Nuclear fusion offers the promise of abundant, clean, low cost energy. The fusion process involves fusing together two nuclei releasing large amounts of energy that can be harnessed for electricity generation. Future power stations will employ the reaction between two isotopes of hydrogen, tritium and deuterium, creating a helium atom and a neutron. Deuterium is available from seawater, however, tritium does not occur naturally due to its short half-life. Therefore, tritium will be created, or bred, in the reactor from lithium in a process called transmutation. Transmutation will occur immediately outside the main chamber of the reactor, in a region called the breeder blanket. One of the leading breeder blanket designs will use lithium containing pebbles, such as lithium metatitanate and lithium orthosilicate. Solid breeder materials are attractive as they have high lithium densities that will ensure excellent tritium production and their low reactivity with other reactor materials means they are safe. However the use of a solid breeder material means that following transmutation the tritium will be trapped in the pebbles and must be extracted from the crystal. For recovery the tritium must diffuse to the pebble surface where it can be carried away by the coolant. The rate at which the tritium can escape from the pebbles is a very important parameter to consider when designing a fusion reactor because if the rate drops too low and tritium is retained in the pebble the fusion reaction will be unsustainable. Therefore, the main goal of this research to understand the process of tritium diffusion in lithium ceramics to design materials that have high tritium release rates. The exact mechanism of tritium release will depend on the microstructure of the host material. All crystals contain defects, such as missing atoms (called vacancies), and these defects can either promote tritium release or act as traps and inhibit it. The types and concentrations of defects in a material depend on the exact conditions (i.e. temperature) and will evolve over time. Therefore, to understand the tritium release process we must first understand the microstructure of the ceramics and what defects are present Previous studies of tritium release have adopted a top down approach where experimentally observed tritium release rates under different conditions are used to infer the exact atomic level mechanism responsible. By contrast this proposal adopts a novel bottom up approach that uses advanced electronic structure calculations to build a tritium release model from first principles. A key advantage of this approach is that the calculations provide detailed understanding of the atomic rearrangement processes that constitute tritium diffusion and allow a rate to be determined for each process. Initially the intrinsic defect chemistry of the host materials will be examined. This will allow the identification of the defects present in the ceramic under different conditions. Once the intrinsic defect populations are established the interaction of tritium atoms with the defects will be studied. By examining the bonding between tritium and the defects it is possible to determine exactly where the tritium will sit in the crystal and to identify which defects will act as traps. The information gathered so far considers where tritium will sit in the crystal but it does not provide information about how quickly the tritium can move through the crystal. Therefore, the next step in the process is to understand how tritium hops between the defects available and to determine which types of hop are most likely under certain conditions. Finally, all of this information will be used to create a tritium release model from lithium ceramics. This model will be used to optimise the microstructure of the ceramics to deliver maximum tritium release to ensure the fusion process is sustainable.

Fatigue is the most pervasive failure mode that affects nearly all industrial sectors - including energy industries involving power plants, anemo-electric and tidal stream generators; transport vehicles and aircraft; national infrastructure such railway and bridges; military equipment from a blade in an engine to a whole ship; medical devices and human body implants. The economic cost of fracture has been enormous, approaching 4% of GDP, whereas 50-90% of all these mechanical failures are due to fatigue. Most fatigue failures are unexpected, and can lead to catastrophic consequences. In safety-critical sectors such as the aero-space and nuclear industries, there are ever increasing demands for better understanding of fatigue with respect to the microstructure of metallic components and the demanding environments that they are placed in. The ultra-small, ultra fast fatigue testing techniques I have created are able to make a breakthrough by addressing the classic needle in haystack problem in fatigue crack initiation (FCI) and short crack growth (SCG). Fatigue at these early stages is localized within a few hundred micro-meters. However, they account for more than 50% life in low cycle fatigue (LCF) and approximately 90% in the high cycle fatigue (HCF) regime, and contribute to the largest portion of scatter. My micro- and meso- cantilever techniques are capable of isolating FCI and SCG in selected microstructure features, allowing for the systematic exploration of slip evolution, slip band decohesion and short crack propagation in the context of an exquisitely well characterised volume of material. The ultra-fast testing rate up to 20 kHz means robust exploration can be achieved to 10^9 cycles and beyond, in hours in contrast to