Takeshi Hikata

Critical currents of superconducting BiPbSrCaCuO tapes in the magnetic flux density range 0--19. 75 T at 4. 2, 15, and 20 K

Critical currents of superconducting silver‐sheathed tapes of Bi1.8Pb0.4Sr2Ca2.2Cu3Ox have been measured in the magnetic flux density range 0–19.75 T at 4.2, 15, and 20 K. One tape achieved a critical current of 60.6 A at 19.75 T and 20 K; the corresponding critical current density is 551 A/mm2. In the same field, the tape has critical currents of 72.3 A (657 A/mm2) at 15 K and 94.2 A (856 A/mm2) at 4.2 K. At 77 K and in zero field, the tape carries 32.9 A (299 A/mm2). These results indicate that ‘‘high Tc’’ superconducting magnets of engineering interest may soon be feasible.

Microstructures and Jc-B Characteristics of Ag-Sheathed Bi-Based Superconducting Wires

We prepared silver-sheathed BiPbSrCaCuO wires by the powder-in-tube method. Maximum critical current densities at 77.3 K were 5.4×10 4 A cm -2 in a zero magnetic field, 4.2×10 4 A cm -2 at 0.1 T and 1.2×10 4 A cm -2 at 1 T. K, as the J c improves, the history effects decrease. J c and J c -B enhancements are due to the decrease and dispersion or nonsuperconducting phases, and to grain boundary improvements

Scaling of current-voltage curves in superconducting Bi-2223 silver-sheathed tape wires

Abstract The current-voltage characteristics are measured for two Bi-2223 tape specimens with different critical current densities at various temperatures under the magnetic field parallel to the c -axis. It is found that the current-voltage curves are scaled on two master curves by normalizing as predicted in the vortex glass-liquid transition theory. However, the obtained dynamic critical indices increased, and the static critical indices decreased appreciably with increasing magnetic field. These experimental results are compared with the numerical calculation based on the flux creep and flow model, taking the distribution of the flux pinning strength into account. Agreement is obtained between the experimental and theoretical results not only on the scaling curve but also on the critical indices and the transition line. The static critical index showing a divergence of the correlation length near the transition temperature can also be explained from the temperature dependence of the pinning correlation length. These results suggest that the scaling behavior is not correlated to the phase transition of fluxoids assumed in the vortex glass-liquid transition theory but seems to be correlated to a kind of transition governed by the flux pinning.

Magnetic field dependence of critical current density in Bi - Pb - Sr - Ca - Cu - O silver sheathed wire

Abstract BiPbSrCaCuO silver sheathed high Tc superconducting wires were fabricated through the solid reaction process. It is proposed in this paper that the magnetic field dependence of Jc of the wire is dominated by the Lorentz force perpendicular to the c-axis, caused by a transport current with c-axis component crossing grain boundaries, when a magnetic field is applied parallel to the plane of the wire. It was found that BiPbSrCaCuO silver sheathed wire had sufficient potential for applications at 4.2 K. The history effect of Jc for high Jc specimens was not observed at 77.3 K and appeared again at 4.2 K

Ag-Sheathed Bi-Pb-Sr-Ca-Cu-O Superconducting Wires with High Critical Current Density

Critical current density (Jc) and its dependence on magnetic field in Ag-sheathed Bi-Pb-Sr-Ca-Cu-O superconducting wire was improved by grain alignment and homogenization of the high-Tc phase (110 K). The maximum transport current density at 77.3 K in a zero magnetic field was increased to 6930 A/cm2. The magnetic field dependence of Jc (0.1 µV/cm criterion) was summarized as follows: 1660 A/cm2 (I ⊥H, a-b plane ∥H, 0.1 T), 900 A/cm2 (I ⊥H, a-b plane ⊥H, 0.1 T). We found that the grain boundaries were bonded strongly in the direction of alignment.

