New x-ray sources illuminate hidden corners of space and time -- revolutionary solid-state science and how we'll get there through the Advanced Photon Source upgrade

Third-generation x-ray storage ring sources have major impact in condensed-matter and materials physics. Many cutting-edge experiments, including nanoscale imaging and studies of fast dynamics, demand shorter and more spatially coherent x-ray pulses. Unfortunately, these parameters are intrinsically limited by the physics of storage rings. Many experiments at sources such as the Advanced Photon Source (APS) could benefit from revolutionary performance that is promised by fourth-generation capabilities. The key element which makes fourth-generation sources better in these respects is that the electron beam does not travel long enough (is not ``stored'') for the pulse to come to equilibrium. We are proposing to introduce such a beam into the APS storage ring through an Energy-Recovery LINAC concept, as part of a major upgrade. I will describe some of the research in condensed matter and materials physics which demand this upgrade, and outline the technical performance and our plans to realize the upgrade.