AC Loss, Inter-Strand Resistance, and Mechanical Properties of an Option-II ITER CICC up to 30,000 Cycles in the Press

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Abstract
In Nb3Sn cable-in-conduit conductors for ITER, the superconducting strands follow complex trajectories defined by the twist pitches of multi-stage cabling and the void fraction of the conductor. The conductor in operation suffers a Lorentz load which results in distributed strand deformations that alter the overall electromagnetic and mechanical behavior of the conductor. With the Twente cable press, a cable specimen is subjected to transverse load up to 30,000 cycles and the changes in the inter-strand contact resistances, the cable deformation, and the coupling loss are monitored. An ITER toroidal field coil conductor with option-II cabling scheme is tested for the first time in the press. In comparison with previously measured conductors, the long twist pitches of option-II result in a higher inter-strand contact resistance, a lower stiffness of the conductor, and initially a higher coupling loss time constant. Within 100 cycles, the time constant decays to a comparable level as the low void fraction conductor with short twist pitches.

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