Underwater spark discharges are used in multiple practical applications including plasma closing switches, water treatment, plasma channel drilling and mineral processing, waste recycling, treatment of metals, and medical lithotripsy. Spark discharges in water have been studied for several decades; however, despite significant research efforts and progress in this area, further investigation into the efficiency of plasma acoustic sources and their optimization is required in order to expand their practical application. This paper is aimed at investigation of the electrical and hydrodynamic parameters of underwater plasma-generated cavities, including plasma resistance, energy delivered into the plasma cavity, period of cavity oscillations, and characteristics of pressure impulses. Different energy levels, breakdown voltages, and gap distances were used in the present study to allow systematic analysis of these electrical and hydrodynamic parameters. Empirical scaling relations that link the maximum acoustic pressure and the period of cavity oscillations with the energization parameters and the resistance of plasma have been obtained. These empirical functions can be used for optimization of the plasma acoustic sources and for tailoring their parameters for specific practical applications.

The presence of a low density area is beneficial to the facilitation of the underwater pulsed spark discharge, which can be achieved by artificially injecting gas bubble in between the inter-electrode gap. The generation of intensive acoustic waves by such gas-bubble-guided spark discharges makes them promising underwater acoustic sources in multiple practical applications. This paper is aimed at comprehensive investigation of the guiding effect of the injected bubble on the pre-breakdown process of underwater pulsed spark discharges and potential correlations between their subsequent electrical and acoustic parameters with the purpose of optimizing the acoustic emission. The breakdown probability and the pre-breakdown delay were used to evaluate the general facilitation effect brought by the injected bubble. Experimental and numerical works have been conducted and allow observation on the dynamics of the injected bubble under the influence of the applied voltage. Different guiding modes of the injected bubble for plasma streamers' propagation have been observed regarding its relative position. The characteristics of the electrical properties of gas-bubble-guided spark discharges, including the plasma resistance and the plasma energy density, were analyzed by relating them with the breakdown voltage. The dependency of the acoustic wave amplitude and the acoustic efficiency on these electrical parameters was verified, which provides solid regulation principles for the optimization of the plasma-acoustic system for target practical applications.

Recently, the applications of cold atmospheric plasma (CAP) in liquid treatment have attracted increasing attention owing to its excellent medical efficacy. It has been proved that CAP can effectively enhance the biological activity of vegetable oils due to the generation of reactive species. Optimising the reactor parameter is an important approach to regulate reactive species in plasma‐activated oil to obtain better biological effects. In this study, a self‐made jet array driven by a pulsed power supply was used to generate large‐area plasma to irradiate perilla seed oil (PSO), with the formation of plasma‐activated perilla seed oil (PAPSO). By means of laser‐induced fluorescence and chemical titration, the relative density of hydroxyl radical radical in plasma jet, as well as the activity of PAPSO were measured under different discharge parameters, and realised the control of the activity of PAPSO. In vitro experiments showed that PAPSO significantly enhanced its ability to inhibit cancer cells proliferation and induce apoptosis after plasma treatment, which provides a reference for cancer treatment. This study is helpful to further understand the influence of plasma dose effect on the activity of media and provide guidance for related plasma medical applications.

The atmospheric pulsed dielectric barrier discharges have been studied extensively for their huge potential in plasma applications. In this paper, a comprehensive study of discharge characteristics in atmospheric He and CO₂ discharges driven by pulsed voltages is carried out by experimental measurements and numerical simulation. The computational data indicate that during a plateau phase in the pulsed CO₂ discharge, a strong electric field of 2.6 kV/cm always sustains to drive the heavy ions of ${\text{CO}}_2^{+}$ and ${\text{CO}}_3^{-}$ to the surfaces of dielectric material, forming a discharge current density of about 2.5 $\text{mA}/\mathrm{c}{\mathrm{m}}^2$ . The experimental measurements and simulation data show that the duration of the plateau phase has a significant influence on the discharge characteristics of pulsed CO₂ discharges but only slightly affects on the discharge evolution in pulsed He discharge. By increasing the duration of the plateau phase, the surface charges accumulated on the dielectric materials are also enhanced, and then, a stronger induced electric field is established in the discharge region, resulting in a larger discharge current density during the pulse fall phase, which is not observed in the pulsed He discharge. In this study, the different discharge behaviors of pulsed He and CO₂ discharges are compared in detail, which can enhance the understanding of the underpinning discharge physics, suggesting the optimized ways to utilize pulsed discharges with various plasma-forming gases.

This paper is focused on investigation of the electrical, hydrodynamic, and acoustic parameters of underwater plasma discharges, stabilized with thin copper wires. The experimental current and acoustic waveforms have been obtained using different combinations of the circuit capacitance, charging voltage, and wire length. The resistances of plasma discharges have been calculated for all combinations of electrical and topological parameters, based on the constant resistance approach. Phenomenological scaling relationships that link the plasma resistance and the total energy delivered to the plasma, the period of discharge cavity oscillation and the peak magnitude of the acoustic impulse have been obtained. These relationships can be used in optimization of the acoustic output from the wire-guided discharges for different practical applications.