Enhancing higher-energy spectral resolution for electron particle simulations in air

In the presence of an electric field, electrons would theoretically accelerate asymptotically to relativistic energies. However, regular collisions with air molecules limit the increase in electron energy. The stochastic nature of collisions leaves a theoretical probability that an electron elude inelastic collisions thereby accumulating an atypically high energy. Such an electron, under specific criteria, could be called a “thermal” or “cold runaway”. Depending on the electric field, the runaway probability might be too low to be computationally observed without resorting to Monte Carlo importance sampling. This article provides a method for fixing the spectral energy resolution of electrons through the combined methodology of Russian roulette and probabilistic splitting in order to render the study of runaway mechanism amenable to electron swarm simulations in various plasma physics applications.在电场作用下，电子理论上会渐近加速至相对论性能量（relativistic energies）。然而，与空气分子的常规碰撞会限制电子能量的增长。碰撞的随机特性使得电子存在理论概率规避非弹性碰撞（inelastic collisions），从而积累出异常高的能量。满足特定条件的此类电子，可被称为“热逃逸电子”或“冷逃逸电子”。根据电场强度的不同，逃逸概率可能极低，若不采用蒙特卡洛重要性采样（Monte Carlo importance sampling）方法，便难以通过计算观测到该现象。本文提出一种结合俄罗斯轮盘赌（Russian roulette）与概率分裂法的方案，以校正电子的光谱能量分辨率，使得针对逃逸机制的研究可适配于各类等离子体物理应用中的电子群模拟。