The Role of CHPD and AIMI processing on enhancing JC and transverse connectivity of in-situ MgB2 strand

F Wan,M A Rindfleisch,E W Collings,M D Sumption

doi:10.1088/1757-899x/756/1/012018

Abstract

Research into in-situ MgB2 strand has been focused on improvements in JC through reduction of porosity. Both of cold-high-pressure-densification (CHPD) and advanced-internal-magnesium-infiltration (AIMI) techniques can effectively remove the voids in in-situ MgB2 strands. This study shows the nature of the reduced porosity for in-situ MgB2 strands lies on increases in transverse grain connectivity as well as longitudinal connectivity. The CHPD method bi-axially applying 1.0 GPa and 1.5 GPa yielded 4.2 K J CM║s of 9.6 × 104 A/cm2 and 8.5 × 104 A/cm2 at 5 T, respectively, with compared with 6.0 × 104 A/cm2 for typical powder-in-tube (PIT) in-situ strand. Moreover, AIMI-processed monofilamentary MgB2 strand obtained even higher J Cs and transverse grain connectivity than the CHPD strands.

Highlights

MgB2 superconducting strands are promising to the practical magnetic application due to its high transition temperature TC (39 K) [1], high coherence length [2, 3], and low anisotropy of upper critical fields (Bc2) [3,4,5,6]
The powder-in-tube (PIT) in-situ MgB2 strands were fabricated by filling a mixture of Mg and B powder into a non-reactive metallic tube and being cold-worked into wires or tapes
The present of voids tends to limit the number of the continuous current path in the in-situ MgB2 strand and suppress the current-carrying-capacity of the strand

Summary

Introduction

MgB2 superconducting strands are promising to the practical magnetic application due to its high transition temperature TC (39 K) [1], high coherence length [2, 3], and low anisotropy of upper critical fields (Bc2) [3,4,5,6]. The previous researches mostly focused on investigating the effect of CHPD and AIMI techniques on the transport properties along longitudinal strand axis of in-situ MgB2 strands, such as transport JCs and longitudinal grain connectivity. Longitudinal transport properties are different with the transport properties along transverse strand axis for MgB2 superconducting wires. According to the previous results of our group, the CHPD technique increased the transport JC of the monofilamentary PIT in-situ MgB2 strand from 3.0 × 104 A/cm to 3.6 × 104 A/cm at 4.2 K and 10 T due to decreased porosity [11] and AIMI-processed MgB2 strands attained the 4.2 K, 10 T transport layer JCs of 1.0 ~ 1.5 × 105 A/cm2 [13,14,15,16]. The relationship between porosity and transverse flux pinning force density Fp∥, which is JCM∥ × B, for the in-situ MgB2 strands was discussed

Sample preparation

Transport and Magnetic Measurements

Results

Conclusion