Radial density distribution of a warm dense plasma formed by underwater electrical explosion of a copper wire

Abstract

Time-and space-resolved evolution of the density (down to 0.07 of solid state density) of a copper wire during its microsecond timescale electrical explosion in water was obtained by X-ray backlighting. In the present research, a flash X-ray source of 20 ns pulse-width and >60 keV photon energy was used. The conductivity of copper was evaluated for a temperature of 10 kK and found to be in good agreement with the data obtained in earlier experiments [DeSilva and Katsouros, Phys. Rev. E 57, 5945 (1998) and Sheftman and Krasik, Phys. Plasmas 18, 092704 (2011)] where only electrical and optical diagnostics were applied. Magneto-hydrodynamic simulation shows a good agreement between the simulated and experimental waveforms of the current and voltage and measured the radial expansion of the exploding wire. Also, the radial density distribution obtained by an inverse Abel transform analysis agrees with the results of these simulations. Thus, the validity of the equations of state for copper and the conductivity model used in the simulations was confirmed for the parameters of the exploding wire realized in the present research.

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

“…The time indicated in the images is the time delay from the beginning of the discharge current rise. One feature immediately noticeable on the radiographs is that the front of the shock wave can be resolved-this could not be observed in previous radiography experiments 15 and is primarily due to the enhancement of the sharp edge of the shock wave by phase contrast effects and due to shorter X-ray pulse width. We can also directly observe the water immediately behind the shock wave-in optical shadow imaging diagnostics, the shock wave scatters any backlighting radiation out of the system-only after several microseconds does the water turns clear again (see, for example, Fig In the radiography images, the boundary of the exploding wire with the water is also very clearly observed.…”

“…Both copper and tungsten wires were used in the experiments, as these have been well explored in previous experiments, mainly through optical diagnostics. 7,[12][13][14][15] The length of the wires was 45 mm, and the wire diameter of each material was chosen to be 200 μm, which critically damped current and maximised energy transfer to the wires. In practice, the wires were stretched and soldered between two electrodes which were screwed in an 8 mm inner diameter 1.5-mm-thick acrylic tube which was filled with deionized water.…”

“…Nitishinskiy et al recently carried out x-ray radiography of copper wire experiments in water. 15 The x-ray source was based on a vacuum diode and photon energies above 60 keV were achieved. The 50-μm spatial resolutions achieved with temporal resolutions ∼20 ns enabled the density of the wire and its radius to be measured.…”

“…In this paper, we present first x-ray radiography results of pulsed power driven, microsecond timescale, underwater copper and tungsten wire explosions performed at the European Synchrotron Radiation Facility (ESRF). The images obtained have much higher spatial and temporal resolutions than those in earlier experiments 15 and employ phase contrast imaging to highlight any edge effects-providing improved detail on the internal structure of the exploding wires, the expansion of the wires during implosion, and the shockwave launched into the water. The structure of the rest of the paper is as follows.…”

X-ray radiography of the overheating instability in underwater electrical explosions of wires

“…It was often argued that these striations were the result of magnetohydrodynamic (MHD) m ¼ 0 instability and that at much faster time scales there would be a much more uniform expansion. This was supported by recent X-ray diode-based radiography experiments 20 which seemed to show a relatively uniform expansion of a wire in water driven by currents on the hundreds of ns-timescale, suggesting that any measurements of conductivity of the wire material could rely on uniform wire expansion. However, the X-ray diode and point projection imaging system used was of limited spatial resolution ($70 lm) and extended over 20 ns in duration.…”