飞秒激光引导高压放电下的SF6等离子体时间分辨光谱特性

Time-resolved spectral characteristics of SF6 plasma under femtosecond laser-guided high-voltage discharge

SF6作为气体绝缘介质广泛应用于气体绝缘设备中,其电弧等离子体得到广泛研究,但对SF6电弧等离子体时间分辨光谱特性的研究还未见报道.本文在SF6环境中利用飞秒激光自聚焦产生的光丝引导高压放电,诱导产生SF6等离子体;利用光谱系统采集300—820 nm波长范围内的SF6等离子体光谱,对光谱谱线开展了识别和归属研究,S和F谱线主要分布在300—550 nm和600—800 nm波段,分析认为S和F原子主要由SF6被高能电子碰撞直接或间接产生,S离子由S原子被高能电子撞击产生.给出了SF6等离子体的时间分辨光谱,等离子体光谱强度先增大后减弱,均由带状光谱和分立光谱叠加而成,带状光谱主要是由轫致辐射和复合辐射共同作用导致,基于时间分辨光谱得到了部分S和F的荧光寿命.给出了电子温度和电子密度随时间的演化规律,二者演化规律基本相同,且都随延迟时间呈指数衰减.最后,利用Mc Whirter准则得到SF6等离子体处于局部热平衡.研究结果对于开展SF6分解机理和高压设备运行状态在线监测技术研究具有重要意义.

SF6 is widely used in gas insulated switchgear due to its excellent insulating and arcing performance. SF6 arc plasma has been extensively studied, but time-resolved spectral characteristics of SF6 arc plasma have not been reported. In this paper, the optical filament generated from focused femtosecond laser is used to guide the high-voltage discharge for generating SF6 plasma in SF6 environment. The SF6 plasma spectrum is obtained in a wavelength range of 300–820 nm, and the identification and attribution of the spectral lines are investigated.The S and F lines are mainly in the 300–550 nm band and 600–800 nm band, respectively. The analysis shows that the S and F atoms are mainly directly or indirectly generated by the collision between SF6 and high-energy electrons during the SF6 decomposition caused by discharge. The S ions are generated by the collision of S atoms with high-energy electrons. The time-resolved spectrum of the SF6 plasma superimposed by the continuous spectrum and the line spectrum is given, and its intensity increases and then decreases. The continuous spectrum is mainly generated by the combined effect of bremsstrahlung and recombination radiation. The recombination radiation is mainly generated by the collision of electron with ions and the recombination between molecular and atoms after SF6 decomposition. The fluorescence lifetime of S ion at 409.91 nm is 57 ns, and the fluorescence lifetime of F atom at 685.60 nm is 341 ns. The evolution law of electron temperature and density with time are given. The electron temperature reaches 2047 K in the early stage of plasma formation. After that, the electron temperature quickly falls to about 1600 K within 300 ns due to the rapid expansion of the plasma and the increase in energy loss during electron movement. At the beginning of discharge, a large number of electrons are generated due to the rapid decomposition of SF6, and the electron density is highest( 10.1 × 1017 cm-3). After that, the electron density drops rapidly within 200 ns because the recombination between electrons and ions decreases with delay time. Finally, it is proved that the SF6 plasma is in local thermal equilibrium based on the Mc Whirter criterion. The results are of great significance for studying the decomposition mechanism of SF6 and the on-line monitoring technique of highvoltage equipment.