We report recent progress in 2G-HTS wire technology at Superpower Inc. The throughputs of 4mm-wide tape have reached 750m/h for sputtering AlO3+Y2O3 base layer, 360m/h for IBAD MgO template, 345m/h for sputtering Homo-epi MgO+LMO buffer, 180m/h for MOCVD REBCO. Critical current (Ic) of 813A/cm-width at 77K and self-field has been achieved on 1 meter length of 12mm-wide tape in which the thickness of GdYBCO film is 3.3 microns. Ic in a magnetic field has been significantly improved through composition modification, doping and MOCVD condition optimization. Ic of 185.6A/cm-width at 77K and 1Tesla has been obtained. For Ic on long lengths, 314A/cm-width on 202m, 221A/cm-width on 610m and 170A/cm-width on 935m have been achieved. A coil of 19.1mm diameter we made with our 2G wires generated 26.8T magnetic field in the magnet. A 30m-long cable made with nearly 10,000 meters of Superpower 2G wires showed excellent overall performance and has been installed and energized in the power grid.

For device applications of a superconducting material, its stability to ambient conditions is an issue of critical concern. The study of the ageing effects of the recently discovered intermetallic compound MgB2 is vital for knowing the degree of usefulness of this material. We report here the study of ageing and fluctuation conductivity behavior in bulk MgB2 pellets and stainless-steel sheathed, in-situ synthesized MgB2 tapes. A possible degradation mechanism is proposed based on ac-magnetic susceptibility and XRD investigations of MgB2 samples exposed to ambient over prolonged durations of time. In addition, the fluctuation induced conductivity behavior is also analyzed based on the observed resistivity (ρ)-vs-T measurements in MgB2 tape samples. This study indicated a three dimensional character of the MgB2 with reasonably good estimates of coherence the length. The scaling of fluctuation induced conductivity enhancement is also investigated from the ρ(H) vs T data obtained for different applied field strengths. These findings support the three-dimensional nature of thermodynamic fluctuations operative in MgB2 in contrast to that prevalent in several other high-temperature superconductors (HTSCs).

Magnesium diboride (MgB2) was successfully produced in a pellet with sandwich-like structure. The sample was prepared by embedding a layer of Mg powder in between layers of boron powder before they were cold-pressed and sintered in argon atmosphere at different temperatures. After sintering, the interfacial regions between the Mg and B layers were examined and hexagonal platelets were observed lying along the interfacial regions in samples sintered at temperatures above 700°C. These hexagonal platelets were confirmed as MgB2. When samples were sintered at higher temperatures, the lateral size of the platelets increased. At 700°C, the average size of the platelets was 0.5 μgm, and it increased to 1.5 μgm in sample sintered at 900°C. In addition, the critical temperature (TC) and the magnetization (M) were also changed from 35.4 K to 37.1 K and −0.7 to −1.8 emu/g, respectively.

Bi2223 multifilamentary tapes with enhanced transverse resistivity by introducing Ca2CuO3 and SrZrO3 as interfilamentary barriers were prepared and their AC loss properties were examined under AC external magnetic field. To improve the deformation properties of these oxide powders, 20-30wt% Bi2212 powders were mixed with them. The mixed oxide powders were introduced among the twisted Bi2223 filaments by using dip-coating method. AC loss properties under AC parallel or perpendicular field were measured and compared with the results for the tape without barriers. The loss measurements were carried out by changing both the amplitude and the frequency of external field. Based on the experimental results, the effect of barrier introduction on the loss reductions was discussed.