Imperial College London

DrSimonBland

Faculty of Natural SciencesDepartment of Physics

Reader in Plasma Physics
 
 
 
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Contact

 

+44 (0)20 7594 7650sn.bland

 
 
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Location

 

739aBlackett LaboratorySouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
to

212 results found

Lavrinovich I, Gusev AI, Bland S, de Ferron AS, Pecastaing L, Parker S, Yan J, Novac BMet al., 2022, 2-kV Thyristor Triggered in Impact-Ionization Wave Mode by a Solid-State Spiral Generator, IEEE TRANSACTIONS ON PLASMA SCIENCE, ISSN: 0093-3813

Journal article

Maler D, Efimov S, Liverts M, Theocharous S, Strucka J, Yao Y, Proud W, Rack A, Lukic B, Bland SN, Krasik YEet al., 2022, Peculiarities of planar shockwave interaction with air-water interface and solid target, PHYSICS OF PLASMAS, Vol: 29, ISSN: 1070-664X

Journal article

Halliday JWD, Crilly A, Chittenden J, Mancini RC, Merlini S, Rose S, Russell DR, Suttle LG, Valenzuela-Villaseca V, Bland SN, Lebedev SVet 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.

Journal article

Halliday JWD, Crilly A, Chittenden J, Merlini S, Rose S, Russell D, Suttle LG, Mancini RC, Valenzuela-Villaseca V, Bland SN, Lebedev SVet 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.

Conference paper

Strucka J, Halliday JWD, Gheorghiu T, Horton H, Krawczyk B, Moloney P, Parker S, Rowland G, Schwartz N, Stanislaus S, Theocharous S, Wilson C, Zhao Z, Shelkovenko TA, Pikuz SA, Bland SNet al., 2022, A portable X-pinch design for x-ray diagnostics of warm dense matter, Matter and Radiation at Extremes, Vol: 7, Pages: 1-11, ISSN: 2468-080X

We describe the design and x-ray emission properties (temporal, spatial, and spectral) of Dry Pinch I, a portable X-pinch driver developed at Imperial College London. Dry Pinch I is a direct capacitor discharge device, 300 × 300 × 700 mm3 in size and ∼50 kg in mass, that can be used as an external driver for x-ray diagnostics in high-energy-density physics experiments. Among key findings, the device is shown to reliably produce 1.1 ± 0.3 ns long x-ray bursts that couple ∼50 mJ of energy into photon energies from 1 to 10 keV. The average shot-to-shot jitter of these bursts is found to be 10 ± 4.6 ns using a combination of x-ray and current diagnostics. The spatial extent of the x-ray hot spot from which the radiation emanates agrees with previously published results for X-pinches—suggesting a spot size of 10 ± 6 µm in the soft energy region (1–10 keV) and 190 ± 100 µm in the hard energy region (>10 keV). These characteristics mean that Dry Pinch I is ideally suited for use as a probe in experiments driven in the laboratory or at external facilities when more conventional sources of probing radiation are not available. At the same time, this is also the first detailed investigation of an X-pinch operating reliably at current rise rates of less than 1 kA/ns.

Journal article

Halliday JWD, Bland SN, Hare JD, Parker S, Suttle LG, Russell DR, Lebedev SVet al., 2021, A time-resolved imaging system for the diagnosis of x-ray self-emission in high energy density physics experiments, Review of Scientific Instruments, Vol: 92, Pages: 123507-123507, ISSN: 0034-6748

A diagnostic capable of recording spatially and temporally resolved x-ray self-emission data was developed to characterize experiments on the MAGPIE pulsed-power generator. The diagnostic used two separate imaging systems: a pinhole imaging system with two-dimensional spatial resolution and a slit imaging system with one-dimensional spatial resolution. The two-dimensional imaging system imaged light onto the image plate. The one-dimensional imaging system imaged light onto the same piece of image plate and a linear array of silicon photodiodes. This design allowed the cross-comparison of different images, allowing a picture of the spatial and temporal distribution of x-ray self-emission to be established. The design was tested in a series of pulsed-power-driven magnetic-reconnection experiments.

