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Studies of the equation of states (EOS) of different materials at extreme pressures and densities are of great importance for various fields of research. A commonly used method to achieve extreme conditions is shock compression. Shock compression can be achieved by numerous techniques, one of them is the flyer plate which can be accelerated using either explosives, gas guns or pulse magnetic field gradients. In our presentation we will describe the experimental setup and results of accelerating flyer plates using a strong shock wave generated by the underwater electrical explosion of a planar wire array. Explosion of a planar Cu wire array was produced using a µs and sub-µs-timescale generators with stored energies of up to ~6 kJ, delivering to the array a current pulse with amplitudes of up to ∼500 kA with rise time of ~400 ns and ~1 µs, respectively. A Photonic Doppler Velocimetry (PDV) is applied for determining the velocity of a free moving target.

The results of an experimental, analytical, and numerical study of the cylindrical shock wave generated by the underwater electrical explosion of copper and aluminum wires are reported. Experiments were conducted using a microsecond timescale generator delivering ∼180 kA pulses with a 1.2 μs rise time. Shadow streak images were used to study the radial expansion of the exploding wire and the generated shock wave. It was found that the shock wave expansion velocity decreases to the velocity of sound in two stages: a fast stage and then a gradual stage. The fast stage occurs during ∼1.5 μs after the maximum of the resistive voltage is reached, and then, a gradual decrease occurs during several tens of microseconds. It was shown that the duration of the fast stage corresponds to the period of time when the main energy deposition into the wire occurs. Hydrodynamic simulations show that the fast decrease in the shock velocity is related to the evolution of the exploded wire's subsonic expansion, which leads to time/spatial compression of the adjacent water layer. For the gradual decrease stage of the shock wave velocity, we developed a simplified model, which considers uniform water density between the wire boundary and the shock wave front. The results of this model agree satisfactorily with the experimentally obtained shock wave trajectory and radial expansion of the wire.

We present X-ray radiography images showing the propagation of shock waves generated by electrical explosion of a cylindrical arrangement of wires in water driven by pulsed power. In previous experiments [S. N. Bland et al., Phys. Plasmas 24, 082702 (2017)], the merger of shock waves from adjacent wires has produced a highly symmetrical, cylindrical shock wave converging on the axis, where it is expected to produce a high density, strongly coupled plasma ideal for warm dense matter research. However, diagnostic limitations have meant that much of the dynamics of the system has been inferred from the position of the front of the cylindrical shock and timing/spectra of light emitted from the axis. Here, we present a synchrotron-based radiography of such experiments—providing direct quantitative measurements on the formation of the convergent shock wave, the increased density of water on the axis caused by its arrival, and its “bounce” after arrival on the axis. The obtained images are compared with two-dimensional hydrodynamic simulations, which reproduce the observed dynamics with a satisfactory agreement in density values.

(Experimental studies of a spherical converging shock wave (SW) interaction with preliminary formed plasma are presented. The SW was generated by an underwater electrical explosion of a spherical Cu wire array (radius of 15 mm, number of wires of 40, and wire diameter of 0.1 mm) supplied by 240 kA amplitude current pulse with rise time of ∼0.8 μs. The plasma was formed by a 40 Pa propane discharge between the cathode and anode electrodes, placed at the distance of 1.5 mm apart, inside of 2 mm inner diameter quartz capillary located at the equatorial plane of the array. The light emission from the plasma was transferred to the inputs of two spectrometers by optical fiber installed from the one side of the capillary and beam splitter with lenses. The spectral lines intensities at the output of spectrometers were recorded prior and during the SW interaction with plasma by intensified framing 4QuikE cameras and by a photomultiplier tube when one of the spectrometers was used as a monochromator.

Underwater electrical explosion of wire arrays is a promising method of obtaining extreme states of water (T > 1 eV, P > 1010 TPa). These extreme states are obtained in the vicinity of implosion of strong converging shock waves generated by the array explosion. Explosions of cylindrical and spherical wire arrays were studied in which the latter results in higher water parameters due to the shock wave convergence to a smaller region (origin of a sphere as opposed to an axis of a cylinder). Latest results obtained in our laboratory show that one can achieve even higher water parameters with the same amount of stored energy than with the spherical wire array. This is achieved by introducing parabola shaped boundaries (super-spherical geometry) in the space where the generated strong shock wave is propagating. The experimental and numerical results of this recent research will be reported.

