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  • Journal article
    Winter RE, Cotton M, Harris EJ, Chapman DJ, Eakins Det al., 2015,

    Generation of ramp waves using variable areal density flyers

    , Shock Waves, Vol: 26, Pages: 395-401, ISSN: 0938-1287

    Ramp loading using graded density impactors as flyers in gas-gun-driven plate impact experiments can yield new and useful information about the equation of state and the strength properties of the loaded material. Selective Laser Melting, an additive manufacturing technique, was used to manufacture a graded density flyer, termed the “bed-of-nails” (BON). A 2.5-mm-thick ×× 99.4-mm-diameter solid disc of stainless steel formed a base for an array of tapered spikes of length 5.5 mm and spaced 1 mm apart. The two experiments to test the concept were performed at impact velocities of 900 and 1100 m/s using the 100-mm gas gun at the Institute of Shock Physics at Imperial College London. In each experiment, a BON flyer was impacted onto a copper buffer plate which helped to smooth out perturbations in the wave profile. The ramp delivered to the copper buffer was in turn transmitted to three tantalum targets of thicknesses 3, 5 and 7 mm, which were mounted in contact with the back face of the copper. Heterodyne velocimetry (Het-V) was used to measure the velocity–time history, at the back faces of the tantalum discs. The wave profiles display a smooth increase in velocity over a period of ∼2.5μs∼2.5μs , with no indication of a shock jump. The measured profiles have been analysed to generate a stress vs. volume curve for tantalum. The results have been compared with the predictions of the Sandia National Laboratories hydrocode, CTH.
  • Conference paper
    Hare JD, Lebedev SV, Bennett M, Bland SN, Burdiak GC, Suttle L, Suzuki-Vidal F, Swadling GFet al., 2015,

    Photo-ionisation of gas by x-rays from a wire array z-pinch
  • Conference paper
    Burdiak GC, Lebedev SV, Bland S, Suzuki-Vidal F, Swadling GF, Suttle L, Bennet M, Williams RJR, Blesener Ket al., 2015,

    Radiative precursors driven by converging blast waves in noble gases
  • Conference paper
    Cotton M, Chapman D, Winter R, Harris E, Eakins Det al., 2015,

    Tailored ramp wave generation in gas gun experiments

    , 11th International Conference on the Mechanical and Physical Behaviour of Materials under Dynamic Loading (DYMAT), Publisher: E D P SCIENCES, ISSN: 2100-014X
  • Journal article
    Eakins D, Chapman D, 2014,

    X-ray imaging of subsurface dynamics in high-Z materials at the Diamond Light Source

    , Review of Scientific Instruments, Vol: 85, Pages: 123708-123708, ISSN: 1089-7623

    In this paper, we describe a new approach enabling study of subsurface dynamics in high-Z materials using the unique combination of high-energy synchrotron X-rays, a hybrid bunch structure, and a new dynamic loading platform. We detail the design and operation of the purpose-built, portable small bore gas-gun, which was installed on the I12 high-energy beamline at the Diamond Light Source and used to drive compression waves into solid and porous metal targets. Using a hybrid bunch structure and broadband X-ray pulses of up to 300 keV, radiographic snapshots were captured during various dynamic deformation processes in cm-scale specimens, thereby contributing to a more complete understanding of the evolution of mesoscale damage. Importantly, we highlight strategies for overcoming the challenges associated with using high-energy X-rays, and suggest areas for improvement needed to advance dynamic imaging through large-scale samples of relevance to engineering scenarios. These preliminary measurements demonstrate the feasibility of probing highly transient phenomena using the presented methodology.
  • Journal article
    Sherlock, Hill EG, Evans, Rose, W Rozmuset al., 2014,

    In-depth Plasma-Wave Heating of Dense Plasma Irradiated by Short Laser Pulses

    , Physical Review Letters, Vol: 113, ISSN: 1079-7114
  • Journal article
    Swadling GF, Lebedev SV, Hall GN, Patankar S, Stewart NH, Smith RA, Harvey-Thompson AJ, Burdiak GC, de Grouchy P, Skidmore J, Suttle L, Suzuki-Vidal F, Bland SN, Kwek KH, Pickworth L, Bennett M, Hare JD, Rozmus W, Yuan Jet al., 2014,

