Status and perspective of the Nb 3Al development

Abstract

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 metastable 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.