$I_{\rm c}$ Measurements on ${\rm Nb}_{3}{\rm Sn}$ Strands Extracted From ITER CICC Prototypes

The unexpectedly low critical current performance of some ITER prototype cable-in-conduit conductors (CICC) measured in the SULTAN test facility during the last two years led to the question whether it arises from a transverse strain in the strands caused by the transverse Lorentz force or from a damage of filaments in the strands. Since the former process is in principle a reversible effect while the latter is not, measurements of the critical current of ~8 cm long strand sections extracted systematically from prototype samples were performed to see if and by how much the critical current dropped relative to the one of the witness sample. Strand witness samples had been mounted on ITER reference barrels, heat treated together with the conductor samples for the SULTAN tests and their I_c measured. Although the short sample lengths caused experimental difficulties and the number of measured strands permitted only a limited statistical analysis, the general trend of the conductor performance in SULTAN samples-high and stable (i.e. without cyclic load degradation) T_cs or not-is reflected in the I_c measurements on extracted strands.