    Diagnosing collisions of magnetized, high energy density plasma flows using a combination of collective Thomson scattering, Faraday rotation, and interferometry

    , REVIEW OF SCIENTIFIC INSTRUMENTS, Vol: 85, ISSN: 0034-6748
  • Journal article
    Kanel GI, Garkushin GV, Savinykh AS, Razorenov SV, de Resseguier T, Proud WG, Tyutin MRet al., 2014,

    Shock response of magnesium single crystals at normal and elevated temperatures

    , Journal of Applied Physics, Vol: 116, Pages: 1-9, ISSN: 0021-8979

    A series of magnesium single crystals, from 0.2 to 3 mm thick, were shock loaded in directions parallel and perpendicular to the c-axis of the hexagonal closed packed (hcp) structure and at 45° to the c-axis. Shock compression along the c-axis is associated with the largest Hugoniot elastic limit (HEL) for this material. Microscopic observation of recovered c-cut samples demonstrated intense twinning with a greater density of twins near the impact surface. The low-energy basal slip was activated by shock loading along the inclined direction and has the smallest HEL. In all cases, we observe the decay of the elastic precursor wave and growth of the HEL with increasing temperature. For the inclined shock compression after the HEL, two plastic waves were found where the stress level of the first plastic wave depends on the peak shock stress. Finally, the largest spall strength was along the transversal direction and the smallest in the off-axis direction. The fracture surface of the sample of transversal orientation contains numerous groves oriented along the base planes of the crystals.
  • Journal article
    Tunnell R, Ashcroft M, Dale R, Tod D, Proud WGet al., 2014,

    Ammonium Perchlorate, Friend or Foe?

    , PROPELLANTS EXPLOSIVES PYROTECHNICS, Vol: 39, Pages: 707-713, ISSN: 0721-3115
  • Journal article
    Turrell AE, Sherlock M, Rose SJ, 2014,

    Effects of Large-Angle Coulomb Collisions on Inertial Confinement Fusion Plasmas (vol 112, 245002, 2014)

    , PHYSICAL REVIEW LETTERS, Vol: 113, ISSN: 0031-9007
  • Journal article
    Tunnell R, Ashcroft M, Dale R, Tod D, Proud WGet al., 2014,

    Ammonium Perchlorate, Friend or Foe? Part 1: The Influence of this Oxidizer on the Aging Behavior of Propellant Compositions

    , PROPELLANTS EXPLOSIVES PYROTECHNICS, Vol: 39, Pages: 504-510, ISSN: 0721-3115
  • Journal article
    Hill EG, Rose SJ, 2014,

    Non-thermal enhancement of electron-positron pair creation in burning thermonuclear laboratory plasmas

    , High Energy Density Physics
  • Journal article
    Hall GN, Burdiak GC, Suttle L, Stuart NH, Swadling GF, Lebedev SV, Smith RA, Patankar S, Suzuki Vidal F, de Grouchy P, Harvey-Thompson AJ, Bennett M, Bland SN, Pickworth L, Skidmore Jet al., 2014,

    Monochromatic radiography of high energy density physics experiments on the MAGPIE generator

    , Review of Scientific Instruments, Vol: 85, ISSN: 1089-7623

    A monochromatic X-ray backlighter based on Bragg reflection from a spherically bent quartzcrystal has been developed for the MAGPIE pulsed power generator at Imperial College (1.4 MA,240 ns) [I. H. Mitchell et al., Rev. Sci. Instrum. 67, 1533 (2005)]. This instrument has been usedto diagnose high energy density physics experiments with 1.865 keV radiation (Silicon He-α) froma laser plasma source driven by a ∼7 J, 1 ns pulse from the Cerberus laser. The design of thediagnostic, its characterisation and performance, and initial results in which the instrument was usedto radiograph a shock physics experiment on MAGPIE are discussed.
  • Journal article
    Turrell AE, Rose SJ, Sherlock M, 2014,

