DOE endorses Advanced Photon Source upgrade

The US Department of Energy granted approval on 25 July for Argonne National Laboratory outside Chicago to begin construction on an $815 million upgrade to its Advanced Photon Source (APS) user facility. The improved facility will produce x-ray beamlines that are between 100 and 1000 times as bright as those at the current APS. Scheduled for completion in 2026, the upgrade will make APS competitive with other synchrotron light sources around the world and advance the frontiers of research on several fronts, including solar cell design, drugs for infectious diseases, neuroscience, and geophysics.

The APS uses groups of bending and focusing magnets to accelerate electrons to nearly the speed of light within a 1.1-kilometer storage ring. X rays emitted by those high-energy electrons are then extracted from the ring, focused into beamlines of different intensities, and shot through samples. The design for the APS’s new storage ring takes advantage of multibend achromat (MBA) technology: By packing more magnets into each group (or achromat), there’s room for more focusing magnets to steer electrons, which makes the emitted x rays brighter and more coherent. The Swedish government employs the technology in its national synchrotron light source, the MAX IV, in Lund (see Physics Today, June 2015, page 21 ).

The European Synchrotron Radiation Facility (ESRF) in Grenoble, France, began a similar upgrade last year. The new APS is expected to be comparable in brightness to the upgraded ESRF (about a factor of three brighter), so the two facilities will have similar scientific capabilities. Other large synchrotron light sources—including DESY (German Electron Synchrotron) and the Super Photon Ring in Japan—have similar plans to improve to the latest accelerator technology. “We are excited about the upgrades that are planned,” says Wim Leemans, director of the accelerator division at DESY. The community “mutually benefits from each other’s developments.”

First proposed in 2010, the design for the APS upgrade has shifted due to technology improvements. The original plan called for developing short x-ray pulses to improve the time resolution of experiments. But DOE didn’t approve that approach because emerging research indicated that MBA technology would be more effective. DOE took a “step back and really looked at each of the projects it had in the pipeline and made sure that we were positioning US technology to be world leading,” says APS director Stephen Streiffer. The new design benefited from recent advances in high-performance computing. “One of the big changes that have allowed us to have confidence that we could build this thing and have it work is our ability to do very accurate accelerator simulations,” says Streiffer.

The APS upgrade promises to advance many research fields. Polycrystalline solar cells, for example, often contain a nonnegligible concentration of impurities that sap some of the energy that would otherwise convert to electricity. Shooting brighter x-ray beams into those cells would provide the nanometer resolution needed to better characterize the impurities and how they affect performance.

The new APS could also improve experiments that re-create the conditions of Earth’s core. In state-of-the-art labs, researchers can use x-ray beams to characterize micron-size samples squeezed between diamond anvils to the roughly 140 gigapascals of pressure at Earth’s core–mantle boundary. With the brighter, more coherent x-ray beams of the upgraded APS, researchers should be able to extract useful information from samples subjected to even higher pressures, of the order observed in Earth’s core and inside our solar system’s gas giants.

The APS facility will minimize downtime during construction for its 5500 annual users. Components will be assembled into subsystems on site. Then the facility will shut down for about a year to allow engineers to build the new storage ring and install the subsystems. Streiffer says the earliest the shutdown could occur is 2022.