Optical characteristics of recrystallized tungsten mirrors exposed to low-energy, high flux D plasmas

The surface topography and optical properties of recrystallized tungsten exposed to a low-energy (38 eV/D), high flux (1022 D/m2 s) deuterium plasma with an ion fluence of 1026 D/m2 at various temperatures was investigated. It was found that the surface morphology weakly depends on the exposure temperature in the range 320–695 K with the exception of the narrow temperature region around 535 K, where large changes to all optical characteristics occurs. After plasma exposure at this temperature, the surface topography of the W sample is characterized by active blistering as has already been indicated in previous publications. The reflectance found in direct measurements at normal incidence drops in the wavelength interval 220–650 nm, whereas the estimations of reflectance using the ellipsometry data demonstrate some increase.