Particle accelerators and the Large Hadron Collider

Current complex

CERN operates a network of six accelerators and a decelerator. Each machine in the chain increases the energy of particle beams before delivering them to experiments or to the next more powerful accelerator. Currently active machines are:

• Two linear accelerators generate low energy particles for injection into the Proton Synchrotron. The 50 MeV Linac2 is for protons, and the 4.2 MeV/u Linac3 is for heavy ions.
• The Proton Synchrotron Booster increases the energy of particles generated by the proton linear accelerator before they are transferred to the other accelerators.
• The Low Energy Ion Ring (LEIR) accelerates the ions from the ion linear accelerator, before transferring them to the Proton Synchrotron (PS). This accelerator was commissioned in 2005, after having been reconfigured from the previous Low Energy Anti-proton Ring (LEAR).
• The 28 GeV Proton Synchrotron (PS), built in 1959 and still operating as a feeder to the more powerful SPS.
• 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, it has been operated as a proton-antiproton collider, and for accelerating high energy electrons and positrons which were injected into the Large Electron-Positron Collider (LEP). From 2008 onwards, it will 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. Particles are initially accelerated in the PS Booster before entering ISOLDE. 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% the speed of light for research into antimatter.

The Large Hadron Collider

Most of the activities at CERN are currently directed towards building a new collider, the Large Hadron Collider (LHC) and the experiments for it. The LHC represents a large-scale, worldwide scientific cooperation project.

The LHC tunnel is located 100 metres underground, in the region between the Geneva airport and the nearby Jura mountains. It uses the 27 km circumference circular tunnel previously occupied by LEP which was closed down in November 2000. CERN's existing PS/SPS accelerator complexes will be used to pre-accelerate protons which will then be injected into the LHC.

Six experiments (CMS, ATLAS, LHCb, TOTEM, LHC-forward and ALICE) are currently being built, and will be running on the collider; each of them will study particle collisions under a different point of view, and with different technologies. Construction for these experiments required an extraordinary engineering effort. Just as an example, to lower the pieces for the CMS experiment into the underground cavern which will host it, a special crane will have to be rented from Belgium, which will be able to lift the almost 2000 tons for each piece. The first of the approximately 5,000 magnets necessary for construction was lowered down a special shaft at 13:00 GMT on 7 March 2005.

This accelerator will generate vast quantities of computer data, which CERN will stream to laboratories around the world for distributed processing (making use of a specialised GRID infrastructure, the LHC Computing Grid). In April 2005, a trial successfully streamed 600 MB per second to seven different sites across the world. If all the data generated by the LHC is to be analysed, then scientists must achieve 1,800 MB per second before 2008.

As of August 2008 the majority of the LHC ring is now cooled to the 1.9 K (−271.25 °C) operating temperature. The initial particle beams are due for injection in August 2008, the first attempt to circulate a beam through the entire LHC is scheduled for September 10, 2008, and the first high-energy collisions are planned to take place after the LHC is officially unveiled, on October 21, 2008.

Decommissioned accelerators

• The original linear accelerator (Linac1).
• The 600 MeV Synchro-Cyclotron (SC) which started operation in 1957 and was shut down in 1991.
• The Intersecting Storage Rings (ISR), an early collider built from 1966 to 1971 and operated until 1984.
• The Large Electron-Positron Collider (LEP), which operated from 1989 to 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 Low Energy Antiproton Ring (LEAR), commissioned in 1982, which 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.

This guide is licensed under the GNU Free Documentation License. It uses material from the Wikipedia.