Tracking the Potential for Damage in Nb3Sn Superconducting Coils from the Hardness of Surrounding Copper

Published March 26, 2021

Electron microscope image showing cracks in a conductor that was extracted from a damaged Nb3Sn coil that was part of a prototype 11T accelerator dipole magnet built at CERN.

High field superconductor magnets greater than 10 T made from brittle Nb₃Sn superconducting wires need special attention to their assembly, strength and endurance. This new study of damage in Nb₃Sn superconducting wire from prototype accelerator coils built at CERN provides a path to designing better superconductor cables for the next generation of higher field accelerator magnets.

What is the finding?

Cracks were discovered in a prototype Nb₃Sn superconducting accelerator magnet coil designed for the High Luminosity Upgrade of CERN's Large Hadron Collider. The nature of conductor damage was characterized. By comparing with control samples, researchers determined that high stresses during assembly led to the formation of the cracks.

In addition, copper hardness within the Nb₃Sn conductor was discovered to be a tell-tale indicator of magnet damage due to excessive stress.

Why is this important?

The results here will help guide future designs of Nb₃Sn magnets for CERN's high-luminosity upgrade, work that will advance the frontier of particle physics. Other large superconducting magnets, including the MagLab's 45T Hybrid and 32T SC magnets, medical magnets, and magnets for particle accelerators also produce extreme stress during operation. While magnets are designed to support high stress, margins are now so close to physical limits that stresses during assembly can lead to unacceptable degradation of magnet conductor. These new methods will allow actual stress levels in complex magnet structures to be compared to computer models.

Who did the research?

S Balachandran¹, J. Cooper¹, O. B. Van Oss², P J. Lee¹, L. Bottura³, A. Devred³, F. Savary³, C. Scheuerlein³, F. Wolf³

¹Applied Superconductivity Center, National MagLab; ²Columbia University; ³CERN

Why did this research need the MagLab?

The MagLab's Applied Superconductivity Center is expert in microstructural evaluation of Nb₃Sn superconductors, including those used by CERN to fabricate these high-field accelerator magnets.