Journal article

Tilikin IN, Shelkovenko TA, Pikuz SA, Bland SNet al., 2021, Multiframe point-projection radiography imaging based on hybrid X-pinch, Review of Scientific Instruments, Vol: 92, Pages: 1-5, ISSN: 0034-6748

This paper demonstrates the possibility of using a new configuration of the hybrid X-pinch to produce a set of spatially and temporarily separate x-ray bursts that could be used for the radiography of dynamic events. To achieve this, a longer than normal wire is placed between the conical electrodes of the hybrid X-pinch, and a set of small spacers (fishing weights) is placed along the wire. Each subsection of the wire then acts as a unique X-pinch, producing its own radiation burst from a small (∼3 µm) spot. The timing between bursts is 20–50 ns, and each is <2 ns in duration. For comparison, if a longer wire is simply employed without spacers, hotspots of radiation occur in random positions and the time between any two bursts does not exceed 20 ns. Examples of two and three frame point-projection radiography of solid-state and plasma test objects are given.

Journal article

Yan J, Parker S, Bland S, 2021, An Investigation Into High-Voltage Spiral Generators Utilizing Thyristor Input Switches, IEEE TRANSACTIONS ON POWER ELECTRONICS, Vol: 36, Pages: 10005-10019, ISSN: 0885-8993

Journal article

Maler D, Efimov S, Rososhek A, Bland SN, Krasik YEet al., 2021, Generation of supersonic jets from underwater electrical explosions of wire arrays, PHYSICS OF PLASMAS, Vol: 28, ISSN: 1070-664X

Journal article

Yan J, Parker S, Gheorghiu T, Schwartz N, Theocharous S, Bland SNet al., 2021, Miniature solid-state switched spiral generator for the cost effective, programmable triggering of large scale pulsed power accelerators, Physical Review Accelerators and Beams, Vol: 24, Pages: 1-10, ISSN: 2469-9888

This paper presents the design and testing of several different configurations of spiral generator, designed to trigger high current switches in the next generation of pulsed power devices. In particular, it details the development of spiral generators that utilize new ultrafast thyristor technology as an input switch, along with a polarity dependent output gap to improve the efficiency of the spiral generator design. The generator produced 50 kV from a 3.6 kV charging voltage, with a rise time of only 50 ns and a jitter of 1.3 ns—directly comparable, if not better than, a generator employing a triggered spark gap as the input switch. The output gap was constructed in house from commonly available components and a 3D printed case, and showed remarkable repeatability and stability—simple alterations to the output gap could further reduce the rise time. The entire spiral generator, along with control and charging electronics, fitted into a case only 210×145×33  mm.

Journal article

Yanuka D, Theocharous S, Chittenden JP, Bland SNet al., 2020, High velocity outflows along the axis of pulsed power driven rod z-pinches, AIP Advances, Vol: 10, Pages: 1-9, ISSN: 2158-3226

We report on initial observations of high velocity outflows from the ends of a rod compressed using pulsed power. 1 mm and 2 mm diameter copper rods were placed in a water bath and driven by ∼0.6 MA currents with rise times of ∼700 ns. Laser backlit framing images and streak photography showed an outflow of the material from the ends of each rod, of the initial velocity of up to 7 km/s, which began ∼500 ns after the start of the current pulse and continued throughout the experiment. Ballistics gel was used to help separate low density gas/plasma from any solid/liquid component in the outflow, successfully capturing the material from larger diameter rods (enabling an estimate of its energy) and tracing the path of the material that passed straight through the gel with smaller rods. Experimental results were compared to 1D and 2D MHD simulations performed with the Gorgon code. These suggested that the outflow had two different components, resulting from two different physical processes. Differences in the resistivity between the copper rod and stainless steel anode result in the opening of a small gap between them and ablated stainless steel being projected above the rod, which is captured in framing and streak images. Later in time, a dense copper material, pinched by the magnetic pressure, is launched—explaining the ballistics gel results. The simulations also suggest that the tamped explosion of the rod surface plays a small role in any outflow.

