双路微波耦合反应腔的等离子体发射光谱分析

Plasma Emission Spectroscopy Analysis of Two-Way Microwave Coupled Reaction Cavity

反应腔作为微波等离子体化学气相沉积法制备光纤预制棒的核心,其结构直接影响到反应腔内的电磁场分布,进而影响到等离子体状态,因此对反应腔的结构进行研究是十分有必要的。为了在反应腔中获得较高密度和较好均匀性的等离子体,提出了一种双路微波耦合反应腔结构,首先模拟计算了不同反应腔结构参数下反应腔内的电场分布规律,并以氧气作为工作气体,通过等离子体发射光谱探究了反应腔结构和工作气压对石英管内的等离子体分布的影响。研究结果表明:双路微波输入方式在石英管中心区域产生了很强的电场耦合增强效果。反应腔的内径对电场分布状态影响较大,在反应腔内径为86 mm时,石英管内的电场分布出现轴对称性,且轴向中心区域的等离子体密度最大。在两路矩形波导的距离为61.2 mm和反应腔的长度为202 mm时,反应腔内等离子体的强度和均匀性具有最佳分布。另外还发现,当气压从1.8 kPa上升到2.8 kPa时,反应腔内等离子体光谱强度减小,但靠近石英管内壁处的变化不明显,这与等离子体中粒子碰撞几率增加造成的能量损失和管壁存在的高温有关。

The reaction chamber is used as the core of the optical fiber preform by microwave plasma chemical vapor deposition.The structure directly affects the electromagnetic field distribution in the reaction chamber,which affects the plasma state.Therefore,it is necessary to study the structure of the reaction chamber.In order to obtain plasma with higher density and better uniformity in the reaction chamber,a two-way microwave coupled reaction chamber structure was proposed.Firstly,the electric field distribution in the reaction chamber under different reaction chamber structural parameters was simulated and calculated.The effect of the reaction chamber structure and working pressure on the plasma distribution in the quartz tube was investigated by plasma emission spectroscopy using oxygen as the working gas.The results showed that the two-way microwave input method produces a strong electric field coupling enhancement effect in the central region of the quartz tube.The inner diameter of the reaction chamber had a great influence on the electric field distribution state.When the inner diameter of the reaction chamber was 86 mm,the electric field distribution in the quartz tube exhibits axis symmetry,and the plasma density in the axial center region was the largest.When the distance between the two rectangular waveguides was 61.2 mm,and uhe length of the reaction chamber was 202 mm,the intensity and uniformity of the plasma in the reaction chamber were optimally distributed.It was also found that when the pressure rises from 1.8 to 2.8 kPa,the spectral intensity of the plasma in the reaction chamber decreased,but the change near the inner wall of the quartz tube was not obvious,which was caused by the energy loss caused by the increase of particle collision probability in the plasma and the high temperature of the tube wall.