High-resolution inelastic x-ray scattering in warm dense matter

该项目旨在通过高分辨率非弹性X射线散射确定温暖致密物质中的低频结构动力学。我们共同开发（a）在高能量密度仪器在欧洲XFEL公司在Schenefeld（EuXFEL）和（B）的实验平台所需的理论框架，通过使用密度泛函理论分子动力学模拟（DFT-MD）在U罗斯托克。在本项目中，我们处理铝和铁。这两种材料在极端条件下的行为非常有趣，但对于我们的目的来说是特定的。首先，我们研究了简单的金属Al，这是实验和理论上很好地管理，使许多数据的结构，热力学，运输光学性质存在的固体和液体状态。本项目将把这套数据集扩展到温暖的稠密物质区。基于对Al的基准研究，我们将在与地球物理学（地球的固体内核和液体外核）以及行星物理学（超级地球）相关的极端条件下处理Fe。温暖的致密物质的特征是温度低至几eV，密度高（凝聚态和更高），压力高（几Mbar）。这样的等离子体参数通过例如，用强光激光脉冲照射靶，从2022年起，EuXFEL将提供DiPOLE-100 X激光器（< 100 J，< 15 ns）。这些高度瞬态激发态，然后将探测明亮的，超短脉冲与几毫电子伏的光谱带宽从EuXFEL。由于实验将允许几赫兹的重复频率，预期数据的质量远远超出了目前的能力，因此将获得对温暖致密物质，特别是Al和Fe的结构和动力学的新见解。同时，X射线光谱将通过使用DFT-MD模拟计算热致密物质（Al和Fe）的动力学结构因子来确定。将实验数据与广义流体动力学模型进行比较，最终使我们能够第一次直接提取热致密物质极端条件下的离子温度、声速、热导率和粘度。特别是，铁的结果将是必不可少的天体物理学和行星物理学，并将允许新的洞察过程中的固体内部和液体外核的地球。此外，新数据还将允许对超级地球的内部结构和演化的当前模型进行基准测试，除了迷你海王星之外，这是最丰富的系外行星。

The project aims at determining low-frequency structural dynamics in warm dense matter by highly resolved inelastic x-ray scattering. We jointly develop (a) the experimental platform at the High-Energy Density instrument at the European XFEL GmbH in Schenefeld (EuXFEL) and (b) the required theoretical framework by using density functional theory molecular dynamics simulations (DFT-MD) at the U Rostock. We treat Al and Fe in this project. The behavior of both materials under extreme conditions is of high interest but specific for our purposes. First, we investigate the simple metal Al which is experimentally and theoretically well manageable so that many data on the structural, thermodynamic, transport an optcial properties exist both for the solid and liquid state. This data set will be extended to the warm dense matter region in this project. Based on this benchmark study for Al we will treat Fe under such extreme conditions which are relevant for geophysics (solid inner and liquid outer core of Earth) as well as forplanetary physics (super-Earths). Warm dense matter is characterized by temperatures of few eV, high densities (condensed matter and beyond) and pressures (several Mbar). Such plasma parameters are generated by, e.g., irradiating the target with intense optical laser pulses for which the DiPOLE-100X laser will be availbale at EuXFEL (< 100 J, < 15 ns) from 2022 onwards. These highly transient excited states will then be probed by bright, ultrashort pulses with few meV spectra bandwidth from the EuXFEL. Since the experiments will allow for repetition rates of several Hz, the quality of the expected data goes far beyond current capabilities so that new insight in the structure and dynamics of warm dense matter, in particular of Al and Fe, will be gained. Simultaneously, the x-ray spectra will be determined by calculating the dynamic structure factor of warm dense matter (Al and Fe) by using DFT-MD simulations. Comparing the experimental data with a generalized hydrodynamic model finally allows us for the first time to directly extract the ion temperature, sound speed, thermal conductivity and viscosity for the extreme conditions of warm dense matter. In particular, the results for Fe will be essential for geophysics and planetary physics and will allow new insight in processes in the solid inner and liquid outer core of Earth. Furthermore, the new data will also allow to benchmark current models for the interior structure and evolution of super-Earths, besides mini-Neptunes the most abundant class of exoplanets.