Journal article

Miller SM, Slutz SA, Bland SN, Klein SR, Campbell PC, Woolstrum JM, Kuranz CC, Gomez MR, Jordan NM, McBride RDet al., 2020, A pulsed-power implementation of “Laser Gate” for increasing laser energy coupling and fusion yield in magnetized liner inertial fusion (MagLIF), Review of Scientific Instruments, Vol: 91, Pages: 1-9, ISSN: 0034-6748

Magnetized Liner Inertial Fusion (MagLIF) at Sandia National Laboratories involves a laser preheating stage where a few-ns laser pulse passes through a few-micron-thick plastic window to preheat gaseous fusion fuel contained within the MagLIF target. Interactions with this window reduce heating efficiency and mix window and target materials into the fuel. A recently proposed idea called “Laser Gate” involves removing the window well before the preheating laser is applied. In this article, we present experimental proof-of-principle results for a pulsed-power implementation of Laser Gate, where a thin current-carrying wire weakens the perimeter of the window, allowing the fuel pressure to push the window open and away from the preheating laser path. For this effort, transparent targets were fabricated and a test facility capable of studying this version of Laser Gate was developed. A 12-frame bright-field laser schlieren/shadowgraphy imaging system captured the window opening dynamics on microsecond timescales. The images reveal that the window remains largely intact as it opens and detaches from the target. A column of escaping pressurized gas appears to prevent the detached window from inadvertently moving into the preheating laser path.

Journal article

Yanuka D, Theocharous S, Bland SN, 2019, Pulsed power driven cylindrical wire array explosions in different media, PHYSICS OF PLASMAS, Vol: 26, Pages: 1-7, ISSN: 1070-664X

Cylindrical copper wire array explosions were carried out in de-ionized water, sodium polytungstate solution, nitromethane, and polyester in order to obtain high energy density conditions in the vicinity of implosion using the generated converging shock waves. The use of different materials in which the array is immersed can contribute to this goal with higher density resulting in higher shock velocities and possible combustion. The generated shock waves were captured by a framing and a streak camera, and shock velocities were calculated and compared. The pressure behind the shock front was calculated using the known hydrodynamic relations (for water, polytungstate, and polyester) and compared to two-dimensional hydrodynamic simulations coupled with the equations of state (for water and polyester). It was shown that despite lower shock wave velocity in polytungstate solution than in water, the pressures generated are similar in both materials. In polyester, both shock velocities and generated pressures are 2–4 times higher than in water. It was also shown that it is possible to carry out these explosions in a solid which has several advantages compared to liquids, such as not relying on waterproof systems and easier transportation.

Journal article

Hare JD, MacDonald J, Bland SN, Dranczewski J, Halliday JWD, Lebedev S, Suttle LG, Tubman ER, Rozmus Wet al., 2019, Two-colour interferometry and Thomson scattering measurements of a plasma gun, Publisher: IOP PUBLISHING LTD

Working paper

Hare JD, MacDonald J, Bland S, Dranczewski J, Halliday J, Lebedev S, Suttle L, Tubman E, Rozmus Wet al., 2019, Two-colour interferometry and Thomson scattering measurements of a plasma gun, Plasma Physics and Controlled Fusion, Vol: 61, ISSN: 0741-3335

We present experimental measurements of a pulsed plasma gun, using two-colour imaging laser interferometry and spatially resolved Thomson scattering. Interferometry measurements give an electron density ne ≈ 2.7 × 1017 cm−3 at the centre of the plasma plume, at 5 mm from the plasma gun nozzle. The Thomson scattered light is collected from two probing angles allowed us to simultaneously measure the collective and non-collective spectrum of the electron feature from the same spatial locations. The inferred electron densities from the location of the electron plasma waves is in agreement with interferometry. The electron temperatures inferred from the two spectra are not consistent, with Te ≈ 10 eV for non-collective scattering and Te ≈ 30 eV for collective scattering. We discuss various broadening mechanisms such as finite aperture effects, density gradients within the collective volume and collisional broadening to account for some of this discrepancy. We also note the significant red/blue asymmetry of the electron plasma waves in the collective scattering spectra, which could relate to kinetic effects distorting the distribution function of the electrons.

