Influence of electric field penetration by a three-electrode beam extraction system on hydrogen negative ion source plasma

Matsumoto, Yoshiyasu; Nishiura, M.; Yamaoka, H.; Sasao, M.; Wada, M.

doi:10.1063/1.4833918

Cited by 2 publications

(1 citation statement)

References 12 publications

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“…The extraction field was observed experimentally to penetrate into the source plasma and influence the plasma properties and ion extraction [52]. According to figure 3(a) and equation ( 9), ∂ 2 ϕ L ∂r 2 can be regarded as a manifestation of the penetration of the extraction field, and it will influence the upstream sheath or even plasma within a certain range from the screen grid.…”

Section: Numerical Analyses Of the Upstream Sheathmentioning

confidence: 99%

Numerical and theoretical modeling of the sheath upstream of ion optics: sheath structure transition and its effect on the beam divergence

Li¹,

Yuan²,

Yang³

et al. 2021

Plasma Sources Sci. Technol.

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The grasp of the sheath characteristics is fundamental to evaluate the extraction capabilities of ion optics and accommodate the wide application of ion sources. A one-dimensional theoretical model is developed to investigate the sheath upstream of ion optics as well as the matching relation between the ion optics and plasma, by simplifying and decomposing the Poisson's equation at the outer surface and centerline of the grid aperture. The one-dimensional model is validated by 2D3V hybrid simulations which are also applied to visualize the sheath structure and ion beam divergence. With the increase of plasma density, it is found that the upstream sheath will transform gradually into a sheath near the plate electrode at first and then enter the screen aperture with a sheath edge approximately paralleling to the meniscus. Accordingly, the structure of the upstream sheath can be classified into four kinds which correspond to different beam divergence. The structure transition of the upstream sheath reflects the interaction between the extraction field and plasma, and the ion optics is considered to work at the matching point when the plasma is relatively balanced with the extraction field. Around the matching point, a small beam divergence angle can be achieved without the occurrence of over-perveance. Then a matching model is proposed based on the characteristics of the potential distribution at the matching point. It is verified to be effective of the model for quickly analyzing the ion beam divergence characteristics and determining an ideal operating range of the ion optics.

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Section: Numerical Analyses Of the Upstream Sheathmentioning

confidence: 99%

Numerical and theoretical modeling of the sheath upstream of ion optics: sheath structure transition and its effect on the beam divergence

Li¹,

Yuan²,

Yang³

et al. 2021

Plasma Sources Sci. Technol.

View full text Add to dashboard Cite

show abstract

Structural characteristics of the upstream sheath of the ion optics and its application in evaluating the beam performance of an ion thruster

Yang

Zhang

et al. 2022

Journal of Applied Physics

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To evaluate the extraction capabilities of ion optics and promote the generation of highly collimated ion beams for propulsion, the properties of the upstream sheath of the ion optics and how those properties relate to the beam divergence are investigated numerically and theoretically. The characteristics of the beam divergence at different grid parameters are studied from the behaviors of the impingement current and divergence angle obtained by simulations. Additionally, the simulations indicate the existence of an optimal structure for the upstream sheath of the ion optics, one that corresponds to a moderate focusing effect and a relatively small divergence angle. The plasma densities at the dividing points of different sheath structures are then derived with the matching model of the ion optics and the Child–Langmuir law, coupled with semi-empirical approaches based on the simulation results. According to the theoretical analyses, the range of existence of the most-desirable sheath structure depends on the strength of the penetration of the extraction field, the voltage between the grid apertures, and the distance between the upstream surfaces of the grids. Also, sensitivity analyses are performed with the numerical partial derivatives of the models to investigate how the grid parameters affect the sheath structures. The plasma densities at the dividing points generally vary synchronously with the changes of grid parameters, but the ranges of variations are different. Consequently, the desirable sheath structure and operating conditions of the ion optics can be achieved by correctly adjusting the grid parameters.

show abstract

Influence of electric field penetration by a three-electrode beam extraction system on hydrogen negative ion source plasma

Cited by 2 publications

References 12 publications

Numerical and theoretical modeling of the sheath upstream of ion optics: sheath structure transition and its effect on the beam divergence

Numerical and theoretical modeling of the sheath upstream of ion optics: sheath structure transition and its effect on the beam divergence

Structural characteristics of the upstream sheath of the ion optics and its application in evaluating the beam performance of an ion thruster

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