Exploding Wire Discharge Research Articles

An Exploding Wire-Compression Method for Evaluating the Electrical Conductivity of Diamond-Like Carbon in a Warm Dense State

We have employed an exploding-wire compression method to measure the electrical conductivity of diamond-like carbon (DLC) in a warm dense matter (WDM) state. We generated a DLC in the WDM state using shock compression driven by an exploding-wire discharge within a rigid capillary. To elucidate the generation of DLC in WDM, we performed a 1-D magnetohydrodynamic simulation. Using the numerical results, we estimated the electrical conductivity of the DLC plasma. By comparing the time-evolutions of the voltage and current for gold and gold + DLC samples, we demonstrated that the voltage–current evolution is different in the two cases. From the absorption spectroscopy, we estimated the DLC temperature to be 8000–9000 K. By comparing the results of the experiment with those of the numerical simulation, we determined the electrical conductivity of the DLC plasma to be 106 S/m. This is relatively high compared with the electrical conductivity of the conventional carbon plasma, but the experimental results are similar to the theoretical values for diamond at solid density.

Study on Exploding Wire Compression for Evaluating Electrical Conductivity in Warm-Dense Diamond-Like-Carbon

To improve a coupling efficiency for the fast ignition scheme of the inertial confinement fusion, fast electron behaviors as a function of an electrical conductivity are required. To evaluate the electrical conductivity for low-Z materials as a diamond-like-carbon (DLC), we have proposed a concept to investigate the properties of warm dense matter (WDM) by using pulsed-power discharges. The concept of the evaluation of DLC for WDM is a shock compression driven by an exploding wire discharge with confined by a rigid capillary. The qualitatively evaluation of the electrical conductivity for the WDM DLC requires a small electrical conductivity of the exploding wire. To analyze the electrical conductivity of exploding wire, we have demonstrated an exploding wire discharge in water for gold. The results indicated that the electrical conductivity of WDM gold for 5000 K of temperature has an insulator regime. It means that the shock compression driven by the exploding wire discharge with confined by the rigid capillary is applied for the evaluation of electrical conductivity for WDM DLC.

A Semiempirical Evaluation of the Thermal Conductivity in Ablated Dense Tungsten Plasma

For understanding the properties of ablated dense tungsten, we have proposed a semiempirical evaluation of thermal conductivity based on the Wiedemann-Franz law. The electrical conductivity of ablated dense tungsten has been evaluated by the exploding-wire discharges in water and the isochoric heating of wire in a vacuum. The results indicate that the thermal conductivity derived from the electrical conductivity ranges from 0.1 to 100 W·K-1m-1 depending on the density at a temperature of 5000 K.

Wire Explosion by Electromagnetic Induction

A conductive plasma channel in the shape of a 360^ helical arc has been realized via the mechanisms of electromagnetic induction and exploding wire (EW). This paper is focused on documenting the restrike (RS) mechanism for a wire exploded via electromagnetic induction. The apparatus is a pair of mutually coupled helical coils, which are arranged on cylindrical polyvinylchloride formers, with a capacitor bank as the energy source. Voltage and current waveforms are presented. The wire explosion by induction exhibits key features that exist in conventional wire explosion by conduction, namely, wire fragmentation, a dwell period, and RS phenomena. Exponential damping envelopes were graphically applied to distinguish between RS and non-RS outcomes of the wire explosions. Photography, visual observation, and copper oxide residue patterns also helped to determine whether an RS took place. Lichtenburg figures in the form of dust trees were found to have formed at some time during the induced EW discharge.

Evaluation of Electrical Conductivity in Warm Dense State using Pulsed-power Discharges

With the aim of producing a well-defined warm dense state, we have demonstrated exploding wire discharge in water. The electrical conductivity of copper was measured directly and found to be lower than conductivities predicted by conventional theoretical models. To describe the experimental results, we proposed an empirical power law for the electrical conductivity at a fixed temperature. The experimental results indicate that the effective relaxation time for copper can be approximated by a power of −1.45 for the density for densities below log10 (ρ/ρs) ∼ −1.5.

