459 research outputs found
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
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
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 resonance in the reaction
We investigate the photo-production in the reaction within the effective Lagrangian method near
threshold. In addition to the "background" contributions from the contact,
channel exchange, and channel nucleon pole terms, which were
already considered in previous works, the contribution from the nucleon
resonance (spin-parity ) is also considered. We show
that the inclusion of the nucleon resonance 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
Local Strain and its Influence on Mechanical - Electromagnetic Properties of Nb3Sn and Nb3Al Strands
- …