Conceptual Design of a 33 T Cryogen-Free Magnet REBCO Insert: Mechanical Aspects and Protection Against Thermal Runaway

The development of a 33 T cryogen-free magnet is taking place at the High Field Lab. for Superconducting Materials, Tohoku University. It consists of a 14 T large bore LTS background magnet with a 19 T REBCO insert, which is the focus of this work. As it is conduction-cooled and must be ramped-up rapidly, a conventional isolated pancake-based design is preferred for the insert coil. It will follow the robust REBCO coil concept already introduced in previous works, with the so-called edge-impregnation technique enabling stress redistribution as well as conduction-cooling and a conductor made of two tapes co-wound for reliability. Still, the exact conductor structure is not yet fixed, in particular in terms of mechanical reinforcement. In this work, the REBCO coil design is discussed from two point of views: coil mechanical behavior and protection against local thermal runaway when operated in combination with the LTS outsert, using modelling approaches. The necessary tradeoff between mechanical and electrical margins is highlighted, guiding the choice for the future 33 T insert conductor structure.