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

Abstract

The three dimensional surface of the critical current density versus field and temperature J/sub 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 presented. The J/sub c/(B) function is described by the relations for flux pinning. The temperature and strain dependencies are added to this relation, This results in a unifying scaling law for A15 materials, which is verified for different niobium-tin conductors with respect to all the relevant variables, i.e. field, temperature and uni-axial strain. Nb/sub 3/Sn conductors from 9 manufacturers 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%. Special attention is paid to the region of compressive axial strain, which is the most relevant state of strain for superconductors under thermal compression in practical applications.