Collector probe measurements of ohmic conditioning discharges in TFTR

Special limiter conditioning techniques using low density deuterium or helium discharges have produced enhanced plasma confinement in TFTR. Measurements with a rotatable collector probe have been made to increase our understanding of the boundary layer during these conditioning sequences. A set of silicon films behind slits facing in the ion and electron drift directions was exposed to four different D⁺ and He²⁺ discharge sequences. The amounts of deuterium and impurities trapped in the surface regions of the samples have been measured by different analytical techniques, including nuclear reaction analysis for retained deuterium, Rutherford backscattering spectroscopy for carbon and metals, and Auger electron spectroscopy for carbon, oxygen and metals. Up to 1.9 × 10^-17 cm^-2 of deuterium was detected in codeposited carbon layers with D/C generally in the range of the bulk saturation limit. Radial profiles and ion drift/electron drift asymmetries are discussed.