加速器高温超导扫描磁铁载流特性及其与磁铁结构关系的研究

With superconducting scanning magnet in accelerator, the scanning magnetic field and scanning range can be increased. It will help to reduce the scanning magnet volume and the distance from the scanning magnet's to the scanned sample. It is applicable for occasions that the space has a certain limit such as proton and heavy ion proton cancer therapy. Compared with LTS ( low temperature superconducting) materials, the cooling system of HTS (high temperature superconducting) materials has have lower cooling cost, higher safety margin and better radiation resistance. At the same time, the superconducting scanning magnet can be subjected to the thermal load caused by radiation, and the temperature safety margin of HTS materials is higher. The key problem to be solved in high energy or proton heavy ion accelerators is how to minimize the size and space of the accelerator.At present, the study of current-carrying characteristics of HTS magnets, especially the law of AC current-carrying characteristics, is not in-depth enough, and the calculation accuracy of current-carrying capacity is insufficient.This is not conducive to give full play to the advantages of HTS materials, and reduce the size of the accelerator magnet and occupied space. In this project, the electromagnetic and thermal characteristics and coupling calculation methods of HTS scanning magnet, AC current carrying property of HTS scanning magnet and the relationship between scanning magnet structure, scanning ability and current carrying property are studied. The purpose of the analysis is to make clear the DC and AC current carrying property and calculation method. and provide a theoretical basis for reducing the size and occupied space of accelerator magnets and have high application value.

超导扫描磁铁用在加速器中，能够提高扫描磁场，增大扫描范围，将有助于减小扫描磁铁体积及扫描磁铁与被扫描样品的距离，适用于对空间有一定限制的质子重离子治癌等场合。相比于低温超导材料，高温超导材料具有更低的冷却成本、更高的安全裕量，抗辐射性能更好。中高能或质子重离子加速器亟待解决的关键问题是如何最大限度地缩小加速器体积及占用空间。目前，高温超导磁铁载流特性，尤其是交流载流特性规律研究不够深入，载流能力计算精度不足。这不利于充分发挥高温超导材料的优势，减小加速器磁铁体积及占用空间。为此，本申请围绕高温超导扫描磁铁电磁-热特性规律及耦合计算方法、交流载流特性规律及计算方法、磁铁结构与扫描能力、载流特性关系等问题展开研究，旨在清晰地掌握超导磁铁在交、直流工况下的载流特性规律，得出准确的载流能力计算方法，为缩小加速器磁铁体积及占用空间提供理论依据，具有很高的应用价值。

超导扫描磁铁用于质子治疗装置旋转机架（gantry）中，有助于提高扫描磁铁磁场，降低扫描磁铁体积及轴源距，从而降低整个gantry体积、重量及建造成本。高温超导磁铁具有更高的温度裕度，更好的抗辐照特性，可以在传导冷却条件下（20-30K温区）运行，比较适合gantry磁体。本项目以高温超导扫描磁铁电磁热特性计算方法、磁体设计方法为主要研究内容。采用Opera及Comsol等商用有限元软件建立了高温超导扫描磁铁仿真计算模型，给出了有铁芯及无铁芯高温超导扫描磁体在不同工况下电磁特性、交流损耗及温升的计算方法。本项目分别给出了单向及双向高温超导扫描磁铁设计方法，对冷屏涡流损耗问题进行了分析，给出了磁体冷却系统设计要点。研究了双向扫描磁铁磁场均匀度、运行电流、用线量、线圈最高场等参量与线圈尺寸参数的关系，给出了高温超导扫描磁体优化设计方法。本项目分别研制了一台单向及一台双向扫描磁铁样机，建了液氦冷却方式的测试系统，完成了双向扫描磁铁通电测试，线圈电流、电压变化规律与理论预期相符，中心磁场测量值与计算结果一致，后期仍需对实验系统进行改进，减小交流损耗等参量测量误差。本项目研究是对质子治疗装置旋转机架(gantry)用扫描磁铁高温超导方案的探索性研究，为减小gantry磁体体积、降低研制成本提供了一种思路。本项目所提出的计算及设计方法可为后续gantry高温超导扫描磁铁的研制提供一定的技术积累，本项目研究过程中建立的测试系统，为完善交流工况高温超导磁体的测试起到一定的推动作用。