Results related to the generation of an extreme state of water with pressure up to (4.3 ± 0.2)·1011 Pa, density up to 4.2 ± 0.1 g/cm3, and temperature up to 2.2 ± 0.1 eV in the vicinity of the implosion axis of a converging strong shock wave are reported. The shock wave was produced by the underwater electrical explosion of a cylindrical Cu wire array. A ∼8 kJ pulse generator with a current amplitude ≤550 kA and rise time of 350 ns was used to explode arrays having varying lengths, radii, and number of wires. Hydrodynamic numerical simulations coupled to the experimental data of the shock wave propagation in water, rate of energy deposition into the array, and light emission from the compressed water in the vicinity of the implosion axis were used to determine the pressure, density, and temperature profiles during the implosion. Results of a comparison between these parameters obtained with the SESAME and quantum molecular dynamics data bases of equation of state for water are reported as well. Also, the dependences of the maximal pressure in the vicinity of the implosion axes on the array radius and the deposited energy density per unit length are reported.
The results of the first experiments on the underwater electrical explosion of a spherical wire array generating a converging strong shock wave are reported. Using a moderate pulse power generator with a stored energy of ≤6 kJ and discharge current of ≤500 kA with a rise-time of ∼300 ns, explosions of Cu and Al wire arrays of different diameters and with a different number and diameter of wires were tested. Electrical, optical, and destruction diagnostics were used to determine the energy deposited into the array, the time-of-flight of the shock wave to the origin of the implosion, and the parameters of water at that location. The experimental and numerical simulation results indicate that the convergence of the shock wave leads to the formation of an extreme state of water in the vicinity of the implosion origin that is characterized by pressure, temperature, and compression factors of (2 ± 0.2) × 1012 Pa, 8 ± 0.5 eV, and 7 ± 0.5, respectively.
The results of experiments on the ignition of aluminum micro-particles' combustion by underwater electrical wire explosion (UEWE) are reported. A compact sub-microsecond timescale duration high-current (240 kA) pulsed power generator was used to explode copper and aluminum wires electrically in different aluminum powder suspensions. The combustion of the aluminum micro-particles was characterized by a target time-of-flight method and optical measurements of the exploding wire and aluminum suspension light emission. It was shown that, by using a proper solution and type of aluminum powder, this method allows aluminum micro-particle combustion in the estimated range of 32-79 % efficiency.
The results of experiments involving underwater electrical explosion of different wire arrays using an outer metallic cylinder as a shock reflector are presented. A pulse generator with a stored energy of about 6 kJ, current amplitude ≤ 500 kA, and rise time of 350 ns was used for the wire array explosion. The results of the experiments and of hydrodynamic simulations showed that in the case of a Cu wire array explosion, the addition of the reflector increases the pressure and temperature of the water in the vicinity of the implosion axis about 1.38 and about 1.33 times, respectively. Also, it was shown that in the case of an Al wire array explosion with stainless steel reflector, Al combustion results, and, accordingly, additional energy is delivered to the converging water flow generating about 540 GPa pressure in the vicinity of the explosion axis. Finally, it was found that microsecond time scale light emission that appears with microsecond time scale delay with respect to the nanosecond time scale self-light emission of the compressed water in the vicinity of the implosion axis is related to water bubbles formation which scattered light of exploded wires.
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