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Journal articleBreach O, Hatfield P, Rose S, 2022,
Inertial Confinement Fusion involves the implosion of a spherical capsule con-taining thermonuclear fuel. The implosion is driven by irradiating the outsideof the capsule by X-rays or by optical laser irradiation, where in each casethe highest uniformity of irradiation is sought. In this paper we consider thetheoretical problem of irradiation of a capsule by point sources of X-rays, andconfigurations which maximize uniformity are sought. By studying the root-mean-square deviation in terms of different order harmonic modes, we ratio-nalise the dependence of uniformity on distance d of the point sources fromthe centre of a capsule. After investigating simple configurations based onthe Platonic solids, we use a global optimisation algorithm (basin-hopping)to seek better arrangements. The optimum configurations are found to de-pend strongly on d; at certain values which minimise nonuniformity, theseinvolve grouping of sources on the vertices of octahedra or icosahedra, whichwe explain using a modal decomposition. The effect of uncertainties in bothposition and intensity is studied, and lastly we investigate the illuminationof a capsule whose radius is changing with time.
Journal articleBeesley JJ, Rose SJ, 2022,
This paper presents an analytic expression for the high-temperature limit of Breit-Wheeler pair production in a black-body field to lowest order in perturbation theory, of interest in early-universe cosmology. The limit is found to be a good approximation for temperatures above about three times the electron rest energy. It is also found that coupling to low-energy processes remains important at arbitrarily high temperatures, due to the exchange of a low-energy virtual fermion near the mass shell. This appears mathematically in the rate as a logarithmic factor of the photon temperature divided by the electron rest mass.
Journal articleLavrinovich I, Gusev AI, Bland S, et al., 2022,
Journal articleSingh RL, White S, Charlwood M, et al., 2022,
We have employed the VULCAN laser facility to generate a laser plasma X-ray source for use in photoionization experiments. A nanosecond laser pulse with an intensity of order 1015 Wcm−2 was used to irradiate thin Ag or Sn foil targets coated onto a parylene substrate, and the L-shell emission in the 3.3–4.4 keV range was recorded for both the laser-irradiated and nonirradiated sides. Both the experimental and simulation results show higher laser to X-ray conversion yields for Ag compared with Sn, with our simulations indicating yields approximately a factor of two higher than those found in the experiments. Although detailed angular data were not available experimentally, the simulations indicate that the emission is quite isotropic on the laser-irradiated side but shows close to a cosine variation on the nonirradiated side of the target as seen experimentally in the previous work.
Journal articleMaler D, Efimov S, Liverts M, et al., 2022,
Journal articleHalliday JWD, Crilly A, Chittenden J, et al., 2022,
We present first results from a novel experimental platform which is able toaccess physics relevant to topics including indirect-drive magnetised ICF;laser energy deposition; various topics in atomic physics; and laboratoryastrophysics (for example the penetration of B-fields into HED plasmas). Thisplatform uses the X-Rays from a wire array Z-Pinch to irradiate a silicontarget, producing an outflow of ablated plasma. The ablated plasma expands intoambient, dynamically significant B-fields (~5 T) which are supported by thecurrent flowing through the Z-Pinch. The outflows have a well-defined(quasi-1D) morphology, enabling the study of fundamental processes typicallyonly available in more complex, integrated schemes. Experiments were fielded onthe MAGPIE pulsed-power generator (1.4 MA, 240 ns rise time). On this machine awire array Z-Pinch produces an X-Ray pulse carrying a total energy of ~15 kJover ~30 ns. This equates to an average brightness temperature of around 10 eVon-target.
Journal articleMcLean KW, Rose SJ, 2022,
We present an in-depth analysis of a Marshak radiation wave moving through an iron-oxide (Fe2O3) foamusing a 1D multigroup diffusive radiation transport model, MDART (Multigroup Diffusion Algorithm forRadiation Transport). We consider the consequences of under-resolving the group structure and addresshow this could lead to incorrect conclusions in the analysis of general supersonic radiation wave experiments. We also provide an analysis of the types of experimental outcome one may incorrectly link tophysical effects but are in fact due to poor simulation practice.
