Interaction between ion source plasma and ion source wall

壁面状况在很大程度上影响离子源的性能。有几个基本的机制导致了可从源中提取的离子的量的变化。这包括由于沉积层的形成而引起的源壁上粒子/能量反射系数的变化，以及源壁附近的直流电磁结构的改变。中性粒子飞行时间能量分析、光学发射光谱和静电探针是研究离子源等离子体中等离子体-表面相互作用的三种主要工具。随着离子源放电功率的增加，流出等离子体的中性粒子的速度分布函数的峰值向高能方向移动。负氢离子源中氢气的真空紫外光谱表明，高温阴极材料的覆盖改变了限制在离子中的气体分子激发能级的分布，因此…更多的猎物。高频电源可以激发等离子体，而不需要任何阴极作为溅射/蒸发粒子源，但它们仍然在离子源壁上形成沉积层。高频放电电源形成的沉积层往往表现出绝缘特性，导致离子引出孔周围的局部电位分布发生变化。在引出电势开启的情况下，测量了局部电势对等离子体的穿透。结果清楚地表明，磁场的存在吸引了要从源中提取的离子。由局域电场计算的引出概率与实验结果进行了比较。用直流激光光解离法对等离子体流速度进行了实验测量，它是理论模型预测引出概率的输入参数。为了进一步加深对离子源和过程等离子体的等离子体-表面相互作用的理解，已经开发了其他表征等离子体表面相互作用的诊断方法，如激光诱导的光电子发射。较少

Condition of the wall largely affects the performance of an ion source. Several fundamental mechanisms are responsible for the change in extractable amount of ions from the source. These include change of particle/energy reflection coefficient at the source wall due to formation of deposition layers, and alteration of dc electromagnetic structures near the source wall. Time-of-flight energy analysis for neutral particles, optical emission spectroscopy, and electrostatic probes were the three major tools employed to investigate factors governing the plasma-surface interactions in ion source plasmas. Peaks of velocity distribution functions of neutrals effusing out of plasma, shift toward the higher energy side with the increasing discharge power into the ion source. Vacuum ultraviolet spectra of hydrogen gas in a negative hydrogen ion source have shown the coverage of high temperature cathode materials alters distributions of molecular excitation levels of the gas confined in the ion so … More urce. High frequency electrical powers can excite plasma without any cathodes acting as sputtering/evaporation particle sources, but they still form deposition layers on ion source walls. The deposition layers formed by high frequency discharge power often show insulating characteristics causing change in local potential distributions around the ion extraction holes. The penetration of local electrical potential into plasma has been measured with the extraction potential turned on. The result has clearly shown the presence of field attracting ions to be extracted from the source. The extraction probability calculated from the local electric field has been compared with the experimental result. Plasma flow speed which is an input parameter for the theoretical model to predict extraction probability has been measured experimentally by dc laser photodetachment method. Other diagnostic methods to characterize plasma surface interaction like laser induced photoelectron emission have been developed to further deepen the understanding the plasma-surface interaction for ion source and process plasmas. Less