Results of one-dimensional numerical simulations of the parameters of the converging strong shock wave generated by electrical underwater explosions of a cylindrical wire array with different array radii and different deposited energies are presented. It was shown that for each wire array radius there exists an optimal duration of the energy deposition into the exploding array, which allows one to maximize the shock wave pressure and temperature in the vicinity of the implosion axis. The simulation results agree well with the 130-GPa pressure in the vicinity of the implosion axis that was recently obtained, which strongly indicates the azimuthal symmetry of the converging shock wave at these extreme conditions. Also, simulations showed that using a pulsed power generator with a stored energy of ~200 kJ, the pressure and temperature at the shock wave front reaches ~220 GPa and 1.7 eV at 0.1 mm from the axis of implosion in the case of a 2.5 mm radius wire array explosion. It was found that, in spite of the complicated equation of state of water, the maximum pressure at the shock wave front at radius r can be estimated as P ≈ (P*(r*/r)α, where P* is the known value of pressure at the shock wave front at radius r* ≥ r and α is a parameter that equals 0.62±0.02. A rough estimate of the implosion parameters of the hydrogen target after the interaction with the converging strong shock wave is presented as well.

Using streak images of underwater electrically exploding copper, aluminum, and tungsten wires (current densities of 107–108 A/cm2 and energy density deposition of 10–50 kJ/g) and generated weak shocks, the onset of each phase transition, its duration, and the time when the wire explosion occurred were determined. The measured discharge current and resistive voltage were used to calculate the energy and energy density deposition. Using the discharge current waveform and the onset of the strong shock wave, the specific action integral was calculated and compared with published data. The thermodynamic parameters during the wire explosion were calculated using one-dimensional magneto-hydrodynamic simulations coupled with equations of state for water, copper, and aluminum. It was shown that the onset times of weak shocks, in general, cannot be related to the melting or the evaporation of the entire wire.Using streak images of underwater electrically exploding copper, aluminum, and tungsten wires (current densities of 107–108 A/cm2 and energy density deposition of 10–50 kJ/g) and generated weak shocks, the onset of each phase transition, its duration, and the time when the wire explosion occurred were determined. The measured discharge current and resistive voltage were used to calculate the energy and energy density deposition. Using the discharge current waveform and the onset of the strong shock wave, the specific action integral was calculated and compared with published data. The thermodynamic parameters during the wire explosion were calculated using one-dimensional magneto-hydrodynamic simulations coupled with equations of state for water, copper, and aluminum. It was shown that the onset times of weak shocks, in general, cannot be related to the melting or the evaporation of the entire wire.

Results of underwater electrical explosions of spherical wire arrays in water and glycerol on the sub-microsecond timescale are presented and compared to those obtained on the microsecond timescale [Rososhek et al., Phys. Plasmas 24, 122705 (2017)]. The time-of-flight of the converging shockwave was found to be approximately the same, despite almost three times faster energy density deposition into the exploding wires for sub-microsecond timescale explosions. This phenomenon was reproduced by numerical modeling, which showed that the exploding wires' expansion on both timescales results in almost identical radii when the convergence of the shockwave becomes self-similar. Thus, to increase the shockwave convergence velocity and consequently, the parameters of the compressed water near the shockwave implosion origin, instead of increasing the energy deposition rate, one must increase the initially stored energy.

The results of a study of shock wave (SW) generation by means of underwater electrical wire explosion with different exploding wire configurations and two high-current microsecond and submicrosecond timescale generators are presented. By using aperiodical generator discharge, a ~85% and ~15% of the stored electrical energy was transferred to the exploding wire and energy of the generated water flow, respectively. The energy of the water flow is distributed between its internal (~25%) and kinetic (~75%) energies. It was shown that the exploding wire zigzag configuration, confinement of the SW propagation region, and an increase in the rate of the energy deposition into the exploding wire allow one to increase the SW pressure ges10 times that attained with microsecond timescale straight wire explosion. The averaged thermophysical properties of nonideal and weakly degenerated plasma formed as a result of the wire explosion were obtained and summarized.

