Current complex together with the
Super Proton Synchrotron at CERN CERN operates a network of seven accelerators and two decelerators, and some additional small accelerators. Each machine in the chain increases the energy of particle beams before delivering them to experiments or to the next more powerful accelerator. The decelerators naturally decrease the energy of particle beams before delivering them to experiments or further accelerators/decelerators. Before an experiment is able to use the network of accelerators, it must be approved by the various
Scientific Committees of CERN. Currently (as of 2022) active machines are the LHC accelerator and: • The
LINAC 3 linear accelerator generating low energy particles. It provides heavy ions at 4.2 MeV/
Da for injection into the Low Energy Ion Ring (LEIR). • The
Low Energy Ion Ring (LEIR) accelerates the ions from the ion linear accelerator LINAC 3, before transferring them to the
Proton Synchrotron (PS). This
accelerator was commissioned in 2005, after having been reconfigured from the previous
Low Energy Antiproton Ring (LEAR). • The
Linac4 linear accelerator accelerates negative hydrogen ions to an energy of 160 MeV. The ions are then injected to the Proton Synchrotron Booster (PSB) where both electrons are then stripped from each of the hydrogen ions and thus only the nucleus containing one proton remains. The protons are then used in experiments or accelerated further in other CERN accelerators. Linac4 serves as the source of all proton beams for CERN experiments. • The
Proton Synchrotron Booster increases the energy of particles generated by the proton linear accelerator before they are transferred to the other accelerators. • The 28
GeV Proton Synchrotron (PS), built during 1954–1959 and still operating as a feeder to the more powerful
SPS and to many of CERN's experiments. • The
Super Proton Synchrotron (SPS), a circular accelerator with a diameter of 2 kilometres built in a tunnel, which started operation in 1976. It was designed to deliver an energy of 300 GeV and was gradually upgraded to 450 GeV. As well as having its own beamlines for fixed-target experiments (currently
COMPASS and
NA62), it has been operated as a
proton–
antiproton collider (the SpS collider), and for accelerating high energy
electrons and
positrons which were injected into the
Large Electron–Positron Collider (LEP). Since 2008, it has been used to inject protons and
heavy ions into the
Large Hadron Collider (LHC). • The
On-Line Isotope Mass Separator (ISOLDE), which is used to study
unstable nuclei. The radioactive ions are produced by the impact of protons at an energy of 1.0–1.4 GeV from the Proton Synchrotron Booster. It was first commissioned in 1967 and was rebuilt with major upgrades in 1974 and 1992. • The
Antiproton Decelerator (AD), which reduces the velocity of antiprotons to about 10% of the
speed of light for research of
antimatter. The AD machine was reconfigured from the previous
Antiproton Collector (AC) machine. • The
Extra Low Energy Antiproton ring (ELENA), which takes antiprotons from AD and decelerates them into low energies (speeds) for use in antimatter experiments. • The
AWAKE experiment, which is a proof-of-principle
plasma wakefield accelerator. • The
CERN Linear Electron Accelerator for Research (CLEAR) accelerator research and development facility.
