Newswise — Henry Wadsworth Longfellow wrote, ​“It is difficult to know at what moment love begins; it is less difficult to know that it has begun.” If the celebrated poet were alive today, he might admit that, when it comes to vague beginnings, love is not alone.

Ask two people when the week begins, and you may get different answers. Ask scientists at the U.S. Department of Energy’s (DOE) Argonne National Laboratory when one of its user facilities got off the ground, and you’ll hear a similar story.

Officially, the Argonne Tandem Linac Accelerator System (ATLAS) was commissioned in 1985, and 2025 marked 40 years of operation. Yet working in this DOE Office of Science user facility — built to reveal the structure and properties of atomic nuclei — are staff whose work predates that milestone by years.

“I came on in 1978,” said Gary Zinkann, an ATLAS principal engineer. ​“That was 47 years ago.”

Zinkann’s long tenure illustrates how ATLAS grew from theories, ideas and technological breakthroughs that enabled its planning, construction and commissioning. It also reflects a culture of continuous improvement — expanding capabilities and generating a steady stream of scientific insights.

“ATLAS stands as a testament to decades of scientific ingenuity and dedication,” said Guy Savard, ATLAS scientific director and Argonne Distinguished Fellow. ​“Its history is one of impactful discovery and continuous renewal. At ATLAS, we are always working to improve, innovate and expand our capabilities.”

A vision takes shape

ATLAS’ origins reach back to the early 1970s, when Argonne physicists set out to push the boundaries of nuclear physics research. The community was tackling fundamental questions about the forces inside atomic nuclei — the building blocks of matter. Argonne scientists envisioned a facility that would use superconducting technology to accelerate heavy‑ion beams and provide an unprecedented tool for nuclear physics studies.

At the time, the idea of a superconducting linear accelerator (linac) for nuclear physics was new. Superconducting materials lose electrical resistance at extremely low temperatures, enabling a high accelerating field at a comparatively low input power. Applying this technology to accelerators was largely uncharted territory.

Researchers, including Lowell Bollinger at Argonne and Caltech physicist Ken Shepard, who later came to Argonne, began collaborating to explore the feasibility of this approach. Their work led to the development of niobium split‑ring resonators, first successfully tested at Argonne in 1977.

“Developing the niobium split‑ring resonator is arguably the major technological breakthrough that made ATLAS possible,” said Benjamin Kay, a group leader at ATLAS. ​“They would ultimately become the technological backbone for the entire facility.”

These resonators, cooled with liquid helium, demonstrated the potential to accelerate heavy ions with unprecedented efficiency. Building on this breakthrough, Argonne scientists constructed a prototype superconducting ​“booster” linac, consisting of 24 resonators. The booster accelerated an ion beam delivered by Argonne’s existing tandem Van de Graaff accelerator, in use since the 1960s, and its negative‑ion source.

“The booster linac was the first part of what later became ATLAS,” said Zinkann, who retired in 2016.

Beginning operation in 1978, the booster served as a testbed for the split-ring resonator technology, allowing scientists to refine designs and address technical challenges.

“It was a very active time: designing, testing, troubleshooting,” said Zinkann. ​“And in the middle of all that, researchers were doing experiments too!”

By the early 1980s, the booster linac had logged more than 10,000 hours of beam time, much of it for experiments conducted by users visiting Argonne from other institutions. These early successes demonstrated the feasibility and promise of superconducting linacs for nuclear physics research and gave Argonne the confidence to build a full‑scale facility.

With funding from the U.S. Congress, construction of ATLAS began in the early 1980s. ATLAS would combine the booster with a second linac — also using split‑ring resonators — and new ​“target areas” equipped with detectors to collect detailed experimental data on the accelerated ion beams.

In 1983, Bollinger, then director of ATLAS, wrote to the Argonne community: ​“Scientists from all over the world will use it to expand the boundaries of research into the forces that hold together atomic nuclei.”

That aspiration helped establish ATLAS as a global hub for nuclear physics research.

The final stages of ATLAS’ construction included fabrication and installation of the superconducting resonators for the new linac (dubbed the ​“ATLAS linac” to distinguish it from the older booster linac), expansion of the liquid helium refrigerator and cryogenic plumbing system, and expansion of the computer control system to manage the new linac and beamlines. The team completed the project on time and within budget.