Results of an investigation of underwater electrical wire explosions using high-power microsecond and nanosecond generators are reported. Different diagnostics, including electrical, optical, and spectroscopic, together with hydrodynamic and magnetohydrodynamic simulations, were used to characterize parameters of the discharge channel and generated strong shock waves. It was shown that the increase in the rate of the energy input into exploding wire allows one to increase wire temperature and amplitude of shock waves. Estimated energy deposition into Cu and Al wire material of up to 200 eV/atom was achieved. The spectroscopic analysis of the emitted radiation has unveiled no evidence for the formation of a shunting plasma channel. Analysis of the generated shock waves shows that ~15% of the deposited energy is transferred into the mechanical energy of the water flow. Also, it was shown that converging shock waves formed by underwater explosion of cylindrical wire arrays can be used to achieve extremely high pressure at the axis of implosion. A pressure up to 0.25 Mbar at 0.1 mm distance from the axis of the implosion at a stored energy of ~4 kj was demonstrated. A model explaining the nature of similarity parameters, which have been phenomenologically introduced in earlier research, was suggested.

Converging strong shock wave, generated by underwater electrical explosion of a spherical wire array, was used to generate plasma inside a copper tube (3 mm outer diameter and 1.4 mm inner diameter) placed at the equatorial plane. The diameter of a spherical wire array consisting of 40 wires each of 100 μm diameter, was 30 mm. The explosion of this array by the current pulse of ∼200 kA in amplitude and rise time of ∼1μs supplied by high-current generator charged up to 27 kV, results in an aperiodic discharge when almost all stored energy was deposited to the exploding wires during ∼0.5 μs. The light emission from the plasma formed inside preliminary evacuated tube was guided by an optical fiber placed inside the tube towards the beam splitter and further to a photomultiplier tube and an imaging spectrometer (2400 grooves/mm) coupled with fast framing 4QuikE camera (the spectral resolution at the CCD of the camera was ∼0.14 A/pixel for λ= 6328 A). The Stark broadening of Cu I spectral lines obtained was used for determination of the plasma electron density and the plasma electron temperature was calculated by the ratio of Cu I spectral lines intensity.

Different methods for measurement of strong underwater shock waves pressure pulses with peak pressures of up to 200 MPa and rise time of tens to hundreds of nanoseconds are described and compared. The experimental techniques include direct methods of pressure measurement using various electromechanical gauges such as quartz, carbon-based, and commercially available PCB gauges, and nondirect methods based on measurement of the velocity of the shock wave such as time-of-flight and fast-streak photography. Advantages and disadvantages of the used gauges and methods are discussed. The shock waves were produced by underwater electrical discharge (discharge current amplitude ≤100 kA, pulse duration ≤5 μs) initiated by an exploding wire. A good correspondence between the pressure amplitudes measured by the various gauges and methods was observed. The obtained dependence of the shock wave pressure on the distance from the discharge channel was found to be best fitted by a r −0.7 law. It is also shown that none of these methods can be used to determine the time evolution of the pressure behind the front of the shock wave.

Investigation of underwater electrical wire explosions occurring in the time scale of few microseconds requires a measurement of pressure waves with nanosecond rise time and microsecond fall time. Various types of pressure gauges are used for this purpose, however, none of them seems to be suitable for the task since the frequency range of the pressure waves lies between 107 and 109 Hz, whereas all types of mechanical gauges have a bandwidth below 107 Hz. Therefore, a mathematical processing of measurements is required for reconstruction of the actual pressure wave forms. In this article, a signal processing algorithm, based on energy conservation requirements and Fourier analysis, for reconstruction of the wave form of the pressure wave generated under water by electrical explosion of wires is proposed. The gauge used in the experiments is a PCB 119A12 type pressure gauge with a bandwidth below 1 MHz produced by Piezo-Electronics, Inc. Pressure waves were produced by underwater electrical explosion of a thin wire made of Cu by a current pulse with an amplitude of 30–60 kA having a rise time of a 3 μs. It is shown that the error of the gauge in the measurement of the peak pressure is more than 100%, which leads to an error in the estimation of the energy of almost 300%.

