215 results found
Datta R, Angel J, Greenly JB, et al., 2023, Plasma flows during the ablation stage of an over-massed pulsed-power-driven exploding planar wire array, Physics of Plasmas, Vol: 30, ISSN: 1070-664X
<jats:p>We characterize the plasma flows generated during the ablation stage of an over-massed exploding planar wire array, fielded on the COBRA pulsed-power facility (1 MA peak current, 250 ns rise time). The planar wire array is designed to provide a driving magnetic field (80–100 T) and current per wire distribution (about 60 kA), similar to that in a 10 MA cylindrical exploding wire array fielded on the Z machine. Over-massing the arrays enables continuous plasma ablation over the duration of the experiment without implosion. The requirement to over-mass on the Z machine necessitates wires with diameters of 75–100μm, which are thicker than wires usually fielded on wire array experiments. To test ablation with thicker wires, we perform a parametric study by varying the initial wire diameter between 33 and 100 μm. The largest wire diameter (100 μm) array exhibits early closure of the cathode-wire gap, while the gap remains open over the duration of the experiment for wire diameters between 33 and 75 μm. Laser plasma interferometry and time-gated extreme-ultraviolet (XUV) imaging are used to probe the plasma flows ablating from the wires. The plasma flows from the wires converge to generate a pinch, which appears as a fast-moving (V≈100kms−1) column of increased plasma density (n¯e≈2×1018cm−3) and strong XUV emission. Finally, we compare the results with three-dimensional resistive-magnetohydrodynamic (MHD) simulations performed using the code GORGON, the results of which reproduce the dynamics of the experiment reasonably well.</jats:p>
Strucka J, Lukic B, Koerner M, et al., 2023, Synchrotron radiography of Richtmyer–Meshkov instability driven by exploding wire arrays, Physics of Fluids, Vol: 35, Pages: 1-11, ISSN: 1070-6631
We present a new technique for the investigation of shock-driven hydrodynamic phenomena in gases, liquids, and solids in arbitrary geometries. The technique consists of a pulsed power-driven resistive wire array explosion in combination with multi-MHz synchrotron radiography. Compared to commonly used techniques, it offers multiple advantages: (1) the shockwave geometry can be shaped to the requirements of the experiment, (2) the pressure (P > 300 MPa) generated by the exploding wires enables the use of liquid and solid hydrodynamic targets with well-characterized initial conditions (ICs), (3) the multi-MHz radiography enables data acquisition to occur within a single experiment, eliminating uncertainties regarding repeatability of the ICs and subsequent dynamics, and (4) the radiographic measurements enable estimation of compression ratios from the x-ray attenuation. In addition, the use of a synchrotron x-ray source allows the hydrodynamic samples to be volumetrically characterized at a high spatial resolution with synchrotron-based microtomography. This experimental technique is demonstrated by performing a planar Richtmyer–Meshkov instability (RMI) experiment on an aerogel–water interface characterized by Atwood number A 0 ∼ − 0.8 and Mach number M ∼ 1.5. The qualitative and quantitative features of the experiment are discussed, including the energy deposition into the exploding wires, shockwave generation, compression of the interface, startup phase of the instability, and asymptotic growth consistent with Richtmyer's impulsive theory. Additional effects unique to liquids and solids—such as cavitation bubbles caused by rarefaction flows or initial jetting due to small perturbations—are observed. It is also demonstrated that the technique is not shape dependent by driving a cylindrically convergent RMI experiment.
Gusev AI, Lavrinovich I, Bland S, et al., 2023, New SOS diode pumping circuit based on an all-solid-state spiral generator for high-voltage nanosecond applications, IEEE Transactions on Plasma Science, Pages: 1-8, ISSN: 0093-3813
Semiconductor opening switch (SOS) diodes are capable to switch currents with a density of more than 1 kA/cm 2 and withstand nanosecond pulses with an amplitude of up to 1 MV. SOS diodes, however, require a specific pumping circuit that must simultaneously provide forward and reverse pumping currents with a time of ∼ 500 and ∼ 100 ns, respectively. Such a pumping circuit with energies > 1 J typically requires a gas-discharge switch or a low-efficient solid-state solution. This study proposes a novel approach to pumping SOS diodes based on a spiral generator (SG) (also known as a vector inversion generator). Due to its wave characteristics, the SG produces a bipolar current discharge that meets the time duration and current amplitude required to pump an SOS diode. Moreover, the initial pulse from the spiral typically has a relatively low current amplitude compared to the opposite polarity secondary pulse, so the SOS diode can operate at very high efficiencies. This idea has been tested using an all-solid-state SG coupled with large-area SOS diodes (1 cm 2 ). With this combination, a voltage pulse of 62 kV having a rise time of only 11 ns was obtained on an open circuit load (3 pF, 1 M Ω ). The experiments were highly repeatable, with no damage to the components despite multiple tests. There is significant scope to further improve the results, with simple alterations to the SG.