    Effects of Large-Angle Coulomb Collisions on Inertial Confinement Fusion Plasmas

    , Physical Review Letters, Vol: 112

    Large-angle Coulomb collisions affect the rates of energy and momentum exchange in a plasma, and it is expected that their effects will be important in many plasmas of current research interest, including in inertial confinement fusion. Their inclusion is a long-standing problem, and the first fully self-consistent method for calculating their effects is presented. This method is applied to “burn” in the hot fuel in inertial confinement fusion capsules and finds that the yield increases due to an increase in the rate of temperature equilibration between electrons and ions which is not predicted by small-angle collision theories. The equilibration rate increases are 50%–100% for number densities of 10^{30} m^{−3} and temperatures around1 keV.
  • Journal article
    Pike OJ, Mackenroth F, Hill EG, Rose SJet al., 2014,

    A photon-photon collider in a vacuum hohlraum

    , Nature Photonics, Vol: 8, Pages: 434-436, ISSN: 1749-4885

    The ability to create matter from light is amongst the most striking predictions of quantum electrodynamics. Experimental signatures of this have been reported in the scattering of ultra-relativistic electron beams with laser beams1,2, intense laser–plasma interactions3 and laser-driven solid target scattering4. However, all such routes involve massive particles. The simplest mechanism by which pure light can be transformed into matter, Breit–Wheeler pair production (γγ′ → e+e−)5, has never been observed in the laboratory. Here, we present the design of a new class of photon–photon collider in which a gamma-ray beam is fired into the high-temperature radiation field of a laser-heated hohlraum. Matching experimental parameters to current-generation facilities, Monte Carlo simulations suggest that this scheme is capable of producing of the order of 105 Breit–Wheeler pairs in a single shot. This would provide the first realization of a pure photon–photon collider, representing the advent of a new type of high-energy physics experiment.
  • Journal article
    Pile D, Pike O, 2014,

    Light into matter

    , NATURE PHOTONICS, Vol: 8, Pages: 496-496, ISSN: 1749-4885
  • Journal article
    Pike OJ, Rose SJ, 2014,

    Dynamical friction in a relativistic plasma

    , PHYSICAL REVIEW E, Vol: 89, ISSN: 1539-3755
  • Journal article
    Lebedev SV, Suttle L, Swadling GF, Bennett M, Bland SN, Burdiak GC, Burgess D, Chittenden JP, Ciardi A, Clemens A, de Grouchy P, Hall GN, Hare JD, Kalmoni N, Niasse N, Patankar S, Sheng L, Smith RA, Suzuki-Vidal F, Yuan J, Frank A, Blackman EG, Drake RPet al., 2014,

    The formation of reverse shocks in magnetized high energy density supersonic plasma flows

    , PHYSICS OF PLASMAS, Vol: 21, ISSN: 1070-664X
  • Journal article
    Keenan FP, Doyle JG, Madjarska MS, Rose SJ, Bowler LA, Britton J, McCrink L, Mathioudakis Met al., 2014,

    INTENSITY ENHANCEMENT OF O VI ULTRAVIOLET EMISSION LINES IN SOLAR SPECTRA DUE TO OPACITY

    , ASTROPHYSICAL JOURNAL LETTERS, Vol: 784, ISSN: 2041-8205
  • Conference paper
    Nguyen TT, Davey T, Proud W, 2014,

    Percolation of Gas and Attenuation of Shock Waves through Granular Beds and Perforated Sheets

    , New Trends in Research of Energetic Materials
  • Journal article
    Winter RE, Cotton M, Harris EJ, Chapman DJ, Eakins Det al., 2014,

    A novel graded density impactor

    , Journal of Physics: Conference Series, Vol: 500, ISSN: 1742-6588

    Ramp loading using graded-density-impactors as flyers in gas-gun-driven plate impact experiments can yield new and useful information about the equation of state and the strength properties of the loaded material. Selective Laser Melting, an additive manufacture technique, was used to manufacture a graded density flyer, termed the «bed of nails» (BON). A 2 mm thick × 100 mm diameter solid disc of stainless steel formed a base for an array of tapered spikes of length 6 mm and spaced 1 mm apart. The two experiments to test the concept were performed at impact velocities of 900 m/s and 1100 m/s using the 100 mm gas gun at the Institute of Shock Physics at Imperial College, London. In each experiment a BON flyer was impacted onto a copper buffer plate which helped to smooth out perturbations in the wave profile. The ramp delivered to the copper buffer was in turn transmitted to three tantalum targets of thicknesses 3, 5 and 7 mm, which were mounted in contact with the back face of the copper. Heterodyne velocimetry was used to measure the velocity-time history, at the back faces of the tantalum discs. The wave profiles display a smooth increase in velocity over a period of ∼2.5 us, with no indication of a shock jump. The measured profiles have been analysed to generate a stress strain curve for tantalum. The results have been compared with the predictions of the Sandia National Laboratories hydrocode, CTH. © Published under licence by IOP Publishing Ltd.
  • Journal article
    Winter RE, Cotton M, Harris EJ, Maw JR, Chapman DJ, Eakins DE, McShane Get al., 2014,

