开放空间等离子体对微波传输影响的模拟研究

以氮气为背景气体,采用脉冲式微波产生等离子体,使用另外一束连续波作为传输模拟对象,并基于扩散效应的全域模型分析等离子体电子温度与电子密度的演化过程。实验中放电气压为300Pa,实验结果表明:在微波脉冲开始之后极短的时间内,连续波接受信号发生剧烈衰减;而在微波脉冲结束后,连续波接受信号则缓慢恢复。微波传输主要受到等离子体电子密度的影响,而全域模型的计算结果显示等离子体电子密度在开始放电时迅速上升,甚至高于放电微波频率对应的临界密度,在放电微波脉冲结束时电子密度则缓慢下降。这说明开放空间中等离子体在失去能量维持之后,由于扩散效应占主导作用,电子密度不会迅速下降,此时连续波依然会被阻碍,直到电子密度下降到连续波频率对应的临界密度以下。

Simulation research on transmission of microwave by plasmas at open space

This paper adopts nitrogen as background gas, pulsed microwave to produce plasmas, another continuous wave as transmission simulation object, and Global Model with diffusion effect to analyze the evolution of electron temperature and density. The discharge pressure of the experiment is 300 Pa. The results of the experiment display that the reception signals of the continuous wave strongly decay in a short time after the beginning of microwave pulse, but the reception signals of the continuous wave recover slowly when the microwave pulse turns off. The microwave transmission is mainly affected by plasma electron density. The results of Global Model show that electron density increases rapidly, even higher than the critical density of discharge microwave, but decreases slowly when the discharge microwave pulse turns off. This means that the diffusion effect is dominant after plasmas at open space lose the sustained energy, so the electron density will not decrease rapidly and the continuous wave is still reflected, until electron density decreases to the value below the critical density of continuous wave frequency.