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Development towards HVDC grids is drawing intense development of HVDC circuit‐breakers (CBs). The increasing rated voltage and capacity requires HVDC CBs with excellent performance to be installed and comprehensive tests on HVDC CBs are indispensable. This paper contributes to clarifying clearer test requirements on the current interruption test, which is the most challenging one and proposing a novel applicable test method. It is the toughest test because when an HVDC CB interrupts fault current, a high transient interruption voltage (TIV) is produced by the operation of metal oxide surge arrester (MOSA), and a large current continues flowing through MOSA simultaneously, which means considerable energy is demanded for the test. To verify an HVDC CB's current interruption ability, voltage withstand ability and energy dissipation ability in single test can be costly and even impractical in extra high voltage classes. Alternatively, a multi‐part test method is reasonable and valuable, in which the HVDC CB can be tested with large current and high voltage one after another, while the energy dissipation ability will be verified separately. At last, a proposed synthetic test circuit is validated by a simulation and a low voltage experiment, creating high equivalence between the simulation and the validation test. [ABSTRACT FROM AUTHOR]

The preparation and storage of aluminum nanoparticles pose significant challenges due to their high chemical reactivity. This paper proposes a one-step method for the production of carbon-coated aluminum nanoparticles using an argon protective arc in a liquid nitrogen environment. The emission spectra of the arc validate that the method proposed in this paper can effectively mitigate the adverse impact of impurity gases such as oxygen and water on the product without the need for expensive vacuum equipment. The obtained nanoparticles underwent characterization through high-resolution transmission electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, Raman analysis, thermogravimetric analysis, and dynamic light scattering. The characterization results demonstrate the successful synthesis of carbon-coated aluminum nanoparticles with nitrogen-doped fullerene shells. With an increase in arc current, the nanoparticles exhibit a corresponding enlargement in diameter, accompanied by a broader distribution. The characterization of the electrode erosion suggests that the aluminum droplet ejection plays a more important role in the nanoparticle generation process as the arc current increases. Optimized strategies are proposed to increase the percentage of successfully-formed carbon-coated aluminum nanoparticles. • One-step preparation of carbon-coated aluminum nanoparticles. • Arc discharge in liquid environment without vacuum and sealing equipment. • Core-shell structure: Al core wrapped in N-doped fullerenes. • The arc current impacts electrode erosion pattern and product characteristics. [ABSTRACT FROM AUTHOR]

Vacuum circuit breakers (VCB) are commonly used in active mechanical direct current circuit breakers (DC CBs) to accomplish the interruption of the fault current. The post-arc current phenomenon of a VCB is related to the dielectric recovery process of the VCB. Thus, we performed experiments to investigate the influence on the post-arc current by taking the electrode separation, breaking current, and interruption of the bi-directional current with the injecting high frequency current in a fixed direction into account. To be in accordance with the practical interruption duty, the breaking current in the experiment ranges from 500 A to 20 kA. At the same time, the di/dt at current zero (CZ) varies between 200 and 1100 A/μs. The experiment results reveal that the peak value of the post-arc current in an active DC circuit breaker can reach more than 100 A with high di/dt at CZ. It is found that with a longer electrode separation, not only the residual charge increases but also the post-arc current increases. The arcing current before CZ can influence the post-arc current but the effective duration before CZ is short. This duration is the memory time and it is derived from the experiment results. The influence of the breaking current and interruption of the bi-directional current with the injecting current in a fixed direction are dependent on the relation of the current commutation time with the memory time. [ABSTRACT FROM AUTHOR]

The anode activities are critical for high-current vacuum arc characteristics, especially the interruption performance of vacuum interrupters. The serious anode melting and sputter of liquid droplets into arc column often lead to interruption failure. In our previous work, the obvious anode melting and swirl flow of melted anode metal were detected at the center of anode surface when arc current exceeded a critical value under axial magnetic field (AMF). It is found that the AMF has great influence on the anode swirl flow, no swirl flow is found on the butt plate anode without AMF, but obvious swirl flow can be found when a moderate AMF is applied. Meanwhile, the swirl flow direction reversed if the AMF direction also reversed. The electromagnetic forcej×Bin anode melting pool and the impact force of ions coming from cathode plasma jets which are inclined to the arc axis on anode surface were thought to be two main possible reasons. In order to discover the physics behind the anode swirl flow phenomenon, special experiments have been conducted in this paper. Both the theoretical analysis and experimental results indicate that it is not the electromagnetic force but the interaction between ions from cathode plasma jets and anode melting pool that leads to the observed anode swirl flow. The inclination direction of cathode plasma jets, which is consistent with the direction of magnetic field vector, determines the direction of swirl flow. [ABSTRACT FROM AUTHOR]

Based on a magnetohydrodynamic model, a numerical simulation of high-current vacuum arc (HCVA) is carried out. In this model, the kinetic energy terms and ion viscosity terms in energy conservation equations are considered. Compared with the supersonic constricted vacuum arc, the ion flow in HCVA is in the subsonic status. Therefore, boundary conditions of cathode and anode sides have to be adjusted for HCVA. According to the simulation results of HCVA, we can find that the maximal plasma pressure appears near the cathode side. The characteristics of HCVA are significantly different from those of supersonic vacuum arc. Then, we make the comparisons between simulation results and experimental results (such as electron number density, electron temperature, ion temperature, high speed charge-coupled device photographs, and so on). The simulation results are in agreement with the experimental results. In addition, we also analyze the influence of different arc models on the distribution of current density in the anode side. [ABSTRACT FROM AUTHOR]

The cathode plasma jets in vacuum arc and the effect of magnetic field on them have been studied for several years and these studies are helpful to understand the arc characteristics and improve the controlling effect of magnetic field on arc plasma. In this paper, the experiments of the cup-shaped axial magnetic field (AMF) contacts were conducted in which a Helmholtz coil was introduced to generate different external imposed AMFs. It was found that the appearance of arc plasma was changed by variation of the external imposed AMF. If the composite AMF in arc column increased gradually, the obvious individual cathode plasma jets were detected, the arc constriction decreased, and the arc stability increased. Meanwhile, the inclination of cathode plasma jets was observed and the inclination direction was found to be consistent with the magnetic field vector direction which is closely related to the composite AMF. By variation of the external imposed AMF and its direction, the inclination direction of cathode plasma jets also changed. The criterion to detect obvious cathode jets in arc column is obtained that at the contact peripheral where R> 80.5% R0 (R0 is the contact radius), the AMF strength is no less than 4.5 mT/kA. It was also found that if the composite AMF in interelectrode gap points to different directions at a certain moment, it may lead to the transfer of arc column from the center to the edge of the interelectrode region and the arc instability until when the composite AMF in the interelectrode gap points to the same direction. It can be concluded that the appearance of individual cathode plasma jets can be manipulated by the variation of AMF, which is helpful to study the interaction between arc plasma and electrodes, especially the anode, and improve the interruption performance at higher current. [ABSTRACT FROM PUBLISHER]

