天琴计划将发射3颗距地心10万公里的圆轨卫星，对mHz频段的引力波进行探测。卫星两两之间将在太阳风和磁层等离子体中建立17万公里长的激光干涉仪来测量引力波带来的激光相位变化。由于其密度的长距离累积效应及在mHz频段的周期性振荡，空间等离子体引起的激光相位变化可能会与引力波造成的变化相混淆。本项目以天琴计划为例，主要进行以下内容：1. 探索引起空间等离子体密度mHz频率振荡的主要物理机制；2. 研究空间等离子体周期性密度振荡对不同轨道位形的卫星星间激光相位的影响；3.分析空间等离子体密度模型精度误差对激光相位功率谱的影响；4. 提出消除或减少等离子体造成的相位误差的解决方案。通过本项目的开展，我们希望定量地评估空间等离子体密度振荡对引力波探测激光相位的影响，并提出一套初步可行的降低或消除此噪声的方案，保证引力波探测顺利开展。本项目的研究将对天琴及其它空间引力波探测计划提供重要参考和理论支撑。

The TianQin space gravitational wave (GW) detector will launch 3 geocentric circularly orbiting satellites in the altitude of 10^5 km, to detect the GWs in the band of milli-hertz. Each satellite pair will establish a 1.7×10^5 km-long laser interferometer in the solar wind and the magnetospheric plasmas to measure the laser’s phase deviation by the GWs. GW detection requires a high precision in the variation of the laser’s phase. The phase deviation of the laser beam is proportional to the integral of the plasma densities along the propagation distance. Thus even the plasma is very thin at the altitude of 10^5 km, the cumulative effects of the long distance may still cause an intolerable error in the phase measurement. More importantly, the plasma density at this altitude has periodic density oscillations in the band of milli-hertz, which could induce phase deviation just in the same way as the GWs. This project takes TianQin GW detector as an example, aiming to 1. Explore the main mechanisms behind the milli-hertz density oscillations; 2. Model real-time phase deviations of the inter-satellites lasers due to the periodic oscillations of the space plasma density; 3.Analyze the uncertainty of the power density spectrum of the phase deviations due to the numerical errors of the adopted plasma density models; 4. Find out a solution to reduce the extra phase deviations by plasmas. Through this project, we will evaluate quantitatively the role of the plasma density oscillations on the phase deviations, meanwhile suggesting a reliable solution to mitigate these phase deviations. This study is critical to the success of the TianQin GW detection. Other GW detection plans may also benefit from this research.