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The discharge plasma channel (DPC) evolution process is observed by taking time-series self-emission intensified charge-coupled device (iCCD) photos and simultaneous shadow images. By adding neutral density filters before iCCD, the subtle structure of the DPC self-emission is observed. It is interesting that a treelike structure is observed soon after the voltage breakdown. Long exposure time photos demonstrate that this structure existed for hundreds of nanoseconds. An inner homogeneously luminous column arises latterly, forming a two-layer self-emission structure. Then, this column gradually occupies the whole DPC. Shadow images show that the expanding DPC maintains good axial uniformity, manifesting the long-standing uneven treelike structure only has limited impact on the energy distribution and the expansion process. The calculated expansion rate reaches its maximum value (4.75 km/s) not at the power peak, but 0.24 $\mu \text{s}$ after that. Then, the expansion rate undergoes fast drop and slow decline. In addition, it seems that the distributions of related plasma parameters experience an evolution from nonuniform to uniform.

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.

Underwater electrical explosions of Cu wires were carried out on a microsecond time scale to produce underwater shock waves. Experimental results show that the radial density distribution of the water flow after restrike contains several oscillations, observed as ∼1 mm-spaced layers in the backlit streak images and laser shadowgraphs. The phenomenon is attributed to the partial reheating of the exploding product (EP) by an interior restrike arc, which stimulates a compression wave propagating back and forth radially in the EP. Simulations are used to support the interior breakdown scenario and to demonstrate that each reflection of the compression wave at the EP–water interface launches a weak shock into the water, forming a multilayer structure. As the surrounding metallic vapor is ionized due to radiation and thermal conduction from the arc, the highly conductive plasma channel continues to extend radially and launches the main compression wave, which drowns out the multilayers when the power injection is sufficiently high.

Strong shock wave (SW) can be generated during underwater electrical wire explosion as the exploding wire rapidly expands and pushes the surrounding water. In this paper, a coupled model that describes the behaviours of the circuit, the exploding wire, and the evolution of SW was established. Wide range equation of state (EOS) data and conductivity data were used, making the calculation from solid state possible. The calculated discharge current, voltage across the wire, and trajectories of the wire radius and SW front were generally in good agreement with the experimental results, manifesting the validity of the model. Evolution of SW peak pressure, the process of energy conversion, and the effect of the discharge period were studied using the model. Simulation results showed that the radial attenuation of SW peak pressure is largely dependent on wire diameter and energy deposition process, while the efficiency of converting the deposited electrical energy to the mechanical energy of SW is not as sensitive, varying from 40% to 50% tens of microsecond after the current starts. Fast discharge tends to generate SW with higher initial SW peak pressure, while slow discharge enables higher initial energy storage within the limit of insulation and generates SW with slower radial attenuation. The presented model and numerical results could serve as a reference for parameter selection in related applications.