VAMAS interlaboratory comparisons of critical current vs. strain in Nb{sub 3}Sn

Abstract

A comparison is made of measurements of the effect of axial tensile strain on the critical current of multifilamentary Nb{sub 3}Sn superconductors by three different laboratories. Two of the laboratories used short sample testing apparatus wherein a straight section of conductor was cooled in a force-free state. One of the laboratories used a spring apparatus wherein a long sample was reacted in a coil shape and attached to a spring sample holder. The agreement between the results for the two laboratories that used the straight sample apparatus was quite good, within 15% for all three conductors at 15 T, except at very high strain for one conductor which had an upper critical field close to the measurement field. To make a comparison with the data obtained using the spring method, it was necessary to fit the data to the compressive prestrain determined using the straight-sample technique. With such a fit, the agreement was variable, between 15 and 25% depending on the conductor. Values of the prestrain and irreversible strain obtained from the straight sample data agreed within 0.06% and 0.05% respectively. Values of the maxi (strain-free) upper critical fields agreed within several tenths of a tesla