Normal spectral emissivity measurement of graphite in the temperature range between 200°C and 500°C

Graphite is an important material constituting the first wall of the Experimental Advanced Superconducting Tokamak (EAST), and the temperature distribution of the first wall is a key parameter which is used to reflect the operating state of the EAST. Therefore, the experimental investigation of emissivity characteristics of the first wall material is necessary for achieving high-precision temperature measurement. In this work, an emissivity measurement model based on the Fourier transform infrared (FTIR) spectrometer was constructed. On this basis, the normal spectral emissivity within 3 μm to 5 μm of graphite in the temperature range between 200 °C and 500 °C is measured, and two nonlinear models are also given to describe the dependence of emissivity on the wavelength and the temperature. In addition, based on these emissivity measurement results, the temperature measurement performance of the FTIR-based radiation thermometer after emissivity correction is also evaluated in this work. Experimental results show the normal spectral emissivity of graphite increases when temperature rises and increases first and then decreases with the increase of the wavelength. And after the emissivity correction, the FTIR-based radiation thermometer can achieve better performance of temperature measurement, where the maximum absolute error can be reduced from 21.1624 °C to 2.4779 °C after emissivity correction. The method and experimental results proposed in this work may provide a valuable guidance on temperature measurement of the first wall of the EAST, and also provide a reference for the normal spectral emissivity measurement of other materials in the mid-infrared region.