The experimental set-up
Contact: ulf.zastrau@xfel.eu
The High Energy Density (HED) instrument and the HIBEF consortium (Helmholtz International beamline for Extreme Fields) at European XFEL are dedicated to the study of matter at extreme conditions of temperature, pressure, and fields, which are generated by X-ray or optical laser excitation, high pressure cells, and pulsed magnets, respectively [1]. The combination of these drivers with hard X-rays delivered by European XFEL enable ground-breaking experiments reaching energy densities of 1011 J/m3 equivalent to pressures above 1 Megabar and field strengths in excess of 500T, relevant to fundamental laser matter interactions, planetary and stellar interiors, and impacts.
HED receives intense (>1012 ph/s), coherent hard X-rays in the range from 5-25keV in SASE and seeded operation. With its unique time structure, European XFEL delivers bursts of ultra-short (≤ 50fs) pulses in individual pulse trains with up to 4.5 MHz intra train repetition rates, making this an ideal source to probe transient conditions and to perform time-resolved experiments.
Figure 1 shows an overview of the HED instrument. The experiment hutch hosts two interaction chambers for a variety of experiments using X-ray diffraction, spectroscopy, and imaging techniques. Two large laser systems are installed in a laser bay on top of the experiment hutch: The ReLAX ultra-high intensity laser delivering up to 300TW in < 25fs pulses at 800nm, and the DiPOLE high energy laser delivering up to 60J at 515nm in pulses from 2-15ns for shock- and ramp-compression experiments.
The present study on recently discovered high-pressure phases of ice was performed in the interaction chamber 2, developed by HIBEF as a high throughput diffraction platform for high pressure experiments in diamond anvil cells [2], dynamic diamond anvil cells [3], and for dynamic laser compression experiments. These MHz time-resolved X-ray diffraction experiments on low-Z materials in diamond anvil cells have only recently become possible at the HED station of European XFEL. A special type of diamond anvil cell was employed for this study, in which the applied pressure could be rapidly varied on the millisecond- to second-scale by means of a piezoelectric actuator. In order to make efficient use of the beamtime, three of these cells were mounted on a revolver-type sample changer. Two different detectors were used to capture snapshots of the sample on different timescales: for ultimate time resolution, an AGIPD (Adaptive Gain Integrating Pixel Detector) detector resolves individual within each pulse-train by recording up to 352 images with MHz repetition rate, while a Varex flat panel detector provided gapless pictures with larger field of view at the 10 Hz train repetition rate of European XFEL.
HED experiment hutch with the two interaction chambers, the ReLAX, and the DiPOLE laser systems.
Interaction chamber 2, in which the dynamic compression experiments on water were performed.
[1] U. Zastrau et al. JSR 28, 1393 (2021)
[2] H.P. Liermann et al. JSR 28, 688 (2021)
[3] R.J. Husband et al. JSR 30, 671 (2023)