A new paradigm for quench protection of high-temperature superconducting magnets for future energy-frontier accelerators

圆形对撞机是加深我们对宇宙理解的独特工具。为了进一步推动我们的知识，必须增加束流能量来探索基本粒子(也是未知的)的行为。然而，更高的束流能量需要增加对撞环的半径或由弯曲束流的偶极磁铁(也称为加速器磁铁)产生的磁场强度。大多数情况下，偶极场是由基于低温超导(LTS)化合物的超导磁体产生的。超导体是一种独特的材料，它具有在给定的临界电流、临界温度或临界磁场下携带无损直流电流的独特性质。为了在不使加速器变得更大的情况下增加束流能量，需要更强的磁场。在这个方向上，一个非常重要的选择是转向高温超导(HTS)材料，这种材料的临界和临界场比高温超导高得多，可以产生20泰尔萨以上的磁场。这将是加速器磁铁技术的重大游戏规则改变者。这里相关的构建块是HTS磁带技术。HTS胶带是我们用来形成柔性电缆的基本导线。然后，我们可以将这些电缆缠绕成加速器磁铁的形状。目前，全球约有10至12家公司以公里长度生产HTS磁带，它们已经相当成熟。然而，由于高温超导材料的特殊性质，当多个磁带以电缆配置排列时，电流如何在多个磁带之间分配尚不清楚，当绕组在磁铁中时，电流如何分配更是不清楚。此外，如果由于任何原因(超导电性局部丧失)出现“热点”(这是可能发生的)，也不清楚磁体的最佳保护策略是什么。在这个项目中，我们将利用Polytech开发的一项专利技术，该技术包含一种名为“CFD Tape”的坚固的HTS磁带体系结构，它具有帮助检测热点并使受热点影响的HTS磁带的温度分布均匀的巨大潜力。我们将探索由CFD胶带制成的电缆在热点下的反应，特别是圆芯导体(CORC)电缆，美国磁体发展计划目前正在考虑将其用于制造未来的加速器磁体，该计划将成为我们在整个项目中的密切合作伙伴。该项目的最终目标是证明CFD磁带技术如预期的那样是为保护未来的加速器磁体而寻求的促进剂，这将加快它们的发展。请注意，该项目中计划的一些实验将在劳伦斯伯克利国家实验室(LBNL)进行，这些实验需要主要的基础设施。该项目是在高度跨学科的环境中培养高素质科学和工程人才的绝佳机会。

Circular colliders are unique tools to deepen our understanding of the Universe. To further push our knowledge, it is mandatory to increase the beam energy to explore the behavior of fundamental (also unknown) particles. However, a higher beam energy requires increasing the radius of the collider ring or the magnetic field strength produced by the dipole magnets (also called "accelerator magnets") that bend the beam. Most of the time, the dipole field is generated by superconducting magnets based on low temperature superconductor (LTS) compounds. Superconductors are materials that have the unique property of carrying lossless DC currents below a given critical current, critical temperature or critical magnetic field. To increase the beam energy without making the accelerator bigger than they already are, stronger magnetic fields are required. One very serious option in this direction is to move towards High Temperature Superconductor (HTS) materials, which have a much higher critical and critical field than LTS and can generate fields above 20 telsa. This would be a major game changer in accelerator magnet technology. The relevant building block here is the HTS tape technology. An HTS tape is the elementary wire that we used to form flexible cables. Then, we can wind these cables in the shape of an accelerator magnet. HTS tapes are currently produced by ~10 to 12 companies worldwide in kilometric lengths, and they are quite mature. However, due to the particular nature of HTS materials, it is not yet clear how the electric current is shared between multiple tapes when the latter are arranged in a cable configuration, and even less when winded in a magnet. In addition, if a "hot spot" (local loss of superconductivity) arises for any reason (this can happen), it is not clear neither what is the best protection strategy to use for the magnet. In this project, we will take advantage of a patented technology developed at Polytechnique, which consist in a robust HTS tape architecture called "CFD tape", which has a great potential to help detect hot spots and homogenize the temperature distribution the HTS tapes affected by the hot spot. We will explore how cables made of CFD tapes react under a hot spot, in particular Conductor On a Round Core (CORC) cables, currently considered for the fabrication of future accelerator magnets by the U.S. Magnet Development Program, which will be a close collaborator of us all along this project. The final goal of this project is to demonstrate than the CFD tape technology is as expected the enabler sought for the protection of future accelerator magnets, which would then speed-up their development. Note that some experiments planned in this project and requiring major infrastructures will be performed at the Lawrence Berkeley National Laboratory (LBNL). This project represents a perfect opportunity to train highly qualified personnel in sciences and engineering in a highly inter-disciplinary environment.