Improved transport properties and connectivity of in situ MgB2 wires obtained by Cold High Pressure Densification (CHPD)

Abstract: The critical current density, J c, of in situ MgB2 wires with C4H6O5 (malic acid) has been strongly enhanced by means of Cold High Pressure Densification (CHPD) at pressures up to 2.5GPa prior to reaction. An increase in J c by factors 2 and 8 was observed at 4.2 and 20K, regardless of the applied field. Densified wires were found to exhibit a higher homogeneity due to enhanced connectivity. In addition, a higher C content was found, as shown by the lattice parameter change, the decrease of T c, the shift of the calorimetric T c distribution and a reduced anisotropy in tapes obtained from the same wires. The higher C content in densified wires is responsible for the observed enhancement of B irr by more than 1T, up to 11T at 20K. Almost isotropic J c values were obtained for C4H6O5 added square wires of 1×0.6mm2 cross section, the values of J c(4.2K)=1×104 A/cm2 for fields // and ⊥ to the wider surface being obtained at 13.8 and 13.1T (1μV/cm criterion), the values for 20K being 6.4 and 6.2T, respectively. The method was successfully applied to mono- and multifilamentary wires with lengths up to several meters, suggesting applicability for industrial lengths. [Copyright &y& Elsevier]