Kunihiro Fukuda

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

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 testing apparatus for 10 kA class AC superconductors

R&D on NbTi and Nb/sub 3/Sn superconductors has been carried out for application to AC power apparatus in the Super-GM project. 5 kA class NbTi stranded cables have already been tested and then the R&D aiming at the final target of 10 kA class conductors is in progress. However there is no testing apparatus which makes it possible to measure over 5 kArms AC quench current (Iq) and AC loss in AC magnetic field (50-60 Hz). The testing apparatus was developed under the specifications required for evaluating the AC characteristics of 10 kA class conductors. The AC magnet generating the maximum magnetic field of 1 Tpeak in the bore of 150 mm was manufactured. For the Iq measurement, the AC current is directly applied to the specimen in the field of 0.5 Tpeak (50-60 Hz), 10 kArms AC quench current was obtained for the developed large NbTi conductors. As regards the AC loss measurement, the magnetization method using pick-up coils was adopted and its sensitivity has been improved by reducing unnecessary output signal.

Electromagnetic properties of bronze processed Nb/sub 3/Sn superconducting wires and multi-strand cables for AC use with a Cu-Sn-X(X; Ge,Ni,Mn,Si) matrix and a Nb-Ta core

A bronze processed 0.275 mm-dia. Nb/sub 3/Sn strand composed of Nb-0.5at%Ta cores and a Cu-2.7at%Sn-1.0at%Ge matrix was fabricated into cables of 6 and 36 strands. Each strand contained 75990 filaments 0.28 /spl mu/m in diameter. The AC quench current for the 36-strand cable reached 2500 A/sub peak/ at 50 Hz and 0.5 T DC field. The 6-strand cable showed a significantly improved irreversible bending strain limit of over 10% due to the fine filament size. This result enabled building of a magnet through the react and wind method. A 50 mm-bore 2T-class magnet wound by the 6 strand cable was successfully operated at 52.7 Hz and 4.2 K. In order to reduce AC losses another bronze processed 0.218 mm-dia. Nb/sub 3/Sn strand with 147510 0.15 /spl mu/m-dia. filaments was fabricated from Nb05%Ta/Cu-4.9%Sn-2.0%Ge/Cu-2.7%Sn-2%Ni-1%Mn double matrix composite. The strand showed a hysteresis loss of 447J/m/sup 3/ at /spl plusmn/0.5 T/cycle and /spl lambda/J/sub c/ of 857A/mm/sup 2/ at 0.5 T after the heat treatment at 500/spl deg/C for 100 h.