Effects of the extraction voltage on the beam divergence for a H ion source.
Journal of Applied Physics; 9/28/2019, Vol. 126 Issue 12, pN.PAG-N.PAG, 7p, 1 Diagram, 1 Chart, 5 Graphs
Negative hydrogen (H −) ion sources have a wide range of applications. The general requirement for these H − ion sources is to produce intense H − ion beams with good beam optics. The purpose of this paper is to clarify the effects of the beam extraction voltage on the beam divergence angle by three-dimensional Particle-in-Cell (PIC) modeling. Perveance matching has been studied for a wide range of the extraction voltage with the model geometry of a Linac4 H − ion source. The extracted H − beam divergence angle is evaluated for extraction voltages ranging from 7 to 14 kV by using the Keio-BFX PIC code. The results show divergence minima in the range of 9.2–11.5 kV for the case without surface H − production, which correspond to experimental results. The dependence of divergence on the extraction voltage is explained by the change of the shape of the meniscus. In particular, a flat meniscus corresponds to low beam divergence, and particles extracted through the center of the meniscus have a lower divergence than particles extracted near the Plasma Electrode. [ABSTRACT FROM AUTHOR]
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