K. Hayashi, K. Hoshino, K. Miyamoto, A. Hatayama, J. Lettry
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引用次数: 0
摘要
为了从氢负离子源中提取具有良好光束光学性能的强离子束,控制等离子体半月板(即光束发射面)的形状非常重要。最近的实验表明,射频负离子源的光束光学性能下降可能是由于等离子体密度 np 的波动引起的半月板与萃取网格之间距离 d eff 的波动造成的。本研究的目的是明确在存在大量表面产生的 H- 离子时 d eff 与 np 的关系,以了解射频负离子源中光束光学的这种波动。在 H- 生成率与大体等离子体密度成正比的假设下,考虑了 PG 上大量的表面 H- 生成。结果表明,即使在大量表面 H- 产生的情况下,有效距离 d eff 也与 np -1/2 成正比。这种依赖关系表明,主体等离子体密度 np 是控制 d eff 和从负离子源提取的光束光学结果的关键参数。
Numerical study of the plasma meniscus shape and beam optics in RF negative ion sources
In order to extract intense ion beams with good beam optics from hydrogen negative ion
sources, it is important to control the shape of the plasma meniscus (i.e. beam emission
surface). Recently, it is suggested experimentally that the degradation of beam optics in the RF
negative ion sources may be due to the fluctuation of the distance d
eff between the meniscus
and the extraction grid caused by the fluctuation of the plasma density np
. The purpose of
this study is to make clear the dependence of d
eff on np
in the presence of a
large amount of surface produced H- ions in order to understand such fluctuation of beam
optics in RF sources For the purpose, 3D electrostatic PIC simulation was conducted taking the
bulk plasma density as a parameter, investigating the extraction region of a H- ion source. A
large amount of the surface H- production on the PG has been taken into account under the
assumption that the H- production rate is proportional to the bulk plasma density. The result
shows that the effective distance d
eff is proportional to np
-1/2 even for a
large amount of surface H- production. This dependence suggests that the bulk plasma density
np
is the key parameters to control d
eff and the resultant beam optics extracted from
the negative ion source.