Pulsed nanosecond discharges at atmospheric pressure produce non-thermal plasmas that can be used in various applications. The dynamics of such discharges are highly dependent on experimental conditions, particularly the propagation medium. In this study, pulsed nanosecond discharges in air in-contact with deionized water are investigated, and the dynamics of plasma emission are studied using an ultrafast imaging technique. Depending on the magnitude of the applied voltage, two discharge modes are observed: (i) highly-organized filaments and (ii) intense and less-organized plasma filaments that superimpose to the organized ones. Based on the acquired 1 ns resolved images, the highly-organized filaments can be considered as plasma dots that propagate at the water surface with velocities in the order of hundreds of km s⁻¹. Detailed analyses of the dots number, by imaging, and of the discharge properties, by current–voltage characteristics, reveal that the charge of each dot is constant (3–5 nC), irrespective of the experimental conditions. After being compared with the plasma bullets, usually produced by jets, the analyzed dots are proposed as plasma quanta.

大气压下的脉冲纳秒放电会产生可用于各种应用的非热等离子体。这种放电的动力学高度依赖于实验条件，尤其是传播介质。在这项研究中，研究了与去离子水接触的空气中的脉冲纳秒放电，并使用超快速成像技术研究了等离子体发射的动力学。根据施加电压的大小，可以观察到两种放电模式：（i）高度组织化的细丝和（ii）与组织化的细丝重叠的强而组织性较弱的等离子体丝。基于所获取的1 ns分辨图像，高度组织化的细丝可被视为等离子点，这些等离子点在水表面传播的速度约为数百km s ^-1。通过成像对点数进行详细分析，并通过电流-电压特性对放电特性进行详细分析，发现无论实验条件如何，每个点的电荷都是恒定的（3-5 nC）。在与通常由喷气机产生的等离子弹比较之后，建议将分析的点作为等离子量子。