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.

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.

Theta pinch is a well-known approach applicable for inertial fusion research. The theta pinch operation is based on plasma generation through gas ionization by induced electric field. The plasma radial compression occurs due to magnetic field pressure produced by an azimuthally driving current. In our research, we use a $1 \mu \mathrm{F}$ capacitor charged to 17 kV. This capacitor is discharged to a singly loop, encompassing a glass tube filled with either hydrogen or helium gas, producing underdamped discharge with $1.5 \mu \mathrm{s}$ rise-time and a peak current of 17.5 kA. We will report on time- and space resolved parameters of the hydrogen and helium which are obtained using frame images of the plasma light emission, microwave cutoff, laser interferometry, plasma spectroscopy, Thompson scattering and Laser Induced Florescence at pressures of $0.1-3$ Torr during plasma compression.

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.

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.

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 implosion of fast, convergent shock waves driven via the electrical explosion of cylindrical wire arrays embedded in insulator offers a highly efficient method of generating extreme pressures. At low currents (~30kA) the increased density on axis was directly observed at the ESRF synchroton; at higher currents - up to 2.5MA on the Cepage generator at First Light Fusion - the implosion dynamics imply pressures >Mbar exist in warm dense plasma on axis. How this process scales to currents >5MA is unclear - a limit could exist on the speed at which the shockwaves are initially projected from the wires, set by the rate of energy deposition into the wires.

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.

New analytical solution of the piston and shock evolution for the wire electrical explosion in water is obtained. This is provided on the base of the compressible Euler equations without usually a prior introduction of any self-similarity hypothesis. It is shown that diverging cylindrical shock is transformed into acoustic wave in a finite time, even without taking into account of dissipation. The correspondence with experimental data on underwater electrical explosion of thin wire is represented.

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 report on results from an experiment conducted at the European Synchrotron Radiation Facility Microtomography Beamline investigating the use of conductors submerged underwater and vaporised by high current densities ~10 12 A/m 2 to seed plasma instabilities.

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.