Electrical conductivities of aluminum, copper, and tungsten observed by an underwater explosion

Conductivities of dense aluminum, copper, and tungsten are evaluated using exploding wire discharges in water. Evolutions of the radius and the electrical resistance of exploding wire are measured together with direct pyrometric estimation of the temperature. The conductivities are evaluated based on the measurements and their density dependence is compared with theoretical predictions at a fixed temperature. The results indicate that regardless of materials, the conductivity has a minimum around 3% of solid density at temperature of 5000 K.

A comparative study of equation of state and conductivity for warm dense matter using pulsed-power wire discharges in water

A method of measuring equation of state and electrical conductivity is proposed relevant to conditions in warm dense matter (WDM). The WDM was produced by exploding wire discharges in water. The wire/plasma parameters were measured spectroscopically and also by a shadow graph method. The density and the temperature were estimated to be typically ∼ 0.01 ρsolid and ∼ 15 kK, respectively, at 2 μsec from beginning of the discharges. We have compared the behaviors of the plasma boundary and an accompanied shock wave in water to a numerical estimation based on a model of equation of state (EOS). We indicate that the comparative study of the experimental and the numerical results, is a possible approach for a ‘semi-empirical’ scaling of EOS.

Electrical Conductivities of Nonideal Iron and Nickel Plasmas

AbstractElectrical conductivities of iron and nickel plasmas are calculated using a nonideal plasma ionization balance model that takes into account the excess free energy due to strong Coulomb couplings between charged particles in the pressure‐ionization regime. The electrical conductivities calculated for partially ionized plasmas are in fair agreement with data measured in exploding wire discharge experiments and effectively demonstrate the insulator‐metal transition near solid densities. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Warm-dense-matter studies using pulse-power discharges in water

Warm dense matters are produced using exploding wire discharges in water. The density and the temperature are estimated to be typically 0.01 ρ solid and a few eV, respectively, at 2 μ s from beginning of the discharges. We have compared the behaviors of the expanding shock wave in water and the plasma boundary with a numerical estimation based on a model of equation of state (EOS). A dark layer is observed in the streak image between the shock surface and the plasma boundary, which is correlated by numerical calculation to be moderate density gradient behind the shock. Based on the experimental and numerical results, we show a possible approach for a ‘semi-empirical’ scaling of EOS.

Pulse-Power Device as a Tool for High-Energy-Density Plasma Physics and its Applications

High energy density plasmas driven by pulse power devices are of interest from the point view of their application to formations of extreme conditions. Dense plasmas are produced using pulse-power driven exploding wire discharges in water. Experimental results show that the plasma is tamped and stabilized by the surrounding water and it cylindrically evolves through a strongly coupled state. A shock-heated, high temperature plasma is produced in a compact pulse power device. Results show that extremely strong shock waves can be produced in the device. At low initial pressure condition, the shock Mach number reaches 250 that exceed well a criterion of radiative shock waves.

Efficiency of the shock wave generation caused by underwater electrical wire explosion

Shearing interferometry, together with shadowgraph and Schlieren photography techniques, has been applied for the visualization of the cylindrical water flow behind the shock wave generated by high-power 6 GW nanosecond time-scale underwater electrical discharge. The flow was visualized during the first microsecond of the wire explosion process in the region between the expanding exploding wire discharge channel and the shock wave. The optical methods, combined with the hydrodynamic calculation, enable an accurate estimation of the energy transferred from the discharge to the water flow. The estimated efficiency of the transformation of the electrical dissipated energy to the mechanical energy of the generated compressed water flow is ∼15%.

Warm-dense-matter studies using pulse-powered wire discharges in water

Dense plasmas are produced using exploding wire discharges in water. Evolutions of radius, electrical conductivity, temperature of plasma and a shock wave in water accompanied with the explosion, are measured. Conductivities of aluminum, copper, and tungsten are compared with theoretical ones. To evaluate the equation of state, trajectories of the shock wave and the plasma boundary are compared with numerical calculations. Results show that the hydrodynamic behaviors are sensitive to the models of equation of state. Controllability of warm dense state in density-temperature diagram is discussed from the voltage-current characteristics of the wire discharges.