Journal articleNguyen TT, Breeze J, Masouros S, 2022,
Penetration of Energised Metal Fragments to Porcine Thoracic Tissues, Journal of Biomechanical Engineering, ISSN: 0148-0731
Energised fragments from explosive devices have been the most common mechanism of injury to both military personnel and civilians in recent conflicts and terrorist attacks. Fragments that penetrate into the thoracic cavity are strongly associated with death due to the inherent vulnerability of the underlying structures. The aim of this study was to investigate the impact of fragment-simulating projectiles (FSPs) to tissues of the thorax in order to identify the thresholds of impact velocity for perforation through these tissues and the resultant residual velocity of the FSPs. A gas-gun system was used to launch 0.78-g cylindrical and 1.13-g spherical FSPs at intact porcine thoracic tissues from different impact locations. The sternum and rib bones were the most resistant to perforation, followed by the scapula and intercostal muscle. For both FSPs, residual velocity following perforation was linearly proportional to impact velocity. These findings can be used in the development of numerical tools for predicting the medical outcome of explosive events, which in turn can inform the design of public infrastructure, of personal protection, and of medical emergency response.
Conference paperHalliday JWD, Crilly A, Chittenden J, et al., 2022,
In this talk we present measurements from a novel platform in which the X-Rays from a wire-array Z-Pinch irradiate a silicon target, producing an outflow of ablated silicon plasma. This ablated plasma expands into ambient, dynamically significant magnetic fields (B ∼ 5 T) which are supported by the current flowing through the Z-Pinch.
Journal articleStrucka J, Halliday JWD, Gheorghiu T, et al., 2022,
We describe the design and x-ray emission properties (temporal, spatial, and spectral) of Dry Pinch I, a portable X-pinch driver developed at Imperial College London. Dry Pinch I is a direct capacitor discharge device, 300 × 300 × 700 mm3 in size and ∼50 kg in mass, that can be used as an external driver for x-ray diagnostics in high-energy-density physics experiments. Among key findings, the device is shown to reliably produce 1.1 ± 0.3 ns long x-ray bursts that couple ∼50 mJ of energy into photon energies from 1 to 10 keV. The average shot-to-shot jitter of these bursts is found to be 10 ± 4.6 ns using a combination of x-ray and current diagnostics. The spatial extent of the x-ray hot spot from which the radiation emanates agrees with previously published results for X-pinches—suggesting a spot size of 10 ± 6 µm in the soft energy region (1–10 keV) and 190 ± 100 µm in the hard energy region (>10 keV). These characteristics mean that Dry Pinch I is ideally suited for use as a probe in experiments driven in the laboratory or at external facilities when more conventional sources of probing radiation are not available. At the same time, this is also the first detailed investigation of an X-pinch operating reliably at current rise rates of less than 1 kA/ns.
Journal articleHalliday JWD, Bland SN, Hare JD, et al., 2021,
A time-resolved imaging system for the diagnosis of x-ray self-emission in high energy density physics experiments, Review of Scientific Instruments, Vol: 92, Pages: 123507-123507, ISSN: 0034-6748
A diagnostic capable of recording spatially and temporally resolved x-ray self-emission data was developed to characterize experiments on the MAGPIE pulsed-power generator. The diagnostic used two separate imaging systems: a pinhole imaging system with two-dimensional spatial resolution and a slit imaging system with one-dimensional spatial resolution. The two-dimensional imaging system imaged light onto the image plate. The one-dimensional imaging system imaged light onto the same piece of image plate and a linear array of silicon photodiodes. This design allowed the cross-comparison of different images, allowing a picture of the spatial and temporal distribution of x-ray self-emission to be established. The design was tested in a series of pulsed-power-driven magnetic-reconnection experiments.
Journal articleTilikin IN, Shelkovenko TA, Pikuz SA, et al., 2021,
This paper demonstrates the possibility of using a new configuration of the hybrid X-pinch to produce a set of spatially and temporarily separate x-ray bursts that could be used for the radiography of dynamic events. To achieve this, a longer than normal wire is placed between the conical electrodes of the hybrid X-pinch, and a set of small spacers (fishing weights) is placed along the wire. Each subsection of the wire then acts as a unique X-pinch, producing its own radiation burst from a small (∼3 µm) spot. The timing between bursts is 20–50 ns, and each is <2 ns in duration. For comparison, if a longer wire is simply employed without spacers, hotspots of radiation occur in random positions and the time between any two bursts does not exceed 20 ns. Examples of two and three frame point-projection radiography of solid-state and plasma test objects are given.
