Temporal and spatial distributions of the electric field in an atmospheric pressure, ns pulse, positive and negative polarity helium plasma jets are measured by ps electric field induced second harmonic generation. The measurements have been done in a quasi-two-dimensional plasma jet impinging on liquid water, using a laser sheet and a focused laser beam positioned at different heights above the water surface. Absolute calibration of the electric field is obtained by measuring a known Laplacian electric field distribution for the same geometry and at the same flow conditions. The vertical component of the electric field is determined by isolating the second harmonic signal with the vertical polarization. The measured electric field is averaged over the span of the plasma jet, in the direction of the laser sheet or the focused laser beam. The spatial resolution of the laser sheet measurements is approximately 15 μm across the sheet, with the temporal resolution of 10 ns. The spatial resolution of the focused laser beam measurements is approximately 180 μm across the beam, with the temporal resolution of 2.5 ns. The results show non-monotonous electric field distribution across the jet, with two maxima produced by the surface ionization waves propagating over water. Considerable electric field enhancement is detected near the surface. Residual charge accumulation on the water surface is detected only in the negative polarity pulse discharge. The results provide new insight into the charge species kinetics and transport in atmospheric pressure plasma jets, and produce data for detailed validation of high-fidelity kinetic models.

中文翻译：

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用 E-FISH 方法测量大气压氦等离子体射流中的电场

电场在大气压力、ns 脉冲、正极性和负极性氦等离子体射流中的时间和空间分布通过 ps 电场感应二次谐波产生来测量。测量是在准二维等离子体射流撞击液态水时完成的，使用激光片和位于水面以上不同高度的聚焦激光束。电场的绝对校准是通过测量相同几何形状和相同流动条件下已知的拉普拉斯电场分布来获得的。通过隔离具有垂直极化的二次谐波信号来确定电场的垂直分量。测量的电场在等离子射流的跨度上，在激光片或聚焦激光束的方向上进行平均。激光片测量的空间分辨率约为 15 μm，时间分辨率为 10 ns。聚焦激光束测量的空间分辨率在整个光束上约为 180 μm，时间分辨率为 2.5 ns。结果显示整个射流的电场分布非单调，表面电离波在水面上传播产生了两个最大值。在表面附近检测到相当大的电场增强。仅在负极性脉冲放电中检测到水面上的残余电荷积累。结果提供了对大气压等离子体射流中电荷物质动力学和传输的新见解，并为高保真动力学模型的详细验证提供了数据。