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.

Pulsed-power-driven underwater electrical explosion of cylindrical or conical wire arrays produces supersonic water jets that emerge from a bath, propagating through the air above it. Interaction of these jets with solid targets may represent a new platform for attaining materials at high pressure (>1010 Pa) conditions in a university-scale laboratory. However, measurements of the internal structure of such jets and how they interact with targets are difficult optically due to large densities and density contrasts involved. We utilized multi-frame x-ray radiographic imaging capabilities of the ID19 beamline at the European Synchrotron Radiation Facility to explore the water jet and its interaction with a 50 μm thick copper foil placed a few mm from the surface of water. The jet was generated with a ∼130 kA-amplitude current pulse of ∼450 ns rise time applied to a conical wire array. X-ray imaging revealed a droplet-type structure of the jet with an average density of <400 kg/m3 propagating with a velocity of ∼1400 m/s. Measurements of deformation and subsequent perforation of the target by the jet suggested pressures at the jet–target interface of ∼5 × 109 Pa. The results were compared to hydrodynamic simulations for better understanding of the jet parameters and their interaction with the foil target. These results can be used in future research to optimize the platform, and extend it to larger jet velocities in the case of higher driving currents supplied to the wire array.

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.

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) x 10(8) A/cm(2). 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. (c) 2024 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).

The intersection of dynamic compression, high-rate material response and X-ray science has seen rapid growth, leading to the establishment of specialized end-stations at international facilities such as Linac Coherent Light Source LCLS (Matter at Extreme Conditions - MEC) and Advanced Photon Source APS (Dynamic Compression Sector - DCS), both USA. Although these facilities excel in working with X-rays tailored for small material volumes (i.e. <1mm(3)), it needs a different approach to delve into subsequent processes. This is particularly the case in the transition from the micro- to mesoscale: here the ESRF distinguishes itself. The large beam size (several cm(2)) of the ID19 beamline, in conjunction with a strong high energy component, source flux density, and outstanding imaging sensitivity, enables sub-surface visualization of engineering-scale structures as well as natural systems in representative volume, under high rate and shock. This is particularly valuable when studying materials with complex mesostructures and heterogeneities on relevant volumetric scales, which often dominate the dynamic material response. The study of the behavior of materials under dynamic loading presents a unique challenge due to inherently spanning over multiple lengths- and timescales. The evolution of sudden (thermo)mechanical excitation, starting from the lattice scale and progressing through grains, phase domains, and ultimately to structures, exhibits a spectrum of responses spanning from the microscopic to bulk length scales. Consequently, a diverse range of diagnostics as well as driver instrumentation is required to identify, study, and characterize this material response spectrum. This article shall introduce platforms available at beamline ID19 and underline their potential by selected showcase applications. Community access proposals such as the beamtime Block Allocation Group (BAG) allow for access in a routine manner.

Underwater electrical explosion is a subject which is related to Warm Dense Plasma and High Energy Density Matter. This explosion is characterized by specific action integral which determines explosion time, i.e. when magnetic pressure of the current becomes smaller than the thermal pressure and materials experience fast expansion. We present the measurements’ results of value of for underwater electrical explosions of foils having butterfly-tie shape and made of different metals, namely Cu, Al, Ta, Zn, Ti and stainless steel. The experiments were carried out in a wide range of the current densities using microsecond [1] and sub-microsecond [2] pulse power generators. Time resolved shadow images obtained by fast frame intensified camera were used to observe the positions of the strong shock wave generated in water for each material at different times and foil cross-sections. These positions allow to determine the time of the explosion using linear extrapolation of shock wave position to its origin. Using waveforms of the discharge current and resistive voltage, as well as COMSOL simulation, we define the value of the current density and current action integral value for the considering foil cross-section. As result, the dependence of the specific current action integral on the explosion current density was obtained. These data are useful for verification of two-dimensional numerical hydrodynamic simulations coupled with equations of state of the metals.

We present results exploring various methods of aluminum flyer acceleration. One method uses the shock wave generated by underwater electrical explosions of thin foils supplied by a pulse generator with stored energy of ∼4.7 kJ. Utilizing the shock created by an exploding foil, a maximal free flyer velocity of ∼2000 m/s is obtained. This acceleration method is compared to results exploiting only magnetic pushing to accelerate flyers using a common strip-line configuration, resulting in much lower velocities of ∼300 m/s. We also present a modified strip-line configuration, for which a significant increase in the flyer velocity to ∼1200 m/s is measured. Finally, a hybrid strip configuration, incorporating both the effects of magnetic pushing and acceleration by exploding foil and its subsequent shock wave, results in ∼1400 m/s flyer velocity. These experimental results are analyzed by numerical simulations and analytical modeling of the conservation equations of mass and momentum.

