METAL IMPURITIES IN ION AND ELECTRON-DRIFT DIRECTIONS, FOR DIFFERENT TEXTOR DISCHARGES

A probe system for time-resolved flux measurements has been used with transmitting slit apertures open in two or four directions, for the collection of impurities in ion and electron drift directions, and perpendiculary (from top and from bottom). Adjustments of limiters caused changes in the connection lengths. We found higher fluxes of impurities on the ion drift side regardless of whether the connection length was larger or smaller than on the electron drift side. A flatter radial decay of impurity fluxes was found on the electron drift side. The impurity fluxes became nearly equal on both the ion and electron drift sides 8 cm into the scrape-off layer. From top and bottom, the collected impurity fluxes were at least 100 times smaller than the fluxes measured on the ion drift side. Experiments performed in hydrogen, deuterium and helium gave similar results, but total impurity production was different.