Filamentary MgB2 Wires With Low Magnetization AC Losses

This paper describes the development of MgB
₂
wires with low magnetization ac losses made by in situ or internal magnesium diffusion methods. A strong contribution of eddy currents was found in a wire with a highly conductive copper sheath, but a GlidCop sheath showed no eddy current loss addition. For minimized hysteresis loss, the filaments have to be small enough, which, however, reduces the critical current. Twisting of filaments was used to achieve a reduction in coupling loss; however, this induced mechanical strain into the filaments and decreased the critical current. Cabling of MgB
₂
strands decreased the coupling loss without degradation. Interfilament resistivity was tuned using different barriers (Nb, Ti, and NbTi), which allowed for an effective reduction in the coupling loss and resulted in a shift of the ac loss maximum into high frequencies.