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We report the results of experiments investigating the implosion of a shock generated by the electrical explosion of a cylindrical aluminum wire array immersed in a >80% hydrogen peroxide/water solution. This solution was chosen as an additional energy source to the supplied electrical energy to generate the imploding flow with higher velocity. The experiments were conducted using a generator with the stored energy of ∼4.8 kJ, delivering to the array a ≤280 kA current rising during ∼1 μs. The backlighted images of the imploding shocks were recorded using a streak camera. Using different diameter wires, the explosion of arrays, characterized by critically damped and under-damped discharges, was studied. The experiments revealed that an array explosion in a 92% H2O2/H2O solution results in the second strong shock generated after the peak of the deposited electrical power, a solid indication of H2O2 detonation. This second shock converges ∼40% faster than the first strong shock generated by the wire explosion. One-dimensional hydrodynamic simulations of the shock convergence in H2O2/H2O solutions support this proposition.

Spectroscopic studies of plasma formed inside a capillary and compressed by a shockwave (SW) generated by the underwater electrical explosion of a spherical wire array (SWA) showed density evolution to be in agreement with those of the model considering the adiabatic compression caused by the SW with a pressure predicted by HD modeling assuming uniformity of the converging SW.1 Studies of converging SW generated by underwater cylindrical wire arrays exploded on ns- and μs timescales, showed that that even in the case of initial azimuthal non-symmetry, the SW self-repairs in the final stages of its motion, leading to a uniform implosion down to the r=30μm.2 To increase liquid compression, the experiments and 1D HD simulations of electrical explosions of SWA arrays in water and glycerol for various stored energy of the pulse generator and sphere diameters were carried out. It was found that the convergence of the SW generated by an exploding array in glycerol is significantly faster than in water. Increasing the initially stored energy (for identical array diameters) or decreasing the sphere diameter (for identical stored energy) leads to an increase in parameters of compressed liquid in the vicinity of the implosion.3 These results are compared with the underwater electrical explosions of SWA on the sub-us-timescale. The time-of-flight of the SW convergence was found to be the same, despite the almost 4 times faster energy density deposition for the shorter timescale. This phenomenon is reproduced by HD modeling showing that the exploding wires' expansion on both timescales results in identical radii when the convergence of the SW becomes self-similar. Thus, to increase the parameters of the compressed water, instead of increasing the energy deposition rate, one must increase the stored energy.

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.

The results of experiments involving underwater electrical explosion of different wire arrays using an outer metallic cylinder as a shock reflector are presented. A pulse generator with a stored energy of about 6 kJ, current amplitude ≤ 500 kA, and rise time of 350 ns was used for the wire array explosion. The results of the experiments and of hydrodynamic simulations showed that in the case of a Cu wire array explosion, the addition of the reflector increases the pressure and temperature of the water in the vicinity of the implosion axis about 1.38 and about 1.33 times, respectively. Also, it was shown that in the case of an Al wire array explosion with stainless steel reflector, Al combustion results, and, accordingly, additional energy is delivered to the converging water flow generating about 540 GPa pressure in the vicinity of the explosion axis. Finally, it was found that microsecond time scale light emission that appears with microsecond time scale delay with respect to the nanosecond time scale self-light emission of the compressed water in the vicinity of the implosion axis is related to water bubbles formation which scattered light of exploded wires.

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.

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.

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.

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

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.

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.

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.

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...