    Plate-impact loading of cellular structures formed by selective laser melting

    , MODELLING AND SIMULATION IN MATERIALS SCIENCE AND ENGINEERING, Vol: 22, ISSN: 0965-0393
  • Journal article
    Burdiak GC, Lebedev SV, Harvey-Thompson AJ, Swadling GF, Suzuki-Vidal F, Hall GN, Khoory E, Pickworth L, Bland SN, de Grouchy P, Skidmore J, Suttle L, Bennett M, Niasse NPL, Williams RJR, Blesener K, Atoyan L, Cahill A, Hoyt C, Potter W, Rosenberg E, Schrafel P, Kusse Bet al., 2014,

    Radiative precursors driven by converging blast waves in noble gases

    , PHYSICS OF PLASMAS, Vol: 21, ISSN: 1070-664X
  • Journal article
    Tear GR, Eakins DE, Chapman DJ, Proud WGet al., 2014,

    Technique to measure change in birefringence under shock compression

    , Journal of Physics: Conference Series, Vol: 500, ISSN: 1742-6588

    A technique has been developed to measure the change in birefringence along the axis of shock propagation, probing the relative refractive indices of the material perpendicular to shock propagation. Experiments were performed on calcite single crystals and the results compared to previous literature studies on calcite quasi-static behaviour. Interface velocities are determined using fibre based homodyne Photon Doppler Velocimetry (PDV) operating at 1550 nm whilst the birefringence technique uses free space 532 nm optics. A change in birefringence of Δn = 0.0029 ± 0.0001 was observed. This was higher than the predicted change found using a hydrostatic model based on previous studies.
  • Journal article
    Jones DR, Chapman DJ, Eakins DE, 2014,

    Gas gun driven dynamic fracture and fragmentation of Ti-6Al-4V cylinders

    , Journal of Physics: Conference Series, Vol: 500, ISSN: 1742-6588

    The dynamic fracture and fragmentation of a material is a complex late stage phenomenon occurring in many shock loading scenarios. Improving our predictive capability depends upon exercising our current failure models against new loading schemes and data. We present axially-symmetric high strain rate (104 s−1) expansion of Ti-6Al-4V cylinders using a single stage light gas gun technique. A steel ogive insert was located inside the target cylinder, into which a polycarbonate rod was launched. Deformation of this rod around the insert drives the cylinder into rapid expansion. This technique we have developed facilitates repeatable loading, independent of the temperature of the sample cylinder, with straightforward adjustment of the radial strain rate. Expansion velocity was measured with multiple channels of photon Doppler velocimetry. High speed imaging was used to track the overall expansion process and record strain to failure and crack growth. Results from a cylinder at a temperature of 150 K are compared with work at room temperature, examining the deformation, failure mechanisms and differences in fragmentation.
  • Journal article
    Chen LE, Eakins DE, Chapman DC, Thadhani N, Swift DC, Kumar Met al., 2014,

    Dynamic behavior of a Ce-Al bulk metallic glass

    , Journal of Physics: Conference Series, Vol: 500, ISSN: 1742-6588

    The mechanisms of stress relaxation in metallic glasses under high strain rates arean area of active study. The lack of extended structure forces strain accommodation throughalternative modes to slip. For example, amorphous Ce3Al has been shown to undergo a phasetransition to the crystalline FCC Ce3Al at 25 GPa under quasistatic loading. Whether thismechanism extends to high strain rates has yet to be determined. We present results ofan initial study into the ultrafast deformation characteristics of a Ce-Al bulk metallic glass.Using the Janus laser at the Jupiter Laser Facility (LLNL), thin targets 30 micron in thicknesswere shocked over a range of pressures up to 30 GPa. The velocity of the target rear surfacewas measured using a line-imaging VISAR to reveal features in the wave profile attributedto stress relaxation. In addition, experiments were performed on crystalline forms of Ce-Alprepared through heat treatment of the amorphous material. Preliminary results reveal adistinct precursor wave above and below 1.5 GPa, which gives way to a complex multiwavestructure around 1.5 GPa, most likely indicative of a polyamorphic transition.
  • Journal article
    Collinson MA, Chapman DJ, Eakins DE, 2014,

