The biggest electron accelerator for the last years was LEP (Large Electron Positron Collider) at CERN. Its circumference was 27 kilometres and the whole accelerator was situated more than 100 meters below ground.
LEP was a collider where the two particle beams consist of electrons and positrons (anti electrons) respectively. The beams of particles were accelerated in opposite directions in orbits next to each other inside the beam tube. There after the beams were made to collide with each other.
To achieve the high energy was needed, the particles were accelerated turn after turn in the circular accelerator. Special acceleration fields increased the energies of the particles for each turn. Different types of magnets forced the particles to move in well-defined orbits.
Four steps of acceleration increased the energies of the particles with up to 400 MeV per turn, to a top energy of about 100 GeV. Four bunches of electrons and positrons could circulate inside the ring for hours, with a speed very close to the speed of light.
Inside LEP there was 3 368 magnets and 272 superconducting acceleration steps. All these parts needed to be frozen down to a temperature of minus 269 degrees Celsius.