Explosion Of Wire Array Research Articles

Comparison of electrical wire explosion characteristics of single wire and wire array in air

In this paper, discharge characteristics of a planar copper wire array explosion driven by a microsecond pulsed current source (500 J stored energy) in atmospheric air medium were studied. Meanwhile, controlled experiments were performed with single wire cases. With a 2 cm distance between electrodes, 2-16 copper wires with a diameter of 100 μm were selected to form planar copper wire arrays, and single copper wires with diameter of 50-400 μm were selected for comparisons. Load voltage, circuit current and light radiation intensity were measured. Electric power and deposited energy were calculated. The experimental results show that for the single wire case, with the increase of mass (diameter), the process of vaporization and ionization become slower, manifested as a delay of the voltage peak and an increase of the full width half maximum (FWHM) of the voltage pulse from 0.07 μs to 0.64 μs. In contrast, although the explosion time of wire array load was delayed with the increase of mass, the duration of vaporization and ionization did not change significantly with a FWHM of 0.11 ± 0.01 μs. In addition, the deposited energy of wire array load before breakdown was lower than that of single wire load with the same mass. As for the optical radiation intensity, under three cases with the same mass, the peak intensity of wire array explosion is about 28%, 49% and 52% higher than that of single wire explosion. There may be two reasons which cause the difference between the single wire load and wire array load. First, the larger specific surface area of the wire array load makes faster phase transitions. Second, the development of thermal or magnetohydrodynamics for the two kinds of loads was different, which should be responsible for the differences in energy deposition and optical emission.

Comparison of electrical explosions of spherical wire arrays in water and glycerol on different timescales

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.

Quasi-isentropic compression using compressed water flow generated by underwater electrical explosion of a wire array

A major experimental research area in material equation-of-state today involves the use of off-Hugoniot measurements rather than shock experiments that give only Hugoniot data. There is a wide range of applications using quasi-isentropic compression of matter including the direct measurement of the complete isentrope of materials in a single experiment and minimizing the heating of flyer plates for high-velocity shock measurements. We propose a novel approach to generating quasi-isentropic compression of matter. Using analytical modeling and hydrodynamic simulations, we show that a working fluid composed of compressed water, generated by an underwater electrical explosion of a planar wire array, might be used to efficiently drive the quasi-isentropic compression of a copper target to pressures ∼2 × 1011 Pa without any complex target designs.

An experimental platform for pulsed-power driven magnetic reconnection

We describe a versatile pulsed-power driven platform for magnetic reconnection experiments, based on the exploding wire arrays driven in parallel [Suttle et al., Phys. Rev. Lett. 116, 225001 (2016)]. This platform produces inherently magnetised plasma flows for the duration of the generator current pulse (250 ns), resulting in a long-lasting reconnection layer. The layer exists for long enough to allow the evolution of complex processes such as plasmoid formation and movement to be diagnosed by a suite of high spatial and temporal resolution laser-based diagnostics. We can access a wide range of magnetic reconnection regimes by changing the wire material or moving the electrodes inside the wire arrays. We present results with aluminium and carbon wires, in which the parameters of the inflows and the layer that forms are significantly different. By moving the electrodes inside the wire arrays, we change how strongly the inflows are driven. This enables us to study both symmetric reconnection in a range of different regimes and asymmetric reconnection.

Spherical wire arrays electrical explosion in water and glycerol

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 structure of bow shocks formed by the interaction of pulsed-power driven magnetised plasma flows with conducting obstacles

We present an experimental study of the development and structure of bow shocks produced by the interaction of a magnetised, collisional, super-Alfvénic plasma flow with conducting cylindrical obstacles. The plasma flow with an embedded, frozen-in magnetic field (ReM ∼ 20) is produced by the current-driven ablation of fine aluminium wires in an inverse, exploding wire array z-pinch. We show that the orientation of the embedded field with respect to the obstacles has a dramatic effect on the bow shock structure. When the field is aligned with the obstacle, a sharp bow shock is formed with a global structure that is determined simply by the fast magneto-sonic Mach number. When the field is orthogonal to the obstacle, magnetic draping occurs. This leads to the growth of a magnetic precursor and the subsequent development of a magnetised bow shock that is mediated by two-fluid effects, with an opening angle and a stand-off distance, that are both many times larger than in the parallel geometry. By changing the field orientation, we change the fluid regime and physical mechanisms that are responsible for the development of the bow shocks. MHD simulations show good agreement with the structure of well-developed bow shocks. However, collisionless, two-fluid effects will need to be included within models to accurately reproduce the development of the shock with an orthogonal B-field.

Convergence of shock waves between conical and parabolic boundaries

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.

Underwater Electrical Explosion of Wires and Wire Arrays and Generation of Converging Shock Waves

A brief review of the results obtained in recent research of underwater electrical explosions of wires and wire arrays using microsecond-, submicrosecond-, and nanosecond-timescale high-current generators is presented. In a microsecond-timescale wire explosion, good agreement was attained between the results of experiments and the results of magnetohydrodynamic calculations coupled with equations of state (EOS) and modern conductivity models. Conversely, in a nanosecond-timescale wire explosion, the wire resistance and the EOS were modified in order to fit experimental data. In experiments with cylindrical and spherical wire arrays, generation of a converging shock wave (SW) was demonstrated allowing formation of an extreme state of water in the vicinity of either the axis or the origin of the SW’s implosion. In addition, it is shown that SW convergence in superspherical geometry allows one to achieve larger values of pressure, density, and temperature of water in the vicinity of the axis of convergence than in the case of a spherical implosion. The results of experiments and numerical analysis showed that a cylindrical SW keeps its symmetry along the main path of its convergence. In addition, it is shown that underwater electrical explosion of an X-pinch wire configuration and a cone wire array allows one to generate fast jets of metal and water, respectively, without using chemical explosions.

