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.
The results of time-resolved spectroscopic measurements of light emission from plasma formed in the vicinity of a converging spherical strong shock wave (SSW) are reported. This approach, together with hydrodynamic (HD) and radiative-transfer simulations, can be used for the characterization of the SSW convergence symmetry and the parameters of water at that location. It was shown that the obtained time-of-flight of the SSW and emission spectra agree well with the results of the simulation, showing that the water density, temperature, and pressure should be larger than ∼3 g/cm−3, ∼1.4 eV, and ∼2 × 1011 Pa, respectively, at radii <25 μm with respect to the origin of the SSW implosion.
Time-resolved parameters of plasma compressed by a shock wave generated by the underwater electrical explosion of a spherical wire array are presented. The plasma was preliminarily formed inside a capillary placed at the equatorial plane along the axis of the array. Temporal evolution analysis of Hα and C II spectral lines showed that the plasma density increases from its initial value of ∼3 × 1017 cm−3 up to ∼5.5 × 1017 cm−3 within 300 ± 25 ns. These results were found to be in agreement with those of the model that considers the adiabatic compression of the plasma by the converging capillary walls caused by interaction with the incident shock wave with a pressure of ∼3 × 109 Pa at a radius of 1.5 mm. The latter results coincide well with those of the 1D hydrodynamic modeling, which assumes uniformity of the converging shock wave.
The generation of strong magnetic fields ($50 T) using single-or multi-turn coils immersed in water was studied. A pulse generator with stored energy of $3.6 kJ, discharge current amplitude of $220 kA, and rise time of $1.5 ls was used in these experiments. Using the advantage of water that it has a large Verdet constant, the magnetic field was measured using the non-disturbing method of Faraday rotation of a polarized collimated laser beam. This approach does not require the use of magnetic probes, which are sensitive to electromagnetic noise and damaged in each shot. It also avoids the possible formation of plasma by either a flashover along the conductor or gas breakdown inside the coil caused by an induced electric field. In addition, it was shown that this approach can be used successfully to investigate the interesting phenomenon of magnetic field enhanced diffusion into a conductor. V
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