The ${\rm J}_{\rm c}({\rm B},{\rm T})$ Characterization of Commercial NbTi Strands for ITER PF 1&6 Coils

The commercial multifilamentary NbTi strands produced for ITER poloidal field coils PF1 and PF6 have been characterized on J c (B,T) at various manufacturing stages: bare strand, Ni-plated strand and the strand after impregnation heat treatment. We present the results of critical current measurements at magnetic fields in the range of 4.5-10 T, and temperature within 4.2-7 K. Current sharing temperature T cs of these strands has been determined with a precision of few tens of mK, using fit formula that provides the critical current density as a function of temperature and field. The results show that T cs of commercial strands exceeds the required value of 5.9 K at 6.4 T and the operating current of 33 A. These measurements allowed us to get a database, essential for the future analysis of the experimental data, and to find the strand characteristic parameters for the J c (B,T) fit.