Transport critical current densities and n factors in mono- and multifilamentary MgB2/Fe tapes and wires using fine powders

TL;DR

This study reports high transport critical current densities and n factors in mono- and multifilamentary MgB2/Fe tapes and wires, highlighting the effects of powder grain size and recrystallization temperature on performance.

Contribution

It introduces optimized fabrication processes for MgB2/Fe tapes and wires, achieving record high critical current densities and n factors, and compares mono- and multifilamentary configurations.

Findings

Critical current density of 10^5 A/cm^2 at 25K and 1T

High n factors (~80 at 5T) indicating sharp resistive transitions

Multifilamentary wires achieved 1.1×10^5 A/cm^2 at 4.2K in 2T field

Abstract

Mono- and multifilamentary MgB2/Fe tapes and wires with high transport critical current densities have been prepared using the powder-in-tube (PIT) process. The fabrication details are described. The effect of powder grain sizes and recrystallization temperature on jc has been investigated. At 25K and 1 T, jc values close to 105 A/cm2 were measured, while jc of 106 A/cm2 were extrapolated for 4.2K/0T in our monofilamentary tape. MgB2/Fe tapes exhibit high exponential n factors for the resistive transition: n ~ 80 and 40 were found at 5 T and 7 T, respectively. The highest transport jc values obtained so far in MgB2/Fe wires with 7 filaments were 1.1 * 105 A/cm2 at 4.2 K and in a field of 2 T, which is still lower than for monofilamentary tapes. Improved deformation and recovering processing is expected to lead to higher jc values.