Analysis of optically and magnetically determined bridging in internal-tin process Nb/sub 3/Sn strands

Abstract

An existing model for bridging induced magnetization and hysteretic loss has been extended to take into account the inhomogeneous morphology of metallurgical bridges. After an appropriate way of calculating the magnetization of a strand with a distribution of filament-bunch sizes had been devised some reasonable conformity between the results of optical image analysis and magnetization measurement was obtained. The previously developed anisotropic continuum model of bridging in multifilamentary (MF) strands led to a description of bridging intensity in terms of a dimensionless parameter /spl gamma//sub 2/ representing the area-fraction of bridged matrix material perpendicular to the filamentary axis. Based on measurements of variously heat treated (HT) internal-Sn ITER strands /spl gamma//sub 2/ was found to have values of 0.2 to 0.7%. At the same time saturation values of the length- and twist-pitch dependent magnetizations of the bridged samples were 3-6 times greater than the estimated un-bridged values. Some attention is also given to the influence of HT time and ramp-rate on the extent of bridging.