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We have studied bulk MgB2 synthesized by reaction of MgH2 and B with and without SiC nanoparticles and at a range of reaction temperatures. All of the samples showed enhanced upper critical fields compared to most bulk MgB2, including the sample with 10 at. % SiC reacted at 600 °C, which showed Hc2(0 K)>42 T. Extensive transmission electron microscopy (TEM) and STEM observations show that using MgH2 instead of pure Mg reduces the concentration of oxide second phases in the tapes, but that adding SiC reintroduces nanoscale grains of MgO, SiO2, and SiOxCy, and larger grains of Mg2Si. SiC causes some C doping of the MgB2, but electron energy loss spectroscopy and x-ray diffraction measurements show that the C concentration is similar to other bulk C-doped MgB2. In all the samples with and without SiC, the grain size is very small, 10–60 nm. Electron scattering from the high density of grains and second-phase boundaries is responsible for the enhanced Hc2 of these samples. However, the Hc2 properties are somewhat compromised by very broad transitions that may have their origin in the local variations of nanostructure. [ABSTRACT FROM AUTHOR]

Critical current (Ic) measurements and microscopic crack investigations were performed on short samples of ITER (International Thermonuclear Experimental Reactor) wires, designed for the CSMC (Central Solenoid Model Coil), that were bent to curvatures ranging up to 03% at room temperature. Ic was found to improve significantly with bending. Microstructural investigation revealed that IGC and VAC samples were nearly crack-free at all bend strains while Furukawa samples had significant cracking due to polishing and unrelated to bending. [ABSTRACT FROM AUTHOR]

Measurement of critical current density Jc, normal state resistivity ρn, and upper critical field Hc2 on pure and 10% SiC-doped MgB2 bulks show systematic enhancement of Hc2 by SiC addition and by lowering reaction temperature. Hc2(10 K) exceeds 33 T, while the extrapolated zero temperature value exceeds 40 T. The Rowell [Supercond. Sci. Technol. 16, R17 (2003)] analysis suggests that only 8%–17% of the MgB2 cross section actually carries current. Higher reaction temperature enhances the connectivity but degrades Hc2 and flux pinning, making the measured Jc a complex balance between connectivity, Hc2, and flux pinning induced by grain boundaries and precipitates. [ABSTRACT FROM AUTHOR]

Measurement of critical current density Jc, normal state resistivity ρn, and upper critical field Hc2 on pure and 10% SiC-doped MgB2 bulks show systematic enhancement of Hc2 by SiC addition and by lowering reaction temperature. Hc2(10 K) exceeds 33 T, while the extrapolated zero temperature value exceeds 40 T. The Rowell [Supercond. Sci. Technol. 16, R17 (2003)] analysis suggests that only 8%–17% of the MgB2 cross section actually carries current. Higher reaction temperature enhances the connectivity but degrades Hc2 and flux pinning, making the measured Jc a complex balance between connectivity, Hc2, and flux pinning induced by grain boundaries and precipitates. [ABSTRACT FROM AUTHOR]