Journal article

Yanuka D, Rososhek A, Theocharous S, Bland SN, Krasik YE, Olbinado MP, Rack A, Oreshkin EVet al., 2019, X-ray radiography of the overheating instability in underwater electrical explosions of wires, Physics of Plasmas, Vol: 26, ISSN: 1070-664X

We present the measurements of the development of striation like instabilities during the electrical driven explosions of wires in a waterbath. In vacuum based wire explosion experiments, such instabilities have long been known. However, in spite of intense research into theexplosion of wires in liquids, the development of these instabilities has either not been observed or has been assumed to play a minor role inthe parameters of the exploding wire due to the tamping of the wire’s explosion. Using synchrotron based multiframe radiography, we haveseen the development of platelike density structures along an exploding copper wire. Our measurements were compared to a 2Dmagnetohydrodynamics simulation, showing similar striation formation. These observed instabilities could affect the measurements of theconductivity of the wire material in the gas-plasma state—an important parameter in the warm dense matter community. The striationscould also act as a seed for other instabilities later in time if the wire is in a dense flow of material or experiences a shock from an adjacentwire—as it would do in experiments with arrays of wires.

Journal article

Yanuka D, Theocharous S, Efimov S, Bland SN, Rososhek A, Krasik YE, Olbinado MP, Rack Aet al., 2019, Synchrotron based X-ray radiography of convergent shock waves driven by underwater electrical explosion of a cylindrical wire array, Journal of Applied Physics, Vol: 125, ISSN: 0021-8979

We present X-ray radiography images showing the propagation of shock waves generated by electrical explosion of a cylindrical arrangement of wires in water driven by pulsed power. In previous experiments [S. N. Bland et al., Phys. Plasmas 24, 082702 (2017)], the merger of shock waves from adjacent wires has produced a highly symmetrical, cylindrical shock wave converging on the axis, where it is expected to produce a high density, strongly coupled plasma ideal for warm dense matter research. However, diagnostic limitations have meant that much of the dynamics of the system has been inferred from the position of the front of the cylindrical shock and timing/spectra of light emitted from the axis. Here, we present a synchrotron-based radiography of such experiments—providing direct quantitative measurements on the formation of the convergent shock wave, the increased density of water on the axis caused by its arrival, and its “bounce” after arrival on the axis. The obtained images are compared with two-dimensional hydrodynamic simulations, which reproduce the observed dynamics with a satisfactory agreement in density values.

Journal article

Theocharous SP, Bland SN, Yanuka D, Rososhek A, Olbinado MP, Rack A, Krasik YEet al., 2019, Use of synchrotron-based radiography to diagnose pulsed power driven wire explosion experiments, Review of Scientific Instruments, Vol: 90, ISSN: 0034-6748

We describe the first use of synchrotron radiation to probe pulsed power driven high energy density physics experiments. Multi-frame x-ray radiography with interframe spacing of 704 ns and temporal resolution of <100 ps was used to diagnose the electrical explosion of different wire configurations in water including single copper and tungsten wires, parallel copper wire pairs, and copper x-pinches. Such experiments are of great interest to a variety of areas including equation of state studies and high pressure materials research, but the optical diagnostics that are usually employed in these experiments are unable to probe the areas behind the shock wave generated in the water, as well as the internal structure of the exploding material. The x-ray radiography presented here, performed at beamline ID19 at European Synchrotron Radiation Facility (ESRF), was able to image both sides of the shock to a resolution of up to 8 μm, and phase contrast imaging allowed fine details of the wire structure during the current driven explosion and the shock waves to be clearly observed. These results demonstrate the feasibility of pulsed power operated in conjunction with synchrotron facilities, as well as an effective technique in the study of shock waves and wire explosion dynamics.

Journal article

McBride RD, Stygar WA, Cuneo ME, Sinars DB, Mazarakis MG, Leckbee JJ, Savage ME, Hutsel BT, Douglass JD, Kiefer ML, Oliver BV, Laity GR, Gomez MR, Yager-Elorriaga DA, Patel SG, Kovalchuk BM, Kim AA, Gourdain PA, Bland SN, Portillo S, Bott-Suzuki SC, Beg FN, Maron Y, Spielman RB, Rose DV, Welch DR, Zier JC, Schumer JW, Greenly JB, Covington AM, Steiner AM, Campbell PC, Miller SM, Woolstrum JM, Ramey NB, Shah AP, Sporer BJ, Jordan NM, Lau YY, Gilgenbach RMet al., 2018, A primer on pulsed power and linear transformer drivers for high energy density physics applications, IEEE Transactions on Plasma Science, Vol: 46, Pages: 3928-3967, ISSN: 0093-3813