The results of experiments and one-dimensional (1D) hydrodynamic (HD) simulations of electrical explosions of spherical Cu wire arrays in water and glycerol for various stored energy of the pulse generator and sphere diameters are presented and discussed. It was found that the convergence of the shock wave generated by an exploding spherical wire array in glycerol is significantly faster than in water. The resulting pressure in the vicinity of the implosion center is several times larger in glycerol than in water. Increasing the initially stored energy from 3.6 to 6.1 kJ (for identical array diameters) or decreasing the sphere diameter from 30 to 20 mm (for identical stored energy) leads to an increase in the pressure, temperature, and density in the vicinity of the implosion center. The pressure in a spherical volume of ∼0.2 mm in diameter at the origin of the sphere is estimated by 1D HD simulations to be in excess of 1012 Pa.

The results of experimental studies of a converging shock wave generated by underwater electrical explosion of a spherical wire array are reported. Two high-current generators, sub-microsecond (∼ 350 ns rise time and ∼550 kA current amplitude) and microsecond (∼1.1 µs rise time and ∼300 kA current amplitude) timescale were used for wire array explosion. In the latter case, addition energy was transferred to the water flow by the imploding wire array due to the global pressure of the discharge current. In experiments, power and spectrum of self-light emission from an optical fiber, deformation of a copper tube and the time depended resistance1 of a carbon resistor placed in the equatorial plane of the wire array were measured to estimate the symmetry of the convergence. The results obtained were compared to the results of one dimensional hydrodynamic simulation, coupled with equation of states of water2. The comparison showed that the shock wave keeps its uniformity along the major part of the convergence towards the implosion origin. The latter allows one to consider generation of water in extreme conditions (∼6·1012 Pa, ∼17 eV, ∼8 g/cm3)3 in the vicinity of the implosion origin.

Summary form only given. (Results of generation of converging Strong Shock Waves (SSW) generated by underwater electrical explosion of cylindrical and spherical Cu and Al wire arrays are presented. High-current generators with stored energy of 10 kJ and 5 kJ and output current amplitudes up to 500 kA and 300 kA and rise time of around 350 ns and 1000 ns, respectively, were used to explode arrays with varying lengths, radii and number of wires. It was shown that the implosion of cylindrical and spherical SSW lead to generation of extreme state of water with pressure up to several tens of Mbar, density up to around 8 g/cm3 and temperature up to several tens of eV in the vicinity of the implosion axis or implosion origin. Hydrodynamic numerical simulations coupled with SESAME equation of state for water and the experimental data of the shock wave propagation, energy deposition rate to the array and light emission from the compressed water in the vicinity of the implosion axis were used to obtain the pressure, density and temperature profiles during the implosion.

Summary form only given. The results of experimental and numerical studies of spherical implosion of converging spherical strong shock waves (SSW) generated using underwater electrical explosion of spherical Cu wire arrays are reported. In the experiment, a ~ 4 kJ pulse generator with discharged current amplitude -300 kA, and a rise time of ~ 1 μs was used for wire array explosion. Spherical wire arrays with radii of 10 mm, 12.5 mm, 15 mm and 20 mm were tested. Number of wires was varied in the range 20-40 for different wire diameters in the range 0.1-0.2 mm. A largest shock wave velocity, pressure, water temperature and density in the vicinity of the implosion origin were achieved for the array with radius of 10 mm. The emission from the plasma formed by SSW near the origin of implosion was collected by optical fibers and detected by photomultipliers. The time of the water self-emission appearance together with the data of energy delivered to the wire array were used for determination of the SSW and water parameters in the vicinity of the implosion center using hydrodynamic simulations coupled with SESAME data base for water.

The results of time-resolved spectroscopic measurements of light emission from plasma formed in the vicinity of a converging spherical strong shock wave (SSW) are reported. This approach, together with hydrodynamic (HD) and radiative-transfer simulations, can be used for the characterization of the SSW convergence symmetry and the parameters of water at that location. It was shown that the obtained time-of-flight of the SSW and emission spectra agree well with the results of the simulation, showing that the water density, temperature, and pressure should be larger than ∼3 g/cm−3, ∼1.4 eV, and ∼2 × 1011 Pa, respectively, at radii

Time-resolved parameters of plasma compressed by a shock wave generated by the underwater electrical explosion of a spherical wire array are presented. The plasma was preliminarily formed inside a capillary placed at the equatorial plane along the axis of the array. Temporal evolution analysis of Hα and C II spectral lines showed that the plasma density increases from its initial value of ∼3 × 1017 cm−3 up to ∼5.5 × 1017 cm−3 within 300 ± 25 ns. These results were found to be in agreement with those of the model that considers the adiabatic compression of the plasma by the converging capillary walls caused by interaction with the incident shock wave with a pressure of ∼3 × 109 Pa at a radius of 1.5 mm. The latter results coincide well with those of the 1D hydrodynamic modeling, which assumes uniformity of the converging shock wave.

