Abstract-Fibre Bragg Grating (FBG) sensors are expected to provide valuable data in extreme radiation environments associated with nuclear research reactors. However, when the fast neutron fluence reaches 10 18 to 10 19 n/cm², the radiation induced changes in the material density and refractive index may drastically bias the measurements. The present study evaluates the radiation effect on the FBG performances by comparing their properties before and after their exposure to fast neutron fluences exceeding 10 19 n/cm² (E > 1 MeV). We studied responses of FBGs manufactured by three different laboratories in the same single-mode optical fibre but using different inscription conditions. The Bragg wavelength and the reflectivity were measured before and after irradiation thanks to a dedicated mounting. For nearly all FBGs, the Bragg peak remains visible after the irradiation while the radiation-induced Bragg wavelength shifts (RI-BWS) vary from a few pm (equivalent temperature error < 1°C) to nearly 1 nm (~100°C error) depending of the FBG inscription conditions. Such high RI-BWSs can be explained by the huge refractive-index variation and compaction observed for bare fibre samples through other experimental techniques. Our results show that by using specific hardening techniques the FBG-based temperature measurements in a nuclear research reactor experiment may become feasible.

In this paper, we compare, by means of simulations using the Jones formalism, the performances of several optical fiber types (low birefringence and spun fibers) for the measurement of plasma current in international thermonuclear experimental reactor (ITER). The main results presented in this paper concern the minimum value of the ratio between the beat length and the spun period, which allows meeting the ITER current measurement specifications. Assuming a high-birefringence spun fiber with a beat length of 3 mm, we demonstrate that the minimum ratio between the beat length and the spun period is 4.4 when considering a 28 m long sensing fiber surrounding the vacuum vessel. This minimum ratio rises to 10.14 when a 100 m long lead fiber connecting the interrogating system to the sensing fiber is taken into account.

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Results of field measurements of the gamma radiation dose with a frequency domain optical reflectometer are presented. The ability to measure doses up to 100 kGy remotely with an accuracy of up to 20% and reconstruct the absorbed dose distribution profile with a resolution of 15 cm for doses up to 9 kGy is demonstrated. The factors affecting the dynamic range and accuracy of measurements are discussed.

The effect of gamma-radiation on the spectral characteristics of FBGs has been studied experimentally. The FBGs were fabricated in optical fibers with a Ge02 concentration in the core in a range from several to 99 mol. 0/0. Various pre-and post-fabrication treatments were applied with the aim to improve the radiation tolerance of the FBGs. The best result was obtained for a Type IIa annealed grating written in SM310 fiber, where the Bragg peak shift saturated at a 12 pm level and an am plitude change of 0.04 dB with the maximal dose of about 50 kGy.

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An accurate measurement of the plasma current is of paramount importance for controlling the plasma magnetic equilibrium in tokamaks. Fiber optic current sensor (FOCS) technology is expected to be implemented to perform this task in ITER. However, during ITER operation, the vessel and the sensing fiber will be subject to vibrations and thus to time-dependent parasitic birefringence, which may significantly compromise the FOCS performance. In this paper we investigate the effects of vibrations on the plasma current measurement accuracy under ITER-relevant conditions. The simulation results show that in the case of a FOCS reflection scheme including a spun fiber and a Faraday mirror, the error induced by the vibrations is acceptable regarding the ITER current diagnostics requirements.

The book is an exciting source of information for individuals interested in learning about and marketing sensors. The book focuses on scientific and commercial advances in Fiber Bragg Grating (FBG) sensor technology since its discovery over 30 years ago. Discussions on new FBG sensor manufacturing and processing methods are provided by leading experts in the field. Novel applications of FBG sensor technology in engineering, energy, chemical and biological sectors are also included along with a clear identification of commercial opportunities in the next decade.