Large Hadron Collider. Composite image showing how the proposed Large Hadron Collider (LHC) accelerator might appear in the existing LEP tunnel at CERN, the European particle physics laboratory near Geneva. A computer illustration of the LHC has been combined with a photograph of the LEP in its 27- kilometre ring-shaped tunnel. The LEP (Large Electron-Positron) accelerator is the rectangular structure on the floor. The LHC design shown here (the large cylinder) is based on magnet units built for engineering test purposes; as of mid-1995 the last design and engineering details had not been finalised.