In real power system, when the three-phase short-circuit fault occurs, the vacuum arc in one phase will be influenced by the transverse magnetic field generated by neighbor phases and bus bars. This kind of effect is the main cause of the unstable arc and deflected erosion of contact plates, which leads to the failure of vacuum circuit breakers interruption. The objective of this paper is to get more insight into the influence of external transverse magnetic field (ETMF) on vacuum arc’s behavior. The experiments were conducted in a demountable vacuum chamber with pressure about 10^-4 Pa. The cup-type axial magnetic field contacts were used, whose material was pure copper and the diameter is 35 mm. The uniform ETMF in the arc region was generated by two parallel bulk permanent magnets. The experiments were conducted under different ETMFs (0, 15, and 25 mT) and current levels (1-, 2.5-, and 4-kA rms) with different gap distances (6, 8.5, and 11 mm). The videos of arc column were recorded by a high-speed charge-coupled device camera. Under the action of ETMF, the vacuum arc got deflected. Due to the retrograde motion of cathode spots and Ampere force acting on arc column, the deflection behaviors during three typical periods (that is, initial, peak value, and close-to-current-zero period) were different. Moreover, the deflection level of vacuum arc at current peak value moment was greatly impacted by ETMF and gap distance. Larger the ETMF and gap distance were, higher the deflection level at current peak value moment was. The simulation results of arc deflection based on magnetic-hydrodynamic model were in agreement with experimental results in trends. [ABSTRACT FROM AUTHOR]

Dielectric energy-storage capacitors are among the main enabling technologies in high-density power converters, in which lead-free relaxor ferroelectric ceramics have been paid particular attention to. However, low energy-storage performance at elevated temperature and high electric field, and the lack of application-oriented evaluation are among the primary blocks stumbling their progress. As a demonstration, 0.87BaTiO3-0.13Bi[Zn2/3(Nb0.85Ta0.15)1/3]O3 (BTBZNT) lead-free relaxor ferroelectric ceramics were modified by linear dielectric CaZrO3 (CZ) with various contents of 0, 0.1, 0.2, and 0.3 (CZ0, CZ1, CZ2, and CZ3). XRD and Raman results reveal major perovskite phases, and densely sintered ceramics were witnessed from the SEM images. Unchanged weakly coupled relaxor behavior was confirmed by the big critical coefficient of 1.6–1.8 from the modified Curie–Weiss law and the large activation energy of 0.29–0.32 eV from the Volgel–Fulcher fittings, and CZ was found to suppress high-temperature loss. From the normal polarization–electric field (P–E) loops, CZ0 is optimal for energy-storage owing to the highest discharged energy density and modest efficiency. Nevertheless, from the application-oriented DC-biased P–E loops, CZ1 is oppositely superior to CZ0 because of the higher permittivity and lower loss leading to higher discharged energy density and efficiency at DC-biased electric field. Moreover, CZ1 outperforms CZ0 in the higher capacitance density and lower temperature rise at higher temperature and electric field. Enhanced DC-biased energy-storage performance in BTBZNT ceramics modified by CZ was achieved, which should enlighten the advance of energy-storage ceramics targeting the application in high-density power converters. [ABSTRACT FROM AUTHOR]

In this paper, a three-dimensional (3d) magneto-hydro-dynamic (MHD) model of axial magnetic field vacuum arcs (AMFVAs) is established. Based on this model, AMFVAs are simulated and analyzed. Three-dimensional spatial distributions of many important plasma parameters and electric characteristics in AMFVAs can be obtained, such as ion number density, ion temperature, electron temperature, plasma pressure, current densities along different directions (x, y, and z), ion velocities along different directions, electric fields strength along different directions, and so on. Simulation results show that there exist significant spiral-shaped rotational phenomena in the AMFVAs, this kind of rotational phenomenon also can be verified by the many related experiments (AMFVAs photographs, especially for stronger AMF strength). For current simulation results of AMFVAs, the maximal rotational velocity at anode side is about 1100 m/s. Radial electric field is increased from arc center to arc edge; axial electric field is decreased from cathode side to anode side. Radial electric field at arc edge can be larger than axial electric field. Azimuthal electric field in most regions is much smaller than radial and axial electric field, but it can reach about 1.19 kV/m. Radial magnetic field is the smallest one compared with other components, it reaches to maximum value at the position near to anode, it can influence arc characteristics. [ABSTRACT FROM AUTHOR]

Based on a 2-D magnetohydrodynamic model, high-current vacuum arcs (HCVAs) under axial magnetic fields (AMFs) with consideration of current density distribution at the cathode are simulated and analyzed. The current density distribution at the cathode used in the simulation is obtained by processing the image of cathode spots from experiments. In order to study the influence of current density distribution at the cathode on vacuum arc characteristics, HCVA is simulated under two kinds of current density distribution at the cathode. Then, for HCVA simulation in a half-sinusoidal period, the current density distribution at the cathode and the AMF delay are both taken into account. The simulation results show that the nonuniform current density at the cathode makes the values of the arc plasma parameters in the interelectrode region larger and their radial distribution more nonuniform than the uniform current density at the cathode. The more uniform current density at the cathode and the stronger AMF at the moments in the second 1/4 cycle make the values of the arc plasma parameters in the central region smaller and their radial distribution broader than those in the first 1/4 cycle. In addition, the simulation results will also be compared with the experimental results. [ABSTRACT FROM AUTHOR]

