Optical diagnosis of a kHz-driven helium atmospheric pressure plasma jet
Optical diagnosis of a kHz-driven helium atmospheric pressure plasma jet
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DOI：
10.1017/s0022377822000538
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发表时间：
2022-06
影响因子：
2.5
通讯作者：
C. McDonnell;R. Irwin;S. White;W. Graham;D. Riley
中科院分区：
文献类型：
--
作者：
C. McDonnell;R. Irwin;S. White;W. Graham;D. Riley
本文着重于利用几种不同的光学诊断来实验表征纯氦大气压等离子体射流。沿等离子体羽流进行轴向电场测量，采用基于氦$492.2$ nm谱线偏振相关Stark光谱的非扰动方法。电场沿羽流长度随距离增加而增加，达到24.5 kV cm ^{-1}$。电场的增加速率与氦气流量有关，较小的氦气流量随距离的增加速度比较大的氦气流量快，典型值保持在相同的范围内。这种灵敏度与氦气和周围空气之间的气体混合有关。包括气体流动的纹影成像来支持这一点。目标的增加表明，进一步增加测量电场在近距离的目标，与这种增加的幅度强烈依赖于管出口和目标之间的距离。电场的相对增加表明，与塑料相比，水的导电靶平均更大。一个最小的设备光学配置，这里被称为快速二维单色成像，介绍了一种估计等离子体内激发态密度的方法。在$706.5$ nm处的上氦态密度为$ 133s $ $ $^{3} $ $ $ {1}$ $ $\rightarrow$ $ 152p $ $ $^{3}P^{0} ${0,1,2}$和$728.1$ nm处的$ 133s $ $ $ $^{1} $ $ $\rightarrow$ $ 152p $ $ $^{1}P^{0}_{1}$的数量级为$10^{10}$ - $10^{11}$ cm${-3}$。
This paper focuses on utilizing several different optical diagnostics to experimentally characterize a pure helium atmospheric pressure plasma jet. Axial electric field measurements were carried out along the plasma plume through the use of a non-perturbing method based on polarization-dependent Stark spectroscopy of the helium $492.2$ nm line. The electric field is shown to increase with distance along the plume length, reaching values as high as $24.5$ kV cm$^{-1}$. The rate of increase of the electric field is dependent on the helium gas flow rate, with lower gas flows rising quicker with distance in comparison with larger flow rates, with the typical values remaining within the same range. This sensitivity is linked to gas mixing between the helium and surrounding ambient air. Schlieren imaging of the gas flow is included to support this. The addition of a target is shown to further increase the measured electric field in close range to the target, with the magnitude of this increase being strongly dependent on the distance between the tube exit and target. The relative increase in the electric field is shown to be on average greater for a conducting target of water in comparison with plastic. A minimal equipment optical configuration, which is here referred to as fast two-dimensional monochromatic imaging, is introduced as an approach for estimating excited state densities within the plasma. Densities of the upper helium states for transitions, $1s3s$ $^{3}S_{1}$ $\rightarrow$ $1s2p$ $^{3}P^{0}_{0,1,2}$ at $706.5$ nm and $1s3s$ $^{1}S_{0}$ $\rightarrow$ $1s2p$ $^{1}P^{0}_{1}$ at $728.1$ nm, were estimated using this approach and found to be of the order of $10^{10}$–$10^{11}$ cm$^{-3}$.