A novel numerical approach for analyzing experimental data on critical current degradation in Nb3Sn wires caused by transverse deformations preceding heat treatment

Abstract

In the framework of studies on high-field magnets for future accelerators, a specific project called ASTRACT focuses on the effect of transverse strain on the critical current of Nb3Sn wires. The first phase of the project addresses the effects of strain imposed on Nb3Sn wires before heat treatment and the development of a procedure to directly compare critical current measurements with values extracted from magnetization cycles. A Nb3Sn RRP-Ti wire was deformed to different values of transverse strain (10%, 15%, 20%, and 25%), and long samples were collected for transport measurements at 4.2 K, in a background field ranging from 10 to 14 T. Short samples were used for magnetization measurements (VSM technique). Additionally, SEM images of the cross-section were collected at different longitudinal positions along the wire for each strain value. This paper proposes a method based on SEM image analysis and magnetization measurements analysis to study the effect of bundle deformation on transport properties. The procedure requires morphological information provided by SEM images after appropriate numerical processing. Verification through statistical comparison between the Ic transport and VSM data is also conducted. Direct critical current measurements showed no degradation due to deformation up to 25%. The method introduced, independent of transport data, can reach the same conclusions by considering the real shape of the bundles.