Building a foundation

The ATLAS facility quickly became a global center for nuclear physics research, hosting a growing community of scientists and delivering high‑quality beams for studies of nuclear structure, astrophysics and fundamental interactions. By the late 1980s, ATLAS was serving hundreds of researchers each year, providing beams of stable isotopes for experiments probing the quantum structure of nuclei and the processes that forge elements in stars.

But even in the facility’s early years, ATLAS leadership was looking ahead.

“Almost immediately after the commissioning, ATLAS leaders announced plans to replace its negative-ion source with a positive-ion source,” said Kay.

Initially, ATLAS used a negative‑ion sputter source to generate ion beams, which were accelerated and stripped to positive ions in the tandem Van de Graaff accelerator for subsequent acceleration in the linacs. Installing a positive-ion source would eliminate a need for the Van de Graaff, improving performance and allowing the facility to access the heaviest elements.

As with the booster in the 1970s, Argonne scientists and engineers collaborated to design and build what they needed. Those efforts led to the development of a new generation of ​“quarter‑wave” resonators to support the positive‑ion source.

“There’s no catalog for ordering positive‑ion sources for superconducting linear accelerators,” said Zinkann.

The Positive Ion Injector (PII) was completed and brought online in 1992. Though only seven years after ATLAS’ 1985 commissioning, PII expanded ATLAS’ capabilities by enabling beams of some of the heaviest elements, including uranium, and increased available beam currents for lighter ions. The 1960s‑era tandem Van de Graaff accelerator still served as an injector until its retirement in 2014. Its former space at ATLAS now houses stopped-beam experimental stations.

New additions

Expanding ATLAS’ capabilities widened its scientific impact. Early instruments enabled studies of nuclear reactions inside stars, shedding light on the processes that created most elements and the role of nuclear reactions in stellar evolution. Other ATLAS‑enabled efforts probed the heaviest elements and the limits of nuclear stability.

“No two days were alike,” said Zinkann. ​“A lot of times, our work was about seeing a need, finding a way to fulfill it, and then we’d see the next need and get started on that. Over time, that can make a big difference.”

Advanced instruments for nuclear structure and reaction studies were developed and deployed, including:

• Fragment Mass Analyzer, brought online in 1992 for high‑precision measurements of nuclear masses and decay processes.
• ATLAS Positron Experiment (APEX), commissioned in 1993 to study electrons and positrons emitted during heavy‑ion collisions.
• Canadian Penning Trap, which began operations in 2000 for high‑precision mass measurements of exotic nuclei.

“Like all of our instruments at ATLAS, these were wise investments that continue to pay scientific dividends today for researchers, the public and the world at large,” said Walter Wittmer, ATLAS operations director.

In 1997, the ATLAS team installed and commissioned Gammasphere, one of the world’s most powerful gamma‑ray spectrometers for nuclear structure research. Gammasphere collects data on gamma‑ray emissions following heavy‑ion fusion reactions, enabling high‑precision studies of nuclear shapes, decay processes and the forces that bind protons and neutrons. Its arrival allowed scientists to explore the quantum structure of nuclei and phenomena such as nuclear superfluidity and shape coexistence.

In cooperation with DOE and other partners, ATLAS was a finalist in the 1990s to host a new facility dedicated to rare‑isotope beams. Although DOE ultimately selected Michigan State University for that facility, ATLAS expanded in complementary directions and continues to grow its role in rare‑isotope science.

Expanding capabilities

In 2009, ATLAS commissioned the Californium Rare Ion Breeder Upgrade (CARIBU) system. Led by Savard and Richard Pardo, then ATLAS’ operations manager, CARIBU enabled production of neutron‑rich isotopes for experiments by harnessing the fission of californium‑252 to generate rare isotopes for acceleration.

“Adding CARIBU to ATLAS enabled the production of neutron‑rich isotopes that were previously inaccessible, opening new avenues for nuclear physics research,” said Savard. ​“CARIBU was particularly valuable for studying nuclear reactions that occur during supernova explosions and neutron star mergers.”

CARIBU allowed researchers to examine nuclear reactions involved in the rapid neutron‑capture process (r‑process) — a key mechanism that creates heavy elements such as gold, platinum and uranium during supernovae and neutron star mergers.

