Thermal-hydraulic analysis of the upgraded EU-DEMO CS1 coil

The European DEMOnstration Fusion Power Plant (EU-DEMO) is planned to be an intermediate step between ITER experimental reactor and a commercial fusion power plant, which should demonstrate feasibility of grid electricity production at a level of several hundred MW. Design and assessment studies on the EU-DEMO superconducting magnets, have been initially focused on several concepts of the winding pack (WP) of the Toroidal Field coil, but recently also first concepts of the Central Solenoid (CS) have been proposed. The EU-DEMO CS coil will be composed of 5 modules, positioned vertically one above the other. The central CS1 module will operate under the most severe conditions. In the present work a thermal-hydraulic analysis of the most recent design of the CS1 module, proposed by the EPFL-SCP team, is performed, aimed at the assessment of the minimum temperature margin at normal operating conditions. The considered WP consists of 10 sub-coils, which are layer-wound using HTS (Re-123), React & Wind Nb3Sn and NbTi conductors in the high, medium and low field sections, respectively. Operation of conductors designed for each sub-coil is simulated using the THEA code. The current scenario of the CS1 coil includes the premagnetization, plasma current ramp-up (PCRU), burn and dwell phases. Our analysis is focused on the fast breakdown at the beginning of the PCRU phase, which features largest heat generation due to AC losses. It is shown, that the temperature margin in all conductors is well above 1.5 K for a value of n tau = 75 ms assumed in the characterization of AC coupling losses.