合肥红外自由电子激光束流注入器改进设计

彭小钰; 张浩然; 胡浩; 胡桐宁; 邓建军; 冯光耀

doi:10.11884/HPLPB202537.250022

合肥红外自由电子激光束流注入器改进设计

doi: 10.11884/HPLPB202537.250022

彭小钰^{1, 4,},
张浩然¹,
胡浩²,
胡桐宁^2, ,,
邓建军³,
冯光耀^1, ,

1.
中国科学技术大学国家同步辐射实验室，合肥 230026
2.
华中科技大学电气与电子工程学院强电磁技术全国重点实验室，武汉 430074
3.
中国工程物理研究院流体物理研究所，四川绵阳 621900
4.
张江实验室，上海 201204

基金项目: 中国科学院百人计划；国家自然科学基金项目(11905074)

详细信息

作者简介:
彭小钰，pengxiaoyuu@yeah.net

通讯作者:
胡桐宁，TongningHu@hust.edu.cn

冯光耀，fenggy@ustc.edu.cn。

中图分类号: O462、TL5
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- 文章访问数: 68
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- PDF下载量: 7
- 被引次数: 0
出版历程
- 收稿日期: 2025-02-10
- 修回日期: 2025-07-29
- 录用日期: 2025-07-29
- 网络出版日期: 2025-08-13

Optimized Design of Hefei Infrared Free Electron Laser Beam Injector

Peng Xiaoyu^{1, 4
,},
Zhang Haoran¹,
Hu Hao²,
Hu Tongning^{2
, ,},
Deng Jianjun³,
Feng Guangyao^{1
, ,}

1.
National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei 230026, China
2.
State Key Laboratory of Advanced Electromagnetic Technology, School of Electrical and Electronic Engineering, Huazhong University of Science and Technology, Wuhan 430074, China
3.
Institute of Fluid Physics, CAEP, Mianyang 621900, China
4.
Zhangjiang Laboratory, shanghai 201204, China

摘要

摘要: 基于正在运行的合肥红外自由电子激光装置注入器的指标要求，对注入器结构进行优化设计，得到更适合红外振荡器型自由电子激光装置的电子束。基于前期电子枪栅网结构的优化结果改进设计，将现有六次次谐波聚束系统的前级增设一个新的十二次次谐波聚束腔，再结合改进的行波聚束结构对束团进行聚束和加速。在束流动力学优化过程中首先设计次谐波聚束腔，扫描束流注入相位、行波聚束器相速度等参数使得电子束在聚束阶段中达到100%捕获，能量提升至接近4.4 MeV。随后，通过装置原有的两个等梯度行波加速管，束流能量被提升至64 MeV。根据红外自由电子激光的实际应用需求，滤除高能散电子，对±1%束团能散的电子束进行统计，优化后核心束团的均方根纵向长度降低至3.1 ps，能散低于0.23 MeV，归一化横向发射度可以降低至9.8 mm · mrad，同时峰值流强达到270 A，为原有优化结果的2.7倍。优化后的注入器能够为光源的运行提供更高品质的电子束，有望驱动产生质量更为优异的红外辐射光。
- 红外自由电子激光 /
- 电子束 /
- 注入器 /
- 次谐波聚束腔 /
- 束流动力学
Abstract: Background
Free electron lasers have emerged as significant advanced light sources owing to their unique advantages, including high power, excellent coherence, and wavelength tunability. Given that the peak and average brightness of an FEL depend on the quality of the electron beam generated by its injector, the optimization of the beam injector constitutes a key technical challenge in FEL development. The Hefei Infrared Free Electron Laser facility, a state-of-the-art, oscillator-type user facility providing continuously tunable mid-to-far-infrared radiation.
Purpose
The injector structure of Hefei Infrared Free Electron Laser is optimized to obtain electron beams with lower emittance, shorter beam length, smaller energy spread and higher peak current intensity, so as to improve the performance of driving infrared free electron laser light source.
Methods
The optimization research is carried out by combining beam dynamics simulation with numerical simulation. Based on the previous optimization of the electron gun’s grid structure, the improved design is carried out. A new 12th sub-harmonic buncher is added to the front stage of the existing 6th sub-harmonic buncher, and then the beam is bunched and accelerated by using the appropriate traveling-wave buncher. Key parameters including the beam injection phase and the phase velocity variation in the traveling-wave buncher’s tapered section are systematically scanned to achieve 100% bunch capture efficiency and accelerate the electron beam to near-light-speed energy during the bunching stage.
Results
Finally, the beam energy is increased to 64 MeV, and the root mean square length of the whole bunch reaches 8.5 ps. The high-energy scattered electrons are filtered out, and the electron beams scattered by ±1% bunch energy are counted. The optimized beam core achieves a root-mean-square longitudinal bunch length of 3.1 ps with an energy spread below 0.23 MeV, while the normalized transverse emittance is reduced to 9.8 mm·mrad. At the same time, the peak current intensity reaches 270 A, which is 2.7 times that of the original optimization results.
Conclusions
The simulation shows that the longitudinal length, energy dispersion and emittance of the core region of the bunch are significantly reduced after optimization, and the peak current intensity is greatly improved. Compared with the original structure, this scheme has significant advantages in the key performance of free electron laser, which has important engineering value for light source upgrading. The optimization method can be extended to the design of other light source injectors.
- free electron laser /
- electron beam /
- injector /
- electron gun /
- sub-harmonic buncher

