Surface temperature measurement of plasma facing components with active pyrometry

In fusion devices like ITER, plasma facing components will be in metal, (Tungsten and Beryllium), with emissivity in the range of 0.1–0.4. Therefore, surface temperature monitoring by infrared system will become more challenging due to low emissivity and consequently non negligible reflected flux. The active pyrometry method proposed in this paper allows surface temperature measurements independently of reflected and parasitic fluxes. A local increase of the surface temperature (ΔT(t)∼10 °C) introduced by a transient heating source (pulsed or modulated) results in an additional component of the flux collected by the detector. A filtering of the signal allows extracting a temporal flux proportional only to the variation of the emitted flux. The ratio of simultaneous measurements at two wavelengths allows solving the unknown emissivity (same as for classical bicolour pyrometry). In this paper, it is described how the active pyrometry method is adapted to the surface temperature measurements of metallic PFCs independently of the reflected fluxes. Experimental results for carbon and tungsten samples are reported. Finally, it is shown how, by using the active pyrometry, the overall 2D standard IR perturbed by a reflected flux is corrected to recover the full 2D surface temperature close to the real surface temperature.