Influence of structure of fine filament NbTi composite on its electromagnetic characteristics

The study of the influence of filament diameter d/sub f/, filament spacing b/sub n/, and B on critical current density J/sub c/ and AC losses p/sub s/ in one type of fine filament composite (FFC) has revealed two components of J/sub c/, the bulk and surface critical current densities J/sub cb/ and J/sub cs/, respectively. A simple relationship between them, J/sub c/, and geometrical parameters of FFC including those with different types of artificial pinning centers (APCs) is formulated. It is used to explain measured J/sub c/(B,d/sub f/) dependence in FFC with island-type APC as well as to discuss the prospects of both types of APC in FFC for AC use. To verify the theoretical results, a series of FFC samples with sheet-type APC has been prepared and measured. Experimental values of J/sub c/(B,d/sub f/) obtained in this series of samples are smaller than expected. One possible reason for this difference is suggested.<>