Generation of highly symmetric, cylindrically convergent shockwaves in water

Journal of Applied Physics

Rososhek

Theocharous

et al. 2018

Self Cite

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.

Section: Comparison Of Results To 2d Hd Simulationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Multi frame synchrotron radiography of pulsed power driven underwater single wire explosions

Journal of Applied Physics

Rososhek

Theocharous

et al. 2018

Self Cite

“…6 Such experiments are often used to perform equation of state studies, and more recently, the shock waves generated in water by exploding wires have become of interest for efficiently producing high pressure conditions at the meeting point of multiple shocks waves generated by arrays of wires in a cylindrical or spherical geometry. 7,8 Wire explosions in water, rather than gas or vacuum, are often preferred as high breakdown voltage prevents the formation of plasma on the wire's surface, and as the low compressibility of water slows the expansion of the wire and ensures high energy density deposition in the wire material.…”

Section: Introductionmentioning

confidence: 99%

Use of synchrotron-based radiography to diagnose pulsed power driven wire explosion experiments

Theocharous

Bland

Review of Scientific Instruments

et al. 2019

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We describe the first use of synchrotron radiation to probe pulsed power driven high energy density physics experiments. Multiframe 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.

“…The results of recent studies indicate that WDM with pressures above 100 GPa can be obtained using strong converging Strong Shock Waves (SSWs) generated by underwater electrical explosions of either cylindrical or spherical wire arrays. 11,12 Different methods (damage of different targets, spectroscopy of the obtained water plasma created by the convergence of the SSW) were applied to determine the water parameters in the vicinity of implosion. [13][14][15] Also, the SSW's time-of-flight to the axis (cylindrical wire array) or origin (spherical wire array) of implosion leading to intense light emission from compressed and heated water at those locations was used for comparison with the results of one dimensional (1D) and two dimensional (2D) Hydrodynamic (HD) simulations, coupled with the EOS of water and copper.…”

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confidence: 99%

“…20 Shadowgraph images of converging cylindrical SSWs generated by underwater electrical explosions of wire arrays obtained in experiments carried out in Technion and Imperial College London showed a near circular shape of the SSW's front down to a radius of 100 lm. 11,21,22 In this paper, the results of cylindrical SSW convergence below a radius of 100 lm are described and analyzed. In addition, beam propagation method (BPM) simulations have been applied to study the propagation of a laser beam that is used to backlight framing and streak images of the implosion.…”

mentioning

confidence: 99%

Uniformity of cylindrical imploding underwater shockwaves at very small radii

Applied Physics Letters

Rososhek

Bland

et al. 2017

Self Cite

We compare the convergent shockwaves generated from underwater, cylindrical arrays of copper wire exploded by multiple kilo-ampere current pulses on nanosecond and microsecond scales. In both 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 framing images of the shock front were achieved down to the radius of 30 l m. It was found that even in the case 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 fringes have been observed in streak and framing images as the shockwave approached the axis. We have been able to accurately model the origin of the fringes, which is due to the propagation of the laser beam diffracting off the uniform converging shock front. The dynamics of the shockwave and its uniformity at small radii indicate that even with only 500 J stored energies, this technique should produce pressures above 10¹⁰ Pa on the axis, with temperatures and densities ideal for warm dense matter research