Integration of fiber Bragg grating temperature sensors in plasma facing components of the WEST tokamak

Yann Corre (1) , Guillaume Laffont (2) , Christine Pocheau (1) , Romain Cotillard (2) , Jonathan Gaspar (1) , Nicolas Roussel (2) , Mehdi Firdaouss (1) , J.L. Gardarein (3) , Dominique Guilhem (1) , Marc Missirlian (1)

1 IRFM - Institut de Recherche sur la Fusion par confinement Magnétique
2 LCFO (CEA, LIST) - Laboratoire Capteurs Fibres Optiques (CEA, LIST)
3 AMU - Aix Marseille Université

Plasma Facing Components (PFC) temperature measurement is mandatory to ensure safe high power and long pulse tokamak operation. IR thermography systems which are widely used in magnetic fusions devices become challenged with the choice of tungsten as a PFC material in the I l'ER tokamak, mainly due to emissivity uncertainties and reflection issues in a hot environment. Embedded temperature measurements are foreseen to cross-check the IR thermography measurements. Fiber Bragg grating sensors are potentially of great interest for this application because they are immune to electromagnetic interference and allow the measurement of a large number of temperature spots on a single fiber. Four optical fiber temperature sensing probes, each of them including 11 regenerated fiber Bragg gratings equally spaced by 12.5 mm (equivalent to one ITER-like tungsten monoblock), have been specifically designed and manufactured for the WEST project (W-tungsten Environment and Steady State Tokamak). The four probes are embedded in W-coated graphite components at two different distances from the surface, 3.5 mm and 7 mm, to cover a wide range of temperatures up to 900 degrees C. This paper addresses the design and integration issues and the qualification and performance assessment performed in the laboratory. It also shows the first measurements of this new diagnostic achieved in a tokamak environment during baking of the machine and during early diverted plasma exposure.

Mots clés: Thermal instrumentation; Optical fibers; Fiber Bragg grating sensors; Plasma confinement; Plasma Facing Components; Tokamaks; Thermography; temperature measurement; Fiber Bragg grating

Domaines: Instrumentations et Détecteurs [physics.ins-det]; Thermique [physics.class-ph]; Physique Nucléaire Expérimentale [nucl-ex]; Optique [physics.optics]

Yann Corre, Guillaume Laffont, Christine Pocheau, Romain Cotillard, Jonathan Gaspar, et al.. Integration of fiber Bragg grating temperature sensors in plasma facing components of the WEST tokamak. Review of Scientific Instruments, 2018, 89 (6), pp.063508. ⟨10.1063/1.5024514⟩. ⟨hal-02011117⟩