Evaluation of High Current Negative Ion Source and Construction of Data Base for Negative Ion Based NBI Design

本计画的目标是发展强流负离子源，并建立负离子束负离子注入器设计所需的资料库，特别是强流负离子源。为达到这一目的，我们调查了E. C和U。S.与卡勒姆实验室、理工学院和伯克利实验室合作。桶式负离子源的实验结果令人满意，因此主要针对纯批量生产操作和含铯操作中的源优化进行研究。通过对实验数据的分析，得出了以下结论，为强流氢负离子源的设计提供了数据基础。1.纯体积源优化实验支持负离子产生的串联模型概念。特别是探针等离子体参数测量表明，引出区的电子温度要求小于1 eV。为了实现该条件，磁性过滤器对于将提取区域与驱动器区域分离是重要的。2.在含Cs的工作模式下，负离子主要产生在Cs覆盖的低功函数壁面，但保持引出区电子温度在1 eV左右仍是重要条件。获得了以下物理和技术问题的详细数据：1.磁性过滤器的位置和强度; 2.负离子电流密度与引出孔径的关系;电子束提取中的电子抑制，4。电极的偏压，5。R. F负离子源有望成为稳定运行的离子源。从目前的认识水平来看，桶式铯负离子源是最有前途的NBI强流负离子源。

The objectives of this project are Evolution of high current negative ion source and Construction of data base which is needed for design of negative ion based NBI, especically high current negative ion sources. To attain the objectives we researched the present status of negative ion development at many laboratories in E. C and U. S. A under the collaboration with Culham Laboratory, Ecole Polytechnique and Berkeley Laboratory. Bucket type negative ion source was mainly researched for the optimization of source in pure volume production operation and operation with Cs because of its promissing experimental results. As the results of analysis of experimental data for some issues, the followings are obtained as data base for design of high current hydrogen negative ion source. 1. Experimets for optimization of pure volume source support Tandem model concept of negative ion production. Especially, the plasma parameter measurement by probe shows that the electron temperature in the extraction region is required to be less than 1eV. To realize this condition, a magnetic filter is important to separate the extraction region from the driver region. 2. In the operation mode with Cs, negative ions are mainly produced at low work function wall surface covered with Cs but it is still important condition to keep the electron temperature in the extraction region around 1eV. Detailed data for following physical and technical issues are obtained : 1. Position and strength of magnetic filter, 2. Relation between negative ion current density and extraction aperture radius, 3. Electron suppression in the beam extraction, 4. Bias potential to electrode, 5. R. F negative ion source which is expected as a steady operation source. At the present status of knowledge it is concluded that bucket type negative ion source wit h Cs is most promising high current negative ion source for NBI.