Performance of ITER (EU-TFPRO-2) Nb3Sn strands under spatial periodic bending, axial strain and contact stress

The Nb3Sn cable in conduit conductors (CICCs) for the International Thermonuclear Experimental Reactor (ITER) show a significant degradation in their performance with increasing electromagnetic load. Knowledge of the influence of bending and contact stress on the critical current (I-c) of the Nb3Sn strands is essential for the understanding of this reduction in performance. We have measured the I-c of Nb3Sn strands in the TARSIS facility, when subjected to spatial periodic bending using bending wavelengths from 5 to 10 mm, periodic contact stress and uni-axial strain on two strand types, manufactured by OST. These strands were used for the cables of the European TFPRO-2 sample tested in SULTAN. A priori predictions with the TEMLOP model led to the discovery that the severe Lorentz force response and degradation can be completely improved by increasing the pitch length in subsequent initial cabling stages. The TFPRO-2/OST-II conductor, especially designed to examine this prediction, verified this significant enhancement. TEMLOP directly uses data describing the behavior of single strands under uni-axial stress and strain, periodic bending and contact loads. Here we give an overview of the TARSIS strand testing results.