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European XFEL is investing in the development of superconducting undulators (SCUs) for future upgrade of its beamlines. SCUs made of NbTi, working at 2 K, with a period length of 15 mm and a vacuum gap of 5 mm allow covering a range between 54 keV and 100 keV. The effect of mechanical errors in the distribution of the undulator parameter K along the undulators is more relevant for working points at lower photon energy, which are obtained using a higher magnetic field in the undulator. In this article we investigate the effect of error distribution in the K-parameter for a working point at 50 keV photon energy obtained injecting an electron beam with 16.5 GeV energy from the XFEL linear accelerator in a undulator line composed by SCUs with 1.6 T peak magnetic field.

European XFEL is a multi-beamline x-ray free-electron laser (FEL) user facility driven by a superconducting accelerator with a nominal photon energy range from 250 eV to 25 keV. An afterburner undulator based on superconducting undulator technology is currently being investigated to enable extension of the photon energy range towards harder x-rays. This afterburner undulator would be installed downstream of the already operating SASE2 FEL beamline, emitting at the fundamental or at a harmonic of the upstream undulator system. In this contribution we describe the layout under study and present numerical simulations.

We propose to develop, characterize and operate a superconducting undulator (SCU) afterburner consisting of 5 undulator modules (1 module = 2 SCU coils of 2 m length and 1 phase shifter) plus a pre-series prototype at the SASE2 hard X-ray beamline of European XFEL. This afterburner will produce an output in the order of 1010ph/pulse at photon energies above 30 keV. The project is divided into the production of a pre-series prototype module and a small-series production of 5 modules. Central goals of this R&D activity are: the demonstration of the functionality of SCUs at an X-ray FEL, the set up of the needed infrastructure to characterize and operate SCUs, the industrialization of such undulators, and the reduction of the price per module. In this contribution, the main parameters and specifications of the pre-series prototype module are described.