Articles you may be interested inMicrostructure-critical current density model for MgB 2 wires and tapes

A significant enhancement of Jc, Hirr, and Hc2 in MgB2 tapes has been achieved by using maleic anhydride (C4H2O3) as dopants. MgB2 tape samples with 0 up to 30wt% C4H2O3 added were prepared by an in situ processed powder-in-tube method. Compared to the pure tapes, Jc for the 10wt% C4H2O3 doped samples was improved by more than an order of magnitude in high fields up to 18T. At 4.2K, the transport Jc for the 10wt% doped samples reached 1.08×104, 5.42×103, and 2.18×103A∕cm2 at 12, 14, and 16T, respectively, and were better than those of the best MgB2∕Fe tapes reported by far. Furthermore, the Hirr for the 10wt% doped sample reached 9.6T at 20K, which was comparable to that of NbTi at 4.2K. The improvement of the superconducting properties in doped tapes can be attributed to the increase of Hc2 and the grain size refinement by C4H2O3 doping.

The effect of the quality of starting powders on the microstructure and superconducting properties of in-situ processed Fe-sheathed MgB 2 tapes has been investigated. Three different types of commercial atomized spherical magnesium powder and two different purities of amorphous boron powder were employed. When using the 10-micrometre magnesium as precursor powders, the Mg reacted with boron more uniformly and quickly, thus the uniformity of the fabricated MgB 2 was improved and the grain size of the MgB 2 was decreased, hence significant critical current density (Jc) enhancements were achieved for MgB 2 tapes. Jc at 4.2 K for MgB 2 tapes made from the 10 μm Mg and high purity boron powders was at least a factor of ten higher than values measured for MgB 2 samples made from all other starting powders. At 20 K, 5 T, the typical Jc values of the tapes were over 1.0×10 4 A/cm 2 and were much better than those of tape samples reported recently.

BSCCO tapes with dispersion hardened AgMg sheaths possess excellent mechanical properties but reach commonly only about 70 -80% of the critical currents of Ag sheathed reference tapes. Investigating the temperature dependence of I, and the (2223) phase content for two annealing steps on 19 filamentary Ag and AgMg sheathed tapes, characteristic differences with respect to the reaction kinetics and the resulting final phase content were found, A detailed characterization of the properties of the AgMg envelope, defining the boundary condition during the tape annealing process, gives first indications, that the oxygen exchange between filament and annealing atmosphere is modified with obviously significant influence on the phase formation kinetics and phase diagram shifts.

In the framework of the R&D for the ITER Poloidal Field Coils (PFC), a testing campaign was achieved on NbTi strands used in PFC-relevant modules. Three candidate NbTi strands have been used for manufacture of two Full-Size Joint Samples (PFIS and PF-FSJS) and the PF Conductor Insert (PFCI): -one strand manufactured by Europa Metalli (Italy), Ni plated and 0.81 mm diameter -one strand manufactured by Alstom (France), with a CuNi barrier and 0.81 mm diameter -one strand manufactured by Bochvar VNIINM (Russia), Ni plated and 0.73 mm diameter An extensive test campaign has been performed at GHMFL (CNRS, Grenoble) in 2003 using the CEA VTC facility at temperatures ranging from 4.2 K to 7.5 K and at magnetic fields ranging from 2.5 to 10.5 T.The results showed that all three strands have quite close performances in the ITER PFC operating range despite their structural differences and that due to the critical current density curvature with temperature, they fail to meet the 1.5 K PFC temperature margin criterion by 0.2 to 0.3 K. Additionally, applications of corresponding fits to PF-FSJS tests showed consistent results and finally a brief discussion on fitting formula is presented.

A significant improvement in J c at both 4.2 and 20 K has been achieved for MgB 2 tapes using C 9 H 11 NO as a dopant. It is found that C 9 H 11 NO doping will cause a small depression in T c while the J c and H c2 values are strongly enhanced. The highest J c was obtained for a C 9 H 11 NO doped sample sintered at 800 • C, namely 3.7 × 10 4 A cm −2 , at 4.2 K, 10 T. This is the highest J c value obtained for a MgB 2 tape using a carbohydrate as a doping material. Moreover, at 20 K, 5 T, a transport J c value as high as 1.9 × 10 4 A cm −2 is observed, suggesting that MgB 2 holds promise for practical applications. Besides the improvement of grain linkage, the clearly enhanced H c2 is thought to be a major reason for the prominent J c performance, in a field, for C 9 H 11 NO doped MgB 2 samples.

International audienceWe have measured intrinsic tunneling spectra of charge density wave (CDW) materials NbSe3 and o-TaS3 in sub-micron scale mesa structures. Beyond the interband tunneling across the CDW gap, , we observe intragap states at the voltage which we associate with creation of the amplitude soliton. The onset of the tunneling occurs only above a threshold voltage followed by a quasi-periodic staircase spectrum. We interpret that behavior as the CDW phase decoupling between neighboring layers via the formation of a grid of dislocation lines. In NbSe3, the application of a high magnetic field (up to 27 T) yields a strong suppression of the tunneling density of states within the CDW gap indicating a possible field induced metal-insulator transition

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