Investigation of liner samples exposed to an in-situ carbidization in TEXTOR

Abstract

A plasmachemical in-situ technique for the deposition of carbon on limiters and first wall of the tokamak TEXTOR has been developed. RG-discharge in a throughflow of hydrogen with admixed 1.5% methane has been used to implant methane ions into the limiters and wall. Different-samples (Inconel 600) in liner position have been exposed and afterwards analyzed with SIMS and AES. It has been shown that during the plasmachemical carbon deposition at 240°C predominantly chromium carbide was formed in the surface near layer. Nickel carbide was traced in a negligibly small amount. Depth profiles indicate an exponential dependence of the chromium carbide concentration up to a depth of about 10 nm. This is in agreement with the estimated diffusion profile of carbon; literature values of the carbon diffusivity in Ni, Ni-Cr and Ni-Co alloys yield a mean characteristic diffusion length of about 8 nm. The total amount of deposited carbon as determined from AES measurements is 6 × 10 15 atoms cm −3 , in reasonable agreement with 1.2 × 10 16 cm −2 as determined from the partial pressure balance during the carbidization process.