The objectives of this tutorial are as follows: 1) to help students and researchers develop a basic understanding of how pulsed-power systems are used to create high-energy-density (HED) matter; 2) to develop a basic understanding of a new, compact, and efficient pulsed-power technology called linear transformer drivers (LTDs); 3) to understand why LTDs are an attractive technology for driving HED physics (HEDP) experiments; 4) to contrast LTDs with the more traditional Marx-generator/pulse-forming-line approach to driving HEDP experiments; and 5) to briefly review the history of LTD technology as well as some of the LTD-driven HEDP research presently underway at universities and research laboratories across the globe. This invited tutorial is part of the Mini-Course on Charged Particle Beams and High-Powered Pulsed Sources, held in conjunction with the 44th International Conference on Plasma Science in May of 2017.

Journal article

Shelkovenko TA, Pikuz SA, Tilikin IN, Mitchell MD, Bland SN, Hammer DAet al., 2018, Evolution of X-pinch loads for pulsed power generators with current from 50 to 5000 kA, Matter and Radiation at Extremes, Vol: 3, Pages: 267-277, ISSN: 2468-080X

A review of X-pinches of various configurations and of different materials as an X-ray source for various applications is presented. The advantages and disadvantages of different designs of X-pinches as a load for generators with a wide range of output parameters and as a source of X-ray radiation for X-ray point-projection imaging were analyzed.

Journal article

Yanuka D, Rososhek A, Theocharous S, Bland SN, Krasik YE, Olbinado MP, Rack Aet al., 2018, Multi frame synchrotron radiography of pulsed power driven underwater single wire explosions, Journal of Applied Physics, Vol: 124, ISSN: 0021-8979

We present the first use of synchrotron-based phase contrast radiography to study pulsed-power driven high energy density physics experiments. Underwater electrical wire explosions have become of interest to the wider physics community due to their ability to study material properties at extreme conditions and efficiently couple stored electrical energy into intense shock waves in water. The latter can be shaped to provide convergent implosions, resulting in very high pressures (1-10 Mbar) produced on relatively small pulsed power facilities (100s of kA-MA). Multiple experiments have explored single-wire explosions in water, hoping to understand the underlying physics and better optimize this energy transfer process; however, diagnostics can be limited. Optical imaging diagnostics are usually obscured by the shock wave itself; and until now, diode-based X-ray radiography has been of relatively low resolution and rather a broad x-ray energy spectrum. Utilising phase contrast imaging capabilities of the ID19 beamline at the European Synchrotron Radiation Facility, we were able to image both the exploding wire and the shock wave. Probing radiation of 20-50 keV radiographed 200 μm tungsten and copper wires, in ∼2-cm diameter water cylinders with resolutions of 8 μm and 32 μm. The wires were exploded by a ∼30-kA, 500-ns compact pulser, and 128 radiographs, each with a 100-ps X-ray pulse exposure, spaced at 704 ns apart were taken in each experiment. Abel inversion was used to obtain the density profile of the wires, and the results are compared to two dimensional hydrodynamic and one dimensional magnetohydrodynamic simulations.

Journal article

Zhang X, Wang G, Luo B, Tan F, Bland SN, Zhao J, Sun C, Liu Cet al., 2018, Refractive index and polarizability of polystyrene under shock compression, JOURNAL OF MATERIALS SCIENCE, Vol: 53, Pages: 12628-12640, ISSN: 0022-2461

Journal article

Shelkovenko TA, Pikuz SA, Tilikin IN, Bland SN, Lall D, Chaturvedi N, Georgakis Aet al., 2018, X-pinch X-ray emission on a portable low-current, fast rise-time generator, Journal of Applied Physics, Vol: 124, ISSN: 0021-8979

We report on experiments exploring X-ray emission from an X-pinch driven by a small Marx-waterline generator supplying 50 kA with a risetime of 50 ns and a peak voltage of ∼250 kV. Both standard crossed wire loads and hybrid loads utilizing conical metal electrodes with a single short wire in between them were studied, and in both cases reliable modes of operation were obtained for X-ray radiography. Soft (few keV) and Hard (>5 keV) X-ray emission characteristics were observed. With standard X-pinches, soft radiation emanated from a small hot spot about 3 μm in size, along with hard radiation from a ∼200 μm region close to this hot spot. With hybrid X-pinches, the hot spot was <7 μm in size. There was a clear correlation between the soft and hard X-ray emission—pinches that produced intense soft X-ray emission from a small hot spot also produced the most intense, localized hard X-ray emission.

