View of one of the acceleration sections 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 particles travel in opposite directions around the ring & collide at 4 points where detectors observe their interactions. The copper spheres in the photo are 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."