Forcat Oller, S. Feng, Y. Krzywiński, J. Ortiz, E. Rowen, M. Wang, H. JACoW Publishing Geneva, Switzerland 978-3-95450-207-3 10.18429/JACoW-MEDSI2018-THPH11 English 358-360 THPH11 photon FEL linac undulator laser Contribution to a conference proceedings 2018 2018-12 https://doi.org/10.18429/JACoW-MEDSI2018-THPH11 http://jacow.org/medsi2018/papers/thph11.pdf The unique capabilities of LCLS, the world's first hard X-ray FEL, have had significant impact on advancing our understanding across a broad range of science. LCLS-II, a major upgrade of LCLS, is being developed as a high-repetition rate X-ray laser with two simultaneously operating FELs. It features a 4 GeV continuous wave superconducting Linac capable of producing ultrafast X-ray laser pulses at a repetition rate up to 1 MHz and energy range from 0.25 to 5 keV. The LCLS-II upgrade is an enormous engineering challenge not only on the accelerator side but also for safety, machine protection devices and diagnostic units. A major part of the beam containment is covered by the FEL beam collimators. The current collimator design is no longer suitable for the high power densities of the upcoming LCLS-II beam. Therefore, a complete new design has been conceived to satisfy this new constrains. Moreover, a special FEL miss-steering detection system based on a photo diodes array has been designed as an integral part of the photon collimator as additional safety feature. This poster describes the new LCLS-II FEL Collimators, their mechanical design and challenges encountered.