Stucy on interaction between electromagnetic wave and rocket exhaust plume

我们估计了固体火箭发动机羽流的微波衰减，假设衰减是由（1）铝/氧化铝颗粒，和（2）自由电子。计算结果表明，真实的火箭发动机中的微波衰减是由自由电子引起的。数值模型包括羽流气体的化学反应模型。数值计算结果表明，通过喷嘴时，化学反应被冻结，电子的摩尔分数保持不变，电子数密度由气体的压强和温度计算得到。电子摩尔分数与发动机药柱中的杂质（如钠）含量密切相关，本文采用二维GEM（Computational Electro Magnetics）模型分析了微波在弱电离羽流气体中的传播。结果表明：微波的衍射和折射效应不可忽略，微波衰减与微波频率的关系很小，微波衰减与电子数密度成正比，微波衰减与电子碰撞频率成反比。理论计算结果与实验结果在定量上一致。由实验结果估算的电子摩尔分数比理论结果小一个数量级，其原因被认为是杂质比假定的少。在通过发动机羽流传播的接收微波中没有观察到微波调制。

We estimated microwave attenuations by a solid rocket motor plumes, assuming that the attenuation is caused by (I)Aluminum/Alumina particles, and (2)free electrons. The expressions and values of the attenuations show that the microwave attenuation observed in real rocket motors is caused by free electorons.We analyzed the plume of the H-IIA SRB-A solid rocket motor plume numerically. The numerical model includes a chemical reaction model of the plume gas. The numerical result shows that the chemical reactions are frozen and the mole fraction of electron is constant through the nozzle ; the electron number density is calculated from the pressure and temperature of the gas. The electron mole fraction is strongly depends on the amount of impurity, such as the sodium, in the motor grainWe analyzed microwave propagation in the weakly-ionized plume gas using a two dimensional GEM (Computational Electro Magnetics) model. Results show that (1)the effect of diffraction and refraction of microwave cannot be neglected, (2)the microwave attenuation depends weakly on the microwave frequency, (3)the microwave attenuation is proportional to electron number density, and (4)the microwave attenuation is in inverse proportion to the electron collision frequency.We conducted a microwave attenuation measurement in the ground firing tests. The theoretical results agrees quantitatively with the experimental result. The electron mole fraction estimated from the experimental result is I order less than that of the theoretical result ; the cause of it is considered the impurities were less than the assumed amount. No modulation of microwave is observed in the received microwave which propagates through the motor plume.