Publications
41 results found
Crilly AJ, Duhig B, Bouziani N, 2024, Learning closure relations using differentiable programming: An example in radiation transport, Journal of Quantitative Spectroscopy and Radiative Transfer, Vol: 318, ISSN: 0022-4073
Reduced order models with a-priori unknown closure relations are ubiquitous in transport problems. In this work, we present a machine-learning approach to finding closure relations utilising differentiable programming. We use the Su Olson radiation transport test problem as an example training data set. We present novel closures for second angular moment (variable Eddington factor), third angular moment and flux-limited diffusion models. We evaluate the improvement of the machine-learnt closures over those from the literature. These improvements are then tested by considering a modification to the Su Olson problem. Comparisons to literature closures show the machine learning models out-perform them in both the trained and unseen problems.
Crilly AJ, Schlossberg DJ, Appelbe BD, et al., 2024, Measurements of dense fuel hydrodynamics in the NIF burning plasma experiments using backscattered neutron spectroscopy, Physics of Plasmas, Vol: 31, ISSN: 1070-664X
The hydrodynamics of the dense confining fuel shell is of great importance in defining the behavior of the burning plasma and burn propagation regimes of inertial confinement fusion experiments. However, it is difficult to probe due to its low emissivity in comparison with the central fusion core. In this work, we utilize the backscattered neutron spectroscopy technique to directly measure the hydrodynamic conditions of the dense fuel during fusion burn. Experimental data are fit to obtain dense fuel velocities and apparent ion temperatures. Trends of these inferred parameters with yield and velocity of the burning plasma are used to investigate their dependence on alpha heating and low mode drive asymmetry. It is shown that the dense fuel layer has an increased outward radial velocity as yield increases, showing that burn has continued into re-expansion, a key signature of hotspot ignition. A comparison with analytic and simulation models shows that the observed dense fuel parameters are displaying signatures of burn propagation into the dense fuel layer, including a rapid increase in dense fuel apparent ion temperature with neutron yield.
Merlini S, Hare JD, Burdiak GC, et al., 2023, Radiative cooling effects on reverse shocks formed by magnetized supersonic plasma flows, Physics of Plasmas, Vol: 30, ISSN: 1070-664X
We study the structure of reverse shocks formed by the collision of supersonic, magnetized plasma flows driven by an inverse (or exploding) wire array with a planar conducting obstacle. We observe that the structure of these reverse shocks varies dramatically with wire material, despite the similar upstream flow velocities and mass densities. For aluminum wire arrays, the shock is sharp and well-defined, consistent with magneto-hydrodynamic theory. In contrast, we do not observe a well-defined shock using tungsten wires, and instead we see a broad region dominated by density fluctuations on a wide range of spatial scales. We diagnose these two very different interactions using interferometry, Thomson scattering, shadowgraphy, and a newly developed imaging refractometer that is sensitive to small deflections of the probing laser corresponding to small-scale density perturbations. We conclude that the differences in shock structure are most likely due to radiative cooling instabilities, which create small-scale density perturbations elongated along magnetic field lines in the tungsten plasma. These instabilities grow more slowly and are smoothed by thermal conduction in the aluminum plasma.
Mannion OM, Taitano WT, Appelbe BD, et al., 2023, Evidence of non-Maxwellian ion velocity distributions in spherical shock-driven implosions., Phys Rev E, Vol: 108
The ion velocity distribution functions of thermonuclear plasmas generated by spherical laser direct drive implosions are studied using deuterium-tritium (DT) and deuterium-deuterium (DD) fusion neutron energy spectrum measurements. A hydrodynamic Maxwellian plasma model accurately describes measurements made from lower temperature (<10 keV), hydrodynamiclike plasmas, but is insufficient to describe measurements made from higher temperature more kineticlike plasmas. The high temperature measurements are more consistent with Vlasov-Fokker-Planck (VFP) simulation results which predict the presence of a bimodal plasma ion velocity distribution near peak neutron production. These measurements provide direct experimental evidence of non-Maxwellian ion velocity distributions in spherical shock driven implosions and provide useful data for benchmarking kinetic VFP simulations.
