Physicist Guy Savard checks a "catcher cell" that will be an integral part of the proposed Rare Isotope Accelerator. The helium-filled cell will slow energetic, unstable ions to a near-stop using a combination of radio frequency and static electric fields. The ions can then be extracted in a few thousandths of a second and re-accelerated toward experiment areas at a known, uniform energy.

RIA to explore the nature of nuclei

Innovative particle accelerator technology developed by Argonne scientists and engineers is helping to make an ambitious physics facility called RIA a reality. RIA, for Rare Isotope Accelerator, will enable physicists to explore the nature of nuclei—the clusters of particles that occupy the center of every atom. RIA will produce intense beams of short-lived nuclei 10,000 times more intense than any now available.

Physicists will use these beams to study the origin of the elements and test current physics models. RIA also holds promise for important applications to medicine, industry and other applied physics research.

RIA has been designated the highest-priority new construction project by both the Department of Energy’s Long-Range Plan for Nuclear Physics and the National Research Council’s Committee on Nuclear Physics.

The Argonne-developed accelerator concept has been approved by a DOE advisory committee. Michigan State University, Oak Ridge, Lawrence Berkeley and Thomas Jefferson national laboratories and other institutions are involved with Argonne in the design and prototyping work.

Argonne is well positioned to be the host site for RIA, based on the laboratory’s expertise in advanced accelerator technology, extensive experience operating user facilities and nuclear materials, and well-established program of basic research in nuclear physics. The Argonne Tandem-Linac Accelerator System (ATLAS) accelerator was the world’s first superconducting heavy-ion accelerator for physics research. Much of the existing ATLAS complex can be incorporated into the new, larger facility, reducing RIA’s cost by nearly $100 million.

While nuclear physicists dream about the data they will gather when RIA becomes reality, Argonne scientists, engineers and technicians are working on the specifics of delivering unprecedented beam intensity to their instruments. Research and development of enabling technologies for RIA is one of the laboratory’s highest priorities.

Hybridizing a radio frequency device
RIA’s post accelerator for short-lived radioisotopes will be able to accelerate every atomic species from protons (hydrogen nuclei) to uranium, thanks to superconducting technology developed at Argonne in the 1970s for ATLAS.

To increase the efficiency of ATLAS in its new role as post accelerator, an innovative device is being developed: the hybrid radio-frequency quadrupole (RFQ). The hybrid RFQ combines in a single structure the two essential components: drift tubes and focusing quadrupoles.

The hybrid RFQ can accelerate even the heaviest singly charged ions providing the highest possible intensities of rare isotopes.

Building on work pioneered in the Soviet Union in the 1970s, Argonne’s Peter Ostroumov and Ken Shepard and A. A. Kolomiets of the Institute of Theoretical and Experimental Physics, Moscow, have designed a marriage of two devices: the pure RFQ and a linear accelerator.

In the new design, series of drift tubes alternate with sets of quadrupoles for focusing. RIA’s hybrid RFQ will be about 12 feet long, with three sections of drift tubes alternating with two RFQ sections, all contained within a single structure.

Tests of a half-scale aluminum prototype began in summer 2002. The final, full-scale product will be made of ultrapure copper. Compared to conventional means of acceleration, the hybrid RFQ will produce double the beam energy while using significantly less power. The technology of continuous-wave room-temperature resonators currently in use at the Advanced Photon Source will be valuable in building the full-power version of the hybrid RFQ.

Argonne researchers continue to develop new technologies, or improve existing technologies for RIA.

• Experiments at ATLAS have confirmed that RIA’s beam intensity can be increased eight times by capturing and accelerating ions with more than one charge state—ions of the same mass but differing numbers of electrons. Plans have also been developed to accelerate two charge states directly from the ion source. In combination, this will boost the power of RIA’s driver beam up to 16 times for the heaviest ions.
• A new technology developed at Argonne called a “fast gas catcher“ assures that very short-lived isotopes of any chemical species can be efficiently captured, reaccelerated and delivered as high quality beams to RIA’s research instruments.
• Argonne and Michigan State University are working together to develop a cost-effective plan for RIA construction.
  

For more information, please contact Dave Jacqué.

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