Development of a ferrite-silicon carbide hybrid high-order mode damper for accelerators
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摘要: 大电流加速器束管中，当带电粒子流通过束管时，会在束管中激励起高频场，为了降低对束流的影响，束管中产生的高次模需要利用阻尼器将高频场能量转换成热量并通过冷却装置导走。介绍了某混合型高次模阻尼器的研制及主要性能。阻尼器采用的吸收材料为铁氧体和碳化硅，吸收材料通过金属化和钎焊实现与金属基板的焊接。通过CST和COMSOL软件分别开展了微波性能仿真和热仿真，对阻尼器的结构进行了优化设计。阻尼器的测试结果表明：该混合型阻尼器的吸收效率与计算结果在1.7 GHz以下频段相接近，在1.7 GHz以上高频段后，仿真吸收效率高于实测结果，相差较大；真空漏率、极限真空、水路耐压均满足超导高频腔设计需求。Abstract: In large current accelerator beam tubes, high-frequency fields are generated when charged particles circulate within the beam pipe. To mitigate the impact on beam current, it is essential to use high-order mode damper to convert the high field energy into heat, which can then be dissipated by a cooling system. This paper presents the research, fabrication, and key performance characteristics of a hybrid high-order mode damper. The absorbing materials utilized in the damper include ferrite and silicon carbide, which can be welded to metal substrates through metallization and welding techniques. Microwave performance simulations and thermal simulations were conducted using CST and COMSOL software, respectively, leading to an optimized damper structure. Test results demonstrate that the absorption efficiency of the hybrid damper aligns closely with the calculated values in the frequency range below 1.7 GHz. However, the simulated absorption efficiency exceeds the measured results significantly above 1.7 GHz. Additionally, the vacuum leak rates, ultimate vacuum, and water resistance meet the design requirements for superconducting high-frequency cavities.
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Key words:
- high-order-mode /
- damper /
- ferrite /
- silicon carbide /
- welding
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随着科学技术的发展，核技术具有零碳排放、能源独立、安全等诸多优势，在人类社会中的地位越来越重要。然而，核辐射事故却为核技术发展迅速蒙上了一层阴影。1986年，苏联切尔诺贝利核电站发生了迄今为止人类历史上最严重的核辐射事故[1]。2011年，日本东北海岸发生了里氏9.0级的强烈地震和海啸，造成了福岛第一核电站的1～3号机组反应堆熔毁[2]。由于反应堆内部高温和高辐射等极端环境，人类无法直接进入进行勘察和处置工作，因此在福岛事故中使用了多种类型和功能的机器人。光纤激光器具有高功率、高光束质量，光束可以远距离柔性传输等优点，可以用于无人区开展激光切割救援等工作[3]。比如Shin等人研究了用10 kW光纤激光器拆除核设施的150 mm厚的厚钢板和大型管道的切割性能[4]。当然，光纤激光器在辐射环境中也会受到影响[5]，高能射线会导致增益光纤产生色心等各类缺陷，这些缺陷引起的额外光吸收增加了传输损耗，降低了光纤激光器性能。
课题组基于光纤激光器存在的自漂白效应，利用60CO辐照源探索不同辐照剂量率下的光纤激光器暗化与自漂白的平衡关系。实验先采用低功率光纤振荡器进行不同辐照剂量率下激光器输出功率演化和去辐照后自漂白研究。使用的光纤激光振荡器实验结构如图1所示，谐振腔由常规商业掺镱光纤（YDF）、高反射光纤光栅（HR-FBG）、低反射光纤光栅（OC-FBG）构成，中心波长为976 nm的泵浦源（LDs）通过前向（2+1）×1泵浦信号合束器（FPSC）注入到谐振腔中，激光经过包层光滤除器（CLS）后由光纤端帽（QBH）扩束输出。
首先，利用较高辐照剂量率研究在去辐照后的自漂白效应，结果如图2（a）所示。图2（a）的(I)为未辐照阶段，持续时间为680 s，由于水冷机周期性制冷使得功率计温度周期变化导致测试激光功率也存在周期变化，激光器功率起伏为1.44%；需要注意的是，这个是主要功率测量误差导致，并不是激光器本身功率起伏。图2（a）中(II)为辐照阶段，在总辐照时间298 s内，辐照总剂量为14 900 rad，激光器输出功率从150 W下降至105 W。图2（a）的(III)为去辐照后的自漂白阶段，在光纤激光器的泵浦光子与热效应的共同作用下，激光器输出功率从118 W恢复di至145 W，与初始功率相差仅5 W，表明自漂白效应可以较为有效地恢复由于辐照导致的激光功率下降。