Journal articleKettle B, Hollatz D, Gerstmayr E, et al., 2021,
We describe a laser–plasma platform for photon–photon collision experiments to measure fundamental quantum electrodynamic processes. As an example we describe using this platform to attempt to observe the linear Breit–Wheeler process. The platform has been developed using the Gemini laser facility at the Rutherford Appleton Laboratory. A laser Wakefield accelerator and a bremsstrahlung convertor are used to generate a collimated beam of photons with energies of hundreds of MeV, that collide with keV x-ray photons generated by a laser heated plasma target. To detect the pairs generated by the photon–photon collisions, a magnetic transport system has been developed which directs the pairs onto scintillation-based and hybrid silicon pixel single particle detectors (SPDs). We present commissioning results from an experimental campaign using this laser–plasma platform for photon–photon physics, demonstrating successful generation of both photon sources, characterisation of the magnetic transport system and calibration of the SPDs, and discuss the feasibility of this platform for the observation of the Breit–Wheeler process. The design of the platform will also serve as the basis for the investigation of strong-field quantum electrodynamic processes such as the nonlinear Breit–Wheeler and the Trident process, or eventually, photon–photon scattering.
Conference paperBaggott RA, Rose SJ, Mangles SPD, 2021,
The charge states of ions in dense plasmas fluctuate due to collisional ionization and recombination. In this work we show how, by modifying the ion interaction potential, these fluctuations can mediate energy exchange between the plasma electrons and ions. We also develop a theoretical framework for this novel electron-ion energy transfer mechanism.
Journal articleYan J, Parker S, Bland S, 2021,
Journal articleRose SJ, Hatfield PW, 2021,
Inertial Confinement Fusion (ICF) is a subject that has been studied for decades, because of its potential for clean energy generation. Although thermonuclear fusion has been achieved, the energy out has always been considerably less than the energy in, so high energy gain with a burning thermonuclear plasma is still some way off. A multitude of new science has come from the ICF programme that is relevant outside the field (typically in astrophysics). What we look at in this text is what new science can come from the much more extreme conditions that would be created in the laboratory if a burning ICF plasma could be created -- in terms of energy density the most extreme macroscopic environment ever created. We show that this could impact science from particle physics through astrophysics and on to cosmology. We also believe that the experiments that we propose here are only a small part of the science that will be opened up when a burning thermonuclear plasma is created in the laboratory.
Journal articleBaggott RA, Rose S, Mangles SPD, 2021,
The charge states of ions in dense plasmas fluctuate due to collisionalionization and recombination. Here we show how, by modifying the ioninteraction potential, these fluctuations can mediate energy exchange betweenthe plasma electrons and ions. Moreover, we develop a theory for this novelelectron-ion energy transfer mechanism. Calculations using a random walkapproach for the fluctuations suggest that the energy exchange rate from chargestate fluctuations could be comparable to direct electron-ion collisions. Thismechanism is, however, predicted to exhibit a complex dependence on thetemperature and ionization state of the plasma, which could contribute to ourunderstanding of significant variation in experimental measurements ofequilibration times.
Journal articleSpencer Kelly R, Hart LJF, Rose SJ, 2021,
We model the energy cost of producing muons for use in muon catalyzed fusion and show that by careful design the cost can be reduced by a factor of 2.5 below current values. This is done by recapturing the kinetic energy of waste particles and generating heat through tritium breeding. When put together with the modeling of muon catalyzed fusion we estimate that electrical output/electrical input of 14% can be achieved currently.
Journal articleMaler D, Efimov S, Rososhek A, et al., 2021,
Journal articleHatfield PW, Gaffney JA, Anderson GJ, et al., 2021,
High-energy-density physics is the field of physics concerned with studying matter at extremely high temperatures and densities. Such conditions produce highly nonlinear plasmas, in which several phenomena that can normally be treated independently of one another become strongly coupled. The study of these plasmas is important for our understanding of astrophysics, nuclear fusion and fundamental physics—however, the nonlinearities and strong couplings present in these extreme physical systems makes them very difficult to understand theoretically or to optimize experimentally. Here we argue that machine learning models and data-driven methods are in the process of reshaping our exploration of these extreme systems that have hitherto proved far too nonlinear for human researchers. From a fundamental perspective, our understanding can be improved by the way in which machine learning models can rapidly discover complex interactions in large datasets. From a practical point of view, the newest generation of extreme physics facilities can perform experiments multiple times a second (as opposed to approximately daily), thus moving away from human-based control towards automatic control based on real-time interpretation of diagnostic data and updates of the physics model. To make the most of these emerging opportunities, we suggest proposals for the community in terms of research design, training, best practice and support for synthetic diagnostics and data analysis.
