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.