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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]

In order to solve the current problems of electronic invoices, such as anti-counterfeiting, privacy leakage and low verification efficiency, an electronic invoice public verification architecture based on the national signature algorithm was proposed.Electronic invoice documents have complex data sources, sensitive user information on the ticket surface, frequent data flow and other characteristics as well as the demand for efficient public verification.Based on these motivations, the e-invoice generation and verification protocol was designed.Besides, a signature code generation scheme for invoice anti-counterfeiting was proposed based on certificate-free joint signature.Then multiple data verification and signatures of the invoicing party and the taxation authority can be realized.All kinds of invoice holders can not only verify the authenticity and data integrity of electronic invoices, but also publicly check the authenticity and data integrity of electronic invoices.The integration of data encryption algorithms protects user privacy data in electronic invoices, and at the same time can fulfill the requirements for authenticity or status verification under various invoice application scenarios.The checking party only needs to verify one signature to confirm the authenticity of the electronic invoice signed by both parties.Scyther security simulation tools were used to analyze the security of the proposed solution, which can verify the integrity and authenticity of the data source and check the confidentiality of the privacy data under various types of attacks.Compared with a typical overseas e-invoice checking scheme and a similar digital signature-based e-invoice checking scheme, the proposed scheme has obvious advantages in terms of checking efficiency and invoice file size.

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]

We investigate the effects of specular reflection on the laser-induced breakdown (LIB) of copper, iron, and tungsten using fast photography and optical emission spectroscopy. The laser parameters include spot diameter ranging from 30.89 to 1589.33 μm, irradiance from 467.10 to 0.17 GW/cm2, with a single pulse of 6 ns duration and 21 mJ energy. As the laser spot defocuses, the plasma morphology changes from a single plasma near the target surface to a separated, independently evolving two-component plasma, and then to a single plasma suspended above. The defocusing distance for this transition is significantly influenced by specular reflectance. The separate plasma, comprising of a metallic component and an air component, occurs only under high specular reflectance conditions: ≥66.7% for copper, ≥51.4% for iron, and ≥44.9% for tungsten. The spectral emission of the metallic component initially increases and then decreases with reducing specular reflectance, due to a trade-off between enhanced surface absorption and reduced irradiance caused by surface roughening. LIB threshold irradiance increases with specular reflectance, rising from 0.31 to 1.22 GW/cm2 for copper, 0.24 to 0.70 GW/cm2 for iron, and 0.38 to 0.87 GW/cm2 for tungsten. These findings show the impact of sample pretreatment on LIB ignition and subsequent plasma evolution, offering insights into potential sources of inaccuracy in LIB applications. [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]

The synergy enhancement of magnetic-spatial confinement using a bar magnet pair was applied to fiber-optic laser-induced breakdown spectroscopy (FO-LIBS). By studying the plasma morphology and emission spectroscopy, the plasma temporal behaviors under free expansion, spatial confinement, and magnetic-spatial confinement have been carefully compared. Temperature distribution and pixel-to-pixel relative standard deviation (RSD) of plasma morphology under the combined effect of magnetic field and the reflected shock wave on fiber-optic laser-induced plasma were studied for the first time. The magnetic field was found to deform the plume mainly at the left and right sides, and the two high-intensity areas in FO-LIBS plasma rose from 8.7% to 13.8% and resisted being compressed together after the shock wave reflected. The magnetic-spatial confinements also demonstrated better enhancements in emission spectra than only spatial confinement, and the magnetic field tended to give around 20% and 50% additional enhancement on line intensity at the early and later stages of evolution, respectively. Besides, the self-reversed effect was significantly reduced in magnetic-spatial confinement, which can be explained by more evenly distributed temperatures calculated by spatially resolved spectra. Pixel-to-pixel RSD distribution of plasma morphology was studied, and it was found that the area of more fluctuated parts was reduced by 40% and concentrated on the left and right sides of the plasma in the magnetic field at the early stage. After the shock wave passed through, the two high-intensity areas were observed to fluctuate less due to the compression of the shock wave. Furthermore, shot-to-shot spectra fluctuation was also reduced by up to 50% under the magnetic-spatial confinement, which is consistent with the results of plasma morphology fluctuation. This study provides evidence of plasma emission signal enhancement and stabilization under magnetic-spatial confinement in the FO-LIBS system. [ABSTRACT FROM AUTHOR]

The proliferation of urbanization and the integration of new energy sources have stimulated the development of gas-insulated transmission lines and switchgear (GIL/GIS). In particular, the compact DC GIS in offshore converter platforms will significantly reduce footprints for DC switchyards, exhibit exceptional climatic resistance, and facilitate the cost-effective connection of remote offshore wind farms and submarine links. Nevertheless, insulators used in GIS/GIL always suffer from surface charge accumulation under DC stress, which could distort and enhance the local electric field and thus trigger a flashover at the gas–solid interface if it exceeds certain magnitude levels. This susceptibility becomes a major concern affecting the reliability of DC gas-insulated systems. Beyond these engineering-related challenges lie fundamental physics problems involving mechanisms of charge accumulation and charge-induced flashover which still require exploration. To this end, this paper presents an overview of recent advancements on this topic whilst highlighting relevant issues to be addressed. Specifically, the surface charge accumulation phenomena under DC fields are reviewed, and the charging mechanisms are summarized from macroscopic to microscopic perspectives. Further, the correlation between surface charge and surface flashover is discussed. Moreover, recent developments in tailoring methods for surface charging are also presented. Finally, perspectives are given on current research progress and future needs. [ABSTRACT FROM AUTHOR]

The gas mixture CO2–O2 has been considered as an insulation and arc-quenching medium in gas-insulated switchgears. In this paper, the dielectric breakdown properties of CO2–O2 mixtures at different O2 concentrations and gas pressures were studied theoretically by considering ion kinetics in a spatial–temporal growth avalanche model. A kinetic scheme that includes all the main reactions likely to occur in CO2–O2 mixtures is presented. An improved method to calculate the dielectric strength of the gas mixture is developed, based on an avalanche model that considers both spatial growth and temporal processes. Next, the reaction rates of ionization, attachment, detachment and ion conversion, the effective ionization Townsend coefficient αeff/N, and reduced critical electric field strength (E/N)cr in CO2–O2 mixtures at different mixing ratios and gas pressures are analyzed in detail. Finally, a pulsed Townsend experiment is performed to verify the validity and accuracy of the calculation method. Based on this, one detachment reaction rate is modified to yield more accurate results. Better consistency between the results and the experimental values supports the validity of the kinetic system, reaction rates, and the improved calculation method. [ABSTRACT FROM AUTHOR]