Sio H, Moody JD, Pollock BB, et al., 2023, Performance scaling with an applied magnetic field in indirect-drive inertial confinement fusion implosions, PHYSICS OF PLASMAS, Vol: 30, ISSN: 1070-664X
Moore AS, Schlossberg DJ, Appelbe BD, et al., 2023, Neutron time of flight (nToF) detectors for inertial fusion experiments, REVIEW OF SCIENTIFIC INSTRUMENTS, Vol: 94, ISSN: 0034-6748
Crilly AJ, Niasse NPL, Fraser AR, et al., 2023, SpK: A fast atomic and microphysics code for the high-energy-density regime, High Energy Density Physics, Vol: 48, Pages: 1-12, ISSN: 1574-1818
SpK is part of the numerical codebase at Imperial College London used to model high energy density physics (HEDP) experiments. SpK is an efficient atomic and microphysics code used to perform detailed configuration accounting calculations of electronic and ionic stage populations, opacities and emissivities for use in post-processing and radiation hydrodynamics simulations. This is done using screened hydrogenic atomic data supplemented by the NIST energy level database. An extended Saha model solves for chemical equilibrium with extensions for non-ideal physics, such as ionisation potential depression, and non thermal equilibrium corrections. A tree-heap (treap) data structure is used to store spectral data, such as opacity, which is dynamic thus allowing easy insertion of points around spectral lines without a-priori knowledge of the ion stage populations. Results from SpK are compared to other codes and descriptions of radiation transport solutions which use SpK data are given. The treap data structure and SpK’s computational efficiency allows inline post-processing of 3D hydrodynamics simulations with a dynamically evolving spectrum stored in a treap.
Hartouni EP, Moore AS, Crilly AJ, et al., 2023, Evidence for suprathermal ion distribution in burning plasmas, NATURE PHYSICS, Vol: 19, Pages: 72-+, ISSN: 1745-2473
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- Citations: 8
Crilly AJ, Appelbe BD, Mannion OM, et al., 2022, Constraints on ion velocity distributions from fusion product spectroscopy, NUCLEAR FUSION, Vol: 62, ISSN: 0029-5515
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- Citations: 4
Moody JD, Pollock BB, Sio H, et al., 2022, Increased ion temperature and neutron yield observed in magnetized indirectly driven D_{2}-filled capsule implosions on the national ignition facility, Physical Review Letters, Vol: 129, ISSN: 0031-9007
The application of an external 26 Tesla axial magnetic field to a D_{2} gas-filled capsule indirectly driven on the National Ignition Facility is observed to increase the ion temperature by 40% and the neutron yield by a factor of 3.2 in a hot spot with areal density and temperature approaching what is required for fusion ignition [1]. The improvements are determined from energy spectral measurements of the 2.45 MeV neutrons from the D(d,n)^{3}He reaction, and the compressed central core B field is estimated to be ∼4.9 kT using the 14.1 MeV secondary neutrons from the D(T,n)^{4}He reactions. The experiments use a 30 kV pulsed-power system to deliver a ∼3 μs current pulse to a solenoidal coil wrapped around a novel high-electrical-resistivity AuTa_{4} hohlraum. Radiation magnetohydrodynamic simulations are consistent with the experiment.
Forrest CJ, Crilly A, Schwemmlein A, et al., 2022, Measurements of low-mode asymmetries in the areal density of laser-direct-drive deuterium-tritium cryogenic implosions on OMEGA using neutron spectroscopy, Review of Scientific Instruments, Vol: 93, Pages: 1-9, ISSN: 0034-6748
Areal density is one of the key parameters that determines the confinement time in inertial confinement fusion experiments, and low-mode asymmetries in the compressed fuel are detrimental to the implosion performance. The energy spectra from the scattering of the primary deuterium–tritium (DT) neutrons off the compressed cold fuel assembly are used to investigate low-mode nonuniformities in direct-drive cryogenic DT implosions at the Omega Laser Facility. For spherically symmetric implosions, the shape of the energy spectrum is primarily determined by the elastic and inelastic scattering cross sections for both neutron-deuterium and neutron-tritium kinematic interactions. Two highly collimated lines of sight, which are positioned at nearly orthogonal locations around the OMEGA target chamber, record the neutron time-of-flight signal in the current mode. An evolutionary algorithm is being used to extract a model-independent energy spectrum of the scattered neutrons from the experimental neutron time-of-flight data and is used to infer the modal spatial variations (l = 1) in the areal density. Experimental observations of the low-mode variations of the cold-fuel assembly (ρL0 + ρL1) show good agreement with a recently developed model, indicating a departure from the spherical symmetry of the compressed DT fuel assembly. Another key signature that has been observed in the presence of a low-mode variation is the broadening of the kinematic end-point due to the anisotropy of the dense fuel conditions.
