Thermal-hydraulic analysis of the HTS part of the hybrid Central Solenoid designed for the next generation experimental fusion device

Recently a new design of the CS for the next-generation experimental fusion device has been proposed. The CS system comprises six stacked subcoils, each split into two modules. The inner modules located in the high-field region use a YBCO high-temperature superconductor (HTS), while the outer low-field submodules utilize Nb₃Sn. Each HTS module is composed of 5 hex‑pancakes wound with the identical conductor based on the HTS Conductor-on-Round Core (CORC) strand concept. We performed simulations of normal operation of four selected HTS conductors during the whole CS current scenario, using the THEA code by CryoSoft. We took into account heat loads due to magnetization, coupling and eddy current AC losses. These were estimated based on the evolution of the magnetic field distribution within the CS modules which was obtained from an electromagnetic analysis using the 2D axisymmetric ANSYS Parametric Design Language (APDL) model. The coupling losses and eddy current losses were evaluated using the n τ values dependent on the magnetic flux density, which were computed for the considered conductor geometry with a dedicated electrostatic FEM model. The goal of the study was the estimation of the minimum temperature margin (Δ T marg ) in the considered conductors to verify the potential possibility of safe operation of the HTS modules. For all considered conductors the global minimum of Δ T marg occurred in the first second of the current scenario (when the current and magnetic field were close to the maximum) and it was sufficiently large (above the 1.5 K criterion).