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Study of reliability in laser Thomson scatturing diagnostics oflow-temperature plasmas

低温等离子体激光汤姆逊散射诊断的可靠性研究

基本信息

批准号：
18540491
负责人：
KONO Akihiro
金额：
$ 2.14万
依托单位：
Nagoya University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2006
资助国家：
日本
起止时间：
2006 至 2007
项目状态：
已结题

项目摘要

In laser Thomson scattering measurements of low-temperature plasmas, the plasma is irradiated with a focused laser beam. The laser energy density in the focal region is very high and it may be possible that the density of electrons produced via multiphoton ionization is not negligible in comparison with that of free electrons exiting in the plasma &um the beginning. Thus, quantitative understanding of this point is important for carrying out reliable Thomson scattering diagnostics. An experimental setup was constructed to detect electrons produced via multiphoton ionization; the electrons are collected by a dc-biased parallel-plate probe placed in a vacuum chamber, between the electrodes of which a NclYAG laser beam is focused. Various gases or spatial afterglow plasmas are introduced into the chamber. The laser beam profile was measured in a separate experiment to estimate the volume in which multiphoton ionization occurs. Preliminary results using a〜200-mJNd:YAG laser(second harmonics, 532 run)focused with a400 mm convex lens indicates the following Metastable Ar atoms are multiphoton ionized with a high probability but the ground-state Ar atoms give no significant signal Ground-state N2 and 02 gases give clear multiphoton ionization signal and the efficiency fir the latter is larger by more than a factor of 20 than the former, suggesting that one must he very careful about measurements for 02 plasma except in low-pressure conditions. The present charge-correction probe needs an improvement in order to obtain better definition of the charge-generating volume. This improvement is in progress and should lead to more quantitative data of multiphoton ionization efficiency for various kinds of molecules in the ground-states and metastable states, which should clarify the conditions for performing reliable Thomson scattering diagnostics of plasmas using various kind of gases.

在低温等离子体的激光汤姆逊散射测量中，用聚焦的激光束照射等离子体。聚焦区的激光能量密度很高，与等离子体中自由电子的密度相比，通过多光子电离产生的电子密度是不可忽略的。因此，定量了解这一点是重要的进行可靠的汤姆逊散射诊断。构建了一个实验装置来检测通过多光子电离产生的电子;电子由放置在真空室中的直流偏置平行板探针收集，在电极之间聚焦NclYAG激光束。各种气体或空间余辉等离子体被引入到腔室中。在单独的实验中测量激光束轮廓以估计多光子电离发生的体积。用400 mm凸透镜聚焦的200-mNd：YAG激光（二次谐波，532 nm）的初步结果表明，下列亚稳态Ar原子有很高的几率被多光子电离，但基态Ar原子没有明显的信号。基态N_2和O_2气体有明显的多光子电离信号，后者的效率比前者大20倍以上。目前的电荷校正探头需要改进，以获得更好的定义的电荷产生体积。这一改进正在进行中，并应导致更多的定量数据的多光子电离效率的各种分子在基态和亚稳态，这应该澄清的条件进行可靠的汤姆逊散射诊断等离子体使用各种气体。