Crilly A, Garin-Fernandez I, Appelbe B, et al., 2022, Efficacy of ICF experiments in light ion fusion cross section measurement at nucleosynthesis relevant energies, Frontiers in Physics, Vol: 10, Pages: 1-11, ISSN: 2296-424X
Inertial confinement fusion (ICF) experiments create a unique laboratory environment in which thermonuclear fusion reactionsoccur within a plasma, with conditions comparable to stellar cores and the early universe. In contrast, accelerator-basedmeasurements must compete with bound electron screening effects and beam stopping when measuring fusion cross sections atnucleosynthesis-relevant energies. Therefore, ICF experiments are a natural place to study nuclear reactions relevant to nuclearastrophysics. However, analysis of ICF-based measurements must address its own set of complicating factors. These include: theinherent range of reaction energies, spatial and temporal thermal temperature variation, and kinetic effects such as speciesseparation. In this work we examine these phenomena and develop an analysis to quantify and, when possible, compensate fortheir effects on our inference. Error propagation in the analyses are studied using synthetic data combined with Markov ChainMonte Carlo (MCMC) machine learning. The novel inference techniques will aid in the extraction of valuable and accurate data fromICF-based nuclear astrophysics experiments.
Meaney KD, Kim Y, Hoffman NM, et al., 2022, Design of multi neutron-to-gamma converter array for measuring time resolved ion temperature of inertial confinement fusion implosions., Review of Scientific Instruments, Vol: 93, Pages: 1-5, ISSN: 0034-6748
The ion temperature varying during inertial confinement fusion implosions changes the amount of Doppler broadening of the fusion products, creating subtle changes in the fusion neutron pulse as it moves away from the implosion. A diagnostic design to try to measure these subtle effects is introduced-leveraging the fast time resolution of gas Cherenkov detectors along with a multi-puck array that converts a small amount of the neutron pulse into gamma-rays, one can measure multiple snapshots of the neutron pulse at intermediate distances. Precise measurements of the propagating neutron pulse, specifically the variation in the peak location and the skew, could be used to infer time-evolved ion temperature evolved during peak compression.
Abu-Shawareb H, Acree R, Adams P, et al., 2022, Lawson criterion for ignition exceeded in an inertial fusion experiment, Physical Review Letters, Vol: 129, ISSN: 0031-9007
For more than half a century, researchers around the world have been engaged in attempts to achieve fusion ignition as a proof of principle of various fusion concepts. Following the Lawson criterion, an ignited plasma is one where the fusion heating power is high enough to overcome all the physical processes that cool the fusion plasma, creating a positive thermodynamic feedback loop with rapidly increasing temperature. In inertially confined fusion, ignition is a state where the fusion plasma can begin "burn propagation" into surrounding cold fuel, enabling the possibility of high energy gain. While "scientific breakeven" (i.e., unity target gain) has not yet been achieved (here target gain is 0.72, 1.37 MJ of fusion for 1.92 MJ of laser energy), this Letter reports the first controlled fusion experiment, using laser indirect drive, on the National Ignition Facility to produce capsule gain (here 5.8) and reach ignition by nine different formulations of the Lawson criterion.
Gopalaswamy V, Betti R, Radha PB, et al., 2022, Analysis of limited coverage effects on areal density measurements in inertial confinement fusion implosions, PHYSICS OF PLASMAS, Vol: 29, ISSN: 1070-664X
Crilly AJ, Appelbe BD, Mannion OM, et al., 2022, Neutron backscatter edges as a diagnostic of burn propagation, PHYSICS OF PLASMAS, Vol: 29, ISSN: 1070-664X
Moody JD, Pollock BB, Sio H, et al., 2022, The Magnetized Indirect Drive Project on the National Ignition Facility, JOURNAL OF FUSION ENERGY, Vol: 41, ISSN: 0164-0313
Mannion OM, Crilly AJ, Forrest CJ, et al., 2022, Measurements of the temperature and velocity of the dense fuel layer in inertial confinement fusion experiments, PHYSICAL REVIEW E, Vol: 105, ISSN: 2470-0045
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- Citations: 5
Bose A, Peebles J, Walsh CA, et al., 2022, Effect of strongly magnetized electrons and Ions on heat flow and symmetry of inertial fusion implosions, Physical Review Letters, Vol: 128, ISSN: 0031-9007
This Letter presents the first observation on how a strong, 500 kG, externally applied B field increases the mode-two asymmetry in shock-heated inertial fusion implosions. Using a direct-drive implosion with polar illumination and imposed field, we observed that magnetization produces a significant increase in the implosion oblateness (a 2.5× larger P2 amplitude in x-ray self-emission images) compared with reference experiments with identical drive but with no field applied. The implosions produce strongly magnetized electrons (ωeτe≫1) and ions (ωiτi>1) that, as shown using simulations, restrict the cross field heat flow necessary for lateral distribution of the laser and shock heating from the implosion pole to the waist, causing the enhanced mode-two shape.
