Summary of ITER TF Nb₃Sn strand testing under
axial strain, spatial periodic bending and contact stress

A. Nijhuis, Y. Ilyin, W. Abbas, W.A.J. Wessel,
H.J.G. Krooshoop, L. Feng, Y. Miyoshi

Abstract— 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 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.

Index Terms— axial strain, bending strain, contact stress, degradation, Nb₃Sn, superconductors, CICC, ITER

Manuscript received August 19, 2008.
This work is supported by the ITER IO and EC under the contract of Association between EURATOM/FOM, carried out within the EFDA/F4E framework.
A. Nijhuis, W. Abbas, W.A.J. Wessel, H.J.G. Krooshoop, Y. Miyoshi are with the University of Twente, Faculty of Science and Technology, Low Temperature Division, P.O. Box 217, 7500 AE Enschede, The Netherlands, phone +31534893140; fax +31534891099; email a.nijhuis@tnw.utwente.nl.
Y. Ilyin has moved to ITER IO, Cadarache, France, L. Feng is with ASIPP, Hefei, China.

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