Laser treatments and testing to increase the infrared emissivity of materials for first wall of nuclear fusion machines

Laser treatment s are performed to roughen the surfaces of plates of materials typically used for manufacturing the f irst wall and in vessel components of nuclear fusion machines. The laser treatment s reduce the optical reflectivity and increase the infrared (IR) emissivity of components to be observed with thermal imaging cameras Nanosecond (21 ns) p ulses of e xcimer la ser (248 nm wavelength) with 2 Hz frequency are filtered by a square mask ( 5 mm x 5 mm ) to form 50 spots on the surface. Each spot is imprinted by one or more, up to 16, superimposed pulses and each pulse carries an energy density within the range 100 1000 mJ/cm 2 The treatments are applied to plates made of pure copper, stainless steel, and molybdenum. Two strips of Molykote ® and M etal V elvet (TM) are applied as optical black coatings close to the laser treat ed spots to be observed with IR camera when heated u p to 600 °C Temperature measurements are performed in quasi steady state condition during cool down using thermocouples for cross calibration. Thermogram s of Molykote® and Metal Velvet(TM) strips (black body) are compared with those of the laser treated spot s in order to calculate the IR emissivity corresponding to each laser treatment and then to determine the most effective treatment with repeatable 0.8 hemispherical emissivity. Surface morphology and material continuity are examined (SEM) together with che mical composition and crystalline configuration (TEM). Optical and chemical analyses of the treated metal s are presented and discussed thus showing l aser surface treatment is a promisin g method for temperature measurement through thermal imaging cameras.