图 2 光纤激光器在辐照环境下的输出特性Figure 2. Output characteristics of the optical fiber laser in an irradiated environment然后，为了探索不同剂量率的自漂白与在线辐照相互作用是否可以达到平衡，开展了不同剂量率的对比研究，结果如图2（b）所示。图2（b）中，总辐照剂量为2 400 rad，红色、蓝色曲线分别对应辐照剂量率为50 rad/s、1 rad/s时激光器归一化输出功率演化情况；在辐照剂量率为50 rad/s时，激光输出功率下降了3%；在辐照剂量率1 rad/s时，功率起伏1.22%，考虑到这里的周期性起伏主要由于水冷机周期性制冷导致，可以认为在低辐照剂量率下，光纤激光器自漂白导致的功率提升与辐照导致的功率下降基本达到平衡。
进一步地，基于图2（b）的实验结果，我们验证了1 kW级光纤激光器中自漂白与辐照平衡的实验现象。在辐照剂量率为0.1 rad/s时，激光器输出激光功率曲线演化如图2（c）所示。从实测功率曲线来看，在总辐照剂量为190 rad的整个辐照过程中，光纤激光器的输出功率都稳定在1 050 W以上，即使考虑前述由于水冷机导致的功率变化，激光器的功率起伏在1.79%以内。如果不考虑水冷机周期性制冷影响，激光器的功率起伏在0.66%以内。
实验首次验证了在一定辐照剂量率下，光纤激光器自漂白效应导致的激光功率提升可以平衡辐照效应导致的功率下降，为相关场景应用的光纤激光器设计提供了有效支撑。后续，我们将继续深入相关研究，探索不同类别、不同结构激光器辐照与自漂白平衡的机理、阈值和可能的应用。
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图 2 混合型高次模阻尼器，内径为320 mm，高度为445 mm
Figure 2. Hybrid high-order mode damper with an inner diameter of 320 mm and a height of 445 mm
图 3 混合型高次模阻尼器仿真与实测吸收效率（无短路活塞）
Figure 3. Simulation and measurement of absorption efficiency of hybrid high-order mode damper (no short piston)
图 4 混合型高次模阻尼器在吸收功率为10 kW时的水路温度分布仿真结果
Figure 4. Simulation results of water temperature distribution for the hybrid high-order mode damper with an absorbed power of 10 kW
图 5 混合型高次模阻尼器在吸收功率为10kW时的吸波材料温度分布仿真结果
Figure 5. Simulation results of absorbing materials temperature distribution for the hybrid high-order mode damper with an absorbed power of 10kW
图 6 不同吸收功率下进出口水的温升(约0.4 MPa水压)
Figure 6. Temperature rise of inlet and outlet water under different absorbed power (about 0.4 MPa water pressure)
图 7 不同输入功率下吸收功率及吸收效率
Figure 7. Absorption power and absorption efficiency under different input power
表 1 混合型高次模阻尼器在吸收功率为10 kW时的温度分布仿真及测试结果
Table 1. Simulation and measurement results of temperature distribution for the hybrid high-order mode damper with an absorbed power of 10 kW
temperature difference between the inlet and outlet cooling water/℃ simulation result 2.3 measurement result 1.1 
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表 2 混合型高次模阻尼器的性能测试结果
Table 2. Performance test results of the hybrid high-order mode damper
vacuum leak rate/(Pa·L·s−1) ultimate vacuum/Pa water-resistant/MPa 5×10−10 4.6×10−8 0.92
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表 3 混合型高次模阻尼器的设计要求及性能测试结果
Table 3. Design requirements and performance test results of the hybrid high-order mode damper
absorbed
power/kWabsorption
efficiencyvacuum leak
rate/
(Pa·L·s−1)ultimate
vacuum/
Pawater-
resistant/
MPatemperature difference
between the outlet and
inlet cooling water/℃design
requirements≥10 operating frequency band(0.6～3.0 GHz)≥30%,
critical frequency bands(0.8～1.5 GHz)≥50%≤1×10−7 ≤6.5×10−8 ≥0.9 ≤5 simulation
results10 operating frequency band(0.6～3.0 GHz)≥53%,
critical frequency bands(0.8～1.5 GHz)≥61%— — — — — — 2.3 measurement
results10.2 operating frequency band(0.6～3.0 GHz)≥38%,
critical frequency bands(0.8～1.5 GHz)≥60%5×10−10 4.6×10−8 0.92 1.1
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