Publications
41 results found
Read J, Burdiak G, Bland SN, et al., 2024, Point projection radiography of electromagnetically accelerated flyer plates with an external X-pinch driver., Rev Sci Instrum, Vol: 95
A platform for flyer plate benchmarking experiments has been developed, with an external X-pinch driver for point projection radiography. The experiments were performed using CEPAGE, a low inductance pulsed power machine at First Light Fusion (2 MA, 1.4 µs), with a new vacuum transmission line and flyer load hardware designed specifically to give a line of sight for radiography. A broadband 10-20 keV x-ray source was produced by a portable X-pinch driver (140 kA, 350 ns) [Strucka et al., Matter Radiat. Extremes 7, 016901 (2021)] and was used to image the flyer. Radiography compliments the pre-existing diagnostic suite, which consists of current probes, velocimetry, and side-on optical probing of the impact shock transmitted into a transparent sample. The platform allows for significant insights into the 2D and 3D nature of the flyer launch, such as deformation and instability formation. It was used to diagnose a 10 × 9 × 1 mm3 aluminum flyer, which reached a peak velocity of 4.2 km s-1 before impact with a poly(methylmethacrylate) sample. The experimental configuration, on-shot source characterization, and the results from two flyer plate experiments on CEPAGE are discussed.
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.
Chaturvedi N, Chittenden J, Niasse N, 2022, Modelling Hedp Systems with Strong Radiative Loss Using Static Mesh Refinement, ISSN: 0730-9244
Radiative collapse occurs in dense plasmas where radiative loss drops the thermal pressure below the compressional magnetic pressure, leading to a runaway collapse to very small scale lengths. This is typically studied in Z-pinch plasmas when the current applied exceeds the Pease-Braginskii current (where the pinch is in pressure equilibrium). Studies have also been extended to X-pinch loads, where the crossing point between two wires forms a micro Z-pinch with even stronger jxB compression. The collapse can be terminated by various processes; development of instabilities, reaching the photon self-absorption (optically thick) limit, or in extreme cases the electron degeneracy limit.
Chapman DA, Pecover JD, Chaturvedi N, et al., 2021, A preliminary assessment of the sensitivity of uniaxially driven fusion targets to flux-limited thermal conduction modeling, Physics of Plasmas, Vol: 28, Pages: 1-15, ISSN: 1070-664X
The role of flux-limited thermal conduction on the fusion performance of the uniaxially driven targets studied by Derentowicz et al. [J. Tech. Phys. 18, 465 (1977) and J. Tech. Phys. 25, 135 (1977)] is explored as part of a wider effort to understand and quantify uncertainties in inertial confinement fusion (ICF) systems sharing similarities with First Light Fusion's projectile-driven concept. We examine the role of uncertainties in plasma microphysics and different choices for the numerical implementation of the conduction operator on simple metrics encapsulating the target performance. The results indicate that choices that affect the description of ionic heat flow between the heated fusion fuel and the gold anvil used to contain it are the most important. The electronic contribution is found to be robustly described by local diffusion. The sensitivities found suggest a prevalent role for quasi-nonlocal ionic transport, especially in the treatment of conduction across material interfaces with strong gradients in temperature and conductivity. We note that none of the simulations produce neutron yields that substantiate those reported by Derentowicz et al. [J. Tech. Phys. 25, 135 (1977)], leaving open future studies aimed at more fully understanding this class of ICF systems.
