Measurement and Modelling of fast electron transport in solid materials

This thesis presents an investigation into the properties of relativistic electron beams generated by the interaction between an intense laser and a solid density target. Described are novel x-ray spectroscopic techniques for measuring the electron beam divergence, electron currents and to explore the electron distribution. A key aim of this work is the constraint of fast electron beam parameters by the comparison of well characterised experimental data to computational plasma models. Multi-dimensional imaging of a single spectral line allows insight into heating and inferred spatially resolved temperatures, which are around 300eV, are compared to simulation. By comparison of imaging data and simulation, the electron beam is found to diverge with a half angle of approximately 70◦ ± 10◦, and is found to have a diameter greater than that of the laser focal spot. Measured hollow ion spectra are shown, and calculations imply that their are two distinct ionisation mechanisms. The generation of hollow ion states is seen to be dominated by photoionisation in the the range of 7.2 ̊A−7.7 ̊A, and by collisional ionisation in the range 7.9 ̊A−8.1 ̊A. This implies the existence of an intense radiation field, and high fast electron flux within the target. The velocity distribution of electrons is explored by observation of polarised x- ray emission. Using a pair of HOPG crystal spectrometers, each of the polarised components of the x-ray spectra are measured independently to obtain the degree of polarisation. The anisotropic population of magnetic sublevels results in a net polarisation in the spectral emission, and the polarisation degree measured is indicative of the degree of anisotropy in the velocity distribution of the return current. The large, positive degree of polarisation found implies that polarised emission is caused by the return current, and that it contains the necessary energy to excite ions into a hydrogenic state

Single shot, temporally and spatially resolved measurements of fast electron dynamics using a chirped optical probe

A new approach to rear surface optical probing is presented that permits multiple, time-resolved 2D measurements to be made during a single, ultra-intense ( > 1018 W cm−2) laser-plasma interaction. The diagnostic is capable of resolving rapid changes in target reflectivity which can be used to infer valuable information on fast electron transport and plasma formation at the target rear surface. Initial results from the Astra-Gemini laser are presented, with rapid radial sheath expansion together with detailed filamentary features being observed to evolve during single shots

Misidentification of Burkholderia pseudomallei as Acinetobacter species in northern Thailand.

Background: Burkholderia pseudomallei is the causative agent of melioidosis, a disease endemic throughout the tropics. Methods: A study of reported Acinetobacter spp. bacteraemia was performed at Chiang Rai provincial hospital from 2014 to 2015. Isolates were collected and tested for confirmation. Results: A total of 419 putative Acinetobacter spp. isolates from 412 patients were re-identified and 5/419 (1.2%) were identified as B. pseudomallei. Four of the five patients with melioidosis died. An estimated 88/419 (21%) isolates were correctly identified as Acinetobacter spp. Conclusions: Misidentification of Acinetobacter spp. as B. pseudomallei or other bacteria is not uncommon and programmes to address these shortfalls are urgently required

Radiation pressure-driven plasma surface dynamics in ultra-intense laser pulse interactions with ultra-thin foils

The dynamics of the plasma critical density surface in an ultra-thin foil target irradiated by an ultra-intense ( ∼ 6 × 1020 Wcm−2 ) laser pulse is investigated experimentally and via 2D particle-in- cell simulations. Changes to the surface motion are diagnosed as a function of foil thickness. The experimental and numerical results are compared with hole-boring and light-sail models of radi- ation pressure acceleration, to identify the foil thickness range for which each model accounts for the measured surface motion. Both the experimental and numerical results show that the onset of relativistic self-induced transparency, in the thinnest targets investigated, limits the velocity of the critical surface, and thus the e ff ectiveness of radiation pressure acceleration

What do child characteristics contribute to outcomes from care: A PRISMA review

This article presents the findings from a systematic review of the literature regarding factors related to positive placement outcomes. Children in care are particularly vulnerable to problems with their emotional and behavioural development. It is important to know which factors affect whether children will have a positive placement outcome or not. Previous research has aimed to examine this, and has found that certain child characteristics can affect placement outcome. Reviews have not reported their search strategy in line with PRISMA guidelines, nor have they always reported the source of the data. This review was particularly interested in which studies had contact with the children or carers themselves, as opposed to a reliance on administrative data. There appear to be child characteristics that affect placement outcome, but findings need to be interpreted with caution due to a high volume of results from administrative data. Future research should aim to conduct full assessments with children when they come into care