Journal article

de Grouchy PWL, Kusse BR, Banasek J, Engelbrecht J, Hammer DA, Qi N, Rocco S, Bland SNet al., 2018, Observations of the magneto-Rayleigh-Taylor instability and shock dynamics in gas-puff Z-pinch experiments, PHYSICS OF PLASMAS, Vol: 25, ISSN: 1070-664X

Journal article

Gurovich V, Virozub A, Rososhek A, Bland S, Spielman RB, Krasik YEet al., 2018, Quasi-isentropic compression using compressed water flow generated by underwater electrical explosion of a wire array, Journal of Applied Physics, Vol: 123, ISSN: 0021-8979

A major experimental research area in material equation-of-state today involves the use of off-Hugoniot measurements rather than shock experiments that give only Hugoniot data. There is a wide range of applications using quasi-isentropic compression of matter including the direct measurement of the complete isentrope of materials in a single experiment and minimizing the heating of flyer plates for high-velocity shock measurements. We propose a novel approach to generating quasi-isentropic compression of matter. Using analytical modeling and hydrodynamic simulations, we show that a working fluid composed of compressed water, generated by an underwater electrical explosion of a planar wire array, might be used to efficiently drive the quasi-isentropic compression of a copper target to pressures ∼2 × 10 11 Pa without any complex target designs.

Journal article

Zhang X, Wang G, Luo B, Bland SN, Tan F, Zhao F, Zhao J, Sun C, Liu Cet al., 2018, Mechanical response of near-equiatomic NiTi alloy at dynamic high pressure and strain rate, Journal of Alloys and Compounds, Vol: 731, Pages: 569-576, ISSN: 0925-8388

Understanding the behavior of near equi-atomic NiTi alloys under high strain rates and high pressures is important for the development of shock mitigating structures, particularly those that protect satellite and space vehicles from the impact of hyper velocity space debris. In this paper, the equation of state and constitutive relationships of NiTi alloy at pressures of 20–50 GPa and strain rates from 104s−1 to 107s−1 were investigated by means of magnetically driven quasi-isentropic compression and by shock compression from the impact of magnetically launched flyer plates. An inflection point at a pressure of 2–3 GPa was found on plots of Lagrangian sound speed versus particle velocity in both quasi-isentropic and shock compression experiments, and it shows the elastic-plastic transition of austenitic NiTi alloy. The effect of the strain rate on the elastic limit of NiTi alloy was clearly seen between strain rates of 104s−1 and 107s−1. We also found that the bulk sound speed calculated from the shock data was lower than that deduced from the ultrasonic measurements. Finally, a rate dependent Johnson–Cook model was modified to describe the dynamic responses of NiTi. With this modified model, hydrodynamic simulations agreed well with our observations.

Journal article

Yanuka D, Rososhek A, Bland SN, Krasik YEet al., 2017, Uniformity of cylindrical imploding underwater shockwaves at very small radii, Applied Physics Letters, Vol: 111, ISSN: 1077-3118

We compare the convergent shockwaves generated from underwater, cylindrical arrays of copperwire exploded by multiple kilo-ampere current pulses on nanosecond and microsecond scales. Inboth cases, the pulsed power devices used for the experiments had the same stored energy ( 500 J)and the wire mass was adjusted to optimize energy transfer to the shockwave. Laser backlit framingimages of the shock front were achieved down to the radius of 30lm. It was found that even in thecase of initial azimuthal non-symmetry, the shock wave self-repairs in the final stages of its motion,leading to a highly uniform implosion. In both these and previous experiments, interference fringeshave been observed in streak and framing images as the shockwave approached the axis. We havebeen able to accurately model the origin of the fringes, which is due to the propagation of the laserbeam diffracting off the uniform converging shock front. The dynamics of the shockwave and itsuniformity at small radii indicate that even with only 500 J stored energies, this technique shouldproduce pressures above 10¹⁰Pa on the axis, with temperatures and densities ideal for warm densematter research.

