Enhanced critical current density of MgB2 superconductor synthesized in high magnetic fields

The effect of high magnetic fields on the current carrying properties of both MgB2 bulks and Fe-sheathed tapes was investigated following different thermal sequences. It is found that application of a large magnetic field during processing results in the quite uniform microstructure and the better connectivity between the MgB2 grains. As a result, the Jc of these samples has shown much higher value than that of the MgB2 samples in the absence of magnetic field. The possible mechanism of the Jc enhancement under an external magnetic field is also discussed.Comment: Presented at ISS2005, Tsukuba, 24-26 Oct., 2005; Revised versio

Significantly enhanced critical current densities in MgB2 tapes made by a scaleable, nano-carbon addition route

Nanocarbon-doped Fe-sheathed MgB2 tapes with different doping levels were prepared by the in situ powder-in-tube method. Compared to the undoped tapes, Jc for all the C-doped samples was enhanced by more than an order of magnitude in magnetic fields above 9 T. At 4.2 K, the transport Jc for the 5 at% doped tapes reached 1.85x104 A/cm2 at 10 T and 2.8x103 A/cm2 at 14 T, respectively. Moreover, the critical temperature for the doped tapes decreased slightly. Transmission electron microscopy showed a number of intra-granular dislocations and the dispersed nanoparticles embedded within MgB2 grains induced by the C doping. The mechanism for the enhancement of flux pinning is also discussed. These results indicate that powder-in-tube-processed MgB2 tape is very promising for high-field applications.Comment: 13 pages, 5 figures. to be published soo

Improved critical current densities in MgB2 tapes with ZrB2 doping

MgB2/Fe tapes with 2.5-15 at.% ZrB2 additions were prepared through the in situ powder-in-tube method. Compared to the pure tape, a significant improvement in the in-field critical current density Jc was observed, most notably for 10 at.% doping, while the critical temperature decreased slightly. At 4.2 K, the transport Jc for the 10 at.% doped sample increased by more than an order of magnitude than the undoped one in magnetic fields above 9 T. Nanoscale segregates or defects caused by the ZrB2 additions which act as effective flux pinning centers are proposed to be the main reason for the improved Jc field performance.Comment: 14 pages, 6 figure

The role of the N∗(2080)N^*(2080) resonance in the γ⃗p→K+Λ(1520)\vec{\gamma} p \to K^+ \Lambda(1520) reaction

We investigate the $\Lambda(1520)$ photo-production in the $\vec{\gamma} p \to K^+ \Lambda(1520)$ reaction within the effective Lagrangian method near threshold. In addition to the "background" contributions from the contact, $t-$channel $K$ exchange, and $s-$channel nucleon pole terms, which were already considered in previous works, the contribution from the nucleon resonance $N^*(2080)$ (spin-parity $J^P = 3/2^-$) is also considered. We show that the inclusion of the nucleon resonance $N^*(2080)$ leads to a fairly good description of the new LEPS differential cross section data, and that these measurements can be used to determine some of the properties of this latter resonance. However, serious discrepancies appear when the predictions of the model are compared to the photon-beam asymmetry also measured by the LEPS Collaboration.Comment: 9 pages,6 figures, 1 tabl