【作者】 吴红；

【导师】 王莉；

【作者基本信息】 哈尔滨工业大学 ， 制冷与低温工程， 2010， 博士

【摘要】 国际μ?介子离子化冷却实验(Muon Ionization Cooling Experiment-MICE)将建造世界上首个μ介子离子化冷却实验装置,论证二十余年来困扰中微子工厂和μ?介子对撞机研究中的最核心技术问题:μ介子冷却。研究结果是未来中微子工厂和μ?介子对撞机成功的关键。MICE冷却通道由相互交替的3个吸收聚焦单元和2个射频耦合单元组成,超导耦合螺线管磁体安装在1组4个201.25MHz常规射频腔外部构成射频耦合单元,用于在轴线上产生2.6T的强磁场保证μ介子通过射频腔的盘形窗口。耦合磁体是内径达1.5m的较大型单线圈低温超导螺线管磁体,其线圈上峰值磁场可达7.4T。本文以MICE超导耦合磁体为研究对象,深入地研究了超导磁体设计中的若干关键问题,包括冷质量支撑设计技术、磁体热稳定性和高温超导电流引线故障保护技术等,研究结果将为超导磁体的长期正常运行和安全保护提供理论依据,具有重要的工程实用价值。1)冷质量支撑是超导磁体的关键部件,本文针对超导耦合磁体的特点系统设计了一套自中心双拉带式冷质量支撑系统。建立了冷质量支撑组件的一维理论分析模型,对比分析了磁体冷运输和常温运输两种运输方式对冷质量支撑系统承载性能和结构设计的影响,确定了磁体常温运输方案。初步分析了磁体在常温运输、降温以及励磁不同状态下支撑拉带内的受力和预紧力参数,给出了冷质量支撑组件的详细结构及尺寸,并分析了不同的拉带材料和不同温区的拉带长度比例对支撑承载能力的影响。2)采用通用有限元软件,建立了一系列数值模型,对耦合磁体冷质量支撑组件从力、热及机械结构方面进行了详细分析。建立了冷质量支撑系统的3-D整体分析模型,验证了支撑系统的自中心性,得到了常温、降温和励磁工况下各支撑组件拉力随支撑载荷的变化,同时得到了各工况下磁体中心位置的变化。建立了支撑组件的3-D热分析有限元模型,得到了在磁体正常运行中支撑组件上的温度分布和支撑系统漏热。建立了支撑组件的3-D结构分析有限元模型,模型中采用ANSYS软件中接触分析技术,准确模拟了支撑拉带和支撑套筒之间的界面实际状况,得到了支撑组件的等效弹性系数,与一维理论分析结果一致,并得到了支撑组件主要部件如拉带、热截断和杆端轴承及销钉上的应力分布情况,校核了支撑组件的强度。模拟结果为确定自中心冷质量支撑的结构尺寸提供了理论依据。3)应用约化临界态法和L-R电路原理对耦合磁体的电性进行了分析。用约化临界态法对耦合磁体所用的NbTi超导线在不同温度和磁场下的临界特性进行预测,根据超导线的临界特性计算了最大工作电流和温度裕度等耦合磁体基本参数。应用L-R电路原理,对磁体的各种励磁和卸载方式进行了分析研究,给出了最佳的耦合磁体励磁、卸载和快速卸载方式。分析设计了耦合磁体快速卸载回路,并对室温端快速卸载二极管的冷却进行了热力学分析。4)采用有限元分析软件,结合自我开发的超导耦合磁体热稳定性分析程序计算并分析了交流损耗及其对液氦间接冷却的超导磁体热稳定性的影响,给出了保持磁体热稳定性的措施。分析结果表明,超导体内的磁滞交流损耗和线圈骨架组件的涡流损耗是耦合磁体交流损耗的主要形式;在励磁、卸载和快速卸载过程中,可利用磁体冷却系统中的液氦的蒸发汽化潜热的方式,以保证磁体励磁卸载过程中的热稳定性,避免失超。因此建议磁体冷却系统中需保持一定的液氦储量。用有限元分析软件结合自我开发的分析程序对励磁、卸载尤其快速卸载过程中耦合磁体的交流损耗和磁体热稳定性进行了数值模拟。模拟结果显示耦合磁体可以实现安全快速卸载,磁体最大温升为0.42K。最后讨论了故障模式如系统断电,小型制冷机系统故障下耦合磁体HTS电流引线的保护,提出了利用快速卸载过程中蒸发的冷氦气的显热冷却高温超导引线热端以保护HTS电流引线的方法,并设计和分析了安置在制冷机一级冷头上的用以实现冷氦气冷却HTS电流引线的小型盘管式换热器。更多还原

