Titan和其他N2：CH4混合物与N2：O2混合物大气中流光传播的比较
Streamer propagation in the atmosphere of Titan and other N2:CH4 mixtures compared to N2:O2 mixtures
摘要：
流光，薄，电离等离子体通道，形成闪电放电的早期阶段。在这里，我们的方法研究地外闪电的形成和传播的流光放电在各种氮-甲烷和氮-氧混合物与氮的水平从20%到98.4%的研究。我们提出的摩擦力和击穿场Ek在各种N2：O2（地球一样）和N2：CH 4（钛一样）的混合物。摩擦力的强度在N2：CH 4混合物中较大，而在与甲烷的混合物中的击穿场是与氧气的混合物中的一半大。我们使用一个2.5维的Monte Carlo粒子在细胞程序与圆柱对称模拟电子雪崩的发展从一个初始的电子-离子补丁在周围电场之间的1.5 Ek和3 Ek。我们比较了甲烷和氧气混合物的电子密度、电场、波前速度以及雪崩-流光跃迁的发生。而我们观察到在所有考虑的情况下，在氧气中的流光的形成，我们观察到流光inceptions在甲烷中的小百分比的氮或大电场。对于大百分比的氮或对于小的场，电离的效率不足以在模拟域的长度内形成流光通道。在氧气中，正和负流光移动更快的小百分比的氮气。在与甲烷的混合物中，电子或流光前沿的移动速度比与氧气的混合物慢10-100倍;甲烷的百分比越高，前沿的移动速度就越快。
英文摘要：
Streamers, thin, ionized plasma channels, form the early stages of lightning discharges. Here we approach the study of extraterrestrial lightning by studying the formation and propagation of streamer discharges in various nitrogen-methane and nitrogen-oxygen mixtures with levels of nitrogen from 20% to 98.4%. We present the friction force and breakdown fields Ek in various N2:O2 (Earth-like) and N2:CH4 (Titan-like) mixtures. The strength of the friction force is larger in N2:CH4 mixtures whereas the breakdown field in mixtures with methane is half as large as in mixtures with oxygen. We use a 2.5 dimensional Monte Carlo particle-in-cell code with cylindrical symmetry to simulate the development of electron avalanches from an initial electron-ion patch in ambient electric fields between 1.5Ek and 3Ek. We compare the electron density, the electric field, the front velocities as well as the occurrence of avalanche-to-streamer transition between mixtures with methane and with oxygen. Whereas we observe the formation of streamers in oxygen in all considered cases, we observe streamer inceptions in methane for small percentages of nitrogen or for large electric fields only. For large percentages of nitrogen or for small fields, ionization is not efficient enough to form a streamer channel within the length of the simulation domain. In oxygen, positive and negative streamers move faster for small percentages of nitrogen. In mixtures with methane, electron or streamer fronts move 10-100 times slower than in mixtures with oxygen; the higher the percentage of methane, the faster the fronts move.
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