Optimization of heating profile for superconductor joint performance made by resistive joule heating process

Abstract

The long-term heating (>60 min) of second generation high temperature superconductor (2G HTS) tape-joints at temperatures above 200 °C leads to the continuous deterioration of their superconducting properties. Previously, we proposed a resistive Joule heating process with a short heating time (∼10 min) that exhibited beneficial critical current (Ic), retention percentages (84–99 %), and joint resistances (74–697 nΩ cm2) in four independent experiments.In this study, we investigated two heating rates and three tape-joint areas. The results show that for the samples with different tape joint areas, the critical current retention percentages (97–100 %) and uniformity of specific joint resistances (82–272 nΩ cm2) were significantly improved at a high heating rate of ∼30 °C/min. The sintering of silver nanoparticles and oxidation characteristics of the copper stabilizers were observed using transmission electron microscopy, scanning electron microscopy, and Raman spectroscopy to elucidate the effect of different heating profiles. This study opens new avenues for improving the quality of 2G HTS tape joint processes for ultrahigh magnetic field applications.

Keywords

• 2G HTS tape
• Solder joint
• Nano-silver paste
• Resistive joule heating
• Specific resistance
• Parallel-joints