Much research has been done on the motion of low-current vacuum-arc cathode spots (CSs). The relationship between the motion velocity of CSs and the magnetic field, particularly the relationship between the direction of CS motion and the ratio of Bz/Bt, has been revealed. However, little investigation on the motion of CSs in high-current vacuum arcs has been conducted before. In this paper, the motion of CSs of high-current vacuum arcs under different axial magnetic fields was experimentally investigated. Simultaneously, calculation of the motion of CSs based on the empirical formula has been done, and comparison with experiments and analysis were given. Experiments were conducted in a detachable vacuum chamber with an arc current of 10 kA (root mean square). Images of CSs were photographed with a high-speed digital camera with an exposure time of 2 \mu\s. With computer-aided numerical processing, the spatial distribution of the CSs was obtained, based on which the magnitude and direction of the CS motion velocity were calculated, and the CS motion trajectories around the current peak were plotted. Results indicated that the properties of the CS motion in high-current vacuum arcs are similar to those in low-current vacuum arcs. [ABSTRACT FROM AUTHOR]

The theoretical and experimental studies of cathode plasma jets in vacuum arc and the effect of magnetic field on them have been under way for several years. In this paper, different axial magnetic field electrodes were tested in a vacuum chamber, obvious individual cathode plasma jets were observed, and the cathode-jet inclination was also detected. Based on the numerical calculation of magnetic field in interelectrode region and the measurement of cathode-jet inclination in experimental results, it is proven that the inclination angle of composite magnetic field (the combination of the axial, the azimuthal, and the radial components) is consistent with the inclination angle of cathode plasma jets, which indicates that the cathode plasma jets in the arc column flow along the magnetic-field direction when the high-current vacuum arc is diffused or even constricted slightly. Meanwhile, it was also found that plasma jets far from the cathode surface mixed with each other and became ambiguous when the electrode gap increases to a certain distance. [ABSTRACT FROM PUBLISHER]

Abstract: To change the structures and yields of carbon nano-products, transverse magnetic field (TMF) was introduced to arc discharge in liquid (de-ionized water, liquid nitrogen). Direct current was used to sustain the arc discharge between two graphite electrodes and cobalt powder was filled in drilled anodes as catalyst sometimes. Scanning electron microscopy and high-resolution transmission electron microscopy were used to investigate the nano-products. Some novel carbon nano-structures were obtained with the effect of TMF. For arc discharge in water, curled multi-walled carbon nanotubes and nano-structures with few layers were found in cathode depositions and floating products, respectively. For arc discharge in liquid nitrogen, twists of single-walled carbon nanotubes appeared in cathode depositions and the yields of spherical nano-particles in floating products increased. [Copyright &y& Elsevier]

Abstract: Based on two-temperature magnetic hydrodynamic (MHD) model, the influence of saddle-shaped distributed axial magnetic field (AMF, linearly increases along radial position) and bell-shaped distributed AMF (linearly decreases along radial position) on plasma loss and heat flux density to anode in subsonic high-current vacuum arc (HCVA) is simulated and analyzed. According to the simulation results, the saddle-shaped AMF can more effectively inhibit plasma loss from arc column than that of bell-shaped AMF. Comparisons between simulation results and experimental results further verify the correctness of model and simulation. [Copyright &y& Elsevier]

Abstract: A magnetic field parallel to the carbon arc in water was used to increase the directionality of moving carbon particles and generate carbon nano-materials. The products were analyzed and compared with those obtained without a magnetic field. The study shows that the purity and quality of multi-walled carbon nanotubes in the cathode deposition formed by an arc in water with a magnetic field were both improved, and cylinder-like carbon structures were also found in the deposition. The influence of the magnetic field on the formation of the products was analyzed. [Copyright &y& Elsevier]

In the vacuum DC circuit breaker based on the artificial current zero, the change of arc luminosity delays the change of current value significantly in the fast current-zero stage. This phenomenon has impacts on the breaking capacity of the DC vacuum circuit breaker. Therefore, it is necessary to study the dynamic characteristics of the arc plasma under the above condition. In this work, a 3D transient magneto-hydro-dynamic model based on the commercial cup-type axial magnetic field (AMF) contact is established to study this phenomenon. The simulation results show that the fast current-zero stage is too short for the plasma to diffuse. The changes of the physical characteristics of the arc plasma lag the change of current value. Moreover, the magnetic field hysteresis caused by the eddy current on the electrode occurs in this stage, resulting in a continuous stronger AMF. It makes the distributions of the plasma uniform, while the diffusion of the arc plasma reduced at low currents, which is detrimental to the post-arc dielectric recovery stage. In addition, in the fast current-zero stage, the AMF near the contact slot is smaller than in other areas. This indicates that the slotting is effective in suppressing eddy currents and avoiding the negative effect of excessive AMF on plasma diffusion at this stage. The simulation results are consistent with the experimental results. [ABSTRACT FROM AUTHOR]

The dielectric recovery process has decisive effects on the current interruption process in vacuum circuit breakers, which has attracted the special attention of researchers. In commercial vacuum interrupters, ions and electrons of the residual plasma between the contact gap are separated and then fly to the electrodes under the effect of the transient recovery voltage after current zero. During this period, the post-arc current forms. During the formation of the post-arc current, ions also enter the post-arc anode due to their thermal motion. Therefore, the number of net electrons, which form the post-arc current, is only part of the total electrons between the contact gap at current zero. During the post-arc sheath expansion process, almost all electrons in the contact gap will enter the post-arc anode under the effects of the transient recovery voltage. If the proportion of ions and electrons, which enter the post-arc anode, can be obtained, the total number of electrons and consequently the residual plasma density between the contact gap could be estimated from the integration of the post-arc current. In this paper, the influences on the absorption of charged particles by the post-arc anode of some factors, e.g., rising rate of transient recovery voltage and metal vapor, have been simulated and discussed with a one-dimensional particle in cell-Monte Carlo collision model. [ABSTRACT FROM AUTHOR]

The dielectric breakdown properties of SF6-CF4 mixtures were investigated at different ratios of SF6, 0.01-1.6 MPa, and gas temperatures up to 3000 K. Initially, the equilibrium compositions of SF6-CF4 mixtures were calculated by minimizing the Gibbs free energy under the assumptions of local thermodynamic and chemical equilibrium. Then the electron energy distribution function was obtained based on those data by solving the Boltzmann equation under the zero-dimensional two-term spherical harmonic approximation. Finally, the critical reduced electric field strength (E/N)cr of SF6-CF4 mixtures, which is defined as the value for which total ionization reaction is equal to total attachment reaction, were determined and analyzed. The results confirm the superior breakdown properties of pure SF6 at relatively low gas temperatures. However, for higher gas temperatures (i.e., T > 2200 K at 0.4 MPa), the (E/N)cr in SF6-CF4 mixtures are obviously higher than that in pure SF6 and the values of (E/N)cr increase with the reduction of the ratio of SF6. [ABSTRACT FROM AUTHOR]

