Distributed real-time strain monitoring for Nb3Sn sextupole superconducting magnets: from assembly to excitation

In pursuit of a fourth-generation electron cyclotron resonance (ECR) source, a powerful Nb3Sn superconducting magnet system employing a sextupole-in-solenoid configuration has been recently developed at the Institute of Modern Physics (IMP) in Lanzhou, China. These superconducting magnets operate under extreme conditions, experiencing high magnetic fields, cryogenic temperatures, and mechanical stresses. Understanding their stress/strain behaviors, therefore, is of utmost importance to ensure reliable operation and optimal performance. However, the conventional single-point strain gauges commonly exhibit certain limitations that pose challenges in measuring global strain within complex and larger structures. The presence of substantial electromagnetic interference further exacerbates the difficulty in obtaining accurate strain measurements. To address these challenges, a novel approach was undertaken in this study to develop a distributed real-time strain monitoring system specifically designed for the sextupole superconducting magnets, which is based on optical frequency domain reflectometry (OFDR) combined with high spatial resolution distributed optical fiber technology. The strain profile and evolution of the magnets system have been comprehensively monitored throughout the entire operational process, including assembly, cooling down, excitation, and quenching stages. Consequently, valuable insights into the global strain characteristics of the superconducting magnets have been attained, revealing intriguing features such as asymmetrical distribution and extreme values. The development of this distributed real-time strain monitoring system represents a notable advancement in the field of superconducting magnet technology.