COLLIDING-BEAM STORAGE RING


Meaning of COLLIDING-BEAM STORAGE RING in English

also called Collider, type of particle accelerator (q.v.) that stores and then accelerates counterrotating beams of subatomic particles before bringing them into head-on collision. Because the net momentum of the oppositely directed beams is zero, all the energy of the beams can go into particle interactions. This is in contrast to interactions between particles in a single beam and a stationary target, in which some of the beam energy is used to conserve momentum by giving kinetic energy to the products of the collision. In a collider, the product can be at rest, with all the energy of the collision converted into the mass of the product. The basic element of most colliders is a synchrotron (accelerator) ring (see also synchrotron). A single ring can accommodate two beams of particles traveling in opposite directions, provided one beam contains particles with the same mass as those in the other but opposite electric charge. This is possible with electrons and their antiparticles, positrons, or with protons and antiprotons. Bunches of each type of particle are fed into the synchrotron ring until a sufficiently large number has accumulated in each beam, and then the two beams are accelerated simultaneously. Once they have reached the desired energy, the beams are brought into collision at predetermined points surrounded by particle detectors. Actual interactions between particles are relatively rare (one of the drawbacks of colliding-beam systems), and the beams can typically circulate, colliding on each circuit, for several hours before the beams are dumped and the machine filled once again. The Large Electron-Positron collider at CERN (European Organization for Nuclear Research), Geneva, is the world's largest collider, achieving collisions between electrons and positrons in a ring 27 km (17 miles) in circumference. The machine generally operates at 45.5 gigaelectron volts (GeV) per beam in order to produce the Z particle, which has a mass of 91 GeV. There were plans to upgrade collision energies to about 90 GeV per beam. The highest-energy proton-antiproton collisions occur at the Fermi National Accelerator Laboratory, Batavia, Ill., U.S., at energies of close to 1,000 GeV per beam. With beams of identical particles or of particles of different mass, a collider must contain two synchrotron rings, interlaced to bring the beams into collision at two or more points. The first colliders, electron-electron machines built in the early 1960s, were of this type, as was the Intersecting Storage Rings, a proton-proton collider that operated at CERN during the 1970s. In 1992 the first electron-proton collider, with two rings, came into operation at DESY (German Electronic Synchrotron), Hamburg, Ger. Christine Sutton

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