On thermal radiation from heated metallic dust grains

We investigate the thermal radiation from small metallic dust grains heated to high temperatures, using a Drude model for the temperature dependence of the optical constants of the grain material. We use both Mie theory and approximate expressions for the absorption efficiency of the grains and compare the corresponding results. The thermal radiation from dust particles composed of fusion relevant metals is computed, and comparisons are made with available data on the emissivity of metal flat surfaces at high temperatures. For fixed temperature T , we find that the maximum of the thermal radiation intensity (normalized by the black body radiation intensity) occurs when the grain radius is roughly of the order of 1/2π times the wavelength where maximum thermal radiation occurs as given by Wien's law. Because of this, in certain parameter ranges smaller grains can have higher emissivity than larger ones. The analysis may have application to several areas including dust in fusion devices.