Composite stacks for reliable > 17 T trapped fields in bulk superconductor magnets

TL;DR

This paper demonstrates a novel composite stacking technique that reliably achieves trapped magnetic fields over 17 T in bulk superconductor magnets, overcoming previous mechanical and thermal limitations.

Contribution

The study introduces a new composite stack design with stainless-steel reinforcement that enables high, reliable trapped fields in bulk superconductors.

Findings

Achieved 17.6 T trapped field at 22.5 K in a composite stack.

Demonstrated the first fabrication of such a composite stack using this technique.

The trapped field is comparable to the highest reported for bulk superconducting magnets.

Abstract

Trapped fields of over 20 T are, in principle, achievable in bulk, single-grain high temperature cuprate superconductors. The principle barriers to realizing such performance are, firstly, the large tensile stresses that develop during the magnetization of such trapped-field magnets as a result of the Lorentz force, which lead to brittle fracture of these ceramic-like materials at high fields and, secondly, catastrophic thermal instabilities as a result of flux movement during magnetization. Moreover, for a batch of samples nominally fabricated identically, the statistical nature of the failure mechanism means the best performance (i.e. trapped fields of over 17 T) cannot be attained reliably. The magnetization process, particularly to higher fields, also often damages the samples such that they cannot repeatedly trap high fields following subsequent magnetization. In this study, we report the sequential trapping of magnetic fields of ~ 17 T, achieving 16.8 T at 26 K initially and 17.6 T at 22.5 K subsequently, in a stack of two Ag-doped GdBa2Cu3O7-{\delta} bulk superconductor composites of diameter 24 mm reinforced with (1) stainless-steel laminations, and (2) shrink-fit stainless steel rings. A trapped field of 17.6 T is, in fact, comparable with the highest trapped fields reported to date for bulk superconducting magnets of any mechanical and chemical composition, and this was achieved using the first composite stack to be fabricated by this technique.