Study for Intense Neutrl Helium Bean

聚变产生α粒子的诊断是燃烧等离子体实验的一项重要任务。将中性粒子分析与能量为0.8MeV/核子的中性He束注入相结合是获得受限α粒子速度分布的一种可能途径。为了实现这种诊断方法，发展一个强束源（1 mA/cm 2）的He是重要的。研制了一种紧凑的桶型He ~+源，采用Rb双电荷交换电池，在11 keV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中操作，进一步开发了这种类型的源。在11 keV能量下，从直径0.6cm的小孔中引出了大于20 mA/cm ~ 2的电子束。这一记录为α粒子诊断提供了一个有前途的束流系统。本文研究了He ~+被俘获到He原子单电子激发态的过程，并对He ~+的形成作了前景展望。在Rb电荷交换池中，注入2 - 10 keV的低能He ~+离子束，进行了光谱测量。随着He ~+离子入射能量的增加，衰减到三重态的发射线与衰减到单重态的发射线的比例增加。计算结果与Smirnov方法的理论计算结果进行了比较。为了寻找一种更好的方法来产生He ~+，同时减少碱金属的消耗，我们测试了通过注入亚稳态He中性束从低功函数金属表面产生He ~+的可能性。实验表明，低功函数表面的不稳定性主要是由入射的高能中性粒子的轰击引起的。本文所研制的紧凑型桶式氦束源为工业应用提供了参考设计。

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.