AC TRANSPORT CURRENT AND APPLIED MAGNETIC FIELD LOSSES IN MgB2 MULTIFILAMENTARY STRANDS WITH NON-MAGNETIC SHEATH MATERIALS

AC transport current and applied magnetic field loss measurements have been made on MgB2 superconducting strands. We tested six-filament strands made via an in-situ route with Nb chemical barriers, a Cu-inter-filamentary matrix, and ODS Cu (glidcop) outer sheaths. Strands were untwisted and measured in self magnetic field at temperatures from 4.2 K to Tc. Transport ac losses agreed reasonably well with theoretical predictions for a wire of round cross-section. AC losses in applied magnetic field perpendicular to the wire axis have been measured in fields up to 140 mT (peak) in frequency range 50-200 Hz in liquid helium bath at 4.2 K. There is a reasonable agreement of the losses with the critical state model at 50 Hz. At 200 Hz the losses are dominated by eddy currents in Cu matrix. Eddy current losses in the glidcop sheath are negligibly small.