X-ray free-electron lasers (XFELs) are the most brilliant sources of x-rays on Earth. The highly coherent, near-monochromatic, sub-picosecond bursts of radiation they deliver make them the ultimate 'high-speed camera', capable of capturing extremely fast, atomic-level phenomena as they unfold in unprecedented detail. XFELs are therefore ideally suited to probing matter undergoing laser-based dynamic compression, whereby one or more high-power optical lasers rapidly vaporise the surface of a solid target, launching into it a compression wave that generates internal stresses many millions of times greater than atmospheric pressure. During the few billionths of a second for which they survive before being disintegrated, these targets reach extreme pressures of the kind ordinarily encountered only in planetary interiors, and experience rates of deformation rivalling those of meteoric impact events. By illuminating these short-lived samples with extremely bright XFEL pulses, we can generate x-ray diffraction or absorption spectra rich with information about their atomic arrangement, structure, and dynamics in the moments before their destruction. This ability to diagnose the dynamic response of matter under extraordinary thermodynamic conditions is transforming experimental high-pressure physics, allowing us to better understand not only the internal structure, formation, and collision dynamics of planetary bodies, but how to synthesise and recover exotic high-pressure phases of matter, and how engineering alloys and ceramics respond to the huge dynamic stresses created by hypervelocity impacts. In this project, we aim to leverage the diagnostic power of the recently commissioned European XFEL (EuXFEL), an international XFEL facility backed by a consortium of twelve countries to which the UK has committed approximately £30M in capital to date. We will exploit the EuXFEL to shed new light on the plasticity and strength of model metals dynamically deforming at extreme pressures and strain rates. Our aim is to take the 'ordinary' physical processes controlling plastic deformation that materials scientists have studied for over a century, and to examine them under the 'extraordinary' thermodynamic conditions accessible via dynamic compression. Using the UK-built, high-repetition-rate, £8M DiPOLE-100 laser recently installed at EuXFEL, we will laser-compress a range of metals and alloys to planetary pressures over nanosecond timescales at an unprecedented shot rate. We will use femtosecond x-ray diffraction to measure the ultrafast rotation experienced by our samples' microstructure, and use it to identify the plasticity mechanisms that relieve the colossal shear stresses accumulated during compression. From these same diffraction measurements, we will extract the strain state of our metallic samples, allowing us to measure their dynamic strength at extreme strain rates. We will also use EuXFEL to study these samples' x-ray absorption properties under extreme loading, with which we can track their temperature dynamics in situ. Together, these XFEL-enabled experimental measurements of plasticity mechanisms, strength, and temperature evolution have the potential to transform our understanding of material deformation physics under extreme loading conditions.

At ambient conditions, the light alkali metals Li, Na and K are nearly free electron (NFE) metals. But rather than becoming MORE free-electron like when compressed, these metals undergo transitions to unusual and complex structural and electronic forms as a result of density-driven changes in the interactions of the ions and electrons. While such behaviour is expected in all high-density matter, the physics is most evident in the alkali metals due to their NFE behaviour at ambient conditions, and their very high compressibilities. They thus offer a unique insight into the behaviour of all other metals at very high densities. We will exploit our team's expertise in experimental high-pressure physics to create solid and fluid alkali metals at unprecedented densities, and then determine their structural behaviour using x-ray diffraction techniques at synchrotrons, x-ray free electron lasers, and high-energy laser facilities. We will then use electronic structure and quantum-molecular-dynamics calculations to understand the physics behind the observed behaviour, and thereby develop new understanding and improved predictive capabilities in the behaviour of matter at ultra-high densities.

The proposed research programme concerns the development of multiscale methods based on the coupling of continuum and molecular dynamics. Multiscale methods aim to enable the simulation of complex problems such as the study of interfacial friction in materials subjected to shock waves, as well as to provide a meso scale modelling strategy for the range of length and time scales, where molecular methods are computationally expensive and continuum methods are not sufficiently accurate. The research programme includes the development of hybrid solution interface (HSI) for coupling multiscale domains; a dynamic-feedback coupling (DFC) strategy; implementation of constitutive equation to account for the elastic-plastic behaviour in the stress-tensor calculation; verification and validation studies; and computational studies of interfacial dynamics phenomena under shock wave conditions. The verification and validation studies include comparisons of the multiscale methods against previous molecular dynamic simulations for sliding interfaces and experimental data from HE-driven dynamic-friction experiments provided by AWE. Both small and large scale simulations of shock wave propagation and sliding interfaces will be carried out to gain insight into: (i) fracture and breaking of small parts of the surface; (ii) change of the geometrical shape of the surface or interface; (iii) melting and formation of a liquid layer; (iv) solidification of temporarily liquefied parts of the surface; (v) structural changes in the materials.

