The High Luminosity Large Hadron Collider (LHC) Project target is to reach an integrated luminosity of the LHC of 3000 fb⁻¹, corresponding to a factor 10 increase in collisions with respect to the current accelerator. One of the main components is the superconducting quadrupole called MQXF. It is based on Nb₃Sn technology and has a 150 mm single aperture with a field gradient of 132.6 T m⁻¹. The MQXF magnets are currently in preseries production in a joint collaboration between CERN and the US-LHC Accelerator Upgrade Project. The first prototype magnet based on 7 m-long coils (MQXFBP1) was assembled and preloaded in 2019. The testing and disassembly was done in 2020. The coils were equipped with optical fiber Bragg grating (FBG) sensors. Some of the FBG values exhibited strain jumps during preload and their signals were lost during cool-down. The magnet did not reach the nominal current, quenching at 15.15 kA. At the time of writing three MQXFB magnets have been preloaded from which the second prototype is soon to be tested. The objective of this paper is to analyze the mechanical behavior of MQXFB magnets in the light of current knowledge, thanks to earlier short model experiments, as well as describe in detail the process of assembly and preload. We synthesize the mechanical theory of preload and present new considerations on symmetric/asymmetric bladder-key operations and their effects. An extensive comparison between long and short model magnets is presented. In our analysis and FE modeling we take into account the measured coil sizes that vary over position. We introduce a novel technique that allows preload homogenization over the length of the magnet after preload has been done. We analyze the role of the stainless steel shell and show its mechanical behavior. Finally, the relevant data at cold is presented and analyzed.

高光度大型强子对撞机 (LHC) 项目的目标是使 LHC 的综合光度达到 3000 fb ^-1，对应于当前加速器的碰撞增加 10 倍。主要组件之一是称为 MQXF 的超导四极杆。它基于 Nb ₃ Sn 技术，具有 150 mm 单孔径，场梯度为 132.6 T m ^-1. MQXF 磁体目前正在欧洲核子研究中心与美国-LHC 加速器升级项目的联合合作中进行预生产。第一个基于 7 米长线圈 (MQXFBP1) 的原型磁铁于 2019 年组装和预加载。 测试和拆卸于 2020 年完成。线圈配备光纤布拉格光栅 (FBG) 传感器。一些 FBG 值在预加载期间表现出应变跳跃，并且它们的信号在冷却期间丢失。磁铁未达到标称电流，在 15.15 kA 时失超。在撰写本文时，已经预加载了三个 MQXFB 磁体，很快将对其进行测试。由于早期的短模型实验，本文的目的是根据当前知识分析 MQXFB 磁体的机械行为，并详细描述了组装和预加载的过程。我们综合了预加载的机械理论，并对对称/非对称膀胱键操作及其影响提出了新的考虑。介绍了长型和短型磁铁之间的广泛比较。在我们的分析和有限元建模中，我们考虑了随位置变化的测量线圈尺寸。我们引入了一种新技术，允许在预加载完成后在磁体长度上进行预加载均质化。我们分析了不锈钢外壳的作用并展示了它的机械性能。最后，对冷时的相关数据进行了介绍和分析。介绍了长型和短型磁铁之间的广泛比较。在我们的分析和有限元建模中，我们考虑了随位置变化的测量线圈尺寸。我们引入了一种新技术，允许在预加载完成后在磁体长度上进行预加载均质化。我们分析了不锈钢外壳的作用并展示了它的机械性能。最后，对冷时的相关数据进行了介绍和分析。介绍了长型和短型磁铁之间的广泛比较。在我们的分析和有限元建模中，我们考虑了随位置变化的测量线圈尺寸。我们引入了一种新技术，允许在预加载完成后在磁体长度上进行预加载均质化。我们分析了不锈钢外壳的作用并展示了它的机械性能。最后，对冷时的相关数据进行了介绍和分析。