Thermal-hydraulic analysis of the DEMO CS coil designed by CEA

Abstract

The superconducting Central Solenoid (CS) of the EU-DEMO tokamak coil will comprise five modules, labeled CSU3, CSU2, CS1, CSL2 and CSL3, situated vertically one above the other. The central CS1 module will be operated under the most severe conditions, i.e. the largest mechanical loads and magnetic field. Two alternative designs of the CS1 module are being developed by the CEA and EPFL-SPC teams. The CS1 module designed by CEA is double-pancake wound using a Nb3Sn Wind&React Cable-in-Conduit Conductor with a central cooling channel. Our work presents the thermal-hydraulic study of the CEA design of the CS1 module based on the EU-DEMO 2018 baseline. The first part of our analysis includes simulations of the CS1 behavior at normal operating conditions, aimed at the estimation of the minimum temperature margin. This part consists of two stages, namely: (i) simulations of the whole simplified “4 points” CS current scenario (not including the breakdown), and (ii) preliminary simulations of the breakdown phase. The second part is focused on quench simulations aimed at the assessment of the maximum hot-spot temperature. The analysis is performed using the THEA code by CryoSoft. We consider the realistic magnetic field and strain profiles along the conductor, heat transfer between neighboring turns and heat loads due to the AC coupling losses. Power of AC coupling losses in all performed simulations is computed based on the effective values of magnetic field and three trial values of the parameter nτ (100 ms, 200 ms and 400 ms). We assume that quench is initiated at the beginning of pre-magnetization phase and we take into account heat generation due to AC losses during the current dump. Minimum temperature margin during the whole simplified current scenario is larger than the 1.5 K acceptance criterion for all considered nτ values. Preliminary simulations of the breakdown phase indicate that the minimum ΔTmarg may drop below 1.5 K, even for the lowest considered nτ value, which calls for attention and requires further more detailed studies. The calculated hot-spot temperatures in all considered cases were safely below the 150 K acceptable limit.