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Zhou Y, Zhai YJ, Jin QY, Liu YG, Li LB, Zhang P, Zhang S, Zhao HW, Sun LT. A compact radio-frequency ion source for high brightness and low energy spread negative oxygen ion beam production. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2023; 94:093301. [PMID: 37655989 DOI: 10.1063/5.0164485] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/22/2023] [Accepted: 08/15/2023] [Indexed: 09/02/2023]
Abstract
A high brightness and low energy spread (∆E) ion source is essential to the production of a high-quality primary ion beam applied in secondary ion mass spectrometry (SIMS). A compact 13.56 MHz radio-frequency (RF) ion source with an external planar spiral antenna has been developed as a candidate ion source for the production of negative oxygen ion beams for SIMS application. This ion source is designed with a three-and-a-half-turn water-cooled planar antenna for RF power coupling, a multi-cusp magnetic field for effective plasma confinement, and a three-electrode extraction system. The experimental results show that more than 50 µA negative oxygen ion beams have been extracted, which consist of 56% O-, 25% O2-, and 19% O3-. The ion energy distribution of the negative oxygen ion beam exhibits a Gaussian distribution with a minimum ∆E of 6.3 eV. The brightness of the O- beam is estimated to be 82.4 A m-2 Sr-1 V-1. The simulation, design, and experimental study results of this RF ion source will be presented in this paper.
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Affiliation(s)
- Y Zhou
- Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000, China
- School of Nuclear Science and Technology, University of Chinese Academy of Sciences, Beijing 100049, China
| | - Y J Zhai
- Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000, China
- School of Nuclear Science and Technology, University of Chinese Academy of Sciences, Beijing 100049, China
| | - Q Y Jin
- Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000, China
- School of Nuclear Science and Technology, University of Chinese Academy of Sciences, Beijing 100049, China
| | - Y G Liu
- Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000, China
- School of Nuclear Science and Technology, University of Chinese Academy of Sciences, Beijing 100049, China
| | - L B Li
- Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000, China
| | - P Zhang
- Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000, China
| | - S Zhang
- Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000, China
- School of Nuclear Science and Technology, University of Chinese Academy of Sciences, Beijing 100049, China
| | - H W Zhao
- Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000, China
- School of Nuclear Science and Technology, University of Chinese Academy of Sciences, Beijing 100049, China
| | - L T Sun
- Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000, China
- School of Nuclear Science and Technology, University of Chinese Academy of Sciences, Beijing 100049, China
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Abstract
Intense ion beam production is of high importance for various versatile applications from accelerator injectors to secondary ion mass spectrometry (SIMS). For these purposes, different types of ion beams are needed and, accordingly, the optimum plasma to produce the desired ion beams. RF-type plasma features a simple structure, high plasma density and low plasma temperature, which is essential for negative ion beam production. A very compact RF-type ion source using a planar coil antenna has been developed at IMP for negative molecular oxygen ion beam production. In terms of high-intensity positive ion beam production, 2.45 GHz microwave power-excited plasma has been widely used. At IMP, we developed a 2.45 GHz plasma source with both ridged waveguide and coaxial antenna coupling schemes, tested successfully with intense beam production. Thanks to the plasma built with an external planar coil antenna, high O2− production efficiency has been achieved, i.e., up to 43%. With 2.45 GHz microwave plasma, the ridged waveguide can support a higher power coupling of high efficiency that leads to the production of intense hydrogen beams up to 90 emA, whereas the coaxial antenna is less efficient in power coupling to plasma but can lead to attractive ion source compactness, with a reasonable beam extraction of several emA.
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