Wang, H. Feng, Y. Forcat Oller, S. Krzywiński, J. Ortiz, E. Rowen, M. JACoW Publishing Geneva, Switzerland 978-3-95450-207-3 10.18429/JACoW-MEDSI2018-TUPH39 English 133-135 TUPH39 photon FEL synchrotron experiment operation Contribution to a conference proceedings 2018 2018-12 https://doi.org/10.18429/JACoW-MEDSI2018-TUPH39 http://jacow.org/medsi2018/papers/tuph39.pdf LCLS-II will produce very powerful photon beams. Unlike conventional synchrotrons, the LCLS-II beam containment components withstand not only the high average beam power and power density, but also the instantaneous thermal shocks from pulsed FEL beam, which can reach ~9mJ/pulse. With beam repetition rate up to 1MHz, regular metal based beam collimators and absorbers will no longer work, because of the likelihood of fatigue failure. And because of the poor thermal conductivity, the old LCLS B4C based absorber would need very shallow glancing angle and take valuable beamline space. Hence, a low-Z and high thermal conductivity CVD diamond based photon beam collimator and absorber systems have been developed in LCSL-II. The initial damage tests using LCLS FEL beam provided positive results that graphite coated CVD diamond can endure per pulse dose level to ~0.5eV/atom. For the beamline and personnel safety, in addition to the passive CVD diamond collimators and absorbers, newly developed photon diode beam mis-steer detection systems and conventional SLAC pressurized burnt-through monitors have been also introduced in the photon beamline system design.