Characterization of converging shock waves generated by underwater electrical wire array explosion

Abstract

Results of ∼200 kbar pressure generation at 50 μm distance from the implosion axis of the converging shock wave produced by an underwater electrical explosion of a cylindrical wire array are reported. The array was exploded using a submicrosecond high-current generator (stored energy of ∼4.2 kJ, current amplitude of ∼325 kA, rise time of ∼1 μs). Multiframe shadow imaging of the shock wave was used to determine its time of flight. These data were applied for calculating the pressure at the vicinity of the implosion axis using one dimensional hydrodynamic calculations and the Whitham approach. However, it was found that in the case of wire array radius ≤5 mm, multiframe imaging cannot be used at the final stage of the shock wave implosion because of possible changes in the optical properties of the water. Optical and spectroscopic methods based on either the change in the refraction index of the optical fiber or spectroscopy of the plasma formed inside the capillary placed at the implosion axes were used for shock wave characterization. A satisfactory agreement was found between the results obtained by these methods.

Spectroscopy of a plasma formed in the vicinity of implosion of the shock wave generated by underwater electrical explosion of spherical wire array

“…Nevertheless, in experiments with the explosion of a 5 mm in radius cylindrical wire array, azimuthal symmetry of converging SW down to a radius r % 100 lm was obtained by shadow imaging. In addition, the results of spectroscopy of the plasma formed inside a copper capillary placed coaxially inside the array indicate the axial and azimuthal symmetry of the cylindrical converging SW. 19 Recently, the results of two-dimensional HD simulations 23 showed that artificially introduced non-uniformity of the cylindrical converging SW should be self-repaired, which agrees with the Whitham model. 24 Self-similar analysis of the converging SW implosion 17 showed that the pressure p behind the SW front located at the radius r can be calculated at instant t as p ¼ p o ðr=r o Þ 2À2=a , where p 0 and r 0 are the pressure and radius, respectively, at some previous instant t 0 < t, and a is the self-similarity parameter that equals 0.75 and 0.6 for cylindrical and spherical SWs, respectively.…”

“…16 This allows this approach for generating converging strong SW by underwater electrical explosion of either cylindrical of spherical wire arrays to be applied in order to obtain an extreme state of water in the vicinity of the SW implosion. 17,18 In the case of a cylindrical wire array explosion, shadow imaging of the generated SW and water light emission in the vicinity of the convergence axis were used to calculate the time-of-flight (TOF) of the SW. 19,20 These data and the $12% efficiency of the stored energy transfer to the converging water flow were used as validation parameters for comparison with the results of one dimension hydrodynamic (HD) simulations, coupled with the experimentally measured energy deposited into the wires and the EOS for water. 21 The results of these simulations showed that in the vicinity of the convergence axis, the values of pressure P % 4.7 Â 10 11 Pa, temperature T % 3 eV, and density q % 4 g/ cm 3 can be reached.…”

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

“…[1][2][3] Different dynamic loading facilities, such as multi-stage light gas guns, 4 Z-pinch, 5 powerful lasers, 6,7 and intense heavy ion beams, 8 with a stored energy in the range of 10 5 -10 9 J, are required to generate extreme states of matter 9 characterized by a pressure P ! 10 11 Pa during a short (in the range 10 À9 -10 À6 s) time duration. Recent research [10][11][12] showed that by using a pulsed power generator with stored energy of only a few kJ as a current source for the underwater electrical explosion of a wire array, one can generate WDM with P 6 Â 10 12 Pa.…”

“…10 11 Pa during a short (in the range 10 À9 -10 À6 s) time duration. Recent research [10][11][12] showed that by using a pulsed power generator with stored energy of only a few kJ as a current source for the underwater electrical explosion of a wire array, one can generate WDM with P 6 Â 10 12 Pa. This method exploits the converging strong shock waves (SWs) generated by the underwater electrical explosion of either a cylindrical or a spherical wire array.…”

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

“…[1][2][3] Several approaches that require stored energy in the range of 10 5 -10 9 J, such as multi-stage light gas guns, 4 Z-pinch, 5 powerful lasers, 6,7 and intense heavy ion beams, 8 are used to generate this state of matter, 9 which is characterized by a pressure !10 11 Pa. Recent research 10,11 showed that underwater electrical explosion of a wire array can be used as an alternative method to generate warm dense matter with 2 Â 10 12 Pa, using generators with moderate (several kJ) stored energy. This method is based on the implosion of the converging strong shock wave (SSW) generated by the underwater electrical explosion of either cylindrical or spherical wire arrays.…”