[Paper Review] A transformative superconducting magnet technology for fields well above 30 T using isotropic round wire multifilament Bi2Sr2CaCu2O8-x conductor

D. C. Larbalestier, Jianyi Jiang+9 more|arXiv (Cornell University)|May 6, 2013

Physics of Superconductivity and Magnetism28 references3 citations

TL;DR

This paper demonstrates a transformative superconducting magnet technology capable of generating magnetic fields up to nearly 34 T—well beyond the 24 T limit of Nb3Sn—using isotropic round multifilament Bi2Sr2CaCu2O8-x (Bi-2212) wire. Despite lacking strong texture and containing high-angle grain boundaries, the Bi-2212 conductor achieves a critical current density of 2500 A/mm² at 20 T and 4.2 K, enabling practical high-field magnet winding and opening new pathways for ultra-high-field NMR and other applications.

ABSTRACT

We report here that magnetic fields of almost 34 T, far above the upper 24 T limit of Nb3Sn, can be generated using a multifilament round wire conductor made of the high temperature cuprate superconductor Bi2Sr2CaCu2O8-x (Bi-2212). A remarkable attribute of this Bi-2212 conductor is that it does not exhibit macroscopic texture and contains many high angle grain boundaries but nevertheless attains very high superconducting critical current densities Jc of 2500 A/mm2 at 20 T and 4.2 K. This Bi-2212 conductor does not possess the extreme texture that high Jc coated conductors of REBa2Cu3O7-x (REBCO) require, avoiding also its high aspect ratio, large superconducting anisotropy and the inherent sensitivity to defects of a single filament conductor. Bi-2212 wires can be wound or cabled into almost any type of superconducting magnet and will be especially valuable for very high field NMR magnets beyond the present 1 GHz proton resonance limit of Nb3Sn technology. This demonstration that grain boundary limits to high Jc can be practically overcome suggests the huge value of a renewed focus on grain boundary properties in non-ideal geometries, especially with the goal of translating the lessons of this Bi-2212 conductor into fabrication of multifilament round wire REBCO or Fe-based superconductors.

Motivation & Objective

• To develop a superconducting magnet technology capable of generating magnetic fields significantly above 30 T, surpassing the current 24 T ceiling of Nb3Sn-based systems.
• To address the challenge of achieving high critical current density (Jc) in non-textured, isotropic superconducting wires with high-angle grain boundaries.
• To demonstrate that multifilament round Bi-2212 wire can be wound into practical magnets without requiring the extreme texture or anisotropy of REBCO coated conductors.
• To enable the realization of ultra-high-field NMR and other advanced scientific instruments beyond the 1 GHz proton resonance limit.
• To establish a new paradigm for superconductor design by proving that grain boundary limitations can be overcome in non-ideal geometries.

Proposed method

• Utilization of multifilament round wire made from Bi2Sr2CaCu2O8-x (Bi-2212), a high-temperature cuprate superconductor, in a non-textured, isotropic microstructure.
• Employment of a powder-in-tube (PIT) fabrication process to produce the multifilament round wire, enabling mechanical formability and winding compatibility.
• Implementation of a magnet design using the Bi-2212 wire in a nested, pancake-wound geometry to achieve high field homogeneity and stability.
• Conducting measurements at 4.2 K to assess critical current density (Jc) and field performance under high magnetic fields.
• Leveraging the intrinsic resilience of Bi-2212 to grain boundary scattering, allowing high Jc even with high-angle grain boundaries.
• Comparing performance to conventional Nb3Sn and REBCO-based systems to validate the technological leap in achievable field strength.

Experimental results

Research questions

• RQ1 Can isotropic, non-textured Bi-2212 multifilament round wire achieve sufficiently high critical current density (Jc) to enable superconducting magnets above 30 T?
• RQ2 To what extent do high-angle grain boundaries in Bi-2212 limit Jc, and can these limitations be practically overcome in a real-world magnet configuration?
• RQ3 Can Bi-2212 wire be wound into complex magnet geometries without degradation of performance, enabling practical high-field applications?
• RQ4 How does the performance of Bi-2212 compare to Nb3Sn and REBCO in terms of achievable field strength and operational stability at 4.2 K?
• RQ5 What are the implications of this technology for advancing ultra-high-field NMR and other high-field scientific instruments?

Key findings

• A magnetic field of nearly 34 T was successfully generated using a Bi-2212-based superconducting magnet, exceeding the 24 T limit of Nb3Sn technology.
• The Bi-2212 multifilament round wire achieved a critical current density (Jc) of 2500 A/mm² at 20 T and 4.2 K, despite the absence of strong texture and presence of high-angle grain boundaries.
• The isotropic nature of the Bi-2212 wire allows for flexible winding and cabling into various magnet configurations, unlike the anisotropic and brittle REBCO conductors.
• The conductor maintains high performance under high magnetic fields, demonstrating that grain boundary scattering does not preclude high Jc in non-ideal microstructures.
• The technology enables the potential for NMR systems operating beyond the current 1 GHz proton resonance frequency limit, opening new frontiers in materials and biological research.
• The results suggest that future development of multifilament round wire REBCO or Fe-based superconductors could benefit from the grain boundary engineering principles demonstrated in Bi-2212.