Thermography of target plates with near-infrared optical fibres at Tore Supra

First spectroscopic near-infrared thermography measurements in the range 0.9–1.95 μm performed with optical fibres are reported. Two set-ups served as test-beds for physical and technical questions for a security system based on fibre optical thermography. It was found that for the interesting temperature range above 600°C atomic and molecular line emission is negligible in comparison with thermal radiation. The observed near-infrared spectra are however different from simple blackbody radiation curves. They are explained by the coverage of the surface with dust and flakes. The dust particles are identified by their spectral emissivity falling off with the square of the wavelength. On one set-up, flakes were identifiable by fast cool-down times and confirmed by post-experiment inspection. In the absence of flakes, surface temperatures on a ripple protection plate were measured, that allowed to determine the mean energy of ripple trapped ions to be 200–300 keV.