The formation of O and H radicals in a pulsed discharge in atmospheric pressure helium with water vapour admixtures
The formation of O and H radicals in a pulsed discharge in atmospheric pressure helium with water vapour admixtures
复制标题
DOI：
10.1088/1361-6595/acd57f
复制
发表时间：
2023-05
影响因子：
3.8
通讯作者：
A. Brisset;M. Bieniek;L. Invernizzi;M. Hasan;J. Walsh;K. Niemi;E. Wagenaars
中科院分区：
文献类型：
--
作者：
A. Brisset;M. Bieniek;L. Invernizzi;M. Hasan;J. Walsh;K. Niemi;E. Wagenaars
在He + H2O（0.1%和0.25%）中，以2.2 mm间隙的针脚几何形状产生的90 ns脉冲放电中O和H自由基的时空分布进行了实验研究和一维流体模拟。利用皮秒分辨率双光子吸收激光诱导荧光测量了O和H自由基的密度及其激发态的有效寿命。实验结果与模拟结果吻合较好。O和H的密度沿放电轴呈均匀分布。尽管高压脉冲长度为90ns，但在电流脉冲结束后约1 μs， O的密度达到峰值，在0.1% H2O下达到2 × 1016 cm−3。在衰减之前，它在10 μs内几乎保持恒定。模拟表明，在放电电流峰值时，容器几何形状中心的电子温度（Te）在6 ~ 4 eV之间，在90 ns后，在约50 ns内降至0.5 eV以下。因此，在放电（<100 ns）期间，O主要通过电子冲击O2直接解离产生，而在余辉初期（100 ns ~ 1 μs）， O主要通过O2 +的解离重组产生。O的主要损失机制最初是电子撞击电离，当T e下降后，主要变成与He2*和He*的Penning电离，以及与O+和He的三体复合。在100 ~ 200 μs时间尺度上，O主要通过径向扩散损失。H的生成表现出类似的行为，在1 μs下达到0.45 × 1016 cm−3，这是由于H2O通过电子冲击（<100 ns）直接解离，然后是电子-离子复合过程（从200 ns到1.5 us）。氢主要通过与He*和He2*的潘宁电离、电子碰撞电离和与O+的电荷交换而损失。水蒸气浓度的增加，从0.1%增加到0.25%，对氢形成过程的性质影响不大，但会引发更强的初始O生成，目前模型不能令人满意地再现这一过程。从这项研究中得出的结论是，脉冲放电中O和H密度的增加在电子碰撞离解过程和额外的余辉过程之后继续进行，尤其是通过O2 +和H2 +的离解重组。
The spatio-temporal distribution of O and H radicals in a 90 ns pulsed discharge, generated in a pin–pin geometry with a 2.2 mm gap, in He + H2O (0.1% and 0.25%), is studied both experimentally and by 1D fluid modelling. The density of O and H radicals as well as the effective lifetimes of their excited states are measured using picosecond resolution two-photon absorption laser induced fluorescence. Good agreement between experiments and modelling is obtained for the species densities. The density of O and H is found to be homogenous along the discharge axis. Even though the high voltage pulse is 90 ns long, the density of O peaks only about 1 μs after the end of the current pulse, reaching 2 × 1016 cm−3 at 0.1% H2O. It then remains nearly constant over 10 μs before decaying. Modelling indicates that the electron temperature (Te) in the centre of the vessel geometry ranges from 6 to 4 eV during the peak of discharge current, and after 90 ns, drops below 0.5 eV in about 50 ns. Consequently, during the discharge (<100 ns), O is predominantly produced by direct dissociation of O2 by electron impact, and in the early afterglow (from 100 ns to 1 μs) O is produced by dissociative recombination of O2 +. The main loss mechanism of O is initially electron impact ionisation and once T e has dropped, it becomes mainly Penning ionisation with He2* and He* as well as three-body recombination with O+ and He. On time scales of 100–200 μs, O is mainly lost by radial diffusion. The production of H shows a similar behaviour, reaching 0.45 × 1016 cm−3 at 1 μs, due to direct dissociation of H2O by electron impact (<100 ns) followed by electron–ion recombination processes (from 200 ns to 1.5 us). H is dominantly lost through Penning ionisation with He* and He2* and by electron impact ionisation, and by charge exchange with O+. Increasing concentrations of water vapour, from 0.1% to 0.25%, have little effect on the nature of the processes of H formation but trigger a stronger initial production of O, which is not currently reproduced satisfactorily by the modelling. What emerges from this study is that the built up of O and H densities in pulsed discharges continues after electron-impact dissociation processes with additional afterglow processes, not least through the dissociative recombination of O2 + and H2 +.