Cyclotrons are a type of particle accelerator in which charged particles, such as protons, are accelerated using a high frequency alternating voltage. The particles move in a spiral so that they meet the same accelerating voltage numerous times. The largest is the 18 m diameter machine at TRIUMF, the Canadian lab for particle and nuclear physics. The protons inside this cyclotron travel 45 km as they spiral outwards, gradually reaching their maximum energy of 520 mega electron volts. The TRIUMF cyclotron has been in operation since 1974.
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