The upgraded Advanced Photon Source (APS) has achieved another key performance goal, reaching its full design beam current of 200 milliamps (mA). 

The APS, a U.S. Department of Energy (DOE) Office of Science user facility at DOE’s Argonne National Laboratory, is in the final stages of a comprehensive upgrade. Central to that upgrade was the installation of a new electron storage ring, which circulates electrons at nearly the speed of light, generating ultrabright X-ray beams for scientific experiments. 

The beam current is a measurement of the number of electrons circulating in the storage ring at any given time. Higher current means brighter and more intense X-ray beams – in the case of the upgraded APS, up to 500 times brighter than the previous storage ring. Brighter beams will facilitate experiments at scales previously impossible with X-rays.

The APS accelerator team has been ramping up to 200 mA since April 2024, when electron beams were first stored in the upgraded APS storage ring. On February 4, 2025, the team first reached the 200 mA target and the APS is now running at this current for user operations. 

“Bringing this extraordinary new accelerator up to 200 mA has been a wonderful challenge,” said Michael Borland, associate director of the Accelerator Systems Division. “We are excited to provide the best and brightest beams in the world for our user community.”

The APS is in the midst of the first general user run of 2025, with early experiments happening at several beamlines. More beamlines will be brought online in the coming months. Follow the progress at the APS Upgrade web page.