【作者】 潘衡；

【导师】 王莉；

【作者基本信息】 哈尔滨工业大学 ， 制冷及低温工程， 2010， 博士

【摘要】 离子化冷却?介子实验装置(Muon Ionization Cooling Experiment,简称MICE)为高能物理未来加速器中微子工厂和?介子对撞机的关键基础性研究装置之一,将在世界上首次以实验验证离子化冷却?介子技术。超导耦合螺线管磁体是MICE实验装置的关键设备之一,用于提供2.6T的中心磁场控制与其耦合的常规射频腔内的?介子束流。由于受射频腔尺寸和结构的限制,其线圈内直径为1500mm,长度285mm,厚度110mm,在最高工作电流时的最大场强达7.3T。考虑到磁体系统的实际漏热和经济性,耦合磁体采用小型制冷机冷却。耦合磁体的尺寸和场强较高,且稳定运行时的温度裕度仅约0.8K,磁体线圈内部的高应力和微小的机械扰动都可能引发磁体运行的不稳定,从而导致失超,甚至造成磁体结构的破坏;而磁体低温冷却系统则是磁体运行稳定性的前提及重要保障。本文以MICE超导耦合螺线管磁体为主要研究对象,从磁体的机械稳定性和冷却稳定性两方面深入地研究了影响磁体稳定运行的各个因素,确定了耦合磁体含滑移面的冷质量结构参数和冷却系统的设计参数。本文研究结果对MICE超导耦合磁体的设计和制造以及类似高场强、大口径超导磁体的设计有一定的理论指导和实际应用价值。对于大口径高场强超导磁体,其稳定运行的关键之一是磁体工作时的结构安全性。本文以磁体横截面内的位移偏微分方程组为基础,发展了磁体二维平面应力理论模型。模型考虑了降温和励磁时的轴向应力和横向剪切力的影响,得出了从绕制到励磁各阶段磁体横截面内各应力分量的理论解。通过计算文献中的磁体降温和励磁后的位移和峰值应力验证了理论模型的正确性。在理论模型基础上,考虑滑移面结构,建立了磁体冷质量有限元分析模型,模拟了给定结构参数下磁体冷质量在绕制-降温-励磁过程中的受力情况,比较了理论和模拟结果,验证了有限元模型的正确性,用该模型深入研究了稳定工况下机械应力对耦合磁体稳定运行的影响。为了得出满足磁体稳定运行要求的冷质量结构参数,应用含滑移面的磁体冷质量有限元模型对线圈的绕制预应力、紧固带的结构参数进行优化设计。给出了线圈绕制预应力的合理范围,为线圈绕制提供理论依据;根据紧固带的作用,从结构和导热方面分别优化了紧固带预应力、厚度和材料选择,得出了紧固带预应力取值范围,给出了紧固带材料和厚度的建议。为了理解耦合磁体由于机械应力原因导致失超或无法稳定运行以及滑移面结构对磁体稳定性的影响,采用有限元程序计算了耦合磁体的最小失超能量,对无滑移面时的环氧破裂和导线移动的耗散能量进行了分析,确定了滑移面对增强磁体稳定性的作用。建立了含滑移面的磁体冷质量非稳态应力有限元模型,模型考虑了滑移面的非线性影响和骨架及紧固带的“诱发失超”效应。应用该模型研究了耦合磁体失超引发的磁体内部过热和分段保护时各段的电磁载荷冲击对磁体结构和稳定性的影响。对滑移面的设计参数进行优化计算,指出线圈底部滑移面与侧滑移面的优化摩擦系数,给出了耦合磁体的滑移面结构。除了机械因素影响磁体的运行稳定性外,考虑到耦合磁体具有较低的运行温度预度,对磁体的小型制冷机低温冷却系统进行优化设计分析。影响磁体冷却稳定性的两个主要因素为制冷机冷头与磁体最高温度点的温差和磁体的热负荷。为了确定磁体的冷却方式,详细分析及计算了磁体在冷屏温度60K和运行温度4.2K的热负荷,尤其对埋入线圈内部的超导线接头的电阻进行了详细计算,选择了制冷机热虹吸再冷凝冷却方式;以减小制冷机冷头与磁体表面的温差为目标,优化了热虹吸回路的设计参数;以减小系统漏热为目标,优化设计了60K冷屏及其支撑。根据优化结果,给出了冷却系统的设计参数。受厂商提供的铌钛超导线材单根长度的限制,耦合磁体线圈将有12-14个超导线接头,受磁体结构内部空间的限制,这些超导线接头将埋在线圈内部,其在低温磁场下的电阻和强度均直接影响磁体的正常工作。通过伏安法和拉伸测试分别研究了超导线接头的电和力学性能,实验结果表明焊接长度为1m时的接头电阻小于2n?,并与计算值较吻合;力学测试表明Sn-Ag焊料存在明显的低温冷脆。环氧树脂是线圈绕制采用的主要粘接绝缘材料,亦是主冷屏支撑组件的粘接材料,其粘接强度是研究磁体机械稳定性和安全运行的基础参数之一。实验测试了环氧粘接面的粘接强度,得到了环氧的断裂应力,为本文非稳态机械特性分析提供了基础数据。更多还原