Convergence of shock waves, generated by underwater electrical explosions of cylindrical wire arrays, between either parabolic or conical bounding walls is investigated. A high-current pulse with a peak of ∼550 kA and rise time of ∼300 ns was applied for the wire array explosion. Strong self-emission from an optical fiber placed at the origin of the implosion was used for estimating the time of flight of the shock wave. 2D hydrodynamic simulations coupled with the equations of state of water and copper showed that the pressure obtained in the vicinity of the implosion is ∼7 times higher in the case of parabolic walls. However, comparison with a spherical wire array explosion showed that the pressure in the implosion vicinity in that case is higher than the pressure in the current experiment with parabolic bounding walls because of strong shock wave reflections from the walls. It is shown that this drawback of the bounding walls can be significantly minimized by optimization of the wire array geometry.

Converging shock waves in liquids can be used efficiently in the research of the extreme state of matter and in various applications. In this paper, the recent results related to the interaction of a shock wave with plasma preliminarily formed in the vicinity of the shock wave convergence are presented. The shock wave is produced by the underwater electrical explosion of a spherical wire array. The plasma is generated prior to the shock wave's arrival by a low-pressure gas discharge inside a quartz capillary placed at the equatorial plane of the array. Analysis of the Stark broadening of Hα and Hβ spectral lines and line-to-continuum ratio, combined with the ratio of the relative intensities of carbon C III/C II and silicon Si III/Si II lines, were used to determine the plasma density and temperature evolution. It was found that during the first ∼200 ns with respect to the beginning of the plasma compression by the shock wave and when the spectral lines are resolved, the plasma density increases from 2 × ...

Summary form only given. Results of generation of extreme state of water in the vicinity of the implosion axis of converging strong cylindrical and spherical shock waves are reported. The shock wave was produced by underwater electrical explosion of cylindrical and spherical either Cu or Al wire arrays. A 10 kJ pulse generator with a current amplitude ≤ 500 kA and rise time of 350 ns was used to explode arrays with varying lengths, radii and number of wires. Hydrodynamic numerical simulations coupled with SESAME equation of state for water and the experimental data of the shock wave propagation, energy deposition rate to the array and light emission from the compressed water in the vicinity of the implosion axis were used to obtain the pressure, density and temperature profiles during the implosion. Dependences of the pressure in the vicinity of the implosion axes on the array radius and deposited linear energy density per unit length were obtained.

Summary form only given. Generation of ultra-high pressure, temperature and density at the axis of converging cylindrical shock wave produced by underwater electrical wire array explosion will be reported. A pulsed sub-microsecond high-current generator with stored energy of ~4.2 kJ and current amplitude of ~340 kA with a rise time of ~lμs was used for underwater explosion of 40 Cu-wire cylindrical array. The velocity of the generated shock wave was obtained by analyzing the sequence of shadow images acquired by a multi frame fast framing camera. The time and space-resolved spectral characteristics of the shock wave self-emission were studied using an imaging spectrometer and photomultiplier tubes. Assuming black body radiation, a temperature up to 5000 K was found at the shock wave front at radius of implosion r≤10 μm. A comparison of the experimental and ID HD simulation results showed that at r≤10 μm. the pressure reaches 100 GPa and density of water of 3.5g/cm3. The duration of this high-density and high-pressure state of water was found to be ~5ns. Results of investigation of water in extreme conditions produced in experiments using a generator with a current amplitude and rise time of ~800 kA and 350 ns, respectively, will be reported as well.

