Friday, July 22, 2011

The Bevatron was a particle accelerator located at Lawrence Berkeley National Laboratory, in USA. It started to operated in 1954. The antiproton was discovered there in 1955, resulting in the 1959 Nobel Prize in physics for Emilio Segrè and Owen Chamberlain. It accelerated protons into a fixed target, and was named for its ability to impart energies of billions of eV. The Bevatron was an accelerator in which protons are raised to energies of several billion electron-volts by modulating the frequency of the accelerating voltage.

To create antiprotons (mass ~938 MeV/c2) in collisions with nucleons in a stationary target while conserving both energy and momentum, a proton beam energy of approximately 6.2 GeV is required. When the Bevatron was constructed, there was no known way to confine a particle beam to a narrow aperture, so the beam space was about four square feet in cross section. The combination of beam aperture and energy required a huge, 10,000 ton iron magnet, and a very large vacuum system.

A large motor/generator system was used to ramp up the magnetic field for each cycle of acceleration. At the end of each cycle, after the beam was used or extracted, the large magnetic field energy was returned to spin up the motor, which was then used as a generator to power the next cycle, conserving energy; the entire process required about five seconds. The characteristic rising and falling, wailing, sound of the motor-generator system could be heard in the entire complex when the machine was in operation. In the years following the antiproton discovery, much pioneering work was done here using beams of protons extracted from the accelerator proper, to hit targets and generate secondary beams of elementary particles, not only protons but also neutrons, pions, "strange particles", and many others.