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图 1 合肥红外自由电子激光装置布局图

Figure 1. Hefei infrared free electron laser device layout diagram

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图 2 预注入器组成部件示意图

Figure 2. Schematic diagram of components of pre-injector

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图 3 12次SHB的结构示意图及调参优化得到的Pareto前沿分布

Figure 3. The structure diagram of 12th SHB and the Pareto frontier distribution obtained by optimization

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图 4 6次SHB的结构示意图及调参优化得到的Pareto前沿分布

Figure 4. The structure diagram of 6th SHB and the Pareto frontier distribution obtained by optimization

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图 5 优化后的12次SHB和6次SHB的结构及轴上电场分布

Figure 5. Structure of the optimized 12th SHB and 6th SHB on-axis electric field distribution

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图 6 束流通过射频腔前、射频腔中及射频腔后的电子及其能量分布

Figure 6. The electron and its energy distribution before, in and after the beam passing through the RF cavity

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图 7 整束团的相空间、电子能量及电子密度分布

Figure 7. Phase space, electron energy and electron density distribution of the whole bunch

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图 8 束流参数随注入行波聚束器的相位变化的曲线

Figure 8. The curve of the beam parameters with the phase change of the injected traveling-wave buncher

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图 9 行波聚束器出口束流纵向分布及不同纵向初始相位电子沿行波聚束器Z轴相轨道的变化

Figure 9. The longitudinal distribution of the beam at the outlet of the traveling-wave buncher and the change of the Z-axis phase orbit of the electrons with different longitudinal initial phases along the traveling-wave buncher

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图 10 注入器螺线管磁场和射频场沿Z方向的分布

Figure 10. The distribution of magnetic field and RF field of the injector solenoid along the Z direction

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图 11 加速管出口束团相空间分布

Figure 11. Phase space distribution of bunch at the outlet of accelerator

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表 1 FELiChEM的注入器电子束参数

Table 1. Electron beam parameters of injector for FELiChEM

	electron energy/MeV	energy spread/keV	bunch charge/nC	micro-pulse RMS length/ps	peak current/A	normalized RMS transverse emittance/(mm·mrad)
Target	15～60	＜240	1.0	1～5	100	＜30

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表 2 优化前的SHB参数

Table 2. Parameters of the SHB before optimization

component	frequency /MHz	cavity voltage /(kV·m⁻¹)	Q	shunt impedance /(MΩ·m⁻¹)	effective shunt impedance /(MΩ·m⁻¹)
12th SHB	238	290	30442	25.47	2.89
6th SHB	476	170	19047	37.99	14.953

