Advanced Photon Source Sets New World Record for Electron Beam Emittance

The upgraded Advanced Photon Source (APS), a U.S. Department of Energy (DOE) user facility at DOE’s Argonne National Laboratory, has once again set a new global benchmark in synchrotron science. The facility’s electron storage ring has achieved a horizontal emittance of just 33 picometers-radians (pm.rad), the lowest ever measured at a synchrotron X-ray light source.

This achievement builds upon previous APS measurements and further confirms the facility’s world-leading status as it resumes operations following a year-long shutdown for a comprehensive upgrade.

“It’s exciting not just for our team, who worked hard to imagine, design, engineer, build and commission the new storage ring, but also for the entire light source community and the scientists who will make use of the brighter beams for decades to come to positively impact science and society.” — Laurent Chapon, director of the APS

“The new APS electron storage ring was designed to deliver the lowest possible emittance for a facility of this size,” said Michael Borland, associate director of the Accelerator Systems Division at the APS and one of the visionaries behind the upgraded design. ​“It relies on several never-before-used ideas: reverse-bending magnets and a novel method of replenishing electrons in the ring.”

Emittance refers to the size and angular spread of the electron beam, a key factor in determining the brightness of X-ray light. Lower emittance means the electron beam is more tightly packed, leading to brighter, more focused X-rays for scientific research.

The recent 33 pm.rad measurement surpasses the previous world record of 134 pm.rad held by the European Synchrotron Radiation Facility’s Extremely Brilliant Source. Earlier APS measurements had already broken that record, with a horizontal emittance of 45 pm.rad at 50 milliamps of beam current. The updated 33 pm.rad figure underscores the facility’s unprecedented capabilities.

The APS upgrade included the installation of a completely new electron storage ring, replacing the original that operated for over 25 years. The new design incorporates advanced features such as reverse-bending magnets and a novel top-up injection scheme to replenish electrons, making it the most advanced of its kind for a facility of this scale.

“This is a significant achievement,” said Laurent Chapon, Argonne associate laboratory director for Photon Sciences and director of the APS. “ We have a beautiful source, as one of our scientists told me right after the measurement. It’s exciting not just for our team, who worked hard to imagine, design, engineer, build and commission the new storage ring, but also for the entire light source community and the scientists who will make use of the brighter beams for decades to come to positively impact science and society.”

Direct measurement of the beam’s emittance is highly challenging due to the electron beam’s minuscule size. APS scientists used high-precision X-ray diagnostics at beamlines 29-ID and 3-ID-B to characterize the beam’s properties during normal operations.

The facility has already resumed hosting its first external user experiments, with more beamlines coming online throughout 2025. More than 5,000 researchers use the APS each year, leveraging its intense X-ray beams to advance fields such as energy storage, microelectronics, quantum materials and medicine.

“It’s thrilling to see it all come together,” said Borland. ​“To go from an idea to a design to a fully functioning storage ring, and then to see a world-leading emittance measurement, is simply unbeatable. We’re all looking forward to what the scientific community will do with these remarkable new capabilities.”