Two interacting supersonic water jets and collisions of a water jet with an aluminum target are studied experimentally and by hydrodynamic simulations. Supersonic water jets form, when shocks generated by underwater electrical explosions of conical wire arrays converge. The arrays are supplied by a ∼250 kA, ∼1 μs rise time current pulse. Underwater explosion of two conical arrays placed face to face produces jets propagating in air with velocities of ∼2.5×103 m/s leading to hot plasma formation at a temperature of ∼2200–3000 K, pressure ∼1.7×1010 Pa, and density >1029 m−3. When a single array explodes underwater in front of an aluminum target, the collision of the jet with the target produces a local pressure of ∼3×1010 Pa on the surface of the target.

The dynamics of high-energy-density plasmas are dominated by the formation of instabilities. These can be seen on at all scales, from the structure of proto-stellar jets and nebulae, to the inertial confinement fusion experiments where instabilities can mix cold, dense, high Z plasma into fusion fuel significantly reducing yield. Measuring how the hydrodynamic instabilities evolve is crucial to providing quantitative comparison to theory and simulations, yet many experiments are limited to exploring relatively small region of parameter space in Mach and Atwood numbers, or provide only a few measurements per experiment, requiring control of the initial conditions (ICs).

Studies of properties of various materials at extreme conditions is subject which is related to Warm Dense Plasma and High Energy Density Matter. We explored how the resistivity and temperature of wires made of tin, molybdenum, silver, and platinum evolves with time during underwater electrical explosion by ~110 kA in amplitude current pulse with rise-time of ~220 ns [1]. The discharge voltage and current were measured using a Tektronix high voltage divider and Rogowski coils, respectively. Shadow streak images of exploding wire and generated shock in water were obtained by streak camera. Time evolution of the spectrum of the light emitted by exploding wire was obtained using a spectrometer and an array of nine photomultipliers, covering a spectral range of 400 – 700 nm. The data obtained was used to determine the energy deposited at instants of solid-state - liquid - vapor phase transitions and was compared with tabulated values.

We present a new technique for the investigation of shock-driven hydrodynamic phenomena in gases, liquids, and solids in arbitrary geometries. The technique consists of a pulsed power-driven resistive wire array explosion in combination with multi-MHz synchrotron radiography. Compared to commonly used techniques, it offers multiple advantages: (1) the shockwave geometry can be shaped to the requirements of the experiment, (2) the pressure (P > 300 MPa) generated by the exploding wires enables the use of liquid and solid hydrodynamic targets with well-characterized initial conditions (ICs), (3) the multi-MHz radiography enables data acquisition to occur within a single experiment, eliminating uncertainties regarding repeatability of the ICs and subsequent dynamics, and (4) the radiographic measurements enable estimation of compression ratios from the x-ray attenuation. In addition, the use of a synchrotron x-ray source allows the hydrodynamic samples to be volumetrically characterized at a high spatial resolution with synchrotron-based microtomography. This experimental technique is demonstrated by performing a planar Richtmyer–Meshkov instability (RMI) experiment on an aerogel–water interface characterized by Atwood number A0∼−0.8 and Mach number M∼1.5. The qualitative and quantitative features of the experiment are discussed, including the energy deposition into the exploding wires, shockwave generation, compression of the interface, startup phase of the instability, and asymptotic growth consistent with Richtmyer's impulsive theory. Additional effects unique to liquids and solids—such as cavitation bubbles caused by rarefaction flows or initial jetting due to small perturbations—are observed. It is also demonstrated that the technique is not shape dependent by driving a cylindrically convergent RMI experiment.

Underwater electrical wire explosion (UEWE) has been demonstrated to be a robust approach in the research of matter at extreme conditions, the main goal of high energy density physics (HEDP). Indeed, applying pulse generators with stored energy of several kJ allows one to achieve $\geq 10^{8}\mathrm{J}/(\text{kg}\times \mathrm{s})$ energy density deposition rate, pressure of $> 10^{9}$ Pa, and temperature of several eV. It was shown that UEWE is accompanied by rapid phase transitions of wire material resulting in the formation of a non-ideal, high-resistivity plasma characterized by fast-rising thermal instabilities, allowing conductivity research of different materials at extreme conditions. Additionally, we demonstrated that a planar shock, generated by the explosion of planar wire arrays, can efficiently (~12% energy transfer) accelerate targets. Moreover, the generation of supersonic (~4.5 km/s) water jets by the explosion of a conical wire array was demonstrated. The latter can be used for sub-Mbar pressure formation when interacting with a target. These results show great promise when considering scaling experiments into more powerful pulse generators. Ongoing research of UEWE employs different diagnostics such as high current and voltage measurements, shadow frame and streak imaging, X-ray radiography, and visible spectroscopy. Experimental results are compared to one-and two-dimensional hydrodynamic and magneto-hydrodynamic simulations, which recreate key experimental results, providing additional insight into the complex process occurring during UEWE. In this presentation selected results from recent advancements in studying and applying the aforementioned processes in the field of UEWE to further understanding HEDP will be discussed.

