Bidirectional reflectance distribution function of recrystallized tungsten mono-block exposed to cyclic heat loading

Abstract

• BRDF of tungsten mono-blocks exposed to cyclic heat was measured. • Overall values of BRDF decreased with increase in cyclic heat loading. • Comparison between a modeled and measured BRDF was performed. • Additional diffused reflection model is necessary to a specular model to fit the measured BRDFs. The bidirectional reflectance distribution function (BRDF) of recrystallized tungsten mono-blocks exposed to cyclic heat loading for ITER divertor outer vertical target was measured using a goniophotometer at a wavelength of 473 nm. Laser microscope observations revealed that the surface roughness of the mono-block increased by an order of magnitude after cyclic heat loads of approximately 20 MWm −2 . Furthermore, the overall values of BRDF decreased with an increase in cyclic heat loading. A comparison between the modeled and measured BRDFs showed that an additional Lambertian component is necessary to a specular function (microfacet model or Gaussian function) to fit the measured BRDFs when the surface of the mono-blocks becomes rough.