Experimental and magnetohydrodynamic simulation results of nanosecond time scale underwater electrical explosions of Al, Cu, and W wires are presented. A water forming line generator with current amplitude up to 100kA was used. The maximum current rise rate and maximum Joule heating power achieved during wire explosions were dI∕dt⩽500A∕ns and 6GW, respectively. Extremely high energy deposition of up to 60 times the atomization enthalpy was registered compared to the best reported result of 20 times the atomization enthalpy for energy deposition with a vacuum wire explosion. Discharge channel evolution and surface temperature were analyzed by streak shadow imaging and by a fast photodiode with a set of interference filters, respectively. A 1D magnetohydrodynamic simulation demonstrated good agreement with experimental parameters such as discharge channel current, voltage, radius, and temperature. Material conductivity was calculated to produce the best correlation between the simulated and experimentally obtained voltage. It is shown that material conductivity may significantly vary as a function of energy deposition rate.

The dynamics of a Gaussian isolated barotropic eddy on a β-plane is considered. The analytical solution of the evolution of an isolated vortex is constructed by analogy to the theory of a point vortex. The results of a numerical experiment are compared with the conclusions of the theory for the case of the Gaussian vortex. Characteristics of the vortex such as its radius, trajectory of movement, kinetic energy, residual vorticity, and the structure of the vortex are discussed. The analysis of the numerical results shows that the experimentally determined radius of the vortex, its energy, and residual vorticity are in good agreement with the theory. On the other hand there is a difference between analytical and experimental values of velocity components, and hence in the trajectory of the centre of the vortex. The location of the separatrix of the streak function and its saddle point are considered as important characteristics of the structure of the vortex. We consider the phenomenon of the generation of the vortex sheet connected with the separatrix location as a cause of the difference between the experimental and analytical estimates of the velocity of the vortex.

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Experimental and hydrodynamic simulation results of submicrosecond time scale underwater electrical explosions of planar Cu and Al wire arrays are presented. A pulsed low-inductance generator having a current amplitude of up to 380 kA was used. The maximum current rise rate and maximum power achieved during wire array explosions were dI/dt≤830 A/ns and ∼10 GW, respectively. Interaction of the water flow generated during wire array explosion with the target was used to estimate the efficiency of the transfer of the energy initially stored in the generator energy to the water flow. It was shown that efficiency is in the range of 18%–24%. In addition, it was revealed that electrical explosion of the Al wire array allows almost double the energy to be transferred to the water flow due to efficient combustion of the Al wires. The latter allows one to expect a significant increase in the pressure at the front of converging strong shock waves in the case of cylindrical Al wire array underwater explosion.

Shearing interferometry, together with shadowgraph and Schlieren photography techniques, has been applied for the visualization of the cylindrical water flow behind the shock wave generated by high-power 6 GW nanosecond time-scale underwater electrical discharge. The flow was visualized during the first microsecond of the wire explosion process in the region between the expanding exploding wire discharge channel and the shock wave. The optical methods, combined with the hydrodynamic calculation, enable an accurate estimation of the energy transferred from the discharge to the water flow. The estimated efficiency of the transformation of the electrical dissipated energy to the mechanical energy of the generated compressed water flow is ∼15%.

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.

Analysis of time- and space-resolved spectrum of radiation emitted from the discharge channel generated by an underwater electrical wire explosion is reported. The purpose of this investigation was to detect a possible shunting corona discharge. During careful analysis of the emitted radiation no evidence for such discharge was found. Discharge temperature of 7eV was estimated by quantitative analysis of the emitted spectra.

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