Accelerators

Accelerators

The accelerator is the basic tool of particle physics. It allows us to createthe particle collisions that we want to study in our own laboratories. The highenergy collisions between particles that physicists are interested in do occurnaturally but the events are unpredictable and the number that can be observed(in cosmic rays) is low.
Accelerators work by accelerating charged particles using electric fields. Alinear accelerator accelerates particles in a straight line: the biggest linearmachine, in Stanford, California, is two miles long. Circular machines are morecommon. As well as accelerating the particles using an electric field, circularaccelerators bend their p aths using a magnetic field. In a machine like LEP atCERN, where they have opposite charges, the particles being accelerated travelin opposite directions until they are forced to collide. The drawback is thatthe faster a particle travels, the harder it is to keep it moving in a circlebut, in the largest circles (LEP is the largest in the world with acircumference of 27km) less energy is wasted when accelerating particles to highspeeds.
Detectors are used to examine tracks made by the new particles that are producedwhen accelerated particles collide. In the early days photographic film, sparkchambers and bubble chambers were used. Since the late 1960s electronicdetectors have taken over. There are two basic kinds - tracking detectors whichreveal the trajectories of individual charged particles, and calorimeters whichmeasure energies. A modern electronic detector is built like an onion, withlayers of trackers and calorimeters to give as much information as possibleabout the particles produced in each collis