Optimized heat treatment of internal tin Nb3Sn strands [for ITER]

The hysteresis and coupling losses, the magnetoresistance of the strands designed by Europa Metalli to reach ITER HP I specifications have been deduced by magnetization and magnetoresistance measurements. Additionally, the critical current density and the n-values have been examined. By varying the temperature and the duration of the final annealing step, a better understanding of the interplay of the annealing parameters with the intrinsic properties can be gained. From these results we will show, that for the use in ITER shorter annealing times at higher annealing temperatures lead to a dramatic decrease of hysteresis and coupling losses accompanied by a decrease of annealing costs.