Summary form only given. We report on experimental and computer modeling research of underwater electrical wire explosions (UEWE) which present a promising method tor generation of strong shock waves (SSW) and non-ideal plasma. Micro-and nano-second time scale generators for UEWE of Al, Cu and W wires were employed. A mus (6 kJ stored energy, current of 80 kA, rise time of 2.5 mus) and ns (400J stored energy, current of 100 kA, rise time of 50 ns) generators were used in mus and ns time scale experiments, respectively. Different time-and space-resolved electrical, optical and spectroscopic diagnostics were used to study parameters of expanding discharge channel and generated SSW. Obtained scaling laws for explosion parameters suggest that the increase in the discharge power rate leads to an increase in the generated pressure amplitudes. Furthermore, increasing the power rate allows for an extremely high energy deposition, namely up to 200 eV/atom was registered in ns Cu UEWE. The high value of the energy deposition is due to the absence of shunting plasma shell which presents in vacuum electrical wire explosions. It was shown that up to 15% of the stored energy is converted top the energy of the SSW. In order to amplify the pressures generated by the exploding wires, accumulation effect in imploding cylindrical wire arrays was implied. High pressures of converging SSW up to 0.2 Mbar were registered near the array axis. Results of a simplified model indicate that, using a spherical geometry setup with 7.5 mm external radius of the water layer and ~35 kJ total deposited energy, 1.5-1014 neutron yield during ~1.5 ns time can be achieved. These re suits suggest that ignition of DT target by implosion in water medium can be considered as a promising method for inertial confinement fusion.

The results of visible spectroscopy of the plasma formed inside a copper capillary placed at the equatorial plane of an underwater electrically exploded spherical wire array (30 mm in diameter; 40 wires, each of 100 μm in diameter) are reported. In the experiments, a pulsed power generator with current amplitude of ∼300 kA and rise time of ∼1.1 μs was used to produce wire array explosion accompanied by the formation of a converging strong shock wave. The data obtained support the assumption of uniformity of the shock wave along the main path of its convergence. The spectroscopic measurements show that this rather simple method of formation of a converging strong shock wave can be used successfully for studying the shock wave's interaction with matter and the evaporation processes of atoms from a target.

Summary form only given. Experimental and magneto-hydro-dynamic simulation results of micro- and nanosecond time scale underwater electrical Al, Cu and W wire explosions are presented. A capacitor bank with stored energy up to 6 kJ (discharge current up to 80 kA with 2.5 mus quarter period) was used in microsecond time scale experiments and water forming line generator with current amplitude up to 100 kA and pulse duration of 100 ns were used in nanosecond time scale experiments. Extremely high energy deposition of up to 60 times the atomization enthalpy was registered in nanosecond time scale explosions. A discharge channel evolution and surface temperature were analyzed by streak shadow imaging and using fast photo-diode with a set of interference filters, respectively. Microsecond time scale electrical explosion of cylindrical wire array showed extremely high pressure of converging shock waves at the axis, up to 0.2 Mbar. A 1D and 2D magneto-hydro-dynamic simulation demonstrated good agreement with such experimental parameters as discharge channel current, voltage, radius, and temperature

Summary form only given. A model of shock wave generation in water by underwater electrical discharge initiated by a conducting wire is presented. We compare the model results with the velocities of the shock wave and the exploding wire expansion as monitored by a streak camera. In addition, different methods of shock wave measurements in a zone far from the explosion are described and compared. These methods include direct measurements of shock wave pressure by various types of gauges such as commercial PCB gauges as well as carbon resistor gauges, indirect methods such as the time of flight method, and optical methods including streak and fast framing photography. It is shown that signal processing is necessary for reconstruction of correct pressure waveforms from signals obtained by the PCB gauges. The comparison shows good agreement between the various methods.

The results of experimental studies of the convergence of shock waves (SWs) generated by the underwater electrical explosion of a spherical wire array supplied by a current pulse with an amplitude ∼300 kA and rise time ∼1.1 μs are reported. In the experiments, the power and spectrum of the light emission from an optical fiber, the explosion of a copper tube, and the time-dependent resistance of a resistor placed in the equatorial plane of the spherical wire array were measured. A comparison of the experimental data with the results of numerical simulations of SW convergence shows that the SW keeps its uniformity along the major part of the convergence towards the implosion origin.

