Accelerator R&D

Our accelerator R&D program focusses on applying superconductivity RF techniques to ions and on producing and accelerating radioactive beams. We are proposing the national Advanced Exotic Beam Laboratory (AEBL), which will be based largely on novel superconducting accelerator technology originally developed at Argonne and used for ATLAS. Our accelerator physicists are conducting a broad range of R&D to establish the technological basis for AEBL. The ATLAS program continues to optimize its operations and develop new linear accelerator technology to provide beams having higher intensity with excellent quality. We review operational issues continuously and enhance the facility’s capabilities frequently. We are investigating technical and research issues relating to acceleration of beams of short-lived nuclei, as a basis for proposing development of the AEBL based on ATLAS.

Argonne Tandem-Linac Accelerator System - A National User Facility

A DOE-designated national accelerator facility for research in nuclear physics, ATLAS employs beams of low-energy heavy ions. The accelerator provides high-quality beams of all the stable elements up to the heaviest, uranium. It also can provide selected beams of short-lived nuclei. ATLAS is based on a technology developed at Argonne that employs superconducting RF accelerator cavities. An accelerator improvement project now nearing completion will increase the facility’s beam energy by about 25%.

Capitalizing on R&D for beams of rare isotopes, we have begun a significant upgrade to ATLAS called the Californium Rare Ion Breeder Upgrade (CARIBU). CARIBU will make available hundreds of neutron-rich isotope beams after they have been produced through th spontaneous fission of californium, captured in a gas cell, and accelerated with ATLAS.

Our Future - Advanced Exotic Beam Laboratory

Both the 20-year facilities plan of DOE’s Office of Science and the broad nuclear science community place high priority on a new facility to provide unparalleled access to beams of exotic atomic nuclei beyond the stable isotopes that exist on Earth. The facility envisioned combines

• a high-power driver accelerator to produce unstable (rare) isotopes, which do not exist naturally because they have short half-lives typically ranging from milliseconds to days, and
• a second accelerator to deliver high-quality beams for experiments.

Unstable isotopes outnumber stable isotopes by more than ten to one, and the systematic study of such rare isotopes is one of the most exciting frontiers in fundamental physics. A rare isotope facility producing these nuclei in unprecedented quantities and capable of accelerating them as beams at unprecedented intensities would answer many pressing questions, including the following:

• What is the full list of nuclei, both stable and unstable, existing in nature?
• How were the chemical elements produced in the cosmos?
• How do stars burn their nuclear fuel?
• Does the current standard model of particles and interactions pass the tests made possible by the new facility?

In addition, the envisioned facility would produce radioactive isotopes enabling valuable new applications for science, technology, medicine, and national security.

In December 2006 the Rare Isotope Science Assessment Committee (RISAC) of the National Research Council strongly emphasized the importance of this new science. RISAC concluded that this science is “a vital component of the nuclear science portfolio in the United States” and that “failure to pursue a U.S. [facility for rare isotope beams] would likely lead to a forfeiture of U.S. leadership in nuclear-structure-related physics and would curtail the training of future U.S. nuclear scientists.” Examining the prospective science in an international context, RISAC concluded that “the science addressed by a rare-isotope facility, most likely based on a heavyion driver using a linear accelerator, should be a high priority for the United States. The facility for rare-isotope beams envisaged for the United States would provide capabilities unmatched elsewhere that would help to provide answers to the key science topics.”

The world-leading AEBL facility would produce beams of many reaccelerated rare isotopes that are tens of thousands of times more intense than the beams of any other facility envisioned worldwide. The power of the Argonne concept results from (1) coupling of a 400-kW, 200-MeV/u superconducting linac driver accelerator with the gas-stopping concept pioneered at Argonne and (2) use of the existing ATLAS accelerator to reaccelerate the exotic beams. This initiative capitalizes on the strength of Argonne’s nuclear physics program, the worldleading astrophysics program at the University of Chicago, Argonne’s experience with accelerator and target technology, its proven track record in building and operating major national user facilities (notably the APS), its ability to deal with radioactivity and operate nuclear facilities, cost savings from incorporating the existing ATLAS facility into AEBL, Argonne’s experience in satisfying DOE operating requirements, and, last but not least, the potential for a strong partnering role with Fermilab and other national laboratories. DOE has announced its plan to proceed with a facility for producing rare-isotope beams, with project engineering and design commencing in 2011. Resources required to implement this major initiative at Argonne will be sought from DOE’s Office of Nuclear Physics.