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Description
The central solenoid (CS) of a tokamak is engineered to withstand significant fluctuations in operating currents and rapid changes in magnetic fields. These capabilities are essential for initiating plasma breakdown and ensuring subsequent plasma shaping and control. A novel design has recently been introduced for the CS system designated for the next-generation experimental fusion device. This new CS system consists of six stacked coils (CS3L, CS2L, CS1L, CS1U, CS2U, and CS3U) ), with each coil further divided into two submodules. The inner submodules, situated in the high magnetic field region, are made from YBCO high-temperature superconductors (HTS), while the outer submodules, located in the lower-field area, use Nb₃Sn. Among all the submodules, the HTS1U and HTS1L are expected to endure the most demanding conditions, experiencing the highest magnetic fields, as well as the greatest mechanical and thermal stresses. Each HTS module is constructed with five hex-pancakes, all wound with an identical conductor based on the HTS CORC (Conductor on Round Core) strands concept.
In the present study, we perform quench simulations in the selected HTS conductors using the THEA code by CryoSoft. The considered conductors follows the normal operation current scenario and quench is initiated by a heat pulse imposed at the moment and location where the global minimum temperature margin is reached. It is assumed that after the quench detection and a certain time delay the operating current is dumped exponentially and magnetic field profile along the conductor decreases proportionally to the operating current. The heat loads due to the magnetization, coupling and eddy current AC losses as well as heat transfer between the adjacent turns and layers of the considered conductor are taken into account. The analysis is aimed at estimation of the maximum hot spot temperature during quench.
