Search

Underwater pulsed spark discharge has been widely used in industrial fields as a source of shock waves or acoustic waves, and numerical modeling of the discharge and pressure wave characteristics is necessary to improve the application performance. In this paper, a numerical model is proposed that couples the circuit equation, the mass and energy conservation equations, and a momentum conservation equation based on the Rankine–Hugoniot conditions. A tabulated wide range equation of state and conductivity data of water are used, and various physical processes during the plasma channel expansion are considered, including the energy flow and mass exchange between the channel and the surrounding water due to thermal radiation, evaporation, and condensation. The model self-consistently solves the circuit current and voltage, the plasma channel parameters including composition, temperature, conductivity, pressure, etc., and the pressure profile at a certain distance from the discharge channel. The calculated results show good consistency with the experimental measurements, and three sets of experimental results from other literature are tested to further verify the applicability and effectiveness of the model. [ABSTRACT FROM AUTHOR]

The Z-pinch is the most powerful X-ray source which can be obtained in the laboratory and it can be applied for many research fields, such as high energy density physics, inertial controlled fusion and laboratory astrophysics. In material experiments the Zpinch Xray source is utilized to radiate the material for carrying out thermodynamic effect researches, which are important for the radiationhardened reinforcement design of the system. In these experiments the radiated Xray power density acted on the sample is one of the most important parameters concerned by the researchers. In this paper the radiation filed of a Zpinch soft Xray source was analyzed. The Zpinch Xray source was treated as a line source and a Lambert radiation source or called as cosine radiator respectively. Based on the fundamental optical rules the expression was deduced which illustrated the Xray power density radiated by the Zpinch source. For the line source model, it shows that the radiation power density in the far filed is inversely proportional to the square of the distance from the source, and the contour surface is the conventional sphere surface, while in the near filed the radiated power density is inversely proportional to the distance, and the contour surface is more like a cylindrical surface. For the cosine radiator model the radiated power density in the far filed is still proportional to the square of the distance from the source, and the contour surface is a modified sphere surface which is multiplied by the cosine value of the angle. In the near filed the cosine radiation source model gives the same distribution for the radiated power density as the line source model. Based on the analysis mentioned above the radiation power density on the sample at Qiangguang Ⅰ accelerator was investigated. In Qianguang Ⅰ experiments the sample was located 5 cm far from the central Zpinch source, which implies that the distance is comparable with the size of the Zpinch source. The analysis results show that the power density radiated of the assessed material is inversely proportional to the square of the distance from the material to the source. In another word the radiation power density of the sample is satisfied the far filed criterion providing that the sample is located further than 5 cm, so it is reasonable in the experiments on Qiangguang Ⅰ that the power density radiated of the sample can be obtained by measuring the power density at the point which is further than 5 cm.

A series of current transport experiments of a conical magnetically insulated transmission line (MITL) and a single post-hole convolute (PHC) had been done on a 12-stage linear transformer driver (LTD). The LTD produced a current with a rise time of about 120 ns and a peak varying from 0.5 to 0.8 MA depending on the terminated connection loads. The conical MITL was designed with a constant gap distance of 8 mm, which was equivalent to the MITL segments that are close to the PHC locations in the multi-level conical MITL in tens of megaampere current drivers. A single PHC was also designed to operate at conditions close to those fielded on tens of MA current drivers such as the Z machine. The experiment results indicated that there was almost no current loss along the constant-gap MITL before the peak current even the MITL figure of merit, i.e., E/cB varied from 0.1 to 1. However, the time when current trails appeared gradually advanced. The effects of the geometric sizes on the current transport efficiency of a single PHC were studied. It was indicated that the current transport efficiency of the single PHC was considerable high while the gap distance is larger than 6 mm. Whereas the PHC current loss was increased to about 30% when the gap is 3 mm. The dynamic impedance of the single PHC was obtained. During the pulse, as the plasma diffused, the convolute shunt impedance rapidly decreased, which was consistent with the known mechanism. [ABSTRACT FROM AUTHOR]

