Studies of electron beam coevaporated Nb3Sn composites: Critical current and microstructure

The critical current pinning force has been measured as a function of the magnetic field for a variety of microstructures of Nb3Sn. These include Nb3Sn structures with columnar grains, codeposited Nb3Sn-Al2O3structures with equiaxed grains, and codeposited Nb3Sn-Cu structures with equiaxed grains. The peak in the pinning force is compared with the grain size. For grains or columns larger than 400 Å an inverse grain size dependence is found. For smaller grains the pinning force appears to decrease. A possible detrimental effect of copper on Nb3Sn is pointed out.