Development of New PIT Process using High Ga Content Compound in V 3 Ga Superconducting Wire

Abstract

Vanadium-gallium (V 3 Ga) superconducting wire is an "old superconducting material", and was one of the original materials famed for the "Cu additive effect" that was extended to the "Bronze route process". The "Cu additive effect" in A15 phase compounds promotes A15 phase formation via diffusion reaction. The V 3 Ga compound has interesting properties for an advanced magnetic confinement fusion reactor beyond ITER. The decay time of induced radio activity for V 3 Ga is within 1 month and is much shorter than that of Nb-based superconductors such as Nb-Ti, Nb 3 Sn and Nb 3 Al. We thought that V 3 Ga wire was one of the candidate materials for "Low activation superconducting wires" to operate under a neutron irradiation environment such as in a fusion reactor. However, the J c and H c2 properties of V 3 Ga wire are insufficient to realize this feature in fusion application. In previous studies, V 3 Ga wire was mainly investigated in term of the "Diffusion process" between Cu-Ga within a 20 at% Ga composition and V filament. For further J c and H c2 enhancements, we investigated the fabrication of V 3 Ga compound multi-filamentary wires using a high Ga content Cu-Ga compound applying the powder-in-tube process. Thicker V 3 Ga layers formed along the boundary between the Cu-Ga powder filaments and V matrix, and the volume fraction of V 3 Ga increased compared to previous diffusion processed samples. We also found that the new route PIT process using a high Ga content Cu-Ga compound is effective for improving the superconducting properties of the V 3 Ga compound wire.