The dielectric breakdown properties of SF6-N2 mixtures were investigated at different concentrations of N2, 0.01-1.6 MPa, and 300-3000 K. The equilibrium compositions of different SF6-N2 mixtures at several gas pressures and temperatures up to 3000 K were first calculated by minimizing the Gibbs free energy under the assumptions of local thermodynamic and chemical equilibrium. The electron energy distribution function was then obtained using the composition data by Boltzmann equation analysis. It was found that adding N2 to SF6 gas can markedly reduce the kinetic energy of electrons at relatively high gas temperatures, which enhances the dielectric field strength. Finally, the critical reduced electric field (E/N)cr, defined as the value for which ionization is equal to attachment, of hot SF6-N2 mixtures was determined. The results indicate that in the gas temperature range around 2000-3000 K, increasing the concentration of N2 effectively enhances the (E/N)cr of SF6-N2 mixtures, and the (E/N)cr of SF6-N2 mixtures at a wide range of concentrations of N2 (5%, 50%, and 95%) are all higher than that of pure SF6 gas. Further, this trend exists at all the gas pressures considered (0.01-1.6 MPa). [ABSTRACT FROM AUTHOR]

The development of electrothermal chemical launch technology and the effective ignition of energetic thermoplastic elastomer (ETPE) propellants all call for a thorough understanding of the plasma propellant interaction mechanism. Therefore in this work, a numerical model is developed to study this process. In this model, special attention is paid to deal with the regression of propellant surface, which is caused by plasma ablation, and is assumed to have considerable influence on the interaction process. By this model, interaction features of four propellants, including two ETPE propellants are studied with the aid of experiments, which are carried out to obtain plasma parameters utilized in the model. Surface temperature, ablation rate, and surface regression rate are obtained for different propellants under plasma impingement. Finally, the influence of propellant composition and charging voltage are analyzed. [ABSTRACT FROM AUTHOR]

The dielectric recovery process is a crucial stage of current interruption in a vacuum circuit breaker (VCB). The postarc current is an important macroscopic electric characteristic of the dielectric recovery process, which has caused many concerns in the past few decades. In this paper, the postarc currents of VCBs with different types of contacts, such as butt contacts, axial magnetic field contacts, and transverse magnetic field contacts with different materials are measured with a high-resolution current-zero diagnostic system. Besides, the appearance of vacuum arcs is recorded using a high-speed camera in the experiments. The relationship between the arc memory effect and the postarc current is analyzed. What is more, the influence of the instability of the vacuum arc shape on the dispersion of postarc current is also studied. [ABSTRACT FROM AUTHOR]

A two-dimensional magneto-hydrodynamic (MHD) model of an ablation-dominated capillary discharge is developed. Special attention is paid to the interaction between the plasma and the capillary in two-dimensional geometry. The mass exchange process is taken into account by adopting a kinetic ablation model and a revised deposition model. The momentum and energy exchange processes associated with the ablated and deposited mass are also considered. By solving this model, key plasma parameters are calculated and presented in the paper. It is shown that distinct two-dimensional features exist in the distribution of these plasma parameters. Further, the calculated temperature results are consistent with previously presented measurements [ABSTRACT FROM AUTHOR]

The air arc impinging to chamber shell during interruption current process were studied by experiments and numerical simulation. Firstly, strain characteristics of chamber shell were measured by the strain gauge, and the strain changing with times were lagging behind the pressure in arc chamber. Experiment strain results 0.0035 and 0.0025 were slightly smaller than the calculation results 0.0055 and 0.0035. Furthermore, the thermal field mathematics model of chamber shell was proposed, and it was found that there was a large temperature gradient in the thickness of the chamber shell. Lastly, stresses-strains of three kinds of coupling methods, which were the fluid-structure coupling, the thermal-structure coupling and the fluid-thermal-structure coupling were compared. It was confirmed that the mechanical stress was concentrated in the middle of the side wall, while the maximum thermal stress was distributed on the vent area. Total stress and total strain were not equal to the algebraic sum of mechanical field and thermal field. The effect of different fixed supports on the thermal field was greater than the effect on the fluid field, and outer side wall fixed support had minimal displacement. [ABSTRACT FROM AUTHOR]

The anode melting in high-current vacuum arcs leads to the increase of metal vapor and liquid droplets around current zero and even the interruption failure. In our recent experiments of the cup-shaped axial magnetic field (AMF) contacts, an obvious clockwise swirl flow of the liquid copper was detected on the anode surface. However, if an additional external AMF which is reverse to the AMF generated by the contacts was introduced, the rotation direction of the liquid copper swirl flow on the anode surface could reverse to anticlockwise. These phenomena indicate that AMF has great influence on the performance of anode melting and its swirl flow. [ABSTRACT FROM AUTHOR]

Electrical explosion of wires has caused the attention of researchers because of its rich physical phenomena and plenty applications. Microsecond electrical explosion of Cu wires in air under various parameters is conducted, and diverse discharge waveforms are displayed and analyzed. By statistically summarizing the experimental results, experimental parameter selection suggestions for specific applications are given. In addition, the experimental results show that the average axial breakdown field strength is greatly changed with the breakdown time. It drops linearly from ~13 to ~3 kV/cm when breakdown time varies from 2 to $6~\mu \text{s}$ , it keeps at a relatively low value about 1 kV/cm when the breakdown occurred after $8~\mu \text{s}$. The effect of current density on the rising edge of the resistivity curve is confirmed by the experimental results. Based on the correlation between the breakdown time and breakdown field strength and the correlation between the maximum current density and specific action when resistivity reaches 200 $\mu \Omega \cdot \text {cm}$ , the specific-action model is improved empirically. The proposed “two-stage” model better reflects the actual physical process and has higher accuracy and a wider scope of application. [ABSTRACT FROM AUTHOR]

This work investigates the arc behaviors with CuCr25 electrodes considering anode vapor using a magneto-hydro-dynamic model. Different kinds of components are considered including ions (Cu and Cr) with different charge numbers, electrons, and atoms (Cu and Cr). The effect of the anode sheath is also considered. The density distributions of these components are analyzed and compared with the experiments during the anode spot mode and the anode plume mode. Simulation results show that the anode vapor can enter the arc column forming a cool and poorly conducting region (i.e., neutral atom vapor area, NAVA) under high anode temperature. Atoms and single-charged ions mainly gather near each electrode. The highest double-charged ion density can be seen in front of the NAVA. Triple-charged ion density is negligibly low and reaches its maximum where the electron temperature is high. Cr is more likely to be ionized to a higher ionization level compared with Cu. Our results agree with experimental measurements of density distributions of different components and plasma temperature. [ABSTRACT FROM AUTHOR]