Halliday JWD, Crilly A, Chittenden J, et al., 2022, Investigating radiatively driven, magnetized plasmas with a university scale pulsed-power generator, Physics of Plasmas, Vol: 29, Pages: 1-13, ISSN: 1070-664X
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.
Walsh CA, O'Neill S, Chittenden JP, et al., 2022, Magnetized ICF implosions: Scaling of temperature and yield enhancement, PHYSICS OF PLASMAS, Vol: 29, ISSN: 1070-664X
Walsh CA, Florido R, Bailly-Grandvaux M, et al., 2022, Exploring extreme magnetization phenomena in directly driven imploding cylindrical targets, Plasma Physics and Controlled Fusion, Vol: 64, Pages: 1-19, ISSN: 0741-3335
This paper uses extended-magnetohydrodynamics (MHD) simulations to explore an extreme magnetized plasma regime realizable by cylindrical implosions on the OMEGA laser facility. This regime is characterized by highly compressed magnetic fields (greater than 10 kT across the fuel), which contain a significant proportion of the implosion energy and induce large electrical currents in the plasma. Parameters governing the different magnetization processes such as Ohmic dissipation and suppression of instabilities by magnetic tension are presented, allowing for optimization of experiments to study specific phenomena. For instance, a dopant added to the target gas-fill can enhance magnetic flux compression while enabling spectroscopic diagnosis of the imploding core. In particular, the use of Ar K-shell spectroscopy is investigated by performing detailed non-LTE atomic kinetics and radiative transfer calculations on the MHD data. Direct measurement of the core electron density and temperature would be possible, allowing for both the impact of magnetization on the final temperature and thermal pressure to be obtained. By assuming the magnetic field is frozen into the plasma motion, which is shown to be a good approximation for highly magnetized implosions, spectroscopic diagnosis could be used to estimate which magnetization processes are ruling the implosion dynamics; for example, a relation is given for inferring whether thermally driven or current-driven transport is dominating.
Halliday JWD, Crilly A, Chittenden J, et al., 2022, An Experimental Study of Magnetic Flux Penetration in Radiatively Driven Plasma Flows, ISSN: 0730-9244
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.
Campbell PT, Walsh CA, Russell BK, et al., 2022, Measuring magnetic flux suppression in high-power laser-plasma interactions, Physics of Plasmas, Vol: 29, ISSN: 1070-664X
Biermann battery magnetic field generation driven by high power laser–solid interactions is explored in experiments performed with theOMEGA EP laser system. Proton deflectometry captures changes to the strength, spatial profile, and temporal dynamics of the self-generatedmagnetic fields as the target material or laser intensity is varied. Measurements of the magnetic flux during the interaction are used to helpvalidate extended magnetohydrodynamic (MHD) simulations. Results suggest that kinetic effects cause suppression of the Biermann batterymechanism in laser–plasma interactions relevant to both direct and indirect-drive inertial confinement fusion. Experiments also find thatmore magnetic flux is generated as the target atomic number is increased, which is counter to a standard MHD understanding.
Sio H, Moody JD, Ho DD, et al., 2021, Diagnosing plasma magnetization in inertial confinement fusion implosions using secondary deuterium-tritium reactions, Review of Scientific Instruments, Vol: 92, Pages: 1-5, ISSN: 0034-6748
Diagnosing plasma magnetization in inertial confinement fusion implosions is important for understanding how magnetic fields affect implosion dynamics and to assess plasma conditions in magnetized implosion experiments. Secondary deuterium–tritium (DT) reactions provide two diagnostic signatures to infer neutron-averaged magnetization. Magnetically confining fusion tritons from deuterium–deuterium (DD) reactions in the hot spot increases their path lengths and energy loss, leading to an increase in the secondary DT reaction yield. In addition, the distribution of magnetically confined DD-triton is anisotropic, and this drives anisotropy in the secondary DT neutron spectra along different lines of sight. Implosion parameter space as well as sensitivity to the applied B-field, fuel ρR, temperature, and hot-spot shape will be examined using Monte Carlo and 2D radiation-magnetohydrodynamic simulations.
