Abstract

We investigated the effects of gamma irradiation on radiation-induced attenuation (RIA) in photosensitive (Ge-doped) and radiation-hard (F-doped) fibers at cryogenic temperatures (77 K) under different photobleaching conditions. We show that increasing the probe power (1550 nm) and injecting lower wavelength light (970 nm) both resulted in a significant reduction in RIA in both fiber types, where radiation-hard fibers were intrinsically more resistant to the RIA. Deconvolution of RIA growth curves revealed that the RIA was composed of transient and long-term growth components that were correlated with distinct radiation-induced defects specific to each fiber composition. The 1550 nm light more effectively suppressed the transient RIA, while 970 nm more effectively suppressed the long-term RIA. Ultimately, we show that cryogenic RIA may be effectively managed in fiber optic sensing systems using radiation-hard fibers and dual-wavelength photobleaching strategies.

My contribution

This paper documents research I conducted at Commonwealth Fusion Systems (CFS) on radiation damage to the fiber-optic quench detection (QD) system in the SPARC tokamak, in collaboration with CFS’ collaborators at the Robinson Research Institute. We jointly designed the experiment, I commissioned and operated the equipment, and I wrote the interal report evaluating the risk to QD from radiation effects based the measurements. This article was written by our collaborators and contains their analysis of the same data for a general audience.

Recommended citation: J. J. Schuyt, O. Duke, D. A. Moseley, B. M. Ludbrook, E. E. Salazar, R. A. Badcock, "Gamma irradiation of Ge-doped and radiation-hard silica fibers at cryogenic temperatures: Mitigating the radiation-induced attenuation with 1550 and 970 nm photobleaching," J. Appl. Phys., vol. 134, no. 4, p. 043103, July 2023.
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