High Spatial Resolution Distributed Brillouin Measurements at Cryogenic Temperatures

Distributed optical fiber sensors are promising tools for quench detection and protection in superconductor-based magnet systems, as they provide continuous monitoring of the temperature at any location within a magnet with high spatial resolution and immunity to electromagnetic interference. Conventional distributed sensors based on Brillouin scattering, however, fails in reaching adequate performance for quench detection due to limited spatial resolution and/or acquisition rate. In this work, we demonstrate the use of a high-spatial resolution Brillouin Optical Frequency-Domain analysis (BOFDA) system to perform distributed temperature measurements at cryogenic temperatures. A custom-made BOFDA prototype was employed to characterize the Brillouin gain spectrum (BGS) in a standard single-mode fiber, at a temperature ranging from ≈ 260 K down to ≈ 2.6 K. A novel algorithm was devised to extract the temperature from BGS measurements at cryogenic temperatures. Finally, the large increase in the Brillouin gain coefficient at temperatures below ≈ 10 K was exploited to realize slope-assisted BOFDA measurements with a temperature sensitivity less than 0.1 K, a spatial resolution of 3 cm, and an acquisition rate of 1.75 Hz.