months or years demanded by the conventional method. This proposal, through further development of state-of-the-art extremely small and fast fatigue testing techniques, looks to radically change the technical scope of fatigue analysis by allowing environmental effects to be systematically explored at the levels of FCI and SCG and across the HCF and LCF regimes. In-situ ultrasonic fatigue testing rig will be installed in an advanced scanning electron microscope, enabling in-situ observation of the progression of HCF FCI and SCG at the resolution of ~ 1 nm. I will apply these cutting edge techniques to underpinning major fatigue issues in Ti and Ni alloys of technologically importance to the aero-engine industry and proton accelerators, specifically: (i) To achieve a breakthrough in mechanistic understanding of HCF FCI and SCG in titanium alloys with respect to the environments and deliver essential HCF FCI and SCG properties; (ii) To make groundbreaking study of fatigue in Alpha Case and dwelling fatigue in titanium alloys, which are major issues in aero-engine industry; (iii) To determine the effect of the heavy irradiation on HCF performance of Ti-alloys that will be used in the next generation proton accelerators; (iv) To achieve comprehensively understanding of the environmental effect on fatigue in single-crystal nickel superalloys that have the heterogeneous distribution of gamma' phase and element segregation; (v) To determine the HCF and LCF performance of the multi-functional coatings on the surface of a nickel turbo blade in the context of atmosphere, temperature and pre-corrosion treatment. A Ultrasonic Fatigue Testing Centre will be established to satisfy the frequent HCF assessment requests from the industry. The new functions developed on the ultrasonic fatigue testing rig in this project will be transferred to the national lab at Culham to update the bespoke rig in a 'hot cell', for study of active materials in support of fission and fusion innovation.

Plasma physics is the study of large collections of charged particles and their interactions. One key application of plasma physics is in magnetically confined nuclear fusion, where nuclei, typically of Hydrogen, are confined by a magnetic field, so that they can reach the high temperatures necessary to fuse together as they collide. A large research effort is underway to develop fusion reactors that exploit the energy release from fusion to produce electricity. In a tokamak, which is a specific kind of fusion reactor design, the vacuum chamber containing the fusion fuel can be conceptually separated into a 'closed field region' where particles cannot escape along magnetic field lines, and an 'open field region' where they can stream along the field lines and hit the wall. The quite sharp boundary between the open and closed field region is particularly interesting and important, because a strong additional 'transport barrier', called a pedestal, can develop there. A large difference in temperature and density is sustained across the narrow pedestal, allowing the core plasma to reach higher pressure, and leading to a major increase in fusion power. How the pedestal is formed, and when it breaks down, are questions of vital importance to fusion reactor operation, but these issues are quite poorly understood at present. This proposal seeks to answer basic questions about the pedestal, and similar structures that develop in other laboratory and space plasmas. This is an investigation of the fundamental properties of magnetised plasmas. How do such structures evolve, and how does this interact with the plasma turbulence? What plasma instabilities develop in these plasmas? To answer these questions, we need models of how the particles individually and collectively respond to electromagnetic fields, and for the hot plasmas of interest we usually need to keep track of the motion of particles, rather that just look at the overall fluid motion. In magnetised plasmas, the basic motion of plasma particles is a circular orbit, or gyration, perpendicular to the magnetic field, as well as a parallel motion along the magnetic field line. This can be formalized mathematically using a framework known as 'gyrokinetics', which has become the dominant way to understand the transport of hot plasma in tokamaks. A new gyrokinetic formalism has been developed by the proposer which is designed to be more accurate in regions with large amplitude structures like the tokamak pedestal. It is based on a rethinking of the assumptions usually made, so that both short wavelength fluctuations and more global physics may be handled in a unified way. We relax the requirement that perturbations be small amplitude but instead require that the 'vorticity', which measures how rapidly blobs of plasma rotate, is relatively limited. This proposal will develop and exploit this mathematical framework to solve a range of fundamental physics problems in magnetised plasmas with large perturbations. A computer code to embody this plasma model will be further developed, and this will require the development of new algorithms. This code will then be deployed to understand both fundamental physics problems of magnetised plasmas, as well as the specific applications to structured regions of tokamaks. As well as computational work, physical understanding of these plasmas requires us to develop a deeper understanding of the mathematical framework. We will use limiting cases to determine how the physics relates to simpler formalisms, and determine the underlying conservation laws to tie the turbulent dynamics to the large scale physics of momentum and energy transport.

