Surface temperature measurements by means of pulsed photothermal effects in fusion devices

摘要

In fusion devices, the surface temperature of plasma facing components is measured using infrared cameras. This method requires a knowledge of the emissivity of the material, the reflected and parasitic fluxes (Bremsstrahlung). For carbon, the emissivity is known and constant over the detection wavelength (similar to 3-5 mu m). For beryllium and tungsten, the reflected flux could contribute significantly to the collected flux. The pulsed photothermal method described in this paper allows temperature measurements independently of both reflected and parasitic fluxes. A local increase of the surface temperature (Delta T similar to 10-15 K) introduced by a laser pulse (few ns) results in an additional component of the photon flux collected by the detector. Few mu s after the pulse, a filtering of the signal allows to extract a temporal flux proportional only to the variation of the emitted flux, the emissivity and Delta T. The ratio of simultaneous measurements at two wavelengths leads to the elimination of Delta T and emissivity. The range of application increases for measurements at short wavelengths (1-1.7 mu m) with no limitation due to the Bremsstrahlung emission. (c) 2007 Published by Elsevier B.V.