy Ion Ring (LEIR) is a particle accelerator at CERN used to accelerate lead ions from the LINAC 3 to the Proton Synchrotron (PS) to provide lead ions for collisions within the Large Hadron Collider (LHC).
LEIR was converted from a previous machine the Low Energy Antiproton Ring (LEAR); 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 in to 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.
LEIR takes long bunches of lead ions from the LINAC 3, and splits them into 4 bunches. Each bunch contains 2.2x108 lead ions which is accelerated from 4.2 MeV to 72 MeV before passing them through to the PS for storage. Each group of two bunches takes about 2.5 seconds to accelerate, with the LHC using 592 bunches of ions, it takes around 10 minutes for a complete fill of the LHC for operations.