稳态等离子体推力器羽流仿真及其对微波的衰减和相移作用

Numerical simulation of the stationary plasma thruster plume and its effects on the microwave attenuation and phase shifts

关键词:  等离子体  羽流  微波衰减  相移 

Key words:  Plasma  Plume  Microwave attenuation  Phase shift

摘要:

为了评估稳态等离子体推力器(SPT)羽流对微波造成的衰减和相位变化,使用二维轴对称的PIC-DSMC方法,在空间及室压6mPa的真空舱两种环境下,计算了SPT-100羽流场中的电子分布。在此基础上,通过分析特征频率和计算衰减因子、相位常数,估算了2,4,8,12.5GHz共4个频率微波穿过羽流场时的衰减量和相移。8GHz和12.5GHz微波未发现明显的衰减,相移为10°～120°。2GHz和4GHz微波在喷口附近衰减量范围为10～50dB。仿真结果表明,C波段和S波段在SPT羽流中容易发生衰减,而X波段以上的高频微波衰减量很小,同时这几个波段微波均发生较大相移。真空舱内6mPa背压下对衰减量的预测仅略高于实际飞行情况,但微波相移会有较大误差。

Abstract:

The aim of this article is to estimate the microwave attenuation and phase shifts due to the stationary plasma thruster plume. A two-dimensional axisymmetric approach that combines the particle-in-cell method with the direct simulation Monte Carlo method has been used to simulate the distribution of electrons in the plume of the stationary plasma thruster, SPT-100, in a vacuum chamber of 6mPa and in space. In addition, the attenuation and phase shifts of the 2GHz/4GHz/8GHz/12.5GHz microwave are estimated, by means of the analyzing of the characteristic frequency of the SPT plume and calculating the attenuation factors and the phase constants. The attenuation of 8GHz/12.5GHz is very small, and the phase shifts are 10°～120°。The attenuation of 2GHz/4GHz microwave is 10~50dB near the exit of the thruster. It is shown that the C-band and S-band microwave is likely to attenuate in the SPT plume while the X-band microwave and the microwave of higher frequencies hardly attenuates in the SPT plume. The microwave attenuation may increase slightly in the vacuum chamber, but the phase shift may be quite different from that in space.