Hare J, Burdiak G, Merlini S, et al., 2021, An imaging refractometer for density fluctuation measurements in high energy density plasmas, Review of Scientific Instruments, Vol: 92, ISSN: 0034-6748
We report on a recently developed laser-probing diagnostic which allows direct measurements of ray-deflection anglesin one axis, whilst retaining imaging capabilities in the other axis. This allows us to measure the spectrum of angulardeflections from a laser beam which passes though a turbulent high-energy-density plasma. This spectrum containsinformation about the density fluctuations within the plasma, which deflect the probing laser over a range of angles. Wecreate synthetic diagnostics using ray-tracing to compare this new diagnostic with standard shadowgraphy and schlierenimaging approaches, which demonstrates the enhanced sensitivity of this new diagnostic over standard techniques. Wepresent experimental data from turbulence behind a reverse shock in a plasma and demonstrate that this technique canmeasure angular deflections between 0.06 and 34 mrad, corresponding to a dynamic range of over 500.
Mannion OM, Woo KM, Crilly AJ, et al., 2021, Reconstructing 3D asymmetries in laser-direct-drive implosions on OMEGA, REVIEW OF SCIENTIFIC INSTRUMENTS, Vol: 92, ISSN: 0034-6748
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- Citations: 8
Appelbe B, Velikovich AL, Sherlock M, et al., 2021, Magnetic field transport in propagating thermonuclear burn, Physics of Plasmas, Vol: 28, Pages: 1-9, ISSN: 1070-664X
High energy gain in inertial fusion schemes requires the propagation of a thermonuclear burn wave from hot to cold fuel. We consider the problem of burn propagation when a magnetic field is orthogonal to the burn wave. Using an extended-MHD model with a magnetized α energy transport equation, we find that the magnetic field can reduce the rate of burn propagation by suppressing electron thermal conduction and α particle flux. Magnetic field transport during burn propagation is subject to competing effects: the field can be advected from cold to hot regions by ablation of cold fuel, while the Nernst and α particle flux effects transport the field from hot to cold fuel. These effects, combined with the temperature increase due to burn, can cause the electron Hall parameter to grow rapidly at the burn front. This results in the formation of a self-insulating layer between hot and cold fuel, which reduces electron thermal conductivity and α transport, increases the temperature gradient, and reduces the rate of burn propagation.
Crilly AJ, Appelbe BD, Mannion OM, et al., 2021, The effect of areal density asymmetries on scattered neutron spectra in ICF implosions, Physics of Plasmas, Vol: 28, Pages: 1-9, ISSN: 1070-664X
Scattered neutron spectroscopy is a diagnostic technique commonly used to measure areal density in inertial confinement fusion experiments. Deleterious areal density asymmetries modify the shape of the scattered neutron spectrum. In this work, a novel analysis is developed, which can be used to fit the shape change. This will allow experimental scattered neutron spectroscopy to directly infer the amplitude and mode of the areal density asymmetries, with little sensitivity to confounding factors that affect other diagnostics for areal density. The model is tested on spectra produced by a neutron transport calculation with both isotropic and anisotropic primary fusion neutron sources. Multiple lines of sight are required to infer the areal density distribution over the whole sphere—we investigate the error propagation and optimal detector arrangement associated with the inference of mode 1 asymmetries.
Walsh CA, Crilly AJ, Chittenden JP, 2020, Magnetized directly-driven ICF capsules: increased instability growth from non-uniform laser drive, Nuclear Fusion, Vol: 60, Pages: 1-8, ISSN: 0029-5515
Simulations anticipate increased perturbation growth from non-uniform laser heating for magnetized direct-drive implosions. At the capsule pole, where the magnetic field is normal to the ablator surface, the field remains in the conduction zone and suppresses non-radial thermal conduction; in unmagnetized implosions this non-radial heat-flow is crucial in mitigating laser heating imbalances. Single-mode simulations show the magnetic field particularly amplifying short wavelength perturbations, whose behavior is dominated by thermal conduction. The most unstable wavelength can also become shorter. 3D multi-mode simulations of the capsule pole reinforce these findings, with increased perturbation growth anticipated across a wide range of scales. The results indicate that high-gain spherical direct-drive implosions require greater constraints on the laser heating uniformity when magnetized.
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