Filament aspect ratio and transport currents of Bi(2223)/Ag at 77 K

Using the tape-in-rectangular tube (TIRT) process, we have made multi-core Bi-2223/Ag tapes with various numbers of filaments (10–162), and with different filament architectures and orientations. We have measured the angular dependence of the transport current of the tape samples with ‘parallel’ and ‘perpendicular’ filaments. The transversal Ic distribution obtained by spatially resolved transport measurements (‘magnetic knife’) illustrates that the filament quality of the TIRT tapes is better at the tape edges than in the centre. The tapes were stressed by two types of tensioning set-up (a short straight sample and a U-shaped spring) and by bending at 77 K. The Ic degradation shows different behaviour for parallel and perpendicular filaments, which is attributed to the difference in filament density and crack propagation.

Section: Resultsmentioning

confidence: 85%

Section: Resultsmentioning

confidence: 99%

Transport currents in Bi-2223/Ag tapes made using the tape-in-rectangular tube process, current distribution andI_cstress degradation

Kòváč

Hušek

Melíšek

et al. 2002

“…No widening and no associated improved filament density and texture was achieved for the 21-filament tape A with perpendicular filaments, and the value of J c only reached 3000 A cm −2 . It is interesting that this value corresponds to the J c of a single-core tape which has a comparable filament aspect ratio b f /a f = 3-4 [13], where a f and b f are the filament thickness and width, respectively (see table 1). The highest J c of around 16 000 A cm −2 was measured for tape C with a Ag-alloy outer sheath, table 1.…”

Section: Resultsmentioning

confidence: 99%

BSCCO/Ag tapes made by a tape-in-rectangular tube process

Kòváč

Hušek

Melíšek

et al. 2001

Multi-core tape composites with various filament configurations have been made by a tape-in-rectangular tube (TIRT) process. This TIRT process is based on the deformation of multifilamentary composites assembled from a rectangular Ag (Ag-alloy) tube filled by pre-deformed single-core BSCCO/Ag tapes. Two-axial rolling induces texture in the filaments in two rolling planes, with the filament planes oriented parallel or perpendicular to the tape width, thus reducing the high Ic anisotropy which can degrade the total current in coils working at high temperatures (77 K). The homogeneity of the filaments was studied by a magneto-optical technique. Roll-sintered samples were measured at 77 K in an external magnetic field up to 1 T and at constant fields (0.1 T and 0.5 T) at various orientations (between parallel and perpendicular) to the tape surface. The results demonstrate the possibility of using these tapes for selected parts of a coil winding to reduce the apparent effect of the radial field component on the reduction of the total coil current.

“…Furthermore, the Ta foil pieces added in the sample space close to the wires as well as the Fe sheath itself absorb a part of the residual oxygen as evidenced by a thin oxide layer formed on the surface of the wires and the Ta pieces. Kováč et al [34] already reported that a 30 min heat treatment at 950 • C in an argon atmosphere results in a non-negligible increase of the MgO phase content in wires prepared from pre-reacted MgB 2 powders. While it cannot be ruled out that residual oxygen in the argon atmosphere surrounding the samples may contribute to the formation of MgO, it is also possible that oxygen is already present inside the samples in relatively large amounts prior to the start of the heat treatment.…”

Section: Mgo Formationmentioning

confidence: 99%

In situinvestigations of phase transformations in Fe-sheathed MgB₂wires

Grivel

Pinholt

Andersen

et al. 2005

The phase evolution inside Fe-sheathed wires containing precursor powders consisting of a mixture of Mg and B has been studied in situ by means of x-ray diffraction with hard synchrotron radiation (90 keV). Mg was found to disappear progressively during the heating stage. At 500• C, the intensity of the Mg diffraction lines is reduced by about 20%. This effect is partly attributable to MgO formation. The MgB 2 phase was detected from 575• C. Fe 2 B was forming at the interface between the sheath and the ceramic core at sintering temperatures of 780 and 700• C, but not at 650• C. The formation rate of this phase is strongly dependent on the heat treatment temperature. Its presence can be readily detected as soon as the average interface reaction thickness exceeds 150-200 nm.