Journal articleRankin I, Nguyen T, McMenemy L, et al., 2021,
Traumatic amputation has been one of the most defining injuries associated with explosive devices. An understanding of the mechanism of injury is essential in order to reduce its incidence and devastating consequences to the individual and their support network. In this study, traumatic amputation is reproduced using high-velocity environmental debris in an animal cadaveric model. The study findings are combined with previous work to describe fully the mechanism of injury as follows. The shock wave impacts with the casualty, followed by energised projectiles (environmental debris or fragmentation) carried by the blast. These cause skin and soft tissue injury, followed by skeletal trauma which compounds to produce segmental and multifragmental fractures. A critical injury point is reached, whereby the underlying integrity of both skeletal and soft tissues of the limb has been compromised. The blast wind that follows these energised projectiles completes the amputation at the level of the disruption, and traumatic amputation occurs. These findings produce a shift in the understanding of traumatic amputation due to blast from a mechanism predominately thought mediated by primary and tertiary blast, to now include secondary blast mechanisms, and inform change for mitigative strategies.
Journal articleYan J, Parker S, Gheorghiu T, et al., 2021,
Miniature solid-state switched spiral generator for the cost effective, programmable triggering of large scale pulsed power accelerators, Physical Review Accelerators and Beams, Vol: 24, Pages: 1-10, ISSN: 2469-9888
This paper presents the design and testing of several different configurations of spiral generator, designed to trigger high current switches in the next generation of pulsed power devices. In particular, it details the development of spiral generators that utilize new ultrafast thyristor technology as an input switch, along with a polarity dependent output gap to improve the efficiency of the spiral generator design. The generator produced 50 kV from a 3.6 kV charging voltage, with a rise time of only 50 ns and a jitter of 1.3 ns—directly comparable, if not better than, a generator employing a triggered spark gap as the input switch. The output gap was constructed in house from commonly available components and a 3D printed case, and showed remarkable repeatability and stability—simple alterations to the output gap could further reduce the rise time. The entire spiral generator, along with control and charging electronics, fitted into a case only 210×145×33 mm.
Journal articlePerez-Callejo G, Marley E, Liedahl DA, et al., 2021,
Demonstration of geometric effects and resonant scattering in the X-Ray spectra of high-energy-density plasmas, Physical Review Letters, Vol: 126, Pages: 1-7, ISSN: 0031-9007
In a plasma of sufficient size and density, photons emitted within the system have a probability of being reabsorbed and reemitted multiple times—a phenomenon known in astrophysics as resonant scattering. This effect alters the ratio of optically thick to optically thin lines, depending on the plasma geometry and viewing angle, and has significant implications for the spectra observed in a number of astrophysical scenarios, but has not previously been studied in a controlled laboratory plasma. We demonstrate the effect in the x-ray spectra emitted by cylindrical plasmas generated by high power laser irradiation, and the results confirm the geometrical interpretation of resonant scattering.
Journal articleRose S, Hatfield P, Scott R, 2020,
Considerable progress towards the achievement ofthermonuclear burn using inertial confinement fusion has beenachieved at the National Ignition Facility (NIF) in the USA inthe last few years. Other drivers, such as the Z-machine atSandia, are also making progress towards this goal. A burningthermonuclear plasma would provide a unique and extremeplasma environment; in this paper we discuss a) differenttheoretical challenges involved in modelling burning plasmasnot currently considered, b) the use of novel machine learningbased methods that might help large facilities reach ignition,and c) the connections that a burning plasma might have tofundamental physics, including QED studies, and the replicationand exploration of conditions that last occurred in the first fewminutes after the Big Bang.
Journal articlePérez-Callejo G, Jarrott LC, Liedahl DA, et al., 2020,
Measuring the oscillator strength of intercombination lines of helium-like V ions in a laser-produced-plasma, Journal of Quantitative Spectroscopy and Radiative Transfer, Vol: 256, ISSN: 0022-4073
We present results of measurements of the oscillator strength of intercombination lines of He-like Vanadium ions in high energy density (HED) laser-produced-plasmas and compare them with the simulations from commonly used codes and data from the NIST database. Whilst not yet sufficiently accurate to constrain different trusted atomic-physics models for the particular system studied, our results are in agreement with the available data within experimental error bars, yet differ from cruder approximations of the oscillator strength used in certain atomic-kinetics packages, suggesting that this general method could be further extended to be used as a measurement of the oscillator strength of additional atomic transitions under the extreme conditions that are achieved in HED experiments.
