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CEPC detector magnet Internal review meeting. Four talks: design, conductor, mechanical, cryogenic
会议名称：CEPC探测器超导磁体内部评审会
日期：2025.05.16
地点：主楼A418
参会人员：徐庆金、陈福三、马晓妍、朱应顺、Joao、王贻芳、宁飞鹏、赵玲、侯治龙、王梦琳、朱柯宇、裴亚田、何苗（在线）、常正则（在线）
报告题目：
1. Physical design of CEPC Detector Magnet
2. Aluminum stabilized superconducting cable developing progress
3. Mechanical design of CEPC detector magnet
4. Cryogenic system design of CEPC detector magnet
报告内容：
会议纪要和总结：
会议介绍了磁体的物理设计、电缆、机械和低温系统，并针对IDRC提出的建议和意见进行了汇报。参会专家提出了很多建议。
TPC磁场均匀性的问题，通过BESIII的经验和软件重建同事的反馈，只要磁场测量的点的密度足够大，磁场测量精度能满足要求，梯度小，就能满足TPC的要求。目前提供的磁场分布和测量的精度能满足磁场均匀性的要求。
铝稳定体应力太大，接近材料极限。修改了电缆结构，铝稳定体低温超导卢瑟福电缆从高强度掺杂纯铝的一次覆铝改为box型电缆的结构。一次覆铝电缆面临的问题68 mm*22 mm的截面积是目前设备的极限，如果想降低电缆上的应力，增加电缆厚度很难实施。通过冷加工的方式提高材料的机械强度遇到了困难，没有找到厂家有对如此大截面的电缆进行冷加工的设备。二次覆铝取得了一定的进展，虽然只加工出5米的电缆就出现断芯的情况，但是掌握了一些电缆加工的工艺，取得了一定的成果，所以改变了电缆的结构。争取今年给出合适的电缆方案。
低温系统，铝合金焊接的问题。焊接接头很多，如果保证每个接头不漏。加速器中心低温组有很多铝合金焊接的经验。需要把这些经验列出来，打消专家的质疑。
机械系统，目前的模拟结果存在一定的局限性，有一些边界条件存在一定的问题，主要体现在目前所有工况的边界条件完全一致，其是否符合真实工况，还需内部讨论。
未来还有很多的预研工作需要抓紧时间进行
1. 调研ATLAS磁体寿命短的原因，查找文献，询问专家。是否是材料的热循环和电磁力导致材料性能出现退化？添加CEPC探测器超导磁体的疲劳模拟和设计验证实验。
2. 超导电缆距离使用还有很长的距离。5米的样缆远不能满足要求，要抓紧时间进行电缆的研制，确定可以使用的电缆的方案。
3. 低温系统，铝合金的焊接问题。如果不用铝合金管道，采用不锈钢和铝合金的双金属管能否满足温差的要求，需要模拟。安排铝合金的焊接实验，焊接一批接头，通过冷热循环，检验焊接的可靠性。未来设计一个类似的低温系统，对CEPC探测器超导磁体的热虹吸冷却结构进行验证。
4. 机械系统，内部讨论，完善系统的模拟。吊挂系统的验证实验。
5. 磁体造价方面，专家质疑造价太低 (1/6 ILD)。未来组织所有相关企业对磁体的造价进行详细的核算。如超导线、电缆、高纯铝、铝合金管道、双金属加工、铝合金的焊接、低温系统、大尺寸不锈钢和铝合金卷筒、真空设备、失超探测设备、磁场测量等，组织企业和专家对磁体的方案和造价进行评估。
English version：
Meeting Name: CEPC Detector Superconducting Magnet Internal Review Meeting
Date: 2025.05.16
Location: Main Building A418
Attendees: Xu Qingjin, Chen Fusan, Ma Xiaoyan, Zhu Yingun, Joao, Wang Yifang, Ning Feipeng, Zhao Ling, Hou Zhilong, Wang Menglin, Zhu Keyu, Pei Yitian, He Miao (online), Chang Zhengze (online)
Presentation Topics:
1. Physical Design of CEPC Detector Magnet
2. Development Progress of Aluminum-Stabilized Superconducting Cable
3. Mechanical Design of CEPC Detector Magnet
4. Cryogenic System Design of CEPC Detector Magnet
Presentation Content:
- Wang Menglin introduced the physical design of the CEPC detector superconducting magnet, including the distribution of the magnetic field, optimization of cable design, stress analysis, and quench protection methods.
