G. Iwaki

Enhanced current capacity of jelly-roll processed and transformed Nb/sub 3/Al multifilamentary conductors

In order to enhance the current carrying capacity, we have developed an improved fabrication process where the wire diameter can be increased from 0.5 to 1.25 mm and the Nb-matrix ratio decreased from 1.5 to 0.52, without degrading the critical current density, J/sub c/, of Nb/sub 3/Al phase. The critical current for a monolithic conductor at 21 T and 4.2 K has now been enhanced to 166 A which used to be 15 A. The compacted-strand-cables were fabricated to investigate feasibility for large-scale application uses. We have found that stranding and flat-rolling the as-quenched Nb/Nb(Al)/sub ss/ composite cause no degradation in J/sub c/. Attempts were made to stabilize the resulting high current conductors.

Development of Nb/sub 3/Al superconducting wire for accelerator magnets

Nb/sub 3/Al superconductors have shown promising performance compared to Nb/sub 3/Sn conductors when processed by rapid heating/quenching process. Therefore we have started an R&D program of Nb/sub 3/Al conductors for future accelerator magnets. Several test wires of around 0.8 mm diameter, which have relatively small filament (/spl sim/50 micron diameter) and low matrix ratio (/spl sim/1.0), were fabricated, and the heat treatment and area reduction conditions after the rapid quenching process were studied. The highest noncopper J/sub c/ achieved during this study was 1734 A/mm/sup 2/ at 10 T and 4.2 K.

Trial Manufacture of a km Class Length of Cu Cladding RHQT

We have produced so far about a 400 m length of Cu stabilized RHQT (rapid-heating, quenching and transformation) Nb3Al flat-wire using a small-sized multi-billet (10 kg). Although our goal is to make a 2.5 km unit length of Cu cladding flat-wire for high-field NMR uses, an attempt was made to fabricate a 1 km class unit-length of conductor as a milestone of commercialization. A long-length of precursor wire over 2.5 km was prepared by using a large-sized multi-billet (50 kg). A 1.3 km length RHQ operation by using a newly installed large-scale RHQ apparatus was performed and then a km-class length Cu cladded flat-wire was fabricated to evaluate the uniformity of resultant superconducting characteristics of wire

rm Nb_3rm Al

Stoichiometric Nb3Al has higher values of T c and H c2 than those of the commercial Nb3Sn superconducting wire, but stoichiometric Nb3Al is unstable except at high temperatures near 2000°C, while non-stoichiometric Nb-rich Nb3Al that has relatively low values of T c and H c2 is stable at low temperatures [1]. In addition, the Nb3Al formation rate through the solid-state diffusion reaction between Nb and Al is very slow.

Flat-Wire

Multifilamentary Nb/sub 3/Al superconducting wires for high field magnets above 20 T have been developed by a rapid-quenching process. A long length wire was produced, and a coil was fabricated using the wire. J/sub c/ of this wire was 195A/mm/sup 2/ at 20 T, 4.2 K and 486A/mm/sup 2/ at 20 T, 1.8 K, B/sub c2/ of the coil was 24.6 T at 4.2 K and 26.9 T at 1.8 K and the T/sub c/ was 17.8 K. In addition to investigating the stability, the residual resistance ratio was measured, the value was 16.9. Scattering of J/sub c/ in the longitudinal direction was examined and found to be within /spl plusmn/10%.

Development of Nb3Al Superconductors

A total of 24 pieces of NbTi CICC with outer dimension of 14.8 mm/spl times/14.8 mm and a piece length of 600 m each have been successfully fabricated for building TF and PF coils. The CICC is made through the roll forming and welding process. The insert cable with a scheme of 3/spl times/3/spl times/3/spl times/5 is made from 0.86 mm diameter multifilamentary NbTi/Cu strand with 10 /spl mu/m diameter NbTi filaments embedded in Cu matrix at a Cu ratio of 4.9. No treatment is applied to the strand surface. A 0.025 mm thick SS304 tape is wrapped on the finished fourth stage cable. A 15 mm thick SS304L strip is then roll formed around the wrapped fourth stage cable and TIG welding 6 applied continuously at the top longitudinal seam. The welded conduit is finished to the final square dimension, by passing it through sizing rolls and turks head rolls set at the end of the jacketing line. The critical current for a CICC, estimated through multiplying an average I/sub c/ (without self-field correction) for the 10 extracted strands by the number of strands of 135 in a CICC, is approximately 38 kA at 5 T, 4.2 K. This means that there is: no significant degradation of I/sub c/s for the strands due to the cabling and jacketing process. It is confirmed that the finished CICC pieces of 600 m each show a He leakage level well below 0.2/spl times/10/sup -3/ Toll 1/s.

