Alternating Gradient Synchrotron

The Alternating Gradient Synchrotron (AGS), shown under construction in 1957 below, was built on the innovative concept of the alternating gradient, or strong-focusing principle, developed by Brookhaven physicists. This breakthrough concept in accelerator design allowed scientists to accelerate protons to energies that would have been otherwise unachievable. The AGS became the world's premiere accelerator when it reached its design energy of 33 billion electron volts (GeV) on July 29, 1960. With the success of the AGS, the Cosmotron gradually lost its value as a research tool and was shut down in December 1966.

Alternating Gradient Synchrotron under construction, c. 1957.

Until 1968, the AGS was the highest energy accelerator in the world, slightly higher than its 28 GeV sister machine, the Proton Synchroton at CERN, the European laboratory for high-energy physics.  While today's newest accelerators can reach energies in the trillion electron volt region, the AGS has earned researchers three Nobel Prizes and today serves as the injector for Brookhaven's Relativistic Heavy Ion Collider; it remains the world's highest intensity high-energy proton accelerator, used to search for new physics; and it is the only U.S. heavy ion accelerator suitable for experiments to determine the biological effects of space radiation.

How the original design worked

In the original configuration of the AGS, protons started on their journey to high energies via a Cockroft-Walton generator (see right), which provided an initial energy of 750,000-electron volts to the protons. They were then injected into a 110-foot long, 50-million electron volt (MeV) linear accelerator (or linac), which in turn injected the protons into the AGS. In 1972, a much more powerful 537-foot, 200-MeV linac began operation, greatly increasing the AGS's efficiency and maximum intensity.

Apart from the injection sequence, the AGS functions as proton accelerator today much in the same way that it did in 1960. In the main accelerating section of the synchrotron, contained in an underground tunnel, particles are accelerated inside of a series of vacuum pipes positioned within 240 bending and focusing magnets . Protons are accelerated by radio-frequency stations spaced around the vacuum chamber. After being accelerated to the proper energy, protons are delivered via beam lines to various targets used to investigate new physics. Two of the most famous early detectors used at the AGS to study the phenomena of the day were the 80-inch and the 7-foot bubble chambers.

Ever-improving performance

At the beginning of its operational history, the AGS's peak intensity (the total number of protons in the beam) stood at 300 billion protons per pulse, a factor of 30 over the original design intensity. By 1986, intensity had been increased more than 1,800 times over the design specifications as the AGS reached a  record intensity of 19 trillion protons per pulse. By 1996, the intensity was increased to 75 trillion protons per pulse, 7,200 times the design specification. 

In 1984,  the AGS began providing  researchers with polarized  protons (protons with spins aligned in the same direction) at the highest energy  ever for polarized protons —  16.5 GeV. Beam energies have increased beyond this level through continued machine upgrades. 

Important Discoveries

Three discoveries made at the AGS -- the muon-neutrino, CP violation and the J particle -- captured the Nobel Prize in physics.  Other important particles found there include the omega-minus (1964) and the charmed lambda (1975).

A detailed history of the important physics discoveries made at the AGS is available as a 1.3 MB PDF file. This document will be of special interest to students of high energy physics as well as researchers interested in the history of this field.

Read about the modern AGS complex

One of ten national laboratories overseen and primarily funded by the Office of Science of the U.S. Department of Energy (DOE), Brookhaven National Laboratory conducts research in the physical, biomedical, and environmental sciences, as well as in energy technologies and national security. Brookhaven Lab also builds and operates major scientific facilities available to university, industry and government researchers. Brookhaven is operated and managed for DOE’s Office of Science by Brookhaven Science Associates, a limited-liability company founded by Stony Brook University, the largest academic user of Laboratory facilities, and Battelle, a nonprofit, applied science and technology organization.

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