Critical-Current Measurements on an ITER Nb3Sn Strand: Effect of Axial Tensile Strain
Najib Cheggour, John (Jack) W. Ekin, Loren F. Goodrich
The dependence of transport critical-current (Ic 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 εmax and the irreversible strain limit εirr were 0.19 % and 0.8 %, respectively; and the ultimate strain where the wire physically broke was about 0.95 %. The pinning force Fp (=Ic × B) was proportional to (i}Bc2*)sbp(1-b)q, where b=B/Bc2* 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 Bc2* (the field at which Fp extrapolates to zero) was well described by Bc2*max[1-a|ε- εmax|u], where Bc2*max is the maximum value of Bc2* 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 Ic at various intrinsic strains between -0.5 % and 0.5 %, and magnetic fields from 12 T to 16 T.
, Ekin, J.
and Goodrich, L.
Critical-Current Measurements on an ITER Nb<sub>3</sub>Sn Strand: Effect of Axial Tensile Strain, IEEE Transactions on Applied Superconductivity, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=32461
(Accessed March 23, 2023)