MEASUREMENTS OF Nb3Sn CONDUCTOR DIMENSION CHANGES DURING HEAT TREATMENT

During the heat treatment of Nb3Sn coils the conductor material properties change significantly. These effects together with the changes of the conductor dimensions during heat treatment may introduce large strains in the coils for accelerator magnets. The US LHC Accelerator Research Program (LARP) has initiated a study aiming at understanding the thermal expansion and contraction of Nb3Sn strands, cables and coils during heat treatment. Several measurements on OST RRP 54/61 and OST RRP 108/127 strands were performed, and a few more are in progress, in order to have sufficient inputs for finite element simulation of the dimensional changes during heat treatment. Three strand quantities were measured: diameter change, length change and twist change. The measured types of strands (OST RRP 54/61 and OST RRP 108/127) demonstrated diameter change by +2.15% and +1.88%, and length change by +0.035% and -0.045% respectively. The measured twist change after reaction was about 4%. In this paper an impact of twist change on strand length change was studied, as well. The results of measurements show a significant contribution of twist change to the strand length change.