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离子引出是激光法分离同位素技术中的关键环节之一, 对产品丰度和产率有重要的影响, 而离子引出中离子和原子间的共振电荷转移过程则会对产品丰度造成污染, 因此在研究离子引出过程时应考虑共振电荷转移的影响. 本文利用粒子模拟(PIC)法以及基于PIC法和杂化PIC法的混合算法研究了考虑共振电荷转移的电场法离子引出过程, 通过对一维平行板法的引出方式进行数值计算, 获得了离子引出过程中共振电荷转移的基本性质和关键影响因素—共振电荷转移截面、引出时间、背景原子密度和蒸气宽度, 并据此得到了离子发生共振电荷转移比例的经验公式; 二维工况下的平行板法、交替偏压法、Π型电场法和M型电场法四种引出方式的计算结果则表明, 在其他条件相同的情况下, M型电场法具有最小的离子引出时间和共振电荷转移损失比例. 本文的研究结论对于指导激光法分离同位素技术中离子引出装置设计和实验工艺设计具有比较重要的参考意义.
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关键词:
- 共振电荷转移 /
- particle-in-cell法 /
- 鞘层 /
- 屏蔽层
The electric ion extraction, which plays an important role in productivity and abundance of product, is a critical step in laser isotope separation (LIS) technology. Several collision processes happen during the electric ion extraction, such as resonant and non-resonant charge exchange between ion and atom, the secondary ionization process and the ion-electron recombination. The resonant charge exchange process between target isotope ions and no-target background atoms is one of the major reasons of product contamination. As a result, the study of ion extraction with the consideration of resonant charge exchange process is essential. However, the resonant charge exchange process in ion extraction has not received enough attention. Besides, contradictory findings have been deduced in published studies. Therefore, it is necessary to clarify the effect of resonant charge exchange process in the electric ion extraction. In this article, the particle-in-cell (PIC) method and preprocessing hybrid-PIC method are adopted in both one- and two-dimensional numerical simulation. The preprocessing hybrid-PIC method is a calculation scheme by which accurate results can be obtained with less computational consumption. In this calculation scheme, the PIC method and hybrid-PIC method are used sequentially in different stages of ion extraction process. One-dimensional parallel type simulation cases are carried out under the circumstances of different initial plasma densities, applied voltages and background atom densities. The results show that the resonant charge exchange process happens in both shield layer and sheath layer. The ionic resonant charge exchange proportion in shield layer and sheath layer are related to the ion extraction time and average travel length in background vapor, respectively. Besides, they are proportional to the resonant charge exchange cross section and background atom density. And an empirical formula for deriving the resonant charge exchange ratio roughly is proposed. Two-dimensional simulations are carried out in four electrode configurations: parallel type, alternately biased parallel type, Π-type, and M-type. The extraction mechanisms are discussed and compared with each other. The simulation results show that M-type electrode configuration has the minimum resonant charge exchange ratio and extraction time among the configurations above. The results and conclusions provide an important reference for designing the LIS device.-
Keywords:
- resonant charge exchange /
- particle-in-cell method /
- sheath layer /
- shield layer
[1] 王德武 1999 激光分离同位素理论及其应用(北京: 原子能出版社) 第218页
Wang D W 1999 Theory and Application of Laser Isotope Separation (Beijing: Atomic Energy Press) p218(in Chinese)
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Google Scholar
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Google Scholar
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Google Scholar
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Google Scholar
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Google Scholar
[15] 严敏 1994 博士学位论文 (北京: 清华大学)
Yan M 1994 Ph. D. Dissertation (Beijing: Tsinghua University) (in Chinese)
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Xie G F 2004 Ph. D. Dissertation (Beijing: Tsinghua University) (in Chinese)
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Google Scholar
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Google Scholar
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图 2 一维平行板电场法离子引出示意图
Fig. 2. Schematic diagram of one dimensional electric ion extraction of parallel type.