Generation of ultra-fast cumulative water jets by sub-microsecond underwater electrical explosion of conical wire arrays

The results of experiments with underwater electrical explosion of modified conical arrays of copper and aluminum wires are presented. A pulsed generator producing a 550 kA-amplitude current with a 400 ns rise time was used in the explosion of the arrays. The array explosion generates water flows converging at the axis of the cone. This flow generates a fast-moving water jet with a velocity exceeding 1.8 × 105 cm/s, which was observed being ejected from the surface of the water covering the array. The positions of the water jet were measured by multiple-exposure fast framing imaging. In experiments, the apex angle of the array, the thickness of the water layer above the arrays, or the material of the wires was altered, which changed the resulting velocities and shapes of the emitted jets. A model that considers the converging stationary flow of a slightly compressible fluid is suggested. The velocities and shapes of the jets obtained by this model agree well with the experimentally measured jet velocities.

Convergence of shock waves generated by underwater electrical explosion of cylindrical wire arrays between different boundary geometries

The results of experiments and numerical simulations of a shock wave propagating between either conical or parabolic bounding walls are presented. The shock wave was generated by a microsecond timescale underwater electrical explosion of a cylindrical wire array supplied by a current pulse having an amplitude of ∼230 kA and a rise time of ∼1 μs. It is shown that with the same energy density deposition into the exploding wire array, the shock wave converges faster between parabolic walls, and as a result, the pressure in the vicinity of convergence is ∼2.3 times higher than in the case of conical walls. The results obtained are compared to those of earlier experiments [Antonov et al., Appl. Phys. Lett. 102, 124104 (2013)] with explosions of spherical wire arrays. It is shown that at a distance of ∼400 μm from the implosion origin the pressure obtained in the current experiments is higher than for the case of spherical wire arrays.

Spectroscopy of a plasma formed in the vicinity of implosion of the shock wave generated by underwater electrical explosion of spherical wire array

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.

Shock wave convergence in water with parabolic wall boundaries

The convergence of shock waves in water, where the cross section of the boundaries between which the shock wave propagates is either straight or parabolic, was studied. The shock wave was generated by underwater electrical explosions of planar Cu wire arrays using a high-current generator with a peak output current of ∼45 kA and rise time of ∼80 ns. The boundaries of the walls between which the shock wave propagates were symmetric along the z axis, which is defined by the direction of the exploding wires. It was shown that with walls having a parabolic cross section, the shock waves converge faster and the pressure in the vicinity of the line of convergence, calculated by two-dimensional hydrodynamic simulations coupled with the equations of state of water and copper, is also larger.

Generation of fast cumulative water jets by underwater electrical explosion of conical wire arrays

The results of experiments with underwater electrical explosion of conical arrays of copper wires are presented. A pulsed generator producing a 300 kA-amplitude current with a 1.2 μs rise time was used in the explosion of the arrays. As a result of the explosion, fast-moving water jets, with velocities of up to 1200 m/s, were observed being ejected from the surface of the water covering the wire array. The position of the water jets was measured by multiple-exposure fast framing imaging. The apex angle of the array or the thickness of the water layer above the arrays was altered from shot to shot, which changed the resulting velocities and shapes of the emitted jets. A numerical model, based on the models of cumulation and penetration of a jet through material of similar density, is suggested. The velocities of jets obtained by this model agree well with the experimentally observed jet velocities.

Transportable High-Energy High-Current Inductive Storage GW Generator

A number of high-power applications require a transportable high-energy, high-current GW generator to drive a pulsed power system at the output. A first prototype, based on exploding wire technology and using an H-bridge circuit configuration, was developed at Loughborough University a few years ago and has been previously reported. The present stage of the work has necessitated the development of a more powerful and energetic source, and this is now based on inductive storage technology. A 400 kJ capacitor bank is connected by a high-Coulomb explosively driven closing switch with an air-cored 0.6 MV transformer, an exploding wire array, and a high-power diode based on a polarity-dependent spark-gap completing the arrangement. The GW generator, including the command and control module, is accommodated in two ISO containers. The various components of the generator are described in this paper, together with results obtained from full-scale tests.

Diagnostics of a converging strong shock wave generated by underwater explosion of spherical wire array

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.

Stability of imploding shocks generated by underwater electrical explosion of cylindrical wire array

The results of two-dimensional hydrodynamic simulations of the dynamics and stability of azimuthal non-uniformities in converging shock waves generated by an underwater explosion of a cylindrical wire array and their effect on the cumulation of energy in the vicinity of the converging axis are presented. It has been shown that in spite of the fact that such non-uniformities are always weakly unstable, for a broad range of experimentally relevant regimes these non-uniformities remain small and do not significantly affect the cumulation of energy. Only the non-uniformities with wavelengths comparable to the distance from the axis of convergence exhibit substantial growth that considerably attenuates the energy cumulation.

Generation of converging strong shock wave formed by microsecond timescale underwater electrical explosion of spherical wire array

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.

Generation of extreme state of water by spherical wire array underwater electrical explosion

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.

Modified wire array underwater electrical explosion

AbstractThe 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.

Simulation of converging cylindrical GPa-range shock waves generated by wire array underwater electrical explosions

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.