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

行星冰化合物（如H2O，CH 4，NH3）构成了太阳系巨冰行星的大部分，并且可能在最近发现的小型海王星系外行星的内部丰富。然而，它们在相关条件下（>100 GPa和2000 K）的物理性质知之甚少。以前在金刚石对顶砧单元（DAC）中的X射线衍射研究受到这些低Z化合物的小散射效率及其与金刚石砧的反应性的限制。这些缺点可以通过使用动态驱动DAC在短时间尺度（毫秒至秒）上压缩样本来避免。在子项目SP 9中，我们将利用DAC中冰相快速压缩研究的新功能，以及PETRA III和欧洲XFEL在FOR 2440期间实施的时间分辨X射线衍射诊断，以研究H2O-NH3系统中冰的行为。在150 GPa和5000 K下，我们将具体确定H2O、NH3和H2O-NH3冰的稳定性、结构和状态方程。初始实验将在PETRA III进行，采用FOR 2440期间委托的电阻加热动态驱动DAC。为了达到超离子冰相的高温条件（>2000$ K），我们将结合联合收割机在PETRA III的传统激光加热实验与连续EuXFEL脉冲（与SP 7合作）的样品的X射线加热的新方法。实验结果将提供新的锚点，以约束计算预测（与SP3合作），并作为大规模数值模型的输入参数，以约束系外行星的内部结构和动力学（与SP 5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 mini-Neptune exoplanets. Yet, their physical properties are poorly understood at relevant conditions (>100 GPa and 2000 K). Previous X-ray diffraction studies in diamond anvil cells (DAC) have been limited by the small scattering efficiency of these low-Z compounds and their reactivity with the diamond anvils. These shortcomings can be avoided by compressing the sample on short time scales (miliseconds to seconds) using dynamically-driven DACs. In subproject SP9, we will take advantage of new capabilities for fast compression studies of ice phases in DACs coupled with time-resolved X-ray diffraction diagnostics implemented at PETRA III and the European XFEL during FOR2440, to investigate the behavior of ices in the H2O-NH3 system. We will specifically determine the stability, structure and equations of state of H2O, NH3 and H2O-NH3 ices up to 150GPa and 5000 K. Initial experiments will be performed at PETRA III employing resistive heated dynamically-driven DACs commissioned during FOR2440. To reach the high temperature conditions of the superionic ice phases (>2000$ K), we will combine conventional laser heating experiments at PETRA III with a novel approach for X-ray heating of the sample with consecutive EuXFEL pulses (in collaboration with SP7). The experimental results will provide new anchor points to constrain computational predictions (in collaboration with SP3) and serve as input parameters for large-scale numerical models to constrain the internal structure and dynamics of exoplanets (in collaboration with SP5).