Quench Analysis of the HTS CrossConductor for a Toroidal Field Coil

In the frame of the EU Demonstration Fusion Power Reactor Program within the EUROfusion consortium, the potential use of the high-temperature superconductor (HTS) material, rare-earth barium copper oxide, for a high-current conductor of a future toroidal field (TF) coil is being investigated. The structural analysis of the winding pack imposed limits on the aspect ratio of the cable space within the jacket, leading to a round cable of 31.2-mm diameter. The HTS CrossConductor (HTS CroCo) developed at the Karlsruhe Institute of Technology is used as a base strand for the cable. In the cable design, the number and the composition of HTS CroCo strands, the amount of additional copper, e.g., a central copper former, is varied with respect to its performance during quench. The cable is embedded in a stainless steel jacket and cooled by 4.5 K supercritical helium. The thermal hydraulic analysis has been done using the code THEA and determines the quench performance of the HTS conductor. The one-dimensional model consists of four homogenized components electrically and thermally coupled via thermal resistances R-th and the heat transfer coefficient h. In the model, a quench is initiated by heat pulses E-i(nit) over a length l(INZ) and for a time t(Q). Important outcomes of the simulations are the hot spot temperatures T hot of the HTS CroCo, copper core, and jacket during a fast discharge of the magnet with a time constant of tau = 27 s after reaching the quench detection voltage V-QD of 100 mV. The dependence of T-hot on different geometrical, material, and thermal parameters is studied to determine the critical ones and to derive general design principles for HTS TF coils for fusion magnets. Finally, the performance of a full conductor length is investigated.