Thermonuclear fusion is the mechanism by which energy is generated in the Sun. For decades scientists have been attempting to harness fusion for electrical power production because of the huge advantages it offers as a safe, clean and almost inexhaustible supply of energy. In laboratory experiments, fusion is normally studied by heating the heavy isotopes of hydrogen to very high temperatures forming a plasma, in which the rapid motion of the positively charged ions is sufficient to overcome their electrostatic repulsion and allow them to undergo nuclear reactions. One of the main approaches to extracting energy from these reactions is Inertial Confinement Fusion. This involves assembly of the thermonuclear fuel to ultra-high density (over 1000 times the density of water) inside a mm-scale capsule through a spherical implosion driven by high-power lasers. Central to this method is the process of ignition in which the energetic alpha particles emerging from the reactions are themselves used to further heat the fuel, resulting in a self-sustaining burn wave which releases copious amounts of energy. This is a very exciting time for fusion research because with the completion of the National Ignition Facility (NIF) at the Lawrence Livermore National Laboratory (LLNL), the first laboratory facility with the capacity to demonstrate ignition is now operational. Early results from the NIF however have highlighted differences between the predictions of computer models and the behaviour observed. Most importantly the number of nuclear reactions has remained too low to initiate ignition. The PI and Co-I on this grant have worked extensively with scientists at LLNL to understand the origins of these discrepancies and participated in the Science of Ignition workshop which identified priority research directions to address these issues. For this proposal we wish to capitalise upon our experience with plasmas of extremely high density and temperature to address key uncertainties in the design of inertial confinement fusion experiments and the physics of ignition and work to provide an explanation of why the current design does not achieve ignition and burn. Key areas of research will include understanding the way in which the radiation used to drive the implosion is absorbed in the surface of the capsule, the susceptibility of the imploding capsule to hydrodynamic instabilities which cause the fuel to disintegrate before it is fully compressed and the tendency of the high temperature and low temperature regions of the fuel to stir and mix together which quenches the burn. We will also investigate the physics of the ignition process itself, evaluating whether the energetic alpha particles are able to escape the fuel before depositing their energy and the role of spontaneously generated magnetic fields which provide a form of thermal insulation and serve to keep the heat within the fuel. Part of the work will involve developing a number of advanced computer modelling capabilities. In addition to their use in fusion research, these capabilities can also be used to exploit large scale laser facilities for fundamental research in plasma physics, nuclear physics and laboratory astrophysics. Using these computer models to simulate a fusion capsule in which we deliberately introduce an imperfection, we can calculate what characteristic signatures of this defect are embedded within the flux of energetic neutrons and X-rays emanating from the reacting fuel. Comparing synthetic diagnostic data with that obtained in experiment then allows us to isolate which physical processes are responsible for limiting fusion performance. The same computer models can then be used to design improvements which mitigate these effects and allow us to make progress towards achieving ignition. The work described in this proposal therefore represents an opportunity for UK science to make a significant contribution to what would be a major scientific achievement.

Quantum computing - in which we use the unusual properties of very small particles or electronic circuits to process information - has the potential to revolutionise high-performance computing as applied across major industry sectors and branches of science. The computational capability of a quantum computer can grow exponentially, so that adding just one quantum bit will double the potential capacity. However, there are important challenges to realising the potential of these devices. These challenges are not only around building the hardware for quantum computing, but also how to programme a quantum computer in order to take advantage of the new opportunities it could offer for a particular calculation. In this project, we explore new techniques for programming quantum computers, both relevant for near-term devices that require noise mitigation and hardware-specific algorithms, and future error-corrected quantum computers. We will begin by developing new techniques to build specific quantum states by changing the parameters of the system time-dependently without adding excess energy to the system (which we refer to as optimised counterdiabatic driving). In addition, we will develop quantum algorithms for specific applications, identifying opportunities for speeding up calculations in computational fluid dynamics, plasma dynamics, or quantum science, and understanding where these might exhibit an advantage over existing conventional algorithms on supercomputers. Finally, we will test implementations of these techniques on current hardware, alongside developing techniques to verify the output of the quantum computer.