The Large Hadron Collider at CERN is a ring-shaped tunnel under the French and Swiss border. How long is one lap of the ring, in metres?
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Answer
About 27,000 metres
Protons in the ring travel so close to the speed of light that they complete more than 11,000 laps every second.
How to estimate it
Physics sets the size. A proton's bending radius in metres equals its energy in GeV divided by 0.3 times the magnetic field in tesla. The LHC was designed for 7,000 GeV with 8.3 tesla magnets: 7,000 / (0.3 × 8.3) = 2,800 m. That circle measures 2 × 3.14 × 2,800 = 17,700 m, and bending magnets fill only two thirds of the ring: 17,700 × 1.5 = 26,500 m. The real lap is about 27,000 metres.
Source: CERN
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