Fresh-slice lasing using wakefield induced time-dependent orbit oscillation is capable of producing high intensity two-color XFEL pulses and high power short pulses at femtosecond level. At the European XFEL, a corrugated structure system for fresh-slice applications for both the hard x-ray beamline SASE1 and the soft x-ray SASE3 beamline is being developed and implemented. In this contribution, we present the novel design of the corrugated structure and the application to advanced lasing schemes.

Phase-locked pulses are important for coherent control experiments. Here we present theoretical analyses and start-to-end simulation results for the generation of phase-locked pulses using the Hard X-ray Self-Seeding (HXRSS) system at the European XFEL. As proposed in Ref. [1], the method is based on a combination of self-seeding and fresh-slice lasing techniques. However, at variance with Ref. [1], here we exploit different transverse centroid offsets along the electron beam. In this way we may first utilize part of the electron beam to produce SASE radiation, to be filtered as seed and then generate HXRSS pulses from other parts of the beam applying appropriate transverse kicks. The final result consists in coherent radiation pulses with fixed phase difference and tunable time delay within the bunch length. This scheme should be useful for applications such as coherent x-ray pump-probe experiments.

Recently, Hard x-ray self-seeding (HXRSS) operations at the European X-ray free-electron laser (EuXFEL) opened a pathway towards the application of pulses with high spectral density (in terms of ph/eV per pulse) in the fields of applied physics, chemistry and biology, where the coherent radiation spectrum is essential. The spectrum of hard x-ray self seeding pulses is generally accompanied by a pedestal around the central seeded photon energy. The pedestal contains two separate components: normal self-amplified spontaneous (SASE) and sideband emissions that can be ascribed to long-wavelength modulations of the electron beam. The pedestal limits the spectral purity and can impact some user applications. In this report, we analyze the purity of HXRSS pulses in the presence of microbunching instability. We look at the spectral contents after and before saturation, and display the contribution of the pedestal in the HXRSS spectrum.

The undulators in the European XFEL are made of permanent magnets that need to be protected from beam losses that could cause demagnetisation. Under current operating conditions, beam losses in the undulators are prevented by a collimation section downstream of the main Linac and upstream of the switchyard. In the future, a slotted foil may be installed in the European XFEL to reduce the X-ray pulse length; however, the insertion of the foil will spoil the emittance of most of the bunch which increases the probability of particles scraping the collimator and continuing to be transported to the undulator section. In this paper, we report a study to assess the level of the beam losses in the undulators in the European XFEL that would be caused by a slotted foil, and to determine the optimal apertures to use in the collimators to minimise the losses. We also assess whether shielding or an additional collimator in front of the undulator could be added to the beamline to prevent the losses.

Ultra-short X-ray pulses in an XFEL can be generated by means of a slotted foil inserted into a bunch compressor. There is an ongoing study into whether such a technique could be used at the European XFEL. One important factor that must be considered is whether the additional beam losses and radiation load caused by the foil is acceptable with a high repetition rate of up to 4.5MHz at the European XFEL. As there is currently no foil implemented in the European XFEL, experimental investigations were carried out by inserting a screen in the bunch compressor at the location where a foil would be inserted. Simulations have been performed using BDSIM to study losses caused by the insertion of the foil. Neutron radiation measurements and beam loss monitor readings were taken and compared with the simulations to provide validation and calibration of the simulations for the case of a slotted foil.