High School Teachers at CERN
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A PARTlCLE ACCELERATOR

Most of us have particle accelerators in our homes - a television picture is produced by accelerated electrons striking a sensitive screen.

In 'real' accelerators, bunches of charged particles pick up energy at regular intervals by being passed through electric fields. During this process they are kept focused by magnetic 'lenses' - focusing magnets. Accelerators may be linear or circular. In the latter, magnetic fields provide an inward force to keep the particles following a circular path. Think of twirling a conker on the end of a string.

The Large Electron-Positron (LEP) collider at CERN has a circumference of 27 km and much of it is 100 m below ground. Beams of electrons and positrons travel the circuit more than 11 000 times a second! There are over 4000 large magnets to steer and focus particle beams, and four highly complex detectors to register the paths of particles produced in collisions.