Nanosecond Electrical Explosion Research Articles

Instability growth mitigation study of a dielectric coated metallic wire in a low current Z-pinch configuration

An experimental and numerical study of the nanosecond electrical explosion dynamics of bare and dielectric coated metallic wires in vacuum is reported. A table top Z-pinch generator down-tuned to generate a peak current of 40 kA with a rise time of 60 ns is implemented for the experiments in the skin effect mode. Optical probing diagnostics as well as multiphysics–multiphase simulations are used to study the spatiotemporal dynamics of the exploded wire from the solid to the plasma phase. The results show that the inclusion of the dielectric coating mitigates the electro–thermo–mechanical instability growth developed prior to plasma formation, which results in a subsequent reduced magnetohydrodynamic instability growth in the plasma phase. The study offers valuable insights into the understanding of the seeding mechanisms for the generation of plasma instabilities and the efforts for their growth rate suppression.

Stratification and filamentation instabilities in the dense core of exploding wires

We report experiments characterizing the stratified and filamentary structures formed in the dense core of nanosecond electrical explosion of aluminum wires to understand the physical scenario of electrothermal instability. Direct experimental observations for stratification and filamentation instabilities, as well as the coexistence state of azimuthal strata and vertical filament in the dense plasma column, are presented. The wire core exhibits remarkable different patterns of instability with the decreasing wire length. The shadowgram of shorter wires demonstrates that the instability is transformed from stratified structures to filamentary structures. According to a radial magnetohydrodynamic computation, the wire enters a phase state of negative temperature dependence of resistivity before voltage breakdown. However, filamentary structures are only observed in exploding wires of 1 cm and 0.5 cm in length. The analyses based on experimental and computational results indicate that the increase in internal energy determines the manifestation of instability in the dense core. Filamentation instability occurs when the total energy input is no less than 1.5 times the vaporization energy at the moment of voltage breakdown. The lower limit of energy deposition ensures that the increase in internal energy covers vaporization energy.

On the phase state of thin silver wire cores during a fast electric explosion

The results of laser (shadow and interferometric) studies of thin silver wire cores during a nanosecond electric explosion in vacuum are presented. Experiments were performed with a small Micro-4 generator (the charge voltage is 20 kV, and the current rise rate is 100 A/ns). The analysis of the data obtained showed that, despite a considerable energy deposition (a few atomization energies) into matter at the resistive stage of the discharge, a conductor is not completely evaporated. This is related to the features of the metal–dielectric transition which occurs nonuniformly in different load regions. Processes proceeding in the case of a rapid energy deposition to a conductor are qualitatively interpreted. It was shown that in this case the bond energy as the unit of measurement of the deposited energy is more appropriate than the energy of atomisation.

Nanosecond electrical explosion of bare and dielectric coated tungsten wire in vacuum

Experiments of the electrical explosion of tungsten wire with and without insulating coatings demonstrate that the insulating coatings exert a significant influence on the exploding characteristics. The shadowgraphy and interferometry diagnostics are applied to present the morphology of the exploding products. In the experiments, energy of ∼3.2 eV/atom is deposited into the bare tungsten wire at the instant of voltage breakdown, giving a velocity of 0.38 km/s for the high density core. The value and structure of the energy deposition for the tungsten wire explosions are substantially improved by employing the thin dielectric coatings. Energy of ∼15.2 eV/atom is deposited into the coated tungsten wire transforming the wire into gaseous state and the expanding velocity of the high density core is 5.64 km/s. The interference phase shift and atomic density are reconstructed from the interferogram for the exploding coated tungsten wire.

Dynamic polarizability of tungsten atoms reconstructed from fast electrical explosion of fine wires in vacuum

For nanosecond electrical explosion of fine metal wires in vacuum generates calibrated, radially expanded gas cylinders of metal atoms are surrounded by low-density fast expanding plasma corona. Here, a novel integrated-phase technique, based on laser interferometry, provides the dynamic dipole polarizability of metal atoms. This data was previously unavailable for tungsten atoms. Furthermore, an extremely high melting temperature and significant pre-melt electronic emission make these measurements particularly complicated for this refractory metal.

Nanosecond electrical explosion of twisted aluminum wires

The experiments on nanosecond electrical explosion of twisted aluminum wires with different wavelengths (λt=0.37, 0.5, 0.75, 1.0 mm) are carried out. The experimental results indicate that a specific wavelength can strongly affect the energy deposition, expansion velocity, and radiation intensity. The energy deposition is about 3.3 times the atomic enthalpy of aluminum when the twisted wavelength is 0.5 mm. While for the other three twisted wavelengths, the energy depositions are all about 1.8 times the atomic enthalpy. The expansion velocity is about 3.8×103 m·s-1 for the wavelength 0.5 mm, and the optical radiation intensity is also strongest for this wavelength. The initial twisted structure is strongly imprinted in the freely expanding aluminum column after the electrical explosion. In the experiments for the wavelength 0.5 mm, a neural particle column with a diameter of 1.6 mm is formed and its density is about 1019 cm-3 at t=246 ns. A periodic structure with the wavelength 0.5 mm and the amplitude 0.3 mm is observed on the surface of this column.

