698 / 2022-03-31 16:09:37

Investigation on Decay Characteristics of Laser-induced Plasma in C4F7N/N2 mixed gases by Thomson Scattering Test

C4F7N/N2,Thomson scattering,Laser-induced plasma

Investigation on Decay Characteristics of Laser-induced Plasma in C4F7N/N2 mixed gases by Thomson Scattering Test

With the rapid development of power system, the society has put forward higher requirements for the development of green and ecological electricity. The traditional insulating gas SF₆ no longer meets the requirements of being eco-friendly because of its severe greenhouse effect and long atmospheric life. As an alternative gas, sevofluoroisobutyronitrile (C₄F₇N) has received wide attention in recent years. Because C₄F₇N boils at a high temperature (-4.7 °C at 1 bar), N₂ or other gases with lower boiling temperatures will be added to it in engineering applications. Therefore, the goal of this work is to investigate the plasma characteristics of C₄F₇N/N₂ mixtures.

Arc plasma experiment has high time and economic cost, and the instability of arc leads to poor repeatability of the experiment. Therefore, in this study, laser-induced plasma with high repeatability is used, and Thomson scattering diagnosis technology is used to measure the electron number density and electron temperature of the plasma with high space-time resolution. Multiple processing of Thomson scattering data ensures the quality of spectral data and the reliability of measurement results. The plasma is generated by a Nd:YAG laser (1064 nm, 200 mJ, 7 ns) focusing into a chamber filled with a C₄F₇N/N₂ mixture at 1 bar pressure. At the same time, another harmonic Nd:YAG laser (532 nm, 40 mJ, 6 ns) is used as a probe laser, which travels radially along the plasma and receives the Thomson scattering signal at a vertical direction of 90 degrees. Radial distribution of electron density and temperature in plasma can be obtained by analyzing Thomson scattering signals.

The results show that when the proportion of C₄F₇N increases , the time index of electron density and electron temperature decreases , which indicates that the plasma decays faster with the increase of C₄F₇N proportion. For comparison, we studied the decay of SF₆ plasma.

In conclusion, as a potential alternative to SF₆, C₄F₇N gas may have low GWP and potentially superior arc extinguishing performance.