Editor’s note: This article was published jointly with Argonne National Laboratory.
With a powerful enough light, you can see things that people once thought would be impossible. Large-scale light source facilities generate that powerful light, and scientists use it to create more durable materials, build more efficient batteries and computers, and learn more about the natural world.
When it comes to building these massive facilities, space is money. If you can get higher-energy beams of light out of smaller devices, you can save millions on construction costs. Add to that the chance to significantly improve the capabilities of existing light sources, and you have the motivation behind a project that has brought scientists at three U.S. Department of Energy national laboratories together.
This team has just achieved an important milestone that has been in the works for more than 15 years: They have designed, built and fully tested a new state-of-the-art half-meter-long prototype magnet that meets the requirements for use in existing and future light source facilities.
This half-meter-long prototype of a niobium-tin superconducting undulator magnet was designed and built by a team from three U.S. Department of Energy national laboratories. The next step will be to build a meter-long version and install it at the Advanced Photon Source at Argonne. Photo: Ibrahim Kesgin, Argonne National Laboratory
The next step, according to Efim Gluskin, a distinguished fellow at DOE’s Argonne National Laboratory, is to scale this prototype up, build one that is more than a meter long, and install it at the Advanced Photon Source, a DOE Office of Science User Facility at Argonne. But while these magnets will be compatible with light sources like the APS, the real investment here, he said, is in the next generation of facilities that have not yet been built.
“The real scale of this technology is for future free-electron laser facilities,” Gluskin said. “If you reduce the size of the device, you reduce the size of the tunnel, and if you can do that you can save tens of millions of dollars. That makes a huge difference.”
That long-term goal brought Gluskin and his Argonne colleagues into collaboration with scientists from Lawrence Berkeley National Laboratory and Fermi National Accelerator Laboratory, both DOE labs. Each lab has been pursuing superconducting technology for decades and has in recent years focused research and development efforts on a compound that combines niobium with tin.
This material remains in a superconducting state – meaning it offers no resistance to the current running through it – even as it generates high magnetic fields, which makes it perfect for building what are called undulator magnets. Light sources like the APS generate beams of photons (particles of light) by siphoning off the energy given off by electrons as they circulate inside a storage ring. The undulator magnets are the devices that convert that energy to light, and the higher a magnetic field you can generate with them, the more photons you can create from the same size device.
There are a few superconducting undulator magnets installed at the APS now, but they are made of a niobium-titanium alloy, which for decades has been the standard. According to Soren Prestemon, senior scientist at Berkeley Lab, niobium-titanium superconductors are good for lower magnetic fields – they stop being superconducting at around 10 teslas. (That’s about 8,000 times stronger than your typical refrigerator magnet.)
“Niobium-3-tin is more complicated material,” Prestemon said, “but it is capable of transporting current at a higher field. It is superconductive up to 23 tesla, and at lower fields it can carry three times the current as niobium-titanium. These magnets are kept cold at 4.2 Kelvin, which is about minus 450 degrees Fahrenheit, to keep them superconducting.”
Prestemon has been at the forefront of Berkeley’s niobium-3-tin research program, which began back in the 1980s. The new design, developed at Argonne, built on the previous work of Prestemon and his colleagues.
“This is the first niobium-3-tin undulator that has both met the design current specifications and been fully tested in terms of magnetic field quality for beam transport,” he said.
Fermilab started working with this material in the 1990s, according to Sasha Zlobin, who initiated and led the niobium-3-tin magnet program there. Fermilab’s niobium-3-tin program has centered on superconducting magnets for particle accelerators, like the Large Hadron Collider at CERN in Switzerland and the upcoming PIP-II linear accelerator, to be built on the Fermilab site.
“We’ve demonstrated success with our high-field niobium-3-tin magnets,” Zlobin said. “We can apply that knowledge to superconducting undulators based on this superconductor.”
Part of the process, according to Emanuela Barzi, Fermilab senior scientist and co-investigator for the project, has been learning how to avoid premature quenches in the magnets as they approach the desired level of magnetic field. When the magnets lose their ability to conduct current without resistance, the resulting backlash is called a quench, and it eliminates the magnetic field and can damage the magnet itself.
The team will report in the IEEE Transactions on Applied Superconductivity that their new device accommodates nearly twice the amount of current with a higher magnetic field than the niobium-titanium superconducting undulators currently in place at the APS.
The project drew on Argonne’s experience building and operating superconducting undulators and Berkeley and Fermilab’s knowledge of niobium-3-tin. Fermilab helped to guide the process, advising on the selection of superconducting wire and sharing recent developments in their technology. Berkeley designed a state-of-the-art system that uses advanced computing techniques to detect quenches and protect the magnet.