In order to ensure the reliable interruption of high voltage direct current circuit breaker (HVDC CB), the breaking test of HVDC CB plays an important role in its performance verification. In this paper, the interruption process of the HVDC CB is analyzed, and the equivalent requirements for the breaking test of HVDC CB are summarized. In the breaking test of high voltage and high current, the transient interruption voltage (TIV) duration is short, which leads to insufficient voltage stress. A new synthetic test circuit for testing the interruption performance of HVDC CBs is proposed, which can solve the problem of insufficient TIV duration caused by insufficient test capacity. Subsequently, the working principle of the test circuit is introduced in detail and the design method of the circuit parameters is given. The short‐circuit current breaking test simulation of HVDC CB is carried out. The simulation results fit most well with the results of actual test cases, which verifies the universality of this test method. Finally, a test platform is built to verify the principle of the test circuit. TIV rose to 2.5 kV compared to the predetermined system voltage of 1.67 kV during the test, which means that the key stress provided by the test circuit can meet the expected requirements. [ABSTRACT FROM AUTHOR]

Due to the peculiar magnetic properties and the ability to function in cell-level biological interaction, superparamagnetic nanoparticles (SMNP) have been being the attractive carrier for gene delivery. The superparamagnetic nanoparticles with surface-bound gene vector can be attracted to the surface of cells by the Kelvin force provided by external magnetic field. In this article, the influence of the oscillating magnetic field on the characteristics of magnetofection is studied in terms of the magnetophoretic velocity. The magnetic field of a cylindrical permanent magnet is calculated by equivalent current source (ECS) method, and the Kelvin force is derived by using the effective moment method. The results show that the static magnetic field accelerates the sedimentation of the particles, and drives the particles inward towards the axis of the magnet. Based on the investigation of the magnetophoretic velocity of the particle under horizontally oscillating magnetic field, an oscillating velocity within the amplitude of the magnet oscillation is observed. Furthermore, simulation results indicate that the oscillating amplitude plays an important role in regulating the active region, where the particles may present oscillating motion. The analysis of the magnetophoretic velocity gives us an insight into the physical mechanism of the magnetofection. It's also helpful to the optimal design of the magnetofection system. [ABSTRACT FROM AUTHOR]

[Display omitted] Polymer-based dielectrics with high thermal conductivity and superb dielectric properties hold great promising for advanced electronic packaging and thermal management application. However, integrating these properties into a single material remains challenging due to their mutually exclusive physical connotations. Here, an ideal dielectric thermally conductive epoxy composite is successfully prepared by incorporating multiscale hybrid fillers of boron nitride microsphere (BNMS) and silicon dioxide coated silicon carbide nanoparticles (SiC@SiO 2). In the resultant composites, the microscale BNMS serve as the principal building blocks to establish the thermally conductive network, while the nanoscale SiC@SiO 2 as bridges to optimize the heat transfer and suppress the interfacial phonon scattering. In addition, the special core–shell nanoarchitecture of SiC@SiO 2 can significantly impede the leakage current and generate a great deal of minicapacitors in the composites. Consequently, favorable thermal conductivity (0.76 W/mK) and dielectric constant (∼8.19) are simultaneously achieved in the BNMS/SiC@SiO 2 /Epoxy composites without compromising the dielectric loss (∼0.022). The strategy described in this study provides important insights into the design of high-performance dielectric composites by capitalizing on the merits of different particles. [ABSTRACT FROM AUTHOR]

Anode material seriously influences the characteristics of vacuum arc and further affects the performance of medium-voltage vacuum switches when the interruption current is high. There are many materials used for electrode manufacture, and different materials are selected for different switches. For a pure metal, its performance usually cannot satisfy the actual requirement. To improve switch’s performance, an alloy is usually used as an electrode material. In this paper, thermal processes of six kinds of metal anodes (including pure metal and alloy anodes) are simulated and researched. The physical parameters of the pure metals all come from experiment results directly or are fitted by the experimental data. The physical parameters of the CuCr alloys are derived from Cu and Cr parameters. Two kinds of temperature calculation methods are used, which are called melting and solidification model and equivalent specific heat method, respectively. Simulation results show that W and Mo anodes have the higher temperature than Cu, Cr, CuCr25, and CuCr50 anodes. A pure Cr anode has the largest melting width and highest saturated vapor pressure and evaporation energy. A Cu anode has the biggest melting depth. A W anode has the smallest melting width and depth. Axial temperature gradient is related to the thermal conductivity, and the Cr anode has the largest axial temperature gradient. The thermal characteristics of CuCr25 and CuCr50 anodes are located between the pure Cu and Cr anodes. There are two melting points appearing in the results of CuCr alloys, and between the two melting points, the alloy anodes are in solid–liquid mixture state. [ABSTRACT FROM PUBLISHER]

Based on a steady-state 3-D magnetohydrodynamic (MHD) model, the high-current vacuum arc (HCVA) under combined effect of actual magnetic field (MF) and external transverse MF (ETMF) is simulated. The actual MF is generated by cup-type axial magnetic field contact system commonly used in commercial vacuum circuit breakers. The ETMF may cause the deflection of arc column, which is the main reason of the contact deflected erosion. According to some experimental results, the electron temperature in HCVA is assumed to be uniform and equal to 3 eV. Therefore, the MHD model is simplified by neglecting the electron energy equation to improve the simulation efficiency. With the three conservation equations (mass, momentum, and energy) of ion flow coupling solved, the spatial distributions of some flow parameters can be obtained. The influence of all three components of the MF is inserted by solving the magnetic transport equations sequentially. Proper boundary conditions are set on the cathode and anode side, which separated the cathode spots mixing region and anode sheath region from computation domain, respectively. Under the influence of the ETMF, the deflection of the plasma flow can be predicted, which may be helpful to understand the mechanism of the contact deflected erosion. [ABSTRACT FROM PUBLISHER]

