page_title: ATLAS experiment
section_title: Magnet system
hierarchical_section_title: ATLAS experiment / ATLAS detector / Components / Magnet system
context_page_description: ATLAS is the largest, general-purpose particle detector experiment at the Large Hadron Collider, a particle accelerator at CERN in Switzerland. The experiment is designed to take advantage of the unprecedented energy available at the LHC and observe phenomena that involve highly massive particles which were not observable using earlier lower-energy accelerators. ATLAS was one of the two LHC experiments involved in the discovery of the Higgs boson in July 2012. It was also designed to search for evidence of theories of particle physics beyond the Standard Model.
  The experiment is a collaboration involving roughly 3,000 physicists from 183 institutions in 38 countries. The project was led for the first 15 years by Peter Jenni, between 2009 and 2013 was headed by Fabiola Gianotti and from 2013 to 2017 by David Charlton. The ATLAS Collaboration is currently led by Karl Jakobs.
context_section_description: The ATLAS detector uses two large superconducting magnet systems to bend charged particles so that their momenta can be measured.  This bending is due to the Lorentz force, which is proportional to velocity.  Since all particles produced in the LHC's proton collisions are traveling at very close to the speed of light, the force on particles of different momenta is equal.  (In the theory of relativity, momentum is not linear proportional to velocity at such speeds.)  Thus high-momentum particles curve very little, while low-momentum particles curve significantly; the amount of curvature can be quantified and the particle momentum can be determined from this value.
  The inner solenoid produces a two tesla magnetic field surrounding the Inner Detector.  This high magnetic field allows even very energetic particles to curve enough for their momentum to be determined, and its nearly uniform direction and strength allow measurements to be made very precisely.  Particles with momenta below roughly 400 MeV will be curved so strongly that they will loop repeatedly in the field and most likely not be measured; however, this energy is very small compared to the several TeV of energy released in each proton collision.
  The outer toroidal magnetic field is produced by eight very large air-core superconducting barrel loops and two end-caps air toroidal magnets, all situated outside the calorimeters and within the muon system.  This magnetic field extends in an area 26 metres long and 20 metres in diameter, and it stores 1.6 gigajoules of energy.  Its magnetic field is not uniform, because a solenoid magnet of sufficient size would be prohibitively expensive to build. It varies between 2 and 8 Teslameters.
caption: The ends of four of the eight ATLAS toroid magnets, looking down from about 90 metres above, in September 2005
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