Impurity Flux Studies in the Limiter Shadow of the TEXTOR Tokamak

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Abstract
The temporal and radial dependence of the flux of impurity particles in the plasma scrape of layer in the TEXTOR tokamak is measured during a series of reproducible discharges by using passive collection probe techniques. Oxygen, titanium, chromium, iron and nickel impurities are detected. The flux of heavy impurities is observed to be reproducable. A typical peak value of the iron flux during a discharge is 2 1015 at./cm2 s. No saturation effects of the measured amount of impurities on the probe surface is observed for surface densities of up to 5 1015 at./cm2, indicating that in this range losses due to possible release mechanisms of collected impurities are negligible. The e-folding length of the radial decay of the impurities detected on the probe surface is observed to vary with the discharge time. The value of the e-folding length is determined to be 20-30 mm at the flat top part of the discharge and about 13 mm at the end, for distances between 10 and 24 mm from the plasma edge.