Studies on pulsed laser deposited Mo, W and Rh thin films for First Mirror application

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The focus of the present research work was to develop mirror-like thin films of Mo, W and Rh by pulsed laser deposition (PLD) technique, for First Mirror (FM) application in fusion reactor. Thin films of Mo, W and Rh were deposited on polished stainless steel (SS) substrate by PLD technique. The optimum deposition parameters obtained from the present study for mirror-like Mo, W and Rh thin films were 500 ओC substrate temperature, ~ 2 J/cm2 laser fluence, ~ 3 cm target-substrate distance and ~ 1.0 mbar Helium ambient gas pressure. The W thin films of thickness ~ 326 nm showed ~ 2 % reduction in FIR specular reflectivity after irradiation of 8 keV H ion beam. In case of 10-30 keV D ion beam irradiation, the specular reflectivity was reduced by ~ 1-9 % and ~ 28-38 % in FIR and UV-visible range, respectively. The Rh thin films of thickness ~ 246 nm, showed ~ 1-7 % and 5-32 % reduction in FIR and UV-visible specular reflectivity after irradiation of 10-30 keV D ions beam. The post exposure degradation in reflectivity of W and Rh mirror-like thin films was explained in terms of damage parameters calculated numerically by using Transport of Ions in Matter (TRIM) Monte Carlo simulation code. The quality and sustainability of single element W and Rh thin film FMs, in the long term exposure of fusion plasma can be enhanced by making multilayer thin film of more than one element. Based on the damage parameters of D ions and the properties of Rh, W, Cu and SS, a three layer composite thin film, Rh/W/Cu on SS, was designed and fabricated for FM application. The performance of the Rh/W/Cu multilayer thin film FM was tested by exposing to 20 and 30 keV D ion beam of particle flux ~ 1.2स1014 ions/cm2/s. The multilayer Rh/W/Cu thin film showed ~ 1-4 % and ~ 3-20 % reduction in FIR and UV-visible specualr reflectivity, respectively. In order to collect large amount of plasma radiation for better reliability of spectroscopic signals, the size of Rh and Rh/W/Cu PLD thin film FMs were increased to 50 mm diameter by modifying conventional PLD technique with substrate rastering stage. The uniformity of deposition was confirmed by distinct, straight and parallel interference fringes from Rh single layer and Rh/W/Cu multi-layer thin films.
Supervisor: Alika Khare