【作者】 孙袁；

【导师】 沈连婠；

【作者基本信息】 中国科学技术大学 ， 精密仪器及机械， 2011， 博士

【摘要】 低能高功率直线加速器在工农业及医疗卫生等领域得到了越来越广泛的应用,随着应用领域的扩展,对直线加速器的小型化和可移动性要求也越来越迫切。然而,剩余功率的输出耦合器及吸收负载结构成为实现这一要求的瓶颈。采用同轴负载取代波导式吸收负载,可使加速器的结构更为紧凑,实现加速器的小型化,同时能简化系统的装配工序,另外,具有对称性的负载段还有利于获得更高的束流品质。前人的同轴负载研究多基于实验的方法,从而局限于较低的剩余功率量级。本文为研制高功率S波段同轴负载,采用理论分析与实验测试相结合的方法,开展了系统的仿真设计研究。研究涉及同轴负载的吸波涂层材料的选择及其电磁参数测试实验的仿真;吸波涂层的电磁特性、几何参数、涂覆位置对负载腔工作频率、品质因子和衰减性的影响分析,以及负载腔频率、损耗性与涂层关系的实验验证和结果分析;根据功率量级和衰减性要求,设计了六腔同轴负载结构,并研究了各负载腔内的功率分布,为同轴负载段的冷却系统的设计提供了结构参数和功率数据;获得了FeSiAl、Kanthal合金两种材料的分别可吸收15 kW和10k W剩余功率的最适吸波材料的涂覆方案和相应的同轴负载结构,为同轴负载的工程应用探索出科学的设计方法,并提供了可靠的技术数据。本文首先通过比较,选择了电磁场仿真软件CST作为同轴负载的分析和设计工具,并与谐振腔计算软件Poisson SuperFish的仿真结果进行对比,验证了CST的仿真精度,确认了其用于同轴负载设计的最适性,并研究了腔体仿真的精度控制问题。针对同轴负载吸波材料FeSiAl合金的电磁参数测试实验中出现的结果误差过大现象,运用CST对实验进行了仿真,通过对PTFE、高介电材料Al2O3、和ZrO2晶体等样品的仿真分析,获得了各样品与测试夹具之间的间隙对测量精度的影响。对FeSiAl材料测试的仿真表明,较小的样品尺寸误差将使最终的测量结果严重偏离其真实值。该仿真工作有效地指导了测量方案的选取,帮助最终获得了稳定的FeSiAl材料电磁参数。对FeSiAl介质材料型的负载腔,分析了材料涂敷体积对腔体工作频率和品质因子的影响,获得了满足2856 MHz频率的腔体尺寸补偿值;利用正交试验法分析了材料介电常数、磁导率对腔体参数影响的敏感度;设计加工了不同涂层尺寸的5个测试负载腔,进行了腔体工作频率和无载Q值的测量,利用精确测量的腔体尺寸建模的CST仿真结果表明,负载腔的工作频率与仿真计算结果一致,并且FeSiAl材料的实际衰减性能与理论预期相符;理论推导出探针法测量中谐振腔Q值与测试探针长度的关系,并最终由谐振腔总Q值推算出单负载腔的Q值。在负载腔仿真分析与实验测试的基础上,提出了同轴负载段的设计流程,针对15 kW剩余功率量级,单路总衰减30 dB的设计目标,设计出六腔同轴负载,以控制负载腔频率漂移为目标,对等功耗型剩余功率分配方案进行了优化,并获得了优化的FeSiAl同轴负载的结构参数。最后,计算出了负载腔内涂层与铜损的详细功率分布,其中FeSiAl涂层处的功率呈均匀分布。对Kanthal合金型负载腔,仿真研究了不同涂敷位置及面积对腔体性能的影响,获得了2856 MHz时的尺寸补偿量;设计加工了4个负载腔,分别对比了工作频率和品质因子的实验测试和仿真结果,对腔体损耗性的分析表明,Kanthal涂层的实际衰减性低于理论计算值约50%,因此仿真中所选取的涂层电磁参数有待考证,须通过进一步的实验测试加以验证。Kanthal合金由于自身衰减性的局限,经过详细的探讨和设计计算,其六腔负载段至多可吸收10 kW平均功率,单路衰减约为16 dB。负载腔功率分布计算表明,Kanthal负载腔腔环涂层处功率均匀分布,而阑片涂层的功率密度则呈类抛物线的形状。本文研究工作受国家自然科学基金《加速器大功率同轴负载研制及高功率微波吸收材料特性研究》(NO. 10775128)资助。更多还原

