Probe measurements of impurities in the scrape-off layer of TEXTOR

Abstract

By using carbon collector probes, deposited impurities in the TEXTOR plasma boundary have been measured. The cylindrical probes rotate behind a fixed slit in order to obtain time resolved information. Impurities on the ion side of the probe were measured. After exposures to TEXTOR discharges the probes were analysed by Rutherford backscattering.Three discharges were studied, two with hydrogen as the filling gas, and one with deuterium. For one of the hydrogen discharges a pumping limiter was used.The dominant impurities are oxygen, titanium, chromium, iron and nickel. The stainless steel components have a radial e-folding length of 30 mm before the breakpoint, while this length is only 5 mm for Ti. The origin of the steel components is the main limiter, while Ti has its origin in the pumping limiter ALT 1.The peak fluxes for the discharge 7024 at a distance of 10 mm from the main limiter were in units of atoms/cm2 s, for oxygen 6×1016, for chromium 3×1015, for iron + nickel 7.5×1015 and for titanium 1.5×1015. These fluxes vary in a systematic way with the filling gas, the use of the pumping limiter, and the distance between the main limiter and the probe.