Influence of field orientation on proximity effect induced filament coupling in NbTi wires

Filament coupling induced by the proximity effect was studied through ac susceptibility measurements on Cu-matrix NbTi multifilamentary wires in fields oriented with various directions to the wire axis. The sample wires with a different twist pitches (1.7, 3.3 and 6.1 mm) are made from VAMAS reference sample H-1. The wires have a diameter of 0.20 mm and a filament number of 931. The orientations of AC and DC fields are varied in the range from 0/spl deg/ to 90/spl deg/. The susceptibilities are measured while increasing the sample temperature after zero field cool down to 4.2 K. From the results of the field orientation and temperature dependencies of peaks in the imaginary part of AC susceptibility, we discuss the magnetic behavior of the superconductivity of the matrix induced by the proximity effect and estimate the critical current density of the matrix at low field.