Some superconducting characteristics of Nb/sub 3/Al composite wires prepared by rapid-quenching process

When building high field, large scale magnets such as those used in fusion applications where large electromagnetic forces are involved in the superconductor, Nb/sub 3/Al conductor provide a great advantage, because the strain sensitivity of the critical current for Nb/sub 3/Al is substantially smaller than that of Nb/sub 3/Sn. A co-project carried out between the Japan Atomic Energy Research Institute (JAERI) and Hitachi Cable, Ltd., has established a procedure for finishing with a long one piece length of Nb/sub 3/Al strands with the high Cu ratio of 4 through the Jelly Roll process. The hydrostatically extruded rod shows excellent workability, and a 0.74 mm dia Nb/sub 3/Al strand with the high Cu ratio of 4 has been successfully drawn in one continuous piece length of 11 km without wire breakage. The strand shows a Jc and n value of 590 A/mm/sup 2/ and 45 at 12 T and 1984 A/mm/sup 2/ and 70 at 7.4 T which is the maximum field experienced in the innermost conductor of the toloidal field coil winding for the modification of JT-60 fusion device being planned in JAERI. A 30 m long Nb/sub 3/Al cable with a cabling scheme 3 /spl times/ 3 /spl times/ 3 /spl times/ 3 /spl times/ 4 was fabricated from the strand.

Production of NbTi CICC's for SST-1 project at IPR

Investigations to improve the critical current density of bronze-processed (NbTi)/sub 3/Sn superconducting wires for the central solenoid model coils in ITER were carried out. The effects of concurrent additions of Ti to the bronze matrix and of Ta to the filaments on the critical current density of the bronze-processed (NbTi)/sub 3/Sn wires were examined. By applying a high Sn concentration bronze matrix, a wire with a non-Cu J/sub c/ of 772 A/mm/sup 2/ at 12 T was developed.<<ETX>>

Production of a 11 km long jelly roll processed Nb/sub 3/Al strand with high copper ratio of 4 for fusion magnets

In this few years, Cu/Nb-Ti superconducting cables for the dipole magnets of SSC projects have been developed in the in-dustrial scale in Hitachi Cable, Ltd. The features of these developed conductors are as follows. (1) The diameter of Nb-Ti filaments is very small, 4–6 µ m. (2) The critical current density (Jc) is very high, 2850–3050 A/mm2 at 5 T on wires, 2750–2950 A/mm2 at 5 T on cables in industrial scale. The champion Jc of wires is 3460 A/mm2 at 5 T in the laboratory scale.(3) The RRR (Residual Resistivity Ratio; ρ at293K/ ρ at4.2K) values of developed cables is very high, approximately 200, due to the newly developed high purity Oxygen Free Copper (0FC).(4) The conductors have been wound to the 1 m length dipole magnet in Hitachi Ltd., and it has generated 6. 7 T in the central magnetic field at 6595 A.

Development of bronze-processed (NbTi)/sub 3/Sn superconducting wires for central solenoid model coil of ITER

Fundamental examinations were carried out of high strength bronze-processed Nb3Sn wires with Ta-reinforced filaments. A long Nb3Sn wire with reinforced filaments was also trial-manufactured to test its practicality and its properties were measured. It is expected that Nb3Sn wires with high strength and high critical current can be realized by reinforcing the filaments with Ta. Our series of examinations and the trial-manufacture revealed the high potential usefulness of the wire in practical applications such as in superconducting magnets fabricated using the R&W method