Cu Stabilized $\hbox {Nb}_{3}\hbox {Al}$ Strands for the High Field Accelerator Magnet

Characteristics of developed Nb₃Al strand though the RHQT (rapid heating/quenching and transformation) process are described. One kilometer-long copper stabilized Nb₃Al round strands were economically fabricated with ion-plating and electroplating. The copper electroplating was successfully done with the high velocity of 5 m/h. A strong bonding between the copper and the precursor was achieved, and the mechanical rolling test did not show the separation of the copper stabilizer from the precursor. The rolled Nb₃Al strands showed no degradation both in critical current density and RRR value. Magnetic instability at 4.2 K at low fields was apparently improved on the F3 strand, relative to the previously F1 stand because a tantalum was used for the interfilament matrix of precursor. The large magnetic flux jumps, which were observed with the Fl strand, were suppressed at 4.2 K, although appeared again below 3.0 K. The twisted strands are shown to be effective to reduce the time-dependent eddy current coupling. It was obtained 48 mum of D_eff on F3 strand with twist pitch of 45 mm. In addition, the transverse pressure test for the Fl Nb₃Al strand was performed at 4.2 K and 12 T. The critical current did not degrade with the transverse pressure up to 210 MPa.