This study describes the development and qualification of strain sensors and thermal compensator for monitoring of ITER vacuum vessel. The operating conditions require 20000h at 200°C and gamma radiation doses up-to 10MGy under high vacuum. A sensor concept was designed based on two spot weldable sensing elements: one weldable strain sensor and one weldable temperature compensator. The developed elements were subjected to qualification tests including optical, thermal cycling, thermal aging, mechanical and radiation. The results validated the solution and proved that the elements comply with requested vacuum vessel environment, withstanding 10MGy radiation, ±1000μm/m for 10E+5 cycles at 100°C, 500 cycles from 100°C to 200°C, 100°C for 120000h, 200°C for 20000h and being fully operational after 80h at 250°C.
A cantilever structure in 3D printed based on a fiber Bragg grating (FBG) sensor embedded in polymer material is proposed. The FBG sensor was embedded in 3D printed coating and was tested under three physical parameters: displacement, temperature and vibration. The sensor was tested in displacement in two different regions of the cantilever, namely, on its midpoint and end point. The maximum displacement sensitivity achieved was (3 ± 0.1) pm/mm for end point displacement, and a temperature sensitivity of (30 ± 1) pm/°C was also attained. In the case of vibration measurements it was possible to obtain a 10.23Hz-low frequency oscillation.