By Broderick K. Johnson

Helix

In June 2024, a group of scientists gathered in a room at Argonne National Laboratory in Lemont, Ill., and stared at a live feed of a featureless grey rectangle hanging in a lead-lined room. Everything was ready. All that was left to do was push a button and they would know if a year of hard work and careful engineering had paid off.

Among the group was Diego Casa, a physicist who had painstakingly aligned a series of complicated mirrors and shutters in preparation for this moment. Now, as Casa watched, another scientist stepped forward and pushed the button. A shutter opened, and an invisible beam of high-intensity X-rays streamed through Casa’s carefully calibrated optics and coursed into the lead-lined room. The beam struck the grey rectangle, causing dye molecules in the unassuming quadrilateral to glow – a bright green sign of success. The room full of scientists erupted. “Everybody cheered. Everybody was pointing at the screen,” Casa said. After fourteen months of darkness, the light at the Advance Photon Source was finally back on.

This was no ordinary light. The Advance Photon Source, or APS, is a type of particle accelerator called a synchrotron that produces beams of X-rays millions of times brighter than the Sun. Scientists from around the world come to this ring-shaped facility, which is large enough to encircle a baseball stadium, and use these X-rays to learn about the atomic-level structure of new materials. These insights enable the development of better batteries, more efficient solar panels, new medicines, and many more life changing inventions.

In April 2023, the APS staff extinguished the facility’s light so that technicians could make extensive upgrades. When Casa and his colleagues watched that grey rectangle begin to glow on June 17, 2024, they were watching these upgrades finally come to fruition. The upgraded APS produces X-ray beams that are brighter and more focused, and the facility is now giving scientists from across the country and around the world access to these enhanced rays. Researchers returning to the APS can expect to find “bigger, better, faster everything,” Casa said.

The brighter, more concentrated light source will produce stronger signals during experiments.  This means researchers can quickly acquire high quality data without needing to take the time to repeat measurements. Scientists can also attenuate the beam down to a smaller size or a narrower energy range without losing so much intensity that the experiment is ruined. This will allow them to analyze small samples and collect high-resolution data.

“With these capabilities, there’s many more experiments that can be done,” said Stephen Gramsch, a research professor at the University of Illinois, Chicago who conducts experiments at the APS. In his experiments, Gramsch squeezes minerals between two diamonds that are less than half a millimeter wide and then aims the X-ray beams at these petite pinched samples to study how their atomic structures change under high pressure.

Because the diamond cell is so small, Gramsch needs to use a narrow beam of X-rays for his experiments. In the past, he achieved this by slimming the beam down to size with an aperture that blocked all but a pinpoint of light. In doing so, he lost a lot of the light source’s available intensity, so it would take up to several hours to acquire quality data. Gramsch remembers one colleague’s experiments took so long that they had time to start a measurement, drive 25 miles to Chicago, enjoy a night out at the city’s famous jazz clubs, and return to the APS just as the data collection ended. But future experiments won’t allow for such musical excursions. Gramsch expects that the upgraded APS’ brighter and smaller beam will make things much faster; some experiments may now take less than a minute.

Gramsch and other scientists like him can thank innovative engineering for these improvements. Like other synchrotrons, the APS generates X-rays by shooting bunches of electrons around its massive ring at nearly the speed of light. These electrons are steered around the circular path by a series of powerful magnets. Each time an electron encounters the force of a magnet, its trajectory turns and the electron loses some of its forward momentum. This lost momentum is converted to another form of energy: X-rays that power experiments at the APS. But as the bunches of electrons make multiple laps around the ring, they lose energy and start to spread out. This causes the X-rays they emit to become dimmer and less focused. The APS upgrade solves both problems.

A first-of-its-kind method of shooting electrons around the ring solves the brightness problem. With this technique, each bunch of electrons is kicked out of the ring after one lap and a new bunch is injected at the exact same moment. No other synchrotron has ever used this injection technique, which is known as multi-bunch swap-out injection, so it was completely untested before the scientists at the APS made it a reality. “The fact that it actually works is amazing,” Casa said.

As for the loss of focus, the APS fixed that problem by upgrading the magnets that guide the electrons around the ring. The new array uses stronger miniaturized magnets that can be packed closer together, said Shirish Chondakar, a physicist at the National Synchrotron Light Source II in Upton, New York. These closely packed magnets keep the electrons confined in tight bunches. This means they emit all their X-rays in a very narrow space, which makes it easy to focus all the precious X-ray photons into a small, concentrated beam.

These improvements will not only speed up science but will also enable experiments that were previously impossible. Because the upgraded APS will provide higher quality data in less time, Chondakar said it may now be possible to study dynamic processes that happen too quickly to be detected by the old system. For example, scientists may be able to observe the movement of atoms and molecules to get a more accurate view of how materials behave over short time spans. This information could enable the development of materials that respond better to sudden shocks or other fast stimulation. As for Casa, he’s hopeful that the stronger signals will allow scientists to directly see things that were previously theorized to exist but have thus far remained elusive, such as small proteins and parts of cells.

“We are on the verge of a transformational change,” Casa said. “And now we have the photons to do it.”

Broderick Johnson is a Ph.D. student in the Department of Chemistry at Northwestern University.

Editor’s note: This story was written in 2024.  On Feb. 5, 2025, APS scientists finished gradually ramping the electron current inside of the upgraded APS up to its target value of 200 milliamps. Exactly one year later, the Department of Energy declared that the APS Upgrade Project was officially complete. As of Feb. 16, 2026, experiments were being conducted at 58 of the facility’s 72 experiment stations.