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为了评估利用发散磁场构型双电层效应的紧凑式螺旋波等离子体推力器的离子加速效果,探索了一种双向偏振态激光诱导荧光测量方法来对螺旋波等离子体源近出口端的离子速度分布函数进行测量。实验中采用Ar作为螺旋波等离子体源工质,中心波长为611.662nm的激光以轴向方式注入等离子体,以激励一价Ar离子获得波长为461.086nm的诱导荧光光谱。为了消除磁化等离子体中逆塞曼效应对激光诱导荧光光谱带来的分裂影响,通过四分之一波片将入射激光分别调制为左旋和右旋圆偏振态,并对其诱导光谱进行了分别测量,结果发现不同磁场强度下两次测量结果的偏移值与理论高度吻合,证明了双向偏振态激光诱导荧光测量方法的理论可行性。进一步,采用高斯型滤波器反卷积算法从测量光谱中去除自然展宽和能量饱和效应,再通过对两次相反偏振态测量结果进行平移处理消除逆塞曼效应,从而分离得到实际的多普勒效应。测量了射频能量600 W,不同轴向位置、磁场大小以及气体压力下的螺旋波Ar等离子体激光诱导荧光光谱,结果表明在该实验条件下离子并没有因双电层效应而达到期望值的加速效果,离子速度的形成可能只是一种磁约束作用下的双极电场所导致,并不能产生好的推力性能。
In order to evaluate the ion acceleration effect of a compact helical plasma thruster using the double-layer effect of a divergent magnetic field configuration, a bi-directionally polarized laser-induced fluorescence measurement method was developed to determine the ion velocity distribution near the exit end of the helical wave plasma source Function to measure. In this experiment, Ar was used as the helical wave plasma source, and the laser with the center wavelength of 611.662 nm was injected into the plasma in the axial direction to excite the monovalent Ar ion to obtain the induced fluorescence spectrum with the wavelength of 461.086 nm. In order to eliminate the influence of the inverse Zeeman effect on the laser-induced fluorescence spectra in magnetized plasma, the incident laser light is modulated into left-handed and right-handed circularly polarized states respectively by a quarter-wave plate and their induced spectra are respectively distinguished The results show that the offset values of the two measurements at different magnetic field strengths are in good agreement with the theoretical ones, which proves the theoretical feasibility of bi-directionally polarized laser-induced fluorescence measurement. Further, the Gaussian filter deconvolution algorithm is used to remove the natural broadening and energy saturation effects from the measurement spectrum, and then the inverse Zeeman effect is eliminated by shifting the measurement results of two opposite polarization states to separate the actual Doppler effect. Laser induced fluorescence spectra of helical Ar plasma at 600 W RF power, different axial positions, magnetic field sizes and gas pressures were measured. The results show that the ions did not reach the expected value due to the double layer effect under the experimental conditions , The formation of ion velocity may only be caused by the bipolar electric field under a magnetic confinement effect and can not generate good thrust performance.