Divertor impurity sources; effects of hot surfaces and thin films on impurity production

Strong continuum emission has been observed from divertor tiles at visible wavelengths and identified as Planck radiation from surfaces with temperatures of typically ∼ 2600 K. Such hot spots (which are not tile edges) can persist for several seconds and are more common at the inner divertor, than the outer. Surprisingly, these hot spots do not usually produce significant impurity fluxes. In contrast, ELMs may produce a significant enhancement of impurity fluxes, depending on strike point location and ELM size.