Hydrogen reflection and desorption at the plasma electrode of a negative hydrogen ion source

2020 Fiscal Year Final Research Report

• Project/Area Number: 17H03512
• Research Category: Grant-in-Aid for Scientific Research (B)
• Allocation Type: Single-year Grants
• Section: 一般
• Research Field: Nuclear fusion studies
• Research Institution: Doshisha University
• Principal Investigator: Wada Motoi 同志社大学, 理工学部, 教授 (30201263)
• Co-Investigator(Kenkyū-buntansha): 津守 克嘉 核融合科学研究所, ヘリカル研究部, 教授 (50236949)
• Project Period (FY): 2017-04-01 – 2021-03-31
• Keywords: 負イオン / 仕事関数 / 粒子反射 / スパッタリング / 負イオン源 / 中性粒子加熱 / 表面生成

Outline of Final Research Achievements

Ion sources delivering negative hydrogen (H-) ion beams for high-energy accelerators and neutral beam heating of the fusion experiment plasmas are operated with addition of Cs into the hydrogen discharge. Hydrogen particle reflection and adsorption at plasma grids (PG) for these sources are studied through two approaches: laboratory experiments and computer simulations based on binary collision approximation. A computer simulation model has predicted that the hydrogen isotope adsorbed layer between a Cs top layer and Mo PG bulk plays an important role in Cs loss through the surface collision cascade excited by a plasma bombardment. Another model has successfully predicted the energy distribution of H- ions produced at a C12A7 electride surface immersed in hydrogen plasma. Hydrogen reflection characteristics are now measured down to 200 eV/H incident energy, while this research project realized the system that enables measurement down to less than 20 eV/H incident energy.

Free Research Field

物理学

Academic Significance and Societal Importance of the Research Achievements

本研究の成果により，Cs導入量の少ない負イオン源運転シナリオの構築が可能となった．本研究でも調査したCsを用いない負イオン生成に加え，省Cs型の負イオン源運転が可能となることにより，将来の核融合実証炉の設計指針策定にあたっての自由度が大きくなった．同時に，プラズマ―固体表面相互作用とプラズマシース領域を繋ぐ計算機科学分野の開拓にも，本研究は貢献した．社会的な意義としては脱炭素社会に向けて，今後研究開発が加速されるものと予想される核融合発電の実現に向けての貢献が期待される．2025年より実験が予定されているITER核融合計画においても本研究が対象とした水素負イオン源が用いられる予定である．