Abstract
The effects of low power discharge cleaning (Te=9–18 eV, ne=1010–1011 cm−3) on wall conditions in the ISX-A tokamak have been studied in detail by means of Auger electron spectroscopy and residual gas analysis. It was found that discharge cleaning caused very little transport of metals and reduced the surface oxygen content on stainless steel samples located between the limiter and the wall to substoichiometric levels. This oxygen was probably removed from the samples as H2O molecules. On the other hand carbon, in the form of a metallic carbide, increased during discharge cleaning. The cleanliness of tokamak plasmas (Zeff=1.6–2) obtained after about three weeks of discharge cleaning was clearly correlated with improvements in the wall conditions and with the reduced level of residual gas species.
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