离子发动机放电阴极的离子声激励溅射腐蚀机理研究

The sputtering erosion of discharge cathode is one of main factors that restrict the life and reliability of the Ion Thrusters. Because the electrostatic potential difference in Ion thruster cannot provide enough energy to accelerate ions to exceed the material sputtering threshold, explaining the high ion sputtering energy and mechanism has been the focus in the sputtering erosion mechanism research of discharge cathode. Recent experiments have found that there are high frequency ion acoustic waves (potential oscillations) near the cathode, which provides intuitive explanation of the high sputtering energy source. But the characteristics and generation mechanism of ion acoustic waves in Ion thrusters are still not quite clear. By analyzing the ion acoustic characters and dispersion relations, this project aims to exploring the internal relations between the amplitude-frequency parameters of ion acoustic wave-potential fluctuation and plasma parameters and electromagnetic parameters, so as to establish the mathematical model of the potential oscillation. And combined with using hybrid-PIC method, the sputtering erosion process simulation study of discharge cathode is going to be performed; the simulation results will also be compared with present experimental results for further analysis. Through the study, we aim to understanding the generation mechanism of ion acoustic waves, and the influence of key physical processes, especially the ion acoustic waves, on the cathode erosion, which will enhance our knowledge on sputtering erosion mechanism of discharge cathode. The study results can also provide important basis for the ion engine improvement, new assessment's reliability and life prediction of Ion thruster.

放电阴极的溅射腐蚀是制约离子发动机可靠性和寿命的主要因素之一。由于离子发动机中的静电势差不足以提供大于材料溅射阈值的能量，因而解释高溅射能量离子的来源和产生机制一直是放电阴极溅射腐蚀机理研究中的焦点。最近的实验发现放电阴极附近存在大幅高频离子声波脉动（电势振荡），直观解释了高溅射能量的来源，但对离子发动机内离子声波的特性和产生机制仍不十分清楚。本项目拟通过分析离子发动机中离子声波的特性、色散关系，得到离子声波电势脉动幅频与等离子体参数、电磁参数的内在关系，从而建立解析的电势振荡数学模型；然后结合混合PIC方法模拟放电阴极的溅射腐蚀过程，并和已有的实验结果进行比较分析。通过该研究明晰离子发动机内离子声波的产生机制，关键物理环节、特别是离子声波电势脉动对放电阴极腐蚀过程的影响，从而加深对放电阴极溅射腐蚀机理的认识。研究可为离子发动机方案改进、新方案可靠性评估、寿命预估等方面提供重要依据。

空心阴极是离子发动机的核心部件，它作为离子发动机的电子源和中和器，是必备核心真空电子器件。空心阴极工作放电时存在一个普遍的现象，阴极附近会有大幅电势脉动。而该电势脉动会产生高能离子，进而造成比预期更为严重的阴极部件腐蚀。空心阴极的溅射腐蚀是制约离子发动机可靠性和寿命的主要因素之一。.本项目通过实验结合理论方法与数值分析方法对离子发动机放电阴极的离子声激励溅射腐蚀机理进行了研究。建立二维Particle-In-Cell(PIC)粒子仿真模型，以实验数据作为输入条件，研究了空心阴极放电羽流离子运动行为及能量分布。实验结果发现直流空心阴极弧光放电电势脉动现象通常发生在大电流或小流量的条件下。不同放电室结构对空心阴极放电放电特性及羽流参数有影响。直流空心阴极弧光放电电势脉动主要由两种原因造成。其一为电离不稳定型电势脉动，电离型电势脉动是由于电离区的形成（氙离子的产生）和空间氙离子消散造成；其二为离子声波型电势脉动，离子声波型电势脉动是由于电子温度的提高及电离率的增大造成。仿真结果表明放电空间中高能离子的产生与空间电势脉动幅值和脉动频率有关，离子能量随着电势脉动的幅值和频率的增大而增大。并与相关实验数据进行比较分析，结果比较吻合。研究结果可为兰州物理研究所离子发动机产品LIPS200+及LIPS300空心阴极筛选方案改进、新筛选方案可靠性评估、寿命预估等方面提供重要依据。