Critical-Current Measurements on an ITER Nb3Sn Strand: Effect of Axial Tensile Strain

Published

June 1, 2007

Author(s)

Najib Cheggour, John (Jack) W. Ekin, Loren F. Goodrich

Abstract

The dependence of transport critical-current (I_c on axial tensile strain ε was measured for a developmental Nb₃Sn multifilamentary strand as a function of magnetic field B between 12 T and 16 T, at the temperature of 4 K. This conductor was from the first stage of strand pre-production for the central solenoid of the International Thermonuclear Experimental Reactor (ITER) project. Measurements were made on straight samples using a stress-free cooling strain apparatus. The compressive pre-strain ε_max and the irreversible strain limit ε_irr were 0.19 % and 0.8 %, respectively; and the ultimate strain where the wire physically broke was about 0.95 %. The pinning force F_p (=Ic × B) was proportional to (i}B_c2^*)^sb^p(1-b)^q, where b=B/B_c2^* is the reduced magnetic field, and the scaling constants had values p=0.58, q=1.86, and s=0.7. The strain dependence of the effective upper critical field B_c2^* (the field at which F_p extrapolates to zero) was well described by B_c2^*_max[1-a|ε- ε_max|^u], where B_c2^*_max is the maximum value of B_c2^* as a function of strain, u=1.7, and a was about 1230 for the compressive strains and 1670 for the tensile strains. Ekin's strain scaling law was applied to calculate the strain sensitivity of I_c at various intrinsic strains between -0.5 % and 0.5 %, and magnetic fields from 12 T to 16 T.

Citation

IEEE Transactions on Applied Superconductivity

Volume

17

Issue

2

Pub Type

Journals

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Keywords

axial strain, critical-current, ITER, niobium-tin, pinning force, stress-free cooling superconductor magnet

Citation

Cheggour, N. , Ekin, J. and Goodrich, L. (2007), Critical-Current Measurements on an ITER Nb₃Sn Strand: Effect of Axial Tensile Strain, IEEE Transactions on Applied Superconductivity, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=32461 (Accessed November 21, 2024)