Influence of laser polarization on collective electron dynamics in ultraintense laser-foil interactions

The collective response of electrons in an ultrathin foil target irradiated by an ultraintense laser pulse is investigated experimentally and via 3D particle-in-cell simulations. It is shown that if the target is sufficiently thin that the laser induces significant radiation pressure, but not thin enough to become relativistically transparent to the laser light, the resulting relativistic electron beam is elliptical, with the major axis of the ellipse directed along the laser polarization axis. When the target thickness is decreased such that it becomes relativistically transparent early in the interaction with the laser pulse, diffraction of the transmitted laser light occurs through a so called 'relativistic plasma aperture', inducing structure in the spatial-intensity profile of the beam of energetic electrons. It is shown that the electron beam profile can be modified by variation of the target thickness and degree of ellipticity in the laser polarization

Towards optical polarization control of laser-driven proton acceleration in foils undergoing relativistic transparency

Control of the collective response of plasma particles to intense laser light is intrinsic to relativistic optics, the development of compact laser-driven particle and radiation sources, as well as investigations of some laboratory astrophysics phenomena. We recently demonstrated that a relativistic plasma aperture produced in an ultra-thin foil at the focus of intense laser radiation can induce diffraction, enabling polarization-based control of the collective motion of plasma electrons. Here we show that under these conditions the electron dynamics are mapped into the beam of protons accelerated via strong charge-separation-induced electrostatic fields. It is demonstrated experimentally and numerically via 3D particle-in-cell simulations that the degree of ellipticity of the laser polarization strongly influences the spatial-intensity distribution of the beam of multi-MeV protons. The influence on both sheath accelerated and radiation pressure accelerated protons is investigated. This approach opens up new routes to control laser-driven ion sources

The Role of Digital Technologies in Responding to the Grand Challenges of the Natural Environment:The Windermere Accord

Digital technology is having a major impact on many areas of society, and there is equal opportunity for impact on science. This is particularly true in the environmental sciences as we seek to understand the complexities of the natural environment under climate change. This perspective presents the outcomes of a summit in this area, a unique cross-disciplinary gathering bringing together environmental scientists, data scientists, computer scientists, social scientists, and representatives of the creative arts. The key output of this workshop is an agreed vision in the form of a framework and associated roadmap, captured in the Windermere Accord. This accord envisions a new kind of environmental science underpinned by unprecedented amounts of data, with technological advances leading to breakthroughs in taming uncertainty and complexity, and also supporting openness, transparency, and reproducibility in science. The perspective also includes a call to build an international community working in this important area

Genetic mechanisms of critical illness in COVID-19.

Host-mediated lung inflammation is present1, and drives mortality2, in the critical illness caused by coronavirus disease 2019 (COVID-19). Host genetic variants associated with critical illness may identify mechanistic targets for therapeutic development3. Here we report the results of the GenOMICC (Genetics Of Mortality In Critical Care) genome-wide association study in 2,244 critically ill patients with COVID-19 from 208 UK intensive care units. We have identified and replicated the following new genome-wide significant associations: on chromosome 12q24.13 (rs10735079, P = 1.65 × 10-8) in a gene cluster that encodes antiviral restriction enzyme activators (OAS1, OAS2 and OAS3); on chromosome 19p13.2 (rs74956615, P = 2.3 × 10-8) near the gene that encodes tyrosine kinase 2 (TYK2); on chromosome 19p13.3 (rs2109069, P = 3.98 ×  10-12) within the gene that encodes dipeptidyl peptidase 9 (DPP9); and on chromosome 21q22.1 (rs2236757, P = 4.99 × 10-8) in the interferon receptor gene IFNAR2. We identified potential targets for repurposing of licensed medications: using Mendelian randomization, we found evidence that low expression of IFNAR2, or high expression of TYK2, are associated with life-threatening disease; and transcriptome-wide association in lung tissue revealed that high expression of the monocyte-macrophage chemotactic receptor CCR2 is associated with severe COVID-19. Our results identify robust genetic signals relating to key host antiviral defence mechanisms and mediators of inflammatory organ damage in COVID-19. Both mechanisms may be amenable to targeted treatment with existing drugs. However, large-scale randomized clinical trials will be essential before any change to clinical practice