图 3 剩余离子比例随引出时间的变化曲线 (算例1)
Fig. 3. Plots of remaining ion ratio versus extraction time (Case 1).
图 4 两侧收集板上的离子沉积能量分布 (算例1) (a) 整体图; (b) 局部放大图
Fig. 4. Energy distribution of ions deposit on the collection plates (Case 1): (a) General distribution; (b) local distribution.
图 5 不同初始等离子体密度条件下, 两侧收集板上的离子沉积能量分布(算例1)
Fig. 5. Energy distribution of ions deposit on the collection plates with several initial plasma densities (Case 1).
图 6 不同引出电压条件下, 剩余离子比例随引出时间的变化曲线(算例1和算例2)
Fig. 6. Plots of remaining ion ratio versus extraction time with several applied voltages (Case 1 and Case 2).
图 7 不同引出电压条件下, 两侧收集板上的离子沉积能量分布(算例1和算例2)
Fig. 7. Energy distribution of ions deposit on the collection plates with several applied voltages (Case 1 and Case 2).
图 8 不同背景原子蒸气密度条件下, 剩余离子比例随引出时间的变化曲线(算例1、算例3、算例4)
Fig. 8. Plots of remaining ion ratio versus extraction time with several background atomic densities (Case 1, Case 3, Case 4).
图 9 不同背景原子蒸气密度条件下, 两侧收集板上的离子沉积能量分布(算例1、算例3、算例4) (a) 整体图; (b) 局部放大图
Fig. 9. Energy distribution of ions deposit on the collection plates with several background atomic densities (Case 1, Case 3, Case 4): (a) General distribution; (b) local distribution.
图 10 两侧收集板上的离子沉积能量分布(算例5)
Fig. 10. Plots of remaining ion ratio versus extraction time (Case 5).
图 11 两侧收集板上的离子沉积能量分布(算例5)
Fig. 11. Energy distribution of ions deposit on the collection plates (Case 5).
图 12 二维电场法离子引出示意图 (a) 平行板电场法; (b) 交替偏压法; (c) Π型电场法; (d) M型电场法
Fig. 12. Schematic diagram of two dimensional electric ion extraction: (a) Parallel type; (b) alternately biased parallel type; (c) Π-type; (d) M-type.
图 13 平行板电场法中, 收集板上的离子沉积能量分布 (a) 同位素A; (b) 同位素B
Fig. 13. Energy distribution of ions deposit on the collection plates in parallel type: (a) Isotope A; (b) isotope B.
图 14 交替偏压电场法中, 收集板上的离子沉积能量分布 (a) 同位素A; (b) 同位素B
Fig. 14. Energy distribution of ions deposit on the collection plates in alternately biased parallel type: (a) Isotope A; (b) isotope B.
图 15 Π型电场法中, 收集板上的离子沉积能量分布 (a) 同位素A; (b) 同位素B
Fig. 15. Energy distribution of ions deposit on the collection plates in Π-type: (a) Isotope A; (b) isotope B.
图 16 M型电场法中, 收集板上的离子沉积能量分布 (a) 同位素A; (b) 同位素B
Fig. 16. Energy distribution of ions deposit on the collection plates in M-type: (a) Isotope A; (b) isotope B.
表 1 一维算例的计算条件
Table 1. Simulation parameters in onedimensional cases.
算
例计算参数 同位素A
电离率/%初始离子密
度/(109 cm–3)引出电
压/kV背景原子密
度/(1011 cm–3)1 2.5 5.0 2.0 4.0 2 2.5 5.0 1.0 4.0 3 5.0 5.0 2.0 2.0 4 1.25 5.0 2.0 8.0 5 50 100.0 10.0 4.0 
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表 2 各算例的数值计算结果和公式评估结果
Table 2. Simulation and empirical formula results of several simulation cases.