This work investigates the dynamic characteristics of vacuum arc in the initial expansion process of a direct current (dc) circuit breaker. Based on the commercial cup-type axial magnetic field (AMF) contact, a 3-D transient magnetohydrodynamic (MHD) model is established. In the model, transient equations are used to study the transient characteristics of the vacuum arc. The effect of magnetic field hysteresis is also considered in the method. The dynamic mesh technique is adopted to simulate the electrode separation, which can make the simulation results more accurate. The simulation results show that, during the initial expansion process, with the increase in the current, the arc gradually expands in the electrode gap. The ion pressure, ion number density, axial current density, and energy flux density to the anode gradually decrease. Ion rotation can be observed under the influence of the magnetic field, and the rotation speed will increase with the increase in the current. Two different arc ignition positions are also compared. The result shows that igniting the arc at the contact center is more helpful to the success of the interruption of the dc circuit breaker. The appearance of the arc predicted by the model is consistent with the experimental results. [ABSTRACT FROM AUTHOR]

Studies of circuit breakers are of interest to high voltage direct current (HVDC) power system. The method for investigation of the switching arc characteristics of a 500 kV metallic return transfer breaker (MRTB) is presented in this paper, by coupling magneto-hydro-dynamics (MHD) arc model with the resonant circuit equations. 2-D MHD arc model taking account of important physical processes of mass flow, Ohmic heating, radiation energy transfer, momentum exchange, Lorentz force and current flow is developed, and then the influence of stray resistor is analyzed under the interrupting current of DC 4 kA. Calculation results of the distribution of temperature and gas pressure in the nozzle region are presented, where the shock wave and negative voltage-current characteristic of arc are discussed. The calculated arc current and voltage are in agreement with the experimental results to some extent, which could verify the validity of the calculation method partially. [ABSTRACT FROM AUTHOR]

Trigatrons have been widely used in many fields. However, the performance of trigatrons typically degrades as operational time increases. Among many influence factors, electrode erosion is a primary cause of trigatrons failure. In this paper, the peak current and pulsewidth of trigatrons are in the order of kiloampere (kA) and microsecond (\mus) , respectively, with an electrode size in the order of millimeters (mm). The discharge images show that the arc appearance looks filamentary in shape during the early period of the discharge. As the discharge process progresses, the arc expands and moves radially to the side surface of the anode. Simultaneously, electrode erosion experiments are conducted on the trigatrons in an atmospheric environment. Experimental results show that the erosion level becomes more serious with an increase of gap distance and discharge current. The weight loss of Mo and W electrodes with erosion times are very close to a linear distribution, however, weight loss rate of W-Cu electrodes increases more dramatically with an increase of erosion times. The erosion of WCu electrode is more pronounced than Mo and W electrodes the volume erosion rate of W is smaller than Mo, but the mass erosion rate of W is higher than Mo. Many cracks always appear on the W and Mo electrode surfaces, which are due to frequent and intensive interaction between the expansion and shrinkage of the electrode material. [ABSTRACT FROM PUBLISHER]

Plasma ignition mechanisms have always been the central issue in the electrothermal–chemical (ETC) launch technology. Generally, there are two types of ignition schemes, namely, the axial discharge scheme and the radial discharge scheme, and the two schemes are supposed to have different ignition characteristics. This work is devoted to study the features of different plasma ignition schemes in the ETC launch devices. A capillary discharge setup and a gap discharge setup are utilized in the experiments to represent the axial and radial discharge ignition schemes, respectively, and three types of propellants are used in the study. Using the measured data in the experiments, plasma heat fluxes are solved by a plasma–propellant interaction model. In addition, the propellant surface conditions are investigated by a scanning electron microscope after the plasma ignition experiments. The surface conditions of propellants in different ignition schemes display distinct features, which are analyzed to shed light on the characteristics of different ignition schemes and the responses of different propellants. Results are supposed to help in interpreting the plasma–propellant interaction mechanisms in different ignition schemes and provide references for the optimization design of plasma ignition installations in the ETC launch devices. [ABSTRACT FROM PUBLISHER]

Reduced critical electric field strength (E/N)cr is an important indicator for the evaluation of dielectric breakdown of SF6 and its mixtures. This paper aims to analytically investigate the dielectric breakdown properties of SF6-N2 mixtures. First, (ɑ-η)/N and (E/N)cr of SF6-N2 mixtures at room temperature, and then (E/N)cr of hot SF6 at several pressures are calculated and compared with other studies. The results confirmed the validity of the present calculation method and parameters. In addition, the electron energy distribution function, reduced ionization coefficient ɑ/N and attachment coefficient η/N of SF6-N2 mixtures are obtained at different proportions and under 1 atm in the gas temperature range 300-3000 K. Then (E/N)cr can be determined when the effective ionization coefficient (ɑ-η)/N = 0. The results show that in a certain temperature range, due to the effect of N2 on reduction in the proportion of high-energy electrons, (E/N)cr of SF6-N2 mixtures will be enhanced by increasing N2. [ABSTRACT FROM AUTHOR]

The initial expansion process in a drawn vacuum arc and the influence of axial magnetic field (AMF) were investigated experimentally in a demountable vacuum chamber. Arc characteristics were investigated with the aid of a high-speed digital camera with an exposure time of 2 \mu\s . In a drawn vacuum arc, the arc sequence begins with the bridge column arc formed after the rupture of the molten metal bridge. This column evolves into the transition mode, which consisted of a central column with few or no cathode spots (CSs) outside the column, and then into the fully diffuse mode. Experimental results indicated that in transition mode arc, the expansion process could be characterized by the appearance of CSs outside the central column, and could be classified into two patterns, “slow” expansion and “quick” expansion according to the characteristics of the formation and motion of new CSs (conducting channels) outside the central column of arc. The influence of AMF and its distribution on the expansion process was also investigated. Investigation results indicated that AMF had two contrary effects, i.e., inhibiting effect and prompting effect, on the initial expansion stage of drawn vacuum arc. Furthermore, saddle-shaped AMF could encourage the arc transition into diffuse mode more effectively than bell-shaped AMF. [ABSTRACT FROM PUBLISHER]

The method of magnetic field calculation and its influence on simulating the motion of cathode spots (CSs) in a vacuum arc were investigated in this paper. A method based on coordinate transformation and magnetic field superposition principle was proposed. In this method, the influence of current passing through an electrode rod and a contact plate was taken into account. Comparison was made between the proposed method and two simplified methods which were on the basis of the Biot–Savart law. Moreover, simulation results of CS motion with magnetic field calculated by different methods were shown and compared. Investigation results indicated that current passing through the contact plate and electrode rod could significantly influence the magnetic field and thus influence the simulation results of CS motion. Furthermore, it was shown that the proposed magnetic field calculation method had higher calculation accuracy with acceptable consumption of calculation time. [ABSTRACT FROM AUTHOR]

