The Advanced Photon Source (APS) at Argonne National Laboratory is a storage-ring-based high-energy X-ray light source facility. It is one of five X-ray light sources owned and funded by the U.S. Department of Energy Office of Science. The APS began operation on March 26, 1995. It is operated as a user facility, meaning that it is open to the world’s scientific community, and more than 5,500 researchers make use of its resources each year.