A study of generation of converging strong shock wave using microsecond underwater electrical explosion of spherical Cu-wire array is presented. Hydrodynamic simulations coupled with the equation of state for Cu and water, deposited energy, and the magnetic pressure were used to calculate the water parameters in the vicinity of the implosion origin. The results of simulations agree with the shock wave time-of-flight and energy delivered to the water flow and show that in the vicinity (diameter of ∼12 μm) of an implosion one can expect water pressure of ∼6 TPa, temperature of ∼17 eV, and compression of ∼8.

The results of the first experiments on the underwater electrical explosion of a spherical wire array generating a converging strong shock wave are reported. Using a moderate pulse power generator with a stored energy of ≤6 kJ and discharge current of ≤500 kA with a rise-time of ∼300 ns, explosions of Cu and Al wire arrays of different diameters and with a different number and diameter of wires were tested. Electrical, optical, and destruction diagnostics were used to determine the energy deposited into the array, the time-of-flight of the shock wave to the origin of the implosion, and the parameters of water at that location. The experimental and numerical simulation results indicate that the convergence of the shock wave leads to the formation of an extreme state of water in the vicinity of the implosion origin that is characterized by pressure, temperature, and compression factors of (2 ± 0.2) × 1012 Pa, 8 ± 0.5 eV, and 7 ± 0.5, respectively.

Results related to the generation of an extreme state of water with pressure up to (4.3 ± 0.2)·1011 Pa, density up to 4.2 ± 0.1 g/cm3, and temperature up to 2.2 ± 0.1 eV in the vicinity of the implosion axis of a converging strong shock wave are reported. The shock wave was produced by the underwater electrical explosion of a cylindrical Cu wire array. A ∼8 kJ pulse generator with a current amplitude ≤550 kA and rise time of 350 ns was used to explode arrays having varying lengths, radii, and number of wires. Hydrodynamic numerical simulations coupled to the experimental data of the shock wave propagation in water, rate of energy deposition into the array, and light emission from the compressed water in the vicinity of the implosion axis were used to determine the pressure, density, and temperature profiles during the implosion. Results of a comparison between these parameters obtained with the SESAME and quantum molecular dynamics data bases of equation of state for water are reported as well. Also, the ...

A brief review of the results obtained in recent research of underwater electrical wire explosions using microsecond and nanosecond generators is presented. It was shown that the increase in the rate of energy input into the exploding wire allows one to increase the wire temperature and amplitude of shock waves (SWs). Estimated energy deposition into Cu and Al wire material of up to 200 eV/atom was achieved. In microsecond time scale wire explosion, a good agreement was attained between the wire resistance calculated using the equation of state (EOS) and that obtained experimentally. Conversely, in nanosecond time scale wire explosion, the wire resistance of EOS was modified in order to fit experimental data. Analysis of the emitted radiation showed that black body approximation cannot be used to characterize exploding wire radiation. It was found that ≤24% of the deposited energy is transferred into the water flow's mechanical energy. Also, it was shown that converging SWs formed by the explosion of cylindrical wire arrays can be used to achieve a pressure up to 250 kbar at the axis of implosion. Hydrodynamic simulations showed that with the use of relatively moderate pulsed power generators with stored energy of several hundred kilojoules, a pressure of several megabar can be achieved at the axis of implosion.

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.

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 fo...

It is shown that the originally corrugated shock wave generated in the process of an underwater electrical explosion of a cylindrical wire array is self-aligned into a cylindrically symmetric converging front. It was found that by increasing the number of the wires in the array this self-alignment process occurs faster. It is also demonstrated that in the case of a large wire number (>20), one-dimensional calculations can be successfully employed for theoretical analysis.

Results and analysis of a microsecond time scale underwater electrical wire explosion are presented. Experiments were carried out with a Cu wire exploded by a current pulse ⩽100kA with microsecond time duration. The analysis is based on shadow and spectrally resolved streak photography which were used to monitor the evolution of the discharge channel and the shock wave. The obtained data were used for hydrodynamic calculation of the generated water flow parameters, such as pressure and flow velocity distribution between the discharge channel and the shock wave. In particular, the pressure at the discharge channel boundary and the energy transferred to the water were estimated. The results of the calculation have been verified by comparing the measured and calculated trajectories of the shock wave. Based on the results of the calculation the energy transferred to the water was estimated. In addition, the analysis shows that the energy initially deposited in the discharge channel continues to produce mechan...