Lavrinovich I, Gusev AI, Bland S, et al., 2022, 2-kV thyristor triggered in impact-ionization wave mode by a solid-state spiral generator, IEEE Transactions on Plasma Science, Vol: 50, Pages: 3443-3451, ISSN: 0093-3813
Impact-ionization wave triggering of a thyristor enables it to switch significantly higher currents with much faster rise times ( dI/dt ) than through conventional triggering; indeed tests on commercial components demonstrate that both current and dI/dt can be increased an order of magnitude over their specified datasheet values by utilizing impact ionization. However, creating an impact ionization wave places stringent requirements on the generator used to trigger the thyristor—particularly the trigger pulse must have a voltage rise rate ( dV/dt ) of more than 1 kV/ns and an amplitude over twice the thyristors static breakdown voltage. Given the capacitance of a thyristor is relatively large, often hundreds of pF, this is difficult to achieve with many common triggering methods. In this study, we present a bespoke, cost-effective, trigger generator that has been developed based on spiral/vector inversion techniques coupled to an optimized sharpening circuit. Using this generator, both a 2-kV single thyristor and a 4-kV stack of two thyristors in series were triggered in the impact-ionization mode. The thyristors had a wafer diameter of 32 mm and capacitances of 370 pF. With a single thyristor 100 shots were performed with it switching a peak current of 1.25 kA and an associated dI/dt of 12 kA/ μs . With two thyristors, peak currents of 2.6 kA and with dI/dt of 25 kA/ μs were achieved. In all experiments no degradation of the semiconductor structure was observed. The work opens the way for developing very powerful, but still compact, solid-state trigger generators and larger pulsers for a wide range of pulsed power applications.
Maler D, Efimov S, Liverts M, et al., 2022, Peculiarities of planar shockwave interaction with air-water interface and solid target, PHYSICS OF PLASMAS, Vol: 29, ISSN: 1070-664X
Halliday JWD, Crilly A, Chittenden J, et 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.
Halliday JWD, Crilly A, Chittenden J, et 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.
Strucka J, Halliday JWD, Gheorghiu T, et 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.
Halliday JWD, Bland SN, Hare JD, et 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.
Tilikin IN, Shelkovenko TA, Pikuz SA, et 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.
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
High-voltage nanosecond pulses are widely used in scientific research, but their wider adoption in industry requires compact, cost-effective, and easy to use generators to be developed. This article presents the modeling and experimental investigations into one method of producing such pulses-a spiral generator with a solid-state-thyristor-based input switch. It includes how the pulses are formed within the spiral, why a high-speed input switch is required, and how the geometry of the spiral dictates its output characteristics and the effects of different loads. Using thyristors, often connected in series to increase the operating voltage of the spiral, enables the spiral generators to have low jitter, high repetition rate, and long lifetime. Modeling of the circuit used a combination of telegraph equations to account for the wave propagation along the spiral and a lumped circuit exchanging charge between the spiral and the input switch and load. The model is verified by the detailed experimental results with the relative error being <; 10% in most cases. The output voltage pulse was often observed to have an initial peak of much lower magnitude than the subsequent peak(s)-which can only be fully explained by considering wave propagation effects. Lower input switch inductance, shorter switching time, larger mean diameter of the spiral, and increasing the width of the copper tape that makes up the spiral can all increase the voltage multiplication efficiency. Although increasing the number of turns that makes up the spiral can increase the output voltage, it can also lower the multiplication efficiency. By understanding the effects of different geometries, the spiral can be optimized to drive different loads-three applications of such spiral generators are then presented-pulses with 10 kV amplitude and 10 kHz repetition rate for driving dielectric barrier discharge plasma, pulses with amplitude of 10 kV and 10 kV/ns rising rate for triggering of advanced solid-sta
Maler D, Efimov S, Rososhek A, et al., 2021, Generation of supersonic jets from underwater electrical explosions of wire arrays, PHYSICS OF PLASMAS, Vol: 28, ISSN: 1070-664X
Yan J, Parker S, Gheorghiu T, et 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.
Yanuka D, Theocharous S, Chittenden JP, et 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.
Miller SM, Slutz SA, Bland SN, et 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.
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.
Hare JD, MacDonald J, Bland SN, et al., 2019, Two-colour interferometry and Thomson scattering measurements of a plasma gun, Publisher: IOP PUBLISHING LTD
Hare JD, MacDonald J, Bland S, et 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.
Yanuka D, Rososhek A, Theocharous S, et 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.
Yanuka D, Theocharous S, Efimov S, et 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.
Theocharous SP, Bland SN, Yanuka D, et 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.
McBride RD, Stygar WA, Cuneo ME, et 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.
Shelkovenko TA, Pikuz SA, Tilikin IN, et 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.
Yanuka D, Rososhek A, Theocharous S, et 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.
Zhang X, Wang G, Luo B, et al., 2018, Refractive index and polarizability of polystyrene under shock compression, JOURNAL OF MATERIALS SCIENCE, Vol: 53, Pages: 12628-12640, ISSN: 0022-2461
Shelkovenko TA, Pikuz SA, Tilikin IN, et 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.
de Grouchy PWL, Kusse BR, Banasek J, et 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
Gurovich V, Virozub A, Rososhek A, et 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.
Zhang X, Wang G, Luo B, et 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.
Yanuka D, Rososhek A, Bland SN, et 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.
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