Doping of MgB 2 by nano-SiC and its potential for improvement of flux pinning was studied for MgB 2-x (SiC) x/2 with x = 0, 0.2 and 0.3 and a 10wt% nano-SiC doped MgB 2 samples. Co-substitution of B by Si and C counterbalanced the effects of singleelement doping, decreasing T c by only 1.5K, introducing pinning centres effective at high fields and temperatures and enhancing J c and H irr significantly. Compared to the non-doped sample, J c for the 10wt% doped sample increased by a factor of 32 at 5K and 8T, 42 at 20K and 5T, and 14 at 30K and 2T. At 20K, which is considered to be a benchmark operating temperature for MgB 2 , the best J c for the doped sample was 2.4x10 5 A/cm 2 at 2T, which is comparable to J c of the best Ag/Bi-2223 tapes. At 20K and 4T, J c was 36,000A/cm 2 , which was twice as high as for the best MgB 2 thin films and an order of magnitude higher than for the best Fe/MgB 2 tapes. Because of such high performance, it is anticipated that the future MgB 2 conductors will be made using the formula of MgB x Si y C z instead of the pure MgB 2 .

An advanced internal Mg infiltration method (AIMI) in this paper has been shown to be effective in producing superconducting wires containing dense MgB 2 layers with high critical current densities. In this study, the in-field critical current densities of a series of AIMI-fabricated MgB 2 strands were investigated in terms of C doping levels, heat treatment (HT) time and filament numbers. The highest layer J c for our monofilamentary AIMI strands is 1.5 × 10 5 A/cm 2 at 10 T, 4.2 K, when the C concentration was 3 mol% and the strand was heat-treated at 675 °C for 4 hours. Transport critical currents were also measured at 4.2 K on short samples and one-meter segments of eighteen-filament Cdoped AIMI strands. The layer J c s reached 4.3 × 10 5 A/cm 2 at 5 T and 7.1 × 10 4 A/cm 2 at 10 T, twice as high as those of the best PIT strands. The analysis of these results indicates that the AIMI strands, possessing both high layer J c s and engineering J e s after further optimization, have strong potential for commercial applications.

Carbon‐encapsulated crystalline boron nanopowder and coarse magnesium powder are used as inexpensive tailored starting materials for the fabrication of high‐performance MgB2 superconducting wire. A low sintering temperature leads to a high critical current density, as a result of nanometer‐sized boron powder, surface oxidation preclusion by carbon encapsulation, and grain alignment by elongated magnesium coarse powder.

Cold high pressure densification, a method recently introduced at GAP in Geneva, was applied for improving the transport critical current density, Jc, and the irreversibility field, Birr, of monofilamentary in situ MgB2 wires and tapes alloyed with 10 wt% C4H6O5 (malic acid). Tapes densified at 1.48 GPa exhibited after reaction an enhancement of Jc from 2 to 4 × 104 A cm−2 at 4.2 K/10 T and from 0.5 to 4 × 104 A cm−2 at 20 K/5 T, while the 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 of B(104), the field at which Jc takes the 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 ratios a/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 isotropic in situ wires with SiC or other carbon based additives. Further improvements are expected on optimizing the cold high pressure densification process, which has the potential for fabrication of MgB2 wires of industrial lengths.

Conventional doping methods that directly add C or a C-bearing species to Mg+B powder have the disadvantage of adding C inhomogeneously, yielding either under-reacted regions or blocking phases. Pre-doped B powder provides a more homogeneous distribution of the C dopant in MgB 2 . Powders containing varying amounts of C were used to produce in-situ MgB 2 strands which showed high values of transport J c (10 4 A/cm 2 at 13.3T). Compared to SiC-added and malic acid-treated strands the pre-doped MgB 2 showed both higher values of B irr and transport J c , indicating that the pre-doping of B leads to more efficient C substitution into the B-sublattice.