The Low Energy Ion Ring (LEIR) is a particle accelerator at CERN used to accelerate ions from the LINAC 3 to the Proton Synchrotron (PS) to provide

ion An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conve ...

s for collisions within the Large Hadron Collider (LHC).

History

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 took 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 Xenon is a chemical element with the symbol Xe and atomic number 54. It is a dense, colorless, odorless noble gas found in Earth's atmosphere in trace amounts. Although generally unreactive, it can undergo a few chemical reactions such as the ...

ions, sending them normally to SPS and, exceptionally to the LHC for one day of physics. In 2018, the machine was running again with

lead Lead is a chemical element with the symbol Pb (from the Latin ) and atomic number 82. It is a heavy metal that is denser than most common materials. Lead is soft and malleable, and also has a relatively low melting point. When freshly cu ...

ions and had the objective to reach an LIU performance of more than charges extracted. On 6 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 In physics and chemistry, a nucleon is either a proton or a neutron, considered in its role as a component of an atomic nucleus. The number of nucleons in a nucleus defines the atom's mass number (nucleon number). Until the 1960s, nucleons were ...

to per nucleon before passing them through to the PS for storage. The most important function of LEIR is not acceleration, but

electron cooling Electron cooling is a method to shrink the emittance (size, divergence, and energy spread) of a charged particle beam without removing particles from the beam. Since the number of particles remains unchanged and the space coordinates and their der ...

to reduce the emittance of the ion beam in order to 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.

References

External links

* CERN accelerators Particle accelerators {{accelerator-stub CERN facilities CERN Particle physics facilities