Development of laser-induced polarization fluorescence spectroscopy for measuring electric fields in magnetic confinement fusion plasma edges

我们开发了一种测量等离子体电场的高灵敏度方法，该方法依赖于激光诱导荧光（LIF）的极化，该荧光是由He原子通过禁止跃迁（例如2^1S→4^1D）激发而产生的。本工作的目的是阐明等离子体中电子的碰撞失调对LIF极化方法的影响，并检查利用斯塔克和电四极（QDP）振幅之间的干扰的方法是否可以在磁约束聚变等离子体这样的高磁场下使用。在Penning放电等离子体中测量了LIF线性极化的时间衰减与电子密度的关系。得到的不对准率与ne成正比。从线性关系出发，推导出电子碰撞失调的速率系数w为（4.9±0.5）x10^<-11> m^3/s。讨论了极化法应用的电子密度上限。在垂直于磁管等离子体鞘层电场的强磁场（500 G< B< 1500 G）下，对覆盖塞曼分裂的激光波长进行扫描，观察了圆极化LIF的激发光谱。结果表明，在4^1D中符号相反的磁亚能级之间形成了各向异性居群（取向）。这表明，与塞曼分裂相比，即使在窄谱宽激光对每个子能级选择性激发的情况下，也会发生Stark-QDP干涉。

We have developed a high-sensitive method for measuring the electric field in plasmas, which relies on polarization of laser-induced fluorescence (LIF) by the excitation of He atoms through forbidden transitions (e.g. 2^1S→4^1D). Purposes of this work are to elucidate the effect of collisional disalignment due to electrons in plasmas on the LIF polarization method and to examine whether the method utilizing the interference between Stark and electric quadrupole (QDP) amplitudes can be available or not under such high magnetic field as in magnetic confined fusion plasmas.Time decay of LIF linear polarization was measured as a function of electron d ensity ne in a Penning discharge plasma. The disalignment rates obtained were proportional to ne. From the linear dependence the rate coefficient for disalignment due to electronic collisions w as deduced to be (4.9±0.5)x10^<-11> m^3/s. The upper limit of elect ron densities for application of the polarization method was discussed.Excitation spectra of circularly polarized LIF were observed by scanning the laser wavelength covering the Zeeman splitting under high magnetic fields (500 G< B< 1500 G) perpendicular to the electric field in the sheath of a magnetron plasmas. It was found that the anisotropic population (orientation) was formed among magnetic sublevels with opposite sign in 4^1D. This shows that the Stark-QDP interference takes place even under the cond ition of the selective excitation to each sublevel by a laser with a narrow spectral width as compared to the Zeeman splitting.