ATLAS continued to add detectors and systems for a broader range of experiments, including:

These projects also gave ATLAS engineers opportunities to innovate. HELIOS, for example, incorporates a solenoid magnet from a hospital’s decommissioned MRI scanner.

“Never underestimate what a top‑rate engineering team can do,” said Kay.

Another major addition was the Gamma‑Ray Energy Tracking In‑beam Nuclear Array (GRETINA), a precision gamma‑ray detector for high‑resolution studies of nuclear structure. Built by the U.S. nuclear physics community, GRETINA arrived at Argonne in 2013 for the first of what would ultimately be four experimental campaigns, the last of which ended in 2025. In between campaigns at ATLAS, it was installed at other accelerator facilities. GRETINA collected detailed data on gamma rays emitted during nuclear reactions, providing insights into nuclear forces and structure. Argonne scientists were instrumental in developing GRETA (Gamma‑Ray Energy Tracking Array), a next‑generation detector that will eventually replace GRETINA at ATLAS. GRETA will provide 3D tracking of gamma‑ray paths and energies for even more precise studies.

“Throughout its recent history, ATLAS has remained at the forefront of nuclear physics research, enabling studies of rare isotopes, nuclear reactions and fundamental symmetries,” said Wittmer. ​“The facility’s research programs continue to address key questions in nuclear astrophysics, nuclear structure and the properties of exotic nuclei.”

ATLAS further expanded its capabilities in 2023 with the installation of the ATLAS Material Irradiation Station (AMIS), which is used to emulate material damage in nuclear reactors. AMIS uses some of the accelerator’s lowest energies to deliver heavy ions that quickly degrade the material properties — without the radioactivity associated with irradiation in a reactor — making the development of new reactor materials safer and more efficient.

Today, ATLAS hosts researchers from across the U.S. and around the world, providing more than 6,000 hours of beam time annually.

“ATLAS has maintained strong engagement with its user community, hosting workshops, meetings and collaborative research projects to ensure that its capabilities align with the needs of scientists worldwide,” said Savard. ​“We move in the directions that will allow our users to deepen the scientific questions they can answer using ATLAS.”

Innovating for the future

Forty years after commissioning, ATLAS continues its tradition of continuous improvement to stay at the forefront of rare‑isotope research.

The team is installing and commissioning nuCARIBU, an upgraded version of the original CARIBU system, that will provide a reliable, on‑demand supply of radioactive isotopes for experiments while simplifying maintenance and improving operational efficiency. nuCARIBU will rely on neutron‑induced fission of uranium to produce isotopes and, for the first time, will allow the source to be turned off when not needed.

ATLAS is also preparing for the next generation of nuclear physics research through the N=126 Factory, an experimental system designed to provide beams of rare, neutron‑rich radioactive isotopes of very heavy elements. These isotopes are difficult to generate by other means and are important for understanding how the heaviest elements in the universe are made.

And to make the most efficient use of these new capabilities, ATLAS is pursuing a multi‑user upgrade that will enable the facility to deliver beams to two experimental stations simultaneously — one stable beam and one rare-isotope.

ATLAS’ beginning may be hard to pin down, and its history is one of continuous change. But its culture of improvement, expansion and excellence has put it on secure footing for tomorrow.

“The history of ATLAS is a story of growth, adaptation and scientific excellence. That will also be its future,” said Savard. ​“This facility’s ability to innovate and grow from its ambitious origins has allowed ATLAS to remain a vital resource for nuclear physics research, even as the field has evolved. As ATLAS looks to the future, it is well‑positioned to tackle the next generation of scientific challenges, continuing its legacy of discovery and its mission to unlock the secrets of the universe.”

Argonne Tandem Linac Accelerator System

This material is based upon work supported by the U.S. Department of Energy (DOE), Office of Science, Office of Nuclear Physics, under contract number DE‐AC02‐06CH11357. This research used resources of the Argonne Tandem Linac Accelerator System (ATLAS), a DOE Office of Science User Facility.

Argonne National Laboratory seeks solutions to pressing national problems in science and technology by conducting leading-edge basic and applied research in virtually every scientific discipline. Argonne is managed by UChicago Argonne, LLC for the U.S. Department of Energy’s Office of Science.

The U.S. Department of Energy’s Office of Science is the single largest supporter of basic research in the physical sciences in the United States and is working to address some of the most pressing challenges of our time. For more information, visit https://​ener​gy​.gov/​s​c​ience.