As a special phenomenon under transverse magnetic field (TMF) contacts, vacuum arc rotation deserves more attention. In this article, rotation characteristics of three typical TMF contacts, i.e., swastika-type, cup-shaped, and double-TMF contacts, are systematically studied. According to arc images, recorded by a high-speed camera, physical terms related to arc rotation such as rotation duration and rotation speed are clearly defined. The magnetic field and Lorentz force are calculated and the force balance of the moving arc is analyzed. On this basis, the effects of arc ignition mode, peak current, and contact type on arc rotation are investigated. Arc voltage noise as well as arc splashing outside caused by rotation is also discussed. The results show that the duration from ignition to rotation in two-point arc ignition (TPAI) mode is usually the shortest because of the rapidest constructed column formation. As the peak current increases, arc rotation becomes easier. Due to stronger TMF, the arc under double-TMF contacts has the longest rotation duration and the highest rotation speed. [ABSTRACT FROM AUTHOR]

Patterning a wide range of colloidal plasmonic nanoparticles into prescribed spatial arrangements, analogous to the formation of natural materials, enables the fabrication of functionalized structures with novel optical properties, such as Fano resonance, magneto-optical Kerr effect, negative refraction, etc. Currently, capillarity-assisted particle assembly is always utilized to place colloidal particles at predetermined positions by exploiting the capillary forces resulting from the motion of an evaporating droplet. However, this technique requires specialized equipment and the assembly process is always carried out in an open system, thereby introducing the risk of contamination and limiting its applications. Here, we present a microfluidic and magnetic field-assisted self-assembly of colloidal magnetic-plasmonic nanoparticles by utilizing magnetic dipole–dipole interactions resulting from the localized magnetic gradient field produced by an array of soft-magnetic elements and external magnetic bias field. The magnetized magnetic-plasmonic nanoparticles are controlled to deposit at the predesigned traps microfabricated onto the soft-magnetic elements. After deposition, the inlet velocity of the microchannel is improved to clear away the particles out of the traps, forming arrays of patterns with consistent structures. Furthermore, a Lagrangian–Eulerian model is introduced for the first time to predict the processing of the microfluidic and magnetic field-assisted self-assembly of colloidal magnetic-plasmonic nanoparticles by taking the magnetic and hydrodynamic forces and particle–fluid interaction into account. Our analysis demonstrates that the particle–fluid interaction not only plays a significant role in determining the final self-assembled nanostructures, but provides an opportunity to improve the consistency of the assembled nanostructures. The microfluidic and magnetic field-assisted self-assembly protocol proposed here enables the patterning of colloidal magnetic-plasmonic nanoparticles to be carried out in a controlled environment and also opens up a new direction for assembling complex structures. [ABSTRACT FROM AUTHOR]

A 3D transient model of a cathode-spot crater and droplet formation in a vacuum arc is developed. The model includes mass, momentum, heat transfer (energy), current continuity and potential equations. Using the energy flux density, current density and pressure as external parameters, the shape of the cathode-spot crater and the temperature, velocity, potential and current density distributions at each time step are determined via numerical simulation. Under symmetrical conditions, the 3D simulation results are highly consistent with those from the previous 2D model. The new cathode spot tends to appear in the direction in which the protrusion is largest because the liquid-metal velocity is lower and the liquid-metal ridge radius is larger in this direction. The effect of the external transverse magnetic field is considered by using a symmetric space function to represent the pressure and energy flux density of the plasma cloud. Simulation results show that even small changes in the plasma cloud distribution have a significant impact on the cathode-spot crater process and droplet formation. Since the pressure is asymmetric, the crater becomes asymmetric and the new cathode spot tends to appear opposite to the direction of the Ampere force. Based on this phenomenon, a possible explanation for the retrograde motion phenomenon of cathode spots is proposed. [ABSTRACT FROM AUTHOR]

The splitting and threshold currents of vacuum arc cathode spots in axial magnetic fields (AMFs) up to 220 mT are investigated experimentally. Measurements are made on electrodes of Cu and CuCr25 with electrode separations of 2 and 6 mm. The electrode diameter is 30 mm. All the experiments are conducted in a demountable vacuum chamber evacuated continuously by a turbo-molecular pump to a pressure of the order of 10−3 Pa. The spots are photographed using a high-speed digital camera with an exposure time of 2 μs. The AMF is applied by means of two permanent magnets placed symmetrically inside the chamber. The experimental results indicate that the splitting and threshold current decrease in the presence of AMF and tend to certain constant values when the field gets stronger. The splitting and threshold currents are considerably larger than Cu electrodes than those with CuCr25 electrodes. With increasing electrode separation, the splitting current decreases while the threshold current increases. Possible explanations are proposed to account for the experimental observations. [ABSTRACT FROM AUTHOR]

The formation of precursor plasma and ablation dynamics of Al thin liner explosion are investigated in this manuscript. The size of 12 mm in diameter, 10 μm in thickness Al liners are exploded on the Qin-1 facility (about 450 ns, 450 kA). An axial laser shadowgraphy and interferometry platform is set up to observe the plasma dynamics inside the liner. To solve the problem that the inside plasma density of the liner cannot be absolutely calibrated due to the lack of a zero plasma density area, we have established a CW laser interference system using a streak camera which can trace the interference lines over time. Low-density (10−7−10−6 g cm−3) precursor plasma is generated from the interior wall and flows towards the center with a velocity of about 150–200 km s−1, thus forming a column with high electron density by accumulation. Simultaneously, a high-density plasma layer flows toward the center at about 10 km s−1. The electron density of the central plasma column rises up rapidly after the precursor reaches the center and achieves 2.5 × 1018 cm−3 at 280 ns after the current starts. To fully understand the process, we have used the resistive magnetohydrodynamic code FLASH to realize a simulation to study interior precursor dynamics. We compared these simulation results with our experiments. Finally, we measured the voltage for the whole process and derived the inductance change and effective current radius. We compared the simulated current density distribution with the experimental result which proves that a considerable amount of current flows through the center plasma column, making the effective radius of current become smaller over time. [ABSTRACT FROM AUTHOR]

