Low Energy Ion Ring

LEIR was converted from a previous machine, the Low Energy Antiproton Ring (LEAR), a facility to decelerate and store antiprotons{{Cite web|url=http://public.web.cern.ch/public/en/research/Antimatter-en.html|title=The matter-antimatter asymmetry problem}} and to deliver them to experiments; the last LEAR antiproton run took place in 1996. LEIR was first proposed in 1993{{Cite web | url=http://cdsweb.cern.ch/record/279362/files/ | title=A low energy accumulation ring of ions for LHC (a feasibility study) - CERN Document Server}} 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{{Cite web | url=http://cerncourier.com/cws/article/cern/29480 | title=LEIR gets ions on course for the LHC – CERN Courier| date=25 November 2005}}{{Cite book|url=http://accelconf.web.cern.ch/AccelConf/e06/PAPERS/WEOBPA02.PDF|title=LEIR commissioning in Proceedings of EPAC 2006, Edinburgh, Scotland|last=Belochitskii|display-authors=etal|first=P.|publisher=JACoW|year=2006|pages=1876–1878|access-date=14 October 2011|archive-date=8 November 2011|archive-url=https://web.archive.org/web/20111108221849/http://accelconf.web.cern.ch/accelconf/e06/PAPERS/WEOBPA02.PDF|url-status=dead}} 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.[https://web.archive.org/web/20101110013909/http://www.telegraph.co.uk/science/large-hadron-collider/8116226/Large-Hadron-Collider-creates-mini-Big-Bang-with-lead-ions.html The Daily Telegraph]

During 2017, LEIR was running with xenon ions, sending them normally to SPS and, exceptionally to the LHC{{Cite web | url=https://home.cern/about/updates/2017/10/one-day-only-lhc-collides-xenon-beams | title=For one day only LHC collides xenon beams}} for one day of physics. In 2018, the machine was running again with lead ions and had the objective to reach an LIU performance of more than {{val|9|e=10}} charges extracted. On 6 June 2018 that performance was achieved and also a new extraction record of {{val|10.35|e=10}} charges was accomplished.

File:LEIR_img_1001.jpg

LEIR takes long bunches of lead-208 ions from the LINAC 3, and splits them into 4 bunches. Each bunch contains {{val|2.2|e=8}} lead ions, which are accelerated from {{val|4.2|ul=MeV}} per nucleon to {{val|72|u=MeV}} per nucleon{{cite conference |title=The LHC Lead Injector Chain |url=http://accelconf.web.cern.ch/AccelConf/e04/PAPERS/TUPLT011.PDF |conference=Ninth European Particle Accelerator Conference (EPAC'04) |author1=A. Beuret |display-authors=etal |location=Lucerne, Switzerland |conference-url=http://accelconf.web.cern.ch/accelconf/e04/ |date=July 2004}} 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 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.{{Cite journal |first=Michel |last=Chanel |title=LEIR: The Low Energy Ion Ring at CERN |journal=Nuclear Instruments and Methods in Physics Research A |volume=532 |issue=1–2 |pages=137–143 |url=http://chanel.home.cern.ch/chanel/design/leir.pub.final.pdf |url-status=dead |archive-url=https://web.archive.org/web/20120329111348/http://chanel.home.cern.ch/chanel/design/leir.pub.final.pdf |archive-date=2012-03-29 |id=CERN-AB-2003-086 |date=September 2003|bibcode=2004NIMPA.532..137C |doi=10.1016/j.nima.2004.06.040 }}

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