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  • 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
  • Conference paper
    Suzuki-Vidal F, Lebedev SV, Ciardi A, Bland SN, Hall GN, Swadling G, Harvey-Thompson AJ, Burdiak G, de Grouchy P, Chittenden JP, Bocchi M, Bott SC, Frank Aet al., 2014,

    Laboratory Astrophysics Experiments with Magnetically Driven Plasma Jets

    , 15th International Congress on Plasma Physics (ICPP) / 13th Latin American Workshop on Plasma Physics (LAWPP), Publisher: IOP PUBLISHING LTD, ISSN: 1742-6588
  • Conference paper
    Proud WG, 2014,

    Gas percolation through sand

    , 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
  • Conference paper
    Garkushin GV, Savinykh AS, Kanel GI, Razorenov SV, Jones D, Proud WG, Botvina LRet al., 2014,

    Response of magnesium single crystals to shock-wave loading at room and elevated temperatures.

    , 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
  • Conference paper
    Lowe M, Rothman S, Chapman D, Robinson Cet al., 2014,

    A comparison of multiple techniques for determining the shock release behaviour of copper

    , 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
  • Conference paper
    Khan AS, Balzer JE, Wilgeroth JM, Proud WGet al., 2014,

    Aspect ratio compression effects on metals and polymers

    , 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
  • Conference paper
    Wilgeroth JM, Nguyen T-TN, Proud WG, 2014,

    Interaction between blast wave and reticulated foam: assessing the potential for auditory protection systems

    , 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
  • Conference paper
    Khan AS, Balzer JE, Wilgeroth JM, Proud WGet al., 2014,

    Temperature effects on the mechanical behaviour of PZT 95/5

    , 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
  • Conference paper
    Butler BJ, Bo C, Tucker AW, Jardine AP, Proud WG, Williams A, Brown KAet al., 2014,

    Mechanical and histological characterization of trachea tissue subjected to blast-type pressures

    , 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
  • Conference paper
    Nguyen T-TN, Wilgeroth JM, Proud WG, 2014,

    Controlling blast wave generation in a shock tube for biological applications

    , 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
  • Conference paper
    Weinwurm M, Bland SN, Chittenden JP, 2014,

    Metal liner-driven cylindrically convergent isentropic compression of cryogenic deuterium

    , 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
  • Journal article
    Suzuki Vidal F, Patankar S, Lebedev SV, Bland SN, Doyle H, Bigourd D, Burdiak G, de Grouchy P, Hall GN, Harvey Thompson AJ, Khoory E, Pickworth L, Skidmore J, Smith RA, Swadling GFet al., 2013,

    Observation of energetic protons trapped in laboratory magnetic-tower jets

    , New Journal of Physics, Vol: 15, ISSN: 1367-2630

    Preliminary results of the self-emission of charged particles frommagnetically driven plasma jets has been investigated. The jets were launchedand driven by a toroidal magnetic field generated by introducing a ∼1.4 MA,250 ns electrical current pulse from the MAGPIE generator into a radialwire array. This configuration has shown to reproduce some aspects of theastrophysical magnetic-tower jet launching model, in which a jet is collimatedby a toroidal magnetic field inside a magnetic cavity. The emission of ions andprotons from the plasma was recorded onto Columbia Resin 39 plates using timeintegratedpinhole cameras. In addition a fly-eye camera, an array of 25–496cylindrical apertures allowed estimating the location of the ion emitting source.The results show the ion emission comes from both the jet and its surroundingmagnetic cavity, with the emission extending to a height of at least ∼9 cm fromthe initial position of the wires. The emission of ions is consistent with the dynamics of the jet obtained from time-resolved imaging diagnostics, i.e. opticallaser probing and self-emission of the plasma in the extreme ultra-violet. Thesepreliminary results suggest the ions are trapped inside the cavity due to the strongtoroidal magnetic field which drives the jet. In addition these studies providefirst estimates of the energy and fluence of protons for future laser-driven protonprobing diagnostics aimed at measuring the magnetic field in these experiments.

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