Publications

Journal article

Torchio R, Occelli F, Mathon O, Sollier A, Lescoute E, Videau L, Vinci T, Benuzzi-Mounaix A, Headspith J, Helsby W, Bland S, Eakins D, Chapman D, Pascarelli S, Loubeyre Pet al., 2016,

Probing local and electronic structure in Warm Dense Matter: single pulse synchrotron x-ray absorption spectroscopy on shocked Fe

, Scientific Reports, Vol: 6, ISSN: 2045-2322

Understanding Warm Dense Matter (WDM), the state of planetary interiors, is a new frontier in scienti c research. There exists very little experimental data probing WDM states at the atomic level to test current models and those performed up to now are limited in quality. Here, we report a proof-of- principle experiment that makes microscopic investigations of materials under dynamic compression easily accessible to users and with data quality close to that achievable at ambient. Using a single100 ps synchrotron x-ray pulse, we have measured, by K-edge absorption spectroscopy, ns-lived equilibrium states of WDM Fe. Structural and electronic changes in Fe are clearly observed for the rst time at such extreme conditions. The amplitude of the EXAFS oscillations persists up to 500 GPa and 17000 K, suggesting an enduring local order. Moreover, a discrepancy exists with respect to theoretical calculations in the value of the energy shift of the absorption onset and so this comparison should help to re ne the approximations used in models.

Journal article

Swinburne TD, Glavicic MG, Rahman KM, Jones NG, Coakley J, Eakins DE, White TG, Tong V, Milathianaki D, Williams GJ, Rugg D, Sutton AP, Dye Det al., 2016,

Picosecond dynamics of a shock-driven displacive phase transformation in Zr

, Physical Review B, Condensed Matter, Vol: 93, ISSN: 0163-1829

High pressure solid state transformations at high strain rates are usually observed after the fact,either during static holding or after unloading, or inferred from interferometry measurements of thesample surface. The emergence of femtosecond X-ray diffraction techniques provides insight intothe dynamics of short-timescale events such as shocks. We report laser pump-probe experiments ofthe response of Zr to laser driven shocks over the first few nanoseconds of the shock event, enablingthe α → ω transition and orientation relationship to be observed in real time with picosecondresolution. A clear orientation relationship of (10¯10)α||(10¯11)ω is found, in conflict with ω → αannealing experiments in zirconium and the two α → ω pathways proposed for titanium.

Journal article

Rutherford ME, Chapman DJ, White TG, Drakopoulos M, Rack A, Eakins DEet al., 2016,

Evaluating scintillator performance in time-resolvedhard X-ray studies at synchrotron light sources

, Journal of Synchrotron Radiation, Vol: 23, ISSN: 1600-5775

The short pulse duration, small effective source size and high flux of synchrotronradiation is ideally suited for probing a wide range of transient deformationprocesses in materials under extreme conditions. In this paper, the challenges ofhigh-resolution time-resolved indirect X-ray detection are reviewed in thecontext of dynamic synchrotron experiments. In particular, the discussion istargeted at two-dimensional integrating detector methods, such as those focusedon dynamic radiography and diffraction experiments. The response of ascintillator to periodic synchrotron X-ray excitation is modelled and validatedagainst experimental data collected at the Diamond Light Source (DLS) andEuropean Synchrotron Radiation Facility (ESRF). An upper bound on thedynamic range accessible in a time-resolved experiment for a given bunchseparation is calculated for a range of scintillators. New bunch structures aresuggested for DLS and ESRF using the highest-performing commerciallyavailable crystal LYSO:Ce, allowing time-resolved experiments with aninterframe time of 189 ns and a maximum dynamic range of 98 (6.6 bits).

