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Description
The slotted core configuration is a promising candidate for the implementation of High-Temperature-Superconducting (HTS) magnets in compact fusion reactors. Quench dynamics is not yet fully understood in this type of cable and experimental and numerical investigations are still required to fully characterize their behavior in the operative conditions relevant to fusion machines.
In this work, a 3D FEM electro-thermal model, under development at the University of Bologna, (Italy) is presented. The model solves the heat balance and charge conservation equations, providing the temperature and electric potential distribution in the solid domains. The cable self-field is computed in the external domain by solving the Poisson equation for the magnetic vector potential. A homogenization procedure is employed to model the electrical and thermal properties of the stack of ReBCO tapes, allowing for considerable savings on the degrees of freedom. The model also accounts for the presence of the tape-to-tape and tape-to-core contact parameters.
The model is applied to the description of the ENEA extruded aluminum slotted core ReBCO cable in conduit conductor. Three non-twisted, non-soldered, 15-kA-class conductors were manufactured at the ENEA Frascati Research Center and tested in the SULTAN test facility (Villigen, Switzerland) to explore their quench behavior under variable conditions of temperature and background magnetic field. The operation of the 3.6-m-long conductors was monitored through voltage taps and thermometers positioned at various locations along the cable length both on the jacket and the HTS stacks.
A benchmark of the model is provided by comparing the spatial and temporal evolution of the simulated temperature and voltage distributions to the measured ones. The model is also applied to compute the current sharing temperature of the cable, the minimum quench energy, and the normal zone propagation velocity. Owing to its 3D nature, the model provides useful insights into the redistribution of heat and current occurring between the different cable components.
