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

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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.