Status of radiation damage on the European XFEL undulator systems

The European XFEL GmbH is a new X-ray FEL user facility and started lasing in 2017. Three movable gap SASE Undulator Systems based on hybrid NdFeB permanent magnet technology were built. Radiation damage due to machine operation affects the magnetic properties of the segments and the quality of the SASE process. Dosimeters monitor the absorbed doses in every undulator segment and each SASE system is equipped with a diagnostic undulator (DU). We report on the profile of the absorbed doses seen in the first year of the Undulator Systems operation. Magnetic field degradation higher than 3.5% in the DU is found and associated to absorbed doses up to 4.4 kGy. An initial limit of 55 Gy for the 5-m undulator segments is recommended based on the precise K-parameter determination for beam operation. (paper)