Beam loss study for the implementation of corrugated structure at the European XFEL

The European XFEL is a free-electron laser facility based on superconducting linac with high repetition rate of up to 4.5 MHz. A corrugated structure is planned to be installed in front of the SASE beam line at the European XFEL, which can be used as a kicker for fresh-slice schemes or a dechirper to control the bandwidth of SASE radiation. When the beam passes through the corrugated structure module, strong longitudinal and transverse wakefields can be excited to introduce a correlated energy chirp and/or a kick along the bunch. However, due to the relatively small gap of the corrugated structure, beam halo particles experience large betatron oscillations after hitting the corrugated structure, which can lead to energy deposition in the undulator beam line. This may cause demagnetization of the undulators especially at high repetition rate. For this reason, we have performed beam loss simulations using BDSIM for two different configurations: double-plate corrugated structure with nominal FODO optics and single-plate corrugated structure with small beta optics. Our simulation results showed that the latter configuration can help us not only to relax the tolerance on beam halo extension, but also to reduce the peak radiation doses by more than factor 2. Besides, the possibility of adding a collimator downstream of the corrugated structure has also been studied, which can further help us to reduce the loss in the downstream cells by factor 100.