Suttle LG, Hare JD, Lebedev SV, et al., 2018, Ion heating and magnetic flux pile-up in a magnetic reconnection experiment with super-Alfvenic plasma inflows, Physics of Plasmas, Vol: 25, ISSN: 1070-664X
This work presents a magnetic reconnection experiment in which the kinetic, magnetic, and thermal properties of the plasma each play an important role in the overall energy balance and structure of the generated reconnection layer. Magnetic reconnection occurs during the interaction of continuous and steady flows of super-Alfvénic, magnetized, aluminum plasma, which collide in a geometry with two-dimensional symmetry, producing a stable and long-lasting reconnection layer. Optical Thomson scattering measurements show that when the layer forms, ions inside the layer are more strongly heated than electrons, reaching temperatures of Ti∼Z⎯⎯⎯Te≳300 eV—much greater than can be expected from strong shock and viscous heating alone. Later in time, as the plasma density in the layer increases, the electron and ion temperatures are found to equilibrate, and a constant plasma temperature is achieved through a balance of the heating mechanisms and radiative losses of the plasma. Measurements from Faraday rotation polarimetry also indicate the presence of significant magnetic field pile-up occurring at the boundary of the reconnection region, which is consistent with the super-Alfvénic velocity of the inflows.
Hare JD, Lebedev SV, Suttle LG, et al., 2017, Formation and structure of a current sheet in pulsed-power driven magnetic reconnection experiments, Physics of Plasmas, Vol: 24, ISSN: 1070-664X
We describe magnetic reconnection experiments using a new, pulsed-powerdriven experimental platform in which the inflows are super-sonic butsub-Alfv\'enic.The intrinsically magnetised plasma flows are long lasting,producing a well-defined reconnection layer that persists over manyhydrodynamic time scales.The layer is diagnosed using a suite of highresolution laser based diagnostics which provide measurements of the electrondensity, reconnecting magnetic field, inflow and outflow velocities and theelectron and ion temperatures.Using these measurements we observe a balancebetween the power flow into and out of the layer, and we find that the heatingrates for the electrons and ions are significantly in excess of the classicalpredictions. The formation of plasmoids is observed in laser interferometry andoptical self-emission, and the magnetic O-point structure of these plasmoids isconfirmed using magnetic probes.
Walsh C, Chittenden JP, McGlinchey K, et al., 2017, Self-Generated magnetic fields in the stagnation phase of indirect-drive implosions on the national ignition facility, Physical Review Letters, Vol: 118, ISSN: 1079-7114
Three-dimensional extended-magnetohydrodynamic simulations of the stagnation phase of inertial confinement fusion implosion experiments at the National Ignition Facility are presented, showing self-generated magnetic fields over 10^4 T. Angular high mode-number perturbations develop large magnetic fields, but are localized to the cold, dense hot-spot surface, which is hard to magnetize. When low-mode perturbations are also present, the magnetic fields are injected into the hot core, reaching significant magnetizations, with peak local thermal conductivity reductions greater than 90%. However, Righi-Leduc heat transport effectively cools the hot spot and lowers the neutron spectra-inferred ion temperatures compared to the unmagnetized case. The Nernst effect qualitatively changes the results by demagnetizing the hot-spot core, while increasing magnetizations at the edge and near regions of large heat loss.
Hare JD, Suttle L, Lebedev SV, et al., 2017, Anomalous heating and plasmoid formation in a driven magnetic reconnection experiment, Physical Review Letters, Vol: 118, ISSN: 0031-9007
We present a detailed study of magnetic reconnection in a quasi-two-dimensional pulsed-power driven laboratory experiment. Oppositely directed magnetic fields (B=3 T), advected by supersonic, sub-Alfvénic carbon plasma flows (Vin=50 km/s), are brought together and mutually annihilate inside a thin current layer (δ=0.6 mm). Temporally and spatially resolved optical diagnostics, including interferometry, Faraday rotation imaging, and Thomson scattering, allow us to determine the structure and dynamics of this layer, the nature of the inflows and outflows, and the detailed energy partition during the reconnection process. We measure high electron and ion temperatures (Te=100 eV, Ti=600 eV), far in excess of what can be attributed to classical (Spitzer) resistive and viscous dissipation. We observe the repeated formation and ejection of plasmoids, consistent with the predictions from semicollisional plasmoid theory.
