27 research outputs found
H(T) Phase Diagram in Nb3Sn: A Different Behavior in Single Crystals, Polycristalline Samples and Multifilamentary Wires
A comparative study of magnetic behavior in a DC magnetic field up to 19
Tesla has been undertaken on different Nb3Sn samples, i.e. single crystals,
polycrystal samples and multifilamentary wires. From the 1st and 3rd harmonics
of the AC magnetic susceptibility a peak effect was experimentally observed in
the single crystal and in the polycrystal, whereas this phenomenon is absent in
the measured wires. The corresponding H vs T phase diagram reveals a different
behavior between wires on one hand and polycrystalline and single crystal
samples on the other. In particular, from the 3rd harmonics it has been
observed that vortex thermally activated flux creep phenomena are relevant in
the wires, whereas the static critical state models are more appropriate to
describe single crystals.Comment: 9 pages, 9 figures, to be published on Advances in Cryogenic
Engineering, Vol. 51-52 (CEC-ICMC05, Keystone, Colorado, 28 August-3
September 2005
High transport currents in mechanically reinforced MgB2 wires
We prepared and characterized monofilamentary MgB2 wires with a mechanically
reinforced composite sheath of Ta(Nb)/Cu/steel, which leads to dense filaments
and correspondingly high transport currents up to Jc = 10^5 A/cm^2 at 4.2 K,
self field. The reproducibility of the measured transport currents was
excellent and not depending on the wire diameter. Using different precursors,
commercial reacted powder or an unreacted Mg/B powder mixture, a strong
influence on the pinning behaviour and the irreversibility field was observed.
The critical transport current density showed a nearly linear temperature
dependency for all wires being still 52 kA/cm^2 at 20 K and 23 kA/cm^2 at 30 K.
Detailed data for Jc(B,T) and Tc(B) were measured.Comment: 21 pages, 13 figures, revised version, to be published in Supercond.
Sci. Techno