Journal article

Zhang Z, Eakins DE, Dunne FPE, 2015,

On the Formation of Adiabatic Shear Bands in Textured HCP Polycrystals

, International Journal of Plasticity, Vol: 79, Pages: 196-216, ISSN: 0749-6419

Adiabatic shear band (ASB) formation in textured HCP polycrystals has been investigatedunder regimes of high rate compression and shear loading using dynamic thermomechanicallycoupled, dislocation-based crystal plasticity modelling. The balance betweenrate of plastic dissipation leading to internal heat generation versus rate of thermal diffusionat a crystallographic length scale has been shown to be pivotal for the formation or otherwiseof ASBs. Micro-texture has been found to have a key role in both advancing and inhibitingshear band growth, and its control offers the possibility of new alloys with higher impactstrength over strain rate range 2 1 10  to 5 110 s-1. Texture has been found to lead to widevariations in applied macroscopic strain at which ASB formation occurs, such that strain levelin isolation is inappropriate as a universal indicator of ASB onset.High-rate shear loading is found to lead to lower onset strains for ASBs compared to highrate compression, but the dependence of both on texture leads to considerable variation instrain level for ASB formation. A preliminary map demarcating ASB onset has beenestablished over regimes of applied strain and texture for dynamic shear and compression.

Journal article

Jones DR, Chapman DJ, Eakins DE, 2015,

A Method for Studying the Temperature Dependence of Dynamic Fracture and Fragmentation

, Journal of Visualized Experiments, Vol: 100, ISSN: 1940-087X

The dynamic fracture of a body is a late-stage phenomenon typically studied under simplified conditions, in which a sample is deformed underuniform stress and strain rate. This can be produced by evenly loading the inner surface of a cylinder. Due to the axial symmetry, as the cylinderexpands the wall is placed into a tensile hoop stress that is uniform around the circumference. While there are various techniques to generatethis expansion such as explosives, electromagnetic drive, and existing gas gun techniques they are all limited in the fact that the sample cylindermust be at room temperature. We present a new method using a gas gun that facilitates experiments on cylinders from 150 K to 800 K with aconsistent, repeatable loading. These highly diagnosed experiments are used to examine the effect of temperature on the fracture mechanismsresponsible for failure, and their resulting influence on fragmentation statistics. The experimental geometry employs a steel ogive located insidethe target cylinder, with the tip located about halfway in. A single stage light gas gun is then used to launch a polycarbonate projectile into thecylinder at 1,000 m/sec-1. The projectile impacts and flows around the rigid ogive, driving the sample cylinder from the inside. The use of a nondeformingogive insert allows us to install temperature control hardware inside the rear of the cylinder. Liquid nitrogen (LN2) is used for coolingand a resistive high current load for heating. Multiple channels of upshifted photon Doppler velocimetry (PDV) track the expansion velocityalong the cylinder enabling direct comparison to computer simulations, while High speed imaging is used to measure the strain to failure. Therecovered cylinder fragments are also subject to optical and electron microscopy to ascertain the failure mechanism.

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

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

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

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Citations: 53

Journal article

Pike OJ, Rose SJ, 2014,

Dynamical friction in a relativistic plasma

, PHYSICAL REVIEW E, Vol: 89, ISSN: 1539-3755

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Citations: 5

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

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Citations: 4

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

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

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

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

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.

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.

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

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Citations: 2

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

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.

Journal article

Jones DR, Chapman DJ, Eakins DE, 2013,

A gas gun based technique for studying the role of temperature in dynamic fracture and fragmentation

, JOURNAL OF APPLIED PHYSICS, Vol: 114, ISSN: 0021-8979

Journal article

Turrell AE, Sherlock M, Rose SJ, 2013,

A Monte Carlo algorithm for degenerate plasmas

, JOURNAL OF COMPUTATIONAL PHYSICS, Vol: 249, Pages: 13-21, ISSN: 0021-9991

Journal article

Scott RHH, Perez F, Streeter MJV, Clark EL, Davies JR, Schlenvoigt H-P, Santos JJ, Hulin S, Lancaster KL, Dorchies F, Fourment C, Vauzour B, Soloviev AA, Baton SD, Rose SJ, Norreys PAet al., 2013,