Three-dimensional analysis of microwave generated plasmas with extended planar laser-induced fluorescence.

We present the development and application of a diagnostic system for the analysis of microwave generated low-pressure plasmas, which might also be used for the investigation of the edge regions in magnetically confined fusion plasmas. Our method uses planar laser-induced fluorescence, which is produced by excitation of neutral metastable atoms through a short, intense, pulsed laser. The beam expansion optics consist of an uncommon setup of four lenses. By controlled shifting of an element of the optics sideways, the location of the laser sheet in the plasma is scanned perpendicular to the excitation plane. Together with a spectrometer observing different observation volumes along the beam path, we are able to map absolute three-dimensional (3D) population density distributions of the metastable ((2)P(12) (o)) 3s[12](0) (o) state of Ne I in an electron cyclotron resonance heating (ECRH) plasma. This optical tomography system was used to study the influence of the microwave power and mode on the spatial structure of the plasma. The results show that the population density of the neutral neon in this metastable state is found to be in the range of 10(16) m(-3), and that its spatial distribution is associated with the 3D structure of the magnetic field. We also report that the spatial distribution strongly varies with the mode structure, which depends on the microwave power.

我们介绍了一种用于分析微波产生的低压等离子体的诊断系统的开发与应用，该系统也可用于研究磁约束核聚变等离子体的边缘区域。我们的方法采用平面激光诱导荧光技术，它是通过短而强的脉冲激光激发中性亚稳态原子产生的。光束扩展光学系统由一种不常见的四个透镜的装置组成。通过对光学元件进行横向可控移动，可垂直于激发平面扫描等离子体中激光片的位置。再结合一个沿光束路径观测不同观测体积的光谱仪，我们能够绘制出电子回旋共振加热（ECRH）等离子体中氖Ⅰ的亚稳态（(2)P(1/2) (o)）3s[1/2](0) (o)态的绝对三维（3D）粒子数密度分布。这种光学层析成像系统被用于研究微波功率和模式对等离子体空间结构的影响。结果表明，处于这种亚稳态的中性氖的粒子数密度在10(16) m(-3)范围内，并且其空间分布与磁场的三维结构有关。我们还报告说，空间分布随模式结构而有很大变化，而模式结构取决于微波功率。