Journal articlePérez-Callejo G, Barrios MA, Liedahl DA, et al., 2020,
A novel method to measure ion density in ICF experiments using x-ray spectroscopy of cylindrical tracers, Physics of Plasmas, Vol: 27, Pages: 112714-1-112714-11, ISSN: 1070-664X
The indirect drive approach to inertial confinement fusion has undergone important advances in the past few years. Improvements in temperature and density diagnostic methods are leading to more accurate measurements of the plasma conditions inside the Hohlraum and therefore to more efficient experimental designs. The implementation of dot spectroscopy has proven to be a versatile approach to extracting space- and time-dependent electron temperatures. In this method, a microdot of a mid-Z material is placed inside the Hohlraum and its K-shell emission spectrum is used to determine the plasma temperature. However, radiation transport of optically thick lines acting within the cylindrical dot geometry influences the outgoing spectral distribution in a manner that depends on the viewing angle. This angular dependence has recently been studied in the high energy density regime at the OMEGA laser facility, which allowed us to design and benchmark appropriate radiative transfer models that can replicate these geometric effects. By combining these models with the measurements from the dot spectroscopy experiments at the National Ignition Facility, we demonstrate here a novel technique that exploits the transport effects to obtain time-resolved measurements of the ion density of the tracer dots, without the need for additional diagnostics. We find excellent agreement between experiment and simulation, opening the possibility of using these geometric effects as a density diagnostic in future experiments.
Conference paperWhite S, Irwin R, Warwick R, et al., 2020,
Implementation of a novel experimental approach using a bright source of narrowband x-ray emission has enabled the production of a photoionized argon plasma of relevance to astrophysical modelling codes such as Cloudy. We present results showing that the photoionization parameter ζ = 4πF/ne generated using the VULCAN laser was ≈ 50 erg cm s−1, higher than those obtained previously with more powerful facilities. Comparison of our argon emission-line spectra in the 4.15 - 4.25 Å range at varying initial gas pressures with predictions from the Cloudy code and a simple time-dependent code are also presented. Finally we briefly discuss how this proof-of-principle experiment may be scaled to larger facilities such as ORION to produce the closest laboratory analogue to a photoionized plasma.
Journal articleBaggott R, Rose S, Mangles S, 2020,
Calculating opacity in hot, dense matter using second-order electron-photon and two-photon transitions to approximate line broadening, Physical Review Letters, Vol: 125, Pages: 145002 – 1-145002 – 5, ISSN: 0031-9007
Calculations of the opacity of hot, dense matter require models for plasma line broadening. How-ever, the most general theories are too complex to calculate directly and some approximation is inevitably required. The most widely-used approaches focus on the line centre, where a Lorentzian shape is obtained. Here, we demonstrate that in the opposite limit, far from the line centre, the opacity can be expressed in terms of second-order transitions, such as electron-photon and two-photon processes. We suggest that this insight could form the basis for a new approach to improve calculations of opacity in hot, dense matter. Preliminary calculations suggest that this approach could yield increased opacity away from absorption lines.
Journal articleYanuka D, Theocharous S, Chittenden JP, et al., 2020,
We report on initial observations of high velocity outflows from the ends of a rod compressed using pulsed power. 1 mm and 2 mm diameter copper rods were placed in a water bath and driven by ∼0.6 MA currents with rise times of ∼700 ns. Laser backlit framing images and streak photography showed an outflow of the material from the ends of each rod, of the initial velocity of up to 7 km/s, which began ∼500 ns after the start of the current pulse and continued throughout the experiment. Ballistics gel was used to help separate low density gas/plasma from any solid/liquid component in the outflow, successfully capturing the material from larger diameter rods (enabling an estimate of its energy) and tracing the path of the material that passed straight through the gel with smaller rods. Experimental results were compared to 1D and 2D MHD simulations performed with the Gorgon code. These suggested that the outflow had two different components, resulting from two different physical processes. Differences in the resistivity between the copper rod and stainless steel anode result in the opening of a small gap between them and ablated stainless steel being projected above the rod, which is captured in framing and streak images. Later in time, a dense copper material, pinched by the magnetic pressure, is launched—explaining the ballistics gel results. The simulations also suggest that the tamped explosion of the rod surface plays a small role in any outflow.
Journal articleSory DR, Amin HD, Chapman D, et al., 2020,
Trauma arising from landmines and improvised explosive devices promotes heterotopic ossification, the formation of extra-skeletal bone in non-osseous tissue. To date, experimental platforms that can replicate the loading parameter space relevant to improvised explosive device and landmine blast wave exposure have not been available to study the effects of such non-physiological mechanical loading on cells. Here, we present the design and calibration of three distinct in vitro experimental loading platforms that allow us to replicate the spectrum of loading conditions recorded in near-field blast wave exposure. We subjected cells in suspension or in a three-dimensional hydrogel to strain rates up to 6000 s-1and pressure levels up to 45 MPa. Our results highlight that cellular activation is regulated in a non-linear fashion - not by a single mechanical parameter, it is the combined action of the applied mechanical pressure, rate of loading and loading impulse, along with the extracellular environment used to convey the pressure waves. Finally, our research indicates that PO MSCs are finely tuned to respond to mechanical stimuli that fall within defined ranges of loading.
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