The European XFEL: new scientific opportunities and first results

In the past decade we have seen very important developments in the field of accelerator based X-ray user facilities, with the advent of 4^th generation synchrotron sources and MHz rate hard X-ray free electron lasers (FEL).  Among the latter, the EuXFEL is the first hard XFEL powered by a superconducting linear accelerator, which enables MHz rate pulse generation, leading to an increase of more than 2 orders of magnitude in the number of delivered photon pulses per second to the sample. A unique feature of X-ray FELs is the combination of the extremely short (fs) photon pulses with the short (Ȧ) wavelengths of hard x-rays produced. These new user facilities are opening novel avenues in the investigation of fundamental processes in many areas of science, from physics to chemistry, biology and materials science, because they allow investigation of matter at the time scales of electron and nuclear dynamics (down to fs), with chemical selectivity and bulk sensitivity.

After many years of construction, user operation at the EuXFEL has finally begun. All the accelerator design parameters have been achieved, and between the fall of 2017 and summer 2019, six instruments started user operation. Applications address fundamental processes of light-matter interaction. ultra-fast dynamic processes in liquids and solids, investigation of electronic and structural properties and their dynamics in biomolecules, nanostructures, disordered materials and high energy density states of matter.

In this talk I will first briefly introduce the present performance of the facility in terms of electron and photon beam characteristics and operation modes. I will then report first results from early user experiments, and comment on some important challenges ahead.