Suttle LG, Hare JD, Lebedev SV, et al., 2016, Structure of a Magnetic Flux Annihilation Layer Formed by the Collision of Supersonic, Magnetized Plasma Flows, Physical Review Letters, Vol: 116, ISSN: 1079-7114
We present experiments characterizing the detailed structure of a current layer, generated by the collision of two counterstreaming, supersonic and magnetized aluminum plasma flows. The antiparallel magnetic fields advected by the flows are found to be mutually annihilated inside the layer, giving rise to a bifurcated current structure—two narrow current sheets running along the outside surfaces of the layer. Measurements with Thomson scattering show a fast outflow of plasma along the layer and a high ion temperature (Ti∼Z¯Te, with average ionization Z¯=7). Analysis of the spatially resolved plasma parameters indicates that the advection and subsequent annihilation of the inflowing magnetic flux determines the structure of the layer, while the ion heating could be due to the development of kinetic, current-driven instabilities.
Chittenden JP, Appelbe BD, Manke F, et al., 2016, Signatures of asymmetry in neutron spectra and images predicted by three-dimensional radiation hydrodynamics simulations of indirect drive implosions, Physics of Plasmas, Vol: 23, ISSN: 1089-7674
We present the results of 3D simulations of indirect drive inertial confinement fusion capsules driven by the “high-foot” radiation pulse on the National Ignition Facility. The results are post-processed using a semi-deterministic ray tracing model to generate synthetic deuterium-tritium (DT) and deuterium-deuterium (DD) neutronspectra as well as primary and down scatteredneutronimages. Results with low-mode asymmetries are used to estimate the magnitude of anisotropy in the neutronspectra shift, width, and shape. Comparisons of primary and down scatteredimages highlight the lack of alignment between the neutron sources,scatter sites, and detector plane, which limits the ability to infer the ρr of the fuel from a down scattered ratio. Further calculations use high bandwidth multi-mode perturbations to induce multiple short scale length flows in the hotspot. The results indicate that the effect of fluid velocity is to produce a DT neutronspectrum with an apparently higher temperature than that inferred from the DD spectrum and which is also higher than the temperature implied by the DT to DD yield ratio.
Burdiak GC, Lebedev SV, Clayson T, et al., 2016, THE EFFECT OF MAGNETIC FIELD ORIENTATION ON THE STRUCTURE AND INTERACTION OF MAGNETISED BOW SHOCKS IN PULSED-POWER DRIVEN EXPERIMENTS, 43rd IEEE International Conference on Plasma Science (ICOPS), Publisher: IEEE
Bott-Suzuki SC, Bendixsen LSC, Cordaro SW, et al., 2015, Investigation of radiative bow-shocks in magnetically accelerated plasma flows, PHYSICS OF PLASMAS, Vol: 22, ISSN: 1070-664X
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- Citations: 10
Burdiak GC, Lebedev SV, Suzuki-Vidal F, et al., 2015, Cylindrical liner Z-pinch experiments for fusion research and high-energy-density physics, Journal of Plasma Physics, Vol: 81, ISSN: 1469-7807
A gas-filled cylindrical liner z-pinch configuration has been used to drive convergentradiative shock waves into different gases at velocities of 20–50 km s−1. On applicationof the 1.4 MA, 240 ns rise-time current pulse produced by the Magpie generatorat Imperial College London, a series of cylindrically convergent shock waves aresequentially launched into the gas-fill from the inner wall of the liner. This occurswithout any bulk motion of the liner wall itself. The timing and trajectories of theshocks are used as a diagnostic tool for understanding the response of the linerz-pinch wall to a large pulsed current. This analysis provides useful data on theliner resistivity, and a means to test equation of state (EOS) and material strengthmodels within MHD simulation codes. In addition to providing information on linerresponse, the convergent shocks are interesting to study in their own right. The shocksare strong enough for radiation transport to influence the shock wave structure. Inparticular, we see evidence for both radiative preheating of material ahead of theshockwaves and radiative cooling instabilities in the shocked gas. Some preliminaryresults from initial gas-filled liner experiments with an applied axial magnetic fieldare also discussed.
