Length-Resolved Measurement of Radiation Induced Attenuation in Quench Detection Optical Fibers With Photobleaching

Fiber-optic temperature and strain measurement systems are a promising technology for quench detection in insulated HTS magnets because of their compact form factor, immunity to electromagnetic noise, and fully dielectric construction. (Salazar et al. 2021) One of the key challenges to implementing these technologies in magnets for fusion devices is that ionizing radiation causes severe attenuation in the quench detection fibers. This attenuation is exacerbated by the low operating temperatures of HTS magnets ($\sim$ 20 K) and the long fiber lengths required for quench detection in power-plant scale magnetic confinement fusion systems ($\sim$ 200 m). (Blanc et al. 2017) In a previous paper we demonstrated that the survivable dose of a quench detection system operating at 1550 nm can be extended by more than 2,000x through continuous photobleaching at 970 nm. (Duke et al. 2024) Here we present an experiment investigating the effect of 970 nm photobleaching on fibers of significant length (up to 250 m) irradiated at 77 K with RIA near 1550 nm monitored using a novel length-resolved measurement technique.