Intrawire resistance, AC loss and strain dependence of critical current in MgB₂wires with and without cold high-pressure densification

The intrawire resistance and alternating current (AC) loss of two MgB 2 wires with filaments surrounded by Nb barriers have been measured and analyzed. Relatively high values of filament-to-matrix contact resistivity are found in the MgB 2 wires; the values are two or three orders higher than those commonly found in NbTi or Nb 3 Sn wires. Considering the high porosity of the MgB 2 filaments, cold high-pressure densification has been applied on the two MgB 2 wires to investigate its impact on intrawire resistance and AC loss. The intrawire resistance is measured with a direct four-probe voltage-current method at various temperatures. The AC loss is measured by vibrating sample magnetometer measurements at 4.2 K. In addition to the intrawire resistance measurements, the critical current of MgB 2 wires before and after densification is measured with a U-shaped bending spring at 4.2 K as function of axial strain. The critical current in densified MgB 2 wires is found to be higher than that in the same wire without densification; it is also less sensitive to the applied axial strain.