Chittenden JP, Lebedev SV, Pecover J, et al., 2015, Alternative preheating mechanisms for MagLIF
Bott-Suzuki SC, Cordaro SW, Bendixsen LSC, et al., 2015, Investigation of magnetized, radiative bow-shocks in magnetically accelerated plasma flows
Ampleford DJ, Hansen SB, Jennings CA, et al., 2015, Scaling and enhancement of non-thermal line emission on z to hν ∼ 22 kev
Mariscal D, McGuffey C, Valenzuela J, et al., 2014, Measurement of pulsed-power-driven magnetic fields via proton deflectometry, APPLIED PHYSICS LETTERS, Vol: 105, ISSN: 0003-6951
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- Citations: 19
Ivanov VV, Anderson AA, Papp D, et al., 2014, UV Laser-Probing Diagnostics for the Dense Z Pinch, IEEE TRANSACTIONS ON PLASMA SCIENCE, Vol: 42, Pages: 1153-1162, ISSN: 0093-3813
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- Citations: 12
Lebedev SV, Suttle L, Swadling GF, et al., 2014, The formation of reverse shocks in magnetized high energy density supersonic plasma flows, PHYSICS OF PLASMAS, Vol: 21, ISSN: 1070-664X
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- Citations: 30
Burdiak GC, Lebedev SV, Harvey-Thompson AJ, et al., 2014, Radiative precursors driven by converging blast waves in noble gases, PHYSICS OF PLASMAS, Vol: 21, ISSN: 1070-664X
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- Citations: 6
Ivanov VV, Papp D, Anderson AA, et al., 2013, Study of micro-pinches in wire-array Z pinches, PHYSICS OF PLASMAS, Vol: 20, ISSN: 1070-664X
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- Citations: 11
Ivanov VV, Anderson AA, Papp D, et al., 2013, Current redistribution and generation of kinetic energy in the stagnated <i>Z</i> pinch, PHYSICAL REVIEW E, Vol: 88, ISSN: 1539-3755
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- Citations: 12
Swadling GF, Lebedev SV, Niasse N, et al., 2013, Oblique shock structures formed during the ablation phase of aluminium wire array z-pinches, PHYSICS OF PLASMAS, Vol: 20, ISSN: 1070-664X
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- Citations: 45
Taylor S, Appelbe B, Niasse NP, et al., 2013, Effect of perturbations on yield in ICF targets-4π 3D hydro simulations, IFSA 2011 - SEVENTH INTERNATIONAL CONFERENCE ON INERTIAL FUSION SCIENCES AND APPLICATIONS, Vol: 59, ISSN: 2100-014X
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- Citations: 4
Ivanov VV, Chittenden JP, Mancini RC, et al., 2012, Investigation of plasma instabilities in the stagnated <i>Z</i> pinch, PHYSICAL REVIEW E, Vol: 86, ISSN: 1539-3755
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- Citations: 17
Ivanov VV, Chittenden JP, Altemara SD, et al., 2011, Study of the Internal Structure and Small-Scale Instabilities in the Dense $Z$ Pinch, Phys. Rev. Lett., Vol: 107, Pages: 165002-165002
Pickworth LA, Bland SN, Lebedev SV, et al., 2011, Preliminary opacity experiments in dense high Z plasmas on the magpie facility, Pages: 1-1, ISSN: 0730-9244
Niasse N, Chittenden J, 2011, Atomic model and synthetic diagnostics for large scale parallel simulations of wire array Z-pinches, Pages: 1-1, ISSN: 0730-9244
Swadling GF, Lebedev SV, Bland SN, et al., 2011, End-on laser probing of the ablation phase of wire array z-pinch implosions on the magpie generator, Pages: 1-1, ISSN: 0730-9244
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