算例 引出时间/μs 负极板引出离子比例/% 共振电荷转移的比例 鞘层/% 通过鞘层发生共振电荷转移的比例/% 屏蔽层/% 总比例/% 1 37.23 84.62 0.780 (0.846) 0.921 (1.000) 0.371 (0.395) 1.151 (1.241) 2 66.78 70.24 0.615 (0.702) 0.876 (1.000) 0.663 (0.691) 1.278 (1.393) 3 37.20 84.61 0.384 (0.423) 0.454 (0.500) 0.192 (0.200) 0.576 (0.623) 4 37.36 84.65 1.151 (1.693) 1.784 (2.000) 0.740 (0.785) 2.250 (2.478) 5 51.62 75.78 0.654 (0.758) 0.864 (1.000) 0.549 (0.533) 1.203 (1.291)
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表 3 四种引出构型中同位素A离子与同位素B原子发生共振电荷转移的比例
Table 3. Resonant charge exchange ratio between A-ion and B-atom in four electrode configurations above.
离子引出构型 共振电荷转移比例/% 平行板电场法 1.097 交替偏压电场法 0.911 Π型电场法 0.859 M型电场法 0.640
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[1] 王德武 1999 激光分离同位素理论及其应用(北京: 原子能出版社) 第218页
Wang D W 1999 Theory and Application of Laser Isotope Separation (Beijing: Atomic Energy Press) p218(in Chinese)
[2] Yamada K, Okada H, Tetsuka T, Yoshioka K 1993 J. Nucl. Sci. Technol. 30 143
Google Scholar
[3] Yamada K, Tetsuka T, Deguchi Y 1990 J. Appl. Phys. 67 6734
Google Scholar
[4] Yamada K, Tetsuka T, Deguchi Y 1991 J. Appl. Phys. 69 8064
Google Scholar
[5] Yamada K, Tetsuka T 1994 J. Nucl. Sci. Technol. 31 301
Google Scholar
[6] Kurosawa H, Hasegawa S, Suzuki A 2002 J. Appl. Phys. 91 4818
Google Scholar
[7] Watanabe J, Okano K 1993 Phys. Fluids. B 1993 3092
[8] Ogura K, Kaburaki H, Shibata T 1993 J. Nucl. Sci. Technol. 30 1248
Google Scholar
[9] Zhidkov A G 1998 Phys. Plasmas 5 541
Google Scholar
[10] Matsui T, Tsuchida K, Tsuda S, Suzuki K, Shoji T 1996 Phys. Plasmas 3 4367
Google Scholar
[11] Matsui T, Tsuchida K, Tsuda S, Suzuki K, Shoji T 1997 J. Nucl. Sci. Technol. 34 923
Google Scholar
[12] Matsui T, Tsuda S, Tsuchida K, Suzuki K, Shoji T 1997 Phys. Plasmas 4 3527
Google Scholar
[13] Matsui T, Tsuchida K, Tsuda S, Suzuki K, Shoji T 1997 Phys. Plasmas 4 3518
Google Scholar
[14] Murakami M, Ueshima Y, Nishihara K 1993 Jpn. J. Appl. Phys. 32 1471
Google Scholar
[15] 严敏 1994 博士学位论文 (北京: 清华大学)
Yan M 1994 Ph. D. Dissertation (Beijing: Tsinghua University) (in Chinese)
[16] 谢国锋 2004 博士学位论文 (北京: 清华大学)
Xie G F 2004 Ph. D. Dissertation (Beijing: Tsinghua University) (in Chinese)
[17] Verboncoeur J P 2005 Plasma Phys. Controlled Fusion 47 A231
Google Scholar
[18] Tskhakaya D, Matyash K, Schneider R Taccogna F 2007 Contrib. Plasma Phys. 47 563
Google Scholar
[19] Lu X Y, Yuan C, Zhang X Z, Zhang Z Z 2020 Chin. Phys. B 29 045201
Google Scholar
[20] Smirnov B M 2001 Phys. Usp. 44 221
Google Scholar
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