At Argonne, the prototype was designed, fabricated, assembled and tested by a group of engineers and technicians under the guidance of Project Manager Ibrahim Kesgin, with contributions in the design, construction and testing by members of the APS superconducting undulator team led by Yury Ivanyushenkov.
The research team plans to install their full-sized prototype, which should be finished next year, at Sector 1 of the APS, which makes use of higher-energy photon beams to peer through thicker samples of material. This will be a proving ground for the device, showing that it can operate at design specifications in a working light source. But the eye, Gluskin says, is on transferring both technologies, niobium titanium and niobium-3-tin, to industrial partners and manufacturing these devices for future high-energy light source facilities.
“The key has been steady and persistent work, supported by the labs and DOE research and development funds,” Gluskin said. “It has been incremental progress, step by step, to get to this point.”
Fermilab is supported by the Office of Science of the U.S. Department of Energy. The 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, please visit energy.gov/science.
A combination of observational data and sophisticated computer simulations have yielded advances in a field of astrophysics that has languished for half a century. The Dark Energy Survey, which is hosted by the U.S. Department of Energy’s Fermi National Accelerator Laboratory, has published a burst of new results on what’s called intracluster light, or ICL, a faint type of light found inside galaxy clusters.
The first burst of new, precision ICL measurements appeared in a paper published in The Astrophysical Journal in April 2019. Another appeared more recently in Monthly Notices of the Royal Astronomical Society. In a surprise finding of the latter, DES physicists discovered new evidence that ICL might provide a new way to measure a mysterious substance called dark matter.
The source of ICL appears to be rogue stars, those not gravitationally bound to any galaxy. The ICL has long been suspected of possibly being a significant component of clusters of galaxies, but its faintness makes it difficult to measure. No one knows how much there is or to what extent it has spread through galaxy clusters.
“Observationally we confirmed that intracluster light is a pretty good radial tracer of dark matter. That means that where intracluster light is relatively bright, the dark matter is relatively dense,” said Fermilab scientist Yuanyuan Zhang, who led both studies. “Just measuring the ICL itself is pretty exciting. The dark matter part is a bonus.”
On the left is a simulated image in which intracluster light is visible as a diffuse haze between discrete peaks of brightness — the galaxies. In observations, as seen in the right, this intracluster light component is largely drowned in noise. Left image: Jesse Golden-Marx; simulation by The IllustrisTNG. Right image: Dark Energy Survey and Yuanyuan Zhang
Although invisible, dark matter accounts for most matter in the universe. What dark matter consists of stands as one of the major mysteries of modern cosmology. Scientists know only that it differs greatly from the normal matter consisting of the protons, neutrons and electrons that dominate everyday life.
But ICL, not dark matter, was initially on the research team’s agenda. Most astrophysicists measure intracluster light at the center of a galaxy cluster, where it is brightest and most abundant.
“We went very far away from the centers of the galaxy clusters, where the light is really faint,” Zhang said. “And the farther away from the center we went, the more difficult the measurement became.”
Nevertheless, the DES collaborators managed to come away with the most radially extended measurement of ICL ever.
The team used weak gravitational lensing to compare the radial distribution of the ICL — how it changes over distance from the center of a cluster — to the radial distribution of the mass of a galaxy cluster. Weak lensing is a dark-matter-sensitive method of measuring the mass of a galaxy or cluster. It occurs when the gravity of a foreground star or cluster bends the light from a more distant galaxy, distorting its apparent shape.
It turned out observationally that ICL reflects the distribution of both the total visible mass of a galaxy cluster and, possibly, the distribution of the invisible dark matter.
“We did not expect to find such a tight connection between these radial distributions, but we did,” said scientist Hillysson Sampaio-Santos, the lead author of the new paper.
Comparing observations with simulations
To gain more insight, the team used a sophisticated computer simulation to study the relationship between ICL and dark matter. They found that the radial profiles between the two phenomena in the simulation didn’t agree with the observational data. In the simulation, “the ICL radial profile was not the best component to trace dark matter,” said Sampaio-Santos, who is with the National Observatory in Rio de Janeiro, Brazil.
Zhang noted that it’s too soon to tell exactly what caused the conflict between observation and simulation.
“If the simulation didn’t get it right, it could mean that the simulated intracluster light is produced at a slightly different time than in observations. The simulated stars didn’t have enough time to wander around and start to trace dark matter,” she said.
Sampaio-Santos noted that further ICL studies could yield insights into the dynamics occurring inside galaxy clusters, including interactions that gravitationally release some of their stars, allowing them to wander around.
