Dynamic Warm Dense Matter Research
Warm Dense Matter (WDM), i.e. the transition regime between solids or liquids and hot plasmas is present in the interiors of many celestial bodies like planets and stars, but also plays a major role in modern laboratory applications like synthesis of new materials, intense laser-matter interaction, fusion research, and many more.
The controlled creation and even more the precise diagnosis of dynamic processes in WDM is extremely challenging. High-quality experiments require homogeneous samples, extreme temporal resolution and need to cover a broad parameter space. Since WDM samples are usually opaque for optical light, most brilliant X-ray sources are required for high-quality experiments. For a complete characterization, “over-diagnosis”, i. e. determining the same observable with different methods at the same time, is highly desirable, since most methods to determine WDM quantities are based on assumptions or require sophisticated theoretical models. This is especially true for measurements in non-equilibrium conditions. The combination of X-ray free electron lasers with high-energy/high-power optical lasers has shown to be capable of WDM experiments of unprecedented quality in terms of precision and time resolution. The HED experimental area at European XFEL equipped with HIBEF will set new standards here.
Various schemes of pump-probe experiments will be possible, including isochoric heating by the XFEL itself, laser-driven electrons or ions as well as laser-driven shock compression. In this way, dynamic processes can be studied over a broad WDM parameter space. Furthermore, the outstanding properties of the XFEL beam (high photon numbers, ultra-short pulse duration, small bandwidth) will allow for determining relevant quantities in different ways: e.g. electron temperature by noncollective X-ray Thomson scattering (XRTS), absorption and emission spectroscopy, ion temperature by collective and non-collective XRTS and diffraction, density by diffraction, and collective XRTS, Ion correlations by diffraction and non-collective XRTS, electronic structure by collective XRTS, emission and absorption spectroscopy.