Performance of first Bi-2212 cable with pre-over pressure and over pressure heat treatment

Abstract

Due to the excellent current carrying performance of Bi2Sr2CaCu2O8+x (Bi-2212) and the development of its industrial manufacturing technology, Bi-2212 is a promising material to be developed as superconductor for application in fusion reactor magnets. The cable-in-conduit conductor (CICC) concept is often chosen for the development of large-scale magnets because of their high stability. Bi-2212 is presently the only kind of copper oxide superconducting material which can be made into solid round wire, which provides a good basis for developing CICCs. The over pressure (OP) heat treatment can significantly improve the superconducting performance of Bi-2212 wires but it also reduces the wire diameter by ∼5%. This leads to an increase of the void fraction of CICCs, typically from 30% to 40% for a CICC with ITER scale dimensions. A pre-OP heat treatment before OP is proposed in this study. The reduction of the wire diameter can be completed before the formation of the continuous superconducting phase, which would dramatically decrease the CICC void fraction. One Bi-2212 cable consisting of 84 wires, was first pre-OP heat treated successfully and after completing the OP heat treatment, the cable’s transport performance was tested. The results showed good performance with a critical current (I c) of 35.7 kA at 5.8 T background field in 4.2 K, which is consistent with the predication.

Change in transition balance between durable tetragonal phase and stress-induced phase of cobalt surface-layered in Bi-2212 materials by semi-empirical mechanical models

“…Additionally, the original microhardness parameters have been inspected in the plateau limit region for the cobalt surface-layered Bi-2212 ceramic system employing the following relation: = H A 1854. 4 7…”

“…We have also compared the experimental hardness parameters and load-independent microhardness values in the saturation limit regions for the pure and Co surface-layered Bi-2212 ceramic materials depending on the HK semi-empirical mechanical modelling approach with the following equation: = H A 1854. 4 9…”

“…On this basis, surface residual compressive stress, internal structural problems, crack initiating defects, internal cracks, stress concentration sites, microvoids, service environment factors (humidity, pressure, temperature, magnitudes and duration of applied loads) and in particular the form/types (tensile, shear, twisting, compressive, and torsional stress) of exposure to loads affect seriously the useful economic life of the material [2]. That is exactly why any improvement in the properties mentioned increases significantly the mechanical strength of the material even when used under harsh conditions, and the potential application areas increase as they do [3][4][5][6][7][8]. Hence, several researchers have endeavored to develop the mechanical properties using many methods focusing sensitively on the different preparation techniques, and heat treatment methodologies [9].…”

The research on the influence mechanism of internal deformation for the performance of Bi-2212

“…Given the operational stability of the magnet system, the porosity of CICC should be carefully controlled. In the Nb 3 Sn CICC made for ITER, porosity was controlled to 30%-32% [13], while the porosity of the stranded Bi-2212 cable is close to 40% [14]. The high porosity of Bi-2212 cable means it should go through a diameter compaction process before practical usage for higher stability.…”

“…Once the force exceeds a certain value, the strain appears in the conductor, which leads to degradation in the current carrying capacity. The degradation phenomenon was recognized by a sub-scale Bi-2212 cable [14,15]. The pre-OP was proposed to densify the superconducting filaments before the compaction process.…”