Absorbed Radiation Doses on the European XFEL Undulator Systems During Early User Experiments

The European XFEL GmbH (EuXFEL) is a FEL userfacility based on a superconducting accelerator with highduty cycle. Three movable gap SASE Undulator Systems using hybrid NdFeB permanent magnet segments are in operation. We observed in a dedicated diagnostic undulator for radiation damage doses up to 4 kGy and 3% demagnetization effect during the commissioning phase. In this work we present characteristics of the absorbed radiation doses in undulators during photon beam delivery for users. Lower absorbed doses are measured since the startof user operation. While ramping up electron beam parameters and repetition rates, individual segments located at the downstream end of the SASE systems show persistent absorbed doses which are proportional to the transmitted charge. In addition, the dose per charge ratio shows photon energy dependence. Portable magnetic flux measurement systems allow in-situ tunnel assessment of undulator magnetic properties in order to estimate radiation dose limits for future user operation