Imperial College London

DrSimonBland

Faculty of Natural SciencesDepartment of Physics

Senior Lecturer
 
 
 
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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

198 results found

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

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

© 2019 IOP Publishing Ltd. 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.

Working paper

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

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

Swadling GF, Lebedev SV, Hall GN, Suzuki-Vidal F, Burdiak GC, Pickworth L, De Grouchy P, Skidmore J, Khoory E, Suttle L, Bennett M, Hare JD, Clayson T, Bland SN, Smith RA, Stuart NH, Patankar S, Robinson TS, Harvey-Thompson AJ, Rozmus W, Yuan J, Sheng Let al., 2016, Experimental investigations of ablation stream interaction dynamics in tungsten wire arrays: interpenetration, magnetic field advection, and ion deflection, Physics of Plasmas, Vol: 23, ISSN: 1089-7674

Experiments have been carried out to investigate the collisional dynamics of ablation streams produced by cylindrical wire array z-pinches. A combination of laser interferometric imaging, Thomson scattering, and Faraday rotationimaging has been used to make a range of measurements of the temporal evolution of various plasma and flow parameters. This paper presents a summary of previously published data, drawing together a range of different measurements in order to give an overview of the key results. The paper focuses mainly on the results of experiments with tungsten wire arrays. Early interferometric imagingmeasurements are reviewed, then more recent Thomson scattering measurements are discussed; these measurements provided the first direct evidence of ablation stream interpenetration in a wire array experiment. Combining the data from these experiments gives a view of the temporal evolution of the tungsten stream collisional dynamics. In the final part of the paper, we present new experimental measurements made using an imagingFaraday rotationdiagnostic. These experiments investigated the structure of magnetic fields near the array axis directly; the presence of a magnetic field has previously been inferred based on Thomson scattering measurements of ion deflection near the array axis. Although the Thomson and Faradaymeasurements are not in full quantitative agreement, the Faraday data do qualitatively supports the conjecture that the observed deflections are induced by a static toroidal magnetic field, which has been advected to the array axis by the ablation streams. It is likely that detailed modeling will be needed in order to fully understand the dynamics observed in the experiment.

Journal article

Haerendel G, Suttle L, Lebedev SV, Swadling GF, Hare JD, Burdiak GC, Bland SN, Chittenden JP, Kalmoni N, Frank A, Smith RA, Suzuki-Vidal Fet al., 2016, Stop layer: a flow braking mechanism in space and support from a lab experiment, Plasma Physics and Controlled Fusion, Vol: 58, ISSN: 1361-6587

The paper presents short summaries and a synopsis of two completely independent discoveries of a fast flow braking process, one realized by a laboratory experiment (Lebedev et al 2014 Phys. Plasmas 21 056305), the other by theoretical reasoning stimulated by auroral observation (Haerendel 2015a J. Geophys. Res. Space Phys. 120 1697–714). The first has been described as a magnetically mediated sub-shock forming when a supersonic plasma flow meets a wall. The second tried to describe what happens when a high-beta plasma flow from the central magnetic tail meets the strong near-dipolar field of the magnetosphere. The term stop layer signals that flow momentum and energy are directly coupled to a magnetic perturbation field generated by a Hall current within a layer of the width of c/ω pi and immediately propagated out of the layer by kinetic Alfvén waves. As the laboratory situation is not completely collision-free, energy transfer from ions to electrons and subsequent radiative losses are likely to contribute. A synopsis of the two situations identifies and discusses six points of commonality between the two situations. It is pointed out that the stop layer mechanism can be regarded as a direct reversal of the reconnection process.

Journal article

Suzuki-Vidal F, Lebedev SV, Ciardi A, Pickworth LA, Rodriguez R, Gil JM, Espinosa G, Hartigan P, Swadling GF, Skidmore J, Hall GN, Bennett M, Bland SN, Burdiak G, de Grouchy P, Music J, Suttle L, Hansen E, Frank Aet al., 2015, BOW SHOCK FRAGMENTATION DRIVEN BY A THERMAL INSTABILITY IN LABORATORY ASTROPHYSICS EXPERIMENTS, Astrophysical Journal, Vol: 815, ISSN: 1538-4357

The role of radiative cooling during the evolution of a bow shock was studied in laboratory-astrophysics experiments that are scalable to bow shocks present in jets from young stellar objects. The laboratory bow shock is formed during the collision of two counterstreaming, supersonic plasma jets produced by an opposing pair of radial foil Z-pinches driven by the current pulse from the MAGPIE pulsed-power generator. The jets have different flow velocities in the laboratory frame, and the experiments are driven over many times the characteristic cooling timescale. The initially smooth bow shock rapidly develops small-scale nonuniformities over temporal and spatial scales that are consistent with a thermal instability triggered by strong radiative cooling in the shock. The growth of these perturbations eventually results in a global fragmentation of the bow shock front. The formation of a thermal instability is supported by analysis of the plasma cooling function calculated for the experimental conditions with the radiative packages ABAKO/RAPCAL.

