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Technical Brief

Analysis of the Effect of Beam Divergence Angle on Back-Streaming Electron Region in Ion Source for EAST-Neutral Beam Injection

[+] Author and Article Information
Hu Chundong

Institute of Plasma Physics Chinese Academy of Sciences,
University of Science and Technology of China,
Shushanhu Road 350 Hefei,
P. O. Box 1126,
Anhui 230031, China
e-mail: cdhu@ipp.ac.cn

Wu Mingshan

Institute of Plasma Physics Chinese Academy of Sciences,
University of Science and Technology of China,
Shushanhu Road 350 Hefei,
P. O. Box 1126,
Anhui 230031, China
e-mail: mswu@ipp.ac.cn

Xie Yahong

Institute of Plasma Physics Chinese Academy of Sciences,
Shushanhu Road 350 Hefei,
P. O. Box 1126,
Anhui 230031, China
e-mail: xieyh@ipp.ac.cn

Wei Jianglong

Institute of Plasma Physics Chinese Academy of Sciences,
Shushanhu Road 350 Hefei,
P. O. Box 1126,
Anhui 230031, China
e-mail: jlwei@ipp.ac.cn

Yu Ling

Institute of Plasma Physics Chinese Academy of Sciences,
Shushanhu Road 350 Hefei,
P. O. Box 1126,
Anhui 230031, China
e-mail: yuling@ipp.ac.cn

Manuscript received October 31, 2017; final manuscript received March 4, 2018; published online May 16, 2018. Assoc. Editor: Michal Kostal.

ASME J of Nuclear Rad Sci 4(3), 034501 (May 16, 2018) (4 pages) Paper No: NERS-17-1266; doi: 10.1115/1.4039694 History: Received October 31, 2017; Revised March 04, 2018

During the process of beam extraction in positive ion source under high voltage region, a large number of electrons are produced in the gaps of grids. After back-streaming acceleration, these electrons go back to arc chamber or impinge grids and then heat back plate or grids, which are harmful for the safety of ion source. Under the situation of poor beam extraction optics, a large part of the primary beam ions bombard the surface of suppressor grid (SG). And this process produces a large number of electrons. Due to the huge extracted voltage, the secondary electron emission coefficient of the SG surface is also high. As a result, the grids' current grows. According to the measurement of the current of SG and the calculation of the perveance of the corresponding shoot, the effect of ion beam divergence angle on back-streaming electrons can be analyzed. When the beam divergence angle increases, the number of back-streaming electrons increases rapidly, and grids' current changes significantly, especially the current of gradient grid and SG. The results can guide the parameters operating on the ion source for Experimental Advanced Superconducting Tokamak-neutral beam injection (EAST-NBI) and find the reasonable operation interval of perveance and to ensure the safety and stable running of the ion source, which has great significance on the development of long pulse, high power ion source.

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Topics: Electrons , Ions , Silencers , Heat
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References

Hu, C. , 2012, “ Conceptual Design of Neutral Beam Injection System for EAST,” Plasma Sci. Technol., 14(6), pp. 567–572. [CrossRef]
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Figures

Grahic Jump Location
Fig. 1

Production processes of back-streaming electrons: (a) is for the first type and (b) is for the second type

Grahic Jump Location
Fig. 2

Simulation of equipotential surface in gaps

Grahic Jump Location
Fig. 3

The beam divergence angle changes with perveance p/p0 and voltage ratio Г

Grahic Jump Location
Fig. 4

(a) is the behavior of tightly focused beam and (b) is the behavior of defocused beam

Grahic Jump Location
Fig. 5

Ion beam spot of EAST-NBI BL1# (left)

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