- Zhao Ling presented the development process and latest progress of the aluminum-stabilized low-temperature superconducting Rutherford cable, as well as the research progress on high-strength doped pure aluminum. She also explained the reason for changing the cable design from high-strength doped pure aluminum with a single aluminum cladding to a box-type cable in the Ref-TDR.
- Hou Zhilong discussed the mechanical design of the superconducting magnet, including the internal 3D and 2D structures of the magnet, the structure of the suspension system, and the stress analysis of the vacuum vessel.
- Zhu Keyu introduced the simulation calculation process using three different low-temperature cooling methods and the reasons for adopting the thermosiphon cooling structure. He also discussed the heat load and cooling structure of the CEPC detector superconducting magnet.
Meeting Minutes and Summary:
The meeting introduced the physical design, cable, mechanical, and cryogenic systems of the magnet and reported on the suggestions and opinions raised by the IDRC. The attending experts provided many suggestions.
- Regarding the uniformity of the TPC magnetic field, based on the experience from BESIII and feedback from software reconstruction colleagues, as long as the density of magnetic field measurement points is sufficient and the measurement accuracy meets the requirements with a small gradient, it can satisfy the requirements of the TPC. The current magnetic field distribution and measurement accuracy meet the requirements for magnetic field uniformity.
- The stress on the aluminum stabilizer is too high, approaching the material's limit. The cable structure was modified, changing the aluminum-stabilized low-temperature superconducting Rutherford cable from a high-strength doped pure aluminum with a single aluminum cladding to a box-type cable structure. The single aluminum cladding cable faces the issue that a cross-sectional area of 68 mm × 22 mm is the limit of current equipment. If the stress on the cable needs to be reduced, it is difficult to increase the cable thickness. Cold working to improve the mechanical strength of the material has encountered difficulties, as no manufacturer has been found with equipment capable of cold working such a large cross-sectional cable. Some progress has been made in secondary aluminum cladding, although only a 5-meter cable was produced before core breakage occurred. However, some cable processing techniques have been mastered, leading to the change in cable structure. Efforts will be made to provide a suitable cable solution this year.
- For the cryogenic system, there is a problem with aluminum alloy welding. With many welding joints, ensuring that each joint is leak-free is a challenge. The cryogenic group has extensive experience in aluminum alloy welding. This experience needs to be documented to address the experts' concerns.
- The mechanical system currently has certain limitations in its simulation results, with some boundary conditions being problematic. The main issue is that the boundary conditions for all operating conditions are currently identical, and whether this conforms to real operating conditions needs further internal discussion.
Future Preparatory Work:
1. Investigate the reasons for the short lifespan of the ATLAS magnet. Conduct literature research and consult experts to determine whether material thermal cycling and electromagnetic forces lead to material performance degradation. Add fatigue simulation and design verification experiments for the CEPC detector superconducting magnet.
2. Superconducting cable development. A 5-meter sample cable is far from sufficient. Accelerate cable development and determine a viable cable solution.
3. Cryogenic system and aluminum alloy welding issues. If aluminum alloy pipes are not used, can a dual-metal pipe made of stainless steel and aluminum meet the temperature difference requirements? Simulations are needed. Conduct aluminum alloy welding experiments, produce a batch of joints, and test their reliability through thermal cycling. Design a similar cryogenic system to verify the thermosiphon cooling structure of the CEPC detector superconducting magnet.
4. Mechanical system. Conduct internal discussions to improve system simulations. Verify the suspension system through experiments.
5. Magnet cost. Experts questioned the low estimated cost (1/6 ILD). In the future, organize all relevant enterprises to conduct a detailed cost estimate for the magnet, including superconducting wire, cable, high-purity aluminum, aluminum alloy pipes, dual-metal processing, aluminum alloy welding, cryogenic systems, large-diameter stainless steel and aluminum alloy coils, vacuum equipment, quench detection equipment, magnetic field measurement, etc. Organize enterprises and experts to evaluate the magnet's plan and cost.