Journal article

Burdiak GC, Lebedev SV, Harvey-Thompson AJ, Hall GN, Swadling GF, Suzuki-Vidal F, Khoory E, Bland SN, Pickworth L, de Grouchy P, Skidmore J, Suttle L, Waisman EMet al., 2015, Characterisation of the current switch mechanism in two-stage wire array Z-pinches, Physics of Plasmas, Vol: 22, ISSN: 1089-7674

In this paper, we describe the operation of a two-stage wire array z-pinch driven by the 1.4 MA,240 ns rise-time Magpie pulsed-power device at Imperial College London. In this setup, an inversewire array acts as a fast current switch, delivering a current pre-pulse into a cylindrical load wirearray, before rapidly switching the majority of the generator current into the load after a100–150 ns dwell time. A detailed analysis of the evolution of the load array during the pre-pulse ispresented. Measurements of the load resistivity and energy deposition suggest significant bulk heatingof the array mass occurs. The 5 kA pre-pulse delivers 0.8 J of energy to the load, leaving itin a mixed, predominantly liquid-vapour state. The main current switch occurs as the inverse arraybegins to explode and plasma expands into the load region. Electrical and imaging diagnostics indicatethat the main current switch may evolve in part as a plasma flow switch, driven by the expansionof a magnetic cavity and plasma bubble along the length of the load array. Analysis ofimplosion trajectories suggests that approximately 1 MA switches into the load in 100 ns, correspondingto a doubling of the generator dI/dt. Potential scaling of the device to higher currentmachines is discussed. V

Journal article

Ampleford DJ, Bland SN, Jennings CA, Lebedev SV, Chittenden JP, McBride RD, Jones B, Serrano JD, Cuneo ME, Hall GN, Suzuki-Vidal F, Bott-Suzuki SCet al., 2015, Investigating Radial Wire Array Z-Pinches as a Compact X-Ray Source on the Saturn Generator, IEEE TRANSACTIONS ON PLASMA SCIENCE, Vol: 43, Pages: 3344-3352, ISSN: 0093-3813

Journal article

Macdonald J, Bland SN, Threadgold J, 2015, A fibre based triature interferometer for measuring rapidly evolving, ablatively driven plasma densities, Review of Scientific Instruments, Vol: 86, ISSN: 1089-7623

We report on the first use of a fibre interferometer incorporating triature analysis for measuring rapidly evolving plasma densities of ne ∼ 1013/cm3 and above, such as those produced by simple coaxial plasma guns. The resultant system is extremely portable, easy to field in experiments, relatively cheap to produce, and—with the exception of a small open area in which the plasma is sampled—safe in operation as all laser light is enclosed.

Journal article

Swadling GF, Lebedev SV, Harvey-Thompson AJ, Rozmus W, Burdiak G, Suttle L, Patankar S, Smith RA, Bennett M, Hall GN, Suzuki-Vidal F, Bland S, Yuan Jet al., 2015, Interpenetration and deflection phenomena in collisions between supersonic, magnetized, tungsten plasma flows diagnosed using high resolution optical Thomson scattering, PHYSICS OF PLASMAS, Vol: 22, ISSN: 1070-664X

Journal article

Burdiak GC, Lebedev SV, Suzuki-Vidal F, Swadling GF, Bland SN, Niasse N, Suttle L, Bennet M, Hare J, Weinwurm M, Rodriguez R, Gil J, Espinosa Get al., 2015, Cylindrical liner Z-pinch experiments for fusion research and high-energy-density physics, Journal of Plasma Physics, Vol: 81, ISSN: 1469-7807

A gas-filled cylindrical liner z-pinch configuration has been used to drive convergentradiative shock waves into different gases at velocities of 20–50 km s−1. On applicationof the 1.4 MA, 240 ns rise-time current pulse produced by the Magpie generatorat Imperial College London, a series of cylindrically convergent shock waves aresequentially launched into the gas-fill from the inner wall of the liner. This occurswithout any bulk motion of the liner wall itself. The timing and trajectories of theshocks are used as a diagnostic tool for understanding the response of the linerz-pinch wall to a large pulsed current. This analysis provides useful data on theliner resistivity, and a means to test equation of state (EOS) and material strengthmodels within MHD simulation codes. In addition to providing information on linerresponse, the convergent shocks are interesting to study in their own right. The shocksare strong enough for radiation transport to influence the shock wave structure. Inparticular, we see evidence for both radiative preheating of material ahead of theshockwaves and radiative cooling instabilities in the shocked gas. Some preliminaryresults from initial gas-filled liner experiments with an applied axial magnetic fieldare also discussed.

Journal article

Zucchini F, Bland SN, Chauvin C, Combes P, Sol D, Loyen A, Roques B, Grunenwald Jet al., 2015, Characteristics of a molybdenum X-pinch X-ray source as a probe source for X-ray diffraction studies, REVIEW OF SCIENTIFIC INSTRUMENTS, Vol: 86, ISSN: 0034-6748

Journal article

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

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

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