Nikita Asmedianov

Building on prior work demonstrating that underwater microsecond timescale electrical explosions of semicylindrical wire arrays produce radially converging strong shock waves and blade-shaped supersonic jets reaching 1.6 km/s [ Experiments in Fluids 67, 25 (2026)], this study presents experimental investigations and two-dimensional hydrodynamic simulations aimed at optimizing jets generation from tamped, V-shaped electrically exploded foils. Aluminum and copper foils with varying apex angles were exploded using μs and sub-μs pulse generators with peak currents up to 300 kA, in two tamping media: water and 20% gelatin/water solution. Shock formation and jet dynamics were characterized using multi-frame shadowgraphy and X-ray imaging. Results show that the highest tip velocities, up to 4.5 km/s, are achieved with a 60° apex angle, sub-μs drivers and gelatin tamping. These high-velocity jets are capable of accelerating gram-scale targets to ~ 0.3 km/s and driving shocks in fluid and solid media at pressures up to ~ 7 GPa, offering a promising platform for dynamic material characterization under extreme loading conditions.

We present x-ray radiographs of underwater electrically driven exploding copper foils of different thickness, captured at the European X-ray Free-Electron Laser (EuXFEL) using 20 keV (∼30 eV bandwidth) self-amplified spontaneous emission photon beams. The foils were exploded by a ∼30 kA amplitude, ∼1.1 μs rise time current pulse produced by a compact pulsed-power generator. The radiographs reveal rapid frontal expansion of foils accompanied by lateral compression. This occurs due to strong magnetic pressure at the foil edges where, due to lateral skin-effect, the temperature reaches ∼1000 K leading to a fivefold decrease in the yield strength. Furthermore, the explosion begins with the foil edges, consistent with enhanced edge heating due to lateral skin-effect. With relatively thick foils, the bulk of the foil material remains in the liquid phase, and initial longitudinal density non-uniformities, coinciding with the current direction, transform into longitudinal striations. For thinner foils which experience explosion into a plasma, spatially non-uniform density structures appear at the edges of the foil and transverse the current direction. These density modulations, which can be estimated by x-ray attenuation, may be associated with the electrothermal instability (ETI); however, the linear theory of ETI growth does not appear to be applicable at the time of observation.

The Richtmyer-Meshkov instability (RMI) poses a major challenge in inertial confinement fusion (ICF) due to its role in mixing and performance degradation. We report the first experimental observation of passive freeze-out of RMI in a low-pressure surrogate regime, an instability stagnation effect induced without modifying the driving pressure pulse or the target surface geometry. Using additively manufactured subsurface voids in a sinusoidal target, we convert a single shock into a sequence of weaker shocks that suppress instability growth upstream of the surface by over 70%. High-speed x-ray imaging and hydrodynamic simulations suggest that this suppression arises primarily from temporal shaping, with lesser contributions from spatial curvature and shock weakening. Our results demonstrate a driver-independent pathway for controlling shock-driven hydrodynamic instabilities relevant to ICF and other high energy density systems.

We present the first x-ray images of electrically exploding wires in air and water, captured at the European X-ray Free-Electron Laser (EuXFEL). These images reveal current shunting in a copper wire during its explosion in air, and the development of electrothermal (and possibly magnetohydrodynamic) instabilities in copper and aluminum wires exploding in water. The experiments were conducted at the Single Particles, Clusters, and Biomolecules and Serial Femtosecond Crystallography instrument (SPB/SFX) at EuXFEL, where fine metallic wires were driven by a pulsed-power generator with a current rise time of ∼1.1 μs and a peak amplitude of ∼28 kA. EuXFEL enabled MHz x-ray radiography of the wires using 20 keV photons and a narrow bandwidth of ∼40 eV. Using the specific current action integral for a copper wire explosion, we provide the first quantitative estimate of the fraction of current that is shunted through the surrounding medium of an exploding wire. Fourier analysis of the electrothermal instability spectrum shows that its wavelength remains mostly independent of the wire diameter once it has exploded, and that the temperature perturbation is similar in magnitude to the average temperature in the wire.

Underwater electrical explosions of single metallic wires driven by microsecond current pulses are investigated and compared with previously reported sub-microsecond experiments. Current and voltage waveforms, streak camera shadow imaging, and one-dimensional hydrodynamic simulations are employed to characterize how the energy density, energy density deposition rate, and the generated shock waves in water depend on the wire parameters. It was found that, similar to the sub-microsecond timescale, the solid–liquid phase transition occurs later than thermodynamic calculations predicted, while the liquid–vapor phase transition happens sooner than expected, leading to a two-phase coexistence. Additionally, most materials show a notable resistance peak (Ti, Fe, Ni, Zn, Ag, Sn, Ta, Au) compared to a quasi-plateau for Cu and Mo or a continuous increase for Al and Pt. Moreover, the specific action integral values are significantly smaller than those observed in wire explosion experiments in vacuum. Finally, the plasma formed at peak resistive voltage is non-ideal but exhibits lower electron density, ionization degree, and temperature compared to the sub-microsecond case.