The x-ray spectrum of a flash radiography source based on wire-shorted rod-pinch diode (RPD) is measured by an absorption spectrometer and calculated by the Geant4 Monte-Carlo code. The RPD is driven by a two-stage linear transformer driver (charging voltage ±45 kV per stage), which delivers ∼300 kA current within ∼200 ns on a short-circuit inductive load (∼30 nH). The spectrometer consists of LiF thermoluminescence dosimeters and metal filters of different materials and thicknesses, and the spectrum is reconstructed based on the Geant4 simulated dosimeter responses to various photon energies through different filters. The measured spectrum reaches an endpoint photon energy of ∼130 keV. The radiation characteristics of the RPD in the experiment are also modeled in Geant4 using measured voltage and current waveforms, and the results show an overestimation in photon number and endpoint energy (∼147 keV) compared to the measured spectrum, which indicates that during the bremsstrahlung process, the effective electron current is ∼27% of the total current, and the effective voltage is ∼12% lower than the directly reconstructed resistive voltage. A rough agreement is found between the spectra results and the non-relativistic Bethe–Heitler model with Sommerfeld correction; therefore, the analytic result can serve as an initial guess for spectrum reconstruction methods such as the perturbation method. [ABSTRACT FROM AUTHOR]

Initial wire resistance is an important parameter in an underwater electrical wire explosion because it directly affects the discharge characteristics of the circuit and indirectly affects the explosion and shock-wave generation. This paper presents a study on how the initial resistance affects electrical and shock-wave characteristics of underwater electrical explosions of aluminum wires with an initial energy storage of ∼53.5 kJ under the optimal mode. Load voltage, circuit current, and shock-wave pressure were recorded and analyzed. The experimental results show that the average of the discharge channel resistance and the total energy deposition all increase with the initial resistance. In addition, there is no simple functional relationship between the energy deposition during the phase transition process and the initial resistance, while the energy deposition during the plasma growth process increases with the initial resistance. As for shock waves at ∼33 cm, it is observed that when the initial resistance increases from 674.82 to 1581.60 μ Ω , the peak pressure, energy density, and impulse increase from 12.65 MPa, 2.67 kJ/m2, and 964.51 Pa s to 42.37 MPa, 18.21 kJ/m2, and 1940.42 Pa s, respectively. In other words, for the optimal mode, an underwater electrical explosion with thinner and longer wire is more conducive to generating strong shock waves in the far-field regime. These results should help select loads for underwater electrical wire explosions in engineering applications. [ABSTRACT FROM AUTHOR]

A rod pinch diode (RPD) is a feasible load configuration to generate a high-brightness, small-size hard x-ray radiation source. In this paper, the radiography performance of a wire-shorted low-impedance RPD on a compactly designed table-top driver (WRPD-1) is demonstrated for the first time. The driver consists of four high-power discharge branches connected in parallel, with each branch consisting of two metal-film capacitors and one multigap field-distortion switch in series. The four branches are triggered synchronously to generate a fast-rising current pulse: the inductance of the load section at the short circuit is ∼10 nH, and the short-circuit current amplitude is ∼325 kA at ±90 kV charging voltage, with a 10%–90% rise time of 110 ns. With a low-impedance RPD shorted by an 18-µm-diameter aluminum wire, a quasi-spherical x-ray focal spot with diameter <0.6 mm (width of the half-maximum grayscale) and a pulse duration of ∼25 ns (half-width of the radiation pulse) is obtained at ±70 kV charging voltage, and the imaging resolution excels 10 lp/mm under 1.56× magnification. According to the transmission–absorption x-ray spectrum estimation, the average emitted photon energy is ∼30 keV with a distinct peak in the 10–15 keV range that corresponds to the L-lines of tungsten, and the total energy of photons >10 keV reaches ∼1.16 J. The present results show that the device can serve well for the flash radiography diagnosis and potentially as an efficient light source for dynamic x-ray diffraction. [ABSTRACT FROM AUTHOR]

