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LARGE HADRON COLLIDER (LHC)

LARGE HADRON COLLIDER (LHC)

  • The Large Hadron Collider (LHC) is the world’s largest and highest-energy particle accelerator. It was built by the European Organization for Nuclear Research (CERN) over a ten year period from 1998 to 2008, with the aim of allowing physicists to test the predictions of different theories of particle physics and high-energy physics, and particularly for the existence of the hypothesized Higgs boson and of the large family of new particles predicted by supersymmetry. It contains six detectors each designed for specific kinds of exploration.
  • The LHC lies in a tunnel 27 kilometres (17 mi) in circumference, as deep as 175 metres (574 ft) beneath the Franco-Swiss border near Geneva, Switzerland. Its synchrotron is designed to collide opposing particle beams of either protons at up to 7 teraelectronvolts per nucleon, or lead nuclei at an energy of 574 TeV per nucleus.
  • On 10 September 2008, the proton beams were successfully circulated in the main ring of the LHC for the first time, but 9 days later operations were halted due to a magnet quench incident resulting from an electrical fault.
  • The following helium gas explosion damaged over 50 superconducting magnets and their mountings, and contaminated the vacuum pipe.
  • On 20 November 2009 low energy beams were successfully circulated again, with the first recorded proton—proton collisions occurring 3 days later. Thus, on 30 November, the LHC achieved 1.18 TeV per beam to become the world’s highest-energy particle accelerator.
  • On 30 March 2010, the first collisions took place between two 3.5 TeV beams, setting the current world record for the highest-energy man-made particle collisions, and the LHC began its planned research program.
  • The LHC will continue to operate at 3.5 TeV per beam, half of its planned capability, until the end of 2012. It will then be shut down for a year for upgrades to allow full energy operation (7 TeV per beam), with reopening planned for early 2015.

PURPOSE OF LHC

Physicists hope that the LARGE HADRON COLLIDER (LHC) will help answer some of the fundamental open questions in physics, concerning the basic laws governing the interactions and forces among the elementary objects, the deep structure of space and time, and in particular the intersection of quantum mechanics and general relativity, where current theories and knowledge are unclear or break down altogether.

DESIGN

  • The LHC is the world’s largest and highest-energy particle accelerator. The collider is contained in a circular tunnel, with a circumference of 27 kilometres (17 mi), at a depth ranging from 50 to 175 metres (160 to 574 ft) underground.
  • The 3.8-metre (12 ft) wide concrete-lined tunnel, constructed between 1983 and 1988, was formerly used to house the Large Electron—Positron Collider.
  • The collider tunnel contains two adjacent parallel beamlines (or beam pipes) that intersect at four points, each containing a proton beam, which travel in opposite directions around the ring.
  • Some 1,232 dipole magnets keep the beams on their circular oath, while an additional 392 quadrupole magnets are used to keep the beams focused, n order to maximize the chances of interaction between the particles in the four Intersection points, where the two beams will cross.
  • Approximately 96 tonnes of liquid helium is needed to keep the magnets, made of copper-clad niobium-titanium, at their operating temperature of 1.9 K (-271.25 °C), making the LHC the largest cryogenic facility in the world at liquid helium temperature.
  • Prior to being injected into the main accelerator, the particles are prepared by a series of systems that successively increase their energy. The first system is the linear particle accelerator LINAC 2 generating 50-MeV protons, which feeds the Proton Synchrotron Booster (PSB).
  • There the protons are accelerated to 1.4 GeV and injected into the Proton Synchrotron (PS), where they are accelerated to 26 GeV. Finally the Super Proton Synchrotron (SPS) is used to further increase their energy to 450 GeV before they are at last injected (over a period of 20 minutes) into the main ring.
  • Here the proton bunches are accumulated, accelerated (over a period of 20 minutes) to their peak 7-TeV energy, and finally circulated for 10 to 24 hours while collisions occur at the four intersection points. The LHC physics program is mainly based on proton-proton collisions.

DETECTORS | LARGE HADRON COLLIDER (LHC)

  • Six detectors have been constructed at the LHC, located underground in large caverns excavated at the LHC’s intersection points.
  • Two of them, the ATLAS experiment and the Compact Muon Solenoid (CMS), are large, general purpose particle detectors.
  • A Large Ion Collider Experiment (ALICE) and LHCb, have more specific roles and the last two, TOTEM and LHCf, are very much smaller and are for very specialized research.

OPERATIONAL CHALLENGES

  • The size of the LHC constitutes an exceptional engineering challenge with unique operational issues on account of the amount of energy stored in the magnets and the beams.
  • While operating, the total energy stored in the magnets is 10 GJ, and the total energy carried by the two beams reaches 724 MJ.
  • Loss of only one ten-millionth part (10-7) of the beam is sufficient to quench a superconducting magnet, while the beam dump must absorb 362 MJ (87 kilograms of TNT) for each of the two beams.
  • These energies are carried by very little matter: under nominal operating conditions (2,808 bunches per beam, 1.15×1011 protons per bunch), the beam pipes contain 1.0×10-9 gram of hydrogen, which, in standard conditions for temperature and pressure, would fill the volume of one grain of fine sand.

 

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