Expanded two-color thermography considering temperature-dependent emissivity of tungsten for ITER divertor infrared thermography

Abstract

This study developed a new correction method to reduce errors in temperature measurement caused by temperature-dependent emissivity for ITER divertor infrared (IR) thermography. In order to develop the method, we measured the spectral emissivity of tungsten from 200 °C to 1900 °C in the wavelength range of 1.5 μm to 4.5 μm and evaluated temperature measurement error of the two-color method. The results indicate that temperature-dependent emissivity is a major factor in temperature measurement errors, which suggests that accurately measuring temperature by using the conventional two-color method would prove difficult. The new correction method uses two emissivity inputs at different temperature points, in contrast to the conventional method, which uses emissivity measured at a single temperature point. Using this new correction method with a suitable wavelength combination for the two-color method, temperature measurement error was reduced to less than 5% at 1900 °C.