Study on Characteristics of Nanopowders Synthesized by Nanosecond Electrical Explosion of Thin Aluminum Wire in the Argon Gas

As a new gas-phase synthesis method for the production of nanosize powders, the wire electrical explosion method has the advantages of high energy efficiency and high product purity through production under pure inert gas conditions and has been applied to the continuous industrial production of nanopowders. In this paper, an experimental device based on the electrical explosion of metallic wires for nanopowder production and collection is designed and built. Also, aluminum nanopowders were produced by electrically exploding an aluminum wire and collected by the microporous membrane filter successfully under different pressures of argon gas. Moreover, the influence of the argon gas pressure on the characteristics of the aluminum nanopowders was analyzed by a transmission electron microscope. The results showed that the particle shape, size, and distribution of the aluminum nanopowders could be controlled by the pressure of argon gas. The aluminum nanoparticles produced in the high-pressure argon gas had better spherical particle shape; meanwhile, the count mean diameter of the aluminum nanopowders increased obviously with the rise of the argon gas pressure. A higher pressure of argon gas could broaden the range of the aluminum nanoparticle size distribution evidently.

10.1007/s11455-008-2013-7

We have studied pressure waves generated during a nanosecond electric explosion of 70-μm-thick tungsten wires in water. The measurements were performed at a distance of 3–8 mm from the exploding conductor. In order to reduce the error caused by two-dimensional effects, we used pressure sensors with dimensions not exceeding 3 mm. The results of measurements revealed a two-component structure of the electric-explosion-induced shock wave.

Nanosecond electric explosion of thin aluminum films

Pulsed electrodynamic breakage of thin (∼20-nm-thick) aluminum films deposited onto polymer substrates have been experimentally studied. The character of film fracture depends on the level of supplied electric energy W. For 3.5 kJ/g < W < 4.3 kJ/g, discontinuities (striations) are formed in the transverse direction relative to the applied electric field. At high current densities on a level of ∼(1–3) × 1012 A/m2 and explosion times within 50–300 ns, the integral of action to explosion varies within (0.79–1.08) × 1017 A s/m2 depending on the rate of energy supply and differs from published data for relatively massive conductors.

Distribution of matter in the current-carrying plasma and dense core of the discharge channel formed upon electrical wire explosion

Distribution of matter in the discharge channel formed upon a nanosecond electrical explosion of a single wire in air and vacuum was studied experimentally. Simultaneous use of optical, UV, and X-ray diagnostics made it possible to distinguish qualitatively different regions of the discharge channel, such as the current-carrying layers and the region occupied by a weakly conducting cold plasma. Several series of experiments with 25-µm-diameter 12-mm-long wires made of different materials were performed. The charging voltage and the current amplitude were varied in the ranges of U 0 = 10–20 kV and I max ∼ 5–10 kA, respectively. Explosion regimes with a current pause and with and without current interruption, as well as with wire preheating in air and vacuum, were studied. Shadow and schlieren images of the discharge channel were obtained using optical probing at the second harmonic of a YAG: Nd+3 laser (λ = 0.532 µm, τ ∼ 10 ns). In the experiments carried out in vacuum, X-ray images of the discharge channel were also obtained using an X-pinch as a point source of probing radiation and UV images were recorded using a four-frame MCP camera.

Laser Imaging of Secondary Breakdown Upon Nanosecond Electrical Explosion of Wire

Copper wires of diameter d = 25 mum were exploded in air by a current pulse with a rise rate of ~25 A/ns. Laser probing measurements were performed with the second harmonic of a YAG:Nd3+ laser (lambda = 0.53 mum and Deltat = 10 ns). For the first time, laser images of the current channels were obtained upon electrical explosion of copper wires in air.

Publisher's Note: Transformation of a tungsten wire to the plasma state by nanosecond electrical explosion in vacuum [Phys. Rev. E77, 056406 (2008)

Publisher's Note: Transformation of a tungsten wire to the plasma state by nanosecond electrical explosion in vacuum [Phys. Rev. E<b>77</b>, 056406 (2008)

Transformation of a tungsten wire to the plasma state by nanosecond electrical explosion in vacuum

Experiment demonstrates the first direct transformation of a tungsten wire core to the plasma state by Joule heating during nanosecond electrical explosion in vacuum. Energy of approximately 130 eV/atom was deposited into the 12 microm W wire coated by 2 microm polyimide during the first approximately 10 ns. All the metal rapidly transformed to highly ionized plasma, while the surrounding polyimide coating remained primarily in a gaseous state. This coating totally suppressed corona formation. The expansion velocity of the wire was approximately 12-18 km/s, the average wire ionization at 50 ns reached approximately 67% with corresponding LTE temperature of approximately 1.2 eV . Explosion of bare W wire demonstrated earlier termination of the wire core heating due to shunting corona generation. Magnetohydrodynamic (MHD) simulation reproduces the main features of coated and uncoated W wire explosion.

