均匀电场下SF_6/CF_4流注放电数值模拟

Streamer Discharge Simulation of SF_6/CF_4 in Uniform Electrical Field

文中从气体放电过程中微观粒子的运动特性出发,针对均匀电场中SF_6/CF_4混合气体的流注放电特性进行数值模拟。基于两项近似求解Boltzmann方程的方法,得到不同压强、混合比下SF_6/CF_4的电子能量分布(electron energy distribution function,EEDF)。根据EEDF计算折合电离系数和折合吸附系数,将该放电参数引入流体模型,以气体压强0.1 MPa、间隙距离5 mm为例模拟SF_6/CF_4的流注放电过程,研究放电过程中空间电子数密度随时间和空间的变化规律。结果表明:混合比一定时α/N随E/N的增大显著提高,E/N一定时混合气体中CF_4体积分数越高α/N值越大;随着电子崩向前发展,崩头的电子迅速增长,放电5 ns时电子数密度峰值达到9.7×10^(12)m^(-3),当间隙完全击穿,电极间形成等离子体导电通道,此时空间电子数密度分布基本均匀,电子数密度达到10^(17)数量级。

Based on the dynamic characteristics of micro particles in a discharge process, the streamer discharge properties ofSF6/CF4 gas mixtures were simulated in uniform electric field. The electron energy distribution functions ofSF6/CF4 at different pressures and mixing ratios were obtained by solving two-term Bohzmann equation, which were used to calculate the reduced ionization coefficients and adsorption coefficients. The coefficients were put into a fluid model to simulate the SF6/CF4 streamer discharge process at 0.1 MPa and in a 5 mm gap. The variation of electron number density with time and space were studied. Results show that α/N is increasing with higher E/N at a certain mixing ratio, as well as with higher CF4 volume fraction at a certain E/N. Electron number density in the streamer head increases rapidly with the development of electron avalanche, and the peak value at 5 ns reaches 9.7×10^12 m-3. However, the plasma conductive channel is formed when gap is broken down totally, and the electron number density is distributed uniformly with an order of magnitude of 10^17.