论文标题
等离子中中性原子非热速度分布的碰撞 - 能量cascade模型
A Collisional-Energy-Cascade Model for Nonthermal Velocity Distributions of Neutral Atoms in Plasmas
论文作者
论文摘要
长期以来，已经观察到比麦克斯韦的尾巴比麦克斯韦元素大得多的非热速度分布。从历史上看，这种速度分布已经通过两个温度的麦克斯韦分布来建模。在本文中，我提出了一个基于碰撞能量级联的模型，该模型已在颗粒材料领域进行了研究。在碰撞的能量级联反应中，粒子合奏在高能区域经历了能量输入，粒子之间的弹性碰撞产生的熵产生以及能量耗散。对于自由基原子，能量输入可能是由分子解离的弗朗克 - 康登能量引起的，或与热离子的电荷交换碰撞，最终通过与墙壁的碰撞来消除输入能量。我表明，碰撞能量级联的稳态速度分布通过广义的Mittag-Leffler分布近似，这是Maxwell分布的一参数扩展。该参数指示非心率的程度，与熵产生的能量耗散的相对重要性有关。将该模型与具有能量输入和耗散壁碰撞的简化气体系统的直接分子动力学模拟进行了比较，以及一些实验观察到的血浆中光自由基的速度分布。
Nonthermal velocity distributions with much greater tails than the Maxwellian have been observed for radical atoms in plasmas for a long time. Historically, such velocity distributions have been modeled by a two-temperature Maxwell distribution. In this paper, I propose a model based on collisional energy cascade, which has been studied in the field of granular materials. In the collisional energy cascade, a particle ensemble undergoes energy input at the high-energy region, entropy production by elastic collisions among particles, and energy dissipation. For radical atoms, energy input may be caused by the Franck-Condon energy of molecular dissociation or charge-exchange collision with hot ions, and the input energy is eventually dissipated by collisions with the walls. I show that the steady-state velocity distribution in the collisional energy cascade is approximated by the generalized Mittag-Leffler distribution, which is a one-parameter extension of the Maxwell distribution. This parameter indicates the degree of the nonthermality and is related to the relative importance of energy dissipation over entropy production. This model is compared with a direct molecular dynamics simulation for a simplified gaseous system with energy input and dissipative wall collisions, as well as some experimentally observed velocity distributions of light radicals in plasmas.