Journal article

Bland SN, Krasik YAE, Yanuka D, Gardner R, MacDonald J, Virozub A, Efimov S, Gleizer S, Chaturvedi Net al., 2017, Generation of highly symmetric, cylindrically convergent shockwaves in water, Physics of Plasmas, Vol: 24, ISSN: 1089-7674

We report on pulsed power driven, exploding copper wire array experiments conducted to generate cylindrical convergent shockwaves in water employing μs risetime currents >550 kA in amplitude and with stored energies of >15 kJ—a substantial increase over previous results. The experiments were carried out on the recently constructed Mega-Ampere-Compression-and-Hydrodynamics facility at Imperial College London in collaboration with colleagues of Technion, Israel. 10 mm diameter arrays consisting of 60 × 130 μm wires were utilized, and the current and voltage diagnostics of the load region suggested that ∼8 kJ of energy was deposited in the wires (and the load region close to the wires) during the experiments, resulting in the formation of dense, highly resistive plasmas that rapidly expanded driving the shockwaves in water. Laser-backlit framing images of the shockfront were obtained at radii <0.25 mm for the first time, and there was strong evidence that even at radii <0.1 mm this front remains stable, resulting in a convergence ratio of >50:1. Framing images and streak photographs showed that the velocity of the shockwave reached ∼7.5 km s−1 at 0.1 mm from the axis. 2D hydrodynamic simulations that match the experimentally obtained implosion trajectory suggest that pressures >1 Mbar are produced within 10 μm of the axis along with water densities of 3gcm−3 and temperatures of many 1000 s of Kelvin. Under these conditions, Quotidian Equation of State suggests that a strongly coupled plasma with an ionization fraction of ∼0.7 would be formed. The results represent a “stepping stone” in the application of the technique to drive different material samples into high pressure, warm dense matter regimes with compact, university scale generators, and provide support in scaling the technique to multi-mega ampere

Journal article

Burdiak GC, Lebedev SV, Bland SN, Clayson T, Hare J, Suttle L, Suzuki-Vidal F, Garcia DC, Chittenden JP, Bott-Suzuki S, Ciardi A, Frank A, Lane TSet al., 2017, The structure of bow shocks formed by the interaction of pulsed-power driven magnetised plasma flows with conducting obstacles, PHYSICS OF PLASMAS, Vol: 24, ISSN: 1070-664X

We present an experimental study of the development and structure of bow shocks produced by the interaction of a magnetised, collisional, super-Alfvénic plasma flow with conducting cylindrical obstacles. The plasma flow with an embedded, frozen-in magnetic field (ReM ∼ 20) is produced by the current-driven ablation of fine aluminium wires in an inverse, exploding wire array z-pinch. We show that the orientation of the embedded field with respect to the obstacles has a dramatic effect on the bow shock structure. When the field is aligned with the obstacle, a sharp bow shock is formed with a global structure that is determined simply by the fast magneto-sonic Mach number. When the field is orthogonal to the obstacle, magnetic draping occurs. This leads to the growth of a magnetic precursor and the subsequent development of a magnetised bow shock that is mediated by two-fluid effects, with an opening angle and a stand-off distance, that are both many times larger than in the parallel geometry. By changing the field orientation, we change the fluid regime and physical mechanisms that are responsible for the development of the bow shocks. MHD simulations show good agreement with the structure of well-developed bow shocks. However, collisionless, two-fluid effects will need to be included within models to accurately reproduce the development of the shock with an orthogonal B-field.

Journal article

Stafford SJP, Chapman DJ, Bland SN, Eakins DEet al., 2017, Observations on the Nucleation of Ice VII in Compressed Water, 19th Biennial American-Physical-Society (APS) Conference on Shock Compression of Condensed Matter (SCCM), Publisher: AMER INST PHYSICS, ISSN: 0094-243X

Conference paper

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