Experimental study of planetary ices at high pressure using dynamically-driven diamond-anvil cells

行星冰化合物（例如H2O， CH4, NH3）构成了太阳巨冰行星的大部分，并且可能在最近发现的系外行星内部大量存在。在行星内部的压力和温度条件下，这些化合物的物理性质和相图尚不清楚。先前在静态金刚石砧细胞中使用x射线衍射的实验研究仅限于相对较低的压力，因为实验困难与这些低z化合物的散射效率小以及与样品材料反应导致的高压细胞减弱有关。在这项研究中，我们将采用最近开发的动态驱动金刚石砧细胞（dDAC和mDAC）在短时间尺度（毫秒到秒）内压缩行星冰化合物。快速压缩将防止化学反应，并将允许达到以前无法通过实验获得的压力。在压缩过程中，我们将用x射线衍射探测样品，研究它们的结构、相稳定性和状态方程。随着新型超高速探测器的发展，这种快速衍射实验直到最近才成为可能。初始实验将在PETRA III， DESY的极端条件光束线上进行。在项目过程中，我们将开始在欧洲XFEL的高能量密度仪器上进行实验，该仪器将于2018年向用户开放。我们的实验结果将为太阳系巨冰行星和系外行星内部的行星冰化合物的稳定场和物理性质提供新的见解。结果还将提供关键的锚点来约束计算预测（在SP3中进行），并作为模拟行星动力学的大规模数值模型的输入参数（与SP4/SP5合作）。

Planetary ice compounds (e.g. H2O, CH4, NH3) constitute large parts of solar giant ice planets and are likely abundant in the interiors of recently discovered exoplanets. The physical properties and phase diagrams of these compounds at the pressure and temperature conditions of planetary interiors are poorly understood. Previous experimental studies using x-ray diffraction in static diamond-anvil cells were limited to comparably low pressures as a result of experimental dfficulties related to the small scattering effciency of these low-Z compounds and weakening of the high-pressure cell resulting from reactions with the sample materials. In the proposed research, we will employ recently developed dynamically-driven diamond-anvil cells (dDAC and mDAC) to compress planetary ice compounds on short time scales (milliseconds to seconds). The rapid compression will prevent chemical reactions and will allow for reaching pressures that were previously not accessibly by experiments. During compression, we will probe the samples by x-ray diffraction to study their structure, phase stability and equations of state. Such fast diffraction experiments have only recently become possible with the development of new superfast detectors. Initial experiments will be performed at the Extreme Conditions Beamline at PETRA III, DESY. During the course of the project, we will start performing experiments at the High Energy Density instrument at the European XFEL that will become available to users in 2018. The results of our experiments will provide new insights to the stability felds and physical properties of planetary ice compounds in the interiors of solar giant ice planets and exoplanets. The results will also provide key anchor points to constrain computational predictions (carried out in SP3) and serve as input parameters for large-scale numerical models to simulate the dynamics of planets (collaboration with SP4/SP5).