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HERA particle collider. Technician climbing through a hatch at the HERA particle collider at DESY (Deutsch Elektronen Synchrotron). HERA (Hadron Electron Ring Accelerator) consists of a pair of accelerator rings mounted in a 6.3km circumference tunnel. The upper (cream-coloured) ring carries protons, whilst the lower (pink) ring carries electrons in the other direction. At four points on the ring the beams cross providing proton/electron collisions at an energy of 850 GeV. 100,000 of these collisions are produced every second. Four detectors (H1, ZEUS, Hermes & Hera-B) ) study these collisions. Photographed near Hamburg, Germany, in May 1999. (KEYSTONE/SCIENCE PHOTO LIBRARY/DAVID PARKER)