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

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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.