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AC loss of \Nb3\Sn cable-in-conduit conductors (CICC) decreases after cyclic mechanical loading, but remains almost the same in case of Nb-Ti ones. It was observed during previous ITER CS, TF, and PF inserts tests in JAEA. The same phenomena have been detected on numerous ITER CS, TF, and PF short samples tested in the SULTAN facility. Experimental methods of ac loss investigation in JAEA-Naka and SULTAN were different, but the final results showed a good agreement. Analysis and numerical investigation of the present work were based on RF PF&TF CICCs SULTAN test results, theory of superconductivity, and our own physical and engineering understanding of evidence. Cyclic mechanical loading in both JAEA and SULTAN was initiated by electromagnetic force. In this paper, we attempt to explain why hysteresis, coupling, and mechanical loss decrease dramatically after cyclic mechanical loading and thermo-mechanical stress caused by WUCD (warm-up and cool-down) in \Nb3\Sn CICC. [ABSTRACT FROM PUBLISHER]

To form a cable-in-conduit conductor (CICC) a cable should be inserted into a jacket under tensile force that is increasing with length of insertion. This tensile force can lead to both elongation and untwisting of a cable with increase of a twist pitch. The untwisting can also be induced by stress accumulated in the material during the cabling process. Understanding the untwisting process is very important, because the twist pitch of a cable inside a CICC strongly affects properties such as ac loss. In this paper, we present the results of an experiment on RF toroidal field (TF) cable sample tensile tests using the «Hitachi Cable» (Japan) tensile machine, and also the results of an experiment performed at the jacketing line in the Russian Scientific R&D Cable Institute (VNIIKP) after TF cable reinsertion. In the latter experiment, twist pitches were measured along the full cable length. A model to calculate untwisting and stretching processes has been developed. The results of the calculations are compared with the experimental data. [ABSTRACT FROM PUBLISHER]