Study for Intense Neutrl Helium Bean

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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.