Carter, J.A. JACoW Publishing Geneva, Switzerland 978-3-95450-207-3 10.18429/JACoW-MEDSI2018-THOAMA05 English 312-315 THOAMA05 vacuum storage-ring lattice photon radiation Contribution to a conference proceedings 2018 2018-12 https://doi.org/10.18429/JACoW-MEDSI2018-THOAMA05 http://jacow.org/medsi2018/papers/thoama05.pdf The APS-Upgrade project will build a diffraction lim-ited storage ring requiring a vacuum system design with small aperture vacuum chambers passing through narrow magnet poles. The small apertures dictate that the walls of the vacuum chambers act as distributed photon ab-sorbers. The vacuum chambers must be designed robustly so a thorough understanding of the synchrotron ray trac-ing with beam missteering is required. A MatLab program has been developed to investigate 3D ray tracing with beam missteering. The program dis-cretizes local phase spaces of deviation possibilities along the beam path in both the horizontal and vertical planes of motion and then projects rays within a 3D mod-el of the vacuum system. The 3D model contains ele-ments in sequence along the beam path which represent both chamber segments and photon absorbers. Ray strikes are evaluated for multiple worst-case criteria such as local power intensity or strike offset from cooling channels. The worst case results are plotted and used as boundary conditions for vacuum chamber ther-mal/structural analyses. The results have also helped inform decisions about practical beam position limits.