Summary of ITER TF Nb3Sn Strand Testing Under Axial Strain, Spatial Periodic Bending and Contact Stress

Numerous manufacturers and different strand processing techniques are involved with the production of the Nb3Sn strand material required for ITER. The superconducting transport properties of brittle Nb3Sn layers strongly depend on their strain state. Hence, the thermal compression and the substantial transverse load in combination with the key choice for the cabling pattern of the CICCs, will determine their performance. Knowledge of the influence of axial strain, periodic bending, and contact stress on the critical current (I-c) of the used Nb3Sn strands is inevitable to gain sufficient confidence in an economic design and a stable operation of ITER. We have measured the I-c and n-value of Nb3Sn strands from various manufacturers in the TARSIS facility, when subjected to spatial periodic bending and contact stress. The I-c and n-values have been determined for applied axial compressive and tensile strain varying from -0.8% up to +0.5%, between T = 4.2 K and 10 K and B = 6 T to 14 T. The strain sensitivity varies appreciably for different strand types. We present a selection of the results obtained so far.