The study of the properties of matter at extreme conditions (>10 9 Pa, >10 4 K 0 ) is imperative for understanding phenomena where such states are reached in planetary astrophysics and confined fusion. To achieve such states of matter, what is often described as warm dense plasma, extremely high energy density deposition should be realized. One of the techniques used to explore matter under extreme conditions is the underwater electrical explosion of wire and wire arrays accompanied by the generation of strong shock waves.

Experimental and magnetohydrodynamic numerical simulation results and analysis of a μs- and sub-μs-timescale overdamped underwater electrical explosion of copper wires having different lengths and diameters are presented. For these explosions, ∼80% of the energy stored in the pulse generator is deposited into the wire during a time comparable or shorter than a quarter period of the underdamped discharge. It was found that the threshold values of the deposited energy density, energy density rate, and energy density per unit area, which satisfy overdamped discharge, depend on the wire parameters and on the timescale of the explosion. It was shown that the mechanism responsible for this is the process during which the wire experiences phase transitions to a low-ionized plasma, the resistivity of which is determined by the electron–neutral collision rate, which, in turn, depends on the wire radial expansion velocity, current density, and temperature.

Results of experimental research and numerical simulations related to two applications of the underwater electrical explosion (UEWE) of various symmetric wire arrays for the study of high energy density physics are presented. We explored how the rise-time of the generator affected energy deposition into underwater wire explosions, and the subsequent effects this had on shockwave generation and water flow. One application is the acceleration of flyer plates (targets) realized by strong shockwaves and subsequent Waterflow, generated by the UEWE of a planar wire array. In experiments, targets were accelerated to velocities of ≤1.3 km/s with energy efficiency transfer of ≤20% from the deposited energy. Another application is the generation of supersonic (~3-4 km/s) water jets by the UEWE of cylindrical/conical wire arrays. Jet generation occurs due to extremely high pressure and density of water formed in the vicinity of the axis by imploding shockwave and cumulation effect of converging shockwave at the edge of the cylindrical/conical array.

We explore the production of highly uniform, initially planar shockwaves in water and other insulators by the pulsed power driven explosion of wire arrays. The shockwaves are then either directly interacted with small, low density spherical targets or focused via shaped reflectors onto these targets to increase the drive pressures.

We present the results of experiments performed at the European Synchrotron Radiation Facility where, using phase-contrast imaging, the explosion of a planar wire array was studied. In experiments, a pulse generator (880 nF, 30 kV, 30 kA, current rise time of ~1 μs ) was used for the critically damped explosion of a planar copper wire array submerged underwater. Following the explosion, a strong shockwave, having planar symmetry, interacted with either an air-water interface or an aluminum target located 4-5 mm above the wire array.

Experiments in which supersonic water jets are generated by underwater sub-μs timescale electrical explosions of cylindrical and conical wire arrays are presented. These are compared with previous experiments [Maler et al., Phys. Plasmas 28, 063509 (2021)] in which the generation of supersonic water jets was demonstrated using a μs timescale generator. Although in the present experiments less energy is deposited into the wire arrays, the water jets acquire higher velocities compared to when the deposited energy is higher but the timescale is slower. That is, with a higher energy density deposition rate, faster radial wire expansion is induced resulting in a stronger converging shockwave and a faster waterflow behind its front. In addition, two dimensional hydrodynamic numerical simulations show that the formation of the water jet is the result of extremely high pressure at the axis of the shockwave implosion and the cumulative edge effect realized at the array output.

We present the design and parameters of a compact and mobile high-current pulse generator which can be applied in the study of warm dense matter in university laboratories. The generator dimensions are 550 mm × 570 mm × 590 mm, weight ~70 kg and it consists of four "bricks" connected in parallel. Each brick, made up of 2×40 nF, 100 kV lowinductance capacitors connected in parallel, has its own multigap and multichannel ball gas spark switch, triggered via a capacitively coupled triggering by a positive polarity pulse of ~80 kV amplitude and ~15 ns rise time. At a charging voltage of ~70 kV, the generator produces a ~155 kA current pulse with a rise time of ~220 ns on a ~15 nH inductive short-circuit load and a ~90 kA amplitude current pulse with an underwater electrical explosion of a copper wire.

Underwater electrical explosion experiments of cylindrical or conical wire arrays accompanied by the generation of fast (up to ∼4500 m/s) water jets are presented. In these experiments, a pulse generator with a stored energy of up to ∼5.7 kJ, current amplitude of up to ∼340 kA, and rise time of ∼0.85 μs was used to electrically explode copper and aluminum wire arrays underwater. Streak and fast framing shadow imaging was used to extract the space–time resolved velocity of the ejected jet from the array while it propagates in air. The jet generation occurs due to high pressure and density of water formed in the vicinity of the array axis by the imploding shockwave. It was shown that the velocity of the jet ejected from the array depends on the array geometry and the thickness of the water layer above the array. The results suggest that ≥50% of the energy deposited into the array is transferred to the kinetic energy of this jet and the axial waterflow.