The LEP is a the world’s largest particle accelerator, a system of magnets and powerful electrical coils set around a vacuum ring 26.7km in diameter, and all housed within a tunnel. At various points there are giant experimental detectors and their computer systems, housed in underground chambers on the ring.
Inside the accelerator, beams of electrons and positrons can be spun around with increasing energy until they are travelling almost at the speed of light. They are then smashed head on into each other.
The debris from these tiny but fabulously energetic collisions, both fragments of subatomic particles and new particles created from the play of energies involved, is followed at the detectors. Some 6,500 visiting physicists from world universities can test theories of the nature and origin of the universe in periods when the book the machine.
But although the LEP can hurl its infinitesimal subnuclear particles around to nearly light speed, its experiments have been reaching their limits. Advances in physics demand a more powerful accelerator. But building them can be cripplingly expensive. One project has already proved too much: the Superconducting Supercollider in Texas, a new type of accelerator sitting in a nearly 100km long ring tunnel outside Dallas, had to be cancelled in the early 1990s, despite worldwide funding pledges from universities. Only a few shafts had been driven.
CERN has found another solution. A new machine can be fitted into the existing LEP ring tunnel which was built in the 1980s (T&TI October 1982, January and September 1985 and May 1986). This would save hugely on costs.
The Large Hadron Collider increases the power of the collisions by accelerating not lightweight electrons and positrons but much more massive protons which can be given greater momentum. Advances in supercooling for magnets greatly increase the accelerating cycles.
Collisions on the new machine will reach 14TeV (14×1012). One TeV is the energy of a mosquito in flight. Here it is concentrated into a space 10-12 times smaller.
It still does not come cheap. The old machine has to be stripped out of the tunnels and the new equipment installed. Larger detectors are needed. The further the physicists look into the incredibly small world of quarks, gluons, photons, mesons and so forth, the bigger the machines needed to spot their transient lives. ATLAS (A Toroidal LHC ApparatuS) will be 44m long, 22m in diameter and weigh 7,000t. The Compact Muon Solenoid, CMS though smaller will weigh 15, 000t. One other detector, ALICE (A Large Ion Collider Experiment), will sit in an existing underground space.
Power for CERN is sufficient for a city, and costs SwFr50M each year. The facility uses spare capacity during the summer and switches off in winter when general demand rises. The time is usually used for maintenance, although this winter the machine will be stripped out instead.
