Anton, J.W.J. Chu, M. Jiang, Z. Narayanan, S. Shu, D. Strzalka, J. Wang, J. JACoW Publishing Geneva, Switzerland 2673-5520 978-3-95450-229-5 10.18429/JACoW-MEDSI2020-TUPC09 English 196-198 photon alignment detector laser scattering Contribution to a conference proceedings 2021 2021-10 https://doi.org/10.18429/JACoW-MEDSI2020-TUPC09 https://jacow.org/medsi2020/papers/tupc09.pdf As part of the Advanced Photon Source Upgrade (APS-U) project, the Coherent Surface Scattering Imaging (CSSI) [1] instrument is currently being developed. One of the most important components of the CSSI instrument at the 9-ID beamline of the APS-U, the Kirkpatrick-Baez (K-B) mirror system, will focus hard X-rays to a diffrac-tion-limited size of 500 nanometers at a working distance of 550 mm. High angular stability (19 nrad for the hori-zontal mirror and 14 nrad for the vertical mirror) is speci-fied no just for the focused beamsize but, more important-ly, to ensure the beam stability at the detector position that is up to 24 m from the K-B mirrors. A large sample-to-detector distance (up to 23 m), one of the beamline’s unique features for achieving a sufficient coherent-imaging spatial oversampling, requires sample angular stability of 50 nrad. In CSSI scattering geometry, the vertically placed sample reflects X-rays in the horizontal direction at an extremely shallow angle. The design in-cludes two high-precision rotary stages for sample pitch (vertical axis) and yaw (horizontal axis). The current design of instrument’s nano-positioning stages [2] and metrology required to satisfy the stability and positioning requirements are discussed in this paper.