The enhanced Jc and Birr of in situ MgB2 wires and tapesalloyed with C4H6O5 (malic acid) after cold high pressure densification

Abstract

Cold high pressure densification, a method recently introduced at GAP inGeneva, was applied for improving the transport critical current density,Jc, and the irreversibilityfield, Birr, of monofilamentaryin situ MgB2 wires and tapesalloyed with 10 wt% C4H6O5 (malic acid). Tapes densified at 1.48 GPa exhibited after reaction an enhancement ofJc from 2to 4 × 104 A cm−2 at4.2 K/10 T and from0.5 to 4 × 104 A cm−2 at20 K/5 T, whilethe Birr was enhanced from 19.3 to 22 T at 4.2 K and from 7.5 to 10.0 T at 20 K.Cold densification also caused a strong enhancement ofB(104), the field atwhich Jc takesthe value 1 × 104 A cm−2. For tapes subjected to 1.48 GPa, and at 4.2 K were found to increase from 11.8 and 10.5 T to 13.2 and 12.2 T, respectively.Almost isotropic conditions were obtained for rectangular wires with aspect ratiosa/b<2 subjected to 2.0 GPa, where and T were obtained. At 20 K, the wires exhibited an almost isotropic behavior, with T and T, Birr(20 K) being ∼10 T. These values are equal to or higher than the highest values reported so far for isotropicin situ wires with SiC or other carbon based additives. Further improvements are expected onoptimizing the cold high pressure densification process, which has the potential for fabrication ofMgB2 wires of industrial lengths.