Radiation effects in sapphire optical fibers

Abstract

Radiation effects on sapphire optical fibers were investigated using off-line gamma-ray, neutron and electron beam irradiation and on-line proton irradiation. The optical attenuation of these optical fibers was studied from UV to IR (200 nm -1700 nm). For the in-situ measurements radioluminescence was also investigated as function of the total irradiation dose.1 Introduction Extensive studies were carried out in the last years in the field of the radiation effects on various optical components to be used in plasma diagnostics for ITER (International Thermonuclear Experimental Reactor) like fusion installations. Mirrors, windows and optical fibers were investigated under gamma-ray, neutron or electron beam irradiation. As plasma facing components, windows are supposed to be subjected to high temperature, particle bombardment, and ionizing radiation exposure. Optical fibers will play an important role in optical data links, distributing sensing systems, light-guides for spectroscopy and for the visualization of thermal field distribution [1, 2]. They will be forced to work under high radiation fields (gamma-rays and neutrons) and, in some situations at high temperatures [3].Until now research was carried out in relation to the evaluation of the irradiation effects on silica glass optical fibers over the entire spectral range UV-visible-IR. The results indicated both a decrease of the optical transmission of the optical fibers, and the presence in same cases of a irradiation induced luminescence (radioluminescence) [4]. These effects depend on the optical fiber type, its ingredients, the manufacturing process, and the irradiation conditions (type of radiation, total dose and dose rate, particle fluence, etc.). These phenomena depend strongly on the wavelength; specific spectral bands are affected. For this reason, they can partially distort the signal they carry by attenuating it or by increasing the signal-to-noise ratio. Special pre and post irradiation treatments (i.e. hydrogen loading) can induce a radiation hardening. In some situations, the irradiation produced distortion exhibits a recovery upon hearting the optical fiber (thermal annealing) or after an optical signal of a specific wavelength is launched over the optical fiber (photobleaching).The overall conclusion to these investigations is that silica optical fibers still are sensitive to irradiation, mostly in the UV-visible spectral range, as irradiation induced color centers appear. For this reason we started to investigate how sapphire optical fibers perform under various irradiation conditions, being known the radiation resistance of this material. According to our present knowledge, irradiation test were performed only on bulk sapphire samples (i.e. windows) [5][6][7], no such investigation was done on optical fibers made of sapphire.

Optical Fibers and Optical Fiber Sensors Used in Radiation Monitoring

“…2 a. The experimental instrumentation was used for online investigations related to the irradiation effects on silica optical fibers (mostly in the UV range where numerous color centers are developed) and sapphire optical fibers (Sporea & Sporea, 2007;Sporea et al, 2010a;Sporea et al, 2010b). By connecting only one end of the tested optical fiber to different spectrometers, according to the case with or without the use of a multiplexer, the radioluminescent signal was acquired during different types of irradiations.…”

“…25 cm long 425 m diameter sapphire optical fibers were measured in relation to the radiation induced attenuation (Fig. 13) and radioluminescence, as they were subjected to gamma-ray, proton and neutron irradiation (Sporea & Sporea, 2007). By analyzing the experimental data we noticed the radiation resistance of these optical fibers and the three peaks spectrum of the RL emission under proton irradiation.…”

“…13. The changes in the optical attenuation in a 25 cm long, sapphire optical fibers under: a -gamma-ray irradiation; b -neutron irradiation (Sporea & Sporea, 2007).…”

“…The radioluminescence emission from a sapphire optical fiber, for proton beam irradiation. The amplitude changes of the RL signal reflects the modifications of the beam current at different irradiation stages (Sporea & Sporea, 2007).…”

The generalized second law of thermodynamics for interacting f(R) gravity

“…In such an approach, the Ricci scalar R in the EinsteinHilbert action is replaced by a general function f (R), (for a review see Refs. [16][17][18][19]). Also, there are other classes of modified gravities that can give an explication for the different cosmological scenarios without take into account to the DE.…”