Pressure waves generated by a nanosecond electric explosion of a tungsten wire in water

We have studied pressure waves generated during a nanosecond electric explosion of 70-μm-thick tungsten wires in water. The measurements were performed at a distance of 3–8 mm from the exploding conductor. In order to reduce the error caused by two-dimensional effects, we used pressure sensors with dimensions not exceeding 3 mm. The results of measurements revealed a two-component structure of the electric-explosion-induced shock wave.

Analysis of the discharge channel structure upon nanosecond electrical explosion of wires

The structure of the discharge channel during nanosecond wire explosions has been studied using laser probing. Wires of 25μm diameter and 12mm length were exploded in air and vacuum by 10kA current pulse having a 50A∕ns rate of rise. Upon electrical explosion of thin wires in the air, the development of shock waves was observed. The propagation of shock waves was analyzed, and it was possible to draw conclusions on the location of the flow of most of the current in the volume of the discharge channel. This permitted distinguishing between two scenarios (shunting and internal) of the interelectrode gap breakdown development. The scenario depends to a large extent on the properties of the exploding wire material. The same two scenarios are valid upon electrical explosion of wire in vacuum. Moreover, if secondary breakdown develops in the internal scenario, the value of the energy deposition in the wire material during explosion in vacuum may be comparable with that found during explosion in air.

Nanosecond electric explosion of a tungsten wire in different media

The effect of surrounding media of different densities and electric strengths on the heating dynamics of a micron wire during its nanosecond electric explosion is investigated. Tungsten wires with diameters of d = 25–50 μm were exploded in air and water at a current rise time of (dI/dt) ∼ 1010 A/s. The diagnostic complex is described.

Nanosecond electrical explosion of thin aluminum wires in a vacuum: Experimental and computational investigations

Experimental and computational investigations of nanosecond electrical explosion of a thin Al wire in vacuum are presented. We have demonstrated that increasing the current rate leads to increased energy deposited before voltage collapse. The experimental evidence for synchronization of the wire expansion and light emission with voltage collapse is presented. Hydrocarbons are indicated in optical spectra and their influence on breakdown physics is discussed. The radial velocity of low-density plasma reaches a value of approximately 100 km/s. The possibility of an over-critical phase transition due to high pressure is discussed. A one-dimensional magnetohydrodynamic (MHD) simulation shows good agreement with experimental data. The MHD simulation demonstrates separation of the exploding wire into a high-density cold core and a low-density hot corona as well as fast rejection of the current from the wire core to the corona during voltage collapse. Important features of the dynamics for the wire core and corona follow from the MHD simulation and are discussed.

State of the metal core in nanosecond exploding wires and related phenomena

Experiments show that an expanding metal wire core that results from a nanosecond electrical explosion in vacuum consists primarily of three different states: solid, microdrop, and gas-plasma. The state of the wire core depends both on the amount of energy deposited before the voltage breakdown and on the heating conditions. For small amounts of deposited energy (on the order of solid-stage enthalpy), the wire core remains in a solid state or is partially disintegrated. For a high level of deposited energy (more than vaporization energy) the wire core is in a gas-plasma state. For an intermediate level of deposited energy (more than melting but less than vaporization), the wire disintegrates into hot liquid microdrops or clusters of submicron size. For a wire core in the cluster state, interferometry demonstrates weak (or even absent) phaseshift. Light emission shows a "firework effect"—the long late-time radiation related to the emission by the expanding cylinder of hot microparticles. For the wire core in a gas-plasma state, interferometry demonstrates a large phaseshift and a fast reduction in light emission due to adiabatic cooling of the expanding wire core. The simulation of this firework effect agrees well with experimental data, assuming submicron size and a temperature approaching boiling for the expanded microparticles cylinder.

Nanosecond electric explosion of wires: from solid superheating to nonideal plasma formation

AbstractThe conception is developed which distinguishes initial stages of the fast (nanosecond) electric explosion of wires: the superheating of the solid conductor, its spontaneous (spinodal) decay and the successive formation of the nonideal plasma column. The molecular dynamics simulation approach is used to simulate homogeneous nucleation at a constant heating rate. The subsequent evolution of the fluid column and the axial plasma uniformity are considered. The results are compared with the experimental data on nanosecond wire explosions. (© 2003 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Superheating of solid metal prior to electric explosion of wires at fast energy deposition

We develop the concept which distinguishes the initial stages of the fast (nanosecond) electric explosion of wires: the superheating of the solid conductor, its spontaneous (spinodal) decay and the successive formation of the non-ideal plasma column. We use the molecular dynamics simulation approach to simulate homogeneous nucleation from a stationary state and at a constant heating rate. We study the parameters of the spinodal, the dependence of the melting temperature on the heating rate and the character of the decay. We consider the subsequent evolution of the fluid column and the axial plasma uniformity. We compare the results with the experimental data on nanosecond wire explosions.