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表 3 12次SHB的结构参数可调范围

Table 3. Adjustable range of 12th SHB’s structural parameters

No.	minimum	maximum
①	R=1	R=40
②	Y=248	Y=327
③	X=175	X=215
④	R=1	R=40
⑤	X=138	X=178
⑥	120°	160°
⑦	X=144	X=184
⑧	X=70	X=90
⑨	Y=37	Y=200

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表 4 6次SHB的结构参数可调范围

Table 4. Adjustable range of 6th SHB’s structural parameters

No.	minimum	maximum
①	R=1	R=30
②	Y=95	Y=195
③	X=124	X=204
④	X=81	X=131
⑤	Y=22	Y=39
⑥	X=59	X=119
⑦	X=15	X=85
⑧	X=21	X=60

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表 5 优化后的SHB参数

Table 5. Parameters of the optimized SHB

component	frequency /MHz	cavity voltage /(kV·m⁻¹)	Q	shunt impedance /(MΩ·m⁻¹)	effective shunt impedance /(MΩ·m⁻¹)
12th SHB	238.044	290	33514	31.65	3.592
6th SHB	476.071	170	31441	64.79	19.983

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表 6 注入器不同位置束流参数

Table 6. Beam parameter at different positions of the injector

Position	longitudinal length/ps	charge/nC	normalized RMS emittance/(mm·mrad)	energy/MeV	RMS Beam energy spread/MeV
Electron gun	600.0	1.5	2.0	0.10	0.001
12th SHB	123.0 (RMS)	1.5	5.7	0.23	0.035
6th SHB	58.0 (RMS)	1.5	14.7	0.30	0.055
Buncher	9.3 (RMS)	1.5	14.8	4.40	0.530
First linear accelerator	8.5 (RMS)	1.5	16.0	42.50	0.860
Second linear accelerator	8.5 (RMS)	1.5	16.5	64.70	1.700

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表 7 本文优化结果与现FELiChEM设计参数对比

Table 7. The comparison between the optimized results in this paper and the FELiChEM’s designed value

	RMS longitudinal length /ps	charge/nC	RMS emittance/ (mm·mrad)	energy/MeV	peak current/A	RMS energy dispersion/MeV
FELiChEM’s designed value	4.5	1.00	＜30.0	60.0	100	0.24
Full bunch	8.5	1.50	16.5	64.7	270	1.75
Core bunch	3.1	1.11	9.8	64.7	270	0.23

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参考文献(18)

