COLLECTION OF OXYGEN IN THE SCRAPE-OFF LAYER DEPENDING ON BORON CONDITIONING OF TEXTOR

An empirical model equation was deduced from oxygen collection experiments made in the scrape-off layer (SOL) of TEXTOR after different conditioning procedures with boron: O(r) = S(r)OI + GB(r) + AD(r). The measured oxygen retention rates, O(r), are explained in terms of ion sticking, gettering by boron and absorption from air. The coefficients G = 0.67 and A = 0.087 at the measured rates B(r) of boron and D(r) of deuterium are independent of the radial position r in the SOL, while the empirical function S(r) relates the OI-light emission measured at r = 50 cm to other radii. S(r)OI represents the sticking contribution of the ion flux. Due to the formation of stable oxides the getter term, GB(r), contributes significantly to the oxygen collection. It keeps the oxygen content low in the plasma as long as boron is present. The term AD(r) is understood as oxygen uptake from air during sample transport. Analyses of the deposits grown on the targets (graphite, aluminum) were made by NRA, RBS, sputter AES, XPS, and interference fringe analysis.