【Abstract】 Muon ionization cooling experiment (MICE) will be a demonstration of muon ionization cooling technology for a neutrino factory. The superconducting coupling solenoid magnet is one of the key components in MICE and will produce a magnetic field 2.6T on the center line to control the muon beam in the RF cavity located inside it. To contain the RF cavities, the inner diameter of the coupling coil is 1500mm. The coupling magnet has a peak induction of 7.3T at the maximum current, and will be cooled by cryocoolers.The high level of stress inside the coil and small mechanical disturbance may cause quench or permanent damage to the magnet due to large scale and high magnetic filed; because the temperature margin of normal operation is only 0.8K, the cooling system should be stable in order to keep the magnet safe operation. This dissertation, studied the crucial factors that affect the operation stability of the MICE superconducting coupling magnet in term of both mechanical stability and cooling stability, optimized the design parameters of the cold mass assembly with slip plane and the cooling system adopting cryocoolers. The research of this dissertation will provide theoretical and practical application guidance for the design of the coupling magnet and similar solenoid magnets.The stress at steady state is the dominant of normal operation. An analytical model to solve the plane stress of the magnet cross section was built. This model considered the effect of the axial stress and the shear stress during cooling and charging. All of stress components after magnet excitation were obtained. The analytical model was verified by an analogous magnet. A finite element model of the coil assembly with slip planes was built and the simulation of normal operation process from winding to charging was performed, and the agreement of the simulation and the analytical results is well. The model was applied to study the effect of steady stress on the normal operation of the magnet.In order to obtain the adequate structure parameters of the cold mass assembly, the finite element model with slip plane was applied to optimize the conductor pre-stress and the structure parameters of banding. The dissertation presents the rational the conductor winding pre-stress. According to the function of banding, the pre- stress, thickness and material of banding were optimized.In order to understand the quench caused by mechanical disturbance and the effect of slip plane on the operation stability of the magnet, study on the mechanical stability at unsteady state was performed. The minimum quench energy of the coupling magnet was calculated by a finite element model, and quantitative analyses of epoxy cracking and conductor motion without slip plane were carried out. The results indicated that the slip planes have great effect on the stability of the magnet. A two dimensional dynamic stress model was built to simulate the dynamic stress during quench. The impact of over- heat and magnetic force of each section of coil was analyzed. Finite element models with and without slip planes for it were developed to simulate the stresses during the process including winding, cooling down and charging. The effect of slip planes on the stress distribution in the coil assembly was investigated. The results show that slip planes with low friction coefficients can improve the stress condition in the coil, and the structure parameters of the slip planes were confirmed.Considering the small temperature margin, the temperature in the magnet must be stable during operation. The key elements in the successful application of cryo cooler to cool magnets are the connection of the cryocooler to the magnet and allowable thermal load. In order to determine the thermosyphon- recondensation cooling scheme, the thermal load of the magnet system at 60K and 4.2K, especially that induced by the resistance of superconducting splices in the coil, were analyzed and calculated in detail. For the purpose of minimizing the ?T between the cooler cold head and the hot point on the magnet and minimizing the thermal load of the magnet, the design of the thermal shields structure was optimized. According to the results, the parameters of cooling system were presented.Because the superconducting splices wiil be wound into the coil, the performance of the splices will affect the stability of magnet. The bonding strength of epoxy used for coil impregnent will directly affect the mechanical stability of the magnet. The resistance of splice was tested by voltammetry method, and the mechanical property was investigated by means of uniaxial tensile test. The results have a good agreement with the calculated values. The bonding strength of epoxy was studied by tensile test. The crack stress was obtained to be used as the base for the magnet design.更多还原