Vulnerability analysis of optical fibers for laser megajoule facility: preliminary studies

The Laser Megajoule project is a major component of the French simulation program to study nuclear fusion by inertial confinement. The future Laser Megajoule facility requires control-command systems that will operate in a harsh radiative environment. Commercial off-the-shelf optical fiber data links are envisaged as a radiation tolerant solution for this application. In this paper, we present our preliminary study of their vulnerability. For this, we firstly have used an original method consisting of ultraviolet (∼5 eV) exposures of the fibers to identify the different germanosilicate optical fibers containing phosphorus, which leads them unacceptable for both steady state γ-rays and successive pulsed X-ray irradiations. We have demonstrated the validity of the γ-UV comparison by spectroscopic measurements. After this first selection, we have tested under pulsed X-rays (dose rate >10 MGy/s dose <0.5 kGy) the resistance of the P-free optical fibers at 1310 nm for the shortest times after an ionization pulse (10^-9 to 10^-1 s). Based on these results, we discuss the validity of the optical fiber data links for the control-command applications in LMJ facility.