GENEVA, March 8 -- Installation of the Large Hadron Collider (LHC), the world's largest particle physics collider, began with the lowering of a 50-foot, 38.6-pound dipole magnet into its accelerator tunnel yesterday by the European Organization for Nuclear Research, or CERN, at its lab near Geneva. The LHC, to be the world's most powerful accelerator, will be comprised predominantly of superconducting dipole magnets -- 1232 all together -- which are the most complex components of the machine. It measures 27 km in circumference and is scheduled to be commissioned in 2007. The magnets' superconducting coil allows them to convey extremely high currents without any loss of energy, enabling them to produce very high magnetic fields in order to bend the trajectory of the protons that are accelerated at close to the speed of light. The collisions between the protons will reach energies of 14 teraelectronvolts (TeV), 70 times higher than those of the former LEP collider, for which the 27-km tunnel was originally built. To reach the superconducting state, the magnets have to be cooled to a temperature of -271°C, close to absolute zero. If the LHC had been made of conventional magnets, it would have needed to be 120-km long to achieve the same energies, and its electricity consumption would have been phenomenal. These superconducting magnets will be lowered 50 meters below the earth's surface via a specially made shaft of oval cross-section. They will then be conveyed through a transfer tunnel to the LHC tunnel, which lies at a depth varying between 50 and 150 meters. Vehicles travelling at 3 km an hour have been designed to deliver the magnets to their final destination. The narrowness of the tunnel complicates these handling operations, making it impossible, for example, for two loads to pass each other. In addition to the dipole magnets, the LHC will be equipped with hundreds of other, smaller magnets. More than 1800 magnet assemblies will be installed. Once in position, the magnets will be connected to the cryogenic system to form a large string operating in superfluid helium, which will maintain the accelerator at a temperature close to absolute zero. CERN said 616 of the superconducting dipole magnets have been delivered so far; the rest are due to arrive by fall 2006. To produce them, 7000 kilometers of niobium-titanium superconducting cable had to be produced. About 100 companies in Europe are manufacturing the magnet components; three of them, Babcock Noell Nuclear in Germany, Alstom in France, and Ansaldo in Italy, are responsible for their assembly. For more information, visit: www.cern.ch