Technicians at work on one of the RF cavities in an acceleration section at LEP, the Large Electron- Positron collider. Located at CERN, the European centre for particle physics near Geneva, LEP accelerates electrons & positrons to an energy of 50 GeV. It is housed in a circular tunnel 100m underground & 27km in circumference. The copper sphere in the photo is one of a line of RF cavities (RF = radio frequency) in which radio waves set up powerful electric fields. These fields give the particles an accelerating "kick" each time they pass through the copper cylinder under the line of cavities. Photo taken April 1989.