高功率微波作用下O-离子解吸附产生种子电子过程

种子电子是高功率微波大气击穿的根源, 研究高功率微波大气击穿时, 一般假设背景大气中存在种子电子, 此假设在低层大气环境中会给模拟结果带来较大误差. 本文建立了高功率微波强电场作用下O^-离子解吸附碰撞过程物理模型, 基于传统的空碰撞模型, 提出了改进的蒙特卡罗仿真方法, 编写了三维仿真程序, 对高功率微波作用下O^-离子的解吸附过程进行了仿真, 分析了O^-离子平均能量随时间的变化过程以及O^-离子与空气分子的碰撞过程, 得到了不同压强、场强、频率和击穿体积条件下种子电子平均产生时间. 理论与仿真结果表明, 随着频率增大, 种子电子平均产生时间变大, 随着击穿体积、场强以及压强增大, 种子电子平均产生时间变小. 最后, 考虑O^-离子与空气分子解吸附碰撞提供种子电子条件下, 给出了大气击穿时间理论与实验对比结果, 发现高功率微波频率较低时, 该种子电子产生机理可以解释实验结果, 而高功率微波频率较高时, 该机理下种子电子平均产生时间过长而与实验数据不符.

Seed electron production from O- detachment in high power microwave air breakdown

The existence of seed electrons is the precondition of air breakdown induced by high power microwave (HPM). Seed electrons are usually assumed to exist in background atmosphere when simulating the air breakdown triggered by HPM. However, this assumption may lead to some large errors especially in lower atmosphere where the number of electrons is very small. We establish a physical model of seed electron production from O^- detachment collision with air molecules using the Monte Carlo method. A three-dimensional Monte Carlo program is developed to simulate this process. The average energies of O^- and the average generation time of seed electrons under different electric intensities, frequencies, air pressures and breakdown volumes are obtained through simulation. The simulations show that the average generation time of seed electrons becomes longer with the increase of air pressure or the HPM frequency. The average seed electron generation time becomes shorter with the increase of electric intensity or breakdown volume. Finally, we simulate the processes of O^- detachment collision with air molecules under the same experimental conditions. The comparative results show that the seed electron generation from O^- detachment can explain the experimental results when the HPM frequency is low, while at higher frequencies, the average seed electron generation time becomes so long that it cannot correspond to the experimental value. Therefore some other mechanisms should be considered in the higher frequency case.