Magnetization measurements on multifilamentary Nb3Sn and NbTi conductors

The effective filament size has been determined for a number of high current Nb3Sn multifilamentary composites. In most cases it is much larger than the nominal filament size. For the smallest filaments (∼ 1 micron) the effective size can be as much as a factor of forty times the nominal size. Samples made by the "internal tin", "bronze route", and "jelly roll" methods have been examined with filaments in the range one to ten microns. Rate dependent magnetization and "flux jumping" have been observed in some cases. NbTi composites ranging in filament size from nine to two hundred microns and with copper to superconductor ratios between 1.6:1 and 7:1 have been examined in the same apparatus. Low field "flux jumping" was only observed in conductors with very large filaments and relatively little stabilizing copper.