D. Yanuka

Generation of converging strong shock wave formed by microsecond timescale underwater electrical explosion of spherical wire array

A study of generation of converging strong shock wave using microsecond underwater electrical explosion of spherical Cu-wire array is presented. Hydrodynamic simulations coupled with the equation of state for Cu and water, deposited energy, and the magnetic pressure were used to calculate the water parameters in the vicinity of the implosion origin. The results of simulations agree with the shock wave time-of-flight and energy delivered to the water flow and show that in the vicinity (diameter of ∼12 μm) of an implosion one can expect water pressure of ∼6 TPa, temperature of ∼17 eV, and compression of ∼8.

Underwater Electrical Explosion of Wires and Wire Arrays and Generation of Converging Shock Waves

A brief review of the results obtained in recent research of underwater electrical explosions of wires and wire arrays using microsecond-, submicrosecond-, and nanosecond-timescale high-current generators is presented. In a microsecond-timescale wire explosion, good agreement was attained between the results of experiments and the results of magnetohydrodynamic calculations coupled with equations of state (EOS) and modern conductivity models. Conversely, in a nanosecond-timescale wire explosion, the wire resistance and the EOS were modified in order to fit experimental data. In experiments with cylindrical and spherical wire arrays, generation of a converging shock wave (SW) was demonstrated allowing formation of an extreme state of water in the vicinity of either the axis or the origin of the SWs implosion. In addition, it is shown that SW convergence in superspherical geometry allows one to achieve larger values of pressure, density, and temperature of water in the vicinity of the axis of convergence than in the case of a spherical implosion. The results of experiments and numerical analysis showed that a cylindrical SW keeps its symmetry along the main path of its convergence. In addition, it is shown that underwater electrical explosion of an X-pinch wire configuration and a cone wire array allows one to generate fast jets of metal and water, respectively, without using chemical explosions.

Diagnostics of a converging strong shock wave generated by underwater explosion of spherical wire array

The results of experimental studies of the convergence of shock waves (SWs) generated by the underwater electrical explosion of a spherical wire array supplied by a current pulse with an amplitude ∼300 kA and rise time ∼1.1 μs are reported. In the experiments, the power and spectrum of the light emission from an optical fiber, the explosion of a copper tube, and the time-dependent resistance of a resistor placed in the equatorial plane of the spherical wire array were measured. A comparison of the experimental data with the results of numerical simulations of SW convergence shows that the SW keeps its uniformity along the major part of the convergence towards the implosion origin.

Generation of highly symmetric, cylindrically convergent shockwaves in water

We report on pulsed power driven, exploding copper wire array experiments conducted to generate cylindrical convergent shockwaves in water employing μs risetime currents >550 kA in amplitude and with stored energies of >15 kJ—a substantial increase over previous results. The experiments were carried out on the recently constructed Mega-Ampere-Compression-and-Hydrodynamics facility at Imperial College London in collaboration with colleagues of Technion, Israel. 10 mm diameter arrays consisting of 60 × 130 μm wires were utilized, and the current and voltage diagnostics of the load region suggested that ∼8 kJ of energy was deposited in the wires (and the load region close to the wires) during the experiments, resulting in the formation of dense, highly resistive plasmas that rapidly expanded driving the shockwaves in water. Laser-backlit framing images of the shockfront were obtained at radii <0.25 mm for the first time, and there was strong evidence that even at radii <0.1 mm this front remains stable, resu...

Comparison of electrical explosions of Cu and Al wires in water and glycerol

The results of experiments on single Cu and Al wire electrical explosions with a current density of ∼108 A/cm2 in water and glycerol on ns- and μs-timescales are presented. Framing and streak images of the exploding wires and generated shock waves were used for the analysis of the possible contribution of Al and glycerol combustion to the shock wave velocity and pressure behind its front. It was shown that on nanosecond and microsecond timescales of wire explosions, one obtains Al and glycerol combustion. However, Al combustion does not contribute to the velocity of the generated shock wave because of a relatively slow rate of energy density deposition into the water flow. Nevertheless, electrical explosion of Al and Cu wires in glycerol showed a significant increase in the generated shock wave velocity and consequently in the pressure behind its front as a result of glycerols higher density and combustion.

Converging shock wave focusing and interaction with a target

Converging shock waves in liquids can be used efficiently in the research of the extreme state of matter and in various applications. In this paper, the recent results related to the interaction of a shock wave with plasma preliminarily formed in the vicinity of the shock wave convergence are presented. The shock wave is produced by the underwater electrical explosion of a spherical wire array. The plasma is generated prior to the shock waves arrival by a low-pressure gas discharge inside a quartz capillary placed at the equatorial plane of the array. Analysis of the Stark broadening of Hα and Hβ spectral lines and line-to-continuum ratio, combined with the ratio of the relative intensities of carbon C III/C II and silicon Si III/Si II lines, were used to determine the plasma density and temperature evolution. It was found that during the first ∼200 ns with respect to the beginning of the plasma compression by the shock wave and when the spectral lines are resolved, the plasma density increases from 2 × ...

Time-resolved spectroscopy of light emission from plasma generated by a converging strong shock wave in water

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.

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

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 conductivit...

Addressing optimal underwater electrical explosion of a wire

The underwater electrical explosion of a wire in the timescale 10−7–10−6 s is characterized by different phase transitions at extreme values of deposited energy density, allowing one to obtain warm dense matter using rather moderate pulse power generators. In order to achieve maximal energy density deposition, the parameters of the wire and the pulse generator should be optimized to realize an overdamped explosion where most of the initially stored energy is delivered to the exploding wire during a time comparable with the quarter of the discharge period. In this paper, the results of 1D magneto-hydrodynamic modeling, coupled with the copper and water equations of state, of the underwater electrical explosion of Cu wires having an identical length and average current density but different discharge current rise time are analyzed and compared with those of a simplified model of a conductivity wave, the propagation velocity of which determines the mode of the wires explosion. In addition, it is shown that ...

Addressing the problem of uniform converging spherical shock wave in water

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.