    Spatially resolved shock response at dry metallic multi-material interfaces

    , Journal of Physics: Conference Series, Vol: 500, ISSN: 1742-6588

    The high strain-rate behaviour of multi-component systems is often dominated by mediation at material interfaces. The extent to which a materials microstructure influences dynamic friction and relative sliding response remains an area of active study. Initial results from a study on the behaviour of dry metallic interfaces under the passage of a controlled loading wave are presented. Held in close contact along a single planar interface, oblique shock waves were generated along the boundary by direct copper flyer impact at velocities in the range 250 ms−1 – 300 ms−1. Both the 100 mm and 13 mm bore gas guns located at Imperial College London were utilised for this purpose. A line-imaging velocity interferometer system for any reflector (VISAR) system was used to directly record the velocity profile across the contact interface, providing a measure of any spatially dependent response while photon doppler velocimetry (PDV) was used to determine the far field response. Comparisons of these results against current generation hydrocode models are presented, with significant deviations from the computationally predicted results identified in the peak shock state immediately following shock breakout.
  • Journal article
    Winters JBR, Bland SN, Stafford SJP, Chapman DJ, Eakins DEet al., 2014,

    VISAR 'cross-hairs': Simultaneous perpendicular line-imaging VISAR

    , Journal of Physics: Conference Series, Vol: 500, ISSN: 1742-6588

    Often the velocity measured at the rear surface of a dynamic compression targetvaries spatially, caused for instance by the tilt/curvature of a gas gun flyer, asymmetries inthe magnetic field on a pulsed power driven experiment, or meso-scale heterogeneous targets.One way to monitor this in an experiment is to employ multiple point velocimetry techniques,but even with multiplexing this can become expensive in terms of hardware, in particular highspeed sensors and scope channels. We report on the initial development of a multi-axis lineimagingVISAR system, which will record the spatial velocity along two orthogonal directions.Cylindrical optics are used to project a set of cross-hairs onto the target, maximising the use ofinput laser light; we then describe the image relay, interferometer configuration and alignment.This ‘quasi’ two dimensional system will become one of the principal diagnostics on the MACH(Mega Ampere Compression and Hydrodynamics) facility at Imperial College London, where themulti-axis measurement will help optimise strip-line design to achieve uniform ramp compressionof targets.
  • Journal article
    Chapman DJ, Eakins DE, Proud WG, Savinykh AS, Garkushin GV, Razorenov SV, Kanel GIet al., 2014,

    On the residual yield stress of shocked metals

    , Journal of Physics: Conference Series, Vol: 500, ISSN: 1742-6588

    ffects of time and strain on material strength. With this objective, we performed a carefulcomparative measurement of the free-surface velocity of shock loaded aluminium AD1 andmagnesium alloy Ma2 samples of various thicknesses in the range 0.2 mm to 5 mm. Weobserved the expected decay in the elastic precursor state with increasing sample thicknessfor both aluminium and magnesium alloy. However, we also observed a small change in themagnitude of hysteresis in the elastic-plastic compression-unloading cycle; where qualitativelythe peak free-surface velocity also increased with increasing specimen thickness. Interestingly,the observed change in hysteresis as function of specimen thickness for the Ma2 alloy wasrelatively smaller than the AD1, in contrast with the larger change in precursor magnitudeobserved for the magnesium. We propose that softening due to multiplication of dislocations isrelatively large in Ma2 and results in a smaller hysteresis in the elastic-plastic cycle.
  • Conference paper
    Bo C, Williams A, Rankin S, Proud WG, Brown KAet al., 2014,

    Integrated experimental platforms to study blast injuries: a bottom-up approach

    , 18th Joint Int Conf of the APS Topical-Grp on Shock Compress of Condensed Matter / 24th Int Conf of the Int-Assoc-for-the-Advancement-of-High-Pressure-Sci-and-Technol, Publisher: IOP PUBLISHING LTD, ISSN: 1742-6588

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