Development of silver-sheathed bismuth superconducting wires and their application (invited)

The development results for silver‐sheathed bismuth (2223 phase) superconducting wires in the past two years have suggested that three different fields of application will be feasible in the very near future. The first field is large current conductor application in liquid nitrogen operation. The second is magnet application (relatively low magnetic field below 1 Tesla, such as for semiconductor crystal pulling and magnetic separation) in liquid nitrogen operation. The third is super‐high field application above 20 Tesla in liquid helium operation. In this paper, we will describe the state of the art of high‐Tc superconducting wires using a combination of bismuth high‐Tc phase and powder‐in‐tube technique. Maximum Jc at 77.3 K reached to 53 700 A/cm2 in a zero magnetic field, 42 300 A/cm2 at 0.1 Tesla and 12 000 A/cm2 at 1 Tesla. Prototypes, such as a 1000 A carrying conductor at 77.3 K, a 1000 Gauss coil at 77.3 K and a super‐high field coil at 4.2 K were made and tested successfully.

Electromagnetic properties and morphology of Ag-sheathed Bi-Pb-Sr-Ca-Cu-O superconducting wires

The critical current density (Jc) in Ag-sheathed Bi-Pb-Sr-Ca-Cu-O superconducting wire increased to 17,400 A/cm2 in a zero magnetic field. The magnetic field dependence of Jc was improved according to the increase of Jc in a zero magnetic field. Fine, dispersed, nonsuperconducting phases were observed through SEM and TEM. These phases are expected to act as pinning sites.

Bismuth superconducting wires and their applications

Abstract The combination of a bismuth high T c phase ( T c = 110 K) and powder-in-tube processing technology enables the fabrication of superconducting wires with high critical current density, mass producibility and flexibility. The maximum critical current density in liquid nitrogen reached 53 700 A cm −2 in zero magnetic field, 42 300 A cm −2 at 0.1 T and 12 000 A cm −2 at 1 T. J c and J c − B enhancements were obtained with finely dispersed non-superconducting phases and clean grain boundaries. Various prototypes were made to clarify their feasibility, such as 114 m long wires ( J c ≈ 10 000 A cm −2 at 77.3 K), large current conductors ( I c = 2300 A at 77.3 K), a 0.21 T coil at 77.3 K, a 20.35 T coil at 20.3 K and a 23.37 T coil at 4.2 K.

Development of Ag-sheathed Bi-2223 superconducting wires and their applications

Silver-sheathed multifilamentary BiPbSrCaCuO 2223 superconducting wires with long length and high Jc of over 3/spl times/10/sup 4/ A/cm (77.3 K, 0 T) were developed by using the powder-in-tube method. For future industrial applications, high Jc with high Ic wires, high strength wires and low AC loss wires were also developed for large scale magnet applications and electric apparatus for AC use. In the case of AC conductor, twist effect was investigated in order to reduce the wire AC loss, PVF coating technology was applied to high strength wire. PVF coating technology made it possible to obtain amperage parallel conductor with low AC loss, because each strand is electrically insulated. As a progress of technology, we could fabricate many application prototypes. In the high amperage conductor application, current leads and cable conductors were developed. In the magnet application, pancake magnets cooled by GM refrigerator and operated at around 20 K were developed, We have also developed the transformer as an AC application operated in the liquid nitrogen.

Transport current properties of silver-sheathed BiPbSrCaCuO wire and coil

Abstract High J c silver-sheathed BiPbSrCaCuO superconducting wires have been developed. The maximum critical current densities at 77.3 K were 4.7 × 10 4 A cm −2 in zero magnetic field, 3.1 × 10 4 A cm −2 at 0.1 T and 1.1 × 10 4 A cm −2 at 1 T. At 4.2 K, the maximum critical current density was 1.03 × 10 5 A cm −2 at 23 T. The anisotropy of critical current density for different magnetic field directions was only 30% at 4.2 K, even at 23 T. Long wires, for example a 60 m wire, were fabricated and different types of coils and conductors were made and tested over a wide temperature range from 4.2 to 77.3 K. This revealed that one could obtain coils generating over 1000 G, conductors transporting over 600 A at 77.3 K operation, current leads transporting over 1500 A with small helium consumption and superhigh field coils generating over 20 T at 4.2 K operation.