APS News | Research

To Become Brighter, Synchrotron Light Sources Must First Go Dark

Around the world, specialized accelerator facilities are going offline in preparation for major upgrades to storage ring technologies.

Published May 11, 2023
view of Berkeley Lab’s Advanced Light Source building
A time-lapse view of Berkeley Lab’s Advanced Light Source (ASL) building. The ALS, like many light sources around the world, are being upgraded to fourth-generation technologies.
Credit: Haris Mahic/Berkeley Lab

Each year, scientists from around the world apply for coveted “beam time” at specialized particle accelerator facilities known as light sources. But while they share facilities, they don’t often share fields: One team might be studying proteins implicated in disease, one might be tinkering with materials that remove toxins from emissions, and still another might be studying biodiesel-producing algae.

What unites their research is the need for very bright light — high fluxes of photons, usually x-rays — that can be controlled and recorded with precision optics and imaging systems. In a synchrotron light source, strong magnets herd a beam of electrons at nearly the speed of light through a curved storage ring. As the beam speeds along, specialized magnets wobble it, shaking out photons that are useful for scientific studies.

Now, the power is being turned off at many light sources, which often operate 24 hours a day. But it’s all part of the plan: These light-emitting storage rings are “going dark” so they can be upgraded, a leap toward fourth-generation light sources.

At the APS April Meeting in Minneapolis, several physicists presented their work tackling critical challenges associated with these upgrades.

Joe Calvey, a physicist at Argonne National Laboratory’s Advanced Photon Source in Illinois, has spent the past eight years studying how tiny amounts of gas in the accelerator chamber, like carbon dioxide or water vapor, can destabilize the electron beam.

“It doesn’t have to be much,” says Calvey. Just a few trillionths of a standard atmosphere — much closer to the pressure of gas in space than here on Earth — is enough to cause problems. The electron beam can ionize residual gas molecules in its path, causing the beam to spread out and eliminating the main advantage of fourth-generation technology: a tight, focused beam.

The next generation of light source technology, enabled largely by new storage ring designs, could bypass some of these problems — and deliver up to three orders of magnitude more light, says Volker Schlott, a senior scientist at the Paul Scherrer Institut, which operates the Swiss Light Source (SLS) in Switzerland.

A simulated profile of the electron beam of Berkeley Lab’s Advanced Light Source today (left) — and the highly focused beam (right) that will be available after the upgrade, substantially increasing its brightness.
Credit: Cristoph Steier/Berkeley Lab

The first major design change in the shift to fourth-generation technology is a storage ring with a smaller internal opening, says Schlott. At the SLS, he says, the opening in the new ring will be just 18 millimeters in diameter, less than one-fifth the size of the facility’s current third-generation storage ring. This change is possible because of a non-evaporable getter coating on the inside of the ring. This special coating, also used at CERN, is designed to trap residual gas molecules, to keep them out of the beam’s path. It’s key to making the storage ring more efficient.

Scientists have also tweaked the magnets that confine the electron beam in the storage ring. Smaller, more compact magnets, arranged in a much denser “lattice,” consume less power during operation, explains Schlott. And with a smaller storage ring cross-section, the magnets sit closer to the beam, bathing it in a stronger magnetic field.

Additionally, some of the electromagnets will be swapped for permanent magnets, similar to refrigerator magnets, “which have no electricity consumption,” says Christoph Steier, lead of accelerator systems for the Lawrence Berkeley National Laboratory’s Advanced Light Source (ALS) upgrade project. “Even more importantly, the permanent magnets do not need any liquid helium for cooling,” he says — an increasingly scarce and expensive resource.

As a result of these and other changes, “all of these facilities will become much more power-efficient,” says Schlott. His team estimates that “SLS 2.0” will guzzle 40% less power. At the ALS, Steier anticipates a more modest reduction — in part because the ALS is adding an additional accelerator, known as an accumulator ring, that will offset the energy savings of the fourth-generation upgrades.

Even so, energy efficiency isn’t the main motivation for the upgrades. Instead, it’s the promise of scientific discovery. “[Scientists] really like asking questions that can’t be answered with the present technology,” says Calvey.

Some light sources are also tuned to deliver infrared light, in addition to x-rays. Because biological molecules absorb infrared light at specific frequencies, based on their composition and structure, scientists can use infrared light to study everything from space dust to living cells, says research scientist Stephanie Corder. She says the ALS upgrade could even open the door to new scientific approaches: “Two-color multimodal capabilities,” for example, could allow scientists to use both x-rays and infrared light to study samples, all at the same beamline.

Other efforts aim to speed up research. Today at light sources, figuring out what to study in heterogeneous samples — like the microbial communities in permafrost, say — is typically very time-consuming. That’s why Elizabeth Holman, a postdoc at Stanford University who specializes in infrared spectroscopy, has collaborated with Lawrence Berkeley staff to develop an autonomous, adaptive data acquisition system, now deployed at one of the ALS’s infrared beamlines, that can drastically speed up data collection. In the future, Holman says the technology will “be adapted for real-time data acquisition and analysis of dynamic experimental systems,” such as live cells, “allowing the researcher to adjust their sampling parameters on-the-fly.”

The Advanced Photon Source, where Calvey works, went dark just one week after the April Meeting. Schlott says the SLS is scheduled to go dark this fall, and Corder says the ALS will be taken offline in 2025. The ALS and Advanced Photon Source upgrades are funded by the US Department of Energy, while the SLS upgrade is funded by the Swiss government.

With much brighter light, the scientists collecting data at light source beamlines will be able to complete their experiments in far less time — and at much higher spatial resolution.

“It’s opening a whole new world,” says Calvey.

Liz Boatman

Liz Boatman is a science writer based in Minnesota.

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