Study for Intense Neutrl Helium Bean

聚变产生α的诊断是燃烧等离子体实验的一项重要任务。获得受限阿尔法粒子速度分布的一种可能方法是将中性粒子分析与注入0.8 MeV/核子的中性He束相结合。为了实现这种诊断方法，研制一种强离子束源（≧1mA/cm2）至关重要。研制了紧凑的桶形He+源，利用Rb双电荷交换电池在11kev下获得了77 μA的直流He”束流，转换效率优于3%。通过优化提取系统和在更高放电功率区域运行，进一步开发了这种类型的源。在11 keV的条件下，从直径0.6 cm的孔中提取出超过20mA/cm2的光束。这一记录为α粒子诊断提供了一个有前途的光束系统。研究了He+进入He原子单电子激发态的电子捕获过程，为后续He形成提供了理论基础。在Rb电荷交换池中，注入2 - 10 keV的低能He+束流，进行了光谱测量。随着He+冲击能量的增大，衰变为三重态和单线态的发射谱线比例增大。用斯米尔诺夫方法与理论计算结果进行了比较。为了寻找一种以更少的碱金属消耗生产He的更好方法，我们通过注入亚稳态He中性束来测试是否有可能从低功函数金属表面生产He。实验表明，低功函数表面的不稳定主要是由于高能中性粒子的轰击。要实现适用的贺氏梁，还需进一步研究。这里开发的紧凑型桶源成为工业使用的参考设计。

Diagnostics of fusion-produced-alphas is an important task for a burning plasma experiment. One possible way to obtain the velocity distribution of confined alphas is combination of neutral-particle-analysis with injection of a neutral He beam at the energy of 0.8 MeV/nucleon. To realize this diagnostic method, development of an intense beam source (≧1mA/cm2) of He is important. A compact bucket-type He+ source was developed and a 77 μA dc He" beam was obtained at 11 keV using a Rb double-charge-exchange cell with conversion efficiency better than 3 %. This type of source was further developed by optimizing the extraction system and by operating in the higher discharge power region. A beam more than 20mA/cm2 was extracted from a 0.6 cm-diameter hole at 11 keV. This record provides a promising beam system for alpha particle diagnostics. The electron capture process of He+ into one-electron excited states of a He atom has been studied in prospect of subsequent He" formation. The spectroscopic measurement in a Rb charge exchange cell was performed when a low energy He+ beam of 2 - 10 keV was injected. The ratio of emission lines decaying into triplet states to those into singlet is increased as the impact energy of He+ increases. The results are compared with theoretical calculation using Smirnov method. Searching for a better way to produce He" with less amount of alkali metal consumption, we tested if He" production was possible from a low work function metal surface by injecting a metastable-He neutral beam. The experiment showed that the low work function surface becomes unstable mostly by bombardment of incoming energetic neutrals. Further study is needed to realize an applicable He" beam.The compact bucket source developed here became a reference design for the industrial use.