Evaluation of warm dense plasma using pulse-power discharges in water

Plasmas at warm dense(WD) states are produced using exploding wire discharges in water. The hydrodynamic behaviors of wire have been observed with a fast framing/streak camera, together with the basic electric characteristics. Evolution of wire plasma and accompanied shock wave are also investigated with a magneto-hydrodynamic(MHD) simulation. The numerical results are strongly affected by equation of state (EOS) models of the plasma. Those results indicate a 'semi-empirical' fitting of them to the experimental observation is a useful method for studies of the plasma with warm dense state.

Categorising exploding-wire discharges for use in detonation studies

Instantaneous power dissipation and total energy released in a number of exploding-wire discharges have been measured on a microsecond time scale. The wire explosions so categorised may now be used for initiating deflagration and detonation in gaseous mixtures, permitting detonation processes to be related to discharge behaviour. Four different energy discharges at 100–400 J are available for detailed detonation studies. Two discharges with similar deposited energies (∼300 J) are available with peak power inputs differing by a factor of 4 (150–600 MW). This should permit the effects of energy-deposition rate on detonation processes to be examined on a microsecond time scale. Examination of the peak powers and energy densities achieved in the present study and comparison with those achieved at lower energies by other workers suggest increasing difficulties in producing detonation-initiating energies greater than 1 KJ. This limit is essentially determined by the regulating nature of transient skin-effect behaviour, which prevents rapid current diffusion into the centre of large-diameter wires.

Dense plasma discharges for solid-target heating

Dense plasma channels formed by exploding-wire discharges have been used to form very-high-current-density electron beams. The interaction of the beam with the plasma lowers the mean electron energy relative to that to be gained in the accelerating potential of 106 V applied across the plasma. The current density of electrons incident on the anode and their energy distribution have been determined. Approximately 10% of the current at the anode contains electrons with energy greater than 25 keV. The current density associated with these electrons exceeds 107 A/cm2. The power delivered to the anode approaches 1012 W/cm2, which leads to strong anode heating. X-ray spectroscopy of the radiation emitted from the anode and of neutron production in deuterated anodes was used to deduce a target temperature of 0.1–1.0 keV.

Neutron Production by Hot Dense Plasmas Generated with High Power Pulsers

Neutron production from plasmas generated by relativistic electron beam and exploding wire discharges is surveyed. Diagnostics appropriate to distinguishing neutrons produced by acceleration mechanisms from thermonuclear sources are discussed. The results of applying these techniques to exploding wire plasmas indicate that the dominant neutron source is thermonuclear fusion.

Precursor Ionization from Exploding Wires

The precursor ionization in an exploding wire discharge is of the order of 1012 electrons cm-3. The quantity of ionization produced is a sensitive function of the gas type, distance from the wire axis, pressure, and capacitor energy.

Direct electrical initiation of freely expanding gaseous detonation waves

Electrical initiation of freely expanding detonation waves has been demonstrated for three gaseous systems. It has been shown that a well-defined minimum stored-energy requirement exists for a given experimental system. Both spark discharges and exploding-wire discharges are discussed as initiation sources, and exploding-wire discharge is shown to produce detonation from smaller stored energies in the systems investigated. In each instance, the existence of a composition, or a range of compositions, requiring discharge of a minimum energy for initiation of freely expanding detonation waves has been established. Typical experimental data have been presented for mixtures of oxygen with the individual fuels ethylene, hydrogen, and propane. The data indicate that initiation of detonation in hydrogen systems requires more energy than in ethylene systems, but less than in propane systems. The pressure dependence of the stored energy required for initiation of detonation is quite complicated; in some instances the pressure sensitivity is large, and in other instances it disappears. Whenever a marked pressure effect exists, increasing the initial pressure decreases the required initiation energy.