Exploiting the European XFEL for a New Generation of High Energy Density and Materials Science

X射线自由电子激光(XFEL)产生准单色、高度相干、低于100秒的X射线脉冲，比任何同步加速器都亮10亿倍。美国的LCLS XFEL于2009年首次激光发射，那里的研究从根本上改变了X射线衍射、光谱和成像的使用方式，提供了探测和理解原子长度和时间尺度上的物质动力学的能力。来自XFELs的超短x射线脉冲长度意味着，它们非常适合对仅存在几十亿秒的物质的极端状态进行详细的x射线散射研究。但LCLS的进展一直受到LCLS相对较低的重复率以及用于创建短寿命状态的光学激光器的质量和重复率的限制。因此，尽管LCLS的申请者在过去5年中展示了XFELs的转型能力，但进展有限。位于汉堡的欧洲X射线自由电子激光器(EXFEL)于2017年9月开始运行，并以前所未有的重复频率产生高能X射线。此外，将于2019年安装在EXFEL的英国提供的偶极二极管泵浦光学激光器将大大优于LCLS同等设备，具有5倍于LCLS的能量，2000倍的重复频率，以及根据需要实时改变激光脉冲形状的能力。为开发北京国际机场在EXFEL项目中投资的3000万GB资金，STFC和EPSRC在偶极项目中投资了800万GB，以及GB 3M pa。考虑到英国对EXFEL运行成本的贡献，我们召集了一支由英国领先的XFEL和高压科学研究人员组成的团队，目的是将EXFEL和偶极技术结合起来，对高能量密度的固体、液体和亚稳定相进行变革性的X射线散射研究。我们的目标是了解不同相物质的非常复杂的性质是如何从原子或电子成分的关联中出现的，以及如何控制和调整这些性质，以便亚稳态可能恢复到环境条件下，从而导致一个具有广泛实际应用的全新领域。

X-ray free electron lasers (XFELs) produce quasi-monochromatic, highly-coherent, sub-100-fsec pulses of x-rays that are a billion times brighter than any synchrotron. The LCLS XFEL in the USA first lased in 2009, and research there is fundamentally changing how x-ray diffraction, spectroscopy and imaging are used by providing the ability to probe and understand the dynamics of matter on atomic length- and time-scales. The ultra-short x-ray pulse lengths from XFELs mean that they are ideal for making detailed x-ray scattering studies of extreme states of matter that exist for only a few billionths of a second. But progress at the LCLS has been constrained by the relatively low repetition rate of the LCLS, and the quality and repetition rate of the optical lasers used to create the short-lived states. As a result, while the transformative capabilities of XFELs have been demonstrated by the applicants at the LCLS over the last 5 years, progress has been limited.The European x-ray free electron laser (EXFEL) in Hamburg commenced operations in Sept 2017, and produces high-energy x-rays at unprecedented repetition rates. Furthermore, the UK-supplied DiPOLE diode-pumped optical laser that will be installed at EXFEL in 2019 will be vastly superior to the LCLS equivalent, having 5 times the energy, 2000 times the repetition rate, and the ability to change the laser pulse shape as required in real time. To exploit the £30M capital being invested by BEIS in the EXFEL project, the £8M invested by STFC and EPSRC in DiPOLE, and the £3M pa. UK contribution to EXFEL running costs, we have brought together a team of the leading UK researchers in XFEL and high-pressure science with the aim of combining EXFEL and DiPOLE to make transformative x-ray scattering studies of high energy density solids and liquids and metastable phases. We aim to understand how the remarkably complex properties of different phases of matter emerge from the correlations of the atomic or electronic constituents, and how to control and tailor these properties so that metastable states might be recovered to ambient conditions, leading to a whole new field with a gamut of practical applications.