Design and analysis of a tunable coupler for application to adjustable beam injectors
-
摘要:
驻波谐振腔是基于直线加速器的束流注入器的基本构造元件，其大功率微波馈入一般选用矩形波导耦合器，但它会引起场不对称和谐振频率的漂移，也难以针对不同流强的束流灵活调节耦合度。建立了带有调配杆的耦合器的等效电路模型，在理论分析的基础上，给出了杆的最佳位置。此外，在耦合器的对称方向插入调谐杆用于补偿结构改变及加工安装等外部因素造成的频率漂移，并使用 CST MICROWAVE STUDIO 的三维电磁仿真给出了两个杆的尺寸和调整范围。联合调整的仿真结果表明，在谐振频率保持稳定的情况下，不同流强的束流均达到临界耦合状态，从而避免了耦合器失配引起的反射功率风险，并减少了由于较小耦合孔引起的场不对称。
Abstract:As a fundamental component of a linac-based beam injector, the rectangular-waveguide coupler is a conventional device for feeding high power, but it will induce field asymmetry and resonant-frequency shifting. Furthermore, it is also difficult to adjust the coupling factor for adjustable beam injectors. In this paper, an equivalent circuit model is established for the coupler with a tuning rod. Based on theoretical analysis, the optimal position for the rod is given. Besides, the frequency shifting is corrected by using another rod inserted to the cavity in the opposite direction. Sizes and adjustment ranges of both rods are given by three-dimensional electromagnetic simulation using CST MICROWAVE STUDIO. Jointly adjusted simulation results show that, critical-coupled states are achieved for different beam intensity while the resonant frequency remains stable, thus the risk of reflected power caused by coupler mismatching can be avoided, and the field asymmetry due to a small coupling hole can be reduced.
-
Key words:
- coupling coefficient /
- resonance tuning /
- standing-wave cavity /
- RF accelerator
-
Figure 2. (a) Equivalent circuit of a one-port-coupled cavity and (b) equivalent circuit of a coupling tuner Tc inserted into the waveguide
Figure 4. (a) Resonant frequency and coupling factor at different hctuner and (b) resonant frequency and coupling factor at different hftuner
Figure 6. Electric field distribution of the dipole in the cavity along the circumference
Table 1. Effect of the Tc radius on coupling factor and resonant frequency
radius/m coupling factor resonant frequency/MHz 2 0.60–2.70 2856.00–2856.02 4 0.60–3.42 2856.00–2856.10 6 0.60–3.90 2856.00–2856.15 
下载: 导出CSV
Table 2. Effect of the Tf radius on coupling factor and resonant frequency
radius/mm coupling factor resonant frequency/MHz 1 1.66–1.67 2856.00–2856.47 3 1.66–1.71 2856.00–2859.80 5 1.66–1.77 2856.00–2865.79
下载: 导出CSV
-
[1] Hu Tongning, Pei Yuanji, Qin Bin, et al. Development of a novel thermionic RF electron gun applied on a compact THz-FEL facility[J]. Nuclear Instruments and Methods in Physics Research Section A:Accelerators, Spectrometers, Detectors and Associated Equipment, 2018, 887: 1-6. [2] Tan Ping, Huang Jiang, Liu Kaifeng, et al. Terahertz radiation sources based on free electron lasers and their applications[J]. Science China Information Sciences, 2012, 55(1): 1-15. [3] Hu Tongning, Pei Yuanji, Feng Guoyao. Bunch length evaluation for typical low-energy beam injectors based on RF-phasing techniques[J]. Nuclear Instruments and Methods in Physics Research Section A:Accelerators, Spectrometers, Detectors and Associated Equipment, 2019, 916: 87-93. [4] Hong J, Parc Y W, Ko I S. Reduction of the higher-order field distribution in a photocathode rf gun for the X-ray free electron laser[J]. Journal of the Korean Physical Society, 2014, 65(12): 2023-2032. doi: 10.3938/jkps.65.2023 [5] Kumar R, Singh P, Unnikrishnan D, et al. A tunable waveguide to cavity coupler for high power accelerator cavities[J]. Nuclear Instruments and Methods in Physics Research Section A:Accelerators, Spectrometers, Detectors and Associated Equipment, 2012, 664(1): 203-213. [6] Kumar R. A novel method for variable coupling using iris rotation in RF couplers[J]. Nuclear Instruments and Methods in Physics Research Section A:Accelerators, Spectrometers, Detectors and Associated Equipment, 2009, 600(3): 534-537. [7] Ego H. RF input coupler with a coupling tuner for an RF acceleration cavity[J]. Nuclear Instruments and Methods in Physics Research Section A:Accelerators, Spectrometers, Detectors and Associated Equipment, 2006, 564(1): 74-80. [8] De Jong M S, Adams F P, Burton R J, et al. Design of a tuner and adjustable RF coupler for a CW 2856 MHz RF cavity[C]//Proceedings of International Conference on Particle Accelerators. 1993: 829-831. [9] Qian Houjun, Tang Chuanxiang, Zheng Shuxin, et al. Analysis and experiments of a waveguide post’s influence on photocathode RF gun[J]. Nuclear Instruments and Methods in Physics Research Section A:Accelerators, Spectrometers, Detectors and Associated Equipment, 2008, 597(2/3): 121-125. [10] Hu Tongning, Pei Yuanji, Feng Guoyao. Electron beamline of a Linac-based injector applied to a compact free electron laser-terahertz radiation source[J]. Japanese Journal of Applied Physics, 2018, 57: 100310. doi: 10.7567/JJAP.57.100310 [11] Li Ji, Pei Yuanji, Hu Tongning, et al. Design of an electron gun for terahertz radiation source[J]. Chinese Physics C, 2014, 38: 047004. doi: 10.1088/1674-1137/38/4/047004 [12] Tang Zhenxing. Research on related technologies of high power compact THz source electron beam device based on FEL[D]. Hefei: University of Science and Technology of China, 2015. [13] Wangler T P. RF linear accelerators[M]. 2nd ed. New York: Wiley-VCH, 2008: 213. [14] Altam D. Microwave circuits[M]. Princeton: Van Nostrand, 1964: 135. [15] Liang Yajuan, Hu Tongning, Tan Ping, et al. Coupler simulation and test of an independently tunable RF gun[J]. High Power Laser and Particle Beams, 2017, 29: 113002. -
点击查看大图
计量
- 文章访问数: 608
- HTML全文浏览量: 266
- PDF下载量: 38
- 被引次数: 0
