Novel experimental setup for MHz X-ray diffraction in the Diamond Anvil Cell at the High Energy Density (HED) Instrument of the European X-ray Free Electron Laser

The high-precision X-ray diffraction setup for work with 60 Diamond Anvil Cells (DACs) in Interaction Chamber 2 (IC2) of the High Energy Density Instrument of the European XFEL is described. This includes beamline optics, sample positioning and detector systems located in the multipurpose vacuum chamber. Concepts for pump-probe X-ray diffraction experiments in the DAC are described and their implementation demonstrated during the 1st User Community Assisted Commissioning experiment. X-ray heating and diffraction of Bi under pressure, using 20 fs X-ray pulses at 17.8 keV and 2.2 MHz repetition, is illustrated through splitting of diffraction peaks and interpreted employing finite element modeling of the sample chamber in the DAC.