Argonne at 50

Argonne's ATLAS accelerator probes secrets of the atom

ARGONNE, Ill. (June 26, 1996) — On this date 15 years ago, Argonne National Laboratory formally commissioned a powerful new research tool that enables scientists to probe the structure of the atomic nucleus and explore the interior of an evolving star.

Over the years, the Argonne Tandem Linear Accelerator System (ATLAS) has been one of Argonne's most successful scientific facilities, hosting thousands of scientists from across the nation and around the world.

The ceremony in 1981 centered on the accelerator's revolutionary superconducting "split-ring" resonators. ATLAS was the world's first accelerator to use superconducting components for both beam focusing and acceleration.

The resonators, machined from pure niobium metal, lose all electrical resistance when cooled to a few degrees above absolute zero. Their double-comma shape produces intense, rapidly alternating electric fields. When ions -- atoms stripped of one or more electrons -- were fed into a string of these resonators in the original accelerator, they were boosted to 400 million electron-volts (MeV).

Superconducting resonators make possible a continuous beam, of high value to physicists. Traditional materials produce heat through electrical resistance, requiring the beam to be pulsed so the accelerator components can cool. The superconducting resonators are also less expensive to operate, using just one-tenth the electricity of conventional acceleration methods.

The formal commissioning of the superconducting linear accelerator (the heart of what would be named ATLAS three years later) took place as the resonators were cooled down to 4.6 degrees above absolute zero (450 degrees below zero Fahrenheit) -- their normal operating temperature.

Dozens of people involved in the 10-year project to design and construct the accelerator gathered in an auditorium, awaiting confirmation that the machine's complex cryogenic system could cool the resonators to the extremely low temperatures required. Applause broke out as word came from the machine's control room that the resonators had reached their frigid working temperature.

Argonne's Lowell Bollinger, director of the project, recalled at the event that many physicists said the technology needed to achieve a superconducting heavy-ion accelerator was impossible.

"Unfortunately, none of those people accepted our invitation to attend," Bollinger said.

Growing flexibility

Over the next 15 years, the superconducting heavy-ion accelerator grew in complexity, power and flexibility.

In 1992, ATLAS accelerated uranium for the first time, the result of a major upgrade incorporating new ion-source technology and the addition of 18 newly designed superconducting resonators -- bringing the total to 57. Previously, ATLAS was capable of accelerating ions only as heavy as tin. The upgrade also produced ions at energies as high as 1.5 billion electron-volts (GeV).

ATLAS is now accelerating ions for a broad range of physics experiments 24 hours a day, seven days a week, stopping only for holidays and maintenance. Scientists from Argonne, universities, other national laboratories and scientific institutions around the world take advantage of ATLAS's unique combination of energies and beam quality. Twice as much time on the machine is being requested as is available.

Next step

Plans are now being developed to use ATLAS as the base for an "Advanced Exotic Beam Facility" capable of accelerating beams of unstable, short-lived ions. Accelerating radioactive ions would allow physicists to probe the edges of nuclear stability, giving them fresh insights into nuclear structure and processes.

The new facility will also allow researchers to study some of the processes that occur in the sun and in stars, including supernova explosions. The nuclear alchemy of these events produces all of the elements in the universe, from carbon -- the basis of all life on earth -- to the silicon in computer chips, the iron in our cars and the gold in our jewelry.

The nation's first national laboratory, Argonne National Laboratory conducts basic and applied scientific research across a wide spectrum of disciplines, ranging from high-energy physics to climatology and biotechnology. Since 1990, Argonne has worked with more than 600 companies and numerous federal agencies and other organizations to help advance America's scientific leadership and prepare the nation for the future. Argonne is managed by UChicago Argonne, LLC for the U.S. Department of Energy's Office of Science.

For more information, please contact Dave Jacqué (630/252-5582 or info@anl.gov) at Argonne.