Feasibility analysis of partially insulated Nb₃Sn EU DEMO toroidal field coil

Abstract The advent of no-insulation (NI) winding technique in high temperature superconducting magnets has marked a milestone, demonstrating enhanced thermal stability and mechanical integrity in various high-field applications. There have been reports on numerical and experimental results of the application of NI-class winding techniques to low temperature superconducting (LTS) magnets, showing improved thermal stability such as significant reduction of training, stable behavior during over-current operations, and even recovery after heater-fired quench as a result of current bypass near a hot spot. Thus, the NI approach might offer potential advantage to large scale LTS fusion magnet such as reduction of peak coil terminal voltage or decrease of the copper fraction within the conductor to achieve a more compact design. However, it is essential to firstly assess the potential risks associated with NI approach to large scale LTS fusion magnet to identify any critical barriers. This paper explores the feasibility of partially insulated Nb 3 Sn EU DEMO toroidal field (TF) coil over a wide range of contact resistivity through two distinct partial insulation winding schemes: (1) inter-turn NI and (2) inter-layer NI scheme. Our investigation encompasses electromagnetic, structural, and thermal-hydraulic analyses to evaluate current distribution, magnet charging time, stress distribution, and temperature rise within the winding pack during magnet charging. The analysis numerically confirms the existence of a feasible design space for a partially insulated TF coil, which enables stable charging and normal operation of the magnet.