Increase of Diagnostic Mirror Lifetime Using TiN Coated Stainless Steel by Using a Plasma Focus Device

Plasma-surface interaction experiments on TiN coated stainless steel 316L (S.S.316L) using a plasma focus (PF) device have been performed in an attempt to investigate whether we can use the hardness property of TiN against erosion to increase the lifetime of the mirrors used in plasma diagnostics equipment. Firstly, two similar S.S.316L samples were chosen for this purpose. One of the samples was coated with TiN by using a PF device, while the other was kept intact as a reference for investigating the effect of TiN coating. Then, in order to study the coating effects, these samples were exposed to 200 shots of hydrogen plasma with a total duration of 7 s in a tokamak. Before and after exposure, samples were analyzed by using atomic force microscopy (AFM), scanning electron microscopy (SEM), X-ray diffraction (XRD) and a spectrophotometer. It was found that the uncoated sample was severely damaged, its reflection dropped significantly, and it developed some cracks and lines, while no significant change was observed on the surface characteristic of the coated sample. Moreover the weight loss of the uncoated sample was higher in comparison to the coated one. Therefore the results of this ex- periment showed that the coating of S.S.316L by TiN using a PF device is a useful method to strengthen it against plasma erosion and with further optimization it could possibly be used in preparing plasma diagnostics mirrors.