Development and operation of fiber-based radiation protection beam-loss monitor for PAL-XFEL

Beam loss monitor using a long optical fiber has been developed and operated for radiation protection in PAL-XFEL, which is an X-ray free electron laser facility using 11 GeV electron beams. The relationship between the beam loss point and the arrival time of Cherenkov light from the loss point to the upstream photo-multiplier tube was confirmed to be 0.12 m/ns, and the maximum fiber length considering the position resolution was determined to be 150 m. The applicability of the beam loss monitor in the aspect of the radiation protection was evaluated by the comparison of the amplitude of attenuation-corrected loss signal and the dose outside the tunnel. The method was proposed to interlock the accelerator operation by monitoring the beam loss and applying a trip threshold at a specific narrow range of locations to ensure the safety of experimental area located in the beam direction.