Large Hadron Collider Many activities at CERN currently involve operating the
Large Hadron Collider (LHC) and the experiments for it. The LHC represents a large-scale, worldwide scientific cooperation project. detector for LHC The LHC tunnel is located 100 metres underground, in the region between
Geneva International Airport and the nearby
Jura mountains. The majority of its length is on the French side of the border. It uses the 27 km circumference circular tunnel previously occupied by the
Large Electron–Positron Collider (LEP), which was shut down in November 2000. CERN's existing PS/SPS accelerator complexes are used to pre-accelerate protons and lead ions which are then injected into the LHC. Eight experiments (
CMS,
ATLAS,
LHCb,
MoEDAL,
TOTEM,
LHCf,
FASER and
ALICE) are located along the collider; each of them studies particle collisions from a different aspect, and with different technologies. Construction for these experiments required an extraordinary engineering effort. For example, a special
crane was rented from Belgium to lower pieces of the CMS detector into its cavern, since each piece weighed nearly tons. The first of the approximately magnets necessary for construction was lowered down a special shaft at in March 2005. The LHC has begun to generate vast quantities of data, which CERN streams to laboratories around the world for distributed processing, making use of a specialized
grid infrastructure, the
LHC Computing Grid. In April 2005, a trial successfully streamed 600 MB/s to seven different sites across the world. In August 2008, the initial particle beams were injected into the LHC. The first beam was circulated through the entire LHC on 10 September 2008, but the system failed 10 days later because of a faulty magnet connection, and it was stopped for repairs on 19 September 2008. The LHC resumed operation on 20 November 2009 by successfully circulating two beams, each with an energy of 3.5
teraelectronvolts (TeV). The challenge for the engineers was then to line up the two beams so that they smashed into each other. This is like "firing two needles across the Atlantic and getting them to hit each other" according to
Stephen Myers, director for accelerators and technology. On 30 March 2010, the LHC successfully collided two proton beams with 3.5 TeV of energy per proton, resulting in a 7 TeV collision energy. This was enough to start the main research program, including the search for the
Higgs boson. When the 7 TeV experimental period ended, the LHC increased to 8 TeV (4 TeV per proton) starting March 2012, and soon began particle collisions at that energy. In July 2012, CERN scientists announced the discovery of a new sub-atomic particle that was later confirmed to be the
Higgs boson. In March 2013, CERN announced that the measurements performed on the newly found particle allowed it to conclude that it was a Higgs boson. In early 2013, the LHC was deactivated for a two-year maintenance period, to strengthen the electrical connections between magnets inside the accelerator and for other upgrades. On 5 April 2015, after two years of maintenance and consolidation, the LHC restarted for a second run. The first ramp to the record-breaking energy of 6.5 TeV was performed on 10 April 2015. In 2016, the design collision rate was exceeded for the first time. A second two-year period of shutdown begun at the end of 2018.
Accelerators under construction As of October 2019, the construction is on-going to upgrade the LHC's luminosity in a project called
High Luminosity LHC (HL–LHC). This project should see the LHC accelerator upgraded by 2026 to an order of magnitude higher luminosity. As part of the HL–LHC upgrade project, also other CERN accelerators and their subsystems are receiving upgrades. Among other work, the LINAC 2 linear accelerator injector was decommissioned and replaced by a new injector accelerator, the
LINAC4.
Decommissioned accelerators • The original linear accelerator
LINAC 1. Operated 1959–1992. • The
LINAC 2 linear accelerator injector. Accelerated protons to 50
MeV for injection into the Proton Synchrotron Booster (PSB). Operated 1978–2018. • The 600 MeV
Synchro-Cyclotron (SC) which started operation in 1957 and was shut down in 1991. Was made into a public exhibition in 2012–2013. • The
Intersecting Storage Rings (ISR), an early collider built from 1966 to 1971 and operated until 1984. • The
Super Proton–Antiproton Synchrotron (SpS), operated 1981–1991. A modification of Super Proton Synchrotron (SPS) to operate as a proton-antiproton collider. • The
Large Electron–Positron Collider (LEP), which operated 1989–2000 and was the largest machine of its kind, housed in a 27 km-long circular tunnel which now houses the
Large Hadron Collider. • The
LEP Pre-Injector (LPI) accelerator complex, consisting of two accelerators, a linear accelerator called
LEP Injector Linac (LIL; itself consisting of two back-to-back linear accelerators called LIL V and LIL W) and a circular accelerator called
Electron Positron Accumulator (EPA). The purpose of these accelerators was to inject positron and electron beams into the CERN accelerator complex (more precisely, to the Proton Synchrotron), to be delivered to LEP after many stages of acceleration. Operational 1987–2001; after the shutdown of LEP and the completion of experiments that were directly fed by the LPI, the LPI facility was adapted to be used for the
CLIC Test Facility 3 (CTF3). • The
Low Energy Antiproton Ring (LEAR) was commissioned in 1982. LEAR assembled the first pieces of true
antimatter, in 1995, consisting of nine atoms of
antihydrogen. It was closed in 1996, and superseded by the
Antiproton Decelerator. The LEAR apparatus itself was reconfigured into the
Low Energy Ion Ring (LEIR) ion booster. • The
Antiproton Collector (AC), built 1986–1987, operations ended in 1997 and the machine was converted into the
Antiproton Decelerator (AD), which is the successor machine for
Low Energy Antiproton Ring (LEAR). Operated in tandem with
Antiproton Accumulator (AA) and the pair formed the Antiproton Accumulation Complex (AAC), == Sites ==