Nobuhiro Shibuta

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.

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.

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.

Silver-sheathed Bi(2223) wire and application

Among many high- T c oxide superconductive materials and processing technologies, a combination of the bismuth high-T c phase and the powder-in-tube technique is revealed to be useful for long-wire fabrication and many applications in various fields, such as large current conductors, cryogenic current leads and magnets. Maximum J c at 77.3 K reached 53 700 A/cm 2 in a zero magnetic field, 42 300 A/cm 2 at 0.1 T and 12 000 A/cm 2 at 1 T. Maximum J c of multifilamentary wire at 77.3 K reached 15 400 A/cm 2 . A 30 m long wire with a multifilamentary structure was fabricated. J c over the whole length of this wire was 5190 A/cm 2 at 77.3 K. Results of prototypes were summarized and revealed that many applications in a wide temperature range from 4.2 to 77.3 K will be feasible in the near future.

Critical currents of silver‐sheathed bismuth‐based tapes at 20 K: Small coils and field orientation anisotropy in external fields up to 20 T

Critical currents, including field orientation anisotropy, of silver‐sheathed bismuth‐based superconducting tapes, for both small coils and short samples, have been measured at 20 K (liquid hydrogen) in external fields up to 20 T. The performance of two small coils is consistent with the critical current data of short samples. One coil, at 20 K and in a field of 20 T, for example, produced a self field of 0.35 T (Ic=136 A; Jc=1.7×104 A/cm2). Short‐sample critical current data indicate that field orientation anisotropy is more pronounced at 20 K than at 4.2 K. At 20 K and 20 T, e.g., Jc(H∥), critical current density in the parallel field orientation, is 5.23×104 A/cm2, while Jc(H⊥), critical current density in the perpendicular field orientation, is 1.75×104 A/cm2, an anisotropy factor, Jc(H⊥)/Jc(H∥), of 0.34. In the field range 2–15 T, the anisotropy factor at 20 K ranges 0.51–0.55.

Transport critical current properties of silver-sheathed Bi-based superconducting tapes and coils at 4.2 K

Transport critical current properties of silver-sheathed bismuth-based superconducting tapes and coils were investigated at 4.2 K and up to 25 T. Critical currents showed isotropic properties when the direction of the applied magnetic field changed from parallel to the tape surface to perpendicular, i.e., Jc of 8.9×104 A/cm2 for H//tape and 6.6×104 A/cm2 for H⊥ tape at 23 T. Critical current properties of a three-double-pancake coil were consistent with those of short specimens, showing little change at from 5 to 23 T.

Bi-Based Silver-Sheathed High-Tc Superconducting Wire and Application

The application of high temperature superconducting wire will be feasible with the improvement in the critical current density and the development of the hundred-meter class flexible wire.

Bismuth Superconducting Wire and Application

The continued R&D results of the silver-sheathed bismuth(2223 phase) superconducting wire have suggested that three different fields of application, large current conductors, low field magnets and super-high field magnets will be feasible in the near future.

Properties of Ag/Bi-Based Superconducting Long Wire and Test Coil

Fundamental problems in the application of high-Tc superconductors, such as fabrication of long wire, strain-resistant conductors and large current conductors, were investigated. A 60 m-long wire showed a uniform transport property of 10.5 A critical currents defined as 10−13 4Ω·m. 1,296-core multifilamentary wires sustained 100% of initial transport property even after a strain of 0.33% repeated 20 times. A composite superconductor 50 cm In length showed a critical current of 573 A. Test coil made by the wind & react process generated 500 Gauss at 77.3 K. A react & wind-processed coil using 4.3 m-long 1,296-core wire could maintain the initial transport current after being covered with polyvinyl formal and wound on 15 mm-diameter steel core (13 turns × 7 layers). 1,500 A class current leads made of high-Tc superconducting wires suppressed the liquid helium consumption of 0.93 W/kA, which is lower than with commercially available copper current leads. A flexible cable conductor of 75 cm in length was fabricated using 22 m-long 1,296-core wire. This conductor was proved to have a critical current of 80 A after winding spirally on a 20 mm-diameter spacer.

Development of High Tc Superconducting Wire by Powder Method

Ag-sheathed high Tc superconducting wires of YBa2Cu3O7-x and Bi0.8Pb0.2SrCaCU1.5Ox were developed. Improvements in the density and the orientation of crystals brought about by press processing have been investigated, and by adopting adequate processing procedures the critical current densities were increased up to 4140A/ cm2 and 4400A/ cm2 for Ag-sheathed YBa2Cu3O7-x and Bi0.8Pb0.2SrCaCu1.5Ox superconductors, respectively.