Coating stainless steel with diamond-like carbon using the hot filament chemical vapor deposition system,and its effects on fusion devices

Internal mirrors are used widely for plasma diagnostics in fusion devices. Therefore, keeping them in good optical condition is essential. The results of this experiment show that coating stainless steel 316l (S.S.316l) mirrors with diamond-like carbon (DLC) reduces the erosion rate and contamination of plasma by evaporation and sputtering and also increases the optical lifetime of these mirrors. For this purpose, firstly two similar S.S.316l samples were chosen. One of these samples was coated with DLC by a Hot Filament Chemical Vapor Deposition device, while the other was kept intact as a reference for investigating the effect of DLC coating. Then, in order to study the coating effects, these samples were exposed to 200 shots of the hydrogen plasma, with a total duration of 7 s in tokamak. Before and after the exposure, samples were analyzed by the atomic force microscopy, scanning electron microscopy, Raman Spectroscopy, and Spectrophotometer. It was found that the uncoated sample was damaged severely and its reflection dropped significantly, and the sample showed some cracks and some melting lines, while no significant change was observed on the surface characteristic of coated sample. Moreover, the weight loss of the uncoated was more in comparison to the coated, sample. Therefore, the results of this experiment showed that coating of S.S.316l by DLC is a useful method to strengthen this material against plasma erosion, and with further optimization, it could possibly be used in preparing plasma diagnostics mirrors.