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

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.

Knowledge Impact: Our research will generate impact in the immediate scientific areas of high energy density physics, metastable materials and electronic structure calculations. Our research will also generate significant cross-disciplinary impact that will benefit chemists, physicists, and materials scientists studying short-lived phenomena and states. XFEL science is very different to synchrotron science, and we are particularly keen that our research will lead to growth of the UK XFEL research user community, thereby further leveraging the UK funding already committed to EXFEL and DiPOLE.

Economic Impact and IP: In the recent STFC Strategic Review of FELs, four fields of industrial research were identified as being ideally suited for study: Pharmaceuticals, Particulates and Pollution, Chemicals, and Engineering. IP generated by our research will find applications in the latter two fields. In Chemicals, the ability to probe material structure over very short timescales is applicable to the study of the basic aspects of catalytic mechanisms, and would be of great value to UK industry. And in Engineering, there is interest in following fast reactions in fuel-additive molecules, and in understanding deformation and phase transformation at very short timescales in advanced engineering materials operating at extremes of temperature and mechanical stress. It is in this last area of research that Rolls Royce are already active at the LCLS XFEL. In each of these areas, we will work with industrialists to help them identify where XFELs might provide transformative information.

People and Training: The scale of this project provides an excellent opportunity to train the next generation of researchers in a variety of state-of-the-art XFEL and laser experimental techniques, as well as computation and theoretical modelling. Each will benefit from the diverse range of techniques we will employ, and also from the range of working environments employed. PDRA 1 and 2 will be based in Hamburg for 6 months and will become highly trained in DiPOLE and EXFEL operations. This importance of this training aspect has been recognized by our Project Collaborator AWE who have funded a CASE studentship for the project. Each student and postdoc involved in the research will benefit from the diverse range of experimental and computational techniques we will employ, making them highly employable at facilities such as synchrotrons (ESRF-EBS & Diamond), XFELs, (EXFEL and LCLS), lasers (Vulcan, Orion) and also at government laboratories, including AWE.

Outreach: We plan two outreach programmes.

Researchers: The first will focus on colleagues in the synchrotron and laser/plasma-physics communities, many of whom have yet to fully appreciate how the transformative technology of XFELs can impact their research. Access to EXFEL will be extremely competitive, which works against first-time users. We will offer academic and industrial researchers access to our experiments so that they can see how they are performed, and the transformative data that can be obtained, thereby strengthening their chances of accessing EXFEL as PIs. Growth of the UK XFEL physical sciences user community - both academic and industrial - is a key outcome of our research.

Public: The project will impact on society through outreach activities aimed at explaining the exciting magnetic and electronic phenomena found in materials which have correlated electrons and dense electrons. Members of the public, high school students and prospective university students will be able to attend our Science Festivals and Open Days or participate in workshops aimed at de-mystifying the fundamental science in the project.