Nb$_3$Sn Films Exhibiting Continuous Supercurrent Across a Diffusion Bonded Seam

TL;DR

This study demonstrates that Nb$_3$Sn superconducting films can be formed across diffusion-bonded seams between bronze pieces, allowing supercurrent flow and potentially improving joining methods for superconducting applications.

Contribution

It introduces a novel diffusion bonding process that creates continuous Nb$_3$Sn superconducting films across seams, enabling supercurrent flow in bonded structures.

Findings

Supercurrent flows freely across the seam at 9 K in several samples.

The process produces uniform Nb$_3$Sn films coating bronze surfaces and spanning seams.

Pre-coating with Nb prior to diffusion bonding was less effective than hot bronze bonding.

Abstract

Multiple pairs of bronze pieces were joined along a common seam and then exposed to Nb vapor via sputter deposition during heating at $\sim$715 $^\circ$C to form a diffusion bond between the pieces. Polishing and alignment of the pieces created smooth surfaces normal to the Nb flux with seams perpendicular to the surface (i.e. parallel to the Nb flux). Conversion of Nb to Nb$_3$Sn took place simultaneously with diffusion bonding, resulting in Nb$_3$Sn thin films that coated bronze surfaces and spanned seams with uniform thickness. Characterization of superconducting properties via magneto-optical imaging suggests that supercurrent flows freely across the seam in several examples when cooled to 9 K and shielding or trapping low magnetic field. Modification of the process to coat the pieces with Nb prior to diffusion bonding and Nb$_3$Sn formation resulted in varying degrees of seam coverage by the resultant Nb$_3$Sn films. The pre-coating method did not produce any example with quality comparable to the examples obtained by the hot bronze approach. This work could enable new approaches to joining Nb$_3$Sn materials in magnet conductor and RF cavity applications.