Characteristics of Cu Stabilized ${\rm Nb}_{3}{\rm Al}$ Strands With Low Cu Ratio

Characteristics of recently developed F4-Nb₃Al strand with low Cu ratio are described. The overall J _c of the Nb₃Al strand could be easily increased by decreasing of the Cu ratio. Although the quench of a pulse-like voltage generation is usually observed in superconducting unstable conductor, the F4 strand with a low Cu ratio of 0.61 exhibited an ordinary critical transition of gradual voltage generation. The F4 strand does not have magnetic instabilities at 4.2 K because of the tantalum interfilament matrix. The overall J _c of the F4 strand achieved was 80-85% of the RRP strand. In the large mechanical stress above 100 MPa, the overall J _c of the F4 strand might be comparable to that of high J _c RRP-Nb₃Sn strands. The Rutherford cable with a high packing factor of 86.5% has been fabricated using F4 strands. The small racetrack magnet, SR07, was also fabricated by a 14 m F4 cable. The quench current, I _q, of SR07 were obtained 22.4 kA at 4.5 K and 25.2 kA at 2.2 K. The tantalum matrix Nb₃Al strands are promising for the application of super-cooled high-field magnets as well as 4.2 K operation magnets.