【Abstract】 Nowadays, electron linear accelerators are more and more employed in industry, agriculture, medical care and so on, while the miniaturization and mobility of LINAC is expected to advance all these applications. Aimed at substituting the output coupler and remnant power absorbing load of the LINAC, collinear load coated with high loss materials in its inner walls is expected to make it a reality. It will make the accelerating structure more compact, the size of the whole system decreased and the assembly procedure more simplified.In addition, the symmetry of the load will contribute to better beam quality. Foregoing researches on collinear load were restricted in lower remnant power levels for their rule-of-thumb means. In order to develop high-power S-band collinear load, systematic research on numerical design is performed and presented in this thesis. Several testing cavities following the design are processed out. The size, the operating frequency and quality factor of the cavities are measured. All they have reached the expected value. Then, A six-cavity FeSiAl collinear loads are designed and fabricated for absorbing 15 kW remnant power and -30db attenuation coefficient, The experimental results and the theoretical simulation predicted results are in agreement.In this thesis, firstly, the software CST is choosed as the main simulation tool, and in contrast, with the software Poisson SuperFish, verified the CST solving accuracy is confirmed for deformed 3D cavities. Then, the design parameters closely related to the performance of the load cavity, like operation frequency f, attenuation factor alpha,the group velocity Vg quality factor q, etc is discussed. A key problem to plan the location of the coating material in the inner wall of the cavities is solved Different from the traditional methods such as uniform power or same attenuation for every cavity, an optimized strategy based on uniform power principle is adopted, to make the actual load cavities with uniform temperature distribution when they are in operation.The electromagnetic parameters of the microwave absorbing material affect the performance of cavities seriously. In measuring the electromagnetic parameters of FeSiAl alloy, some uncertainty appeared. Simulation with CST is utilized to analyze the test results and find the uncertainty is caused by the uncertain gap between the test sample and test fixture. The simulation is very deliberate with several samples of the hollow test fixture, PTFE, crystals of Al₂O₃ and ZrO₂. The experiment simulations of the FeSiAl demonstrate that minor error of the sample size makes the experiment results great deviation from the true values.In the case of load cavities with FeSiAl coating, the accuracy control of the cavity simulation is studied. The effect of the coating volume upon the cavity frequency and Q factor is analyzed and the dimension compensations of the cavities are suggested for tuning the load cavities at 2856 MHz. The Orthogonal experimental method is utilized to investigate the sensitivity of the material permittivity （both real part and imaginary part） and permeability （both real part and imaginary part） to cavity characteristics. Five cavities with different coating dimensions are manufactured and their operating frequencies and Q values are measured. Meanwhile, the results are compared with the simulations of the cavities with actual dimensions. It is shown that the Q factor, which is characterization of the actual attenuation of the FeSiAl, agrees very well with the theoretical value. the Q factor of the resonant cavity is measured with the probe method. The relationship between Q factor and the length of the test probe is deduced and eventually the individual Q value of a load cavity is extracted. Simulation shows the FeSiAl load can support average power over 15 kW and the one-way attenuation is about 30 dB.As for Kanthal load cavities, the influence of coating position and area to the cavity properties is studied and the cavity dimensions under 2856 MHz are gained. Four cavities are produced and corresponding tests are executed. The measured operating frequencies and Q values are compared with CST simulations. The Q values indicate that the loss of the Kanthal coating is approximately 50% in contrast with theory.On the basis of the simulation analysis and experiment tests of the load cavities, in accordance with the targets of 15 kW average remnant power and 30 dB one-way attenuation, the structure design of six-cavity collinear load is accomplished. Firstly the design flow of the collinear load is summarized and generalized, Two collinear load are designed and both satisfy with the attenuation requirement. With the limitation of absorbing capacity, Kanthal load can only to support average power of 10 kW and the one-way attenuation is about 16 dB. The power distribution calculations point that the power of FeSiAl coating is uniform, the power of Kanthal coating on the cavity ring is also uniform, and the power density of Kanthal coating on the disk surface appears parabola-like.This work is supported by the NSFC （NO. 10775128）.更多还原