An XPS study on the evolution of type 304 stainless steel surface during routine TCSU operation

A surface analysis study was carried out to monitor the first-wall evolution in the Translation, Confinement, and Sustainment Upgrade (TCSU) experiment. A type 304 stainless steel sample was exposed to processes including the standard ex-situ surface preparation, helium glow discharge cleaning (He-GDC), plasma discharges, and backfilling the vacuum chamber with filtered N2. After each process, the sample was carried to a surface analysis chamber for X-ray photoelectron spectroscopy (XPS), using a custom designed in-vacuum transfer device. Results indicated that He-GDC was effective in removing both physically and chemically bound carbon and oxygen on the stainless steel surfaces due to the physical impact of the glow. The plasma discharges resulted in oxidation on the surface. The use of filtered nitrogen during vacuum breaks was verified as an effective method for minimizing carbon and oxygen contamination.