Speaker
Description
Improvement of the performance on a hydrogen/deuterium negative ion source for a nuclear fusion device are reported. In particular, the suppression of the co-extracted electron current, $I_{e}$, is an important issue to ensure the stable beam acceleration. Improvement of the $I_{e}$ has been confirmed by optimizing the magnetic field of the electron deflection magnet in the extraction grid. The mismatch of beam deflection angle will be verified in 2021. Other two methods for reduction of the $I_{e}$ were validated. First method is an outer iron yoke. The ratio of the $I_{e}$ to the deuterium negative ion current, approximately $I_{e}/I_{acc}$ decreased by 0.1 compared with that in hydrogen. Second method is an electron fence (EF) whose rods are set between the rows of apertures on the plasma grid. The $I_{e}/I_{acc}$ was greatly improved from 0.7 to 0.25 in deuterium. These attempts have improved the total deuterium injection beam power of 8.4 MW by three negative ion based NBIs.
| E-mail for contact person | ikeda.katsunori@nifs.ac.jp |
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| Funding Information | NIFS-ULRR702 |
