Improvement of deuterium injection power in the negative-ion-based NBIs (n-NBIs) for the Large Helical Device (LHD) are reported. Co-extracted electron current at acceleration of deuterium negative ions (D− ions) limits the injection power. The electron current is reduced by decreasing the extraction gap, and the injected D− current evaluated from the injection power increased from 46 to 55 A. Greater electron reduction was achieved by installing a structure named an 'electron fence' (EF), with which D− beam power was successfully improved from 2.0 MW to 3.0 MW. The injection power in three configurations − without EF, with EF of 5 mm and 7 mm distance from the plasma grid (PG) surface − have been compared in both cases of hydrogen and deuterium operations, and it was found that the configuration with the EF of 5 mm distance was the best to satisfy the performance for both of hydrogen and deuterium injections. Although the co-extracted electron current is reduced in the negative ion sources applied for JT-60SA and ITER by utilizing the PG filter, it is possible to achieve more effective electron reduction by combining the PG filter and the EF.
大型螺旋装置（LHD）用负离子基中性束注入器（NBI）中，负离子（D⁻）加速时的共萃取电子限制了注入功率。通过减小引出间隙，共萃取电子流得到抑制，由注入功率评估的D⁻注入流从46 A提升至55 A。进一步安装名为“电子围栏”（EF）的结构后，电子抑制效果更为显著，D⁻束功率成功从2.0 MW提升至3.0 MW。在氢和氘两种运行条件下，比较了三种构型——无EF、EF距等离子体栅极（PG）表面5 mm、EF距PG表面7 mm——的注入功率，结果表明，EF距PG表面5 mm的构型在氢和氘注入中均表现出最佳性能。尽管在JT-60SA和ITER用负离子源中，通过采用PG滤网已能减少共萃取电子流，但将PG滤网与EF相结合有望实现更有效的电子抑制。