Upgrades and new research at Argonne are helping physicists push boundaries, from basic science to the development of new technologies.
The world’s first controlled, self-sustaining nuclear reaction was achieved at the University of Chicago as part of the Manhattan Project during World War II. This achievement not only advanced nuclear energy but also influenced early research in many areas of physics at what would eventually become the U.S. Department of Energy’s (DOE) Argonne National Laboratory.
Today, Argonne’s physicists tackle challenges that span from particles at the core of atoms to the vast structures of the cosmos. The laboratory is undergoing a series of ambitious upgrades — including several at the Argonne Tandem Linac Accelerator System (ATLAS), a DOE Office of Science user facility and the prime national facility for nuclear research — and pursuing new research directions to further its work.
To stay at the forefront of scientific research, we must constantly develop new capabilities and pursue new directions while ensuring that we align with the wider physics community and our primary sponsor, the DOE Office of Nuclear Physics.”
Fredrik Tovesson, director of Argonne’s Physics division
Key to their success is collaboration with researchers worldwide and across Argonne, bringing together expertise in high-energy physics, materials science, nuclear reactor physics and computational science.
“No group of researchers is an island at Argonne,” Tovesson added.
Physicists at Argonne cover numerous atom types. These types include ions (charged atoms), stable isotopes (atoms with varying numbers of neutrons) and radioactive isotopes (unstable atoms that decay over time). Researchers also study fundamental particles such as quarks and gluons, which form protons and neutrons.
Upgrading ATLAS: Argonne’s National Facility for Probing Atomic Nuclei
For decades, a global community of researchers has brought their physics experiments to ATLAS, the world’s first superconducting linear accelerator for heavy ions at energies needed by nuclei to get close enough to undergo a nuclear reaction. ATLAS accelerates ions across the periodic table — from hydrogen to uranium — at velocities up to 20% the speed of light. These accelerated ions collide with targets to enable studies of atomic nuclei and nuclear reactions.
ATLAS hosts roughly 400 users each year, and worthy proposals asking for ATLAS beam time have consistently exceeded availability. To reduce the difference between the time requested and the time available, an upgrade is underway that will enable ATLAS to deliver ion beams to two separate experiments simultaneously.
“And with other added capabilities, we’ll be able to probe nuclear structures that we haven’t been able to access before,” noted Clay Dickerson, accelerator physicist and ATLAS technical manager, who leads the ATLAS upgrade effort. “We are constantly pushing the limits of what theory can describe by exploring rarer and shorter-lived ions.”
Among the new ATLAS capabilities coming online is the N=126 Factory. This capability is designed to study neutron-rich isotopes around the neutron “magic number” of 126, a scarcely explored area in nuclear physics. Analysis of new ATLAS data from these isotopes will provide deeper insights into the formation of heavy elements in stellar explosions and neutron star collisions. By allowing access to rare, short-lived isotopes that were previously impossible to study, the N=126 Factory will offer a new tool for understanding the universe.
Another ATLAS component — the Californium Rare Isotope Breeder Upgrade (CARIBU) — has provided users with beams of radioactive isotopes produced by a californium source for over a decade. These isotopes spontaneously undergo fissions — meaning they split — that create neutron-rich isotopes invaluable for nuclear research. Because the source material is extremely difficult and costly to obtain, CARIBU is being upgraded to nuCARIBU, a system that will rely on the neutron-induced fission of uranium. This upgrade will ensure a more reliable, on-demand supply of radioactive isotopes. It will also allow researchers to turn off the source when not needed, which will simplify system maintenance.
Another new beamline, the ATLAS Material Irradiation Station (AMIS), uses accelerated heavy-ion beams to irradiate materials without making them radioactive. It allows researchers to assess material degradation rapidly and efficiently, replicating the extreme environments encountered in outer space or inside nuclear reactors. The research conducted with AMIS will be valuable for understanding how materials perform in intense conditions.
Enhancing Nuclear Research with Laser Spectroscopy
As ATLAS continues to push the boundaries of nuclear physics with these new capabilities, the facility is also enhancing existing components to further support groundbreaking research. These enhancements aim to optimize the facility’s efficiency and expand its research potential. For instance, the CARIBU beamline requires advanced tools to analyze the rare and highly radioactive isotopes it produces. To meet this need, ATLAS has recently integrated a laser spectroscopy setup capable of measuring elements and isotopes at a precision not possible before. That includes probing difficult samples with brief lifetimes of seconds or minutes or samples of only a few hundred atoms.
“This laser spectroscopy setup enables the precise analysis of short-lived isotopes, supporting studies in nuclear structure and astrophysics,” said physicist Peter Mueller.
Plans are in place to extend this capability to both nuCARIBU and the N=126 Factory. The integration of laser spectroscopy exemplifies ATLAS’ commitment to refining its existing capabilities to support cutting-edge research.