We present the results of experimental studies and two-dimensional hydrodynamic simulations of underwater electrical explosions of semi-cylindrical wire arrays. In the experiments, a pulse generator delivers a current pulse of ~ 250 kA amplitude rising in ~ 1 µs to a 5-mm radius semi-cylindrical array of copper or aluminum wires. Experiment and simulation results display the generation of a radially symmetric and converging strong shock wave (SSW) and the generation of a blade-shaped supersonic jet (SJ) with a velocity reaching 1.6 km/s. Simulations predict that in the vicinity of the implosion axis, the density, pressure, and temperature can reach 1.5 g/cm ³ , 6 × 10 ⁹ Pa and 500 K, respectively. Thus, this approach can be used for studies of properties of materials placed at the convergence axis or by interaction with the blade-shaped SJ with easy access of diagnostics. Additionally, the simulations show that the internal structure of the jet is not uniform, consisting of bubbles and voids that result in significantly smaller density than the normal density of water. Finally, explosions of arrays of different diameter wires result in the generation of converging SSW with satisfactorily uniform azimuthal distribution. This indicates a resistance positive feedback mechanism that stabilizes the explosion process across wires of different diameters.

We present the results of experimental studies and two-dimension hydrodynamic simulations of underwater electrical explosions of semi-cylindrical wire arrays. In the experiments, a pulse generator delivers a current pulse of ∼250 kA amplitude rising in ∼1 µs to a 5-mm radius semi-cylindrical array of copper or aluminium wires. Experiment and simulation results display the generation of a radially symmetric and converging strong shock wave (SSW) and the generation of a blade-shaped supersonic water jet with a velocity reaching 1.6 km/s. Simulations predict that in the vicinity of the implosion axis, the density, pressure and temperature can reach 1.5 g/cm ³ , 6×10 ⁹ Pa and 500 K, respectively. Additionally, the simulations show that the internal structure of the jet is not uniform, consisting of bubbles and voids that result in significantly smaller density than the normal density of water. Finally, explosions of arrays of different diameter wires result in the generation of converging SSW with satisfactorily uniform azimuthal distribution. This indicates on a resistance positive feedback mechanism that stabilizes the explosion process across wires of different diameters.

We present results of an experimental study of underwater strip line configurations with exploding or non-exploding foil electrodes, using a sub-microsecond generator delivering a ∼100 kA current pulse rising in 290 ns. For thin (≤15-μm) exploding copper and aluminum foils, the onset of visible and infrared light emissions, obtained by fast photomultiplier tubes, was found to coincide with the onset of melting and boiling, respectively. This suggests that this method can be applied for studies of phase transitions in conductors. For thick (>100-μm) non-exploding foils, streak shadow imaging and photonic Doppler velocimetry reveal that foil vibrations are synchronous with current oscillations, driven by a restoring compressed water pressure of ∼90 MPa. A water flow propagating at the speed of sound is observed ∼100 ns after the onset of the current. Current distribution simulations confirm that mechanical deformations, rather than magnetic or thermal diffusion, are responsible for this effect. This finding provides a means to probe the elastic behavior of conductors under extreme pulsed-current loading.

We present the results of two studies: (1) on the specific action integral h and (2) on the electrothermal instability (ETI) during underwater electrical explosions of different material foils. Values of h were studied in experiments with the explosion of tapered (“butterfly”) foil geometries using current pulses with an amplitude of ∼300 kA and ∼400 ns rise time using the MAGEN [Kovalchuk et al., Rev. Sci. Instrum. 80, 083504 (2009)] generator at Technion. Shadow images of foils, together with strong shock waves generated in the surrounding water by their explosion and results of COMSOL [Asmedianov et al., J. Appl. Phys. 136, 133303 (2024)] numerical simulations, were used to determine the values of h. These values were found to be significantly smaller than those stated in earlier research of wire explosions in vacuum. ETI was studied with butterfly and rectangular shaped foils explosion using pulsed driver generating current pulses with an amplitude of ∼120 kA and ∼450 ns rise time and multi-frame x-ray radiography at the European Synchrotron Radiation Facility . In the case of the butterfly, x-ray radiography showed the ETI instability initially appeared at the “waist,” where later explosion starts. In the case of the rectangular foil, it was found that the ETI perturbations have a minimum wavelength and a broad spectrum of larger wavelengths.