The implementation and further improvements of superconducting undulators is part of the European XFEL facility development program. Within this program, a magnetic field test facility is being developed. Named SUNDAE2 (Superconducting UNDulAtor Experiment 2), it aims to perform in-vacuum magnetic field measurements of superconducting undulators (SCUs) with three techniques: Hall probe, moving wire, and pulsed wire. This contribution presents the updates and status of SUNDAE2.

The energy loss of the electron beam due to synchrotron radiation and wakefields determines an undulator tapering in order to keep the resonance condition along the undulator. The contribution of synchrotron radiation to energy loss can be calculated analytically, whereas the calculation of wakefield energy loss requires knowledge of the beam current profile and the wakefield function at the undulator section. We present an experimental method for accurate measurement of the energy loss due to wakefields in the undulator section for the European XFEL. We compare the results of the measurements with earlier developed analytical model of the wakefunction.

A cavity based free-electron laser (CBXFEL) is a next generation X-ray source promising radiation with full three-dimensional coherence, nearly constant pulse to pulse stability and more than an order of magnitude higher spectral flux compared to SASE FELs. In this contribution, an R&D project for installation of a CBXFEL demonstrator experiment at the European XFEL facility is conceptually presented. It is composed of an X-ray cavity design in backscattering geometry of 133 m round trip length with four undulator sections of 20 m total length producing the FEL radiation. It uses cryocooled diamond crystals and employs the concept of retroreflection to reduce the sensitivity to vibrations. Start to end simulations were carried out which account for realistic electron bunch distributions, inter RF-pulse bunch fluctuations, various possible errors of the X-ray optics as well as the impact of heat load on the diamond crystals. The current state of the project shall be presented in this contribution.