We present results on underwater electrical explosions of thin aluminum and copper foils using a generator delivering ∼200 kA current amplitude, ∼0.9 μs rise time pulses. Time-resolved shadow imaging displays the generation of a strong planar shock wave in water in the vicinity of the exploding foil. Using time-resolved spectroscopy, aluminum oxide (AlO) absorption bands were observed in a Planckian-like spectrum, indicating that aluminum combustion starts when aluminum vaporizes. It is also shown that the strongest shock wave is obtained for the largest linear energy deposition rate to the foil.

Results of an experimental research and one-dimensional hydrodynamical simulations of critically damped sub-microsecond timescale underwater electrical explosions of wires made of 12 different materials are presented. Using current and voltage waveforms, streak shadow images of the shocks generated in water and wire expansion obtained by one-dimensional hydrodynamic simulations, the maximal values of the energy density, energy density deposition rates, and specific action integrals were determined. It is shown that for all study materials, the deposited energy density significantly exceeds the energy density required for the solid–liquid phase transition but is substantially smaller to induce a full liquid–vapor phase transition of the wire. At the time when the maximal value of the deposited power is realized, the deposited energy densities were found to be larger than the atomization energy for all materials. Estimates of the plasma parameters show that the explosion of the wires can be characterized by a high resistance and lowly ionized weakly coupled plasma. Three groups of materials were distinguished by either decrease, plateau, or increase in the resistance after the maximum of the deposited power. It was confirmed that the observed maximum Planckian temperature for all wire material does not exceed 6000 K due to the “bath” effect and that there is a correlation between the wire radial expansion and the strong shock wave velocities.

We present measurements of the wavelength of electrothermal instabilities (ETI) formed during underwater electrical explosions of aluminum (Al), silver (Ag), and molybdenum (Mo) wires. Wires were exploded using a ∼450 ns rise time and ∼120 kA amplitude current pulse delivered by a pulse generator. Images of the exploding wires were captured by multi-frame synchrotron radiography at the ID19 beamline of the European Synchrotron Radiation Facility. Resolvable ETI was observed only in Al and Ag wires after the vaporization phase, whereas no such instabilities were detectable in Mo wires. Fourier analysis revealed that the ETI wavelengths in Al and Ag wires were comparable within the spatial resolution error, despite their different minimal instability wavelengths, which were predicted to develop during the melting phase. These minimal wavelengths were calculated using the linear ETI development theory and the simulated average wire temperature. The latter was calculated using one-dimensional hydrodynamic simulations, considering uniform current density across the wire cross-sectional area.

The results of experiments and numerical modeling show that a polyoxymethylene (Delrin) flyer is accelerated to nearly the same velocity (∼800 m/s) by either the underwater electrical sub-μs timescale explosion of 15 μm thick Al and Cu foils, or by the shock and water flow generated by the explosion of these foils. Experiments were carried out on the high-current generator delivering to the foil, a current of ∼280 kA with a rise time of ∼450 ns. The velocity of the flyer was determined using a photonic Doppler velocimeter and multi-frame shadow images of the flyer. It was shown that thermal expansion of the foil leads to the destruction of the flyer but it is not so when the flyer is accelerated by the shock and the water flow. Additionally, spallation of the methyl methacrylate disk used as a support to the flyer was observed, with a spall velocity of up to ∼1200 m/s.

Results of experimental research and two-dimensional hydrodynamical simulations of close to critically damped microsecond timescale underwater electrical explosions of butterfly-shaped foils for six different materials are presented. Using current and voltage waveforms along with multi-frame shadow images of the shocks generated in water, the values of the specific action integral, h, were determined. It is shown that values of h can be calculated based on the average current density and that its value (within error bars) does not change in the range of current densities (0.5–1) × 108 A/cm2. The values of h were found to be consistent with those obtained for sub-microsecond underwater electrical explosions of wires made of the same material but differ from those obtained in earlier research with explosion of wires in vacuum.

This study investigates the ionization pressure threshold of a gas (air, helium, argon, and SF6 across a wide pressure range) filled dielectric tube when a ∼300 MW, ∼0.7 ns, 9.6 GHz high-power microwave (HPM) pulse propagates through it. The thresholds are determined as the pressure for which the energy of the transmitted HPM pulse decreases to ∼30%, which is close to the same HPM pulse's transmission coefficient when a metal rod fills the tube. These thresholds are found to be 0.4 × 105 Pa,105 Pa, 1.8 × 105 Pa, and 0.2 × 105 Pa, for air, argon, helium, and SF6, respectively. The measured intensity of the plasma light emission starts to decrease at a pressure which coincides with the pressure threshold determined by HPM pulse propagation. Additionally, at gas pressures 105 Pa transforms into streamer like plasma. Simplified numerical simulations of a microwave discharge in air at 1 × 105 Pa and 4 × 105 Pa are consistent with the experimental plasma light observations.