“I’m planning to study the intracluster light and the effects of relaxation,” or spreading out, he said. For example, some clusters have merged together. These merged clusters should have different properties of ICL compared to clusters that are relaxed.
Enhancing signals in noisy data sets
The ICL that the team measured is about a hundred to a thousand times fainter than what DES scientists normally attempt. That means the team had to deal with a lot of noise and contamination in the signal.
The technical aspect of the feat was challenging, Zhang said, “but because we had quite a bit of data from the Dark Energy Survey, we were able to cancel out a lot of noise to do this kind of measurement. It’s statistical averaging.”
Astrophysicists typically make ICL measurements using a handful of galaxy clusters at a time.
“That’s a great way to get information about the individual systems,” Zhang said.
To get the bigger picture and to beat down the noise, the DES team statistically averaged about 300 galaxy clusters in the first study and more than 500 clusters in the second. All of them are a couple of billion light-years from Earth.
Teasing the signal from the noise of each cluster takes a lot of data, which is exactly what the DES has generated. In early 2019, DES completed its six-year mission of observing hundreds of millions of distant galaxies in the southern skies and publicly issued its second data release in mid-January.
The ICL measurements probe clusters that are up to 3.3 billion light-years from Earth. In future studies, Zhang would like to study the redshift evolution of ICL — how it changes with cosmic time.
“My dream is to go all the way to redshift one — 10 billion light-years,” Zhang said. “Studies say that’s when the ICL has just started to evolve.”
Going that far would enable scientists to see ICL building over time.
“But that’s really hard because it’s three times as far as the distance of our latest measurements, so everything is going to be extremely faint there,” she said.
Editor’s note, Jan. 29, 2021: This article has been revised with a more precise characterization of the nature of the result.
The Dark Energy Survey is a collaboration of more than 300 scientists from 25 institutions in six countries. For more information about the survey, please visit the experiment’s website.
Funding for the DES Projects has been provided by the U.S. Department of Energy, the U.S. National Science Foundation, the Ministry of Science and Education of Spain, the Science and Technology Facilities Council of the United Kingdom, the Higher Education Funding Council for England, the National Center for Supercomputing Applications at the University of Illinois at Urbana-Champaign, the Kavli Institute of Cosmological Physics at the University of Chicago, Funding Authority for Studies and Projects in Brazil, Carlos Chagas Filho Foundation for Research Support of the State of Rio de Janeiro, Brazilian National Council for Scientific and Technological Development and the Ministry of Science, Technology and Innovation, the German Research Foundation and the collaborating institutions in the Dark Energy Survey.
Fermilab is supported by the Office of Science of the U.S. Department of Energy. The 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 science.energy.gov.
On Jan. 4, Richard Verhaagen stepped into his new role as Department of Energy Fermi Site Office manager for the Office of Science. Verhaagen replaces interim manager Roger Snyder, who succeeded Mike Weis.
Verhaagen was most recently the deputy manager for technical operations at the DOE National Nuclear Security Administration Field Office at Los Alamos National Laboratory, following a period as NNSA senior technical safety advisor. As deputy manager, he led the federal team responsible for oversight of all laboratory operations, primarily focused on the nuclear and high-hazard facilities, as well as emergency management, engineering and operational readiness.
“I’m glad to be here, and I’m excited about learning a new scientific mission and working with a new group of people to get a different perspective on DOE science,” Verhaagen said.
As DOE Fermi Site Office manager and a liaison between the lab and the Office of Science, Verhaagen will collaborate with Fermilab to enable the lab’s mission, ensuring that the work is done safely and within Office of Science requirements.
“The success of the laboratory is our success, and when the laboratory succeeds, we succeed as well,” he said.
Verhaagen has worked with DOE in some capacity for nearly 15 years. Before his time at NNSA, he worked for 10 years for the Defense Nuclear Facilities Safety Board, an independent agency in the federal executive branch that provides oversight of all DOE sites conducting work related to defense nuclear activities. His work there included a five-year period as resident inspector at Los Alamos National Laboratory.
Prior to this, Verhaagen worked for the U.S. Navy for 24 years, including 13 years as a submarine officer and eight as an electronics technician.
Verhaagen holds a bachelor’s and master’s degree in mathematics from Purdue University and a master’s in nuclear engineering from Pennsylvania State University.
He looks forward to being closer to family, who live in the area, and going to Wisconsin in the summers.
“Fermilab is a true science lab – science for the sake of science,” he said. “This is an opportunity to focus less on production, like I’m accustomed to, and more on the exciting fundamental research Fermilab is known for.”
Fermilab is supported by the Office of Science of the U.S. Department of Energy. The 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 science.energy.gov.