We propose a computationally efficient algorithm to calculate a single statistical realization of partially coherent synchrotron radiation fields at a given frequency. The proposed algorithm relies on a method for simulating Gaussian random fields. We cross-checked the algorithm’s consistency with other well-established approaches, and, in addition, we show its advantage in terms of computational efficiency. The algorithm exploits the assumption of quasi-homogeneity of the source. However, we show that it is applicable with reasonable accuracy outside of this assumption. This algorithm can be extended to other types of sources that follow Gaussian statistics beyond the assumption of the quasi-homogeneity. Finally, the demonstration of the algorithm is well-suited for educational purposes.

The Hard X-ray Self-seeding system at the European XFEL started to be available for user delivery in summer 2021. A large number of user requests of HXRSS showed the interest and the importance of longitudinally coherent X-ray FEL pulses with narrow bandwidth for different applications. In this paper, we will summarize user requirements, tuning procedures and performance we achieved during user delivery.

We study THz radiation generation from a few-periods magnetic device for THz pump – x-ray probe experiments at the European XFEL, or at other facilities like the LCLS-II. We compute THz radiation accounting for the boundary conditions imposed by a vacuum pipe. Calculations were performed for a single-period magnetic device as well as for a nine-period one. We address the problem of modes matching when entering the iris line and the final radiation distribution at the sample. With the help of wavefront propagation techniques, we simulate the propagation of THz radiation in an overmoded iris line downstream to the users’ sample.

We review the theory of optical klystrons with SASE FEL applications in mind. Previous theories miss terms in the power gain factor that cannot be neglected, and we illustrate differences between the previously known analytical expressions, new ones discussed here, and numerical calculations. We then consider the use of optical klystrons for electron energy-spread and radiation coherence-time diagnostics purposes.