Sealing of the critical current in ITER type niobium-tin superconductors in relation to the applied field, temperature and uni-axial applied strain

The three dimensional surface of the critical current density versus field and temperature J(c)(B,T) of niobium-tin is a function of the strain state of the superconductor, A brief review of literature on this subject is pres ented. The J(c)(B) function is described by the relations for flux pinning. The temperature and strain dependencies are added to this relation. This r esults in a unifying scaling law for A15 materials, which is verified for d ifferent niobium-tin conductors with respect to all the relevant variables, i.e. field, temperature and uni-axial strain. Nb3Sn conductors from 9 manu facturers are measured in the frame work of the third ITER benchmark tests on critical current*. The investigated ranges are: applied field from 7 to 13 T, temperature from 4.2 to 8 K and applied strain from -0.4 to +0.8 %, S pecial attention is paid to the region of compressive axial strain, which i s the most relevant state of strain for superconductors under thermal compr ession in practical applications.