RADIOLUMINESCENCE PROBLEMS FOR DIAGNOSTIC WINDOWS

Radioluminescence from 200 to 800 nm has been measured in UV grade sapphire at ionizing dose rates and temperatures of relevance for ITER optical diagnostic windows. The intensity has been quantified in terms of photon emission and has been found to be comparable to present day tokamak plasma emission intensities. Furthermore the light emission shows a complex dose, dose rate, and temperature dependence. It is concluded that without careful design it will prove extremely difficult to separate out the plasma emission from the window emission, High-temperature operation which in general produces thermal quenching, is seen not to be a complete answer. While emission from about 200 to 500 nm is significantly reduced, over the range 600 to 800 nm it markedly increases due to the broadening chromium emission. However, despite the high intensity and complex behaviour, a possible operational wavelength region from 500 to 600 nm has been identified.