[1]	范伟杰, 冯超, 赵明华. 上海软X射线自由电子激光外种子运行模式的模拟研究[J]. 强激光与粒子束, 2022, 34:031016 doi: 10.11884/HPLPB202234.210262 Fan Weijie, Feng Chao, Zhao Minghua. Simulation studies of external seeding schemes for Shanghai soft X-ray free electron laser[J]. High Power Laser and Particle Beams, 2022, 34: 031016 doi: 10.11884/HPLPB202234.210262
[2]	陈思富, 黄子平, 石金水. 带电粒子加速器的基本类型及其技术实现[J]. 强激光与粒子束, 2020, 32:045101 Chen Sifu, Huang Ziping, Shi Jinshui. Basic types and technological implementation of charged particle accelerators[J]. High Power Laser and Particle Beams, 2020, 32: 045101
[3]	李和廷, 何志刚, 吴芳芳, 等. 合肥红外自由电子激光装置[J]. 中国激光, 2021, 48:1700001 doi: 10.3788/CJL202148.1700001 Li Heting, He Zhigang, Wu Fangfang, et al. Hefei infrared free-electron laser facility[J]. Chinese Journal of Lasers, 2021, 48: 1700001 doi: 10.3788/CJL202148.1700001
[4]	Li Heting, Jia Qika. Commissioning and first lasing of the FELiChEM: a new IR and THz FEL oscillator in China[C]//39th Free Electron Laser Conference. 2019: 15-19.
[5]	Li Heting, Jia Qika, Zhang Shancai, et al. Design of FELiChEM, the first infrared free-electron laser user facility in China[J]. Chinese Physics C, 2017, 41: 018102. doi: 10.1088/1674-1137/41/1/018102
[6]	Li Heting, Jia Qika, Zhang Shancai, et al. Design of the mid-infrared FEL oscillator in China[C]//Proceedings of FEL2015. 2015: 427-429.
[7]	He Zhigang, Xu Wei, Zhang Shancai, et al. Linac design of the IR-FEL project in China[C]//37th International Free Electron Laser Conference. 2015: 46-48.
[8]	贾启卡. 自由电子激光物理导论[M]. 北京: 科学出版社, 2021 Jia Qika. Introduction to free electron laser physics[M]. Beijing: Science Press, 2021
[9]	邓建军, 丁伯南, 王华岑, 等. "神龙一号"直线感应加速器物理设计[J]. 强激光与粒子束, 2003, 15(5):502-504 Deng Jianjun, Ding Bonan, Wang Huacen, et al. Physical design of the Dragon-I linear induction accelerator[J]. High Power Laser and Particle Beams, 2003, 15(5): 502-504
[10]	Peng Xiaoyu, Hu Tongning, Peng Yufei, et al. Optimized design of a thermionic electron gun applied to a high-power FEL injector[C]//2023 IEEE 4th China International Youth Conference on Electrical Engineering (CIYCEE). 2023: 1-6.
[11]	Peng Xiaoyu, Hu Hao, Hu Tongning, et al. Emittance optimization of gridded thermionic-cathode electron gun for high-quality beam injectors[J]. Nuclear Science and Techniques, 2024, 0482. R1.
[12]	Hu Tongning, Li Junyang, Pei Yuanjie, et al. Indirect estimations of energy and energy spread for a compact free electron laser-terahertz pre-injector using RF measuring parameters[J]. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2021, 1016: 165775. doi: 10.1016/j.nima.2021.165775
[13]	钟少鹏, 赵明华, 汪宝亮. 上海光源150 MeV直线加速器次谐波腔耦合器的设计与调试[J]. 强激光与粒子束, 2010, 22(5):1125-1128 doi: 10.3788/HPLPB20102205.1125 Zhong Shaopeng, Zhao Minghua, Wang Baoliang. Design and test of sub-harmonic cavity's coupler for 150 MeV linac of Shanghai synchrotron radiation facility[J]. High Power Laser and Particle Beams, 2010, 22(5): 1125-1128 doi: 10.3788/HPLPB20102205.1125
[14]	周文振, 李文琴, 浦德修, 等. 强流射频电子直线加速器中的分频预聚束器的研制[J]. 强激光与粒子束, 1990, 2(3):311-318 Zhou Wenzhen, Li Wenqin, Pu Dexiu, et al. Development of subharmonic prebuncher in RF electron linear accelerator with high current[J]. High Power Laser and Particle Beams, 1990, 2(3): 311-318
[15]	Hu Tongning, Pei Yuanji, Qin Bin, et al. Study of beam transverse properties of a thermionic electron gun for application to a compact THz free electron laser[J]. Review of Scientific Instruments, 2014, 85: 103302. doi: 10.1063/1.4897481
[16]	Hu Tongning, Wang Haimeng, Zeng Yifeng, et al. Fault locating for traveling-wave accelerators based on transmission line theory[J]. Nuclear Science and Techniques, 2023, 34: 116. doi: 10.1007/s41365-023-01279-z
[17]	Zeng Yifeng, Hu Hao, Hu Tongning. Improvement and correction for transverse emittance diagnosis based on Q-scanning techniques[J]. Nuclear Science and Techniques, 2025, 36: 38. doi: 10.1007/s41365-024-01597-w
[18]	杨国君, 张卓, 何小中. 750 keV射频四极注入器射频结构的优化[J]. 强激光与粒子束, 2008, 20(8):1349-1352 Yang Guojun, Zhang Zhuo, He Xiaozhong. RF optimization design of a 750 keV radio frequency quadrupole injector[J]. High Power Laser and Particle Beams, 2008, 20(8): 1349-1352