Reduction of gas bubbles and improved critical current density in Bi-2212 round wire by swaging

TL;DR

This study demonstrates that swaging significantly increases the critical current density in Bi-2212 round wire by reducing voids and gas bubbles, thereby enhancing filament packing density and superconducting performance.

Contribution

It introduces swaging as an effective method to densify Bi-2212 wire, leading to substantial improvements in critical current density over traditional as-drawn wires.

Findings

Swaging increased JE from 486 to 808 A/mm2 at 5 T, 4.2 K.

Densification reduces voids and gas bubbles, improving filament packing.

Enhanced filament density correlates with higher superconducting performance.

Abstract

Bi-2212 round wire is made by the powder-in-tube technique. An unavoidable property of powder-in-tube conductors is that there is about 30% void space in the as-drawn wire. We have recently shown that the gas present in the as-drawn Bi-2212 wire agglomerates into large bubbles and that they are presently the most deleterious current limiting mechanism. By densifying short 2212 wires before reaction through cold isostatic pressing (CIPping), the void space was almost removed and the gas bubble density was reduced significantly, resulting in a doubled engineering critical current density (JE) of 810 A/mm2 at 5 T, 4.2 K. Here we report on densifying Bi-2212 wire by swaging, which increased JE (4.2 K, 5 T) from 486 A/mm2 for as-drawn wire to 808 A/mm2 for swaged wire. This result further confirms that enhancing the filament packing density is of great importance for making major JE improvement in this round-wire magnet conductor.