Measurement of plasma parameters during the ablation phase in the Z-pinch is crucial for investigating the dynamic behaviors. In this study, optical Thomson scattering was employed to measure the temperature and velocity of the ablation plasma in a double-wire Z-pinch. The scattering spectra profiles were fitted using a model that considered the velocity distribution. The experimental results revealed the energy evolution of ablation plasma, the establishment of the global magnetic field and the development of axial non-uniformities. The precursor plasma was found to play a key role in strengthening the global magnetic field. A resistive layer near the wire core with a size of 1.5 mm was observed in the ablation plasma after the precursor plasma column formed. The plasma underwent rapid heating in this layer, the electron temperature rises from 17 eV to 22 eV. Upon leaving this layer, electron the temperature is stable at around 22 eV. The radial distribution of the ablation rate increases and decreases, indicating the axial motion of the ablation plasma, which could be caused by the tilt motion of the stream and the secondary modulation of the natural wavelength. [ABSTRACT FROM AUTHOR]

In this paper, Fe10Co25Ni34Cu23Al8 high-entropy-alloy nanoparticles have been synthesized by the in situ instantaneous electrical wire explosion method. Based on the thermodynamic parameters of the face-centered cubic phase of high-entropy-alloy, the parameters of the five kinds of wires were calculated and controlled, and the stable face-centered cubic structure with good crystallinity was synthesized in one step. The influence of the energy deposition during the electrical explosion on the nanoparticles and their electromagnetic absorption performance was explored. The results show that the face-centered cubic structure high-entropy-alloy with high crystallinity has better electromagnetic wave absorption performance when the energy deposition of the wires is increased. The minimum reflection loss can reach −39.37 dB at 15.34 GHz when the thickness is 1.9 mm and the effective absorption bandwidth is 6.63 GHz. It can provide a strategy for the microstructure and morphology design of high-entropy-alloy nanoparticles in electromagnetic wave absorption and magnetism in the electronics industry. [ABSTRACT FROM AUTHOR]

With an initial energy storage of approximately 53.5 kJ, experiments on underwater electrical explosions of metallic wire and thin-wall tube were conducted. Two sets of controlled experiments were designed, and the wire and tube for each set were of the same length, cross-sectional area, and material. Load voltage, circuit current, and shock wave pressure were measured and analyzed, and electric power, energy deposition, and energy deposition rate were also calculated and investigated. Experimental results indicated that the underwater electrical tube explosion (UETE) always has higher and earlier local resistance peak, voltage peak, and electric power peak, as well as faster phase transition and ionization process than the underwater electrical wire explosion (UEWE). In addition, the energy deposition rate from the beginning of discharge or the decrease in current to the voltage peak is significantly increased when replacing a wire with a tube. For the shock-wave characteristics, the peak pressure, energy density, and impulse of the shock wave generated by UETE are greater than that generated by UEWE. The peak pressure at ∼33 cm increased from 21.1 to 24.5 MPa in the first set and from 18.1 to 21.7 MPa in the second when a tube was used instead of a wire. These experimental results help us understand the physical process of UETE and provide an alternative methodology for load design in industrial applications. [ABSTRACT FROM AUTHOR]

This paper proposed and verified a method for adjusting parameters of underwater shock waves. In the experiments, a metal wire with an energetic material coat was exploded by applying a pulsed current on it. Under different matches of size/material of wire, mass/type of energetic material, and injected pulsed current, characteristics of shock waves were obtained. It has been proven that peak pressure, impulse, and energy of shock waves can be conveniently regulated by simply changing the explosion of either the wire or its energetic material coat. Finally, the mechanisms of this method were analyzed and potential applications discussed. [ABSTRACT FROM AUTHOR]