【Abstract】 The muon ionization cooling experiment (MICE) will be a demonstration of muon cooling in a configuration of superconducting solenoids and absorbers that may be useful for a neutrino factory or moun collider. The MICE cooling channel consists of alternating three absorber focus coil modules (AFC) and two RF coupling coil modules (RFCC). The RFCC module comprises a superconducting coupling solenoid magnet mounted around four conventional conducting 201.25MHz closed RF cavities bounding by thin beryllium windows. The function of the coupling magnet is to produce enough magnetic field up to 2.6T on the magnet centerline to keep the beam within the iris of the thin RF cavity windows. MICE coupling magnet is a single superconducting solenoid magnet, with an inner diameter of 1.5m and a peak magnetic field of 7.4T. The thesis researches several key technical issues in the superconducting magnet design including cold mass support, AC losses, magnet thermal stability and HTS leads protection. The results are helpful for the long-term stable operation and failure protection of the coupling magnet, which have important engineering value.1) The cold mass support is the key component of a superconducting magnet. A self-centered double-band cold mass support system is designed in detail for MICE superconducting coupling magnet. A 1-D theory analysis model is built to compare and analyze the influences of cold and warm shipment schemes on the support performances and structure, and the warm shipment scheme is adopted. The parameters of pre-tension and tension in the cold mass support bands are analyzed during warm shipment, cooling down and charge. The structure and major dimensions of cold mass support assembly are introduced in detail. And the effects of support materials and ratio between 60K~300K band and 4.2K~60K band on the cold mass support capacity are discussed also.2) A series of numerical model are built based on the general finite element software. The detailed numerical simulations on the cold mass support system assemblies are carried out using ANSYS. A 3-D integral analysis model for the whole cold mass support system is built, and the self-centered characteristics for the support system are verified using the model. The tension in each support assembly, the displacement of the magnet center and the co-axial departure of magnet axis in different modes, such as warm, cold and charge are obtained. A 3-D thermal and structure FE model are built for the support assembly. The temperature profile and the heat leak along the support assembly are obtained, which is coincident well with the 1-D theory analyzed results. The contact analysis technology is applied on the stress simulation on the support assembly, which is close to the real contact condition between support band and support cylinder. The von-Mises stress distribution on the major components, such as support bands, thermal intercept, rod end and pins are obtained in detail. The strength of the cold mass support assembly is verified, and the results are used to determine the final dimensions of the support structure.3) The electrical characteristics of coupling magnet are analyzed based on the reduce-state method and the principle of L-R circuit. The critical current density of MICE superconductor under different temperature and magnetic field are predicted using reduced-state method and the basis parameters for the coupling magnet such as the maximum operation current and temperature margin are obtained. Various charge and discharge schemes for the coupling magnet are compared, and the optical charge and discharge schemes are obtained according to the present power supply. The rapid discharge circuit is designed, and the thermal dynamic analysis for the diode cooling during rapid discharge is discussed also.4) The analysis of the AC losses and their influence on the thermal stability of superconducting magnet indirectly cooled by helium are carried out using FE software combined the developed program. The thesis provides the methods to keep the thermal stability of the MICE coupling magnet. The primary calculation of the AC losses for the coupling magnet shows that the hysteric AC loss and the eddy current loss in mandrel are the major souses of AC losses. During charge, discharge and rapid discharge, the liquid helium around the coil can be vaporized to utilize the latent heat to keep the thermal stability of the coupling magnet. So certain volume of liquid helium should be kept in the cooling system. The transient temperature distributions in coupling magnet during charge, discharge and rapid discharge are numerical simulated using the FE software together with the developed program. The results show that the coupling magnet can be rapid discharged safely with maximum temperature rise of 0.42K. At last, the protection of HTS leads in failure modes such as power off or fault of small coolers is discussed. A new HTS lead protection method utilizing the sensible heat of vaporized helium gas during rapid discharge is provided to protect the HTS leads. A small coiled heat exchanger attached on the first stage of small cooler is designed and analyzed.更多还原