This paper presents the design and test of a gas-insulated linear transformer driver (LTD) cavity aimed at the Z-pinch experimental device CZ-34. The LTD cavity has a diameter of 2290 mm and a height of 346 mm. It consists of 23 main bricks and 1 trigger brick. Each main brick is comprised of two 100 nF capacitors connected electrically in series with a field-distortion gas switch. The trigger brick is comprised of two 50 nF capacitors connected in series with a compact multi-gap gas switch. All bricks are placed in the cavity filled with compressed SF6 and are pluggable like drawers. The trigger pulse generated by the trigger brick passes through an azimuthal transmission line to the trigger ring and makes the main bricks discharge synchronously. The LTD cavity can deliver ∼1 MA current pulse with a rise time of 115 ns to 0.08 Ω liquid resistance load when the charging voltage is ±100 kV, which is in good agreement with the circuit simulation results. Experimental results demonstrate the successful application of using gas insulation and pluggable bricks. The technical feasibility of the charging configuration, triggering method, and isolation resistors is verified. There is little difference in output performance as return-current rods replaced the outside metal cylinder, which provides a new path for the design of LTD cavities in series. [ABSTRACT FROM AUTHOR]

In this article, the plasma decay in the postarc stage of vacuum circuit breakers and the influence of the transverse magnetic field (TMF) on this process are investigated with a 2-D particle-in-cell model. In this model, distributions of electric field and plasma are solved by Poisson’s equation and Newton’s law, respectively, in 2-D Cartesian coordinate system. The distributions of charged particles and the velocity of the sheath development in the simulation without magnetic field in this article agree well with those in the simulation solved in cylindrical coordinate system in the published work. The TMF in the postarc phase leads to asymmetric distributions of charged particles, which slows down the plasma decay process in the postarc phase. In addition, the TMF results density fluctuations in the plasma and makes the plasma discontinuous and cluster, which can disturb the ion sheath near the postarc anode and result the local electric fields in the plasma. Electrons can be accelerated and gain high velocities in these local fields. These effects of TMF will slow down the dielectric recovery in the postarc stage of vacuum circuit breakers and may increase the risk of rebreakdown in the postarc stage when the vacuum circuit breaker interrupts large fault currents. [ABSTRACT FROM AUTHOR]

We investigate the evolution of the species from both the target and the air, and the plasma parameter distribution of the nanosecond laser-produced plasmas in atmospheric air. The technique used is spatially resolved optical emission spectroscopy. It is argued that the N II from the air, which is distributed over a wider region than the target species in the early stages of the discharge, is primarily formed by the shock wave. The ionized species have a larger expansion velocity than the excited atoms in the first ∼100 ns, providing direct evidence for space-charge effects. The electron density decreases with the distance from the target surface in the early stages of the discharge, and both the electron density and the excited temperature variation in the axial direction are found to become insignificant at later stages. [ABSTRACT FROM AUTHOR]

The objective of this paper is to investigate anode plume in high-current vacuum arc through experiments and simulations. A series of experiments are carried out in a demountable vacuum chamber at different current levels with the CuCr40 contact. Combined with arc voltage and arc image, the formation and evolution of typical anode modes, especially anode plume, are analyzed. The contact erosion and scanning electron microscopy (SEM) results are also discussed after experiments. Based on the experimental results, a two-dimensional (2D) magneto-hydro-dynamic (MHD) model is adopted to study the physical characteristics of anode plume. The experimental results show that a larger current leads to a more intense anode mode forming at smaller gap distance with a bigger and brighter arc column. Anode plume is generated between anode spot type 2 and current zero due to the obvious pressure difference between anode vapor and cathode plasma, which is confirmed by the simulation results of different anode temperatures. The contact erosion is more severe in the area where anode plumes frequently appear. The spatial distribution of number density, temperature, pressure, and electrical conductivity of anode plume are analyzed by simulations, and therefore the related experimental phenomena are explained. [ABSTRACT FROM AUTHOR]

Laser produced copper plasmas of different spot sizes in air were investigated using fast photography and optical emission spectroscopy (OES). The laser energy was 33 mJ. There were dramatic changes in the plasma plume expansion into the ambient air when spot sizes changed from ∼0.1 mm to ∼0.6 mm. A stream-like structure and a hemispherical structure were, respectively, observed. It appeared that the same spot size resulted in similar expansion dynamics no matter whether the target was located in the front of or behind the focal point, although laser-induced air breakdown sometimes occurred in the latter case. Plasma plume front positions agree well with the classic blast wave model for the large spot-size cases, while an unexpected stagnation of ∼80 ns occurred after the laser pulse ends for the small spot size cases. This stagnation can be understood in terms of the evolution of enhanced plasma shielding effects near the plasma front. Axial distributions of plasma components by OES revealed a good confinement effect. Electron number densities were estimated and interpreted using the recorded Intensified Charge Coupled Device (ICCD) images. [ABSTRACT FROM AUTHOR]

Focusing and separation of particles and cells by magnetophoresis are important steps in many applications. In simple terms, the magnetophoresis can be classified into a positive one and a negative one. The most important characteristic of negative magnetophoresis is that particles and cells can be manipulated in a label-free manner. In this paper, continuous separation based on negative magnetophoresis is studied numerically using a three-dimensional model considering the interaction between particles and the ferrofluid. Firstly, the separation of two sized particles is investigated with a straight microchannel with two opposite permanent magnets for focusing particles before their separation by another bias magnet. Then the influence of size and position of permanent magnets and geometry of microchannel are investigated to achieve a better particle separation. Moreover, the effects of the concentration of the ferrofluid, the size difference of the particles, the magnet-channel distance and the flow velocity on the particle separation are analyzed. [ABSTRACT FROM AUTHOR]

Experiments are performed on the 'Qin-1' double pulse current generator at Xi'an Jiaotong University to study the effect of the prepulse current on the implosion dynamics of two-wire Z-pinches. An independent prepulse current with an adjustable time-delay (Tdelay) is introduced to preheat the wires before the start of the main pulse current. An estimation of the deposited energy and the areal density reconstructed from the interferogram suggest that the wires are partly vaporized with a gasification fraction of ∼67%. The prepulse preconditioning has a redistribution effect on the load mass, which determines the subsequent implosion process. The planar implosion of the two-wire load with a preset Tdelay ⩽ 450 ns can be divided into the two-layer phase and the merged implosion phase. The snowplow-like implosion is the main characteristic of the shot with a 1050 ns Tdelay. The ablation streams gradually disappear with the increasing Tdelay. The proportion of the mass that participates in implosion is increased as the preset Tdelay increases from 120 ns to 1050 ns. [ABSTRACT FROM AUTHOR]