Status and perspective of the Nb_3Al development

摘要

Nb_3Al has advantages of better tolerance to strain/stress and a higher critical magnetic field (30 T at 4.2 K) for stoichiometric composition over Nb_3Sn. The rapid-heating, quenching and transformation annealing (RHQT) process enables to form a stoichiometric Nb_3Al with fine grain structures via metasta-ble bcc supersaturated-solid-solution. As a result a large critical current density of Nb_3Al is achieved over the whole range of magnetic fields without trading off the excellent strain tolerance. A long-length of RHQ processing has been established, and a rectangular but Cu stabilized Nb_3Al strand is about be commercially available for NMR uses. Ag or Cu internal stabilization and Cu ion-plating/electroplating techniques have been also developed to enable the stabilized round wire for accelerator and fusion magnets. Successfully energized test coils that were manufactured with a wind-and-react technique have demonstrated that a long piece of Cu stabilized RHQT Nb_3Al wire is really available for practical applications.