Collaborating on Superconducting Cavities for Enhanced Efficiency
Furthermore, Michael Kelly’s group in the Physics division is collaborating with DOE’s Fermi National Accelerator Laboratory (Fermilab) to develop new superconducting radio-frequency cavities that could revolutionize accelerator technology at ATLAS.
Superconducting materials such as niobium-tin are a common component in accelerator technology. They carry electricity with nearly zero resistance when cooled to temperatures similar to those in outer space. Such cooling requires the use of liquid helium. However, liquid helium is expensive and in limited supply. Kelly’s group developed niobium-tin coatings for cavities to address that problem.
“By reducing surface resistance, our coating lowers liquid helium usage and could enable smaller cavity sizes, shrinking from the size of a water heater for today’s cavities to something as small as a Coke can,” Kelly said.
This downsizing can dramatically reduce accelerator costs and their physical footprint, benefiting not only ATLAS but also future ion accelerators.
Uncovering the Fundamentals of Matter with the Electron-Ion Collider
One such future accelerator is the Electron-Ion Collider (EIC), a trailblazing project that will further our understanding of nuclear matter. Argonne physicists are designing a key detector for the EIC, to be built at DOE’s Brookhaven National Laboratory within the next decade.
Physicists have long known that protons and neutrons are made up of smaller particles called quarks and gluons, which are held together by what’s called the strong force — a fundamental interaction between subatomic particles. Yet much remains unknown about how quarks and gluons interact and govern particle properties such as mass and spin. The EIC aims to unravel these mysteries.
This accelerator will collide electrons with protons and atomic nuclei, capturing detailed images of the internal structure of the atomic nucleus — similar to an MRI device for 3D scanning the fundamental structure of an atom.
Argonne scientists are leading the development of one of the main components of the EIC’s particle detector, the barrel imaging calorimeter. Under the leadership of the Argonne team, researchers at 18 laboratories and universities in the U.S., Canada, the Republic of Korea and Germany are participating in the monumental development and construction task.
The calorimeter’s primary job is to detect electrons that scatter from protons or ions during collisions, yielding vital data about the structure of matter. This calorimeter design will provide unmatched precision to distinguish electrons from other subatomic particles, which can interfere with data accuracy.
“The final calorimeter will definitely not fit in a laboratory room,” said assistant physicist Maria Żurek.
It measures about 154 feet long, half as tall and weighs more than 40 tons. The whole detector, including its unique subcomponents located close to the colliding particle beams, spreads roughly 300 feet in all directions and weighs hundreds of tons.
When the calorimeter comes online, it will generate an avalanche of data that will enable precise imaging of the characteristic patterns left by different particles when they travel through the detector. This is made possible by incorporating more than 1,000 square feet of silicon AstroPix sensors, developed by Argonne in collaboration with NASA, into the calorimeter. The addition of these sensors will make the calorimeter one of the largest silicon detectors in the world. The vast amount of multidimensional data it collects will require complex computation enabled by artificial-intelligence-driven processing methods that Argonne is developing.
The final design and construction of the EIC calorimeter will represent a significant engineering and scientific feat. Preliminary tests of the calorimeter have taken place at DOE’s accelerator facilities at Thomas Jefferson National Accelerator Facility and Fermilab.
Exploring Beyond the Standard Model with CeNTREX
Meanwhile, physicists in the fundamental symmetry group, which includes David DeMille, are also busy these days setting up a new experiment. DeMille is also a professor of physics at Johns Hopkins University and a research professor of physics at the University of Chicago.
DeMille and other researchers on the team are working on the Cold Molecule Nuclear Time Reversal Experiment (CeNTREX), a collaboration with Johns Hopkins University, the University of Chicago, Columbia University and the University of Massachusetts Amherst. The experiment aims to uncover new forces that could explain why the universe contains matter but almost no antimatter — a discrepancy that remains unexplained by the Standard Model, the best theory of particle physics at present.
According to current understanding, the intense energy of the Big Bang converted into mass, creating particles of matter and antimatter. When these particles met, they annihilated each other. Yet, for reasons unknown, a considerable amount of matter but not antimatter survived this annihilation process. This leftover matter is what formed all the stars, planets and galaxies.
In its quest to discover why there is so little antimatter, the CeNTREX experiment will attempt to detect subtle “egg-shaped” deformations in protons. A slight shape-shift away from perfectly spherical would indicate the presence of previously undetected forces.
“These deformations would be unambiguous evidence for forces beyond those currently described by the Standard Model,” DeMille said. “Uncovering them would transform our understanding of fundamental physics.”
CeNTREX represents a complementary approach to exploring fundamental physics questions traditionally addressed by experiments conducted with large instruments, like Fermilab’s Deep Underground Neutrino Experiment or CERN’s Large Hadron Collider.
Investigating Quantum Phenomena with Ultracold Atoms
Argonne physicists are also setting up a unique experiment for studying quantum phenomena by manipulating single atoms of the element ytterbium at temperatures near absolute zero in a vacuum chamber.
“We are creating an experimental platform employing isolated, ultracold atoms to better understand the subatomic world,” explained assistant physicist Michael Bishof.