# Mechanical characterization of Bi-2212 composite winding pack samples for high-field superconducting magnet design

## TL;DR

This paper studies how different materials and reinforcement strategies affect the mechanical properties of Bi-2212 superconducting wires used in high-field magnets.

## Contribution

The study experimentally evaluates winding pack configurations to improve mechanical stress management in Bi-2212 superconductors.

## Key findings

- Pure alumina braid insulation and co-wind reinforcements increase stiffness by over 2.5 times compared to aluminosilicate braids.
- Rule of mixtures analysis quantifies the contribution of non-wire components to overall winding pack stiffness.
- Insulation material and reinforcement design significantly impact Bi-2212 coil performance under stress.

## Abstract

Bi₂Sr₂CaCu₂O8−x (Bi-2212) multi-filament round wire is a high-temperature superconductor (HTS) capable of carrying high transport currents, which makes it suitable for high-field magnet applications. However, its weak Ag–Mg sheath leaves it vulnerable to mechanical stress, posing challenges for high-field magnet design. To better understand and improve mechanical stress management in Bi-2212 winding packs, we conducted an experimental study evaluating the axial stress–strain behavior of five winding pack configurations with varying insulation materials, reinforcement strategies, and construction quality. Using uniaxial tensile testing at 77 K, we measured Young’s modulus and Poisson’s ratio for each composition. Our results show that pure alumina braid insulation and co-wind reinforcements significantly enhance stiffness compared to aluminosilicate braids, with more than 2.5 times increased winding pack Young’s modulus. Rule of mixtures analysis further quantified the contribution of non-wire composite components to overall stiffness. These findings highlight the critical role of insulation material selection and reinforcement design in optimizing Bi-2212 coil performance under stress, providing a foundation for improved mechanical models and more reliable high-field HTS magnet designs.