Fusion reactors could some day provide a clean and nearly inexhaustible source of energy, but their development has proven to be challenging. Nevertheless, great progress has been made in recent decades and fusion research is now at a critical stage: ITER, the first test reactor anticipated to generate a surplus of energy, is being built and operation is planned to start around 2025. It will serve as a testbed for DEMO, a prototype for a commercially viable fusion power plant to be completed by 2050. The Culham Centre for Fusion Energy (CCFE) is a key contributor to this development: it operates the Joint European Torus (JET) which is currently the world's largest fusion test reactor. JET is important for experimental results and validation of simulation software, both of which are used to inform the design of the much larger ITER Computer simulations complementing experiments with test reactors are critical for the design and operation of ITER but also to explore alternative reactor designs. The immense complexity of the physics involved translates into complex mathematical models which take a long time to solve numerically, even on modern computer architectures. As reactors grow in size and complexity, so do the employed models and therefore solution times. LOCUST, for example, is a state-of-the-art particle tracker used operationally at CCFE and optimised heavily to exploit graphical processing unit (GPU) accelerators. However, one simulation of the trajectories of fast ions generated from neutral beam injection in the JET test reactor still takes around 10 hours to complete. Because of the higher energies, a similar simulation for ITER already takes 4 to 7 days. Therefore, at the moment, design choices can be informed only by a small number of simulations with carefully selected parameters. However, systematic exploration of a wide range of design parameters in computer simulations is not yet possible. The project will develop a new and more efficient algorithm and deploy it as a particle tracker in CCFE's operational simulation software. This will help to significantly reduce solution times and contribute toward the order of magnitude reduction of runtimes needed for effective in-silico design of components for ITER. While the new algorithm will be deployed for a specific application, the mathematical ideas developed during the project can help to improve the efficiency of computer simulations in other applications such as manufacturing processes involving plasmas, for example for flat panel displays or solar panels.

Fatigue is the most pervasive failure mode that affects nearly all industrial sectors - including energy industries involving power plants, anemo-electric and tidal stream generators; transport vehicles and aircraft; national infrastructure such railway and bridges; military equipment from a blade in an engine to a whole ship; medical devices and human body implants. The economic cost of fracture has been enormous, approaching 4% of GDP, whereas 50-90% of all these mechanical failures are due to fatigue. Most fatigue failures are unexpected, and can lead to catastrophic consequences. In safety-critical sectors such as the aero-space and nuclear industries, there are ever increasing demands for better understanding of fatigue with respect to the microstructure of metallic components and the demanding environments that they are placed in. The ultra-small, ultra fast fatigue testing techniques I have created are able to make a breakthrough by addressing the classic needle in haystack problem in fatigue crack initiation (FCI) and short crack growth (SCG). Fatigue at these early stages is localized within a few hundred micro-meters. However, they account for more than 50% life in low cycle fatigue (LCF) and approximately 90% in the high cycle fatigue (HCF) regime, and contribute to the largest portion of scatter. My micro- and meso- cantilever techniques are capable of isolating FCI and SCG in selected microstructure features, allowing for the systematic exploration of slip evolution, slip band decohesion and short crack propagation in the context of an exquisitely well characterised volume of material. The ultra-fast testing rate up to 20 kHz means robust exploration can be achieved to 10^9 cycles and beyond, in hours in contrast to months or years demanded by the conventional method. This proposal, through further development of state-of-the-art extremely small and fast fatigue testing techniques, looks to radically change the technical scope of fatigue analysis by allowing environmental effects to be systematically explored at the levels of FCI and SCG and across the HCF and LCF regimes. In-situ ultrasonic fatigue testing rig will be installed in an advanced scanning electron microscope, enabling in-situ observation of the progression of HCF FCI and SCG at the resolution of ~ 1 nm. I will apply these cutting edge techniques to underpinning major fatigue issues in Ti and Ni alloys of technologically importance to the aero-engine industry and proton accelerators, specifically: (i) To achieve a breakthrough in mechanistic understanding of HCF FCI and SCG in titanium alloys with respect to the environments and deliver essential HCF FCI and SCG properties; (ii) To make groundbreaking study of fatigue in Alpha Case and dwelling fatigue in titanium alloys, which are major issues in aero-engine industry; (iii) To determine the effect of the heavy irradiation on HCF performance of Ti-alloys that will be used in the next generation proton accelerators; (iv) To achieve comprehensively understanding of the environmental effect on fatigue in single-crystal nickel superalloys that have the heterogeneous distribution of gamma' phase and element segregation; (v) To determine the HCF and LCF performance of the multi-functional coatings on the surface of a nickel turbo blade in the context of atmosphere, temperature and pre-corrosion treatment. A Ultrasonic Fatigue Testing Centre will be established to satisfy the frequent HCF assessment requests from the industry. The new functions developed on the ultrasonic fatigue testing rig in this project will be transferred to the national lab at Culham to update the bespoke rig in a 'hot cell', for study of active materials in support of fission and fusion innovation.